New Technology for Wastewater Control– Cutting-Edge Treatment Technology to Reduce Odors in Biosolids –Daniel WOLTERING1
Water Environment Research Foundation
1. Introduction
The overall purpose of this research is to seek ways to enhance anaerobically digested
and dewatered biosolids to reduce odor intensity in biosolids cake and thereby reduce the impact
on the environment of its beneficial use or disposal. Reduction of biosolids cake odors is one of
the most important needs expressed by Water Environment Research Foundation (WERF)
members. At a WERF-sponsored specialty workshop at the 2000 Water Environment Federation
Technical Exposition and Conference (WEFTEC) in Anaheim, California, the WERF members
voted biosolids odor issues as the highest priority for future research and specifically the
influence of in-plant solids treatment processes (such as storage, thickening, anaerobic digestion,and dewatering) on biosolids odor quality. In addition, the biosolids management industry is in astate of flux as to how to properly handle, treat, dewater, and store biosolids to prevent odors
while assuring compliance with present and anticipated changes to the USEPA 40 CFR Part 503
regulations governing biosolids quality.
This study focuses on the dewatering and digestion processes and equipment currently
used by wastewater treatment plants (WWTPs), as well as those that are proposed to meet 40
CFR Part 503 requirements. Equipment or process vendors were invited to demonstrate theirproducts full-scale at one or two WWTPs while the WERF team collects and analyzes data andcompares results. Any promising laboratory study result will be considered for full-scale fieldtesting in this project, in anticipation that it would lead to changes in how biosolids are digested,
handled, dewatered, treated, or stored. Practical economic considerations were also be factored
into the evaluation and selection of promising laboratory results to be translated to full-scale.
The conclusions of this study are intended to provide a wastewater treatment plant ownerwith a roadmap to develop approaches and strategies that will reduce dewatered biosolids cakeodors. Biosolids cakes with minimal odors lead to better public acceptance near biosolids
management sites and in neighborhoods adjacent to WWTPs. Reduced odors also could open thisdewatered biosolids cake to other biosolids recycling or disposal opportunities currently not used
due to odor concerns (including on-plant site composting or storage). Additionally, significant
cost savings could be realized by not requiring extensive odor control or other expensive options
for containment and management of biosolids.
2. Overview
This research is a multi-year study (2000–2007) conducted in three distinct phases by thesame team of researchers. Different team members participated in the phases depending upon
expertise required and the objectives of each phase. At the time of the January 2007 Japan-US
Conference, the research team is preparing the final report including the “roadmap” to guidewastewater treatment plant owners to reduce odors associated with biosolids at their plants.
1635 Slaters Lane, Suite 300, Alexandria, Virginia, 22309, USA- 323 -

