Will crops for direct human
consumption be grown on the
land within 18 months of septic
Might there be contact between tank pumpings application?
the septic tank pumpings and the
edible portion of the crop?

Septic tank pumpings must be
treated by PSRP or PFRP prior Either:
to land application. @ Septic tank pumpings must
© If treated by PSRP, public be treated by PSRP or
access to the site must be PFRP prior to land
restricted for at least 12 application. No further
months and grazing by restrictions apply.
animals whose products are Or.
consumed by humans must Untreated septic tank

be prevented for at least 1
month following application.
If treated by PFRP, no
further restrictions apply.

pumpings may be applied to
land if public access to the
site is restricted for at least
42 months and grazing by

animals whose products are
consumed by humans is
Septic tank pumpings must be prevented for at least
treated by PFRP prior to land 1 month following
application. No further restrictions application.

apply.

+

Figure 3-2. Federal requirements for management of septic tank pumpings applied to land.



absolute densities of indicator organisms in the output
sludge (no. organisms/g TSS), a minimum of nine
measurements are needed. If the process variability is
high, more measurements should be taken. Standard
deviation of the mean should be less than or equal to
0.3 logio of the organism density (no/g TSS).

© A pair of input and output samples can be drawn
simultaneously. However, to ensure that measurements,
are independent, samples should not be taken on
successive days. At least 3 days should separate each
successive pair of input and output samples.

@ The sample should be taken at the point where process)
conditions are likely to be least favorable for microbe
destruction. For example, if the process is a thermal
process, the sample should be taken at the point where|
the temperature is lowest. If the process depends on
high pH, the sample should be taken from the point
where pH is lowest.

@ If ambient conditions affect sludge microbial
characteristics, sludge should be sampled after
treatment under the least favorable conditions. (This
guidance would apply, for example, to aerobic
digestion, which has a low operating temperature in the
winter, and thus would be expected to be least
effective at reducing microorganism densities during
this season.)

‘e Sampling, packaging, and shipping procedures should
not alter the sludge character or quality.

@ Proper quality assurance procedures appropriate for
collecting samples for microbiological analysis should
be defined and adhered to.

The draft POTW Sludge Sampling and Analysis Guidance
Document (EPA, 1988a) provides guidance on sampling
and quality control procedures. (The document Sampling
Procedures and Protocols for the National Sewage
Sludge Survey [EPA, 1988b] also provides information on
sludge sampling; however, its relevancy to microbiological
sampling is limited since it focuses on sampling sludge for:
toxic chemicals.)

Table 6-3 lists some recommended procedures for
analysis of municipal wastewater sludge.

Data Quality

The quality of the data you provide will be an important
factor in EPA’s equivalency determination. You can help
ensure the quality of your data by using accepted, state-
of-the-art sampling and analytical techniques such as
those described above; obtaining samples that are
representative of the expected variation in sludge quality;
developing and following quality assurance procedures for
sampling; and using an independent, experienced
laboratory to perform the analysis.

Since processes differ widely in their nature, effects, and
processing sequences, the experimental plan to
demonstrate that your process meets the requirements for
PSRP or PFRP equivalency must be tailored to the
process. Field verification and documentation by
independent or third-party investigators is desirable. EPA
will evaluate the study design, the accuracy of the data,

and the adequacy of the results for supporting the
conclusions drawn.

Can Pilot-scale Data Be Submitted?

Operation on a full-scale is desirable. However, if a pilot-
scale operation truly simulates full-scale operation, testing
on this reduced scale is possible. In such cases, you
should indicate that the data were provided from a pilot-
scale operation, and you should discuss why and to what
extent you think that this simulates full-scale operation.
For example, include any data available from existing full-
scale operations.

It is critical that the conditions of the pilot-scale operation
be at least as severe as those of full-scale operation. The
arrangement of process steps, degree of mixing, nature of
the flow, vessel sizing, proportion of chemicals used, etc.
are all part of the requirement. Any substantial degree of
departure in process parameters that might reduce the
severity of the procedure will invalidate any approvals
given and will require a retest at the new condition.

How Do | Prepare an Application for
Equivalency?

The following outline and instructions are provided as a
guideline for preparing applications for equivalency.7 Be
sure to include all the information discussed below that
may be relevant to demonstrating equivalency for your
particular process. Inadequate information may
substantially delay the review process.

Summary Fact Sheet

As part of the application, you must submit a brief fact
sheet that summarizes key information about your
process. Refer to Appendix E for guidance on what to
include in the fact sheet. Provide any additional facts you
feel are important if they are not included on the sample
fact sheet in Appendix E.

Introduction ,

Provide the full name of the facility and the treatment
process. Indicate whether you are applying for:

@ Equivalency for a process or for stockpiled sludge.
@ PSRP or PFRP equivalency.
© Site-specific or national equivalency.

Process Description

Describe the type of sludge used in the process. Describe
other materials used in the process. Provide specifications
for these materials as appropriate. Provide definitions for
any terms used. Break the process down into key steps.
Graphically display these steps in a quantified flow
diagram of the wastewater and sludge treatment
processes. Provide details of the wastewater treatment

‘Your Regional and State Sludge Coordinators may have additional
guidance on preparing an application in the form of memos and ather
guidance from the Pathogen Equivalency Committee issued subsequent
to publication of this document. It is advisable to contact them to obtain
the latest information before preparing your application.

35



Table 6-2. Reduction in Vector Attractiveness: Ctiteria for Demonstrating Equivalency
Type of Sludge Criteria
All types Reduction of volatile solids content of the sludge by at least 38% during treatment. See

Appendix D for guidance on calculating this parameter.

‘Sludges from aerobic processes (aero- Treated sludge has|an oxygen intake of less than 1 mg oxygen/hour/g TSS as demonstrated
bic digestion or extended aeration) by the Specific Oxygen Uptake Rate (SOUR) test at 20°C (68°F).

Anaerobic sludges Volatile solids reduction in treated sludge after 40 days additional batch mesophilic digestion
is less than 15%.

Sludges that contain no raw primary Total suspended solids content of treated sludge is 75% or greater and remains at this level
sludge until the point of tang application.

High pH sludges Treated sludge maintains a pH of 11.5 or greater up to the time of land application.
Stockpiled sludge Lack of odor throughout the sludge pile.

Table 6-3.
Organism or Parameter of interest
Microbial Populations
Indicator Organisms:
Fecal coliform
Fecal streptococcus
Enterococci
Salmonella spp.
Total enteroviruses

Helminth ova (including Ascaris spp.,
Toxocara spp., Trichuris trichiura)

Vector Attraction Potential

Recommended Analytical Methods to Demonstrate PSRP or PFRP Equivalency
Method/Reference

Standard Methods, Methods 908 and 909 (APHA, 1985).

Standard Methods, Method 910A (APHA, 1985) or Slanetz and'Bartley, 1957.
Levin et al., 1975.

Standard Methods, Method 912C.1 (APHA, 1985) or Kenner and Clark, 1974.
EPA, 1984c or Goyal et al., 1984.

Fox et al., 1981 or Yanko, 1987 or Tulane University, 1981.

Specific Oxygen Standard Methods, Method 213A. (APHA, 1985)
Uptake Rate (SOUR)
Sludge Characteristics
Total solids Standard Methods, Method 209A (APHA, 1985).
Total suspended solids Standard Methods, Method 209C (APHA, 1985).
Volatile solids

Standard Methods, Method 209D (APHA, 1985).

Volatile suspended solids

Standard Methods, Method 209D (APHA, 1985).

attractiveness. For all sludges, the requirement can be
met by demonstrating that the volatile solids content of

the sludge was reduced during treatment by at least 38%.

Appendix D provides guidance on how to calculate this
reduction. For sludges with a high proportion of aerobic
bacteria (i.e., produced by aerobic processes such as

aerobic digestion or extended aeration),the requirement
can be met by performing the SOUR (Specific Oxygen
Uptake Rate) test (see Table 6-3) to show that the sludge
has an oxygen uptake of less than 1 mg oxygen/hour/g

total suspended solids (subsequent guidance may change
these numbers). The SOUR test is not appropriate for
limed or anaerobically digested sludges. Sludges from

~ anaerobic processes (including lagooned sludge that has

not been chemically treated) are considered to have
adequately reduced vector attraction if the volatile solids
reduction from 40 days additional batch mesophilic
digestion is less than 15%. Sludges that contain no raw
primary sludge are considered to have adequately
reduced vector attractiveness if their total suspended

3



reductions in pathogenic bacteria and viruses that occur
during wastewater treatment.

The 503 option of demonstrating a density of 6 logo (i.e.,
108) or less in each of the fecal indicator organisms
corresponds to the PSRP equivalency criteria to
demonstrate an average log density of less than 6.0 for
fecal coliforms and fecal streptococci in the treated
sludge.

The proposed 503 requirement does not include an option ©

corresponding to the PSRP equivalency option of
demonstrating a 2-log reduction in indicator organisms.
This is because the proposed 503 option to demonstrate
an indicator organism density of 108 or less requires only
half the testing necessary to demonstrate a 2-log
reduction, and therefore supercedes the reduction option.

Class B sludges have use and access restrictions similar
to those of PSRP sludges. These are compared in Table
7A.

Class C Standards

The proposed Class C requirements under 503 are based
on the performance of treatment works that have aerobic
processes with long detention times and no primary
settling processes (e.g., NP/LSA plants). The Class C
pathogen reduction requirements are less stringent than
the Class B requirements; consequently, the Class C use
and access restrictions are more stringent than those of
lass B.

The proposed 503 regulations state that "Class C
pathogen reduction is achieved when processes reduce

the density of bacteria and animal viruses per unit of
volatile suspended solids in the sludge 1.5 orders of
magnitude lower than those densities in incoming
wastewater... Treatment works may also demonstrate that
the density of fecal coliforms in sewage sludge does not
exceed 6.3 logig or less per gram of volatile suspended
solids and the density of fecal streptococci (enterococci)
in the sewage sludge does not exceed 6.7 logj or less
per gram of volatile suspended solids prior to disposal."
Vector attraction must also be reduced in Class G
sludges, as discussed below.

The proposed Class C requirement to show a reduction in
the density of bacteria and animal viruses resembles the
equivalency criteria developed by the PEC for NP/LSA
processes (Figure 6-3). However, the 1.5-order-of-
magnitude reduction that must be achieved under the
proposed 503 regulations is higher than the reduction of
0.7 log in total enterovirus or Salmonella (whichever is
least susceptible to the process) that must be
demonstrated to meet the PSRP equivalency criteria for
NP/LSA processes. This is because the 503 reduction is
measured as the difference between the incoming
wastewater and the treated sludge, whereas the
equivalency reduction is the difference between untreated
and treated sludge. Thus, the 503 requirement includes
the additional pathogen reductions that can be achieved
by wastewater treatment.

The proposed 503 option of demonstrating absolute
densities of 6.3 logyg {i.e., 106-3) or less fecal coliforms
and 6.7 logig (i.e., 1067) or less fecal streptococci in the
sludge prior to disposal is similar to the PSRP

equivalency option for NP/LSA sludges of demonstrating
an average density of less than 108-0 for fecal coliforms
and fecal streptococci in the treated sludge from
conventional processes.

Collectively, the use and access restrictions for Class C
sludges are slightly more stringent than those for Class B
sludges. The food crop restrictions are the same for Class
B and Class C. However, both the harvesting of feed
crops and the grazing of animals on land where Class C
sludge has been applied are restricted for 60 days - 30
days longer than for Class B. The 12-month restriction on
access to land where Class C sludge has been applied
pertains to both the public and to agricultural workers,
except personnel applying the sludge, for 12 months.
These more stringent use and access requirements for
Class C sludges are necessary to compensate for the
reduced pathogen reduction requirements.

Reduction of Vector Attraction

All three classes of sludge must demonstrate reduction of
vector attraction. Under the proposed 503 regulations, a
sludge is considered to have adequately reduced vector
attraction if it meets any of these six criteria:

@ The volatile solids of the processed sludge are 38%
lower than the volatile solids in the influent.

@ A less than 15% reduction in volatile solids occurs in
40 days of additional batch digestion at mesophilic
temperatures (30° to 38°C). :

The specific oxygen uptake rate of the sludge is
reduced to 1 mg oxygen/hour/gram of sewage sludge
solids or less. (This applies only to sewage sludge
treated in aerobic processes.)

Alkali is added to raise the pH of the sludge to 12 or
above and, without the further addition of alkali, the pH
remains at 12 or above for 2 hours and then at 11.5 or
above for an additional 22 hours.

The sludge is dried to a 75% solids content prior to
mixing with other materials.

The sludge is injected below the soil surface (unless
the sewage sludge is intended for distribution and
marketing).

These proposed requirements are very similar to the
criteria established by the PEC for reduction of vector
attractiveness (see Table 6-2). Some are identical. The
maior difference is the option, under the proposed 503
regulations, of injecting sludge below the soil surface. This
is not an option under the PEC’s current criteria for
equivalency.



Entamoeba coli cyst, 15 ym, from anaerobically digested
sludge.

Preparing compost for pathogen analysis. (Photo credit: U.S.
Department of Agriculture, Beltsville, Maryland)

heated is critical to the effectiveness of heat-based
treatment processes.

The 40 CFR Part 257 sludge regulations protect human
health by requiring sludge to be treated prior to land
application. The regulations specify the treatment
processes and operating conditions that will ensure
adequate pathogen and vector attraction reduction. The
sludge regulations also protect human health by
controlling exposure to land-applied sludge until sufficient
time has elapsed for environmental factors to reduce
pathogens to a reasonable level for the intended land use.

Measuring Pathogen Reduction

Microbiological analysis of sludge is often an important
means of determining the effectiveness of a sludge
treatment process in reducing pathogens (see photo
above). Methods have not yet been developed to detect
all pathogens that may occur in sludge, and it would be
impractical to run all the tests that do exist. Instead, only a



Digestion, Aerobic Fact Sheet

Description — Aerobic digestion is a method of sludge stabilization in an open tank that can be regarded as a
modification of the activated sludge process. Microbiological activity beyond cell synthesis is stimulated by aeration,
oxidizing both the biodegradable organic matter and some cellular material into COz, HzO and NO3. The. oxidation of
cellular matter is called endogenous respiration and is normally the predominant reaction occurring in aerobic
digestion. Stabilization is not complete until there has been an extended period of primarily endogenous respiration
(typically 15 to 20 days). Major objectives of aerobic digestion include odor reduction, reduction of biodegradable
solids and improved sludge dewaterability. Aerobic bacteria stabilize the sludge more rapidly than anaerobic
bacteria, although a less complete breakdown of cells is usually achieved. Oxygen can be supplied by surface
aerators or by diffusers. Other equipment may include sludge recirculation pumps and piping, mixers and scum
collection baffles. Aerobic digestors are designed similarly to rectangular aeration tanks and use conventional
aeration systems, or employ circular tanks and use an eductor tube for deep tank aeration.

Common Modifications — Both one- and two-tank systems are used. Small plants often use a one-tank batch system
with a complete mix cycle followed by settling and decanting (to help thicken the sludge). Larger plants may
consider a separate sedimentation tank to allow continuous flow and facilitate decanting and thickening. Air may be
replaced with oxygen (see Fact Sheet 6.4.3).

Technology Status — Primarily used in small plants and rural plants, especially where extended aeration or contact
stabilization are practiced.

Applications - Suitable for waste primary sludge, waste biological sludges (activated sludge or trickling filter sludge)
or a combination of any of these. Advantages of aerobic digestion over anaerobic digestion include simplicity of
operation, lower capital cost, lower BOD concentrations in supernatant liquid, recovery of more of the fertilizer value
of sludge, fewer effects from interfering substances (such as heavy metals), and no danger of methane explosions.
The process also reduces grease content and reduces the level of pathogenic organisms, reduces the volume of the
sludge and sometimes produces a more easily dewatered sludge (although it may have poor characteristics for
vacuum filters). Volatile solids reduction is generally not as good as anaerobic digestion.

Limitations — High operating costs (primarily to supply oxygen) make the process less competitive at large plants.
The required stabilization time is highly temperature sensitive, and aerobic stabilization may require excessive
periods in cold areas or will require sludge heating, further increasing its cost. No useful by-products, such as
methane, are produced. The process efficiency also varies according to sludge age, and sludge characteristigs, and
pilot work should be conducted prior to design. Improvement in dewaterability frequently does not occur.

Performance —
Influent Effluent Reduction
Total solids 2-7% 3-12% -
Volatile solids 50 - 80% of above 30 - 70% (typical 35 - 45%)
Pathogens Up to 85%

Physical, Chemical, and Biological Aids - pH adjustment may be necessary. Depending on the buffering capacity of
the system, the pH may drop below 6 at long detention times, and although this may not inhibit the process over
tong periods, alkaline additions may be made to raise the pH to neutral.

Residuals Generated — Supernatant Typical Quality: SS 100 to 12,000 mg/l, BODs 50 to 1,700 mg/l, soluble BODs 4
to 200 mg/l, COD 200 to 8,000 mg/l, Kjeldahl N 10 to 400 mg/, Total P 20 to 250 mg/l, Soluble P 2 to 60 mg/, pH
5.5 to 7.7. Digested sludge.

Design Criteria — Solids retention time (SRT) required for 40% VSS reduction: 18 to 20 days at 20°C for mixed
sludges from AS or TF plant, 10 to 16 days for waste activated sludge only, 16 to 18 days average for activated
sludge from plants without primary settling; volume allowance: 3 to 4 ft3/capita: VSS loading: 0.02 to 0.4 Ib/ft3/d; air
requirements, 20 to 60 ft3/min/1000 ft3; minimum DO: 1 to 2 mg/l; energy for mechanical mixing: 0.75 to 1.25
hp/1,000 ft3; oxygen requirements: 2 Ib/lb of cell tissue destroyed (includes nitrification demand), 1.6 to 1.9 Ib/lb of
BOD removed in primary sludge.

Reliability - Less sensitive to environmental factors than anaerobic digestion. Requires less laboratory control and
daily maintenance. Relatively resistant to variations in loading, pH and metals interference. Lower temperatures
require much tonger detention times to achieve a fixed level of VSS reduction. However, performance loss does not
necessarily cause an odorous product. Maintenance of the DO at 1 to 2 mg/l with adequate detention results in a
sludge that is often easier to dewater (except on vacuum filters).

68



eSon Denver e
Francisco

Dallas/Ft Worthe

Reg XX

Reg IX, Reg IL
Fag VIRGIN ISLANDS 1
~ Bp PUERTO RICO i
_- HAWAII o> Cor

GUAM

Figure B-1. EPA regions.





Louisiana

Ken Fledderman

Construction Grants Unit

LA Department of Environmental Quality
11720 Airline Highway

Baton Rouge, LA 70814

504-295-8900

Bijan Sharafkhani

Solid Waste Division

LA Department of Environmental! Quality
P.O. Box 44307

Baton Rouge, LA 70804

504-342-1216

New Mexico

Cordelia Snow

Construction Grants Section

Water Pollution Control Bureau

NM Health and Environment Department
Environmental Improvement Division
P.O. Box 968 - Harold Runnels Building
1190 St. Francis Drive

Sante Fe, NM 87503

505-827-2808

Oklahoma

David Hardgrave and

Danny Hodges

OK State Department of Health
P.O. Box 53551

1000 N.E. 10th Street
Oklahoma City, OK 73152
405-271-5205

Texas

Milton R. Rose

Construction Grants Division

TX Water Development Board
P.O. Box 13231 - Capital Station
Austin, TX 78711-3231
512-463-8513

T.A. Outlaw

Permits and Programs Branch
Bureau of Solid Waste Management
Texas Dept. of Health

1100 W. 49th St.

Austin, TX 78756

512-458-7271

Region 7

lowa

Darrell McAllister, Chief

Surface and Groundwater Protection Bureau
IW Department of Natural Resources
Wallace Building

900 East Grand Avenue

DesMoines, |W 50309

515-281-8869

Kansas

Rodney Geisler

Forbes Field

KS Department of Health & Environment
Topeka, KS 66620

913-296-5527

Missouri

Ken Arnold

Waiter Pollution Control Program

MO Department of Natural Resources
P.O. Box 176

Jefferson City, MO 65102
314-751-6624

Nebraska

Rudy Fieldler

Water Quality Division

NB Department of Environmental Control
P.O. Box 98922

Statehouse Station

Lincoln, NB 68509-8922

402-471-4239

Region 8

Colorado

Phil Hegeman

Water Quality Controi Division
CO Department of Health
4210 East 11th Avenue
Denver, CO 80220
303-331-4564

Montana

Scott Anderson
Water Quality Bureau

MT Department of Health & Environmental Sciences

Cogswell Building (A-206)
Helena, MT 59620
406-444-2406

North Dakota

Jeff Hauge

Division of Water Supply and Pollution Control
ND Department of Health

1200 Missouri Avenue

Bismark, ND 58505

701-224-2354

South Dakota

Dave Templeton

Division of Water Quality

Department of Water & Natural Resources
Joe Foss Building

523 East Capitol

Pierre, SD 57501-3181

605-773-3151



The "Full Mass Balance" Method

The "full mass balance" method must be used when
steady conditions do not prevail over the time period
chosen for the calculation. The chosen time period must
be substantial, at least twice the nominal residence time in
the digester (nominal residence time = average volume of
sludge in the digester + average volumetric flow rate.
Note: when there is supernatant withdrawal, volume of
sludge withdrawn should be used to calculate average
volumetric flow rate). The reason for the long time period
is to reduce the influence of short-term fluctuations in feed
or product flow rates or compositions. If input
compositions have been relatively constant for a long
period of time, then the time period can be shortened.

An example where the full mass balance method would be
needed is an aerobic digester operated as follows:

1) Started with the digester 1/4 full (time zero).

2) Raw sludge is fed to the digester daily until
digester is full.

3) Supernatant is periodically decanted and raw
sludge is charged into the digester until not
enough settling occurs to accommodate daily
feeding. (Hopefully this will not occur until enough
days have passed for adequate digestion.)

4) Draw down the digester to about 1/4 full (final
time), discharging the sludge to sand beds.

The full mass balance is written as follows:

Sum of total volatile solids inputs in feed streams
during the entire digestion period = sum of volatile
solids outputs in withdrawals of decantate and
bottoms + loss of volatile solids + accumulation of
volatile solids in the digester. (a)

Loss of volatile solids is calculated from Equation 1. FVSR
is calculated by Equation 2:

loss in volatile solids (2)
sum of volatile solids inputs

FVSR =

The accumulation of volatile solids in the digester is the
final volume in the digester after the drawdown times final
volatile solids concentration less the initial volume at time
zero times the initial volatile solids concentration.

To properly determine FVSR by the full mass balance
method requires determination of all feed and withdrawal
volumes, initial and final volumes in the digester, and
determination of volatile solids concentrations on all
streams. In some cases, which will be discussed later,
simplifications are possible.

The “Approximate Mass Balance" Method

If volumetric inputs and outputs are relatively constant on
a daily basis, and there is no substantial accumulation of
volatile solids in the digester over the time period of the
test, an approximate mass balance (AMB) may be used.
The basic relationship is stated simply:

volatile solids input rate = volatile solids output
rate + loss of volatile solids. (3)

The FVSR is given by Equation 2.

No Decantate, No Grit Accumulation

Calculation of FVSR is illustrated for Problem 1 in Table
D-1 which represents a simple situation with no decantate
removal and no grit.accumulation. An approximate mass
balance is applied to the. digester operated under constant
flow conditions. Since no decantate is removed volumetric
flow rate of sludge leaving the digester equals flow rate of
sludge entering.

Applying Equations 3 and 2,
FY; = BY, + loss (4)
Loss = 100 (50-30) = 2000 (6)

pvsr = 2% (6)

=——— = 040
(100) (60)

Nomenclature is given in Table D-1. Note that the
calculation did not require use of the fixed solids
concentrations.

