INTRODUCTION TO TOXICITY REDUCTION AT
PUBLICLY OWNED TREATMENT WORKS
September 1989
U.S. Environmental Protection Agency
Office of Water
Office of Municipal Pollution Control
401 M Street, S.W.
Washington, D.C. 20460
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INTRODUCTION TO TOXICITY REDUCTION AT PUBLICLY OWNED
TREATMENT WORKS
Prepared For
U. S. Environmental Protection Agency
Office of Water
Office of Municipal Pollution Control
401 M Street, SW
Washington, DC 20460
Prepared By
ENGINEERING-SCIENCE, INC.
290 ELWOOD DAVIS ROAD
LIVERPOOL, NY
SEPTEMBER 1989
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TABLE OF CONTENTS
Acknowledgenients . 1
Section 1 lnfr u Ion .1 -1
1.1 BACKGROUND 1-1
1.2 SIGNIFICANCE OF WASTEWATER TOXICS AND TOXICITY 1-2
1.3 IDENTIFICATION AND QUANTIFICATION OF TOXICS/TOXICITY 1-2
1.3.1 Effluent Toxics and Toxicity :1-3
1.3.2 Toxics and Toxicity in Wastewater 1-3
1.3.3 Sludge Toxics 1-3
1 3.4 AIr Tox lcs 1-4
Section 2 Sources and Fate of Toxics and Toxicity in POTWs 2-1
2.1 SOURCES OF TOXICITY 2-1
2.1.1 Major Industrial Users 2-1
2.1 2 Secondary Industrial and Commercial Users 2-3
2.1.3 RCRA and CERCLA Users 2-3
2.1.4 Domestic Users 2-4
2.1.5 In-Plant Toxics Sources 2-4
2.2 FATE OF TOXICS AND TOXICITY IN POTWS 2-4
2.2.1 Treatment 2-6
2.2.1.1 BIodegradation 2-6
2.2.1.2 TransformatIon 2-6
2.2.2 VolatilIzation 2-6
2.2.3 Sedimentation and Sorption on Solids 2-8
2.2.4 Pass-Through 2-8
SectIon 3 Removal of Toxics and Toxicity In POTWs 3-I
3.1 INTRODUCTION 3-1
3.2 REMOVAL CAPABIUT1ES IN POTW TREATMENT SYSTEMS 3-1
3.3 TOXICS REM9VAL CAPABIUTY OF POTW UNIT PROCESSES 3-2
3.3.1 Removal During Primary Treatment
3.3.2 Removal During Secondary Treatment 3-6
3.3.3 Removal During Advanced Treatment 3-7
3.3.3.1 CoagulatIon/Flocculation/Sedimentation 3-7
3.3.3.2 FiltratIon 3-9
3.3.3.3 Activated Carbon Adsorption 3-9
3.4 SUMMARY 3-11
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TABLE OF CONTENTS, CONTINUED
SectIon 4 Enhanced Removal of Toxics and Toxicity 4-1
4.1 CORRECTION OF PERFORMANCE UMITING PROBLEMS 4-1
4.2 PROCESS OPTIMIZATION 4-1
4.2.1. On-Une Monitoring With Diversion Control 4-1
4.2.2 Biological Process Control 4-7
4.2.3 Modification of Biological Reactor Configuration 4-8
4.2.4 Chemical Addition 4-8
4.2.4.1 NutrIents 4-9
4.2.4.2 pH Adjustment 4-9
4.2.4.3 Coagulants 4-9
4.2.4.4 Powdered Activated Carbon 4-9
4.2.5 Disinfection Process Optimization/Alternatives 4-9
4.3 ADDITIONAL TREATMENT 4-10
4.3.1 Influent Flow Equalization 4-10
4.3.2 Effluent Equalization 4-10
4.3.3 Physical/Chemical Treatment 4-10
4.4 SUMMARY 4-11
SectIon 5 Source Control of Toxics and Toxicity 5-1
5.1 INTRODUCTION 5-1
5.2 TOXICITY SOURCE EVALUATION - TIER I 5-1
5.3 TOXICITY SOURCE EVALUATION - TIER II 5-2
5.4 DEVELOPMENT OF LOCAL UMITS 5-2
5.5 SUMMARY 5-2
SectIon 6 Summary
Appendix A References
Appendix B Ust of Abbreviations and Acronyms
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LIST OF TABLES
Table 2-1 PredomInant Fates of Toxic Pollutants In POTWa .2-7
Table 3-1 Volatile Organic. Present In P01We 3-3
Table 3-2 Semi-VolatIle Organic. Present In P01W. 3-4
Table 3-3 Toxic Metals Present In POT’Ns 3-5
Table 3-4 Toxic Removal Performance Secondary Treatment Processes 3-8
Table 3-5 Toxic Removal Performance of
CoagulatIon/Flocculation/SedImentatIon and FIltratIon 3-10
Table 3-6 Toxic Removal Performance of Granular Activated and
Powdered Activated Carbon 3-12
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UST OF FIGURES
Figure 2.1 Major/Secondary Industrial and Domestic Toxic Contributions
to POTWe 2-2
Figure 2-2 Potential Pathways and Environmental Impacts Associated
with Toxics/Toxicity
