processes, the filtration step will be followed by a granular-carbon-adsorption step. The filter
effluent from the pressure filter can pass through the downstream carbon columns without having

to be repumped, often eliminating a pumping step that would be required with a gravity filter. All
filter wash waters must be reprocessed in sewage applications. The use of the pressure filter will re-
duce the amount of wash water because of its ability to operate to higher headlosses. The back-
washing of the filter is accomplished by reversing the flow at a rate of three to four times the normal
throughput rate of 5 gpm/ft2. Direct return of the wash waters to the head of the plant would
create a very substantial hydraulic surge, which may cause the upstream clarifier to fail. Therefore,
the backwash wastewater should be collected in a storage tank and recycled to the head of the
plant at a controlled rate. The surge storage tank should be sized adequately to handle successive

backwashes from two or three filters.

It is desirable to precede the filtration step with a flow-equalization pond so that the filters
may be operated at essentially a constant rate. Provisions should be made for a feed of polymer
directly to the filter influent as a filter aid. Filter effluent turbidity and headloss should be moni-
tored continuously, with high filter headloss being used to initiate an automated backwash program.

GRANULAR-CARBON ADSORPTION

Because of the unproven economics of recovery and reuse of powdered carbon, the use of
granular carbon is the only current, practical technique available for removal of soluble organics
from coagulated raw wastewater. Chemical-oxidation techniques are not yet practical for the large
quantities of organics involved. The major design decisions facing the engineer are the selection of
a contact time (30 minutes in the example discussed earlier), the dose of carbon required (can be
conservatively estimated by assuming a removal of 0.5 pound of COD per pound of carbon before
regeneration), and the configuration of carbon contactor to be used. Typically, the carbon doses
will be substantially higher than when granular carbon is applied to coagulated and filtered second-
ary effluent. In the earlier example, a carbon dose of slightly more than 1,000 pounds per million
gallons was estimated. This magnitude of dose is not unusual when applying carbon to coagulated
raw sewage.

Contact times of about 30 minutes have been reported by many investigators as marking the
point of diminishing returns. That is to say, a drastically longer contact time would not provide any
proportionately greater removal of organics.

The two major alternative contactor configurations to be considered are open concrete vessels
of either an upflow or downflow type, and upflow, countercurrent columns in steel vessels. The
countercurrent approach (see fig. III-2) offers a more efficient utilization of the carbon, as only the
most saturated carbon is withdrawn for generation. This effect results from the fact that as the
carbon becomes saturated with organics, it becomes heavier. When the carbon column is back-
washed, the more saturated, heavier carbon migrates to the bottom of the column where it is with-
drawn for regeneration. A semicountercurrent approach can also be achieved by using two down-
flow columns in series. As indicated in figure II-3, water is first passed down through column A,
then down through column B. When the carbon in column A is exhausted, the carbon in column B
is only partially spent. At this time, all carbon in column A is removed for regeneration and is
replaced with fresh carbon. Column B then becomes the lead column in the series. When the carbon
in column B is spent, the carbon is removed for regeneration and is replaced with fresh carbon. This
type of operation gives only some of the advantages of countercurrent operation, because only the

- carbon near the inlet of the lead bed is saturated fully with impurities removed from the water, and
some capacity is unused in much of the rest of the carbon sent to regeneration. Also, the piping
and valving is more complex and costly than for an upflow, countercurrent column. Unless one is
attempting to use the carbon for the dual purpose of filtration and adsorption (which is not recom-
mended for most cases), there is no advantage to using the downflow approach while there are the
foregoing disadvantages.

17


oF

EAST FITCHBURG

|. TOWN OF WESTMINSTER (FUTURE) PRIMARY SEDI- STP
2. MONTACHUSETT REGIONAL VOCA- MENTATION
TIONAL TECHNICAL HIGH SCHOOL PRIMARY
3. CITY OF FITCHBURG SLUDGE
| SLUDGE CARBON
LAGOONS REGENER-
ma a (OFF SITE) ATION
COMMINU- FLOW CHLORINA-
TION MEASURE- TION
MENT 4 + I
> »wW
az lo | |
adja
FLOW 243 |
MEASURE- a |? i |
MENT l l 1
> a's C4
' COAGULATION CARBON |
FLOCCULATION FILTER |
|. WEYERHAUSER CO. CHEMICAL LSEDIMENTATION —
2. FITCHBURG PAPER CO. ADDITION FILTER BACKWASH _

Figure A-2.—Schematic of wastewater-treatment plant, West Fitchburg, Mass.

EFFLUENT TO NASHUA RIVER



9€

CARBON

BAR RAPID FLOCCULATION CONTACT
RACK MIXER BASIN CLARIFIERS BEDS
INFLUENT | . |. i
~
CARBON y
4 | REGENERATION
VACUUM —- SLUDGE
FILTERS THICKENERS
SLUDGE TO, | va < CHLORINE
DISPOSAL CONTACT
CHAMBERS

EFFLUENT
TO RIVER

Figure A-1.—Schematic of wastewater-treatment facility, Niagara Falls, N.Y.


TOTAL ORGANIC CARBON, mg/I

30
20+ DAY 1 4
°
10F \ 4
‘0. q
——_» ——"
0
20F DAY 2 4
\
0°.
10F ~~ 4
oO
0
2- % DAY 3 4
°.
10h 4
oo
on
0 1 n
0 20 40 60

CARBON DETENTION TIME, MIN.

TOTAL ORGANIC CARBON, mg/l!

30

°.
20F \ DAY 8 4
oN
oN
10 °——s
0
206- DAY 10 5
Pm,
10- \ 7
°. o——g
0
20k DAY 14 4
Vo
x
x,
ror QO 7
DAY 22 —
—. q
x]
0] n 1
20 40 6

CARBON DETENTION TIME, MIN.

Figure ||-1, Pilot carbon-column data.

11


Chapter IV
PHYSICAL-CHEMICAL TREATMENT OF SMALL WASTE FLOWS

GENERAL

The basic unit processes discussed earlier are directly applicable to any size treatment plant,
including the less-than-500,000-gpd package-plant range. A number of manufacturers are develop-
ing or have developed package physical-chemical wastewater-treatment plants.

Examples of different types of small physical-chemical processes are discussed in the follow-
ing paragraphs. Some of the information has been taken from Kugelman et al.!3 Mention of com-
mercial products does not imply endorsement by the EPA or by CH2M/HILL.

CLARIFICATION-FILTRATION-CARBON TREATMENT

Two physical-chemical systems using clarification, filtration, and activated-carbon adsorption
are the package units developed by Neptune MicroF LOC@ and AWT Systems Inc.b The MicroFLOC
system employs powdered activated carbon whereas the AWT system uses granular activated carbon.

In the MicroFLOC system powdered carbon and a coagulant are introduced into the raw waste
stream just prior to coagulation. The waste stream then flows through a two-stage flocculator,
through inclined settling tubes for clarification, and through a mixed (trimedia) filter. Alum or lime
may be used as the primary coagulant. With alum, a soda ash feed system is provided for pH con-
trol. If lime is used, pH adjustment is provided following the tube settlers. Polymer can be fed at
both the flocculation and filtration steps.

In the AWT system’s physical-chemical unit a metal salt coagulant and an acid-alkaline control
additive are added to the raw waste before coagulation. Following coagulation, a polymer is intro-
duced to improve clarification. The effluent from the clarifier is treated with a magnetic additive
and fed through a magnetic filter for further solids removal. An upflow carbon contactor with granu-
lar activated carbon is used after filtration to remove dissolved organics.

SLUDGE PRODUCTION

It is difficult to obtain an accurate gravimetric measurement of sludge quantities in a laboratory
test, owing to loss of solids during decanting, and so forth. It is possible, however, to estimate the
quantities of sludge from the chemistry involved and the data collected from the jar tests.

The basic equations required for these calculations may be simplified as follows:

3PO,43- + 5Ca2+ + OHTM > Cas OH(PO,)34 (1)

Mg2+ + 20H- > Mg(OH)24 (2)

Neptune MicroF LOC, 1965 S.W. Airport, Corvallis, Oreg.
bAWT Systems Inc., 910 Market Street, Wilmington, Del.

21


Estimated Costs

Bids were taken for construction of the west plant, and a contract was let in January 1973 for
$10,700,000. The plant should go into operation in early 1975. The estimated first-year operating
cost is $515,000, based on 1971 prices. Amortizing the plant construction cost of 6 percent over
20 years, the treatment cost, including operation and maintenance, is $280 per million gallons.

SUMMARY

At Niagara Falls a physical-chemical treatment process was selected largely because the wastes
to be treated would have been toxic to biological processes, and many of the objectionable constit-
uents would not have been removed by biological processes. At Fitchburg the process was chosen
because of the better quality effluent produced, and the greater stability in operation, as compared
with biological treatment. In each case the choice was clear.

41


INTRODUCTION

Much work has been done recently to evaluate the feasibility of applying physical-chemical
treatment techniques—such as chemical coagulation, filtration, and activated-carbon adsorption—
directly to raw wastewaters or primary effluents to eliminate entirely the need for biological
processes.1-12 Chemical coagulation and filtration are used to remove the raw-wastewater sus-
pended matter, whereas activated carbon is used to adsorb the remaining soluble organics. Phos-
phorus removal normally occurs with chemical coagulation. If nitrogen removal is also required,
physical-chemical processes such as ion exchange and breakpoint chlorination are adaptable.
Special sludge disposal and recovery considerations, dissimilar to biological systems, are included
in the physical-chemical approach.

The purpose of this publication is to discuss typical design parameters for the unit processes
involved in physical-chemical treatment of raw wastes, and how the design engineer may deter-
mine the design criteria best suited for a given wastewater.

PLANT PERFORMANCE SPECIFICATIONS

For illustrative purposes, the raw waste characteristics and effluent requirements shown in
table 1 have been assumed. The effluent standards cannot be met with secondary treatment alone,
as chemical coagulation would be required to meet the phosphorus standard and, at least, filtration
of a secondary effluent to meet the biochemical oxygen demand (BOD) and suspended solids require-
ments. On the other hand, the effluent standards are not so stringent as to permit certain knowledge
that physical-chemical techniques must be used in series with biological treatment. Therefore, a
design engineer faced with the foregoing situation should conduct the necessary tests to determine
if the standards could be met by physical-chemical treatment alone, and, if so, what design criteria
should be used.