The calculation is so simple that one wonders why it is so
seldom used. One possible reason is that the input and
output volatile solids concentrations (Y; and Yp) may show
greater coefficients of variation (standard deviation +
arithmetic average) than the fraction volatile solids (VS,
fraction of the sludge solids’ that is volatile--note the
difference between VS and Y).

Grit Deposition

Grit deposition can be a serious problem in both aerobic
and anaerobic digestion. The biological processes that
occur in digestion dissolve or destroy the substances
suspending the grit and it tends to settle. If agitation is
inadequate to keep the grit particles in suspension they
will accumulate in the digester. The approximate mass
balance can be used to estimate accumulation of fixed
solids.

For Problem 1, the balance yields the following:
FX; = BX, + loss (8)
(100)(17) = (10017) + Fixed Solids Loss (9)
Fixed Solids Loss = 0 (10)

The material balance compares fixed solids in output with
input. If some fixed solids are missing, this loss term will
be a positive number. Since we know that digestion does
not consume fixed solids, we assume that the fixed solids
are accumulating in the digester. As Equation 10 shows,
the fixed solids loss equals zero. Note that for this case
where input and output sludge flow rates are equal, the
fixed solids concentrations are equal when there is no grit
accumulation.

The calculation of fixed solids is repeated for Problem 2.
Conditions in Problem 2 have been selected to show grit
accumulation. Parameters are the same as in Problem 1
except for the fixed solids concentration (Xp) and

parameters related to it. Fixed solids concentration in the



calculation of residence time for several commonly used
digester operating modes:

Case 1
Complete-mix reactors
Constant feed and withdrawal at least once a day

No substantial increase or decrease in volume in the
reactor (V)

One or more feed streams and a single product
stream (q)

Case 1 fits the situation that the regulators had in mind
when the regulation was written. The residence time
desired is the nominal residence time. Use Equation 3 as
shown below:

ve.

=
a qa

vw ¥
q

The concentration terms in Equation 4 cancel out because
Cy = Cy
Case 2a

Complete-mix reactor

Vessel contains a "heel" of liquid sludge Vj}, at the
beginning of the digestion step

Sludge is introduced in daily batches of volume vj and
solids concentration C;

When final volume V; is reached, sludge is discharged
until volume Vj, remains and the process starts again

Some aerobic digesters are run in this fashion. This
problem is a special case of a batch reaction. We know
exactly how long each day's feeding remains in the
reactor. We must calculate an average residence time as
shown in Equation 2:

B,C; X time that batch i remains in the reactor

@ =
n Bic;
The following problem illustrates the calculation:
Let Vp, = 30 m3 (volume of “heel")
Vg = 130 m3 (total digester volume)
4, = each day 10 m3 is fed to the reactor
CG = 12 kg/m3
Vy is reached in 10 days. Sludge is discharged at
the end of Day 10.

Then 6, = (10-12-10 + 10-12-9 +--+ 10-12-1)
10-12 + 10-12 ++-- + 10-12)

0, = 10-12-55 = 5.5 days
10-12-10

Notice that the volume of the digester or of the "heel" did
not enter the calculation.

Case 2b
Case 2 bis the same as Case 2a except:

® The solids content of the feed varies substantially from
day to day.

 Decantate is periodically removed so more sludge can
be added to the digester.

The following problem illustrates the calculation:
Let V, = 30 m3, Vg = 130 m3

Day vj, (m3) _ Solids Content (kg/m3)__ Decantate (m3)

1 10 10 0
10 15
10 20

15

15

10

20

25

© ov on &F OD

15

3

10

15

ry

20

On = (10-10-12 + 10-15-11 + 10-20-10 +---
se) #10-10-3 + 10-15-2 + 10-20-1)

(10-10 + 10-15 + 10-20 +
15 + 10-20)

®n= = 11,950/1,900 = 6.29d

The volume of "heel" and sludge feedings equaled 150
m3, exceeding the volume of the digester. This was made
possible by decanting 20 m3.

Case 3

Same as Case 2 except that after digester is filled it is run
in batch mode with no addition or withdrawals for several
days.

A conservative 6, can be calculated by simply adding the
number of extra days of running to the @, calculated for
Case 2. The same applies to any other cases followed by
batch mode operation.

Case 4

@ Complete-mix reactor
Constant feed and withdrawal at least once a day
No substantial increase or decrease in volume in the
reactor
One or more feed streams, one decantate stream
returned to the plant, one product stream. The
decantate is removed from the digester so the sludge
in the digester is higher in solids than the feed.

+++ + 10-10 + 10-



Compost mixing equipment turns over a windrow of
compost for solar drying prior to screening. (Photo credit:
East Bay Municipal Utility District)

approximately 90% (10-fold). Helminth ova are reduced,
but some species remain substantially unaffected.

Composting

There are several different methods of composting
sewage sludge. Three of the most common methods are
windrow, static aerated pile, and within-vessel composting.
Composting may be a PSRP or a PFRP depending on the
time and temperature variables of the operation. This
section discusses the process conditions necessary for
PSRPs. Those relevant to PFRPs are discussed in
Chapter 5.

Sludge composting involves the aerobic decomposition of
organic constituents at elevated temperatures (ideally
under thermophilic conditions) (see photo, bottom of p.
18). The end result of composting is a highly stable,
humus-like material. Although there are several
composting techniques, the basic process is similar.
Bulking agents such as wood chips, bark, sawdust, straw,
rice hulls, or even finished compost are added to the
sludge to absorb moisture, increase porosity, and add a
source of carbon. This mixture is stored in windrows, large
aerated piles or reactor vessels for a period of time
sufficient to allow substantial decomposition of organic
matter (generally 3 to 4 weeks). The biological activity in
the mixture creates temperatures ranging from 55° to
65°C (131° to 149°F). Pathogen destruction depends on
time and temperature variables. Bulking agents may or
may not be screened from the completed compost and
recycled (see photo, p. 19).

The windrow composting process involves stacking the
mixture to be composted in long windrows. The piles are

18

Taulman Weiss in-vessel composting facility in
Portland, Oregon.

frequently aerated by mechanical turning and mixing (e.g.,
using a front-end loader) to keep an adequate supply of
oxygen available to the microorganisms (see photo, top
left, p. 18). The active windrows are typically placed in the
open air except in areas with heavy rainfall.

The aerated static pile method uses a forced-air supply
instead of mechanical aeration (see Figure 4-3). The
sludge/bulking agent mixture is placed on top of either (1)
a fixed underlying forced aeration system, or (2) a system
involving perforated piping laid on the compost pad
surface and covered with a bed of bulking agent. These
systems are used to blow air into or withdraw it from the
pile. The entire pile is covered with a layer of cured
compost for insulation and containment of noxious odors.

ua Bist
Compost operator measures compost pile temperatures as
part of process monitoring. (Photo credit: East Bay Municipal
Utility District, Oakland, California)



process. Define precisely which steps constitute the
beginning and end of sludge treatment.8 The earliest point
at which treatment can be defined as beginning is the
point at which the sludge is collected from the wastewater
treatment process. For sludges with a high potential for
regrowth, such as heat-treated sludges, the end of
treatment should be as close as possible to the point at
which the treated sludge leaves the site for distribution or
land application. Provide sufficient information for a mass
balance calculation (i.e., actual or relative volumetric flows
and solids concentration in and out of all streams, additive
rates for bulking agents or other additives). Provide a
description of process parameters for each step of the
process, giving typical ranges and mean values where
appropriate. The specific process parameters that should
be discussed will depend on the type of process and
should include any of the following that affect pathogen
reduction or process reliability:

Sludge Characteristics

Moisture/solids content of sludge before and after
treatment

Total suspended solids of sludge before and after
treatment

Volatile solids content of sludge before and after
treatment

Volatile suspended solids of sludge before and after
treatment

Chemical characteristics (as they affect pathogen
survival/destruction)

Type(s) of sludge (unstabilized vs. stabilized, primary
vs. secondary, etc.)

Wastewater treatment plant performance data (as it
affects sludge type, sludge age, etc.)

Sludge quantity

Sludge age

Sludge detention time

Process Characteristics

Sludge feed process (¢.g., batch vs. continuous)

Organic loading rate (e.g., kg VS/m3/day)

Operating temperature(s) (including maximum,

minimum, and mean temperatures)

Operating pressure(s) if greater than ambient

Type of chemical additives and the loading rate
IH

pl

Mixing

Aerobic vs. anaerobic

Duration/frequency of aeration

Dissolved oxygen level maintained
Residence/detention time

Depth of sludge

Mixing procedures

Duration and type of storage (e.g., aerated vs.
nonaerated)

Climate

Ambient seasonal temperature range
Precipitation

8When defining which steps constitute your “treatment process," bear in
mind that all steps included as part of a process equivalent to PSAPs or
PFRPs must be continually operated according to the specifications and
conditions that are ctitical to pathogen destruction and reduction of vector
attraction. Thus, the operational and monitoring burden may be greater
for a multi-step process.

Humidity

Describe how the process parameters are monitored.
Describe the process uniformity and reliability. Provide
actual monitoring data whenever appropriate.

If you are applying for equivalency of stockpiled sludge,
describe how the sludge was produced, how long and
under what conditions it has been stored, the pile volume,
and the relevant sludge characteristics.

Product Description

Describe the type and use of product. Describe the
product monitoring program for pathogens if you have
one. How and when are samples taken? What is analyzed
for? What are the results? How long has this program
been in operation?

Sampling Technique(s)

The PEC will be evaluating the representativeness of the
samples and the adequacy of the sampling and analytical
techniques. For both PSRP and PFRP equivalency,
samples must be taken before and after the process. The
sampling points should correspond to the beginning and
end of the treatment process as defined previously under
Process Description. Samples should be representative of
the sludge product in terms of location of collection within
the sludge pile or batch. The samples taken should
include samples from treatment under the least favorable
operating conditions that are likely to occur, ¢.g.,
wintertime. Describe:

@ Where the samples were collected from within the
sludge mass. (If samples were taken from a pile,
include a schematic of the pile and indicate where the
subsamples were taken.)

Date and time the samples were collected. Discuss
how this timing relates to important process parameters
(eg., turning over, beginning of drying, etc.).
Sampling method used.

How any composite samples were compiled.

Total suspended solids (TSS), volatile solids (VS), and
volatile suspended solids (in mg/l) of each sample.
Ambient temperature at time of sampling.
Temperature of sample at time of sampling.

Sample handling, preservation, packaging, and
transportation procedures.

@ The amount of time that elapsed between sampling and
analysis.

Spiking

If you want to demonstrate equivalency to PFRPs and the

untreated sludge contains low levels of Salmonella spp.,

total enteroviruses, or Ascaris spp. ova, you will have to
spike the untreated sludge with the pathogen(s) just prior
to treatment to ensure sufficient levels to demonstrate
pathogen destruction (see footnote 1, p. 29). Spiking will
generally be necessary for enteroviruses and Ascaris
eggs, since these are normally found in low densities in
sludge. Eggs for this purpose should be eggs obtained
from fecal discharges of humans or pigs (not milked from

"gravid" worms) since these eggs will have developed

maximum hardiness. The added eggs should be

thoroughly blended into the sludge. This is best
accomplished before the sludge is dewatered. However, if
the sludge is being chemically conditioned for dewatering



Composting Sludge, Windrow Fact Sheet
Flow diagram
|
Sludge
—T-_ 1 Compost
Bulking Agent Mixing ‘Composting Curing Screening
non-digestible
materials

67


Contents

Acronyms and Abbreviations

1.
2.

Introduction

Pathogen Reduction

Pathogens of Concern

Routes of Exposure

Approaches to Pathogen Reduction
Measuring Pathogen Reduction

Current Federal Regulations

Sludge Treatment

Requirements for Sites with PSRP-treated Sludges

Requirements for Sites with PFRP-treated Sludges

Requirements for Application of Septic Tank
Pumpings

Protecting Surface Waters

Protecting Ground Waters

Processes to Significantly Reduce Pathogens
Aerobic Digestion

Anaerobic Digestion

Lime Stabilization

Air Drying

Composting

Other Methods

Processes to Further Reduce Pathogens

Composting

Heat Drying

Heat Treatment

Thermophilic Aerobic Digestion

Processes that Are PFRPs When Combined with
PSRP

Other Methods

Determining Equivalency of Sludge Treatment
Processes to PSRPs and PFRPs

Pathogen and Vector Attraction Reductions
that Must Be Achieved by PSRPs and PFRPs

How Does the Pathogen Equivalency
Committee Function?

Who Should Apply for Guidance on Equivalency?

How Long Does the Review Process Take?

How Do | Apply for Equivalency?
Confidential Business Information

How Is Equivalency Defined?

How Do | Demonstrate Equivalency?

Can Pilot-scale Data Be Submitted?

How Do | Prepare an Application
for Equivalency?

Examples of Approvals

Relationship Between the Proposed 503 Sludge
Land Application Regulations and the
PEC's Criteria for Equivalency

Introduction

Class A Standards

Class B Standards

Class C Standards

Reduction of Vector Attraction

References

Appendix A Determination of Residence
Time for Anaerobic and
Aerobic Digestion

Appendix B_ EPA Regional Sludge
Coordinators and Map of
EPA Regions

Appendix C State Sludge Coordinators

Appendix D Determination of Volatile Solids
Reduction in Digestion

Appendix E Examples of Process Summary

Sheet

51

63



Digestion, Two-Stage Anaerobic Fact Sheet

Description - A two vessel system of sludge stabilization, where the first tank is used for digestion and is equipped
with one or more of the following: heater, sludge recirculation pumps, methane gas recirculation, mixers and scum
breaking mechanisms. The second tank is used for storage and concentration of digested sludge and for formation of
a supernatant. Anaerobic digestion results in the breakdown of the sludge into methane, carbon dioxide, unusable
intermediate organics and a relatively small amount of cellular protoplasm: This process consists of two distinct
simultaneous stages of conversion of organic material by acid forming bacteria and gasification of the organic acids
by methane forming bacteria. The methane producing bacteria are very sensitive to conditions of their environment
and require careful control of temperature, pH, excess concentrations of soluble salts, metal cations, oxidizing
compounds and volatile acids. They also show an extreme substrate specificity. Can operate at various loading rates
and is therefore not always clearly defined as either standard or high rate. Digester requires periodic cleanout (from 1
to 2 years) due to buildup of sand and gravel on digester bottom.

Technology Status - Widespread use (60 to 70 percent) for primary or primary and secondary sludge in plants
having a capacity of 1 Mgal/d or more.

Applications ~ Suitable for primary sludge or combinations of primary sludge and limited amounts of secondary
sludges, Digested sludge is reduced in volume and pathogenic organism content, is less odorous and easily
dewatered, and is suitable for ultimate disposal. Advantages over single stage digestion include increased gas
production, a clearer supernatant liquor, necessity for heating a smaller primary tank thus economizing in heat, and .
more complete digestion. Process also lends itself to modification changes, such as to high-rate digestion.

Limitations - |s relatively expensive, about twice the capital cost of single-stage digestion. It is the most sensitive
operation in the POTW and is subject to upsets by interfering substances, e.g., excessive quantities of heavy metals,
sulfides, chlorinated hydrocarbons. The addition of activated and advanced waste treatment sludges can cause high
operating costs and poor plant efficiencies. The additional solids do not readily settle after digestion. Digester
requires periodic cleanout due to buildup of sand and gravel on digester bottom.

Performance —
Influent Effluent Reduction

Total solids 2-7% 25-12% 33 - 58%
Volatile solids 35 - 50%
Pathogens 85 - <100%
Odor Reduction -
Sidestream ~ Gas Production
Quantity -8 to 12 ft3/lb volatile solids added, or 12 to 18 ft3/Ib volatile solids destroyed or 0.6 to 1.25 ft3/cap,
or 11 to 12 ft3/Ib total solids digested.

Quality — 65 to 70% methane No, Hg, H2S, NH, e.tal.,-trace 25 to 30% CO2 550 to 600 Btu/fi3

Physical, Chemical, and Biological Aids — Heat; maintain pH with lime, also ammonia, soda ash, bicarbonate of
soda, and lye are used; addition of powder activated carbon may improve stability of overstressed digesters;
precipitate heavy metals with ferrous or ferric sulfate; control odors with hydrogen peroxide.

Residuals Generated - Supernatant ~ Quality: SS 200 to 15,000 mg/l, BODs 500 to 10, 000 mg/I,, COD 1,000 to
30,000 mg/l, TKN 300 to 1,000 mg/l, Total P 50 to 1,000 mg/l, scum, sludge, gas.

Design Criteria — Solids retention time (SRT) required at various temperatures (22).
Mesophilic Range
Temperature, °F 50 67 75 85 95
SRT, days 55 40 30 25 20

Volume Criteria, (ft3/capita): Primary sludge 1.3-3, Primary and Trickling Filter Sludges 2.6-5, Primary and Waste
Activated Sludges 2.6-6. Tank Size (ft): diameter, 20-115; depth 25-45; bottom slope 1 vertical/4 horizontal. Solids
Loading (Ib vss/ft3/d): 0.04-0.40. Volumetric Loading (ft3/cap/d): 0.038-0.1. Wet Sludge Loading (b/cap/d): 0.12-0.19.
PH 6.7-7.6.

Overall Reliability - Successful operation subject to a variety of physical, chemical and biological phenomena, e.g.,
pH, alkalinity, temperature, concentrations of toxic substances of digester contents. Sludge digester biomass is
relatively intolerant to changing environmental conditions. Under one set of conditions particular concentrations of a
substance can cause upsets, while under another set of conditions higher concentrations of the same substance are
harmless. Requires careful monitoring of pH, gas production, and volatile acids.

Miscellaneous Information — Digester gas can be used for on-site generation of electricity and/or for any in-plant
purpose requiring fuel. Can also be used off-site in a natural gas supply system. Off-site use usually requires
treatment to remove impurities such as hydrogen sulfide and moisture. Removal of COs further increases the heat
value of the gas. Utilization is more successful when a gas holder is provided.



Digestion, Aerobic

Fact Sheet

Flow diagram Primary Sludge

Excess Activated or

Trickling Filter Sludge

Settled Sludge Returned

to Digester

Clear Oxidized Overflow
to Plant

Waste Sludge

69




identification and handling by EPA. if you desire
confidential treatment only until a certain date or until th
occurrence of a certain event, the notice should state this.
If a business has been notified of the requirement of
40 CFR Section 2.208 to assert a claim of
confidentiality and no claim of confidentiality
accompanies the information when it is received b'
EPA, the information may be made available to the
public by EPA without further notice to the business.

How Is Equivalency Defined?

The PEC'’s criteria for equivalency are based on the same
rationale used in developing the 40 CFR 257 regulations,
As explained at the beginning of this chapter, the
operating conditions for the listed PSRPs and PFRPs
were specified to ensure that these processes would
consistently achieve certain levels of pathogen and vector
attraction reduction. To be “equivalent,” other (i.e.,
nonlisted) technologies must achieve these same levels
reduction, as described below. EPA (1989c) discusses tl
scientific data and rationale used to develop some of
these equivalency criteria.

og

PSRP Equivalency

To be equivalent to PSRPs, a process must (1)
consistently reduce the density of pathogenic viruses and
bacteria (measured as the number/gram total suspended
solids sludge [no./g TSS] at 5% solids) in mixed sludge
from a conventional plant by equal to or greater than 1 log
(base 10), and (2) reduce vector attractiveness to the

same degree as properly conducted anaerobic digestion|

The reduction in pathogenic viruses and bacteria can be
demonstrated in different ways, depending on whether th
process is conventional or nonconventional. The
requirements are modified slightly for sludges produced
by no primary/long sludge age (NP/LSA) wastewater
treatment processes, because of the consistently lower
pathogen densities in these sludges. The various criteria!
for demonstrating PSRP equivalency are described belo’
and summarized in Figure 6-3.

o

Conventional Processes

Daia indicate that, for conventional biological and
chemical treatment processes (e.g., digestion, lime
treatment, chlorine treatment), a reduction of 1 log (base!
10) in pathogenic virus and bacteria density correlates
with a reduction of 1 to 2 logs (base 10) in the density of|
indicator organisms (Farrell et al., 1985; Farrah et al.,
1986). On this basis, a 2-log (base 10) reduction in fecal
indicator density is accepted as satisfying the requiremet
to reduce pathogen density by 1 log (base 10) for these
types of processes (EPA, 1989c). Specifically, you must
demonstrate a 2-log (base 10) reduction (measured in
no./g total suspended solids) in either (1) fecal coliforms
and fecal streptococci, or (2) fecal coliforms and
enterococci. In the past, this has been the standard
reduction required to demonstrate equivalency to PSAPs
for conventional processes.

Recently, however, a substantial amount of data have
been generated to indicate that sludge produced by
conventional wastewater treatment and anaerobic

digestion at 35°C (95°F) for more than 15 days contains
fecal coliforms and fecal streptococci at average log (base
10) densities (no./g TSS) of less than 6.0 (Farrell, 1988).
Thus, for processes or combinations of processes that do
not depart radically from conventional treatment (gravity
thickening, anaerobic or aerobic biological treatment,
dewatering, air drying, and storage of liquid or sludge
cake), or for any process where there is a demonstrated
correlation between pathogenic bacteria and virus
reduction and indicator organism reduction, the PEC
accepts an average log (base 10) density (no/g TSS) of
fecal coliforms and fecal streptococci of less than 6.0 in
the treated sludge as indicating adequate viral and
bacterial pathogen reduction. (The average log density is
the log of the geometric mean of the samples taken.
Calculations of average log density should be based on
data from approximately nine sludge samples to account
for the natural variability and the variability of the
microbiological tests.)

Nonconventional Processes

For nonconventional sludge treatment processes, such as

radiation, for which no data are available or data indicate
an inappropriate correlation between pathogen reduction
and indicator organism reduction, indicator organism data
are not acceptable. Instead, you must demonstrate that
your process is capable of causing at least a 1-log (base
10) reduction in the density of the least susceptible
organism (i.e., total enteroviruses or Salmonella spp.).

Processes Treating Sludges Generated by No
Primary/Long Sludge Age (NP/LSA) Wastewater
Treatment

The original PSRP criterion of a 1-log (base 10) reduction
in pathogenic viruses and bacteria was based on
reductions achieved by processes treating mixed sludge
produced by conventional wastewater treatment. Recent
data indicate that sludges produced by no primary/long
sludge age wastewater treatment processes,! such as
extended aeration and oxidation ditch treatment, have
pathogen densities that are approximately 0.3 log (base
10) lower than sludges produced by conventional primary
and waste-activated wastewater treatment processes
(Farrell et al., 1989). Therefore, if NP/LSA sludges are
treated by processes that provide an additional 0.7 log
(base 10) reduction in the density of pathogenic bacteria
and viruses, they will have achieved a pathogen reduction
equivalent to that achieved in a conventional sludge
treated by a PSRP. Thus, to be considered equivalent to
PSRPs, processes that are treating NP/LSA sludges need
only demonstrate a 0.7-log (base 10) reduction in the
density of either pathogenic bacteria or viruses (i.e., total
enteroviruses or Salmonella spp.), whichever is the least
susceptible organism. If the sludge treatment process is a
conventional process, then indicator organism data can be
used to demonstrate pathogen reduction. For NP/LSA
sludges, a conventional process must achieve a 1.4-log
reduction in the density of either (1) fecal coliforms and
fecal streptococci, or (2) fecal coliforms and enterococci.

No primary/iong sludge age treatment processes are processes where
wastewater directly enters a secondary treatment system and sludge
circulates through the system (i.e., “ages") for 20 or more days.



4. Processes to Significantly Reduce Pathogens

Processes to Significantly Reduce Pathogens (PSRPs) are
broadly defined as sludge treatment technologies that
reduce both pathogen levels and the attractiveness of
sludge to disease vectors. These processes effectively
reduce (but do not eliminate) pathogenic viruses and
bacteria; however, they are less effective in reducing
helminth eggs. This level of pathogen reduction is the
minimum requirement if sludge is to be applied to land. It
is acceptable only if the risk of human exposure is
minimized by restricting public access to the application
site, restricting grazing, and delaying the cultivation of
human food crops whose edible parts may contact the
sludge (see Chapter 3). Processes identified in the
Federal regulations (40 CFR 257, Appendix Il) as PSRPs
are aerobic digestion, anaerobic digestion, lime
stabilization, air drying, and composting (Table 3-1).