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ACKNOWLEDGEMENTS
This document was prepared by Engineering-Science, Inc., under EPA Contract No. 68-
C8-0022. Mr. David G. Johnson was the project manager and Mr. Leslie Cordone was the project
engineer. Additional guidance was provided by John A. Botts, Jonathan W. Brasweli, William H.
Kornegay, Ph.D., and Timothy G. Shea, Ph.D.
This booklet was prepared under the technical direction of Atal Eraip of the U.S. EPA
Office of Municipal Pollution Control (OMPC). Additional guidance and assistance were provided
by Lam Urn and Robert Bastian of OMPC, Dick Brandes and Martha Segal of U.S. EPA Office of
Permits, and Doiloff Bishop and Richard Dobbs of U.S. EPA Risk Reduction Engineering
Laboratory - Cincinnati.
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SECTION 1
IN T RODUCTION
1.1 BACKGROUND
The Clean Water Act (CWA) provides the basis for control of toxic substances discharged
to waters of the United States. The Declaration of Goals and Policy of the Federal Water Pollution
Control Act of 1972 states that “..it Is the national policy that the discharge of toxic pollutants In
toxic amounts be prohibited.” This policy statement has been maintained in all subsequent
versions of the CWA.
The National Pollutant Discharge Elimination System (NPDES) permits for wastewater
discharges are used to achieve this goal; The five-year NPDES permits contain technology-based
effluent limits reflecting the best controls available. Where these technology-based permit limits do
not protect water quality, additional water quality-based limits are included in the NPDES permit In
order to meet the CWA policy of “no toxic pollutants in toxic amounts”. State water q alfty
standards are used In conjunctIon with Environmental Protection Agency (EPA) criteria and toxicity
data bases to determine the adequacy of technology-based permit limits and the need for
additional water quality-based controls.
To insure that the CWA’S prohibitions of toxic discharges are met, EPA has issued a
“Policy for the Development of Water Quality-Based Permit Umftatlons for Toxic Pollutants” (40 FR
9017, March 9, 1984). This national policy recommends an integrated approach for controlling
toxic pollutants that utilizes whole effluent toxicity testing to complement chemical-specific
analyses.
EPA has developed standardized methods for measuring acute and chronic toxicity to
determine the toxicity of effluents to aquatic life. Whole effluent toxicity limits and blomonitoring
conditions using these methods are Included in NPDES permits as necessary.
It Is the responsibOity of each P01W to test for toxicity In its effluent and to eliminate or
reduce effluent toxicity. Several major approaches are avaliable, IncludIng: 1) the elimination of
the source of toxicity; and 2) conversion of toxic constituents Into non-toxic forms through In-plant
treatment processes. Toxicants may also be removed from the wastewater during treatment In the
P01W through volatilization or sedimentation/sorption with settled sludge; however, this results in
the transfer of toxic constituents to air or solid media which can create additional problems. This
booklet covers the major removal mechanisms for toxicants within a P01W. Areas covered
include:
1) Sources and fate of toxic pollutants in PO1Ws.
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2) The removal of toxicants in commonly used POTW treatment processes.
3) Methods of enhancing the removal of toxicants through improvements in operation and
maintenance (O&M).
4) Identification of new and developing treatment processes which may be useful in removing
toxicants.