e-mail:dwoltering@werf.org
The first phase, conducted between 2000 and 2001 involved literature and practitioner
surveys of odors in the municipal wastewater environment. The intent was to summarize
information on odor characterization for wastewater treatment systems including applicable odor
sampling and measurement approaches for potential sources, state-of-the-art odor control
technologies and strategies, lessons learned for viable and innovative odor control strategies andtechnologies, and key gaps in knowledge of technology in addressing odor issues from collection
through final treatment and effluent disposal including biosolids disposal. These findings weresummarized in a WERF report entitled Identifying and Controlling the Municipal Wastewater
Odor Environment.
In the second phase of research, conducted between 2002-2003, field work at 11 WWTPs
lead to a better understanding of the various locations and possible causes of odors during
digestion and dewatering. It was confirmed that biosolids cakes, following dewatering, typically
produce the worst odors in a wastewater treatment plant. Further it was found that high shear
dewatering processes such as high speed centrifugation produces more odors than pressing typeprocesses. Biologically available protein was confirmed to be the main contributor to the odor
potential of biosolids. Odorous compounds are produced as proteins degrade to form
polypeptides and amino acids which are consumed by microbes. Also as part of the research, a
new method for sampling and analyzing odors in biosolids cake was developed. Biosolids
samples were collected and incubated (under ambient conditions) in small, air-tight sample
bottles for at least 6 days. The olfactometry measurements in the bottle headspace were muchhigher than would be sensed by an individual onsite, or from the olfactory analysis of an air
sample gathered by flux chamber or another type of field headspace (as opposed to sample-bottle
headspace). While it is recognized that the bottle-headspace sampling method may not represent
actual field conditions, the consistency of sampling and analytical protocols that were used for all
11 WWTPs in the study resulted in a useful and statistically valid comparison of the large numberof samples collected. The complete results of the second phase are reported in a WERF
publication entitled Impacts of In-Plant Operational Parameters on Biosolids Odor Quality.
An ancillary part of the second phase of research was an evaluation of whether theexperience of odors, i.e., odors as sensations, from biosolids at wastewater treatment plants(WWTPs) might cause illness. There exists no repository of information on the numbers ofcomplainants with illness, their specific complaints, or the relationship between degree of
exposure and complaints. Anecdotal reports nevertheless imply a pattern much like thatassociated with other industrial malodors. Symptoms claimed in connection to odors frombiosolids in particular seem to come from olfactory rather than chemesthetic (irritating)stimulation. Although not inappropriate to the experience of malodors, the symptoms seem tooccur via intermediate variables, such as annoyance, anxiety, and frustration. Persons who
experience no such distress apparently experience no symptoms. Any connection between odor
and illness has received little note among the large number of articles in the medical literature.
This state of affairs presumably exists because odors per se generate no objective signs of illness
in otherwise healthy persons. However, malodors may exacerbate both symptoms and signs of
illness in persons with certain chronic disorders, such as asthma and migraine. Vulnerability tosuch effects may vary considerably from person to person. The WERF report is entitled Health
Effects of Biosolids Odors: Literature Review and Analysis.
As a follow on to this work, WERF is currently conducting research to develop a protocol
for the timely characterization of reports of adverse health effects following likely exposure toland-applied biosolids. The intent is that local health officials would use the protocol in theirevaluation of reported health incidents and that the information would be used to identify and- 324 -

reduce exposures if, in fact, there are any health effects or risks identified. The protocol should beavailable by the end of 2007.
The third and current phase of this research program began in 2004. The laboratory andfield work has been completed and the data analyzed. The final report is expected to be available
by the end of the first quarter of 2007. This phase is entitled Biosolids Processing Modifications
for Cake Odor Reduction.
This phase focuses on the dewatering and digestion processes and equipment currently
used by WWTPs as well as those that are proposed to meet 40 CFR Part 503 requirements.
Evaluate cake odors and reduction as a function of chemical addition, and digestion anddewatering process. Eleven WWTPs across the USA were involved in the collection of
information and data as well as sampling and analysis. Eight commercial vendors of agents
intended to reduce biosolids odors were invited to submit their chemical, biological or enzymatic
agents (CEBAs) for test demonstrations in the laboratory and at the full-scale if they showedpromise in the laboratory.
The laboratory studies done at the beginning of the third phase confirmed that volatileorganic sulfur compounds (VOSCs) are the main source of odors in anaerobically digested
biosolids. The principal components of VOSCs and those that were monitored in the study
include methyl mercaptan (MT), dimethyl sulfide (DMS) and dimethyl disulfide (DMDS). These
VOSCs and odors are produced and then degraded during biosolids storage.
The effects of chemical addition before and after digestion and dewatering were
evaluated for iron, aluminum sulfate (alum) and a wide range of CEBAs. More iron in wastewater
leads to more VOSCs and more odor. This was demonstrated in the laboratory and confirmed in
the field at one wastewater treatment plant. Eight (8) proprietary CEBAs were tested. 4 wereadded pre-digestion and 4 added post-digestion (either before or after dewatering). The dosage
amount and frequency was done according to the directions from the vendor. Only one of theeight CEBAs tested appeared to improve cake odor reduction over the untreated controls, but thatone severely inhibited the digestion process and thus was not a viable solution. One of the eight
actually increased the odor in the biosolids cakes. Post-digestion alum addition showed promisefor odor reduction in the laboratory. Alum field trials showed less consistent, but largely positive
results in reducing odor. Peak VOSC levels were significantly reduced with the addition of both
2% and 4% alum by weight.
The evaluation of various anaerobic digester processes on odor included the study ofdigestion time (SRT or solids retention time), the homogenization of the sludge prior to digestion,and the configuration of the digester comparing egg-shaped digesters with two-phase (acid-gas)digesters with a more conventional mesophilic digester.
While VOSC was reduced with SRTs extended beyond 10 days up to 30 days, the levels
did not get below 1000 ppmv which is still an odorous sludge. Utilizing the MicroSludge™
process before mesophilic anaerobic digestion significantly reduced cake odors. The MicroSludge
System uses chemical pre-treatment and a cell disrupter to burst the microbial cells in waste
activated sludge (WAS). The resulting liquefied WAS is readily converted to biogas in ananaerobic digester. The egg-shaped digester produced less odor than the two-phase (acid/gas)digester. And both of these configurations produced considerably less odor in biosolids cake than
did the conventional mesophilic anaerobic digester.
A Centrifuge Scroll Test was conducted on a high speed centrifuge as part of the study todetermine the effect of dewatering processes on cake odor. Several locations within the- 325 -