The unit processes involved are proven to the degree that extensive, onsite pilot tests are not
necessary for most wastewaters and design criteria can be obtained in laboratory tests. Of course,
if time and funds permit, an onsite pilot test over several months will permit even more accurate
determination of design criteria under a wider variety of operating conditions. Should onsite pilot
studies be considered, the scale of the equipment can be tailored to meet the individual needs of the
project. Small-diameter filters and carbon columns (about 6 inches diameter) are adequate for column
studies and can often be obtained from suppliers of carbon and filter manufacturers on loan or rental
terms. Pilot clarifiers of 6-10 feet in diameter usually can be rented from clarifier manufacturers.
Pilot sludge-thickening and -dewatering equipment also can be rented. The overall cost of pilot
studies will vary widely depending upon the extent of the data collected. A meaningful study should
span several months if any seasonal variations in raw-wastewater quality are anticipated. Although
pilot studies unquestionably provide a firmer basis of design, experience indicates that, except in
unusual circumstances, the design criteria for the physical-chemical unit processes here considered
can be determined with suitable accuracy in properly conducted laboratory tests on representative
raw waste samples.


Pilot-Plant Operations

A small pilot plant was constructed at the existing wastewater-treatment plant and operated for
approximately 3 months in mid-1970. Because of the high pH of the influent waste, the chemical
used for phosphate removal was lime, operating at a pH of 11.2-11.6. An average dose of 90 mg/l of
lime was required to maintain this pH. The average removal of COD in clarification was only about
40 percent, but the suspended solids removal was close to 80 percent. Phosphorus removal averaged
only about 65 percent in the clarification stage. The carbon columns increased the overall removal
of COD to about 75 percent, of suspended solids to over 90 percent, and of phosphorus to 70 per-
cent. Phenol removal was about 95 percent. The carbon columns were operated at a 30-minute
empty-bed contact time. Acid was used to reduce the pH to around 7.0 before application to the
carbon columns to avoid precipitation of calcium carbonate on the carbon. The clarifier sludge in
filter leaf tests dewatered readily to a solids content of more than 30 percent. The cake produced
was not putrescible. The indicated carbon exhaustion rate was about 250 pounds per million gallons.

The pilot-plant work was discontinued after about 3 months, because it was known that the
waste characteristics would change markedly by the time the plant was built owing to reduced con-
tributions of waste from industry.

The only specific organic compound analyzed for was phenol and, as indicated in the foregoing,
it was effectively removed. The nature of organics that failed to be adsorbed are not known, but.
substantial amounts of organic chlorine were found in the effluent and samples analyzed by mass
spectrometry showed the presence of mono- and dichlorobenzene in both influent and effluent
samples.

Negotiations with Industry

From the start of the project, close contact was maintained with the local industries through a
committee on which all important liquid-waste contributors were represented. The entire pollution-
abatement program was to be financed by user charges, and each major industry knew that it would
be obliged to sign a long-term contract to pay its share of the cost. Rough preliminary cost figures
were given to the industries as soon as possible to enable them to determine what in-plant changes
could be made to reduce their treatment charges. A three-part rate based on flow, suspended solids,
and COD was used with the 18 larger industries, each of which was contributing more than 100,000
gpd of liquid waste, or 250 lb/day of suspended solids, or 250 lb/day of COD.

As the work progressed it was possible to refine the cost estimates as better estimates of flow
and waste load were received from the industries. In the end, the industrial waste flow provided for
in the final design was 28 mgd (1.2 m3/sec); the contribution of suspended solids was reduced to
less than one-third and of COD to less than half of what was going to the municipal sewers in 1970.

Plant Design

With such uncertainties as to the changes in the amounts and strength of the waste it was neces-
sary to provide for considerable flexibility in designing the treatment plant.

Final design on the initial construction program began in February 1971 and was concluded in
April 1973. The treatment process will be similar to that used in the pilot plant. Some of the basic
design criteria include 48 mgd average flow with 86 mgd peak flow (estimated 2020 dry weather
flow), 100,000 lb/day suspended solids, and 145,000 lb/day COD. A composite population equiv-
alent based on these criteria is about 500,000.

The wastewater from the east side of the city will enter the main pump wet well in the new
treatment plant from the Southside Interceptor. The main pumping station will include four

34



EFFLUENT
MANIFOLD.

¢

EFFLUENT.
RATE-OF-FLOW
CONTROL

VALVE —OPEN

FINAL
EFFLUENT CARBON COLUMN:
BYPASS VALVE

CLOSED

CARBON COLUMN
(TYPICAL)

INFLUENT

INFLUENT
MANIFOLD
+>

3-WAY VALVE

way VAL CARBON COLUMN
ta

INFLUENT HEADER
VALVE — OPEN
7

3-WAY VALVE
~~

A

INFLUENT _<—e
HEADER:

WASTE
AND
DRAIN LINE

Figure II1-2. Typical arrangement for upflow countercurrent carbon con-
tactor, From Culp and Culp.'0

INFLUENT
WASTE TO CARBON
RECLAMATION
WASTE
BACKWASH
BYPASS a]
WASH WATER
SUPPLY
EFFLUENT

FILTER TO
PIPING DIAGRAM WASTE

J FIRST
= FLOW ATOR,
RENEW CARBON IN A
THEN
cou [Af cou , con Ja} cou
FLOW 8 TO A,
a 8 RENEW CARBON IN —= | 4 8
THEN,
FLOW ATO, AND
Ty — crtieis compete

Figure I1!-3. Two downflow carbon contactors in series. From Culp and Culp.!0

18


Table !V-2,—Estimate of alum-sludge quantities

Raw sewage suspended solids 250 mg/l

Raw sewage volatile suspended solids 150 mg/l

Raw sewage PO,3- 11.5 mg/l as P

Raw sewage total hardness 170.5 mg/l as CaCO.

Raw sewage Ca2* 60 mg/!

Raw sewage Mg?* 5 mg/l

Effluent PO, 0.3 mg/I as P

Effluent Ca2+ 60 mg/t

Effluent Mg2* 5

Effluent AlS* 0

Alum dosage 200 mg/I as Alz(SO4)3 14H20 — fw = 594
From equation 6 AIPO, formed is 1 mole per mole of P

11

30.07 0.365 mole P removed

Therefore 0.365 mole of AIPO, are formed; fw is 122
Therefore weight is 0.365 X 122 = 44 mg/l

From equation 12 A\S* in = AIS* out; AlS* in = 18.1 mg/t

AIS* content of AIPO, = 0.365 X 27 = 9.9 mg/l

AIS* not accounted for = 18.1 - 9.9 = 8.2 mg/l

From equation 7 A\(OH)g formed is 1 mole per mole AlS*

3 = 0,31 mole AKOH)3; fw = 78

So weight of Al(OH) is 0.31 X 78 = 24 mg/l

Therefore

Sludge composition

Sludge species Total weight Ash

Pounds per million gallons

Raw sewage solids 250 mg/! = 2,080 pounds per million gallons 832
AIPO, 44 mg/I = 368 pounds per million gallons 368
Al(OH) 24 mg/l = 200 pounds per million gallons 133

Total 2,648 pounds per million gallons 1,333

Lime recovery involves the conversion of calcium carbonate to carbon dioxide and calcium
oxide (quicklime).

When lime-recovery systems are employed, recycling solids necessarily appear as a part of the
reclaimed coagulant feed. Again pursuing the previous example, it may be seen from table IV-1 that
if recalcination for coagulant reuse is employed, each cycle of coagulant recovery will increase the
total dry solids to be processed by the amounts shown in tableIV-6. Following this line of reasoning,
unless blowdown of inerts from the system occurs, regardless of plant size, coagulant-recovery sys-
tems must in time approach an infinite capacity. Purely as a coarse approximation, equation 13 can
be used to illustrate this point.

Feed = CaCO3 + organics + [inerts X (C - 1)] (13)

24



SPENT CARBON FROM

{ CARBON COLUMNS
SPENT CARBON DRAIN
| [AND FEED TANKS.
_ SCREW
~ CONVEYORS CARBON
C 4 REGENERATION
/( FURNACE

MAKEUP.
CARBON |

CARBON

SLURRY

PUMPS QUENCH
CARBON \ TANK

SLURRY BIN \ \
SI \
¥ A RATED CARBON
CARBON SLURRY ~~) REGENERATED
PUMPS STORAGE TANKS
REGENERATED CARBON
TO CARBON COLUMNS

Figure Il1-4, Illustrative carbon regeneration system. From Culp and Culp.1°

20


15,000-gpm mixed-flow pumps, any three of which will have the capacity to pump the design flow
from the east side, with one standby. The discharge from the two sources (the main pumping
station and the new pumping station on the existing treatment-plant site) will flow through
mechanically cleaned bar screens and into two rapid-mix basins with a combined detention time
of about 1 minute at 86 mgd.

The materials that may be fed to the wastewater in the rapid-mix basins include lime, a metal
salt (ferric chloride, alum, or, most likely, chlorinated ferrous sulfate), a coagulant aid, return
sludge from the primary sedimentation basins, acid (if the treatment process includes depressing
the pH rather than elevating it), and the spent backwash water from the activated-carbon beds. The
change from the lime system to a metal-salt system could be made in a matter of minutes, and the
choice would be dependent on the pH of the incoming waste, the cost and availability of chemicals,
the ease of sludge dewatering, and other factors. There is a strong possibility that the lime dis-
charges to the sewers will be eliminated to reduce user charges and that either aluminum or iron
may be more economical chemicals.

From the rapid-mix basin the wastewater will be split hydraulically into five flocculation
basins, each followed by a sedimentation basin. The flocculation basins will be 60 feet square and
each will have nine flocculators. The flocculators will give decreasing G values in the direction of
flow, with 100 sec-1 possible at the influent end and as little as 10 sec”! at the effluent end of the
flocculation basin. The detention time in the basins will be about 20 minutes at the peak flow.

Sedimentation basins will be 60 feet by 250 feet long, with an average depth of 12 feet. The
overflow rate at the peak flow will be 1,400 gpd/ft2 and about 800 gpd/ft? at the average flow.
The detention time at peak flow will be 1.4 hours. Sludge will be drawn off from the sedimenta-
tion basins to one of two 70-foot-diameter gravity thickeners, although some of the sludge may be
returned to the rapid mix tank to aid in floc forming.

The flow from the primary basins will go through an acid-mix tank to adjust the pH to between
6.0 and 7.0 (if the high lime process is used), and from there the liquid will be pumped to the
activated-carbon beds. The pumping facility will include four 27,000-gpm mixed-flow pumps, any
three of which will pump the peak flow plus the spent backwash water, with one standby.

The granular activated-carbon beds will be downflow gravity beds. There will be 28 beds, each
17 feet by 42 feet with a 9-foot depth of activated carbon. For a plant this size, gravity concrete
beds are considerably more economical than steel pressure vessels. The underdrain system will con-
sist of precast concrete slabs with plastic nozzles placed 8 inches on center. The rate controllers on
the effluent piping of each of the beds will split the flow equally among all of the beds online. The
superficial velocity through the beds will be 3.3 gpm/ft® at the peak flow. The treated effluent will
flow to a chlorine contact chamber with a detention time of 15 minutes at 86 mgd.