This booklet is intended to serve as a primer on toxics management in PO TWs and does
not present detailed guidance on the design of upgrade alternatives for enhancing toxics removal.
It does, however, assume that the reader has a basic knowledge of common POTW unit
operations. Additionally, in managing toxicity, P01W operators should be familiar with many
federal and state laws and regulations. A good summary of current federal laws and regulations Is
presented in Overview of Selected Regulations and Guidance Affectlna P01W Management (19).
1.2 SIGNIFICANCE OF WASTEWATER TOXICS AND TOXICITY
The presence of toxicants in wastewater can have detrimental effects on the environment
and human health as well as interfere with the efficiency of treatment processes. Toxicants which
pass through PO1Ws and are discharged in the effluent may affect aquatic organisms in the
receiving water. Moreover, human health may be affected through direct contact, consumption of
potable waters drawn from the receMng water body, or ingestion of fish or other aquatic
organisms which concentrate toxic compounds. Toxic releases from PO1Ws also occur when
organic compounds volatilize into the atmosphere during wastewater collection and treatment and
when toxic organic compounds and metals are released during sludge incineration or land
application of sludge.
The introduction of toxicants into a P01W can Inhibit or disrupt wastewater treatment,
sludge processing, or sludge disposal operations. Additionally, toxicants can cause health and
safety problems for P01W operators, sewer laborers or other Individuals who may come in contact
with contaminated wastewater or air emissions.
Loss of treatment efficiency can be caused by shock loads of toxicants which are
incompatible with the treatment process or excessive amounts of toxic materials which in low
concentrations are normally compatible with the treatment system. Typicaily, biological treatment
systems are especially susceptible to interference from toxic loading. These Inciude secondary
wastewater treatment technologies (e.g. activated sludge, trickling filters, lagoons, and rotating
biological contactors), aerobic and anaerobic sludge digestion, and nitriflcatlon.
1.3 IDENTiFICATiON AND QUANTiFICATION OF TOXICS/TOXICITY
Various techniques for measuring interfering substances, particularly toxicants that inhIbit
biological treatment, are presented in several EPA publications, including the GeneraIlz
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Methodoloav for Conducting Industrial Toxicity Reduction Evaluations. ToxiciW Reduction
Evaluation Protocol for Municiqal Wastewater Treatment Plants, and Methods For Aquatic Toxicity
Identification Evaluations: Phase 1 Toxicity Characterization Procedures (18, 17, 16). The basic
methods for identifying and quan ying toxicants and toxicity In P01W effluents, sludges, and air
emissions are briefly described In the following paragraphs.
1.3.1 Effluent Toxics and Toxicity
Two general approaches exist for identifying and quantifying toxics in P01W effluents.
Overall P01W effluent toxicity can be measured by biomonitoring techniques which quantify the
adverse effects of exposing an Indicator organism to an effluent sample. The second method of
toxics measurement Is the chemical specific approach, which utilizes analytical techniques to
identify and quantify known toxicants.
The use of blomonitoring involves quantification of the effect of P01W effluent on
biological indicator species. Two biomonitoring approaches can be utilIzed: (1) direct
measurement of end-of-pipe toxicity effects using aquatic toxicity tests, and (2) investIgation of in.
stream effects through surveys of aquatic life Indigenous to the receMng water (biosurveys).
Aquatic toxicity tests are laboratory based and include the quantification of adverse effects (e.g.,
mortality, low growth rates, and low reproductive rates, etc.) on a specific test organism over a
period of time and range of sample concentrations. Blosurveys identify and quantify the effects
that a discharge has on biological communities In the receMng water. Blosurveys, therefore,
provide a direct measurement of receMng water Impacts that cannot be obtained by laboratory-
based aquatic toxicity testing or chemical specific toxicity testing. Discussion of biomonftoring
approaches are presented In several publIcations (16, 17).
The chemical-specific approach utilizes standard analytical techniques to quantity specific
toxic compounds. Quantitative results are then compared to compound-specific toxicological data
to determine the potential toxic effects on organisms in the receiving waters or on human health.