Aerobic Digestion

In aerobic digestion, sludge is biochemically oxidized in
an open or enclosed aerobic tank (see photo, this page,
and Figure 4-1). To supply the sludge with adequate
oxygen, either the contents of the reactor are agitated by
means of a mixer that introduces air into the sludge, or air
is forcibly injected. The aerobic bacteria decompose
much of the volatile organic matter in the sludge,
converting it primarily to water, nitrate nitrogen, and
carbon dioxide.

Aerobic digestion systems operate in either a batch or
continuous mode. In the batch mode, the tank is filled with
untreated sludge and aeration is maintained for 2 or 3
weeks. Then aeration is discontinued, the stabilized solids
are allowed to settle, and the settled solids and clarified
liquid are separated. The process is begun again with a
small amount of stabilized sludge from the previous batch,
to supply the necessary microbial population, and a new
batch of untreated sludge. In the continuous mode,
untreated sludge is fed into the digester once a day or
more frequently while thickened, stabilized solids and
clarified liquids are removed.

The regulation defines aerobic digestion as a process
“conducted by agitating sludge with air or oxygen to
maintain aerobic conditions at residence times
ranging from 60 days at 15°C (59°F) to 40 days at
20°C (68°F), with a volatile solids reduction of at
least 38%." The regulation does not differentiate between
semi-batch or continuous operation so either method is
acceptable.

These operational requirements are based on a caiculation
of residence time. The appropriate method for calculating
residence time depends on the type of operation of the
digestion process.

® Continuous-mode, No Supernatant Removal. For
continuous-mode digesters where no supernatant is
removed, nominal residence times may be calculated

Digester in Vancouver, Washington.

by dividing liquid volume in the digeSter by the average
daily flow én or out of the digester.

® Continuous-mode, Supernatant Removal. in
systems where supernatant is removed from the
digester and recycled, the volume of sludge product
can be much less than the input volume of sludge. For
these systems, the flow rate of the sludge product out
of the digester is used to calculate residence time.

® Continuous-mode Feeding, Batch Removal of
Product. For some aerobic digesters, the digester is
initially filled above the diffusers with treated effluent
and sludge is wasted daily into the digester.
Periodically, aeration is stopped to allow for settling

* and removal of supernatant. As supernatant is

removed, the solids content in the digester gradually
increases. The process is complete when either settling
and supernatant removal is inadequate to provide
space for the daily sludge wasting requirement or
sufficient time for digestion has been provided. The
batch of digested sludge then is removed and the
process begins again. If the mass of sludge solids
introduced daily has been constant, nominal residence
time is one-half the total time from initial change to final
withdrawal of the digested sludge.

 Batch-mode. In the batch mode, the residence time is
the actual time of the batch.

© Other. Frequently digesters are operated in unique
ways that do not fall into the above categories.



5. Processes to Further Reduce Pathogens

Processes to Further Reduce Pathogens (PFRPs)
effectively reduce bacteria, viruses, and helminth ova in
sludge to below detectable levels. The risk of infection
from PFRP sludge products is therefore minimal. This
level of sludge treatment is required when the land
application process (and thus the potential for human
exposure) cannot be adequately controlled. PFRPs listed|
in the regulation are composting, heat drying, heat
treatment, and thermophilic aerobic digestion (Table 3-2)
If added to a PSRP, the following processes are
considered to be a PFRP: high-energy irradiation, gamma
ray irradiation, and pasteurization.

Composting

As described in Chapter 4, composting reduces sludge,
which has generally been mixed with.a bulking agent, to a
humus-like material through biological degradation. There
are three commonly used methods of composting:
windrow, aerated static pile, and within-vessel.

To be considered a PFRP, the composting operation must
meet certain operating conditions. These regulatory
conditions are specific to the method of composting
practiced. For windrow composting, the sludge must|
attain a temperature of 55°C (131°F) or greater for a
least 15 days during the composting period. In
addition, during the high-temperature period, the
windrow must be turned at least five times. If the
Static aerated pile or the within-vessel method is
used, the sludge must be maintained at operating
temperatures of 55°C (131°F) or greater for 3 days.

in general, within-vessel composting attains the required
conditions in approximately 10 days. The static-pile and
windrow processes generally require about 3 weeks. If the
conditions specified by the regulation are met, all
pathogenic viruses, bacteria, and parasites will be reduced
to below detectable levels. However, composting under
these conditions may not adequately reduce vector
attraction. Longer composting periods may be necessary
to fully stabilize the sludge (see Composting, in Chapter
4). The PFRP definition of composting will likely be
modified in the new regulations.

Heat Drying

Heat drying is used to reduce both pathogens and the
water content of sludge. The regulation defines heat
drying as a process in which “dewatered sludge cake i
dried by direct or indirect contact with hot gases,
and moisture content is reduced to 10% or lower.
Sludge particles reach temperatures well in excess
of 80°C (176°F), or the wet bulb temperature of the
gas stream in contact with the sludge at the point
where it leaves the dryer is in excess of 80°C
(176°F)." Properly conducted heat drying will reduce

G

pathogenic viruses, bacteria, and helminth ova to below
detectable levels.

Four processes are commonly used for heat drying of
municipal sludge: flash dryers, spray dryers, rotary dryers,
and the Carver-Greenfield process (EPA, 1979). Flash
dryers were the most common heat drying process
installed at wastewater treatment plants, but current
practice favors rotary dryers.

Flash Dryers

Flash dryers pulverize sludge in the presence of hot
gases. The process is based on exposing fine sludge
particles to turbulent hot gases long enough to attain at
least a 90% solids content. A schematic of a cage mill
flash drying process is provided in Figure 5-1. In this
system, wet sludge and recycled dried sludge are
combined to create a free-flowing mixture. This mixture
and hot gases are then fed into a cage mill; drawn through
a duct where the particles lose most of their moisture; and
finally drawn through a cyclone, where the sludge
particles are separated from the gases.

Spray Dryers

A spray dryer uses centrifuga! force to atomize liquid
sludge into a spray that is directed into a drying chamber.
The drying chamber contains hot gases that rapidly dry
the sludge mist. Some spray drying systems use a nozzle
to atomize sludge.

Rotary Dryers

Rotary dryers function as horizontal cylindrical kilns. The
drum rotates and may have plows or louvers that
mechanically mix the sludge as the drum turns. There are
many different rotary kiln designs, utilizing either direct
heating or indirect heating systems. Direct heating
designs maintain contact between the sludge and the hot
gases. Indirect heating separates the two with steel shells.

Carver-Greenfield Process

The Carver-Greenfield process is a patented multipie-
effect evaporative oil-immersion process in which
dewatered sludge is mixed with a light oil. This mixture is
pumped through a series of evaporators which selectively
remove the water in sludge, which has a lower boiling
point than the oil carrier. The oil maintains the mixture in a
liquid state, even when virtually all the water has been
removed. The product of this process, an oil and dry
sludge mixture, is put through a centrifuge to separate the
dry sludge solids from the oil. The recovered oil can be
reused in the process.

21



GAS STORAGE

GAS STORAGE

RAW
SLUDGE
stuoce [— f&
HEATER:
FIRST STAGE
(completely mixed)
Figure 4-2. Two-stage anaerobic digestion.

Lime Stabilization

Lime stabilization is a simple process in which lime is
added to sludge in sufficient quantities to produce a pH of
12 after 2 hours of contact. Lime may be introduced to
liquid sludge in a mixing tank. Alternatively, lime may be
mixed with dewatered sludge provided mixing is intimate
and the cake is moist enough to allow aqueous contact
between sludge and lime.

The effectiveness of lime stabilization in controlling
pathogens depends on maintaining the pH at levels that
destroy microorganisms and inhibit growth should
contamination occur after treatment. Lime stabilization
does not reduce volatile solids. Therefore, if the pH drops’
below 11, regrowth of pathogenic bacteria can resume.

Lime stabilization reduces pathogenic bacteria and viruse:
by well over 90 percent (i.e., 10-fold). Some helminth ova
will be destroyed, but certain species are not substantiall
affected by this process.

Air Drying

The air drying process is simply a system that allows the
sludge to dry naturally in the open air (see photo, this
page). Wet sludge is generally applied to sand beds,
paved or unpaved basins to a depth of approximately 23
cm (9 inches). (Sludge depths in basins often exceed 23
cm.) The sludge is left to drain and dry by evaporation.
While sand beds have an underlying drainage system,
basins frequently involve some type of mechanical mixing
or turning. The effectiveness of the drying process
depends very.much on the local climate.

For air drying to be considered a PSRP, the regulations
require at least 3 months of air drying on under-
drained sand beds or paved or unpaved basins with
sludge piled to a maximum depth of 23 cm. (After
drying, the sludge layer will be much thinner.) For at}
least 2 of the 3 months (60 of the 90 days, which do

DIGESTED,
SLUDGE

SECOND STAGE
* (stratified)

not have to be consecutive), the temperature must
average above 0°C (32°F) on a daily basis. During the
2 months that temperatures are above 0°C (32°F), the
sludge beds must be exposed (i.e., not covered with
snow). The sludge should be at least partially digested
before air drying.

Air drying, under the conditions specified above, will
reduce the density of pathogenic bacteria and viruses by

Sludge drying operation. (Photo credit: East Bay Municipal
Utility District)



4s your process a conventional process or one
for which there is a demonstrated correlation

between reductions of pathogenic bacteria and

viruses and reduction of indicator organisms?

Is the sludge to be treated an

i lt
NP/LSA sludge? Is the sludge to be treated an

NP/LSA sludge?

You must demonstrate that your process
is capable of causing at least a 0.7-log
reduction in total enterovirus or
Salmonella spp., whichever is least
susceptible to the process.

You must demonstrate either:

@ An average log density (no./g. TSS)
of less than 6.0 for fecal coliforms
and fecal streptococci in the treated
sludge, or

@ A 1.4-log reduction in either (1) fecal
coliforms and fecal streptococci or
(2) fecal coliforms and enterococci.

|

You must demonstrate either:
An average log density (no./g. TSS)
of less than 6.0 for fecal coliforms
and fecal streptococci in the treated
sludge, or
A 2-log reduction in either (1) fecal
coliforms and fecal streptococci or
(2) fecal coliforms and enterococci.

You must demonstrate that your process |
is capable of causing at least a 1-log |
reduction in total enterovirus or
Salmonella spp., whichever is least i
susceptible to the process.

You must demonstrate
reduction in vector
attraction

(see Table 6-2).

Figure 6-3. Requirements for demonstrating equivalency to PSRP.

NP/LSA plants generally use treatment processes that do
not depart radically from conventional treatment. In such
cases, these plants can also use an average log density of
less than 6.0 for fecal coliforms and fecal streptococci in
the treated sludge to demonstrate adequate viral and
bacterial pathogen reduction. This option is discussed in
Conventional Processes above. Since this approach
involves half the sampling and analytical effort of the
indicator organism reduction approach, it is expected that
most NP/LSA plants will choose the log density option.

Reduction of Vector Attractiveness

To demonstrate that your process is equivalent to PSRPs,
you must also show that it reduces vector attractiveness
to the same degree as properly conducted anaerobic
digestion. This requirement can be satisfied in several
ways depending on the type of sludge.2 Table 6-2
summarizes the equivalency criteria for vector

PSSST SOU i
‘Sludge with demonstrated reduced vector attraction may later attract
vectors if it is improperly handled (e.g., exposed to precipitation or applied
to land at high rates). Applying the sludge to land at agronomic rates will

maintain the reduction in vector attraction. Heat-dried undigested sludges
should not be applied during or shortly after precipitation.



Table 3-1. Regulatory Definition of Processes to Significantly Reduce Pathogens (PSRPs)#.>

Aerobic Digestion: The process is conducted by agitating sludge with air or oxygen to maintain aerobic conditions at residence times
ranging from 60 days at 15°C to 40 days at 20°C, with a volatile solids reduction of at least 38%.

Alr Drying: Liquid sludge is allowed to drain and/or dry on underdrained sand beds, or on paved or unpaved basins in which the sludge
depth is a maximum of 9 inches. A minimum of 3 months is needed, for 2 months of which temperatures average on a daily basis
above 0°C.

Anaerobic Digestion: The process is conducted in the absence of air at residence times ranging from 60 days at 20°C to 15 days at
35°C to 55°C, with a volatile solids reduction of at least 38%.

Composting: Using the within-vessel, static aerated pile, or windrow composting methods, the solid waste is maintained at minimum
operating conditions of 40°C for 5 days. For 4 hours during this period the temperature exceeds 55°C.

Lime Stabilization: Sufficient lime is added to produce a pH of 12 after 2 hours of contact.

Other Methods: Other methods or operating conditions may be acceptable if pathogens and vector attraction of the waste (volatile
solids) are reduced to an extent equivalent to the reduction achieved by any of the above methods.

Source: 40 CFR 257, Appendix Ii.
815°C = 59°F, 20°C = 68°F, 0°C = 32°F, 35°C = 95°F, 55°C = 131°F, 40°C = 104°F.
9 inches = 23 centimeters.

Table 3-2. Regulatory Definition of Processes to Further Reduce Pathogens (PFRPs)*

Composting: Using the within-vessel composting method, the solid waste is maintained at operating conditions of 55°C or greater for
8 days. Using the static aerated pile composting method, the solid waste is maintained at operating conditions of 55°C or greater for 3
days. Using the windrow composting method, the solid waste attains a temperature of 55°C or greater for at least 15 days during the
composting period. Also, during the high temperature period, there will be a minimum of five turnings of the windrow.

Heat Drying: Dewatered sludge cake is dried by direct or indirect contact with hot gases, and moisture content is reduced to 10% or
lower. Siudge particles reach temperatures well in excess of 80°C, or the wet bulb temperature of the gas stream in contact with the
sludge at the point where it leaves the dryer is in excess of 80°C.

Heat Treatment: Liquid sludge is heated to temperatures of 180°C for 30 minutes.

Thermophilic Aerobic Digestion: Liquid sludge is agitated with air or oxygen to maintain aerobic conditions at residence times of 10
days at 55°C to 60°C, with a volatile solids reduction of at least 38%.

Other Methods: Other methods or operating conditions may be acceptable if pathogens and vector attraction of the waste (volatile
solids) are reduced to an extent equivalent to the reduction achieved by any of the above methods.
Any of the processes listed below, if added to a PSRP, further reduce pathogens.

Beta Ray Irradiation: Sludge is irradiated with beta rays from an accelerator at dosages of at least 1.0 megarad at room temperature
(ca. 20°C),

Gamma Ray Irradiation: Sludge is irradiated with gamma rays from certain isotopes, such as 6°Cobalt and '37Cesium, at dosages of
at least 1.0 megarad at room temperature (ca. 20°C).

Pasteurization: Sludge is maintained for at least 30 minutes at a minimum temperature of 70°C.

Other Methods: Other methods or operating conditions may be acceptable if pathogens are reduced to an extent equivalent to the
reduction achieved by any of the above add-on methods.

Source: 40 CFR 257, Appendix Il.
355°C = 131°F, 80°C = 176°F, 180°C = 356°F, 60°C = 143°F, 70°C = 158°F.

12



Digestion, Two Stage Anaerobic Fact Sheet
Flow diagram
Gas Release | | GasRelease |
Gas Gas
Sludge Inlet zone of Mixed Liquor | prrreenrereecrererr Supernatant
Mixing Supernatant — >
Actively
Digesting a
Sludge

Sludge Return

Digested Sludge





Mine spoil land before sludge treatment. Note sparse, Corn grown on sludge-treated soil (right) and untreated soil
weedy growth incapable of supporting grazing cattle. (left).
(Photo credit: City of Tulsa, Oklahoma)

Cross-section of a Douglas fir tree showing how sludge
application increases tree growth. Note increased size of
outer rings indicating more rapid growth after sludge
Mine spoil land after sludge treatment. Note lush vegetative i

cover on reclaimed soil which will support grazing. (Photo application. (Photo credit: Metro Silvigrow)

credit: City of Tulsa, Oklahoma)



Table 6-1.

Processes Determined to Be Equivalent to PSRP jor PFRP

Operator Frocess Description Status
Town of Telluride, Combination oxidation ditch, aerated storage, and drying process. Sludge is treated in an PSRP
Colorado oxidation ditch for at least 26 days and then stored in an aerated holding tank for up to a week.
Following dewatering to 18% solids, the sludge is dried on a paved surface to a depth of 2 feet.
The sludge is turned over during drying! After drying to 30% solids, the sludge is stockpiled prior
to land application. Together, the drying) and stockpiling steps take approximately 1 year. To
ensure that PSRP requirements are met, the stockpiling period must include one full summer
season.
Comprehensive Use of cement kiln dust (instead of lime) to treat sludge by raising sludge pH to at least 12 after PSRP
Materials 2 hours of contact. Dewatered sludge is mixed with cement kiln dust in an enclosed system and
Management, Inc., then hauled off for land application.
Houston, Texas
N-Viro Energy Use of cement kiln dust and lime kiln dust (instead of lime) to treat sludge by raising the pH. National
Systems Ltd., Sufficient lime or kiln dust is added to sludge to produce a pH of 12 for at least 12 hours of PSRP
Toledo, Ohio contact.
Public Works" Anaerobic digestion of lagooned sludge.) Suspended solids had accumulated in a 30-acre PSRP
Department, Everett, aerated lagoon that had been used to aerate wastewater. The lengthy detention time in the
Washington lagoon (up to 15 years) resulted in a level of treatment exceeding that provided by conventional
anaerobic digestion. The percentage ofjfresh or relatively unstabilized sludge was very small
compared to the rest of the accumulation (probably much less than 1% of the whole).
Haikey Creek Oxidation ditch treatment plus storage. Sludge 1s processed in aeration basins followed by PSRP.
Wastewater Storage in aerated sludge holding tanks.| The total sludge aeration time is greater than the
Treatment Plant, aerobic digestion operating conditions ified in the Federal regulations of 40 days at 20°C
Tulsa, Oklahoma (68°F) to 60 days at 15°C (59°F). The oxidation ditch sludge is then stored in batches for at
least 45 days in an unaerated condition or 30 days under aerated conditions.
Ned K, Burleson & Aerobic digestion for 20 days at 30°C (86°F) or 15 days at 35°C (95°F). PSRP
Associates, Inc., Fort
Worth, Texas
Scarborough Sanitary Static pile aerated "composting" operation that uses fly ash from a paper company as a bulking PFRP
District, Scarborough, agent. The process creates pile temperatures of 60° to 70°C (140° to 158°F) within 24 hours
Maine and maintains these temperatures for up, to 14 days. The material is stockpiled after 7 to 14
days of “composting” and then market
Mount Holly Sewage — Zimpro 50-gpm low-pressure wet air oxidation process. The process involves heating raw PFRP
Authority, Mount. primary sludge to'177° to 204°C (350°|to 400°F) in a reaction vessel under pressures of 250
Holly, New Jersey to 400 psig for 15 to 30 minutes. Small yolumes of air are introduced into the process to oxidize
the organic solids.
N-Viro Energy Advanced alkaline stabilization with sul juent accelerated drying. National
Systems Ltd., ® Alternative 1: Fine alkaline materials (cement kitn dust, lime kiln dust, quicklime fines, PFRP
Toledo, Ohio pulverized lime, or hydrated lime) are uniformly mixed by mechanical or aeration mixing into
liquid or dewatered sludge to raise the pH to greater than 12 for 7 days. If the resulting
sludge is liquid, it is dewatered. The/stabilized sludge cake is then air dried (while pH
remains above 12 for at least 7 days) for at least 30 days and until the cake is at least 65%
solids. A solids concentration of at l¢ast 60% is achieved before the pH drops below 12.
The mean temperature of the air surrounding the pile is above 5°C (41°F) for the first 7
days. f
© Alternative 2: Fine alkaline materials, (cement kiln dust, lime kiln dust, quicklime fines,
pulverized lime, or hydrated lime) are, uniformly mixed by mechanical or aeration mixing into
liquid or dewatered sludge to raise the pH to greater than 12 for at least 72 hours. If the
resulting sludge is liquid, it is dewatered. The sludge cake is then heated, while the pH
exceeds 12, using exothermic reactions or other thermal processes to achieve temperatures
of at least 52°C (126°F) throughout the sludge for at least 12 hours. The stabilized sludge is
then air dried (while pH remains above 12 for at least 3 days) to at least 50% solids.
Miami-Dade Water Anaerobic digestion followed by solar drying. Sludge is processed by anaerobic digestion in two Conditional
and Sewer Authority, well-mixed digesters operating in series jn a temperature range of 35° to 37°C (95° to 99°F). PFRP

Miami, Florida

Total residence time is 30 days. The si

ige is'‘then centrifuged to produce a cake of between
15 to 25% solids. The sludge cake is dried for 30 days on a paved bed at a depth of no more
than 46 cm (18 inches). Within 8 days of the start of drying, the sludge is turned over at least
‘once every other day until the sludge reaches a solids content of greater than 70%.The PFRP
approval was conditional on the microbiological quality of the product (see Examples of

Approvals at the end of Chapter 6).



Appendix E

Examples of Process Summary Sheets

The process summary sheets in this Appendix are provided

solely to illustrate the type of information and level of detail

appropriate for process summary fact sheets submitted as|part of an equivalency guidance application for PSRP or

PFRP. The sample sheets in this Appendix are modified fr
provided may be out of date.

TEPA. 1980. Innovative and alternative technology manual. EPA Pub. No.
Ohio.

m a 1980 document.! Therefore, the actual information

}30/9-78-009. EPA Municipal Environmental Research Laboratory, Cincinnati,

63



Composting Sludge, Static Pile

Fact Sheet

FLOW DIAGRAM

SCREENED
‘compost

PERFORATI
PIPE

WATER TRAP
FOR CONDENSATES:

FILTER PILE
SCREENED COMPOST

65



Composting Sludge, Windrow Fact Sheet

Description - Composting is the microbial degradation of sludge and other putrescible organic solid material by
aerobic metabolism in piles or windrows on a surfaced outdoor area. The piles are turned periodically to provide
oxygen for the microorganisms to carry out the stabilization and to carry off the excess heat that is generated by the
process. When masses of solids are assembled, and conditions of moisture, aeration and nutrition are favorable for
microbial activity and growth, the temperature rises spontaneously. As a result of biological self-heating, composting
masses easily reach 60°C (140°F) and commonly exceed 70°C (150°F). Peak composting temperatures
approaching 90°C (194°F) have been recorded. Temperatures of 140° to 160°F serve to kill pathogens, insect
larvae and weed seeds. Nuisances such as odors, insect breeding and vermin harborage are controlled through
rapid destruction of putrescible materials. Sequential steps involved in composting are preparation, composting,
curing and finishing.

Preparation - To be compostable, a waste must have at least a minimally porous structure and a moisture content
of 45 to 65 percent. Therefore, sludge cake, which is usually about 20 percent solids, cannot be composted by
itself but must be combined with a bulking agent, such as soil, sawdust, wood chips, refuse, or previously
manufactured compost. Sludge and refuse make an ideal process combination. Refuse brings porosity to the mix,
while sludge provides needed moisture and nitrogen, and both are converted synergistically to an end product
amenable to resource recovery. The sludge is suitably prepared and placed in piles or windrows.

Composting - The composting period is characterized by rapid decomposition. Air is supplied by periodic turnings.
The reaction is exothermic, and wastes reach temperatures of 140°F to 160°F or higher. Pathogen kill and the
inactivation of insect larvae and weed seeds are possible at these temperatures. The period of digestion is normally
about six weeks.

Curing — This is characterized by a slowing of the decomposition rate. The temperature drops back to ambient, and
the process is brought to completion. The period takes about two more windrow weeks.