Each of the carbon beds will be backwashed at least once each day with an air wash followed by
a water wash. The maximum air-wash rate will be 3,000 scfm, and the water wash will be up to
20,000 gpm from pumps taking suction from the plant-effluent line. The 20,000-gpm rate corresponds
to a rise rate of 44 in./min in the bed. This high rate would be needed only when removing carbon
for regeneration. The spent backwash water either could flow to the rapid-mix basin, where it would
be mixed with the incoming flow and treated, or it could be directed to its own rapid-mix basin,
where it would be mixed with the incoming flow and treated, or it could be directed to its own rapid-
mix basin and into an end flocculation basin. It is likely that even plain sedimentation may improve
the spent backwash-water quality to the point where it could be discharged to the river, with chlorina-
tion, without having to go through the activated-carbon beds again.

Carbon in beds that have reached their adsorptive capacities will be taken out of the beds
hydraulically for regeneration. The regeneration facility will include a six-hearth furnace, in which

85


CLARIFIER SIZING

The critical clarifier design parameter is the peak hourly surface overflow rate. Gross carry-
over of solids can cause the downstream filter or adsorption processes to fail due to excessive head-
loss, which, in turn, will result in a total failure of the plant. Thus, it is of little consolation to know
the clarifier will perform properly under average flow conditions, only to have a carryover of exces-
sive solids during the peak hourly flow shut down the entire plant. A maximum peak hourly rate of
1,400 gpd/ft? for conventional horizontal or radial flow clarifiers is recommended when using lime
as a coagulant, unless pilot tests indicate that other rates should be used. A maximum average rate
of 900 gpd/ft? is recommended. Whichever of these two criteria results in the larger clarifier size

should be used.

Several attempts have been made to use upflow, sludge-blanket-type clarifiers on coagulated
primary or secondary effluents. Difficulty in holding a sludge blanket has been reported in every
case. Successful operation has been achieved with these units by lowering the overflow rate to con-
ventional clarifier rates and eliminating the sludge blanket, which, in essence, converts the unit to a
conventianal radial flow basin. The instability of the sludge-blanket or solids-contact units is due to
the organics found in the raw sewage and the wide variations in incoming flow. These units have
been most successful in treating ground waters of uniform composition at a constant flow rate. Their
use is not recommended on coagulated wastewaters.

Provision should be made for recirculation of controlled amounts of sludge from the bottom
of the clarifier to the rapid-mix inlet. The high pH of lime-treated water will form deposits of calcium
carbonate on structures and in pipelines with which this water is in contact. Lime-sludge suction
lines should be glass lined to facilitate cleaning. Provisions must also be made for regular cleaning of
all other pipelines that carry the high pH effluent. Use of the new polyurethane cleaning pigs should
be compatible with the layout of the pipelines. Mechanical sludge-collection equipment used in
lime-settling basins should be of the bottom-scraper type rather than the vacuum-pickup style, be-
cause of the dense sludge to be handled.

RECARBONATION

Lime treatment of wastewaters for phosphorus removal often raises the pH to values of 10.0-
11.0. At this pH, the water is unstable and calcium carbonate floc will precipitate readily. This floc
is very tenacious and would encrust any downstream filters or carbon particles to a serious degree.
The pH may be lowered by injecting CO, gas obtained from the incinerator stack gases. Primary
recarbonation is used to reduce the pH from 11.0 to 9.3, which is near that of minimum solubility
for calcium carbonate. In domestic wastewater, primary recarbonation to pH of 9.3 results in the
formation of a heavy, rapidly settling floc that is principally calcium carbonate, although some
phosphorus is also removed from solution by adsorption on the floc. If sufficient reaction time,
usually about 15 minutes in cold water, is allowed for the primary recarbonation reaction to go to
completion, the calcium carbonate floc does not redissolve with subsequent further lowering of pH
in secondary recarbonation. If lime is to be reclaimed by recalcining and reused, this settled primary
recarbonation floc is a rich source of calcium oxide, and may represent as much as one-third of the
total recoverable lime. If the pH were not reduced to less than about 8.8 before application to the
filters and carbon beds, calcium carbonate would be deposited extensively on the surface of the
grains. This effect could reduce filter efficiency, and also could reduce drastically the adsorptive
capacity of granular activated carbon for organics. It would produce rapid ash buildup in the carbon
pores upon regeneration of the carbon, and would lead to early replacement of the carbon.

It is possible to reduce the pH of a treated wastewater from 11.0 to 7.0, or to any other de-
sired value in one stage of recarbonation. Single-stage recarbonation eliminates the need for the
intermediate settling basin used with two-stage systems. However, by applying sufficient carbon
dioxide in one step for the total pH reduction, little, if any, calcium is precipitated with the bulk of

15


COMPARISON OF COAGULANT COSTS

The delivered cost of the various coagulants in this test example is as follows:
© Lime = $16.75 per ton of CaO.
@ Alum = $70 per ton.
© Ferric chloride = $90 per ton (or $262 per ton of Fe).
The estimated costs for coagulation at the listed doses are as follows:
© 200 mg/l lime [as Ca (OH), ] = $10.60 per million gallons.
@ 160 mg/l alum = $46.50 per million gallons.
e@ 23 mg/l Fe = $25.10 per million gallons.

It is apparent that lime is the lowest cost coagulant, even when the lime dosage involved reduces
the phosphorus to less than 0.3 mg/l.

Of course, the total economic comparison also must include the relative cost of sludge disposal
associated with each coagulant. Many times the lime sludges may be disposed of at significantly
lower costs than the sludges resulting from either alum or iron coagulation. Thus, in the foregoing
example, there is little doubt that lime will remain the most economical coagulant when sludge
disposal costs are included. Of course, costs vary from area to area, and any comparison should be
based on unit chemical costs specific to the area. In selecting the coagulant in any given situation,
factors such as neutralization costs, maintenance costs, sludge disposal costs, labor, safety, and
availability of chemicals should be evaluated.

The general dewatering characteristics of the sludge may be determined by laboratory tests.
A 100-ml sludge sample is dewatered with a Whatman No. 2 filter paper in a Buchner funnel with
laboratory vacuum. The volume of filtrate versus time is then plotted and compared to similar data
for sludges for which field experience has also been obtained. Figure I-1 presents an example com-
parison which shows that the sludges resulting from coagulation of this wastewater dewatered even
more readily in the lab than did another sludge that later proved to dewater very well in a centrifuge.
Thus, the dewatering of the sludge does not appear to be a limiting factor in this case.


REFERENCES

1J, L. Rizzo and R. E. Schade, “Secondary Treatment with Granular Activated Carbon,”
Water Sewage Works, 307, Aug. 1969.

2 Anonymous, “Carbon Makes Debut in Secondary Treatment,” Environ. Sci. Technol. 809,
1969.

3]. J. Kugelman and J. M. Cohen, “Chemical-Physical Processes,” presented at the Advanced
Waste Treatment and Water Reuse Symposium, Cleveland, Ohio, Mar. 1971.

4W. Weber, C. B. Hopkins, and R. Bloom, “Physiochemical Treatment of Wastewater,” J.
Water Pollut. Cont. Fed., 83, 1970.

5A. J. Shuckrow, W. F. Bonner, N. L. Presecan, and E. J. Kazmierczak, ‘(A Pilot Study of
Physical-Chemical Treatment of the Raw Wastewater at the Westerly Plant in Cleveland, Ohio,”
unpublished, 1971.

6D. F. Bishop et al., Session on the Blue Plains Advanced Waste Treatment Pilot Plant, AIChE
Meeting, Houston, Tex., Mar. 1, 1971.

7“The Development of a Fluidized-Bed Technique for the Regeneration of Powdered Acti-
vated Carbon,” Federal Water Quality Administration Water Pollution Control Research Series,
ORD-17020FBD03/70, Mar. 1970.

8A. J. Shuckrow, G. W. Dawson, and D. E. Olesen, ‘Treatment of Raw and Combined Sewage,”
Water Sewage Works, 104, Apr. 1971.

9A. J. Shuckrow, G. W. Dawson, and W. F. Bonner, “Pilot Plant Evaluation of a Physical-
Chemical Process for Treatment of Raw and Combined Sewage Using Powdered Activated Carbon,”
presented at the WPCF Annual Conference, San Francisco, Calif., Oct. 1971.

10R. L. Culp and G. L. Culp, Advanced Wastewater Treatment, Van Nostrand Reinhold, New
York, N.Y., 1971.

11J, N. English et al., “Removal of Organics from Wastewater by Activated Carbon” (Water-
1970), Chemical Engineering Symposium Series, 67, 147-153, 1970.

12Wilson, Evans, Culp, and Moyer, “Phase I—Engineering Design Report, Supplemental Ammonia
Stripping with Further Nitrogen Removal by Selective lon Exchange and Breakpoint Chlorination,”
EPA Program no. 17010 EEZ, Apr. 1970.

13], J, Kugelman, W. A. Schwartz, and J. M. Cohen, ‘“‘Advanced Waste Treatment Plants for

Treatment of Small Waste Flows,” presented at the Advanced Waste Treatment and Water Reuse
Symposium, EPA, South Central Region, Dallas, Tex., Jan. 12-14, 1971.

31


© Classification of solids content

© Chemical treatment of unprocessed sludges

© Indirect blowdown of recovered coagulant

© Combinations of the above methods

Regardless of the methodology employed for blowdown of unwasted constituents, some frac-
tion of inert materials will be present as a recycle in any solids-handling system employing coagulant
recovery and reuse. Therefore, the design engineer must be able to determine what this fraction is,
as well as its characteristics, prior to design of a proper solids-handling system. This determination is
made most easily by calculation of mass balance under conditions when equilibrium is reached in the

system. In the example system, from table IV-1, equilibrium would occur when blowdowns of inerts
are

@ 2,080 pounds per million gallons organics
@ 510 pounds per million gallons hydroxyapatite
© 100 pounds per million gallons magnesium hydroxide

Continuing the example, assume a coagulant-recovery system employing the following unit
processes:

© Centrifugal dewatering and classification
© Recalcination
@ Dry blowdown of 25 percent of calciner output

Calculate the theoretical centrifuge feed, cake output, calciner output, and blowdown of solids re-
quired and enumerate by type, assuming the following test results are available:

@ 30 percent of hydroxyapatite is wasted in centrate.

@ 25 percent of magnesium hydroxide is wasted in centrate.

25 percent of organics are wasted in centrate.

@ 10 percent of calcium carbonate is lost in centrate.

@ 10 percent of ash is wasted in centrate.