centrifuge were sampled and the analysis of VSOC clearly indicated the level of odor was higher
immediately after the digested sludge was sheared and as it left the centrifuge. The overall
comparison of various dewatering processes indicated that cake produced by centrifuge had thehighest odors produced followed by rotary press and then belt filter press. Centrifuge type andoperation (bowl speed, torque, and feed rate) was also seen to impact odor production. The
dewatering effect appears to be related to centrifugal shearing of the biosolids, which appears tomake protein more bioavailable, thereby producing more TVOSC from protein decay.
In summary, the aspects of the digestion and dewatering processes that appear to have thebest potential for reducing biosolids cake odor include: sludge homogenization before digestion,
increased solids retention time, lower iron in the wastewater, digester configuration, and reduced
shear during dewatering and handling. The addition of alum post-digestion but prior to
dewatering was also found to help reduce cake odor. These aspects may work in acomplementary manner, and some or all may be needed for significant odor reduction in biosolids
cake. The eight commercially available CEBAs that were tested did not reduce cake odor.
While much was learned from this research program, it only forms the foundation forwhat will need to be numerous further trials, demonstrations and the sharing of findings by
wastewater treatment plants to build a database of experience. This experience will provide
guidance as to what adjustments work and are cost effective. The final report (available by theend of the first quarter of 2007) will provide an initial “roadmap” of approaches and strategies
that a wastewater treatment plant owner can try in order to reduce dewatered biosolids cake odors.
It will cover both the processing equipment and the chemical addition aspects of operational
decisions as well as the designs of digesters and dewatering to minimize cake odors.

- 326 -

Japan - US Governmental Conference on Drinking Water
Quality Management and Wastewater Control

Water Environment Research
Foundation Top Issues for Wastewater

January 22-25, 2007, Bankoku Shinryokan, Okinawa

 Nutrient removal

Treatment Technology to
Reduce Odors in Biosolids

 Sustainable asset management
 STP operation optimization
 Risk of trace contaminantspresented by Health risks of wastewater microbes

Dan Woltering, Ph.D.
Director of Research Stormwater management
 Biosolids health risks and odors

1

2

Project Goals

Project Participants To cost-effectively produce dewatered biosolidsof significantly reduced odor intensity

Principal Investigators
 CH2M Hill
 Los Angeles County Sanitation Districts
Additional Research Participants Virginia Polytechnic Institute & State University
 Bucknell University
 Moore Engineering Consultants
 11 participating wastewater utilities
 8 participating commercial product vendors