Finishing - If municipal solid waste fractions containing non-digestible debris have been included, or if the bulking
agent such as wood chips is to be separated and recycled, some sort of screening or other removal procedure is
necessary. The compost may be pulverized with a shredder, if desired.

Common Modifications - Composting by the static pile method is discussed in Fact Sheet 6.2.3. Composting within
a vessel is an emerging technology.

Technology Status — Successfully demonstrated.

Applications — A sludge treatment method that successfully kills pathogens, larvae and weed seeds. Is suitable for
converting undigested primary and/or secondary sludge to an end product amenable to resource recovery with a
minimum capital investment and relatively small operating commitment.

Limitations - A small porous windrow may permit such rapid air movement that temperatures remain too low for
effective composting. The outside of the pile may not reach temperatures sufficiently high for pathogen destruction.
Pathogens may survive and regrow. Sale of product may be difficult.

Performance ~ Sludge is converted to a relatively stable organic residue, reduced in volume by 20 to 50 percent.
The residue loses its original identity with respect to appearance, odor and structure. The end product is humified,
has earthy characteristics; pathogens, weed seeds and insect larvae are destroyed.

Chemical Requirements - None
Residuals Generated - None

Design Criteria - Approximate land requirement: 1/3 acre/dry ton sludge daily production, which is roughly
equivalent to a population of 10,000 with primary and secondary treatment. Windrows can be 4 to 8 ft high, 12 to 25
ft wide at the base, and variable length. Sludge cannot be comiposted by itself but must be combined with a bulking
agent to provide the biomass with the necessary porosity and moisture content. Biomass criteria: moisture content,
45 to 65 percent; C/N ratio between 30 to 35:1; C/P, 75 to 150:1; air flow 10 to 30 ft3 air/d/lb VS. Detention time, six
weeks to 1 year.

Process Reliability — Highly reliable. Ambient temperatures and moderate rainfall do not affect the process.



therefore are introduced by passing a thin layer of sludge
under the radiation source (Figure 5-3).

Pasteurization

Pasteurization involves heating sludge to above a
predetermined temperature for a minimum time period.
The regulation requires sludge to be heated to at
least 70°C (158°F) for a minimum of 30 minutes.
Proper pasteurization destroys bacteria, viruses, and
helminth ova.

Sludge can be heated by heat exchangers or by steam
injection. Although sludge pasteurization is uncommon in
the United States, it is widely used in Europe. The steam
injection method is preferred because it is more effective
at maintaining even temperatures throughout the sludge
batch being processed. Sludge is pasteurized in batches
to prevent recontamination that might occur in a
continuous process. Sludge must be properly stored after
processing because the organic matter has not been
stabilized and, therefore, odors and regrowth of
pathogenic bacteria can occur if sludge is reinoculated.

INPUT
(UNTREATED OR
DIGESTED SLUDGE)

CONSTANT
HEAD
TANK

UNDERFLOW
WEIR

INCLINED
FEED RAMP

Figure 5-3 Electron beam scanner and sludge spreader.
Source: EPA, 1979.

24

In Europe, serious problems with regrowth of Salmonella
species have occurred, so pasteurization is rarely used
now as a terminal treatment process. Pre-pasteurization
followed by mesophilic digestion has successfully
replaced the use of pasteurization after digestion in many
European communities.

Other Methods

The regulation states that other treatment methods or
other operating conditions may be acceptable if they
reduce pathogens and vector attraction to an extent
equivalent to that achieved by the listed PFRPs. "Other
methods" may be a modification of a listed PSRP or
PFRP, a new process, or a combination of processes. As
noted previously, EPA’s Pathogen Equivalency Committee
provides guidance on the equivalency of other methods or
operating conditions. To obtain this guidance, data
demonstrating the required reductions in pathogens and
vector attraction should be submitted to EPA’s Pathogen
Equivalency Committee for review. The specifics of the
review process are discussed in Chapter 6. Processes
that have been found by the Committee to be equivalent
to PFRPs are described in Table 6-1.

ELECTRON
BEAM

ELECTRON BEAM
— SCANNER
HIGH ENERGY

SLUDGE
J—t—__ RECEIVING
TANK

OUTPUT
(DISINFECTED
SLUDGE)



1. Introduction

Municipal wastewater sludge — a by-product of wastewater
treatment (Figure 1-1) - is used as a soil conditioner and
Partial fertilizer in the United States and many other
countries. It is applied to agricultural land (pastures and
cropland), disturbed areas (mined lands, construction
sites, etc.), plant nurseries, forests, recreational areas
(parks, golf courses, etc.), cemeteries, highway and airport
runway medians, and home gardens (see photos, pp. 3-4).
Certain wastewater treatment plants own or have access
to land dedicated solely to repeated sludge applications.
The U.S. Environmental Protection Agency (EPA), the
primary Federal agency responsible for sludge
management, encourages the beneficial use of sludge
wherever environmentally feasible (Figure 1-2). Some
estimates suggest that as much as 40% of the municipal
sludge generated in the United States is currently applied
to land (EPA, 1984b).

Wastewater sludge has beneficial plant nutrients and soil
conditioning properties; however, it may also contain
bacteria, viruses, protozoa, parasites, and other
microorganisms that can cause disease. All land
application of sludge creates a potential for human
exposure to these organisms through direct and indirect
contact. To protect human health from these organisms
and from the chemical contaminants that some sludges
contain, many countries now regulate land application of
sludge.

In 1976, Congress passed the Resource Conservation and
Recovery Act (RCRA), which required the EPA to regulate
the application of solid waste to land. Under RCRA,
wastewater sludge was defined as a solid waste to be
regulated under the Act. In addition, Section 405 of the
Clean Water Act (CWA) was amended in 1977 to require
EPA to issue regulations for controlling all sewage sludge
use and disposal practices. Under the joint authority of
RCRA and CWA, EPA promulgated regulations governing
the application of wastewater sludge to {and under 40 CFR
Part 257 in September 1979. These regulations were
designed to protect public health by mandating treatment
of sludge to reduce its disease-bearing potential, and by
controlling land use following sludge application.

This document describes the Federal requirements
promulgated in 1979 for reducing pathogens in
wastewater sludge and provides guidance in determining
whether individual sludge treatment systems provide the
level of pathogen and vector control mandated for
particular tand application settings. It is intended for:

®@ Owners and operators of municipal wastewater
treatment works.

@ Developers or marketers of sludge treatment
processes.

© Groups that distribute and market sludge products.

© Individuals involved in applying sludge to land.

@ Regional, state, and local government officials
responsible for implementing and enforcing the land
application regulations. These include the Regional and
State Sludge Coordinators and permit writers.

© Consultants to these groups.

@ Anyone interested in understanding the Federal
pathogen and vector control requirements placed on
land application practices.

Chapter 2 of this document discusses why pathogen
control is necessary, and Chapter 3 summarizes the
pertinent Federal regulations. These regulations list
specific sludge treatment technologies that provide
acceptable levels of pathogen reduction as specified
under 40 CFR Part 257. Chapters 4 and 5 describe these
listed sludge treatment systems. Sludge from other
treatment technologies can be applied to land if the
alternative treatment provides a level of pathogen control
equivalent to that provided by the listed technologies. A
special EPA committee - the Pathogen Equivalency
Committee - was established to review alternative sludge
treatment technologies and to provide technical guidance
on whether they are equivalent. Chapter 6 of this
document describes how the Committee evaluates
equivalency and what information is needed for an
equivalency evaluation. It lists processes that the
Committee has determined to be equivalent. This chapter
is particularly useful for developers and operators of
sludge treatment systems and for those involved in the
permitting process at the regional and state level.

Many municipal wastewater sludges also contain heavy
metals and other toxic organic chemicals that may pose
public health and environmental concerns if applied to
land in excessive amounts. In addition to controlling.
pathogens, the Federal regulations under 40 CFR Part 257
limit the loading rates of some chemicals of concern when
the sludge is applied to land. This document focuses on
pathogen control and does not discuss the requirements
for controlling chemicals. Information concerning sludge
chemical limitations under 40 CFR Part 257 can be found
in EPA (1984b), state regulatory programs, EPA (1983),
and EPA (1989a).

The EPA is currently revising its technical regulations for
ail municipal sludge use and disposal practices, including
land application and distribution and marketing (D&M) of
sludge products. The new regulations covering land
application and D&M were proposed on February 6, 1989
(EPA, 1989b) and are currently scheduled for final
promulgation by October 1991. Land application will
continue to be governed by the 40 CFR Part 257
regulations, as described in this document, until the final
503 regulations are promulgated. The pathogen control
provisions of the proposed new regulations incorporate



Abbreviations and Acronyms

degrees Centigrade

Code of Federal Regulations

centimeters

distribution and marketing

U.S. Environmental Protection Agency

degrees Fahrenheit

Federal Register

gram(s)

gallons per minute

kilogram(s)

liter

logarithm

cubic meter(s)

milligram(s)

milliliter(s)

most probable number

number

no primary/long sludge age

EPA Office of Water Enforcement
and Permits

EPA Office of Water Regulations
and Standards

EPA Pathogen Equivalency Committee

process to further reduce pathogens

plaque-forming unit

pounds per square inch gauge

process to significantly reduce pathogens

EPA Regional Sludge Coordinator

specific oxygen uptake rate

species

State Sludge Coordinator

total suspended solids

volatile solids



Might there be contact betwes

Will crops for direct human

consumption be grown on the
land within 18 months of sludge
application?

Sludge must be treated by PSRP
or PFRP prior to land application.
® If treated by PSRP, public
access to the site must be
restricted for at least

the sludge and the edible portion
of the crop?

Yes

Sludge must be treated by PFRP-
Prior to land application. No
further restrictions apply.

Figure 3-1. Federal requirements for management of municipal

(Surface Water) of the Criteria prohibits discharges (e.g.,
runoff) from solid waste disposal facilities (including land
application sites) that would violate Sections 402, 404, and
208 of the Clean Water Act. Sections 402 and 404 do. not
concern land application sites. (Section 402 establishes
the National Pollutant Discharge Elimination System to
regulate point sources, and Section 404 controls the
discharge of dredged and fill material.) Until the passage
of the Water Act Amendments in 1987, Section 208 of the
Clean Water Act was the primary mechanism for
controlling nonpoint source pollution such as runoff. Under
this section, state and local officials have established
comprehensive plans for water quality control in areas
with substantial water quality problems. Land application
is prohibited if seepage or runoff from the site would
violate these plans.

Section 319 of the 1987 Water Act Amendments instituted
new requirements for control of nonpoint source pollution.
Under this section, each state is required to submit to
EPA a report identifying state waters that are not expected
to meet water quality standards because of nonpoint
source pollution. Each state must also submit to EPA and
implement a management program for controlling
nonpoint pollution. A sludge land application site could be
affected by this program if it is identified as contributing to
nonpoint source pollution of state waters.

Finally, Subpart 257.3-1 (Floodplains) of the Clean Water
Act’prohibits the application of sludge to land in
floodplains where there is the potential of washout that

12 months and grazing by
animals whose products are
consumed by humans must
be prevented for at least
1 month following
application.

if treated by PFRP, no
further restrictions apply.

fastewater sludge applied to land.

may pose a hazard to human health, wildlife, or land or
water resources.

Protecting Ground Waters

Another potential route of human exposure to pathogens
is by drinking water from contaminated groundwater
aquifers. The Criteria protect groundwater resources by
requiring that land application sites may not “contaminate
an underground drinking water source beyond the solid
waste boundary or beyond an alternative boundary” .
(Subpart 257.3-4 [Ground Water]). In the case of sludge
application, "boundary" means the outermost perimeter of
the area where sludge has been applied. An alternative
boundary may be established by a state with an EPA-
approved solid waste management plan only if it does not
result in contamination of ground water that may be
needed or used for human consumption. The
hydrogeologic characteristics of the site and ‘surrounding
land must be considered when setting an alternative
boundary. If sludge application is properly managed, the
potential for groundwater contamination is minimal.



Highway median strip in Illinois after land application of
dried sludge. (Photo credit: Metropolitan Water Reclamation
District of Greater Chicago)

injection of liquid sludge into sod.

Flower beds amended with sludge compost in Tulsa,
Oklahoma. (Photo credit: City of Tulsa, Oklahoma)

Oat field showing sludge-treated (right) and untreated
(left) areas. (Photo credit: City of Tulsa, Oklahoma)



* reduce pathogenic viruses and bacteria at least 90% (ten:

Composted
Sludge

Bulking Agent /
Sludge Mixture
Porous Base:
Wood Chips or
Compost

Figure 4-3. Aerated static pile composting.

Within-vessel composting systems vary greatly in terms
design; however, the basis for each technique is similar.
The process takes place in a reactor vessel where
operating conditions can be carefully controlled (see
photo, top right, p. 18). The compost mixture is actively
aerated and may or may not be actively mixed within the
container by mechanical means, depending on the type of
in-vessel composting system involved.

The regulatory requirements for composting to be
classified as a PSRP are as follows: "Using the within-
vessel, static aerated pile, or windrow composting
methods, the solid waste is maintained at minimum
operating conditions of 40°C (104°F) for 5 days. For
4 hours during this period the temperature exceeds
55°C (131°F)."

Composting under the conditions outlined above will

fold). Helminth ova populations are diminished but not
necessarily eliminated. However, composting as defined
above does not satisfactorily reduce vector attraction. Five
days of composting is not adequate to fully stabilize the
sludge. Fortunately, composting facilities generally
compost actively for longer periods of time (14 to 21 days
for within-vessel; 21 days or more for static aerated pile;
and 30 days or more for windrow) and frequently allow th
compost to "mature" in storage piles for at least several
weeks. The PSRP definition of composting will likely be
changed in the new regulation.

Other Methods

The regulation states that other methods or operating
conditions may be acceptable as PSAPs if they reduce
pathogens and vector attraction of the waste to an extent
equivalent to the reduction achieved by any of the listed
PSRPs operated under the conditions specified (Table
3-1).

perforated

Pipe

Filter Pile of
Composted Sludge

Composted sludge is screened to remove the bulking
agent prior to land application.

EPA has established a Pathogen Equivalency Committee
to provide guidance on whether other methods or
operating conditions are equivalent. To obtain guidance on
whether a proposed process is equivalent to PSRPs, data
demonstrating the required reductions in pathogens and
vector attraction should be submitted to EPA's Pathogen
Equivalency Committee for review. The specifics of the
review process are discussed in Chapter 6. Processes
that have been found by the Committee to be equivalent
to PSRP are described in Table 6-1.

19


United States
Environmental Protection

Agency

Center for Environmental
Research Information
Cincinnati, OH 45268

EPA/625/10-89/006
September 1989

Technology Transfer

SEPA Environm
Regulatio
Technolo

Conirol of P

Municipal We

ental
ns and

gy

thogens in

astewater Sludge >

Sea are





Table 2-1. Principal Pathogens of Concern in Municipal Wastewater and Sludge
Organism Disease/Symptoms

Bacteria
Salmonella spp. Salmoneliosis (food poisoning), typhoid fever
Shigella spp. Bacillary dysentery
Yersinia spp. Acute gastroenteritis (including diarrhea, abdominal pain)
Vibrio cholerae Cholera
Campylobacter jejuni Gastroenteritis
Escherichia coli (pathogenic strains) Gastroenteritis
Viruses
Poliovirus Poliomyelitis
Coxsackievirus Meningitis, pneumonia, hepatitis, fever, common colds, etc.
Echowrus Meningitis, paralysis, encephalitis, fever, common colds, diarrhea, etc.
Hepatitis A virus Infectious hepatitis
Rotavirus Acute gastroenteritis with severe diarrhea
Norwalk agents Epidemic gastroenteritis with severe diarrhea
Reovirus Respiratory infections, gastroenteritis
Protozoa
Cryptosporidium Gastroenteritis
Entamoeba histolytica Acute enteritis
Giardia lamblia Giardiasis (including diarrhea, abdominal cramps, weight loss)
Balantidium coli Diarrhea and dysentery
Toxoplasma gondii Toxoplasmosis
Helminth Worms
Ascaris lumbricoides Digestive and nutritional disturbances, abdominal pain, vomiting, restlessness
Ascaris suum May produce symptoms such as coughing, chest pain, and fever
Trichuris trichiura Abdominal pain, diarrhea, anemia, weight loss
Toxocara canis Fever, abdominal discomfort, muscle aches, neurological symptoms.

Taenia saginata Nervousness, insomnia, anorexia, abdominal pain, digestive disturbances

Taenia solium Nervousness, insomnia, anorexia, abdominal pain, digestive disturbances
Necator americanus Hookworm disease
Hymenolepis nana Taeniasis

Source: EPA (1985) and EPA (1989c).



2. Pathogen Reduction

Pathogens of Concern

Municipal wastewater generally contains four major types
of human pathogenic (disease-causing) organisms:
bacteria, viruses, protozoa, and helminths (parasitic
worms) (EPA, 1985). The actual species and density of
pathogens present in wastewater from a particular
municipality (and the sludge produced when treating the
wastewater) depend on the health status of the local
community and may vary substantially at different times.
The level of pathogens present in wastewater sludge also
depends on the reductions achieved by the wastewater
and sludge treatment processes.

The pathogens in wastewater are primarily associated with
insoluble solids. Primary wastewater treatment processes
concentrate these solids into sludge, so untreated or raw
primary sludges have higher densities of pathogens than
the incoming wastewater. Biological wastewater treatment
processes such as lagoons, trickling filters, and activated
sludge treatment may substantially reduce the number of
pathogens in the wastewater (EPA, 1989c). Nevertheless,
the resulting biological sludges may still contain sufficient
levels of pathogens to pose a public health concern. Table
2-1 lists some principal pathogens of concern that may be
present in wastewater and/or sludge (also see photos, pp.
9-10). These organisms and other pathogens can cause
infection or disease if humans and animals are exposed to
infectious doses. Infectious doses vary for each pathogen
and each host.

Routes of Exposure

When sludge is applied to land, humans and animals can
be exposed to sludge pathogens by coming into direct
contact with the sludge, or indirectly by consuming
drinking water or food that has been contaminated by
sludge pathogens. Insects, rodents, and even farm
workers can contribute to these exposure routes by
transporting sludge and sludge pathogens away from the
land application site. Potential routes of exposure include:

Direct Contact
@ Inadvertent contact with sludge. while applying it to
land.

@ Walking through an application area - such as a forest,
reclamation area, or farmland - shortly after the sludge
application.

@ Handling soil and raw produce from home gardens
where sludge has been applied.

@ inhaling microbes that become airborne (via aerosols,
dust, etc.) during and/or after sludge spreading.

© Contact with dust raised by strong winds or by plowing
or cultivating the soil.

Indirect Contact

© Consumption of pathogen-contaminated crops grown
‘on sludge-amended soil or of other food products that
have been contaminated by contact with these crops.

@ Consumption of pathogen-contaminated milk or other
food products from animals grazing in pastures or fed
crops grown on sludge-amended fields.

@ Ingestion of untreated drinking water or recreational
waters contaminated by runoff from nearby land
application sites or by organisms from sludge migrating
into groundwater aquifers.

@ Consumption of inadequately or uncooked pathogen-
contaminated fish from water contaminated by runoff
from a nearby sludge application site.

® Contact with sludge or pathogens that have been
transported away from the land application site by
rodents, insects, or other vectors.

The potential for exposure diminishes over time as
environmental conditions such as heat, sunlight,
desiccation, and other microorganisms destroy pathogens
that may be present in land-applied sludge. Table 2-2
summarizes the survival rates of four types of pathogenic
organisms on soil and plants. Because protozoan cysts
are rapidly killed by environmental factors, the public
health threat from protozoa in land-applied sludge is
minimal. Bacteria, viruses, and helminths (particularly
helminth eggs which are the hardiest part of the helminth
life cycle) are of much greater concern. Some bacteria are
unique among sludge pathogens in their ability to regrow.
Even very small populations of certain bacteria can rapidly
proliferate under the right conditions. Viruses, helminths,
and protozoa cannot regrow outside their specific host
organism(s). Once reduced by treatment, their populations
stay reduced.

Approaches to Pathogen Reduction

The pathogens in sludge can be reduced to below
detectable levels by adequately treating sludge prior to
land application. Chapters 4 and 5 of this document
describe treatment processes that have been shown to be
effective in controlling pathogens and in controlling the
attractiveness of sludge to disease vectors (insects and
rodents). These processes use a variety of approaches to
reduce pathogens and alter the sludge so that it becomes
a less effective medium for microbial growth and vector
attraction (Table 2-3). They vary significantly in their
effectiveness. For example, some processes may
completely destroy bacteria and viruses but have little or
no effect on helminth eggs. The effectiveness of a
particular process can also vary depending on the
conditions under which it is operated. For example, the
length of time and the temperature to which sludge is



Utah

Kiran Bhayani

Bureau of Water Pollution Control
P.O. Box 16690

Sait Lake City, UT 84116-0690
801-538-6146

Wyoming
Mike Hackett
Water Quality Division
Department of Environmental Quality
Herschler Building
4th Floor West
122 West 25th Street
Cheyenne, WY 82002
307-777-7781

Region 9

Arizona

Barry Abbott, Manager

Solid Waste Unit, Rm. 402

AZ Department of Environmental Quality
2005 North Central Avenue

Phoenix, AZ 85004

602-257-6989 ©

California

Archie H. Matthews, Chief

Regulatory Section

Division of Water Quality

State Water Resources Control Board
P.O. Box 100

Sacramento, CA 95801-0100
916-322-4507

Hawaii
Dennis Tulang, Chief
Wastewater Treatment Works
Construction Grants Branch
HI Department of Health
P.O. Box 3378
633 Halekauwila Street, 2nd Floor
Honolulu, HI 96813
808-548-6769

Nevada

Robert Carlson

Water Quality Offices

NV Department of Conservation and Natural
Resources

Division of Environmental Protection

Capitol Complex

201 South Fall Street

Carson City, NV 89710

702-885-4670

Region 10

Alaska

Glenn Miller

Solid Waste Program Manager
Department of Environmental Conservation
P.O, Box O

Juneau, AK 99811-1800

907-465-2671

Dick Markum

Solid Waste Program Manager
Department of Environmental Conservation
P.O. Box O

Juneau, AK 99811-1800

907-465-2611

Idaho

Al Murrey, Chief

Water Quality Bureau

Division of Environmental Quality

ID Department of Health and Welfare
450 West State Street

Boise, ID 83720

208-334-5860

Robert Braem

Water Quality Bureau

Division of Environmental Quality

ID Department of Health and Welfare
450 West State Street

Boise, ID 83720

208-334-5855,

Washington

Al Hanson

Department of Ecology
Mailstop (PV-11)

Olympia, WA 98504-8711
206-438-7266

€d O’Brien

Department of Ecology
Mailstop (PV-11)
Olympia, WA 98504-8711
206-459-6059

Oregon
Mark Ronayne
OR Department of Environmental Quality
811 S.W. 6th Avenue
Portland, OR 97204
503-229-6442

55



maximize pathogen destruction. When operational
requirements are followed and the product meets the
monitoring requirements, the process is considered a
PFRP. If either requirement is not met, the process is not
a PFRP and the resulting sludge cannot be utilized as
such.



If the members of the PEC determine, based on the
information submitted, that a process is equivalent to
PSRPs or PFRPs, they specify the operating parameters
and any other conditions critical to adequate disinfection
and reduction of vector attraction. These conditions are
communicated to the applicant in the equivalency
determination letter. The process then is considered
equivalent to PSRPs or PFRPs only when operated under
the specified conditions.

\f the Committee determines that a process is not
equivalent, the committee will provide an explanation for
this finding. If additional data are needed, the committee
will describe what those data are and work with the
applicant, if necessary, to ensure that the appropriate data
are gathered in an acceptable manner. The committee
then will review the revised application when the additional
data are submitted.

The PEC’s equivalency determination is reviewed and
approved by the EPA Office of Water Regulations and
Standards before being sent to the applicant. The PEC’s
determinations are not formal binding Agency
decisions. Rather, they constitute technical guidance and
are advisory.