@ 25 percent of calciner output is blown down.
The solution is as follows:

Apatite to waste = 0.3X + 0.25(0.7X) (14)
510 = 0.3X + 0.175X

= 1,075 pounds apatite per million gallons reports in centrifuge feed

27


Chapter |
SELECTION OF COAGULANT

CLASSES OF COAGULANTS
There are four major classes of coagulants that may be considered singly or in combination:

Polymers

Some investigators have reported successful coagulation of raw sewage with polymers alone.
The authors have examined polymers as the primary coagulant on many wastewaters without
finding them economically attractive when compared to the inorganic coagulants available. The
cost of polymers is $1-$2 per pound. When used as the primary coagulant, polymers do not provide
phosphorus removal. One of the following inorganic coagulants is required if phosphorus removal
is of concern, Polymers used in conjunction with an inorganic coagulant are effective settling and
filtration aids. When used as coagulant aids typical dosages are 0.25 mg/l to 1 mg/1.

Iron Salts

Ferric chloride or ferric sulfate may be used for both suspended solids and phosphorus
removal. Experience has shown that efficient phosphorus removal requires the stoichiometric amount
of iron (1.8 mg/l Fe per mg/l of P) to be supplemented by at least 10 mg/l of iron for hydroxide
formation. Typically, 15-30 mg/1 of Fe (45-90 mg/1 ferric chloride) are required to provide phospho-
rus reductions of 85-90 percent. When considering iron for coagulation of raw wastes, it must be
remembered that in an anaerobic environment, as may be encountered in a downstream carbon
column, iron sulfide may be formed. This black precipitate is obviously not desirable in the final
effluent.

Aluminum Salts

Both aluminum sulfate (alum) and sodium aluminate have been used for coagulation of waste-
waters. Alum is generally a much more effective coagulant than sodium aluminate. Alum doses of
75-250 mg/l are typically required for 85-90 percent phosphorus removal (an aluminum-to-
phosphorus ratio of 2 to 3). Most aluminum sulfate is supplied in liquid form requiring simple
pumping equipment.

Lime

Lime has been used successfully in several locales for wastewater coagulation and phosphorus
removal. The amount of lime required is independent of the amount of phosphorus present; rather,
it is a function of the wastewater alkalinity and hardness. When the pH reaches 9.5 due to the
addition of lime, the orthophosphate is converted to an insoluble form. Total typical doses may
range from 200 to 400 mg/l. Operation at pH values of 10-11 is not uncommon. In some cases,
additional quantities of lime may be required to form a readily settleable floc. Lime has been
recalcined and reused in some cases when used to coagulate secondary effluent. As will be
illustrated later, however, recalcination and reuse often may not be practical when used to


Table 1.—-Wastewater characteristics and effluent quality requirements

Influent, Desired effluent,

Constituent
mean annual mean monthly

Milligrams per liter

BOD 180 15
coD.. 520 30
Suspended solids .......... 250 10
Hardness, as CaCO3 170.5 -
Total phosphorus... 2... 11.5 1
Orthophosphorus.......... : 10 -
Totalnitrogen . 2... ee ee 20 5
Ammonia nitrogen . 2... 22-20 - 15 -
AlkalinityasCaCOz.......--.. 220 -

PRELIMINARY DATA COLLECTION

In order to proceed with the design in a rational manner, a characterization of the raw waste-
water in terms of its amenability to physical-chemical treatment must be made. There follows a
description of tests on a wastewater, illustrating techniques that may be used.

The goals of the tests are to provide answers to the following major questions, which must be
known before the design can proceed:

@ What is the best coagulant?

@ How much sludge is produced?

© How well does the sludge dewater?
@ Is coagulant recovery practical?

@ What is the particulate, colloidal, soluble, and nonadsorbable fraction of organics in the raw
wastewater?

@ What is the fraction of soluble organic phosphorus and nitrogen in the raw wastewater?

@ How much carbon contact time will be required?

@ What effluent quality can be expected?

Physical-chemical processes are limited in their ability to remove colloidal and nonadsorbable

organics, and soluble organic phosphorus and nitrogen. If these constituents are present in high
concentrations, various combinations of biological-physical-chemical treatment may be required.


calcium remaining in solution. Thus, the calcium hardness of the finished water increases and, in
addition, a large quantity of calcium carbonate is lost which otherwise could be settled out, recal-
cined to lime, and reused. If lime is to be reclaimed, or if calcium reduction in the effluent is
desired, then two-stage recarbonation is required. Otherwise, single-stage recarbonation may be used
with substantial savings in initial cost and a reduction in the amount of lime sludge to be handled.

In the example wastewater discussed earlier, there would be no need for two-stage recarbona-
tion because

@ No reuse of lime is planned.

© The phosphorus goals can be achieved without the slight additional phosphorus that may be
provided by two-stage recarbonation.

©@ The low lime dosage required does not add a significant quantity of calcium to the effluent.

If two-stage recarbonation is considered only for the purposes of lime recovery, the value of
the lime recovered should be compared against the cost of providing two-stage recarbonation. Peak
hourly overflow rates for the intermediate clarifier in two-stage recarbonation should not exceed
1,400 gpd/ft?. Provision should be made for polymer addition to the intermediate clarifier influent.

FILTRATION

Whether filtration is needed prior to activated-carbon adsorption is subject to debate. There is
no question that filtration ahead of a downflow granular-carbon adsorption bed will reduce the rate
at which the pores of the activated carbon become plugged with inert materials. Also, the use of an
efficient filter permits downstream use of upflow, packed-carbon beds, which may be operated in
the more efficient countercurrent mode discussed later. The question is whether the cost of provid-
ing the filtration exceeds the benefits mentioned earlier. Only long-term operating data from plants
using granular carbon with and without prior filtration will answer this question. In the interim, a
conservative design will include filtration before carbon adsorption. In addition to protecting carbon
pores from plugging by inerts, mixed-media filtration also provides a more efficient means of solids
removal than carbon alone, resulting in a higher effluent quality. Filtration equipment is available
that will provide simple, reliable, and automatic operation. Carbon is not a particularly effective
filter, because basically it acts as a surface-type filter and, as such, is subject to all the shortcomings
of other surface filters applied to wastewaters. Any high solids loading will blind a surface-type
filter in short order. The use of dual-media or mixed, trimedia filters provides a much more efficient
filtration device that is capable of tolerating a much higher solids loading than is a surface-type filter.

In instances where an uptlow expanded-bed carbon contactor is used, the filter may be located
downstream of the carbon column to remove the bacterial floc that is flushed from the carbon.

For the removal of the trace amounts of chemical floc that are to be expected from the chem-
ical clarifier, a properly designed dual-media or mixed trimedia bed may operate at rates of 5-10
. gpm/ft2. The use of 5 gpm/ft2 will provide a conservative basis for design. Surface wash is a must
when filtering sewage. It has been observed, with air-water wash techniques and hydraulic surface
wash techniques, that the water savings with the air techniques are insignificant, if they exist at all,
and the hydraulic surface wash offers a much simpler technique. -

The remaining question is whether the filter structure should be of the gravity or pressure type.
The pressure system offers significant advantages in wastewater applications. In many instances,
the applied solids loading will be higher and more variable than in a water-treatment application.
Thus, it is desirable to have higher head available than p actical with gravity filter designs, prefera-
bly up to 20 feet of head when operating at 5 gpm/ft2. In many physical-chemical treatment

16


@ Sample 3 = 110 mg/l as Ca(OH)p.

© Sample 4 = 130 mg/l as Ca(OH)».

One milligram per liter phosphorus was achieved at a pH of 9.1-9.5. The lime dosage required
for optimum solids removal varied from 100 to 300 mg/l. In general, a somewhat higher dose of
lime was required for optimum solids removal than was required for phosphorus removal. A lime
dose of 200 mg/l achieved adequate solids removal for all four samples, and this dose will be used
in subsequent calculation of the cost of lime coagulation. Suspended solids analyses showed that
settled supernatant contained less than 5 mg/l suspended solids at this dose, and that the filtered
supernatant generally contained no measurable suspended solids. A lime dose of 200 mg/l results

in an effluent phosphorus concentration of 0.07-0.26 mg/l and a pH of 9.6-10.1. The lime and
polymer dosage produced a rapidly settling floc, as it does in most wastewaters.

ALUM COAGULATION
The alum dosages required to achieve a filtrate phosphorus concentration of 1 mg/l were as
follows:
@ Sample 1 = 120 mg/l (11 mg/l Al).
@ Sample 2 = 153 mg/l (14 mg/l Al).
@ Sample 3 = 165 mg/l (15 mg/l Al).
© Sample 4 = 150 mg/l (14 mg/l Al).

The pH was reduced to 6.7-7.1 by these alum dosages. Adequate solids removal was achieved
at alum doses equal to or less than those required for phosphorus removal.

IRON COAGULATION
The ferric chloride dosages required to achieve a filtrate phosphorus concentration of 1 mg/l
were as follows:
@ Sample 1 = 20 mg/l as Fe.
© Sample 3 = 27 mg/las Fe.
@ Sample 4 = 23 mg/l as Fe.

The required Fe/P ratios were 2.7, 2.4, and 2.5, respectively. It appeared that the dose required for
phosphorus removal would equal or exceed that required for solids removal.


Ca2* + CO32- + CaCO34 (3)
1800°F

CaCO3 —~ > CaO + COz4t (incineration) (4)
CaO + H)O > Ca(OH)» (5)

AI3* + PO43- > AIPO4L (6)

Al8+ + 830H- > Al(OH)34 (7)

2A(OH); ME AlgOg + 3H20 (incineration) (8)
Fe3+ + PO43- > FePO4s (9)

Fe3* + 30H" > Fe(OH)34 (10)

2Fe(OH), M228 FeO, + 3Hg0 (incineration) (41)
~ coagulant in = E coagulant out (12)

Tables IV-1 to IV-3 describe the computations used to estimate the quantities of sludge produced.
The total quantities of raw and chemical sludges produced are as follows:

© Lime at 400 mg/l [Ca(OH),] = 6,290 pounds per million gallons
© Alum at 200 mg/l [Al,(SO4)3 + 14H2O] = 2,648 pounds per million gallons

@ Ferric chloride at 80 mg/l [FeCl3] = 2,662 pounds per million gallons

SLUDGE DISPOSAL

Sludge disposal is perhaps the most important factor governing the choice of chemical coagulants.
Unfortunately, the least is known about this particular facet.

Alum and iron sludges normally can be added to existing anaerobic digesters. The higher digester
loadings resulting from additional sludge production usually will not be detrimental to operation unless
an organic overloading condition exists. Release of soluble phosphorus from the sludge during diges-
tion is considered to be minimal. Final disposal of the digested sludge can be on land or by dewatering
and incineration.