 Provide treatment plant owner with a “roadmap”

of process modifications that can be considered
to reduce dewatered biosolids cake odor
 Focus on digestion and dewatering equipment

and processes now in use to meet regulations

3

4

Phase 2 confirmed that biosolids cakes
typically produce the worst odors in a
Wastewater Treatment Plant (WWTP)

Project History/Overview
 Phase 1 (2000-2001): Literature survey of odors in the municipal wastewater

900

environment. Product: Literature Search, Review, & Analysis

Mean P eak S u lfu r
C o n cen tratio n (m g S /m 3)

 Phase 2 (2002-2003): Field work at 11 WWTPs that helped understand thevarious locations and possible causes of odors during digestion anddewatering. Product: Impacts of In-Plant Parameters on Biosolids Odors

 Health Effects Addendum (2004): Review and summarize evidence

surrounding potential health effects of biosolids odors. Product: Health
Effects of Biosolids Odors: Literature Review and Analysis

 Phase 3 (2004-2006): Laboratory and field tests with additives to determine if

odor reductions can be achieved and recommendations on what a plant can
do to reduce odors. Product: Biosolids Processing Modifications for Cake
Odor Reduction

800
700

Dewatering
Cake
Conveyance,
Storage

600
500
400
300
200
100

DigesterFeedPrimary & Secondary
Clarification/Thickening

0

A

B

C1

Phase 3 Objectives

C2

D

F1

F2

G

I1

I2

Sampling Locations
H2S

5

Liquid,Digested
SolidsMethane thiol

Total sulfide species

6Components of Phase 2 Research Evaluate cake odors and reduction as a function of: Develop sampling methods for total volatile Chemical addition

organic sulfur compound (TVOSC) as asurrogate for odors
 Confirm correlation between TVOSC andodors from biosolids

 Digestion Dewatering process

 Lab scale first and then try it in the field

78- 327 -

Closed cake sample bottle simulates
anaerobic cake storage environment:

Findings from Phase 2
 Volatile organic

350

sulfur compounds(VOSCs) are themain source ofodors inanaerobicallydigested biosolids

MT, DMS, DMDS (ppm) VOSCs and odors
Org S-

250
200
150
100
50

are produced anddegraded duringstorage

Org S-

MT
DMS
DMDS

300

0
0

2

4
6
8
Storage Time (d)

10

9

10

Correlation between TVOSC and odors as measured
by dilutions-to-threshold (D/T) was corroborated

Why are TVOSCs and Odors Reduced ?

7500

y = 0.8248x + 3.7568
R2 = 0.9824

Pr
o

C
ns

du

300

ge
no
tha

ce
Od
o

rs

Me

400

o
Od

Ba
d

me
su

Bu
gs

on

200

LOG dilution to threshold (D/T)

6

TVOSC Concentration (ppmv)

12

100

5

Closed bottle samples,
WERF project 2006

4

3

Flux chamber samples, Webster et al, 2006
2

rs

1

0

0
0

2

4

6
8
10
Storage Time (days)

12

-1

14

Proteins

methionine

Methyl mercaptan + VOSCs

cysteine

Hydrogen sulfide

tryptophan

Indole + skatoletyrosinep-cresol

1

1.5

2

2.5

3

3.5
12

CEBA,
Alum,
or Iron
Addition
Point

X

CEBA, Alum,
Iron &Polymer
Addition Point

Mesophilic
Anaerobic
Digestion

X

Sampling
Location

Lime Addition
Point

High Solids
Centrifuge

X

ConveyanceX

Odorous
Compounds

Amino
Acids

Polypeptides

0.5

Effect of Chemical Addition

are produced from protein degradation

Peptidase
Enzymes0

LOG or ganic s ulfur (ppm )Cause of Biosolids Odor: Odorants

Protease
Enzymes-0.5

11

CEBA = chemical, enzymatic or biological agent
Alum = aluminum sulfate (Al2(SO4)3
13

14

More iron in the wastewater leads to more
TVOSC - blue are lab and pink are field data

Tests of Chemical, Enzymatic,
and Biological Agents (CEBAs)