In its first 2 years of operation, the PEC received 13
requests for equivalency determination. Most of these
processes were determined to be equivalent to PSAPs or
PFRPs (see Table 6-1).

Who Should Apply for Guidance on
Equivalency?

All municipal wastewater sludge or sludge-derived
products applied to land must be treated by a PSRP or a
PFRP. No demonstration of equivalency is necessary for
processes listed in the 40 CFR Part 257 regulations that
consistently meet the specified operating conditions (see
Tables 3-1 and 3-2). Processes that deviate in any way
from the specified operating conditions or novel
processes or process combinations not described in
the regulations must reduce pathogens and vector
attraction to an extent equivalent to a PSRP or PFRP;
if you own or operate such a process, you may wish
to obtain guidance on whether your process is
equivalent to either PSRPs or PFRPs before the
sludge product is applied to land.

How Long Does the Review Process
Take?

Generally, the review process takes 1 to 2 months from
the PEC’s receipt of application to recommendation ff the
application is complete. Additional time must be allowed
for state and regional review of the application. If the
application is incomplete the process will take longer or
the applicant may have to reapply at a later date.

How Do | Apply for Equivalency?

Figure 6-1 shows a flow chart for the equivalency
guidance application process. If you have questions about
how to apply, you should contact the Regional Sludge
Coordinator (RSC) in the EPA Water Management Division
of your EPA regional office, or the State Sludge
Coordinator (SSC) in your state's environmental agency

that regulates land application of sludge. (Appendices B
and C provide phone numbers and addresses for the
RSCs and SSCs.) The RSC or SSC will either answer your
questions or direct you to the PEC. The RSCs and SSCs
may also have additional information on equivalency (in
the form of memos and other guidance issued by the PEC
subsequent to the publication of this document) that may
be useful in preparing your application.

There is no application form to fill out. You should prepare
an application according to the instructions and outline
provided on p. 35 (How Do | Prepare an Application for
Equivalency?) and submit two copies to the Regional
Sludge Coordinator at your EPA regional office (see
Appendix B) and one copy to your State Sludge
Coordinator (see Appendix C). The RSC will forward a
copy to the PEC, together with any comments on the
process from the RSC, SSC, or other state or regional
staff who are familiar with the process. The RSC and the
SSC may participate with the PEC in the equivalency
evaluation if they are familiar with your process (e.g.,
through site visits, research activities, etc.).

If you have questions about how to obtain the necessary
microbiological data, you may submit a work plan
describing your proposed approach to sampling and
analysis of the sludge product. The PEC or a designated
representative will review your plan and indicate whether
the approach would be expected to yield acceptable and
complete data.

The PEC forwards a copy of the application to the EPA
Office of Water Enforcement and Permits and the EPA
Office of Water Regulations and Standards (OWRS). The
PEC also forwards copies of any correspondence with you
(e.g., requests for additional data) to the RSC and the
SSC. If the PEC requests additional data, you should
submit that data directly to the PEC. The PEC will forward
it, as appropriate, to the RSC, SSC, and OWRS.

The PEC documents its recommendation concerning each
application and includes any supporting information. A
copy of the final recommendation is forwarded to OWRS
for approval. OWRS forwards the PEC’s conclusions to
the RSC, who forwards a copy to the SSC. The SSC
forwards a copy to the applicant. Figure 6-2 shows the
channels of communication for the equivalency guidance
process.

Confidential Business Information

If you wish to assert a business confidentiality claim
covering part or all of the information submitted to the
PEC, you should follow the procedures spelled out in 40
CFR Part 2 - Subpart B (Confidential Business
Information).

You can assert a business confidentiality claim covering
the information by placing on (or attaching to) the
information, at the time it is submitted to EPA, a cover
sheet, stamped or typed legend, or other form of notice
indicating the claim of confidentiality. Suitable notice
would include language such as "trade secret,"
"proprietary," or "company confidential." If documents for
which confidentiality is asserted are submitted with other
nonconfidential documents they should be clearly
identified and may be submitted separately to facilitate



8. References

APHA (American Public Health Association). 1985.
Standard methods for the examination of water and
wastewater. 16th edition. APHA, Washington, DC.

EPA. 1989a. Guidance for writing case-by-case permit
requirements for municipal sewage sludge. Permits
Division, EPA Office of Water Enforcement and Permits,
Washington, DC.

EPA. 1989b. Standards for the disposal of sewage sludge;
proposed rule. Federal Register 54(23):5746-5902.

EPA. 1989c. Technical support document for pathogen
reduction in sewage sludge. Publication no. PB 89-
136618. National Technical Information Service,
Springfield, Virginia.

EPA. 1988a. POTW sludge sampling and analysis
guidance document. EPA Office of Water Enforcement
and Permits, Washington, DC. Draft.

EPA. 1988b. Sampling procedures and protocols for the
national sewage sludge survey. EPA Office of Water
Regulations and Standards, Washington, DC.

EPA. 1985. Health effects of land application of municipal
sludge. EPA Pub. No. 600/1-85/015. EPA Health Effects
Research Laboratory, Research Triangle Park, North
Carolina.

EPA. 1984a. EPA policy on municipal sludge
management. Federal Register 49:24358. June 12, 1984.

EPA. 1984b. Use and disposal of municipal wastewater
sludge. EPA Pub. No. 625/10-84-003. EPA Center for
Environmental Research Information, Cincinnati, Ohio.

EPA. 1984c. Manual of methods for virology. EPA Pub.
No. 600/4-84/013. Chapter 8, revised 4/86, EPA 600/4-
84/013 (R-8); Chapter 9, revised 4/87, EPA 600/4-84/013
(R-9); Chapter 10, revised 12/87, EPA 600/4-84/013 (R-
10); Chapter 11, revised 3/88, EPA 600/4-84/013 (R-11).
EPA Environmental Monitoring and Support Laboratory,
Cincinnati, Ohio.

EPA. 1983. Process design manual: Land application of
municipal sludge. EPA Pub. No. EPA-625/1-83-016. EPA
Center for Environmental Research Information,
Cincinnati, Ohio.

EPA. 1979. Process design manual for sludge treatment
and disposal. EPA Pub. No. 625/1-79-011. EPA Water
Engineering Research Laboratory and EPA Center for
Environmental Research Information, Cincinnati, Ohio.

Farrah, S.R., G. Bitton, and S.G. Zan. 1986. Inactivation of
enteric pathogens during aerobic digestion of wastewater
sludge. EPA Pub. No. EPA/600/2-86/047. Water
Engineering Research Laboratory, Cincinnati, OH. NTIS
Publication No. PB86-183084/A5. National Technical
Information Service, Springfield, Virginia.

Farrell, J.B. 1988. Evaluating performance of processes
for PFRP. Memo to Larry Fradkin, Chairman, Pathogen

Equivalency Committee. EPA Risk Reduction
Environmental Laboratory, Cincinnati, Ohio. September
13.

Farrell, J.B., G.V. Salotto, and A.D. Venosa. 1989.
Reduction in bacterial densities of wastewater solids by
three secondary treatment processes. Submitted to J.
Water Poll. Control Fed. for publication.

Farrell, J.B., G. Stern, and A.D. Venosa. 1985. Microbial
destructions achieved by full-scale anaerobic digestion.
Workshop on Control of Sludge Pathogens. Series IV.

Water Pollution Control Federation, Alexandria, Virginia.

Fox, J.C., P.R. Fitzgerald, and C. Lue-Hing. 1981. Sewage
organisms: a color atlas. Lewis Publishers, Chelsea,
Michigan. 116 pp.

Garber, W.F. 1982. Operating experience with
thermophilic anaerobic digestion. J. Water Poll. Control
Fed. 54(8):1170-1184,

Goyal, $.M. et al. 1984. Round Robin investigation of
methods for recovering human enteric viruses from
sludge. Appl. Envir. Micro. 48(3):531- 538.

Kenner, B.A. and H.A. Clark. 1974. Determination and
enumeration of Salmonella and Pseudomonas aerugiosa.
J. Water Poll. Control Fed. 46(9): 2163-2171.

Levin, M.A., J.R. Fischer, and V.J. Cabelli. 1975.
Membrane filter technique for enumeration of enterococci
in marine waters. Appl. Microbiol. 30:66-71.

Slanetz, L.W. and C.H. Bartley. 1957. Numbers of
enterococci in water, sewage, and feces determined by
the membrane filter technique with an improved medium.
J. Bacteriol. 74:591-595.

Sorber, C.A. and B.E. Moore. 1986. Survival and transport
of pathogens in sludge-amended soil, a critical literature
review. Rept. No. EPA 600/2-87- 028. EPA Office of
Research and Development, Cincinnati, Ohio.

Tulane University. 1981. Parasites in southern sludges
and disinfection by standard sludge treatment. EPA Pub.
No. 600/2-81-166. NTIS No. PB 82 102344. National
Technical Information Service, Springfield, Virginia.

Whittington, W.A. and E. Johnson. 1985. Application of 40
CFR Part 257 regulations to pathogen reduction preceding
land application of sewage sludge or septic tank pump-
ings. Memorandum to EPA Waiter Division Directors. U.S.
EPA Office of Municipal Pollution Control, November 6,
1985.

Yanko, W.A. 1987. Occurrence of pathogens in distribution
and marketing municipal sludges. EPA Pub. No. 600/1-87-
014. NTIS PB 88-154273/AS. National Technical
Information Service, Springfield, Virginia.

43



6. Determining Equivalency of Sludge Treatment
Processes to PSRPs and PFRPs

Pathogen and Vector Attraction
Reductions that Must Be Achieved by
PSRPs and PFRPs

The Federal regulations governing land application of
municipal sludge require sludge to be treated by either a
Process to Significantly Reduce Pathogens (PSRP) or a
Process to Further Reduce Pathogens (PFRP) prior to
land application. The regulations list acceptable processé
in each of these categories. They also define operating
conditions for these processes that must be followed to
easure that pathogens and vector attraction are
adequately reduced before the sludge is applied to land
(see Tables 3-1 and 3-2 and Chapters 4 and 5 of this
document).

The operating conditions for the listed PSRPs were
selected to ensure the processes would consistently
reduce the density of pathogenic viruses and bacteria in
mixed sludge from a conventional plant by 1 log (base 10)
(Whittington and Johnson, 1985). This is the reduction
achieved by anaerobic digestion under the operating
conditions described in the regulation, which was used a:
the standard to define adequate reduction by PSRPs.

The operating conditions for the listed PFRPs were
selected to ensure that pathogens (as represented by
Salmonella spp., total enteroviruses, and helminth ova)
would be reduced to below the detection limits of the
methods in use in 1979 when the regulations were
promulgated (Whittington and Johnson, 1985). These
detection limits were 3 MPN (most probable number)/100,
ml sludge at 5% solids for Salmonella spp., 1 plaque-
forming unit (PFU)/100 mi sludge at 5% solids for total
enteroviruses, and 1 viable ovum/100 ml sludge at 5%
solids for Ascaris spp.

In addition, both PSRPs and PFRPs must reduce vector
attraction to the same extent as the reduction achieved b:
good anaerobic digestion.

The regulations recognize that other sludge treatment
processes or operating conditions may be able to reduce
pathogens and vector attraction to an extent equivalent to
or greater than the listed PSRPs and PFRPs. They state
that alternative methods "may be acceptable" if
equivalent reductions can be demonstrated.

In 1985, EPA created a Pathogen Equivalency Committee,
(PEC) to review requests for guidance on PSRP and
PFRP equivalency on a case-by-case basis (Whittington
and Johnson, 1985). This chapter explains the review
Process and describes how to apply for PEC guidance.

How Does the Pathogen Equivalency
Committee Function?

The PEC consists of approximately six members with
expertise in microbiology, wastewater engineering,

a

statistics, and sludge regulations. It includes
representatives from EPA's Office of Research and
Development and Office of Water. The committee reviews
and makes recommendations to EPA management on
applications for PSRP or PFRP equivalency. Its members
also provide guidance to applicants on the data necessary
to determine equivalency. The committee does not
recommend process changes or appropriate uses of
sludge products.

ach application is considered on a case-by-case basis.
Applicants submit information on process operating
parameters and/or the sludge product. The committee
evaluates this information in light of the current state of
knowledge concerning sludge treatment and pathogen
reduction.

The applicant is notified in writing by the State Sludge
Coordinator about the Committee’s decision regarding the
application. The committee recommends one of five
decisions about the process or process sequence:

® itis equivalent to PFRPs.

© tis not equivalent to PFRPs.

© itis equivalent to PSRPs.

© Itis not equivalent to PSRPs.

© Additional data or other information are needed.

Most processes have been found equivalent on a site-
specific basis only. That is, the equivalency applies only
to that particular operation run at that location under the
conditions specified. For site-specific PSRP or PFRP.
determinations, equivalency cannot be assumed for the
same process performed at a different location, or for any
modification of the process.

The PEC has considered applications for national
equivalency status. To show national equivalency, the
applicant must demonstrate that the process will produce
the desired reductions in pathogens and vector attraction
under the variety of conditions that may be encountered at
different locations in the country. Processes affected by
local climatic conditions or that use materials whose
properties may vary significantly from one part of the
country to another are unlikely to be found equivalent on a
national basis.

The committee has also evaluated stockpiled sludge. For
example, a municipality may have a pile of sludge created
from a past treatment operation that is no longer in use. If
the municipality can demonstrate that pathogens and
vector attraction have been reduced to PSRP or PFRP
levels throughout the pile, then the sludge may be applied
to land under the same conditions as sludge produced by
a PSRP or PFRP. A finding of equivalency would pertain
only to that pile of sludge.

25



determine if grit accumulation is occurring. If grit is not
accumulating, the Van Kleeck equation could be used. If
decantate is withdrawn, the Van Kleeck equation still
cannot be used unless VS, is nearly equal to VSq.

Average Values

The concentrations and VS values used in the equations
will all be averages. For the material balance methods, the
averages should be weighted averages according to the
mass of solids in the stream in question. The example
below shows how to average the volatile solids
concentration for four consecutive sludge additions.

Volatile Solids
Concentration

50 kg/m?
45 kg/m?

Addition Volume
4 10 m3
2 7m
3 15 me 40 kg/m?
4 12 m3 52 kg/m

a 1OX 0+ 7X4 + 15 x 40 + 12 x 52

x
“ W+7+ 15+ 12

= 46.3 kgm?
(33)

For the Van Kleeck equation, the averages of VS are
required. Properly they should be weighted averages
based on the weight of the solids in each component of
the average although an average weighted by the volume
of the component or an arithmetic average may be
sufficiently accurate if variation in VS is small. The
following example demonstrates the calculation of all three
averages.

Total Solids
Addition Volume Concentration

1 12 m3 72 kgim?
2 8m3 50 kg/m?
3 13 m3 60 kg/m?
4 10 m3 55 kg/m3

Weighted by Mass

vs

72x72 +8 x 50
= 0.795

Weighted by Volume

VS av = 12x0.75+8Xx0.82+13x0.80+ 100.77 (35)
12 +8+13+10

= 0.783

Arithmetic Average
VS av = 0.75 + 0.82 + 0.80 + 0.77
a

= 0.785 (36)

In this example the arithmetic average was nearly as close
as the volume-weighted average to the mass-weighted
average, which is the correct value.

Literature Cited

1. Fisher, W.J. 1984. Calculation of volatile solids during
sludge digestion. In Bruce, A. (ed.) Sewage Sludge
Stabilization and Disinfection. Water Research Centre,
£. Horwood Ltd., Chichester, England, pp. 499-529.

. EPA. Code of Federal Regulations, Title 40, part 257
(40 CFR 257), Part 257--Criteria for Classification of
Solid Waste Disposal Facilities and Practices.

. Water Pollution Control Federation. 1968. Manual of
Practice No. 16, Anaerobic Sludge Digestion. Water
Pollution Control Federation, Washington, DC.

. Van Kleeck, L.W. 1945. Sewage Works J., Operation of
Sludge Drying and Gas Utilization Units. (17 (6), 1240-
1255).

. EPA. 1989. Technical Support Document: Pathogens.
Office of Water Regulation and Standards, Washington,
DC.



WASTEWATER
a

WASTEWATER
TREATMENT

6
fat

mp | < Heal treatment

SLUDGE TREATMENT
* Digestion

* Drying

* Composting

* Lime stabilization

+ Etc,

a"

EFFLUENT —~
one
eae

oO
OOo

PRETREATMENT
BY INDUSTRY

Land Application;
Distribution and
Marketing

* Agricultural tand
* Strip-mined land
+ Forests

* Plant nurseries
emeteries

* Parks, gardens

J DISPOSAL * Landfill cover
+ Ete.

* Incineration
* Landiilling

Figure 1-1. Generation, treatment, use, and disposal of municipal wastewater sludge.

much of the knowledge and experience that has been
gained in implementing 40 CFR Part 257. Thus there are
many similarities between the pathogen control provisions
of the proposed regulations and the guidance provided in
Chapter 6 of this document. It is likely that the information
provided in this document will be of value in implementing
the final 503 regulations. Chapter 7 discusses the
relationship between the proposed 503 regulations and
the guidance in this document.

The U.S. Environmental Protection Agency (EPA) will
actively promote those municipal sludge management
practices that provide for the beneficial use of sludge while
maintaining or improving environmental quality and protecting
public health. To implement this policy, EPA will continue to
issue regulations that protect public health and other
environmental values. The Agency will require states to
establish and maintain programs to ensure that local
governments utilize siudge management techniques that are
consistent with Federal and state regulations and guidelines.
Loca! communities will remain responsible for choosing
among alternative programs; for planning, constructing, and
operating facilities to meet their needs; and for ensuring the
continuing availability of adequate and acceptable disposal or
use capacity.

Figure 1-2. EPA policy on sludge management.
Source: EPA, 19842.



AERODIGESTER

RETURN SLUDGE
TO AERODIGESTER

SETTLING
TANK

OXIDIZED
OVERFLOW
TO PLANT

Figure 4-1. Aerobic digestion.
Appendix A provides information that should be helpful
in developing a calculation procedure for these cases.

Aerobic digestion carried out according to the conditions
specified in the regulation typically reduces viral and
bacterial pathogens by 90% (i.e, by a factor of ten, or 1
log to the base 10). Heiminth ova are reduced to varying
degrees depending on the hardiness of the individual
species. Aerobic digestion typically reduces the volatile
solids content (the microbial food source) of the sludge by
40 to 50% depending on the conditions maintained in the
system.

Anaerobic Digestion

Anaerobic digestion is a biological process similar to
aerobic digestion; however, the bacteria it uses to
decompose the organic matter thrive under conditions
devoid of oxygen. Anaerobic digestion takes place in an
enclosed reactor (Figure 4-2) that may or may not be
heated. The volatile solids are degraded by anaerobic
bacteria and converted primarily to methane and carbon
dioxide. Since the biological activity consumes most of the
elements needed for further bacterial growth, the volatile
solids in the sludge are stabilized.

Most anaerobic digestion systems are classified as either
standard-rate or high-rate systems. Standard-rate systems
take place in a simple storage tank. Mixing, which
accelerates the biological process, is not provided beyond
the natural mixing that occurs from sludge gases rising to
the surface. Sometimes heat is supplied to increase
biological activity.

High-rate systems provide mixing by mechanical means
and are heated, with temperatures being carefully
controlled. In addition, high-rate systems may use pre-
thickened sludge that is introduced into the tank at a

STABILIZED
SLUDGE
TO DISPOSAL

uniform rate in order to maintain constant conditions in the
reactor. Conditions in the high-rate system foster more
efficient sludge digestion.

The regulations define anaerobic digestion as a process
that is “conducted in the absence of air at residence
times ranging from 60 days at 20°C (68°F) to 15 days
at 35° to 55°C (95° to 131°F), with a volatile solids
reduction of at least 38%." (See previous section on
Aerobic Digestion for calculation of residence times.)
Under heated conditions at mesophilic (32° to 38°C [90°
to 100°F]) or thermophilic (48° to 55°C [118° to 131°F])
temperatures, at least 15 days of digestion are required,
assuming the digester is well mixed. Thermophilic
digestion proceeds at a faster rate than mesophilic
digestion, but is more susceptible to upsets, particularly
due to temperature fluctuations. A residence time of 15
days is required to compensate for potential instability in
the process.

Anaerobic digestion conducted under the conditions
outlined above typically reduces viral and bacterial
pathogens by approximately 90% (i.e., 10-fold) or more.
Helminth ova are not substantially reduced under
mesophilic conditions, and may not be completely
reduced at thermophilic conditions less than 53°C
(127°F). (At the time the regulation was written, there was
substantial doubt that anaerobic digesters could be
operated reliably at temperatures above 49°C [1 20°F]
[Garber, 1982], so anaerobic digestion was not included in
the list of PFRPs.) Anaerobic digestion reduces volatile
solids by 35 to 60% depending on the nature of the
sludge and the operating conditions of the digestion
system. If conditions specified by the regulation are
maintained, the process typically reduces volatile solids
by at least 38%.



Arthur Mouberry

Water Quality Section

NC Division of Environmental Management
512 No. Salisbury St.

P.O. Box 27687

Raleigh, NC 27611-7687

919-733-5083

South Carolina

George (Mike) Caughman

Domestic Wastewater Division

Bureau of Water Pollution Control

SC Department of Health and Environmental Control
2600 Bull Street

Columbia, SC 29201

803-734-5300

David Thompson

Domestic Wastewater Division

Bureau of Water Pollution Control

SC Department of Health and Environmental Control
2600 Bull Street

Columbia, SC 29201

803-734-5289

Tennessee

Bob Slayden, Manager

Municipal Facilities Section

Division of Water Pollution Control

TN Department of Health & Environment
4th Floor, T.E.R.R.A. Building

150 Ninth Avenue, North

Nashville, TN 37219-5404
615-741-0633

Bob Odett

Municipal Facilities Section

Division of Water Pollution Control

TN Department of Health & Environment
4th Floor, T-E.R.R.A. Building

150 Ninth Avenue, North

Nashville, TN 37219-5404
615-741-7883

Region 5
Mlinois

Al Keller

IL Environmental Protection Agency
2200 Churchill Road

Springfield, IL 62706
217-782-1696

Indiana

Pat Carroll, Supervisor

Acting Sludge Coordinator (2/9/89)

Land Application Group

Office of Water Management

IN Department of Environmental Management
105 South Meridian

Indianapolis, IN 46206

317-232-8736

Michigan

Dale Brockway

Land Application Unit

Waste Management Division

MI Department of Natural Resources
P.O. Box 30028

Lansing, MI 48909

517-373-8751

Minnesota |

Steven Stark

Municipal Wastewater Treatment Section
Water Quality Division

MN Pollution Control Agency

520 Lafayette Road

St. Paul, MN 55155

612-296-7169

Ohio
Stuart M. Blydenburgh
Technical Assistants Unit
Supervisor, Permits Section
Division of Water Pollution Control
P.O. Box 1049
1800 Water Mark Drive
Columbus, OH 43266-0149
614-644-2001

Wisconsin

John Melby

WI Department of Natural Resources
P.O. Box 7921

Madison, WI 53707

608-267-7666

Robert Steindorf

WI Department of Natural Resources
P.O Box 7921

Madison, WI 53707

608-266-0449

Region 6
Arkansas

Mike Hood

AR Department of Pollution
Control & Ecology

P.O. Box 9583

Little Rock, AR 72219
501-562-8910

Bob Makin

Division of Engineering

Bureau of Environmental Health Services
Arkansas Dept. of Health

State Health Building

4815 Markham

Little Rock, AR 72201

501-661-2623

53



balance and a fixed solids balance, provided it can be
assumed that loss of fixed solids, i.e., accumulation in the
digester is zero.

Selecting a basis for F of 100 m3/d,
Volume balance: 100 = B + D (14)
Fixed solids balance: 100 X; = BX, + DXa (15)
Since the three Xs are known, B and D can be found.