Alum, iron, and lime sludges can be disposed of directly onto land. Depending on temperature
requirements, alum and iron sludges could need lime treatment to prevent odors, unless the sludges
are first digested.

In larger systems, sludge thickening or dewatering prior to lagooning or incineration can be con-
sidered. Here the type of sludge becomes important. Alum and iron sludges are much more difficult
and expensive to thicken or dewater than are lime sludges. The data in table IV-4, although only an
educated guess, should serve to demonstrate the magnitude of the problem.

Sludge incineration, particularly for larger cities, could be an integral part of physical-chemical
processes. The advantages of converting organic solids to ash, and thereby reducing the weight and
volume of solids, cannot be ignored. Alum, iron, and lime sludges can be incinerated. The relative

22


mosre  Bilhysical-Chemical
Wastewater Treatment
Plant Design

EPA Technology Transfer Seminar Publication



Chapter II
CARBON ADSORPTION

There are organics (e.g., sugars) that may be readily biodegradable but are very difficult to
adsorb on carbon. The amount of these nonadsorbable materials will vary greatly from wastewater
to wastewater, and their presence will be the governing factor concerning the quality of effluent
that can be achieved by carbon adsorption. Owing to this fact, the same physical-chemical process
may produce a BOD of 10 mg/l in one locale and 30 mg/l in another. The ability to remove the
soluble organics may be measured in the laboratory by two methods.

One method involves a batch process in a beaker; the other is a flowthrough, carbon-column
experiment. In the first case, the raw sewage is placed in contact with 1,000 mg/l of Aqua Nuchar A,
a powdered carbon, for 1 hour. Alternatively, a sample of the granular carbon under consideration
may be ground and applied to the sample. The sample is then coagulated, settled, and the super-
natant filtered through Whatman No. 2 filter paper before analysis. Past work with powdered carbon
indicates that an Aqua Nuchar dose of 600 mg/l and a contact time of 5 minutes is generally adequate
for removal of all adsorbable organics. Thus, the preceding conditions insure that all adsorbable
materials are, in fact, removed. The technique is a quick method of determining the nonadsorbable
fraction of organics.

The column tests may be conducted using Calgon Filtrasorb 400 carbon, or equivalent, in
five 3/4-inch-diameter columns in series. The columns are sized so that cumulative contact times of
7.5, 15, 30, 45, and 60 minutes are provided at the end of the respective columns. Four to 5 gallons
of raw sewage are coagulated with either lime or alum, and are settled. The supernatant is decanted
(pH adjusted to 7.0 when lime is used), and the clarified wastewater is pumped through the columns.
This quantity of sewage will provide several days of operation in columns of this size. The tests should
be continued as long as possible to determine accurately the effects of biological activity. The sludge
should be saved for analysis. The results from these small columns have been found to be consistent
with those obtained in larger units. For example, in one study spanning several months, the results
concerning contact time from small laboratory columns in the first 4 weeks were essentially the same
as those observed from both 6-inch-diameter and 3-foot-diameter columns operated over several months.

Preferably, both the powdered-carbon and column tests should be conducted to determine
whether the effluent from the columns could be lower in BOD than would be the case for adsorption
alone due to the biological growth in a column, and to determine the effects of contact time on
column performance.

POWDERED CARBON RESULTS

The effluent quality achieved by the powdered-carbon technique should represent closely the
nonadsorbable fraction of the organics contained in the raw-waste samples tested. The results
obtained with the wastewater in question are given in table II-1.

The three parameters show similar trends from sample to sample, with the fourth sample con-
taining substantially less nonadsorbable organics than samples 2 and 3 and somewhat less than
sample 1. It appears that the BOD of 2 mg/l measured for sample 4 may be low, as the COD/BOD
ratio is considerably out of line with the other samples. The COD appears valid as the COD/TOC


100

VOLUME FILTRATE (MLS)

90

80

~
3

8

a
3

~
6

30

20

T
SS
‘\

SAMPLE 1 gtum
= —— 2 IN
an LIME < LIME
°
4 xa SAMPLE NO. 3 gum
- ° xo 0
Vy a
L Ox x °
a
So om — —_—
—
° a a
x °
L “
A ~~ Lime SLUDGE FROM ANOTHER
° WASTE COAGULATED WITH
a“ 200 MG/L WHICH PROVED
/ a READILY DEWATERABLE IN

CENTRIFUGE.

* = 160 MG/L ALUM
O 150 MG/L Ca (OH)

0.5 MG/L NOPCOFLOC 930
IN BOTH CASES.

100 ML SLUDGE SAMPLES

1
100

1
150 200 250 300
TIME (SECONDS)

Figure |-1. Sludge-dewatering characteristics.



Table |V-9,—Theoretical calciner output at equilibrium in a coagulant-recovery system
[in pounds per million gallons (dry solids)]

Product
Component
CaO CagOH(PO,4)3 Ash Mg(OH)o
Calciner output... 2... 2. eee 1,820 752 1,920 170
Blowdown (25 percent)... . . . - 455 187 480 43
Remainder to reuse... 2... 1 ee 1,365 565 1,440 127

Table IV-10.—Comparison of inerts actually wasted with theoretical inerts wastage required at equilibrium ina

coagulant-recovery system
Theoretical
Source of wastage required
Inert Total a

table V-1
Centrate Blowdown total
CagOHIPOg)g. 2. 2 eee 323 187 510 510
Mg(OH)g. 2 2. eee ee ee 57 43 100 100
ASH. ee 208+144 480 832 832

Table !V-11.—Solids handling and lime requirements with or without lime recovery at equilibrium

With lime Without lime

Component
recovery recovery

Pounds per million gallons

Sludge from primary clarifier ........ 8,422 6,920
Sludge to be disposed of; assuming incineration . 1,442 3,462
1,135 2,500

Makeup lime requirements (CaO)

alternative methods of solids handling, ranging from no recovery to sophisticated recovery systems;
he can, therefore, make a sound decision. In addition, the designer is assured that adequate capacity
is provided for the system’s needs. Weak points in the system can then be evaluated, and standby
capacity or redundancy can be added as may be required or deemed advisable.

29


Magnesium hydroxide to waste = 0.25X + 0.25(0.75X) (15)
100 = 0.25X + 0.19X
= 227 pounds magnesium hydroxide per million gallons reports in centrifuge feed
Organics to waste = 2,080 pounds per million gallons (16)
wasted in two forms; i.e., ash and organics.
Organic equivalent as ash = 0.40 (2,080) = 830 pounds per million gallons.
Centrate wastage = 0.25 X 830 = 208 pounds per million gallons.
622 pounds per million gallons remain and are wasted as ash.
Ash to waste = 0.1X + (0.25)(0.9X) + (0.25)(622)
622 = 0.1X + 0.225X + 156
= 1,440 pounds of actual ash per million gallons report in centrifuge feed
Calcium carbonate to waste = 0.1X + (0.25)(0.9X) (17)
X = 3,600 pounds per million gallons (from table IV-1)
Calcium carbonate wasted = 3,600 X 0.325
= 1,170 pounds per million gallons
Using equations 14 through 17, tables IV-8, IV-9, and IV-10 may be constructed. The example
assumes that there will be a net positive blowdown of the inert solids itemized in table IV-10. The

inerts cannot be recycled.

Table IV-11 compares solids handling and lime requirements for a solids-handling system with
and without lime recovery.

The arrangement of the calculations required to determine equilibrium values for chemical
sludges in the manner illustrated provides the design engineer with a concise tabulation of the amounts
of each type of sludge under any condition he may choose to investigate. This tabulation, in turn,
allows an orderly economic evaluation to be made. The designer may choose to evaluate several

Table |V-8.—Theoretical feed, centrate, and cake content at equilibrium in a coagulant-recovery system
Un pounds per million gallons (dry solids)]

Sludge
Component
CaCO3 CagOH(PO,4)3 Organics Ash Mg(OH) >
Centrifuge feed. oe 3,600 1,075 2,080 1,440 227
Centrate..... 1... : 360 323 520 144 57
Cake 3,240 752 1,560 1,296 170

28


coagulate raw wastewaters, owing to the large amount of inert materials present in the combined
raw-sewage-chemical sludges. In any case, lime sludges usually dewater more readily than those
resulting from iron or aluminum coagulation, Lime requires dry feeding equipment. If unslaked
lime (CaO) is used, slakers are involved.

Disadvantages—fron and Aluminum Salts and Lime

e Iron and alum both form gelatinous hydroxide flocs that may be difficult to dewater in
many cases.

@ With iron and alum, large amounts of ions (chloride or sulfates) are added to the wastewater.

@ No proven techniques are currently available for recovery and reuse of iron or aluminum
when phosphorus removal is required.

@ Lime coagulation raises the pH, requiring treatment with CO, ora mineral acid for down-
ward adjustment of pH prior to subsequent processing.

© The quantity of sludge formed from lime treatment may be considerably greater than with
other metal salts.

TEST EXAMPLE

The choice of coagulant usually can be made rather quickly by laboratory jar tests. The
following illustrative example is based on data collected on a raw wastewater from a community
in the Midwest:

In the technique used, six 1-liter samples are dosed with the coagulants under study while
being rapidly mixed with a jar-test device. (In this example, 0.5 mg/l of an anionic polymer
(Nopcofloc 930, manufactured by Diamond Shamrock) was added as a settling aid.) Following
a 60-second rapid mix, the samples are slowly mixed for about 5 minutes. They are then allowed
to stand quiescently to permit settling of the floc. Samples of the supernatant then are obtained
with a pipette from a point just below the liquid surface in the jar. This method is used to avoid
including any of the floating solids invariably found in raw sewage. This supernatant sample is then
analyzed for turbidity, pH, hardness (when lime is used as a coagulant), and phosphorus. A portion
of the remaining supernatant is filtered through a Whatman No. 2 filter paper. The filtrate is ana-
lyzed for turbidity, phosphorus, and, in some cases, total organic carbon (TOC), chemical oxygen
demand (COD), BOD, and suspended solids. Past experience has shown that the filtrate quality
obtained with this filter paper will be about the same as that which will be achieved with a
mixed-media filter.

LIME COAGULATION
By plotting the jar-test data, it was determined that the lime dosages required to achieve a
filtrate phosphorus concentration of 1 mg/l were as follows:
@ Sample 1 = 132 mg/l as Ca(OH).

@ Sample 2 = 100 mg/l as Ca(OH)g.