2500

2000

TVOSC (mg/m3)

R2 = 0.94
1500

 Eight (8) proprietary CEBAs were tested, 4 added pre-BESA is a chemical
That inhibits
methanogens,
So TVOSC isgenerated
But not consumed

digestion and 4 added post-digestion The dosage amount and frequency was according to thedirections from the Vendor

 Digestion was batch-wise with two different 50% exchangesof fresh sludge on days 7 and 14 with an additional 21 daysof digestion An initial 20% seed of digested sludge and a balance of
50/50 mix of primary/secondary sludge was used
 Post-digestion CEBAs were added before & after dewatering Only one of the eight (8) CEBAs tested appeared to improve
cake odor reduction over the untreated controls, but that one
severely inhibited the digestion process…

Philadelphia SW

1000

500
Philadelphia NE
0
0

20

40

60

Fe in feed sludge (mg/gTS)

80

100

120
15

16

- 328 -

CEBA No. 1: Added Pre-digestion
30

CEBA No. 8: Added post-digestion,prior to dewatering

MethaneCarbon Dioxide

25
Gas Volume (L)

40%
35%
30%

Control 1

25%

Control 2

20%

CEBA No 1

15%

20120,000

15

CEBA No. 8 produced
higher odor…

10
5

10%
5%

0

0%
first 7 days

second 7 days

Control 1

final 21 days

Control 2

CEBA No 1

1,200

90
80

60

We would expect that,
if the inhibition were
eliminated, TVOSC
would be generated

50
CEBA No 1
40

Control 2

30

Control 1

20

Control

1,000

CEBA-8100,000

80,000Control

60,000

CEBA-840,000800

20,000

600

0
0

5

10
Storage Time (days)

15

400

200

10

…and had lower methane production

0

0

0

17
0

5

10

15

20

25

30

35

5

40

10
Storage Time (days)

15

18

Time (days)

Post-digestion Alum Addition Showed
Promise for Odor Reduction in the Lab

Alum Field Trials showed lessconsistent, but largely positive results
500

250

5

Control
0.5% Al
2% Al
4% Al

5

Methane (ppmv)

1.5 10150

100

Average Headspace TVOSC(ppmv)

2 10Control
0.5% Al
2% Al
4% Al

200

TVOSC (ppmv)

5

1 10

4

5 10

50

0
0

5

10
15
Storage Time (days)

20

25

SW Cake Control 1
SW Cake 0.5% Al
SW Cake 1% Al
SW Cake 2% Al
SW Cake 4% Al
SW Cake Control 2

400

300

200

100

0
0

5

10
15
Storage Time (days)

20

25

0

TVOSC and Methane Production vs. Cake Storage Timeat Varying Alum Doses (Optimum Polymer Dose)

0

19

5

10
Storage Time (days)

15

20

20

Digested solids dewatering from Philadelphia WWTP

Same Alum Field Trial Results
as a Bar Chart, Comparing Peak
TVOSC at Different Alum Doses

Effects of Anaerobic Digestion
Processes on Cake Odor

500

 The next three slides show:

400



300



200



Effect of Mesophilic Anaerobic Digestion Time
(SRT) on Volatile Solids Reduction and TVOSC
Effect of Activated Sludge Homogenization priorto Anaerobic Digestion on TVOSC
Effects of Egg-shaped Digesters and Twophase (Acid-gas) Digestion compared with
Conventional Mesophilic Anaerobic Digestion

100

0
Control 1

0.5%

1%

2%

4%

Control 2

21

22

The MicroSludge™ Process before
Mesophilic Anaerobic Digestion
Reduced Cake Odors

Lab digestion – the SRT study

Mannich polymer

3000
set 1

2500

set 2

2500

Control (1500G)

set 3

Control (2500G)

set 4

2000

2000

Microsludge (1500G)
Microsludge (2500G)

1500TVOSC (ppm)

TVOSC (ppmv)

TVOSC (ppmv)