Substituting 100-D for B and the values for the Xs from
Problem 3 and solving for D and B,

(100X17) = (100 - D)(23.50) +(D)(7.24) (16)
D = 40.0 md, B = 60.0 m3/d (17)

The FVSR can now be calctilated by drawing a volatile
solids balance:

FY; = BY, + DYq + loss (18)
FY, - BY, — DY, (19)
Fvsr = 138 = b d
FY,

FVSR = (100) (50) — (60) (41.42) — (40) (12.76) = 040 (20)
(100) (50)

Unless information is available on actual volumes of

decantate and sludge, there is no way to determine

whether grit is accumulating in the digester. If it is

accumulating, the calculated FVSR will be in error.

When we make the calculation shown in Equations 18-20,
we assume that the volatile solids that are missing from
the output streams are consumed by biological reactions
that convert them to carbon dioxide and methane. We
assume accumulation is negligible. Volatile solids are less
likely to accumulate than fixed solids but it can happen. In
poorly mixed digesters, the scum layer that collects at the
surface is an accumulation of volatile solids. FVSR
calculated by Equations 18-20 will be overestimated if
volatile solids accumulation rate is substantial.

Decantate Withdrawal and Grit Accumulation

In Problem 4, there is suspected grit accumulation. The
quantity of B and D can no longer be calculated by
Equations 14 and 15 because Equation 15 is no longer
correct. The values of B and D must be measured. All
parameters in Problem 4 are the same as Problem 3
except measured values for B and D are introduced into
Problem 4. Values of B and D calculated assuming no grit
accumulation (Problem 3 — see previous section), and
measured quantities are compared below:

Calculated Measured
B 60 49.57
D 40 50.43

The differences in the values of B and D are not large but

they make a substantial change in the numerical value of

FVSR. The FVSR for Problem 4 is calculated below:

_ (100)(50) —(49.57)( 41.42) — (50.43)(12,76)
(100)(50)

(21)

FVSR: =0.461

60

if it had been assumed that there was no grit accumula-
tion, FVSR would equal 0.40 (see Problem 3). It is pos-
sible to determine the amount of grit accumulation that
has caused this change. A material balance on fixed
solids is drawn:

FX; = BX, + DX, + Fixed Solids Loss (22)

The fractional fixed solids loss due to grit accumulation is
found by rearranging this equation:

FixedSolids Loss _ "Xp — BXg — PXa (23)

FX, - FX,
Substituting in the parameter values for Problem 4,

Fixed Solids Loss __(100)(17) — (49.57)(28.50) — (50.43)(7.24) (24)
FX, (100) (17)
= 0.100

If this fixed solids loss of 10 percent had not been
accounted for, the calculated FVSR would have been 13
percent lower than the correct value of 0.461. Note that if
grit accumulation occurs and it is ignored, calculated
FVSR will be lower than the actual value.

The Van Kieeck Equation

Van Kleeck first presented his equation without derivation
in a footnote for a review paper on sludge treatment
processing in 19454. The equation is easily derived from
total solids and volatile solids mass balances around the
digestion system. Consider a digester operated under
steady state conditions with decantate and bottom sludge
removal. A total solids mass balance and a volatile solids
mass balance are:

‘My = My + Mg + (loss of total solids) (25)
Mr VS; = My:VSp + Ma-VSq

+ (loss of volatile solids) (26)
where

Mr, Mp, and Mg are the mass of solids in the feed,
bottoms and decantate streams.

The masses must be mass of solids rather than total
mass of liquid and solid because VS is an unusual type of
concentration unit--it is "mass of volatile solids per unit
mass of total solids.

It is now assumed that fixed solids are not destroyed and
there is no grit deposition in the digester. The losses in
Equations 25 and 26 then comprise only volatile solids so
the losses are equal. It is also assumed that the VS of the
decantate and of the bottoms are the same. This means
that the bottoms may have a much higher solids content
than the decantate but the proportion of volatile solids to
fixed solids is the same for both streams. Assuming then
that VS, equals VSq and making this substitution in the
defining equation for FVSR (Equation 2),

(M,+MQ VS, (27)

FVSR = Loss of vol. solids =i
My x VS,

My x VS,



You must demonstrate that:

100 mi sludge at 5% solids
Are you applying for PFRP equivalency for a Sludge contain
treatment process or for stockpiled sludge? ed <3 MPN Salmonella spp.

<1 PFU total enteroviruses.
<1 viable Ascaris spp. ovum.

<1 viable Toxocara spp. oyum.
Process <1 viable Trichuris trichiura ovum.
@ — Vector attraction is reduced.

For the type of process in question, do data

in the literature indicate a correlation

between indicator organism reduction and

reduction of pathogenic viruses and No
bacteria?

For the type of process in question, do data

in the literature indicate that one of these

Yes pathogens is more susceptible than others:
4 Salmonella spp., total enteroviruses,

7 ~ Ascaris spp. ova?
It may be possible to substitute indicator
organism data for total enterovirus and
Salmonella spp. data, Submit a request
and rationale for this to the PEC.

Le

You must complete the testing

No requirements listed in the following box
but may limit testing to the least
‘susceptible organism(s) where
appropriate.

PEC approves substitution?

you must demonstrate that:
You must demonstrate that: 100 ml treated sludge at 5% solids
© — Fecal coliforms and fecal contains:
streptococci or fecal coliforms and <3 MPN Salmonella spp.
enterococci are < 100/g TSS. <1 PFU total enteroviruses.
© 100 mi sludge at 5% solids contain <1 viable Ascaris spp. ovum.
<1 viable Ascaris spp. ovum. @ = Vector attraction is reduced.
© Vector attraction is reduced.

The untreated sludge must be spiked to
No these levels to demonstrate reduction.

—_—*

No
Does the untreated sludge contain at least q
100 viable Ascaris spp. ova/g TSS?

Does the untreated sludge contain at least:

Yes | ® 1,000 MPN Salmonella spp./g TSS.

Yes © = 1,000 PFU total enteroviruses/g TSS.
No spiking is necessaty |] © 100 viable Ascaris spp. ova/g TSS.

Figure 6-4. Requirements for demonstrating equivalency to PFRP,

33



Is your process similar
to one of the PSRPs
or PFRPs described in
the regulations?
Yes

N

You may be able to
demonstrate
equivalency by
providing
performance data
showing that your
process consistently
¢ meets or exceeds

the operating
conditions specified
in the regulations.

Do data in the
literature establish a
reliable relationship

‘between process
operating conditions
and pathogen
reduction?

No

You may be able to
demonstrate equiv-
alency by providing
well-maintained
operating records
and the supporting
literature data.

You must submit
performance data
and microbio-
logical data to
demonstrate
equivalency.

Figure 6-5. | Approaches to demonstrating equivalency.
operating conditions were satisfied may be acceptable as
a substitute for actual microbiological sampling and
analysis. In such cases, you must include adequate
supporting operational and literature data.

Process-specific Performance Data and
Microbiologic Data

In all other cases, both performance data and
microbiological data will be necessary to demonstrate
process equivalency. Specifically, you will need to provide
the following information:

© A description of the various parameters (e.g., sludge
characteristics, process operating parameters, climatic
factors, etc.) that influence (1) the microbiological
characteristics of your sludge product and (2) the
attractiveness of the product to vectors (see Process
Description, p. 35, for more detail on relevant
parameters).

Sampling and analytical data to demonstrate that the
process has reduced pathogens and vector attraction to
the required levels (see previous section for a
description of levels).

A discussion of the reliability of your treatment process
in consistently operating within the parameters
necessary to achieve the appropriate reductions.

Stockpiled Sludge

Stockpiled sludge from a past process can be found
equivalent to PSRP or PFRP. If you are applying for PFRP
equivalency, you must either (1) provide microbiological
data to demonstrate that pathogens are reduced to the
PFRP limits throughout the stockpiled sludge (see PFRP
Equivalency in previous section), or (2) demonstrate that
the treatment process (including, if relevant, the storage
time) that produced the sludge was sufficient to reduce
pathogens to the required PFRP levels (for example, it
may be sufficient to submit indicator organism and
parasite data for a sludge pile produced by a thermal
process, since data indicate a correlation between
indicator organism reduction and reduction of viruses and
pathogenic bacteria when heat is used as the method for
disinfection).

If you are applying for PSRP equivalency, you must
provide microbiological data to demonstrate that the
average log density (no./g TSS) of fecal coliforms and
fecal streptococci is less than 6.0 throughout the
stockpiled sludge and provide data to show that the
treatment process either did not depart radically from
conventional treatment or was a process for which there is
a demonstrated correlation between pathogenic bacteria
and virus reduction and indicator organism reduction.

Reduction of vector attraction must also be demonstrated
for both PSRP and PFRP equivalency. There is a
qualitative correlation between the odor of stockpiled
sludge and its attractiveness to vectors. A finding of no
odors throughout the pile is acceptable as demonstrating
that vector attraction has been adequately reduced in
stockpiled sludge.

Sampling and Analytical Methods

You should use accepted, state-of-the-art techniques for
sampling and analyzing sludge. Important points to
consider when conducting microbiological sampling
include:

@ The choice of sampling device should be appropriate
for the physical characteristics of the sludge (viscosity
and solids content).

Effort must be made to minimize the possibility of
sample contamination.

The samples should be representative of the random
and cyclic variation in sludge characteristics that occur
during treatment. Representative samples can be
obtained by compiling composite samples over volume
(composites over time are generally not appropriate for
microbiological sampling); by ensuring that each grab
sample, or aliquot of a composite sample, is as
representative as possible of the total stream flow
passing the sampling point; by establishing an
appropriate frequency of sampling that accounts for
variation; and by taking an appropriate number of
samples to account for variation.

A minimum of nine measurements on input sludge and
nine measurements on output sludge are needed to
determine log reductions in the densities of viruses,
pathogenic bacteria, and indicator organisms. For



Appendix B
EPA Regional Sludge Coordinators!
and Map of EPA Regions

Bill Butler

U.S. EPA - Region |

Municipal Facilities Branch
(WMT-2111)

Water Management Division

John F. Kennedy Federal Building

Boston, MA 02203

617-565-3564

Ari Harris

U.S. EPA - Region 1!

Water Management Division
26 Federal Plaza

New York, NY 10007
212-264-4707

Ed Ambrogio

U.S. EPA - Region Il

Water Management Division (3WM32)
841 Chestnut Street

Philadelphia, PA 19106

215-597-4491

Vince Miller

U.S. EPA - Region IV
Technology Transfer Unit
Water Management Division.
345 Courtland Street
Atlanta, GA 30365
404-347-3633

Almo Manzardo

U.S. EPA - Region V

Water Division

Technology Section (TUB-9)
230 South Dearborn Street
Chicago, IL 60604
312-353-2105

This list was compiled in May 1989. Some names may have changed si

Ancil Jones

U.S. EPA - Region VI

Water Management Division

Allied Bank Tower at Fountain Place
1445 Ross Avenue

Dallas, TX 75202

214-655-7130

Rao SuramPalli

U.S. EPA - Region VII
Construction Grants Branch
Water Management Division
726 Minnesota Avenue
Kansas City, KS 66101
913-236-2813

Jim Brooks

U.S. EPA - Region VIII

Water Management Division/Municipal
Facilities Branch

999 18th Street

Denver, CO 80202

303-293-1549

Lauren Fondah!

U.S. EPA - Region IX
Water Division

215 Fremont Street

San Francisco, CA 94105
415-974-8587

Dick Hetherington

U.S. EPA - Region X

Municipal Facilities Branch
(WD 133)

1200 Sixth Avenue

Seattle, WA 98101

206-442-1941

\ce that time.


EXHAUST
GAS

RELIEF
VENT

CYCLONE
= STACK”

AUTOMATIC
DAMPERS

EXPANSION SCRUBBER
JOINT

pousLe
MANUAL FLAP VALVE
ORY
DIVIDER

DRY PRODUCT
CONVEYOR

|

WET SLUDGE
CONVEYOR
—>

MIXER,

DISCHARGE SPOUT

WN

AUTOMATIC
DAMPERS

— INDUCED VAPOR FAN

DRAFT FAN

EXPANSION
EXPANSION JOINT
JOINT REMOTE
MANUAL
DAMPERS

COMBUSTION
AIR PREHEATER

INLET
AIR

—_——

DEODORIZING
PREHEATER

BURNERS FURNACE

CAGE MILL.

COMBUSTION AIR FAN

HOT GAS DUCT <————=

Figure 5-1. Flash dryer system (Courtesy of C.E. Raymond).

Source: EPA, 1979.

Heat Treatment

Heat treatment processes are used both to stabilize and
condition sludge. The processes involve heating sludge
under pressure for a short period of time. The sludge
becomes sterilized and bacterial slime layers are
solubilized, making it easier to dewater the remaining
solids. The regulation requires that heat treatment
processes heat liquid sludge to 180°C (356°F) for 30
minutes. If operated according to these requirements, the
process effectively destroys pathogenic viruses, bacteria,
and helminth ova. Sludge must be properly stored after
processing because organic matter has not been reduced

and, therefore, regrowth of pathogenic bacteria can occur
if treated sludge is reinoculated with such organisms.

Two processes have been used for heat treatment: the
Porteous and the Zimpro process. In the Porteous process
the sludge is preheated and then injected into a reactor
vessel. Steam is also injected into the vessel under
pressure. The sludge is retained in the vessel for
approximately 30 minutes after which it is discharged to a
decant tank. The resulting sludge can generally be
concentrated and dewatered to high solids concentrations.
Further dewatering may be desirable to facilitate sludge
handling.



Region 3

Delaware

Ronald E. Graeber

DE Department of Natural Resources and
Environmental Control

Division of Water Resources

Waste Utilization Program

89 Kings Highway

P.O. Box 1401

Dover, DE 19903

302-736-5731

District of Columbia

James R. Collier

DCRA Environmental Control Division
Water Hygiene Branch

5010 Overlook Avenue, S.W.
Washington, D.C. 20037
202-767-7370

Maryland

William E. Chicca, Administrator

Solid Waste Program

Hazardous & Solid Waste Management Administration
MD Department of the Environment

2500 Broening Highway

Baltimore, MD 21224

301-631-3318

Pennsylvania

Stephen Socash

Municipal & Residual Waste Permits Section
Bureau of Waste Management

P.O. Box 2063

Harrisburg, PA 17120

717-787-1749

West Virginia
Clifton Browning
Department of Natural Resources
Division of Water Resources
1201 Greenbrier Street
Charleston, WV 25311
304-348-2108

Virginia
Cal M. Sawyer, Director
Division of Wastewater Engineering
VA Department of Health
109 Governor Street
Room 927
Richmond, VA 23219
804-786-1755

ALL. Willett

Office of Engineering Applications
State Water Contro! Board

2111 North Hamilton Street
Richmond, VA 23230
804-367-6136

Region 4

Alabama

Cliff Evans, Environmental Engineer

Water Division

Municipal Waste Branch

AL Department of Environmental Management
1751 Congressman W.L. Dickinson
Montgomery, AL 36130

205-271-7816

Florida

Tom Connardy

Bureau of Waiter (Planning) Facilities & Regulation,
Domestic Waste Section

FL Department of Environmental Regulation

Twin Towers Office Building 2600 Blairstone Road

Tallahassee, FL 32399-2400

904-488-4524

Georgia
Mike Thomas
GA Department of Natural Resources
205 Butler Street, S.E.
Floyd Towers East
Atlanta, GA 30334
404-656-7400

Kentucky

Arthur S. Curtis, Jr.
Division of Water
Ft. Boone Plaza

18 Reilly Road
Frankfort, KY 40601
502-564-3410

Shelby Jett

Division of Waste Management
Ft. Boone Plaza

18 Reilly Road

Frankfort, KY 40601
502-564-3410

Mississippi
Glen Odoms
Bureau of Pollution Control
P.O. Box 10385
Jackson, MS 39289-0385
601-961-5171

North Carolina

Allen Wahab

Construction Grants Section

NC Division of Environmental Management
512 No. Salisbury St.

P.O. Box 27687

Raleigh, NC 27611-7687

919-733-6900



From Equation 25, recalling that we have assumed that
loss of total solids equals loss of volatile solids,

‘My + Ma = M;—loss of vol. solids (28)
Substituting for M, + Mg into Equation 27,

My, — loss of vol. solids) . vs, (29)
FVSR = 1— 3
My. Vi sp
Simplifying further,
(1 - FVSR) . VS, (30)
FVSR =1-— VS
f
Solving for FVSR,
VS, — VS, (31)
FVSR = £ b

VS, - VS, x vs,

This is the form of the Van Kleeck equation found in
WPCF's Manual of Practice No. 163. Van Kleeck4
presented the equation in the following equivalent form:

VS, x (1 — V8,) (32)

FVSR =1- —————__
VS, x (1 = VS))

The Van Kleeck equation is applied below to Problems
1-4 in Table 1 and compared to the approximate mass
balance equation results:

7 2 3 4
aagmee Mass Balance 0.40 0.40 0.40 0.461
¢

Van Kleeck (VK) 0.40 0.318 0.40 0.40

Problem 1: No decantate and no grit accumulation. Both
methods give correct answers.

Problem 2; No decantate but grit accumulation. VK is
invalid and incorrect.

Problem 3: Decantate but no grit accumulation. AMB
method is valid. VK method is valid only if
VSp = VS.

Problem 4: Decantate and grit accumulation. AMB.

method valid only if B and D are measured.
VK method is invalid.

The Van Kleeck equation is seen to have serious
shortcomings when applied to certain practical problems.
The AMB method can be ‘completely reliable whereas the
Van Kleeck method is useless under some circumstances.

Review and Discussion of Calculation
Methods and Results

Complete Mass Balance Method

The complete mass balance method allows calculation of
volatile solids reduction of all approaches to digestion,

even processes where final volumes in the digester does
not equal initial volume and where daily flows are not
steady. A serious drawback is the need for volatile solids
concentration and volumes of all streams added to or
withdrawn from the digester as well as initial and final
volumes and concentrations in the digester. This can be a
daunting task particularly for the small plants which are
most likely to run their digesters in other than steady flow
modes. For plants of this kind, an "equivalent" method
that shows that the sludge has undergone the proper
volatile solids reduction is likely to be a better choice than
trying to demonstrate 38 percent volatile solids reduction.
An aerobic sludge has received treatment equivalent to a
38 percent volatile solids reduction if specific oxygen
uptake rate is below a specified maximum. Anaerobically
digested sludge has received treatment equivalent to a 38
percent volatile solids reduction if volatite solids reduction
after batch digestion of the product sludge for 40 days is
less than a specified maximums.

Approximate Mass Balance (AMB) Method

The approximate mass balance method assumes that
daily flows are steady and reasonably uniform in
composition, and that digester volume and composition do
not vary substantially from day to day. Results of
calculations and an appreciation of underlying
assumptions show that the method is accurate for all
cases, including withdrawal of decantate and deposition of
grit, provided that in addition to composition of all streams
the quantity of decantate and bottoms (the digested
sludge) are known. If the quantities of decantate and
bottoms are not known, the accumulation of grit cannot be
determined. If accumulation of grit is substantial and
FVSR is calculated assuming it to be negligible, FVSR will
be lower than the true value. The result is conservative
and could be used to show that minimum volatile solids
reductions are being achieved.

The Van Kleeck Equation

The Van Kleeck equation has underlying assumptions that
should be made clear wherever the equation is presented.
It is never valid when there is grit accumulation because it
assumes the fixed solids input equals fixed solids output.
Fortunately, it produces a conservative result in this case.
Unlike the AMB method it does not provide a convenient
way to check for accumulation of grit. It can be used when
decantate is withdrawn provided VS, equals VSq. Just
how big the difference between these VS values can be
before an appreciable error in FVRS occurs is unknown,
although it could be determined by making up a series of
problems with increasing differences between the VS
values, calculating FRVS using the AMB method and a
Van Kleeck equation, and comparing results.

The shortcomings of the Van Kleeck equation are
substantial and may eventually lead to a recommendation
not to use it. However, it has one strong point. The VS of
the various sludge and decantate streams are likely to
show much lower coefficients of variation (standard
deviation + arithmetic average) than volatile solids and
fixed solids concentration. Review of data are needed to
determine how seriously the variation in concentrations
affect the confidence interval of FVSR calculated by both
methods. A hybrid approach may turn out to be
advantageous. The AMB method could be used first to

61



This document was produced by the U.S. Environmental
Protection Agency's Pathogen Equivalency Committee,
consisting of Robert Bastian, Joseph Farrell, Larry
Fradkin, Walter Jakubowski, James E. Smith, Jr., and
Albert Venosa. Jan Connery and Lynn Knight of Eastern
Research Group, Inc., in Arlington, Massachusetts,
prepared the document under the committee’s direction
and from information and data supplied by the committee.
The document was reviewed by several Regional and
State Sludge Coordinators, and by Alfred Dufour (EPA
Environmental Monitoring Systems Laboratory), Vincent
Olivieri (Johns Hopkins University), Charles Sorber
(University of Pittsburgh), and Cris Morrison (EPA Office
of Water Enforcement and Permits). The contributions of
all these individuals are gratefully acknowledged.

This report has been reviewed by the U.S. Environmental
Protection Agency and approved for publication. The
process alternatives, trade names, or commercial products
are only examples and are not endorsed or recommended
by the U.S. Environmental Protection Agency. Other
alternatives may exist or may be developed.

This guidance was published by

U.S. Environmental Protection Agency

Center for Environmental Research Information

Office of Technology Transfer and Regulatory Support
Office of Research and Development

Cincinnati, OH 45268

COVER PHOTOGRAPH: Application of Liquid Sludge to
Forest Land in Washington



Table 7-1. Comparison of Use and Access Restrictions for PSRP Sludges and Class B Sludges

PSRP Sludges Class B Sludges (Proposed Restrictions)
Public Access: Must be restricted for Public Access: Must b¢ restricted for 12 consecutive months following land application.
at least 12 months following sludge
application.
Grazing: Animals whose products are Grazing: Animals must not graze on agricultural land for 30 days after application of sewage
consumed by humans must not graze _ sludge.
‘on the land for at least 1 month
following application.

Food Crops: If the edible portion of Food Crops: Food aa harvested parts above the ground touching the sludge-soil

crops for direct human consumption mixture cannot be grown|for 18 months after application of the sewage sludge. Food crops
may come in contact with the sludge, _with harvested parts below the ground cannot be grown for 5 years unless it is shown that
growing of the crops must be delayed _ there are no viable helminth ova in the soil (in which case the waiting time shall then be 18
for 18 months from the time of months).
application.

Feed Crops: May not be harvested for 30 days after application of sewage sludge.

a



7. Relationship Between the

Proposed 503 Sludge Land

Application Regulations and the PEC’s Criteria for

Equivalency

Introduction

Subpart F of the proposed Part 503 "Standards for
Disposal of Sewage Sludge" (EPA, 1989b), published on
February 6, 1989, describes the requirements for land
application of sludge to replace the 257 regulations. The
proposed 503 land application regulations are
performance-based; they specify reductions and densities
of pathogens that must be achieved in sludges before
they are applied to land. The proposed 503 rule defines
three classes of sludge: Class A, Class B, and Class C.
There is a close correspondence between the proposed
Class A standards and the PFRP equivalency criteria,
Class B standards and the PSRP equivalency criteria, and
Class C standards and the PSAP equivalency criteria for
sludges produced by no primary/long sludge age
(NP/LSA) treatment. Like 257, the proposed 503
regulations also specify some restrictions concerning
access to and use of land where sludge has been applied,
depending on sludge quality.

In part, EPA chose to propose performance-based
standards rather than continue with the technology-based
standards of 257 (PSRPs and PFRPs, see Chapter 3)
because of the potential confusion concerning the
question of equivalency. As discussed in this document,
treatment technologies that are not explicitly listed under
257 as a PSAP or PFRP must reduce pathogens and
vector attraction to an extent equivalent to a listed
technology before the treated sludge can be applied to
land. EPA felt it would be more expedient to replace the
requirement of equivalency with an explicit statement of
the performance requirements that sludge treatment
technologies must meet. EPA developed these new
proposed pathogen performance requirements based on
the knowledge and experience that has been gained from
implementation of the 257 regulations. Therefore, one
important source for the new proposed pathogen
requirements was the equivalency criteria developed by
the Pathogen Equivalency Committee. Thus, there are
many similarities between the proposed 503 requirements
and the pathogen equivalency criteria discussed in
Chapter 6.