The choice of contactor design is also dependent on the method selected for control of hydro-
gen sulfide generation in the carbon columns. The upflow, expanded bed with a downstream filter
has been used with injection of oxygen into the carbon influent for hydrogen sulfide control. The
prolific biological growth resulting from this approach would result in excessive headloss in a down-
flow, packed bed. Frequent backwashing of a downflow, packed bed has been reported effective at
Rocky River, Ohio, in controlling hydrogen sulfide. Also, breakpoint chlorination prior to down-
flow beds, although expensive, has been reported effective at the Washington, D.C., Blue Plains plant
in controlling hydrogen sulfide. Higher operating pressures and, hence, greater carbon depths may
be used in steel pressure contactors. As a result, a concrete contactor generally has a shallower car-
bon depth and a greater surface area of carbon to maintain the same contact time. Thus, there are
substantially more underdrain area and influent and effluent headers per unit of contact time in the
gravity concrete structures. Economic comparisons between the two approaches show that there is
not a great deal of cost difference in most cases. The EPA Technology Transfer Process Design
Manual and Advanced Wastewater Treatment!° present detailed carbon-contactor design alternatives.

There are, however, a few points related to contactor design to which attention should be given
in addition to those in the preceding comments. When using steel contactors, it is imperative that
the interior be protected properly from the very corrosive effects of partially dewatered activated
carbon. Two 8-mil-thick coatings of a coal-tar epoxy have proven to be effective at South Lake
Tahoe, Calif., over 4 years of continuous operation. Fiberglas-polyester coatings also would be
effective, although more costly than the coal-tar epoxy coatings. Costs for shop-applied coatings
would vary from about 50 cents per square foot to $2 per square foot, depending on the material
and thickness selected. Costs for field-applied coatings would be about twice as high. Also, in most
cases, the costs of fabricating steel vessels in the field will be substantially higher per pound of steel

than for a shop-fabricated vessel.

Another point to consider is the effect of the pH of the upstream coagulation step on the effi-
ciency of the carbon process. One available process is based on a claim that use of extremely high
pH in the lime-coagulation process will hydrolyze some organic materials, making them more readily
adsorbable. Duplication of these results has been attempted on six different wastewaters with no
attributable benefit associated with using a high pH of coagulation. Thus, before incurring the dis-
advantages of the high-pH approach (massive quantities of sludge plus greatly increased carbon
dioxide requirements for pH adjustment), the effects of pH on the specific wastewater involved

should be evaluated carefully.

CARBON REGENERATION

As granular activated carbon adsorbs organics from wastewater, the carbon pores eventually be-
come saturated and the carbon must be regenerated for reuse. The best way to restore the adsorp-
tive capacity of the carbon is by means of thermal regeneration. By heating the carbon in a low-
oxygen steam atmosphere, in a multiple-hearth furnace at temperatures of 1,650°-1,750° F, the dis-
solved organics are volatilized and released in gaseous form. The regenerated carbon is cooled by
water quenching. By proper treatment, carbon can be restored to near virgin adsorptive capacity
while limiting burning and attrition losses to 5-10 percent. Regeneration-furnace off-gas odors can
be controlled by afterburning, if necessary, and particulates and soluble gases can be removed by
use of venturi or jet-impingement-type scrubbers. Figure III-4 illustrates a typical regeneration
system.

The carbon furnace should be sized with recognition of the fact that substantial downtime may
be required for maintenance of the furnace. An allowance of 40 percent downtime provides a con-
servative basis for selecting the furnace size.

19


Nature of Wastes

The wastewater from the two mills is primarily white water containing paper fiber along with
chemicals used in papermaking, such as alum, starch, pigments, and fillers. The total wasteflow
from the two industries averages about 13.8 mgd (0.6 m3/sec). The waste has an average BOD of
about 50 mg/l and suspended solids of 360 mg/l.

Effluent Quality Requirements

Because the effluent from the west treatment plant will constitute the entire stream flow during
low flow periods, a BOD of 5-7 mg/l was needed. To avoid esthetically objectionable color from the
pigments used in making colored paper, good removal of color is necessary. Suspended solids should
also be kept to low concentrations.

Pilot-Plant Operations

When the pollution-abatement problems of Fitchburg were studied in 1968, biological treat-
ment was proposed for both the east and west Fitchburg plants, and in 1970 pilot-plant studies were
made for both types of waste. The paper-mill wastewater contains substantial amounts of alum and,
by adding an alkali to increase the pH to about 6.7, a good floc is formed that settles readily and
removes some 50 percent of the BOD and more than 90 percent of the suspended solids. Although
the activated-sludge pilot plant did a satisfactory job of removing BOD, color was not consistently
removed and there was some carryover of the biological floc in the effluent. It was necessary to add
nitrogen and phosphorus to the waste, as it was deficient in both nutrients. In addition, some prob-
lems were anticipated in operation because both mills operate on a 5-day week and shut down for a
2-week period each summer. This schedule would complicate the operation of a biological treatment
plant.

Asmall pilot-plant facility was established at the Weyerhaeuser mill, where waste was available
from one of the mill’s primary clarifiers. Wastes from the Fitchburg Paper mill were trucked to the
site and mixed in suitable proportion to Weyerhaeuser waste. The combined wastes were settled in
a tank truck and then pumped to four carbon columns in series. About 90 percent of the settled
BOD and COD were removed by the carbon columns operated at a rate that would provide an empty-
bed contact time of 23 minutes. Very good color removal was obtained. The exhaustion rate was
such that about 1,600 pounds of carbon per million gallons would be used. This rate was much
higher than was found at Niagara Falls, and about double the rate commonly reported in treating
domestic wastewater.

Negotiations with Industries

The west plant is to be paid for primarily by the industries that will provide most of the flow.
A thorough economic analysis of the relative costs of the physical-chemical system was compared
with activated sludge. This comparison showed that the physical-chemical system would be about
6 percent more expensive; nevertheless the industries, as well as the city and the State regulatory
agency, chose the more expensive system because of its better effluent quality and operating stabil-
ity in the face of major changes in flows.

Plant Design

In the west plant, municipal wastewater will be settled and chlorinated heavily before being
combined with the industrial wastewaters. The primary sludge from the municipal clarifiers will be

38


processed at the east treatment plant. The combined wastes will be coagulated, flocculated, and
settled. The chemicals normally used will be lime and a polymer. The industrial wastewater normally
has a pH in the range 4.2-4,7, and upon adjustment of pH to 6.7 the alum in the waste forms a good
floc, At times of high turbidity, when large amounts of titanium are being used in papermaking, it
will be necessary to add alum.

Two circular municipal clarifiers will be provided initially. These are designed for an overflow
rate of 1,000 gal/ft2/day. Two rapid-mix and two two-stage flocculation basins will provide 5-minute
and 30-minute detention periods, respectively, at maximum daily flow rates. Two industrial clari-
fiers, each 130 feet in diameter, will provide an overflow rate of 840 gal/ft? /day at maximum daily
flow rate. Sludge will be pumped offsite to four sludge lagoons.

Vertical turbine pumps will deliver the settled wastewater to the activated-carbon columns.
Four variable speed pumps will be provided, each with a maximum capacity of 8,500 gpm at a design
head of 145 feet. These have been designed to provide for 10 feet of head loss through prefiltration
facilities, if these should be needed.

Twelve activated-carbon columns are provided, each 20 feet in diameter with a 15.5-foot bed
depth. They will be operated in parallel. The columns and piping allow for two vessels to be out of
operation—one for backwashing and the other for regeneration. Ten active vessels were selected to
permit maximum utilization of the carbon. The surface loading and empty-bed contact time for
the 10 active vessels will be about 8 gal/min/ft? and 15 minutes, respectively, at peak hourly flow,
and the flow through the vessels will be divided uniformly and controlled by individual rate con-
trollers. The vessels have been designed to operate at a maximum pressure of 50 psi. The overall
vessel height, from dished end to dished end, is approximately 33 feet, which will allow for a 40-
percent expansion of the carbon bed on backwashing. The filter bottom will consist of 1 foot of
gravel over Leopold tiles.

The columns will be backwashed with plant effluent utilizing two variable-speed, vertical turbine
pumps, one of which will serve as a standby. A maximum wash-water rate of 9,100 gpm will insure
40 percent expansion of the filter at 75° F, and the water will be discharged to a backwash lagoon.

It is anticipated that each column will be washed for 15 minutes daily, with one column backwashed
every 2 hours on a time cycle, and will also use a surface wash. A clear well with a volume equal to
approximately the volume of a single backwash is provided, but the effective volume is greater because
there is a continuous flow into the clear well at all times except at shutdown. A backwash basin

(two 65-foot-diameter tanks) will be provided to return uniformly the backwash water together with
the carbon-transfer motive water to the head end of the plant. Under the most adverse conditions,
the maximum rate of return to the head end of the plant will be 2.2 mgd, about 12 percent of the
plant throughout. Because the DO will be depleted in passing through the carbon columns, the
effluent will be aerated to maintain a level of 5 mg/] of DO.

Approximately once a week it will be necessary to replace the carbon in one of the vessels.
Spent carbon will be transferred to a spent-carbon storage vessel through water eductors sized to
empty or refill one vessel in less than 6 hours. The volume of the spent-carbon and regenerated-
carbon storage vessels will be equal to two times the carbon in any one filter vessel. The carbon will be
regenerated in a six-hearth furnace, 10 feet 9 inches in diameter, utilizing steam. The furnace has
been sized based on continuous operation with a loading rate of 100 pounds of carbon per day per
square foot of hearth. An impingement scrubber will be used to remove particulates from the gas
stream. In transferring the carbon, two water streams are required: fluidizing water for maintaining
the carbon-to-water ratio (1-2 pounds of carbon per gallon of slurry), and motive water to operate
the eductors.

Fluidizing water essentially will be pumped against the static head and motive water at the most
efficient combination of pressure and volume. Fluidizing water and motive water to and from the
carbon vessels will be provided by separate constant-speed pumps that will operate at 100 psi, with
suction from the process water header.

39


Table |V-3.—Estimate of iron-sludge quantities

Raw sewage suspended solids 250 mg/l
Raw sewage volatile suspended solids 150 mg/l
Raw sewage PO,3~ 11,5 mg/l as P
Raw sewage total hardness 170.5 mg/I as CaCO3
Raw sewage Ca2+ 60 mg/t
Raw sewage Mg?* 5 mg/l
Effluent PO, 0.3 mg/l as P
Effluent Ca2* 60 mg/I
Effluent Mg2* 5
Effluent Fe3* 0
FeCl dosage 80 mg/I
From equation 9 FePO, formed is 1 mole per mole P
11.2

= 0.365 mole P removed

30.97

Therefore 0.365 mole of FePO, are formed; fw= 151
Therefore weight is 0.365 X 151 = 55 mg/I

From equation 12 Fe3+ in = Fe3* out; Fe3* in = 28 mg/l

Fe3* content of FePO, = 0.365 X 55.8 = 20.4 mg/t
Fe3+ not accounted for = 28 ~ 20.4 = 7.6 mg/I
From equation 10 Fe(OH)3 formed is 1 mole per mole Fe3*

Therefore = 0.136 mole Fe(OH)3; fw = 107

16,
55.8
So weight of Fe(OH); = 0.136 X 107 = 15 mg/l

Sludge composition

Sludge species Total weight Ash

Pounds per million gallons

Raw sewage solids 250 mg/I = 2,080 pounds per million gallons 832
FePO, 55 mg/l = 460 pounds per million gallons 460
Fe(OH) 15 mg/I = 122 pounds per million gallons 105

Total 2,662 pounds per million gallons 1,397

where CaCO3, organics, and inerts are in pounds per million gallons, and C = the number of cycles
starting with the initial feed as No. 1.