70

Average Headspace TVOSC (ppmv)

Appeared to be inhibitory,
probably due to low pH. Low
TVOSC but also low VS
destruction and gas production

100

Avg Peak TVOSC (ppmv)

Volatile Solids Reduction (%)

45%

Average Headspace Methane (ppmv)

Volatile Solids Reduction
50%

1000
500
0
0

10

20

30

40

1500

1000

500

50

Digestion Time (days)

0

What do we see?
•Improved TVOSC reduction to 30 days
•Can’t seem to get below 1000 ppmv
•This is still an odorous sludge after 40 days digestion time

0

5

10

15

20

25

Tim e (da ys)
2324- 329 -

Two-phase (Acid/gas) & Egg-shaped
Digesters are Better than Mesophilic
Anaerobic Digestion For Odor Reduction

3

Headspace organic sulfur(mg/m )2500

Effect of Dewatering Processes on Cake Odor
Centrifuge Scroll Test – Sample locations

Conventional(pancake)
Conventional(egg)Gas(pancake)Acid-gas (pancake)

Sample C: After Disk
Sample A: Entry Point

2000

1500

1000

500

Sample D: Discharge Point

Sample B: Before Disk

0
0

5

10

15

20

25

30

Incubation time(days)

Cake Sample Incubation Time (days)

25

26

Centrifuge Scroll Test: odor
results by sample location
2500

28%
32%

TVOSC (ppmv)

2000

Dewatering Conclusions
 Dewatering process has significant impact on odor

Location A
Location B
Location C
Location D

production:


1500

Centrifuge >> Rotary Press > Belt Filter Press, interms of cake odors produced

 Centrifuge type and operation (bowl speed, torque,feed rate) can also impact odor production1000

 Main effect appears to be related to centrifugal

shearing of the biosolids, which appears to makeprotein more bioavailable, thereby producing more
TVOSC from protein decay

500
22%
17%
0
0

5

10
15
20
Storage Time (days)

25

30

27

28

Potential Reduction Measures of Biosolids Cake Odors
Options Summary Chart [“Roadmap”]

Phase 3 - Overall Observations

Operational Decisions

Process
Equipment

Sludge homogenization before digestion can reduce odor
Increased solids retention time can reduce odor
Higher iron in the wastewater can lead to increased odor
Digester configuration can affect cake odor
Addition of alum post-digestion but prior to dewatering canreduce odor
 Reduced shear during dewatering and handling can reduceodors These aspects may work in a complementary manner, andsome or all may be needed for significant odor reduction inbiosolid cake The commercially available CEBAs that were tested did not
reduce odor






Anaerobic Digestion
Digester pretreatment
Improve mixing
Increase VS reduction
Operate in seriesMultiple phases
Increase temperature
Other?

Dewatering & Cake
Conveyance/ Storage
Decrease centrifuge bowl
speed
Decrease centrifuge
torqueIncrease cake moisture
content
Consider BFPs
Belt Conveyors
Cake storage/aging
Other?

29

Thank you
The final report, which will include the “roadmap” isexpected in Q1 of 2007
Contact information:
Dr. Dan Wolteringdwoltering@werf.org

31- 330 -

Design Decisions

Chemical
Addition

Pre-Digestion
Aluminum
Iron
Other cations
pH control
CEBAs
Other?

Pre- or PostDewatering
Aluminum
Iron
Other cations
pH control
Polymer dose and
type
CEBAs
Other?

Anaerobic Digestion
Digester pretreatment
Better mixing
Longer SRTs
Egg-shaped
Acid-Gas (multi-phase)
Thermophilic
Temperature-phased
Other?

Dewatering &Cake Storage
Belt Filter Press
Rotary Press
Variable-speed
centrifuges
Adjust cake solids
Minimize
conveyance
Belt conveyors
Enclose cakestorage areas
Other?

Each decisionmust consider
any other direct
or indirect
impacts ofdesign andoperationalchanges onwastewater
treatment andsolids handlingprocesses

30