The 503 standards described here are proposed
standards. They will be reviewed and revised before final
promulgation, currently scheduled for October 1991. Thus
the final 503 standards will almost certainly differ from
those described here. The extent of the differences will
depend on the extent of the comments received and the
revisions made.

Class A Standards

The proposed requirements for Class A sludges are
similar to the criteria used by the PEC to define
equivalency to PFRPs. The proposed Class A standards

state that "to achieve Class A reduction, the pathogenic
bacteria, viruses, protozoa, and helminth ova in the
sewage sludge must be reduced to below detectable
limits." Alternatively, "when the temperature of sewage
sludge is raised (53°C for 5 days or 55°C for 3 days or
70°C for one-half hour) and the density of fecal coliforms
and fecal streptococci (enterococci) per gram of volatile
suspended solids (VSS) are each equal to or less than
100, the Class A pathogen reduction requirement are
achieved." Class A sludges must also meet vector
attraction reduction requirements as described below.

The proposed 503 Class A requirement to reduce
pathogens to below detectable limits corresponds to the
general guidance for PFRP equivalency-- that Processes
to Further Reduce Pathogens must reduce pathogens to
below detectable limits (Whittington and Johnson, 1985).
The alternative option proposed in 503 of demonstrating
an indicator organism density of equal to or less than 100
organisms/g VSS applies only to certain processes
meeting the specified time and temperature requirements.
This is very similar to the option of demonstrating PFRP
equivalency by showing an indicator organism density of
less than 100/g TSS (Figure 6-4). This option applies only
to processes where there is a correlation between
indicator organism reduction and reduction of pathogenic
viruses and bacteria; these processes include primarily
time- and temperature-controlled processes.

As with PFRP sludges, there are no access and use
restrictions for Class A sludges.

Class B Standards

To achieve the proposed Class B pathogen reductions,
treatment works must demonstrate either "that the
treatment processes reduce the average density of
pathogenic bacteria and of viruses per unit mass of
volatile suspended solids in the sludge two orders of
magnitude lower than those densities in the incoming
wastewater or demonstrate that the densities of each of
the fecal indicator organisms is 6 logig or less." Class B
sludges must also have reduced vector attraction as
discussed below.

These proposed requirements resemble the equivalency
criteria for PSRPs (Figure 6-3). The 503 requirement to
demonstrate a two-order-of-magnitude (i.e., 2-log)
reduction in the density of pathogenic bacteria and viruses
corresponds to the PSAP equivalency requirement to
demonstrate a 1-log reduction in the density of total
enterovirus or Salmonella species (whichever is least
susceptible to the process). The 1-log difference in these
two requirements is because the 503 reduction is
demonstrated by comparing the incoming wastewater to
the treated sludge, whereas the PSRP equivalency
reduction is demonstrated by comparing sludge before
and after treatment. Thus, the 2-log requirement includes

39



Composting Sludge, Static Pile ; Fact Sheet

Description - Wastewater sludge is converted to compost in approximately eight weeks in a four-step process:

Preparation — Sludge is mixed with a bulking material such as wood chips or leaves, in order to facilitate handling, to
provide the necessary structure and porosity for aeration, and to lower the moisture content of the biomass to 60
percent or less. Following mixing, the aerated pile is constructed and positioned over porous pipe through which air
is drawn. The pile is covered for insulation.

Digestion — The aerated pile undergoes decomposition by thermophilic organisms, whose activity generates a
concomitant elevation in temperature to 60°C (140°F) or more. Aerobic composting conditions are maintained by
drawing air through the pile at a predetermined rate. The effluent air stream is conducted into a small pile of
screened, cured compost where odorous gases are effectively absorbed. After about 21 days the composting rates
and temperatures decline, and the pile is taken down, the plastic pipe is discarded, and the compost is either dried
or cured, depending upon weather conditions.

Drying and Screening ~ Drying to 40 to 45 percent moisture facilitates clean separation of compost from wood
chips. The unscreened compost is spread out with a front end loader to a depth of 12 inches. Periodically a tractor-
drawn harrow is employed to facilitate drying. Screening is performed with a rotary screen. The chips are recycled.

Curing — The compost is stored in piles for about 30 days to assure no offensive odors remain and to complete
stabilization. The compost is then ready for utilization as a low grade fertilizer, a soil amendment, or for land
reclamation.

Modifications - 1. Extended High Pile - pile height is extended to 18 ft using a crane (still experimental). Can result
in savings of space and materials. 2. Aerated Extended Pile — each day’s pile is constructed against the shoulder of
the previous day’s pile, forming a continuous or extended pile. Can result in savings of space and materiais.

Technology Status - Successfully demonstrated at four locations and projected to be capable of serving large cities.
Experiments are ongoing on various operating parameters.

Applications - Suitable for converting digested and undigested sludge cake to an end product of some economic
value. Insulation of the pile and a controlled aeration rate enable better odor and quality contro! than the windrow
process from which it evolved.

Limitations ~ The drying process is weather-dependent and requires at least two rainless days. The use of compost
on land is limited by the extent to which sludge is contaminated by heavy metals and industrial chemicals. Industrial
pretreatment of wastewater treatment plant influent should increase the availability of good quality sludges for
composting.

Performance - Sludge is generally stabilized after 21 days at elevated temperatures. Maximum temperatures of
between 60° to 80°C are produced during the first three to five days, during which time odors, pathogens and weed
seeds are destroyed. Temperatures above 55°C (131°F) for sufficient periods can effectively destroy most human
pathogens. The finished compost is humus-like material, free of malodors, and useful as a soil conditioner containing
low levels of essential plant macronutrients such as nitrogen and phosphorus and often adequate levels of
micronutrients such as copper and zinc.

Chemicals Required — None
Residuals Generated — Final product is compost.

Design Criteria (79) — Construction of the pile for a 10 dry ton/d (43 wet tons) operation: 1. A 6-in. layer of
unscreened compost for base. 2. A 94-ft loop of 4-in. dia. perforated plastic pipe is placed on top (hole dia. 0.25 in.).
3. Pipe is covered with 6-in. layer of unscreened compost or wood chips. 4. Loop is connected to a 1/3 hp blower
by 14 ft of solid pipe fitted with water trap to collect condensate. 5. Timer is set for cycle of 4 minutes on and 16
minutes off. 6. Blower is connected to conical scrubber pile (2 yd3 wood chips covered with 10 yd3 screened
compost) by 16 ft of solid pipe. 7. Sludge (wet) - wood chip mixture in a volumetric ratio of 1:2.5 is placed on
prepared base. 8. A 12-in. layer of screened compost is placed on top for insulation. Air Flow: 100 ft3/h/ton of sludge;
land area requirement for 10 dry tons processed daily: 3.5 acres, including runoff collection pond, bituminous
surface for roads, mixing, composting, drying, storage, and administration area. Pile dimension: 53 ft x 12 ft x 8 ft
high. Population equivalent, 100,000.

Process Reliability - High degree of process reliability through simplicity of operation. Thoroughness (percent
stabilization) is a function of recycle scheme, porosity distribution in pile, and manifold design.

Toxics Management — Heavy metals entering the process remain in the final product. The degree of removal of
organic toxic substances is not defined.

64



Table 2-3. | General Approaches to Controlling Pathogens in Wastewater Sludge
Approach Effectiveness Process Examples@
Kill pathogens with high temperatures Depends on time and temperature. Sufficient © Composting (uses biological processes to
(temperatures may be generated by temperatures maintained for sufficiently long generate heat).

chemical, biological, or physical
processes).

time periods can destroy
tozoan cysts, and helmi
are the most resistant to

Kill pathogens with radiation. Depends on dose. Suffic}
destroy bacteria, virvseo |
helminth ova. Viruses ar

radiation.

Kill pathogens using chemical
disinfectants.

Substantially reduces ba
vector attraction. Probab!
cysts. Does not effectivel
unless combined with hea

Reduces viruses and bac}
attraction as long as the
Probably effective in destt
cysts. Does not effectivel
unless combined with oth
high temperature.

Inhibit pathogen growth by reducing
the sludge’s volatile organic content
{the microbial food source).

Reduces viruses and bact
attraction as long as the

Probably effective in desti
cysts. Does not effectivel
ova unless combined with
‘such as high temperature;

Inhibit pathogen growth by removing
moisture from the sludge.

‘h

acteria, viruses, pro- © Heat drying and heat treatment ( use
th ova. Helminth ova physical processes to generate heat, e.g.,
igh temperatures. hot gases, heat exchangers).
® Pasteurization (physical heat, e.g., hot
gases, heat exchangers).
® Aerobic digestion (biological heat).b
Anaerobic digestion (biological heat).®
jent doses can Gamma and high-energy electron beam
protozoan cysts, and radiation.
most resistant to
teria, viruses, and © = Superchlorination.
reduces protozoan @ Lime stabilization.
reduce helminth ova
it.
teria. Reduces vector @ Aerobic digestion.
ludge remains dry. © Anaerobic digestion.
foying protozoan ® Composting.®
reduce helminth ova
br processes such as
teria. Reduces vector @ Air drying.

luge remains dry.
roying protozoan
ly reduce helminth
other processes

@ See Chapters 4 and 5 for a description of these processes. Many
» Effectiveness depends on design and operating conditions.

few representative pathogens and nonpathogenic indicator
organisms are generally included in the analysis.

For routine testing of municipal wastewater sludge, fecal
coliform and fecal streptococci bacteria are commonly
used as indicators of the potential presence of pathogens
in wastewater sludges. These bacteria are abundant in
human feces and therefore are always present in
untreated sewage sludges. They are easily and
inexpensively measured. Although fecal coliforms and
fecal streptococci themselves are usually not harmful to
humans, their presence indicates the presence of fecal
waste which may contain pathogens.

When more specific information is needed on the levels of
pathogens in sludge, it is generally considered acceptable
to test for one representative of each of the three more
common types of organisms of concern — bacteria,
viruses, and helminth ova. Deciding which organism to
test for depends on several factors: the effectiveness of
the treatment process, the hardiness of the organism

processes use more than one approach to reduce pathogens.

relative to other organisms of that type, the likelihood that
it was present in the raw sludge, the availability and
reliability of the testing procedures, and cost.

Testing requirements should be based on a knowledge of
how the operating conditions of the sludge treatment
process affect pathogen survival. For example, heating
sludge to particular temperatures (e.g., 45° to 50°C [113°
to 122°F]) for a sufficient period of time will destroy all
viruses and bacteria, but may not adequately reduce
helminth ova. In this case, fecal indicator tests could be

_used to confirm the level of reduction of bacteria and
viruses; however, helminth ova would have to be tested
for directly.

The processes described in Chapters 4 and 5 of this
document are assumed to consistently provide an
adequate level of pathogen control for particular land
application settings. No testing is necessary for sludges
produced by these processes if they are properly
operated.



Appendix C
State Sludge Coordinators

Region 1
Connecticut

Warren Herzig

Department of Environmental Protection
Water Compliance Unit

State Office Building

165 Capital Avenue

Hartford, CT 06106

203-566-8652

Maine

Brian Kavanah

ME Department of Environmental Protection
Bureau of Solid Waste Management

State House Station 17

Augusta, ME 04333

207-582-8740

Massachusetts

Dennis Dunn
MA Department of Environmental Quality Engineering
Division of Water Pollution Control
1 Winter Street

Boston, MA 02108

617-556-1130

New Hampshire

Richard Flanders, Jr., Supervisor

Water Supply and Pollution Contro! Division
Department of Environmental Services

P.O. Box 95

6 Hazen Drive

Concord, NH 03301

603-271-3571

Carl F. Woodbury

NH Solid Waste Bureau

Health and Human Services Building
6 Hazen Drive

Concord, NH 03301

603-271-2925

Rhode Island

Chris Campbell

Senior Environmental Planner

Department of Environmental Management
291 Promenade Street

Providence, RI 02908-5657

401-277-3961

Vermont

George Desch, Chief

Residuals Management Section
Department of Environmental Conservation
103 South Main Street

Building 9 South

Waterbury, VT 05676

802-244-8744

Region 2

New Jersey

Helen Pettit-Chase

Acting Bureau Chief

Bureau of Pretreatment and Residuals
Division of Water Resources (CN-029)

NJ Department of Environmental Protection
Trenton, NJ 08625

609-633-3823

New York

Richard Hammond, Supervisor
Residuals Management Section
Division of Solid Waste

50 Wolf Road

Albany, NY 12233-4013
518-457-2051

Puerto Rico

Eva Hernandez
Environmental Quality Board
P.O. Box 11488

Santurce, Puerto Rico 00916
809-723-0733

Virgin Islands

Leonard G. Reed, Jr.

Assistant Director, Environmental Protection Division
Vt Department of Planning and Natural Resources
45 A Nisky, Suite 231

St. Thomas, VI 00802

809-774-3320



Appendix D

Determination of Volatile Solids Reduction in Digestion

By J. B. Farrell

Introduction

When sewage sludge is utilized on land, Federal
regulations require that it be treated by a "process to
significantly reduce pathogens" (PSRP) or a "process to
further reduce pathogens" (PFRP). A requirement of both
of these steps is a reduction in “vector attraction" of the
sludge. If the PSRP or PFRP is anaerobic or aerobic
digestion, the requirement for vector attraction reduction ig
achieved if volatile solids are reduced by 38 percent. As
Fischer? has noted, ihe Federal regulation2 does not
specify a method for calculating volatile solids reduction.
Fischer observed that the United Kingdom has a similar
requirement for volatile solids reduction for digestion (40
percent), but also failed to prescribe a method for
calculating volatile solids reduction. Fischer has provided
a comprehensive discussion of the ways that volatile
solids reduction may be calculated and their limitations.
He presents the following equations for determining
volatile solids reduction:

1. Full mass balance equation

2. Approximate mass balance equation
3. "Constant ash" equation

4. Van Kleeck equation

The full mass balance equation is the least restricted but
requires more information than is currently collected at a
wastewater treatment plant. The approximate mass
balance equation assumes steady state conditions. The
“constant ash" equation requires the assumption of
steady state conditions as well as the assumption that ash
input rate equals ash output rate. The Van Kleeck
equation, which is the equation generally suggested in
publications originating in the United States? is equivalent
to the "constant ash" equation. Fischer calculates volatile
solids reduction using a number of examples of
considerable complexity and illustrates that the different
methods frequently yield different results. He closes with
the recommendation, obviously directed to rulemakers,
that "if it is necessary to specify a particular value for
FVSR (fractional volatile solids reduction) then the
specification should indicate the method of calculation of
FVSR."

Fischer's paper is extremely thorough and is highly
recommended for someone trying to develop a deep
understanding of potential complexities in calculating
volatile solids reduction. However, it was not written as a
guidance document for field staff faced with the need to
calculate volatile solids reduction in their own plant. The
nomenclature is precise but so detailed that it makes
comprehension difficult. In addition, two important
troublesome situations that complicate the calculation of
volatile solids reduction--grit deposition in digesters and
decantate removal--are not explicitly discussed.
Consequently, this presentation has been prepared to

present guidance that describes the maior pitfalls likely to
be encountered in calculating volatile solids reduction and
assists the practitioner of digestion to the best route to
take for his situation.

The recommendation of this presentation is not the same
as Fischer's. He suggests that the authorities should have
provided a calculation method when they required specific
volatile solids reductions. From a review of Fischer’s
results and this presentation, it will be clear that
sometimes very simple calculations will give correct
results and in other cases the simple methods will yield
results seriously in error. Selecting one method and
requiring that it be followed is excessively restrictive. The
best solution is to require that the calculation be done
correctly and then provide adequate guidance. This
presentation attempts, belatedly, to provide that adequate
guidance.

It is important to note that the calculations of volatile solids
reduction will only be as accurate as the measurement of
volatile solids content in the sludge streams. The principal
cause of error is poor sampling. Samples should be
representative, covering the entire charging and
withdrawal periods. Averages should cover extended
periods of time during which changes in process
conditions are minimal. For some plants it is expected that
periodic checks of volatile solids reduction will produce
results so erratic that no confidence can be placed in
them. In this case, adequacy of stabilization can be
verified by the method suggested in the text--periodically
batch digest the product for 40 days. If VS reduction is
less than 15%, the product is sufficiently stable.

The Equations for FVSR

The equations for fractional volatile solids reduction
(FVSR) that will be discussed below are the same as
developed by Fischer', except for omission of his
“constant ash” equation: This equation gives identical
results to the Van Kleeck equation so it is not shown.
Fischer's nomenclature has been avoided or replaced with
simpler terms. The material balance approaches are
called "methods" rather than "equations." The material
balances are drawn to fit the circumstances. There is no
need to formalize the method with a rigid set of equations.

In the derivations and calculations that follow, both VS
(total volatile solids content of the sludge or decantate on
dry solids basis) and FVSR are expressed throughout as
fractions to avoid the frequent confusion that occurs when
these terms are expressed as percentages. "Decantate"
is used in place of the more commonly used
“supernatant” to avoid the use of "s" in subscripts.
Similarly, "bottoms" is used in place of “sludge” to avoid
use of "s" in subscripts.

57



3. Current Federal Regulations

The current Federal regulations governing land application
of municipal wastewater sludge were created under the
joint authority of the Resource Conservation and Recovery
Act (RCRA) and the Clean Water Act (CWA). They are
contained in 40 CFR Part 257 - Criteria for Classification
of Solid Waste Disposal Facilities and Practices (see also]
44 Federal Register 53460, September 13, 1979; and 44
FR 54708, September 21, 1979). (Land application of
sludge is considered a form of solid waste disposal and is
subject to these Criteria.) These regulations protect public!
health by requiring sludge management practices that
eliminate or minimize human contact with sludge
contaminants. The 40 CFR 257 regulations concerning
pathogen control are described below. They apply to all
municipal sludge destined for land application, including
sludge products that are distributed and marketed.

Sludge Treatment

Part 257.3-6 (Disease) of the Criteria requires that
wastewater sludge be treated before it is applied to land td
reduce pathogen levels and to reduce the attractiveness
of sludge to disease vectors (rodents, flies, mosquitoes,
etc., that could transmit disease to humans). Appendix II
of Part 257 lists specific treatment processes and
operating conditions that must be followed to ensure
appropriate pathogen and vector attraction reduction.
These processes are divided into two categories based on
the level of pathogen control they can achieve:
"Processes to Significantly Reduce Pathogens” (PSRPs),
which reduce pathogens to a level comparable to that
achieved by a well-run anaerobic digester, and
"Processes to Further Reduce Pathogens” (PFRPs),
which reduce pathogens to below detectable levels. The
listings of PSRPs and PFRPs found in Appendix I! of Part
257 are reproduced in Tables 3-1 and 3-2. Chapters 4 and
5 of this document describe these processes. Sludge
treated by any of these processes can be applied to land,
as long as the management practices detailed in Part
257.3-6 of the regulation are followed (Figure 3-1).

Requirements for Sites with PSRP-
treated Sludges

Since PSRPs reduce but do not eliminate pathogens,
PSRP-treated sludge still has a potential to transmit
disease. To protect public health, the regulations minimize
the potential for direct and indirect exposure to sludge by
controlling public access, the growing of human food
crops, and grazing by dairy or meat-producing livestock at
sites where PSRP-treated sludges have been applied.
Specifically, public access to the site must be restricted
for at least 12 months following application of the PSRP-
treated sludge, and grazing by animals whose products
are consumed by humans must be prevented for at least
1 month following application. The 1-month waiting period
is based on the typical survival rate of viruses and

bacteria on vegetation. Crops for direct human
consumption (i.e., crops such as fruits and vegetables that
will not be processed to minimize the presence of
pathogens prior to distribution to the consumer) can be
grown on the land only if the edible portion of the crop will
not come in contact with the sludge, or if the growing of
these crops is delayed by at least 18 months from the
time of sludge application. The 18-month waiting period is
based on the anticipated survival of the hardiest
pathogens, helminth eggs.

Requirements for Sites with PFRP-
treated Sludges

PFRPs reduce pathogens to below detectable levels,
therefore there are no pathogen-related restrictions to
managing sites where PFRP-treated sludges have been
applied. Treatment by a PFRP is important to protect
human health (1) in situations where access to the land
application site or food products from that site cannot be
controlled, such as with home gardens, and (2) at sites
where crops for direct human consumption will be grown
within 18 months of application and there may be contact
between the sludge and the edible portion of the crop.

Requirements for Application of Septic
Tank Pumpings

The 40 CFR 257 regulations treat septic tank pumpings in
a slightly different manner from sludge (Figure 3-2).
Septic tank pumpings can be applied without any form of
treatment if (1) public access to the site is restricted for at
least 12 months; (2) grazing by animals whose products
are consumed by humans is prevented for at least 1
month; and (3) crops for direct human consumption are
not grown within 18 months of application. If crops for
direct human consumption will be grown within 18 months
of application, septic tank pumpings must be treated prior
to application. PFRP treatment is required if the septic
tank pumpings might contact the edible portion of the
crop. If no such contact will occur, PSRP-treated
pumpings can be applied if public access to the site is
restricted for at least 12 months and grazing by animals
whose products are consumed by humans is prevented
for at least 1 month following application. The
requirements for septic tank pumpings are more relaxed
because the pumpings have generally been stored for
long periods of time (which reduces pathogen levels) and
land applications of septic tank pumpings are most often
small-scale operations in rural settings.

Protecting Surface Waters

Humans may be exposed to sludge pathogens in drinking
water or recreational waters if land application practices
result in the contamination of surface waters. (If sludge
application is properly managed, this route of exposure is
unlikely.) To protect surface waters, Subpart 257.3-3

1



Technology Transfer

EPA/625/10-89/006

Environmental
Regulations and
Technology

Control of Pathogens i
Municipal Wastewater
For Land Application

Under 40 CFR Part 25

This guidance was prepared by
Pathogen Equivalency Committee
U.S. Environmental Protection Agency
Cincinnati OH 45268

Printed on Recycled Paper

n
Sludge

7



solids content is 75% or greater and remains at this level
until the point of land application (such sludges may
spontaneously combust unless dried to 95% solids or
greater so caution in storage is suggested). Sludges that
maintain a pH of 11.5 up to the time of land application
are also considered to have adequately reduced vector
attraction. For stockpiled sludge, a finding of no odors
throughout the pile is accepted as evidence of adequately
reduced vector attraction.

PFRP Equivalency

Figure 6-4 summarizes the requirements for PFRP
equivalency. To be equivalent to PFRPs, a process must
reduce microorganisms to below the following limits:

@ Salmonella spp. - 3 MPN/100 mi sludge at 5% solids
(100 ml sludge at 5% solids equals approximately 5 g
dry solids).3.4.5

Total enteroviruses - 1 plaque-forming unit (PFU)/100
ml sludge at 5% solids.3.4.5

Helminth ova - 1 viable ovum/100 mi sludge at 5%
solids.5 For treatment processes, you must
demonstrate this reduction for Ascaris spp. only.3 If
you are applying for PFRP status for stockpiled sludge,
you must demonstrate that Ascaris spp., Toxocara
spp., and Trichuris trichiura have been reduced to no

more than 1 viable egg per 100 ml sludge at 5% solids.

(These additional requirements for stockpiled sludge
are necessary because it is impossible to know

570 demonstrate adequate pathogen destruction, the untreated sludge
must contain 1,000 MPN Salmonella spp./g total suspended solids (TSS);
1,000 PFU total enteroviruses/g TSS; and 100 viable Ascaris spp. ovalg
8S prior to treatment. If your untreated sludge does not naturally
contain these densities, you must spike it to achieve these levels (see
Spiking later in this chapter).