Note that equation 13 is usable only for > 1 cycle.

Table IV-7 illustrates for the example what would occur at the 5th, 10th, and 20th cycle of such
a system.

Clearly such a buildup of inerts as indicated in table IV-7 is unacceptable in the design of solids-
handling systems. This problem has spurred research into better techniques of separating or classi-
fying chemical sludges one from another. Several techniques for reducing the buildup of inert solids
within a coagulant-recovery system are available, including the following:

@ Direct blowdown of unprocessed sludges

© Blowdown of dewatered chemical sludges

25


CONTENTS

Introduction .
Plant Performance Specifications
Preliminary Data Collection .

Chapter I, Selection of Coagulant
Classes of Coagulants
Test Example
Lime Coagulation
Alum Coagulation
Iron Coagulation .
Comparison of Coagulant ‘Costs

Chapter II. Carbon Adsorption
Powdered Carbon Results
Column Tests .

Chapter III. Process Design .
Flow
Preliminary Treatment . woe .
Chemical Feed, Rapid Mix, and Flocculation .
Clarifier Sizing . . soe
Recarbonation .
Filtration .
Granular-Carbon ‘Adsorption
Carbon Regeneration

Chapter IV. Physical-Chemical Treatment of Small Waste Flows

General

Clarification- Filtration-Carbon ‘Treatment
Sludge Production

Sludge Disposal

References
Appendix A. Design Project Description.
Niagara Falls, N.Y. . . te

Fitchburg, Mass.
Summary .

iii

Page

Nee

noo RR wo


% TOC REMAINING

20

oO 1 1 1

x
a
°

DAY 1
DAY 14 7
DAY 22

75 15 30
CARBON CONTACT TIME, MINUTES

Figure 1-2. Pilot carbon-column data,

12


las

SURGE BACKWASH WASTEWATERS,
a storage [* — — — of _- 7
| | |
g | |
ind CHLORINE
rd
RAW comminuTion | $ | RAPID Mix RECARBONATION FLOW GRANULAR
E AND AND EDIMENTATION| (QF LIME EQUALIZATION FILTRATION P= CARBON
SEWAG! crit removat| # | eLoccucation (a) COAG USED) POND (8) (B)
(Q avG, (a)
Q PEAK HOUR)] g
| T TF
ASH 1
| ' ‘ ‘CARBON
COAGULANTIS) SLUDGE '
| | ! i
| L SLUOGE
SLUDGE CARBON
— THICKENING INCINERATION
| TOPTIONALY DEWATERING REGENERATION
| T CENTRATE SCRUBBER
| OVERFLOW oR OnbeRELow ___ UNDERFLOW ANO
FILTRATE CARBON WASH WATERS
en [ona —-—— —_——

(A) DESIGN FLOW BASED ON Q PEAK HOUR PLUS Q@ RECYCLE
(Bi DESIGN FLOW BASED ON Q AVERAGE PLUS Q RECYCLE.

Figure II|-1. Illustrative schematic of a physical-chemical treatment plant.


ACKNOWLEDGMENTS

This seminar publication contains materials prepared for the
U.S. Environmental Protection Agency Technology Transfer Program
and has been presented at Technology Transfer design seminars
throughout the United States.

The information in this publication was prepared by Gordon Culp,
Clean Water Consultants—Culp, Wesner, Culp, El Dorado Hills, Calif.; L.
Gene Suhr, Director, Advanced Waste Treatment Group; and David R.
Evans, Project Manager, Advanced Waste Treatment Group, representing
CH2M/HILL, Engineers, Planners, and Economists, Corvallis, Oreg.

Appendix A was prepared by Richard L. Woodward, representing
Camp Dresser & McKee Inc., Boston, Mass.

NOTICE

‘The mention of trade names or commercial products in this publication is
for illustration purposes, and does not constitute endorsement or recommendation
for use by the U.S, Environmental Protection Agency.

Revised January 1974


carbon will be applied to the top hearth and slowly pushed from one hearth to the next lower one.
About 3 days will be required to regenerate one bed. The regeneration will be done in the absence
of oxygen, and steam will be applied as a source oxygen for the adsorbed organic carbon to be driven
off as COg. Above the top hearth, the gases from the regeneration will be burned at about 1,800° F
to break down any chlorinated hydrocarbons that exist in.the gas into CO, and HCl. The gases will
go through a wet scrubber, which will dissolve the HCl and remove the particulate matter from the
stack gas. The scrubber effluent will be recycled to the front end of the plant.

Sludge Handling and Disposal

About 80 tons of dry-sludge solids per day is the expected sludge production, if lime is used.
Smaller amounts of sludge are expected if iron or aluminum is used. The sludge will be pumped
from the gravity thickeners and will be dewatered on four 500-ft? vacuum filters, which will operate
about 120 hours per week. Ferric chloride, a polymer, and lime will be available for conditioning
the sludge.

The dewatered sludge will be hauled to landfill for burial. Incineration of the sludge was con-
sidered, during both the preliminary and the final design phases, but it would be more costly than
burial. The plant-influent suspended solids contain a low percentage of volatile material, which,
together with the inorganic chemical additions, would make incineration little more than a drying
process with most of the heat having to be applied externally. The reduction in volume and dry-solids
weight of the evaporated sludge would not be significant over the vacuum-filtered cake. Similarly,
the large amounts of inert suspended solid in the sludge made lime recovery appear unprofitable.
Changes in the waste characteristics as industries reduce their waste loads may call for a review of
this decision.

Costs

The estimated cost of the treatment plant is $37 million, and various necessary sewers, a pump-
ing station, and a force main will add another $16 million. Annual operating costs are estimated at
$1.8 million. The capital cost for the treatment plant is amortized in 20 years at 6 percent interest;
the total cost of treatment alone based on a flow of 48 mgd (2.1 m3/sec) is $290 per million gallons.

FITCHBURG, MASS.

Geographic Situation

Fitchburg is an industrial city located in central Massachusetts and has a population of 43,000.
It is located at the headwaters of the Nashua River. Near the upstream end of the city two paper
mills, the Weyerhaeuser Co. and the Fitchburg Paper Co. (a division of Litton Industries) use all of
the flow of the stream during low flow periods. In fact, Fitchburg Paper depends on Weyerhaeuser’s
wasteflow for its raw water supply. Thus it is not feasible to intercept the waste from these mills
and treat it at a downstream plant which will serve most of the city.

Two wastewater-treatment plants are proposed. One plant, in the west, primarily will serve the

two paper mills along with some domestic waste from Fitchburg and an adjoining community. In
the east, a second plant will serve the remainder of the area.

37


Table IV-1,—Estimate of lime-sludge quantities

Raw sewage suspended solids 250 mg/l
Raw sewage volatile suspended solids 150 mg/l
Raw sewage PO,3~ 11.5 mg/l as P
Raw sewage total hardness 170.5 mg/l as CaCO.3
Raw sewage Ca?* 60 mg/t
Raw sewage Mg2* 5 mg/l
Effluent PO, 0.3 mg/l as P
Effluent Ca2* 80 mg/l
Effluent Mg2* 0
Lime dosage 400 mg/l as Ca(OH), or
216 mg/l as Ca2*
From equation 1 CasOH(PO,)3 formed is 1 mole per 3 moles P

Spa 7 0.365 mole P removed

0.365

Therefore or 0.122 mole CasOH(PO,)3 are formed; fw is 502

Therefore weight is 0.122 X 502 = 61 mg/I as CagOH(PO,)3
From equation 2 Mg(OH)» formed is 1 mole per mole Mg?*
5
4.31 7 0.206
Therefore 0.206 X 58.31 = 12 mg/l as Mg(OH)9
From equation 12 Ca2* in = Ca2* out; Ca2* in = 60 + 216 = 276
Ca?* content of CagOH(PO,4)3 formed = 5 X 40 X 0.122 = 24 mg/l
Ca?* lost in effluent = 80 mg/l
Therefore Ca2* not accounted for = 276 - (80 + 24) = 172 mg/l

From equation 3 CaCO, formed is 1 mole per mole Ca2t+
Therefore R = 4.3 moles CaCO3; fw = 100

So weight of CaCO, = 430 mg/!

Sludge composition

Sludge species Total weight Ash

Pounds per million gallons

Raw sewage solids 250 mg/I = 2,080 pounds per million gallons 832
CasOH(PO,)3 61 mg/l! = 510 pounds per million gallons 510
Mg(OH)> 12 mg/l = 100 pounds per million gallons. 100
CaCO3 430 mg/l = 3,600 pounds per million gallons 2,020

Total 6,290 pounds per million gallons 3,462

amounts of water and solids described earlier control the incinerator size. Table IV-5 illustrates the
weight reduction achieved by incineration.

Generally speaking, of the three coagulants listed, only lime can be recovered using current
technology. Even lime recovery may not be economically practical when used to coagulate raw
wastewater. An effective means must first be found to separate the lime from the inert organic raw-
sewage ash.

23


EPA 625/4-73-002a

PHYSICAL-CHEMICAL WASTEWATER
TREATMENT PLANT DESIGN

Environmental Protection Agency
Region V, Library

230 South Dearborn Street
Chicago, Illinois 60604

ENVIRONMENTAL PROTECTION AGENCY e@ Technology Transfer

August 1973


Appendix A
DESIGN PROJECT DESCRIPTIONS

NIAGARA FALLS, N.Y.

Geographic Situation

Niagara Falls is a famous tourist center. It is also the center of a large chemical complex with
such well-known names as Hooker, Union Carbide, Du Pont, Goodyear, National Lead, Olin, and
Carborundum. The Niagara River, which flows by the city, is an international boundary water con-
necting Lake Erie and Lake Ontario and has a flow of about 200,000 ft3 /sec (5,700 m/sec). The
city has a population of about 86,000. Camp Dresser & McKee Inc. was retained by the city in

January 1970
© To study its water-pollution-control problems
© To submit a preliminary design report by February 1971
© To have the project under construction by March 1, 1972

Financing problems delayed construction.

Nature of Wastes

A sampling-and-gaging program of all major industrial wastewater discharges in early 1970
showed a total flow of 164 mgd (7.2 m?/sec), a suspended-solids load of 274,000 lb/day (124,000
kg/day), and a COD load of 242,000 Ib/day (110,000 kg/day). Only 63 mgd (2.8 m?/sec) went
directly to the municipal sewers, but this flow contained some 70 percent of the suspended solids,
about 55 percent of the COD load. This load, of course, completely overshadows the domestic
waste load.

The waste reaching the existing treatment plant in 1970 frequently had a pH of close to 11.0,
but acid dumps would occasionally drop this to below 3.0. Lime waste was evident and caused
much of the discoloration of the river that was noticeable below the treatment plant. Volatile
vapors from chlorinated hydrocarbons were occasionally so irritating to the eyes and lungs of
workers at the treatment plant that they had to leave. Occasionally chlorine residuals could be
measured at the plant. BOD measurements on this wastewater were meaningless. During pilot-
plant work, it would sometimes be found that the BOD increased in going through physical-chemical
treatment. A few coliform tests on the raw wastewater showed concentrations of only 100 to 400
coliforms per 100 ml. Clearly this wastewater was not a suitable candidate for biological treatment.

Effluent Quality Requirements

Phosphorus removal is required for all wastewater discharges to the Great Lakes and Niagara
River in New York. A limit of 1 mg/l of phosphorus is the general requirement for wastewater dis-
charged to these waters. The usual requirement for secondary treatment was not defined in terms
of BOD, but a limit of 112 mg/l of COD has been prescribed by the New York Department of
Environmental Conservation, along with a limit of 35 mg/l of suspended solids and 0.23 mg/l of
phenol.

33


METRIC CONVERSION TABLES

Recommended Units

Recommended Units

Customary Customary
Deseription Unit Symbol Comments Equivalents Description Unit Symbol Comments Equivalents
Length metre m Basic SI unit 39.37 in =3.28 Velocity
109 yd linear metre per mis 3.28 fps
kilometre km 0.62 m “te secon
mm 0003937 in. mimete mms 0.00328 fps
micrometre - 3.937 X 10-9=109A per secon
a 4 kilometres km/s 2.230 mph
Area ‘square metre m2 per second
square kilometre km? angular“ radians per rad/s
second
square millimetre mm? 0.00155 sq in.
hectare ha The hectare (10.000 2.471 acres Flow (volumetric) cubic metre ms Commonly called 15,850 gpm
m2) is a recognized per second the cumec = 2.120 chm
multiple unit and
will romain in inter- litre per second H/s 15.85 gpm
national use,
Viscosity pascal second Pas 0.00672
Volume cubic metre m 35.314 cu ft= poundals/sq ft
1.3079 cu yd
Pressure newton per Nim? 0.000145 tb/sq in
Iitre 1 The litre 1s now 1.057 qt = 0.264 gal square metre
recognized as the 81 X 10-4 acre- or pascal Pa
special name for
‘the cubic decimetre kilometre per N/m? 0.145 Ib/sq in,
square metre
Mass kilogram kg Basic SI unit 2.205 Ib or kilopascal kPa
gram 9 0,035 o2 = 15.43 gr bar bar 14.5 bisa in.
milligram mg 001543 gr |
tonne or t Ttonne= 1000 kg 0.984 ton (long) = Temperature Kelvin K Basic Slunit $F
megagram Mg 1Mg=1000kg 1.1023 ton (short) degree Celsius =. Thekelinand —“g -12.77
Time second s Baste SI unit
day d Nerther the day nor
the year is an SI unit
year year but both are impor- recommended at
tant. itis the former
centigrade scale.
Force newton N ‘The newton ss that 0.22481 Ib (weight)
force that produces = 7.233 poundals Work, energy, joule J ‘joule=1N-m 2.778 X 10-7
an acceleration of quantity of heat where metres are kw hr=
1 m/s? in a mass measured along 3.725 X 107
of Tg. the line of hp-hr = 0.73756
action of fth = 9.48 X
Moment or newton metre = Nem The metre is 0.7375 ttbt force N. 104 Btu
torque measured perpendicu- kilojoule kK 2.778 kwehr
lar to the line of
action of the force Power watt w Twat = 1 J/s
N. Not a joule, kilowatt kw
joule persecond J/s
Stress pascal Pa 0.02089 Ibf/sq ft
kilopascal kPa 0.14465 Ibt/sq in
Application of Units Application of Units
. Customary Customary
Description Unit Symbol Comments Equivalents Description Unit Symbo! Comments Equivalents
Precipitation, millimetre ‘mm For meteorological Concentration milligram per mg/t Top
tun-off, purposes it may be hitre
evaporation convenient to meas- -
ure precipitation in 800 loading kilogram per kg/m 0.0624 Ibfcu-ft
terms of mass/unit, cubic metre day
area (kg/m3). per day
1mm of rai
1 kg/m? Hydraulic load cube metre m3/m2d—Iftthisiscon- 3.28 cu ft/sq ft
. . per uni verted toa
River flow cubic metre m3/s Commonly called 35.314 cfs e.g. filty
‘per second ‘the cumec: fates:
pressed in mm)
cubie metre per m/s, presed in canis
second m3/m? day).
pumping litre persecond ts 15.85 gpm Hydraulicload cubic metre m3/m3d
‘ 5 er unit volume; per cubic metre
Discharges or cubic metre md 11/s= 864 m3/d 1.83 X 10° gpm eg, biological per day
abstractions, per day filters, goons
viel
cubic metre m/year Air supply cubic metre or — m3/s
per year litre of free air
second
Usage of water litre per person I/person 0.264 gepd a "s
per day day Pipes
. diameter millimetre mn in
Density Kilogram per kg/m? Thedensty of 0.0624 Ib/eu ft length metre m sarin
cubic metre water under stand- 3.28 ft
ard conditions is “
1000 kg/m$ or Optical units lumen per tumen/m? 0.092 ft
1000 9/ or square metre candie/sq ft

1 g/ml.



Table !V-4,—Probable sludge concentrations

A Percent
Chemical coagulant solids

Gravity thickening:

Alumandiron. . 2... 2.06% 2-5

Lime... 2... 2. ee ee 10-25
Dewatering:

Alumandiron..........- 10-20

Lime... .....00- an 20-40

Table !V-5.—Physical-chemical solids reduction by incineration

Dry weight
Coagulant Before After
incineration incineration
Pounds per million gallons
Alum... 2... ee ee 2,648 1,333
fron se ee ee 2,662 1,397
Lime... . 2... ee ee 6,920 3,462

Table !V-6.—Theoretical buildup of inerts in a recycling coagulant-recovery
system

Increase of inerts
Constituent per cycle, pounds
per million gallons

Ash (from raw sewage solids). . 2... 2.2. ee 832
Hydroxyapatite... . 510
Magnesium hydroxide . 100

Total inertspercycle .........008 1,442

Table | V-7.—/ncinerator feed rates theoretically required
for a nonblowdown coagulant-recovery system

Feed, pounds per

Cycles million gallons,
dry solids
To... 6,290
5B... 11,440
10 18,640
20 33,040

26


Table II-1.—Effluent quality resulting from powdered-carbon technique

Sample
Constituent

1 2 3 4
COD, mg/l . . 21 30 44 16
BOD, mg/! 12 7 18 2
TOC, mg/l. . 6 12.5 15 6
COD/TOC ratio... 2... ee ee 3.5 24 2.9 27
COD/BOD ratio. ....-. 2. eee 1.74 1.76 2.4 8

ratio compares closely with the other samples. It is possible, however, that there was a change in the
nature of the unadsorbable organics so that, in fact, a smaller portion was biodegradable.

The nonadsorbable BOD ranged from 2 to 18 mg/l, with an average of 12.2 mg/l for the four
samples.

COLUMN TESTS

Figures II-1 and II-2 summarize the data collected from the laboratory columns. As can be seen
from the figures, the benefits achieved by contact times greater than 30 minutes are slight. The
carbon-column effluent-BOD values after 60 minutes contact ranged from 5 to 15 mg/l and averaged
11.0 mg/l. The BOD samples collected at a 30-minute contact time averaged 12.5 mg/l.

An estimate of the required carbon dosage can be made by assuming that carbon will be with-
drawn for regeneration when the carbon loading is 0.5 pound of COD removed per pound of carbon.
This loading has been achieved in several studies. An average soluble influent COD of 86 mg/l was
achieved with lime clarification in the four series of jar tests. COD averaged 23 mg/l in the four
powdered-carbon tests, and 24 mg/l after 30 minutes contact in the columns. Thus, an average COD
removal of about 62 mg/l would be expected from these tests. The corresponding carbon dosage is
1,030 pounds per million gallons. Carbon dosages calculated from short-term laboratory column tests
are usually conservatively high, as biological action usually results in greater permissible loadings in a
continuous, plant-scale operation.

10


Chapter III
PROCESS DESIGN

The purpose of this chapter is to discuss those design criteria necessary for plant design. Fig-
ure III-1 illustrates the flowsheet upon which the discussion is based.

FLOW

Both the average and peak flows are of concern. In a physical-chemical plant, a substantial
volume of flow is recycled to the head of the plant from the following major sources:

© Furnace scrubber underflow
@ Filter and activated-carbon backwash flows
@ Sludge thickener overflow

@ Sludge dewatering filtrate or centrate

For example, a 15-mgd average flow rate may be associated with a peak hourly rate of 30 mgd. To
these values must be added the volume of recycle streams. If these recycle streams total 3.5 mgd
in the example, then the design hydraulic flow rates become 18.5 mgd average and 33.5 mgd peak

hour.

PRELIMINARY TREATMENT

Comminution and grit-removal facilities designed in accordance with standard sewage-treatment
design practices should be provided.

CHEMICAL FEED, RAPID MIX, AND FLOCCULATION

Chemical feed, rapid mix, and flocculation all may be carried out in accordance with standard
practices followed in the water-treatment field for years.

Proper rapid mixing is important to efficient utilization of the coagulating chemicals. The use
of a mechanical rapid-mixing device in the basins with a total of 2 minutes detention time of the
average flow is recommended. When using lime as coagulant, scaling of the mixer shaft will occur
and may cause excessive bearing wear if not cleaned regularly. In any case, provision of two parallel
rapid-mixing units, each with a nominal capacity of one-half the design flow, is prudent to provide
flexibility in operation. Should one mixing unit be down for repair, the entire flow can be passed
through the remaining basin, which will still provide 1 minute mixing with the foregoing criteria.

A mechanically mixed flocculator with 15 minutes detention is generally adequate for waste-
waters. In many cases, the flocculation resulting from the large coagulant doses added to waste-
waters results in very rapid flocculation, and even shorter detention times may be feasible. Provisions
should be made to add up to 1 mg/I polymer at the rapid mix or at the flocculator inlet or outlet,

or split among these points.

13