However, if you can demonstrate that one organism is more susceptible
than others, it may be sufficient to test only for the least susceptible
organism, For example, viruses are much less sensitive to radiation than
bacteria and helminth ova. For radiation-based processes, it is sufficient
to demonstrate that the process reduces viruses to the required level. If
you think your process might qualify for this reduction in testing, provide
the PEG with the data necessary to substantiate your claim.

4 For processes for which data in the literature indicate a correlation
between indicator organism reduction and reduction of pathogenic viruses
and bacteria (for example, thermal processes using temperatures of
sufficient degree and duration to anticipate pathogen destruction, e.g., 3
days at 53°C (127°F], 30 minutes at 70°C [158°F)), it may be possible
to substitute indicator organism data for total enterovirus and Salmonella
spp. data. If you think your process might qualify for such a substitution,
consult with the PEC prior to performing microbiological testing, and
provide the committee with the data necessary to substantiate your claim.
Processes that qualify for this substitution must demonstrate the
capability to reduce either fecal coliforms and fecal streptococci or fecal
coliforms and enterococci to densities below 100/g total suspended solids.

5For sludges with a different solids percentage, the volume or weight
equivalent of § grams dry solids must be calculated to determine the
appropriate units of sludge for demonstrating PFRP pathogen reduction.
This is done by dividing § grams by the density of the sludge. For
‘example, for a 1% sludge, the density (an a volume basis) is
approximately 1 9/100 ml. For this sludge, the volume equivalent of 5 g is:

S.q dry solids = 500 ml,

79/100 mi
Thus, to meet PFRP requirements, a 1% sludge must contain less than 3
MPN Salmonella spp., 1 PFU total enteroviruses, and 1 viable helminth
‘ovum per 500 ml sludge. For an 18% sludge, the density (on a weight
basis) is 0.18 g dry solids/t g total sludge cake. The weight equivalent of
8 g dry solids is:__5.q dry solids = 28 grams sludge cake.
0189 dry solids/1 g sludge cake

whether the untreated sludge contained helminths. A
negative finding for one helminth species alone does
not necessarily indicate helminth reduction. It may
simply mean that species was not present initially.
Negative findings in three species provides greater
reassurance of destruction.)

In addition, as part of PFRP equivalency, you must
demonstrate that your process reduces vector
attractiveness to the same degree as properly conducted
anaerobic digestion (see above).

How Do | Demonstrate Equivalency?

Equivalency must be demonstrated either directly, by
measuring microbe levels and vector attraction in sludge
as described above, or indirectly by relating process
parameters to reduction of pathogens and vector
attraction.6 Three basic approaches can be taken to
demonstrate equivalency, as described below and.
summarized in Figure 6-5.

Note: Conventional design methods do not ensure that
your process will meet the pathogen and vector attraction
reduction requirements. Likewise, a reduction in volatile
solids does not necessarily correlate with adequate
pathogen destruction.

Comparison to Operating Conditions for Existing
PSRPs or PFRPs

If your process is similar to a PSRP or PFRP described in
the regulations (see Tables 3-1 and 3-2), you may be able
to demonstrate equivalency by providing performance
data showing that your process consistently meets or
exceeds the conditions specified in the regulations.

For example, a process that consistently produces a pH of
12 or greater for 2 hours of contact (the conditions
required in the regulations for lime stabilization) but uses a
substance other than lime to raise pH would qualify as a
PSRP. In such cases, microbiological data would not be
necessary.

Use of Literature Data to Demonstrate Adequacy
of Operating Conditions

If scientific data from the literature establish a reliable
relationship between operating conditions (time,
temperature, pH, etc.) and pathogen reduction, well-
maintained operating records verifying that the necessary

®Gertain conventional and commonly used wastewater treatment and
sludge treatment processes, such as oxidation ditch and extended
aeration wastewater treatment systems and aerobic sludge digesters with
traditional detention times (20 to 30 days) may not qualify. as equivalent
to PSAPs or PFRPs without some modification. However, it is possible
that they may meet new regulatory requirements that will eventually be
promuigated under the Part 503 Sewage Sludge Regulation. (Proposed
Part 503 regulations were published for public comment in the Federal
Register on February 6, 1989 [EPA, 1989b]. They contain a special Class
G sludge category for sludges generated in systems such as but not
limited to oxidation ditch and extended aeration wastewater treatment
systems, See Chapter 7.) To avoid the expense of permanent process
modifications that may not be necessary once the new regulations are
promulgated in final form, operators of these technologies may wish to
make less expensive temporary modifications, such as combining the
process with lime treatment or providing additional aerobic digestion
through aerated storage, in order to qualify as a PSAP or PFRP.









Are there questions about the application process?

Applicant prepares application and sends two
Yes { copies to the RSC and one copy to the SSC.
The RSC compiles comments on the

- applications from the SSC and any
Contact State or Regional Sludge Coordinator appropriate state or regional EPA personnel

(SSC or RSC). who may have knowledge of the facility. The
RSC then forwards a copy of the application
L and comments to the PEC. The PEC forwards

Yes a copy to the EPA Office of Water
Question(s) answered? Regulations and Standards (OWRS) and the
Office of Water Enforcement and Permits.
No L
Contact Pathogen Equivalency Committee (PEC).

mi it A i d
PEC communicates additional data needs to applicant in Aro additions)

writing with copies to SSC, RSC, and OWRS.

J

Applicant submits additional data to PEC. The PEC with input from the RSC and the SSC,
makes an equivalency recommendation and
documents its decision. The recommendation is
forwarded to OWRS for approval. OWRS forwards
the PEC’s conclusions to the RSC, who forwards a
copy to the SSC. The SSC forwards a copy to the
applicant.

Figure 6-1. PSRP and PFRP equivalency application and determination process.

Applicant
*

EPA Regional Sludge Coordinator State Sludge Coordinator

EPA Regional Office EPA Pathogen Equivalency Committee

of Water
Enforcement and mI EPA Office of Water

Permits Enforcement and Permits

a4

EPA Office of Water
Regulations and Standards

Figure 6-2. Channels of communication for equivalency guidance.



and this conditioning is severe (e.g., lime conditioning)
and has not been defined as part of the sludge treatment
process, the blending may have to be done afterwards.

Analytical Methods

Identify the analytical techniques used and the
laboratory(s) performing the analysis.

Analytical Results

Summarize the analytical results, preferably in tabular
form. Provide a discussion of the results and a summary
of major conclusions. Where appropriate, present the
results graphically. Provide copies of original data in an
Appendix.

Quality Assurance

Describe how you have assured the quality of the
analytical data. Subjects appropriate to address are: Why
your sample(s) are representative; your quality assurance
program; the qualifications of your laboratory or the
Contract laboratory used; and the rationale for selecting
your sampling and analysis technique (if it was not one
recommended in this document).

Reduction of Vector Attraction

Describe the ability of your process to reduce the
attractiveness of the sludge to vectors (see Table 6-2 for a
description of ways to demonstrate reduction of vector
attraction). If you used the criterion of volatile solids
reduction to demonstrate reduction of vector attraction,
you must describe how the VS reduction was calculated.
Appendix D provides guidance on caiculating VS
reduction.

Rationale for Why Process Should Be
Determined PSRP or PFRP Equivalent

Describe why you think your process qualifies for PSRP
or PFRP equivalency. Provide complete references for
any data that you cite. You may wish to describe or review
particular aspects of the process that contribute to
Pathogen reduction and/or vector attraction, and why you
are confident that the process will operate consistently. If
you are applying for national approval, discuss why you
expect that process effectiveness will be independent of
the location of operation.

Appendices
If you have provided sampling and analytical data, attach
a copy of the complete laboratory report(s) as an

appendix. Attach any important supporting literature
references as appendices.

Examples of Approvals

Table 6-1 lists processes that have been found by the
PEC to be equivalent to PSRPs or PFRPs. Three of these
Processes are discussed below.

Raising Sludge pH Using an Alternative Chemical

A Texas-based company requested approval of a
treatment process as a PSRP. The process was similar to
lime stabilization except that cement kiln dust was used
instead of lime to raise sludge pH. The data provided by
the applicant showed that the process reliably raised

sludge pH to greater than 12 for at least 2 hours, so the
PEC found that the process was equivalent to PSRPs.

Use of a Chemical to Generate Heat for
"Composting"

The Scarborough Sanitary District in Maine requested
approval of their sludge treatment process as a PFRP.
The process was described as composting using fly,ash
as a bulking agent. The applicant provided time and
temperature data demonstrating that the piles reached
temperatures of 60° to 70°C (140° to 158°F) within 24
hours and maintained them for up to 14 days. The
process exceeded the PFRP requirements for static
aerated pile composting. However, the PEC found that the
process might not in fact be a composting process since it
worked by adding an inorganic agent (fly ash) that
produced high temperatures. The regulatory requirements
for composting were based on the generation of heat by
the biological processes that occur when an organic
bulking agent is used. Thus, a determination of
equivalency was necessary.

The applicant provided information on the location of the
samples from the compost pile, so that the PEC could
determine that sufficient temperatures were maintained
throughout the pile to provide adequate pathogen
destruction. The applicant demonstrated that the product
would not attract vectors because it was dry and would
not putrefy. The PEC found that the process was
equivalent to PFRPs because it met the regulatory PFRP
operating conditions for composting.

Combined Anaerobic Digestion and Solar Drying

The Miami-Dade Water and Sewer Authority requested
PFRP approval for a combination process involving
anaerobic digestion followed by solar drying. In this
process, sludge is anaerobically digested for 30 days at
temperatures of 35° to 37°C (95° to 99°F). After
centrifugation, the sludge is dried for 30 days on a paved
bed at a depth of no more than 46 cm (18 inches). The
drying process is a batch process.

Microbiological analysis of the sludge showed that the
drying process caused reductions in bacteria, viruses, and
helminth ova that met or exceeded PFRP criteria.
However, the process depends on natural conditions
(sunlight, ambient temperature, and precipitation) that
cannot be controlled. The PEC was therefore unable to
approve the process as a PFRP on the basis of a
technology description alone, since the operator could not
guarantee that the process would always meet the
necessary operating conditions. Instead, the PEC required
monitoring of each batch of treated sludge.

Because this treatment process involved biological
treatment, desiccation, and elevated temperatures, there
was likely to be some correlation between indicator
organism densities and reduction of pathogenic bacteria
and viruses. The PEC therefore approved the substitution
of fecal indicator densities for expensive and
technologically complex viral and bacterial pathogen tests;
however, specific tests for helminth ova were required.
The PEC specified the number, frequency, and location of
samples required for monitoring. The PEC also specified
operational procedures that the process must follow to

37



The Zimpro process is similar to the Porteous process.
However, air is injected into the sludge before it enters th,
reactor and the vessel is then heated by steam to reach
the required temperature. Temperatures and pressures
are approximately the same for the two processes.

Thermophilic Aerobic Digestion

Thermophilic aerobic digestion is a refinement of the
conventional aerobic digestion processes discussed in
Chapter 4. In this process, feed sludge is generally pre-
thickened and an efficient aerator is used. In some
modifications, oxygen is used instead of air. Because
there is less sludge volume and less air to carry away
heat, the heat released from biological oxidation warms
the sludge in the digester to as high as 60°C (140°F).

Because of the increased temperatures, this process
achieves higher rates of organic solids destruction than
conventional aerobic digestion which operates at ambient
air temperature. The biodegradable volatile solids content
of the sludge can be reduced up to 70% in a relatively
short period of time. The digested sludge is effectively
pasteurized due to the high temperatures. Pathogenic
viruses, bacteria, and parasites are reduced to below
detectable limits if temperatures exceed 55°C (131 °F).

This process can either be accomplished using auxiliary
heating of the digestion tanks or through special designs
that allow the energy naturally released by the microbial
digestion process to heat the sludge. The regulation
fines thermophilic aerobic digestion as a process wher.
uid sludge is agitated with air or oxygen to
maintain aerobic conditions at residence times of 10
days at 55° to 60°C (131° to 140°F), with a volatile
solids reduction of at least 38%." The thermophilic
process requires significantly lower residence times than
conventional aerobic processes designed to qualify as a
PSRP, which must operate 40 to 60 days at 20° to 15°C
(68° to 59°F) respectively. Residence time is normally
determined by dividing the volume of sludge in the vessel]
by the volumetric flow rate.

Processes that Are PFRPs When
Combined with a PSRP

EPA has determined that certain combinations of
processes, if carried out in series, will attain the pathogen!
reduction of a PFRP. The current regulation specifies
three processes that, if combined with a PSRP, would be
considered a PFRP: high-energy irradiation, gamma ray
irradiation, and pasteurization. These three processes do
not reduce vector attraction. The addition of a PSRP is
necessary to ensure this reduction.

Electron and Gamma Ray Radiation

Radiation can be used to disinfect municipal wastewater
sludge. Radiation destroys certain organisms by altering
the colloidal nature of the cell contents (protoplasm).
Gamma rays and high-energy electrons are the two
potential energy sources for use in sludge disinfection.
Gamma rays are high-energy photons produced by
certain radioactive elements. High-energy electrons are
electrons accelerated in velocity by electrical potentials in

the vicinity of 1 million volts.1 Both types of radiation
destroy pathogens that they penetrate if the doses are
adequate.

The regulatory requirements for irradiation systems are as
follows:

@ High-energy electron irradiation — Sludge is
irradiated with energized electrons from an
accelerator at dosages of at least 1.0 megarad at
room temperature (ca. 20°C [68°F]).

Gamma ray irradiation — Sludge is irradiated with
gamma rays from certain isotopes, such as 60
Cobalt and 137 Cesium, at dosages of at least 1.0
megarad at room temperature (ca. 20°C [68°F]).

The effectiveness of radiation in reducing pathogens
depends on the radiation dose, which is measured in rads.
A dose of 1 megarad or more will reduce pathogenic
viruses, bacteria, and helminths to below detectable
levels. Lower doses may successfully reduce bacteria and
helminth ova but not viruses. Sludge must be properly
stored after processing because organic matter has not
been reduced and, therefore, regrowth of pathogenic
bacteria can occur if sludge is reinoculated.

Although the two types of radiation function similarly to
inactivate pathogens, there are important differences.
Gamma rays can penetrate substantial thicknesses of
sludge and can therefore be introduced to sludge by
either piping liquid sludge into a vessel that surrounds the
radiation source (Figure 5-2) or by carrying composted or
dried sludge by hopper conveyor to the radiation source.
High-energy electrons have limited penetration ability and

SLUDGE
INLET

GROUND
LEVEL

ROAR

HEGRE Sal

COBALT

CONCRETE
SHIELDING

SLUDGE
OUTLET

Figure 5-2 Schematic representation of cobalt-60 (gamma ray)
irradiation facility at Geiselbullach, West Germany.

Source: EPA, 1979.

(Certain radioactive elements also produce high-energy electrons, called
beta rays. This term is generally reserved for electrons generated by
naturally occurring radioactive decay.



Table 2-2. Survival Times of Pathogens in Soil an

\d on Plant Surfaces?

Pathogen Absolute eae Com jaximum Absolute sn Ca Maximum
Bacteria 1 year 2 months 6 months 1 month
Viruses 6 months 3m res 2 months 1 month
Protozoan cysts 10 days 2 days 5 days 2 days
Helminth ova 7 years 2 years 5 months 1 month

Source: EPA, 1985.

4 For survival rates, see Sorber and Moore (1986).

» Greater survival time is possible under unusual condi
sheltered conditions (e.g., helminth ova below the soi

¢ Little, if any, data are available on the survival times

Ascaris lumbricoides (or var. suum) eggs, 65 ym, from
anaerobically digested sludge. Two-cell stage.

itions such as consistently low temperatures or highly
| in fallow fields).
of Giardia cysts and Cryptosporidium oocysts.

Toxocara sp. egg, 90 ym, from raw sewage.

Ascaris lumbricoides (or var. suum) eggs, 65 ym, from
anaerobically digested sludge.

Trichuris sp. egg, 80 um, from anaerobically digested
sludge.



Table D-1. Quantitative information for Example Problems?.2.3
Problem Statement Number
Parameter Symbol Unis 1 2 3 4
Nominal residence time a d 20 20 20 20
Time period for averages - d 60 60 60 60
Feed Sludge
Volumetric flow rate F m9) f 100 100 100 100
Volatile solids % + kg/m 50 50 50 50
concentration
Fixed solids X kg/m? 17 7 7 7
concentration
Fraction volatile solids VS_ kg/kg 0.746 0.746 0.746 0.746
Mass flow rate of solids My kg/d 6700 6700 6700 6700
Digested Sludge (Bottoms)
Volumetric flow rate B mid 100 100 49.57
Volatile. solids Yo kg/m3 30 30 41.42 41.42
concentration
"Fixed solids Xp kg/n3 7 15 23.50 23.50
concentration .
Fraction volatile solids VS, kg/kg 0.638 0.667 0.638 0.638
Mass flow rate of solids Mp. kg/d 4700 4500
Decantate
Volumetric flow rate D mad 0 t) 50.43
Volatile solids Ya kg/m : - 12.76 12.76
concentration
Fixed solids Xq kg/m - - 7.24 7.24
concentration
Fraction volatile solids VSq ka/kg - - 0.638 0.638
Mass flow rate of solids Mg kg/d : :

digester, although grit may be settling out in the

2. Numerical values are given at 3 or 4 significant
accuracy in measuring solids concentrations ant
is to allow more understandable comparisons to

3. All volatile solids concentrations are based on the

digested sludge is lower than in Problem 1. Consequently,|
VS is higher and mass flow rate of solids leaving is lower
than in Problem 1. A mass balance on fixed solids (input
rate = output rate + rate of loss of fixed solids) is
presented in Equations 11-13.

FX; = BX, + Fixed Solids Loss (11)

Fixed Solids Loss = FX;-BX, (12)
Fixed Solids Loss
= (100X17) - (100115) = 200 kg/d (13)

The material balance, which only looks at inputs and
outputs, informs us that 200 kg/d of fixed solids have not
appeared in the outputs as expected. We know that fixed

Conditions are steady state; all daily flows are constant. Volatile solids are not accumulating in the

ligester.

igures. This is unrealistic considering the expected
sludge volumes. The purpose of extra significant figures
e made of the different calculation methods.

@ total solids, not merely on the suspended solids.

solids are not destroyed and conclude that they are
accumulating in the bottom of the digester. The
calculation of FVSR for Problem 2 is exactly the same as
for Problem 1 (see Equations 4-7) and yields the same
result. The accumulation of solids does not change the
result.

Decantate Withdrawal, No Grit Accumulation

In Problem 3, supernatant is withdrawn daily. Volatile and
fixed solids concentrations are known for all streams but
the volumetric flow rates are not known for decantate and
bottoms. It is impossible to calculate FVSR without
knowing the relative volumes of these streams. However
they are easily determined by taking a total volume

59



Appendix A
Determination of Residence

Time for

Anaerobic and Aerobic Digestion

Introduction

The PSRP and PFRP specifications in 40 CFR 257 for
anaerobic and aerobic digestion not only specify
temperatures but also require minimum residence times o}
the sludge in the digesters. The residence time is the time
that the sludge particles are retained in the digestion
vessel under the conditions of the digestion. The
calculation of residence time is ordinarily simple but it can
become complicated under certain circumstances. This
presentation describes how to make this calculation for
most of the commonly encountered modes for operating
digesters.

Approach

The discussion has to be divided into two parts: residence!
time for batch operation and for plug flow and residence
time for fully mixed digesters. For batch operation,
residence time is obvious--it is the duration of the
reaction. For plug flow, the liquid-solid mixture that makes
up sludge passes through the reactor with no back or
forward mixing. The time it takes to pass through the
reactor is the residence time. It is normally calculated by
the following equation:

9, = Viq (1)
where

= plug flow solids residence

V_ = volume of the liquid in the reactor

q = volume of the liquid leaving the reactor

Normally volume of liquid leaving equals volume entering.
Conceivably, volume leaving could be smaller (e.g.,
because of evaporation losses) and residence time would
be longer than expected if 8, were based on inlet flow.
Ordinarily, either inlet or outlet flow rate can be used.

For a fully mixed reactor, the individual particles of the
sludge are retained for different time periods--some
Particles escape very soon after entry whereas others
circulate in the reactor for long periods before escaping.
The average times in the reactor is given by the
relationship:

_ 2(88 X 0)
= (8s)

(2)

n

where
6s in an increment of sludge solids that leave the
reactor
9 is time period this increment has been in the
reactor
8, = nominal average solids residence time

When the flow rates of sludge into and out of the
completely mixed vessel are constant, it can be
demonstrated that this equation reduces to

ve. (3)
ao
cat
where
q_ = flow rate leaving
Cy = concentration of solids in the reactor
Cg = concentration of solids in exiting stream

It is important to appreciate that q is the flow rate leaving
the reactor. Some operators periodically shut down
reactor agitation, allow a supernatant layer to form, decant
the supernatant, and resume operation. Under these
conditions, flow rate entering is higher than flow rate of
sludge leaving.
Note that in Equation 3, VC, is the mass of solids in the
system and qC_ is the mass of solids leaving. Ordinarily,
al C_ and thése terms could be canceled. They are left
inthe equation because it shows us the essential form of
the residence time equation:

mass of solids in the digester
mass flow rate of solids leaving

oe 4)

Using this form we can calculate residence time for the
important operating mode in which sludge leaving the
digester is thickened and returned to the digester.

in many aerobic digestion installations, digested sludge is
thickened with part returned to increase residence time
and part removed as product. The calculation follows
Equation 4 and is identical with the SRT (solids retention
time) calculation used in activated sludge process
calculations. We focus on the solids in the digester and
the solids that ultimately leave the system. Applying
Equation 4 for residence time then gives Equation 5:

(5)

where
P = flow rate of processed sludge leaving the
system
Cp = solids concentration in the processed sludge

The subscript p indicates the final product leaving the
system, not the underflow from the thickener. This
approach ignores any additional residence time in the
thickener since this time is relatively short and not at
proper digestion conditions.

Sample Calculations

In the following paragraphs, these equations and
principles presented above are used to demonstrate the

45



This mode of operation is frequently used in both
anaerobic and aerobic digestion in small plants.

Equation 3 is used to calculate the residence time:
Let V = 100 m3

gr = 10 m3/d (feed stream)
Cr = 40 kg solids/m3
q = 5 mi/d (exiting sludge stream)
Cy = 60 kg solids/m3
o= 100 x 60 =2d
5x 60
Case 5
®@ Complete-mix reactor
® Constant feed and withdrawal at least once a day
@ Volume in digester reasonably constant
@ One or more feed streams, one product stream that is

thickened, some sludge is recycled and some is drawn
off as product

This mode of operation is sometimes used in aerobic
digesters. Equation 5 is used to calculate residence time.

Let V = 100 m3

Feed flow rate = 10 m3/d

Feed solids content = 10 kg/m3

Flow rate from the digester = 12 m3/d

Solids content of sludge from the digester = 13.3
kg/m3

Flow rate of sludge from the thickener = 4 m3/d

Solids content of sludge from the thickener = 40 kg/m3
Flow rate of sludge returned to the digester = 2 m3/d
Flow rate of product sludge = 2 m3/d

9 = 100x133
n= 2x 40
The denominator is the product of the flow rate leaving the
system (2 m3/d) and the concentration of sludge leaving
the thickener (40 kg/m3). Notice that flow rate of sludge
leaving the digester did not enter into the calculation.

Comments on Plug Flow and Batch
Operation

The above calculations of solids residence time for
pathogen reduction are conservative for plug flow and
batch operation. In fully mixed reactors, the sludge that
exits is contaminated with pathogens in sludge that has
only been in the reactor for a short time. As residence
time increases, the effect of this contamination decreases.
For plug flow or batch operation, this contamination does
not occur. It is not yet possible to properly credit these
modes of operation for this advantage. If sufficient kinetic
pathogen decay data are eventually collected, it will be
possible to calculate directly pathogen reductions from the
kinetic rate equations for the operating mode utilized.

= 166d

47