1.3.2 Toxlcs and Toxicity In Wastewater
Wastewater toxicants can cause biological process interferences in P0TWs. The chemical
specific approach and aquatic toxicity testing, as described above, can be used to quantify
toxicants or toxicity In wastewaters. This Information can aid In the ImplementatIon of source or
operational controls at a P01W
1.3.3 Sludge Toxics
The concentration of toxlcants In sewage sludges derived from wastewater Is a key toxics
removal process In POTWs. The presence of toxicants In sludge may affect the performance of
solids stabIlization processes such as digestion and can limit the sslectton of a disposal method for
sewage sludge such as land spreading or incineration. Toxicants In sewage sludge should be
monitored to determine compatIb Ity with regulatory requirements for disposal.
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Toxic contaminant concentrations measured in sewage sludge are used to determine the
extent to which local pretreatment regulations are needed to protect sludge quality. Techniques
are available for the chemical analysis of raw and stabilized sludge. The toxics concentration in
raw sludge can eithar be measured directly or estimated. Estimates of the raw sludge
concentrations of pollutants which are not readily biodegradable or volatilized can be based on the
influent loading and the removal efficiency of such compounds in the P01W. Other pollutants
which are biodegradable or volatile must be measured directly using EPA’s Test Methods for
Evaluatina Solid Waste (12).
1.3.4 Air Toxics
Toxic organic compounds can volatilize from the sewer collection system and P01W unit
processes and be emitted by sewage sludge incinerators with inadequate emission control
systems. These emissions can affect ambient air quality and worker health and safety.
Although overall treatment facility air emissions are difficult to measure, total volatile
concentrations in a specific volume of air at specific locations can be measured by several
methods including lower explosive limit (LEL) monitoring, sample headspace monitoring, flash
point tests, portable organic vapor screening devices, and direct analysis of influent wastewater or
process wastestreams for volatile organic compounds (VOCs).
In situations where informatIon on specific compounds is needed, direct VOC
measurement in the P01W influent or process streams is recommended. Methods for VOC
analysis of wastewater and sludge are described In Methods for Oraanic Chemical Analysis of
Municinal and Industrial Wastewater (8). VOC data for aqueous wastestreams can be used to
estimate the amount of VOCs that could theoretically volatilize during treatment. Toxic emissions
from sewage sludge incinerators can be quantified by directly measuring incinerator stack
emissions. Methods for monitoring incinerator stack emissions are described in 40 CFR Part 60,
Appendix A.
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SECTION 2
SOURCES AND FATE OF TOXICS AND TOXICITY IN PO1WS
This section provides a summary of the typical sources of toxics and an overview of the
pathways by which toxicants can pass through a P01W. An understanding of the contributing
sources of toxicity arid the fate of toxics/toxicity within the treatment plant are necessary to
achieve effective toxics management.
2.1 SOURCES OF TOXICITY
Typical sources contributing toxicants to P01W Influent wastewater include major and
secondary industries, commercial users, and residential users. In addition, at specific PO1Ws,
dischargesirom facilities regulated under the Resource Conservation and Recovery Act (RCRA)
and those derived from actMties regulated under the Comprehensive Environmental Response,
Compensation and Uability Act (CERCLA) may also contribute toxicants. Toxic wastewater
constituents, and other compounds formed by the breakdown of these compounds during the
wastewater treatment process, contribute to effluent toxicity. Effluent toxkity may also be created
by disinfection procedures.
The relative toxics contribution, on a national basis, from malor and secondary Industrial
and domestic users before and after the implementation of pretreatment standards for existing
sources (PSES) Is presented in Figure 2-1. Currently, major Industrial users are estimated to
contribute the largest percentage of metallic and organic toxicants (83% on a mass basis) to
POTWs (FIgure 2-1). However, after the implementation of PSES, the major industrial contribution
of toxics is expected to decrease to 42 percent, with secondary Industrial and domestic users
contributing 45 and 13 percent, respectively. While the absolute contribution from domestic users
is not expected to increase, they are predicted to become a relatively significant source of toxic
metals In the future as these limitations are applied to major industrial contributors. In fact, It Is
estimated that, after PSES implementation, the sum of the domestic and commercial contribution
of hazardous metals is expected to increase from 8 to 63 percent of the total relative input from all
sources (11).
2.1.1 Major Industrial Users
Major Industrial users include 26 specific industrial categories with over 14,000 IndustrIes
(11). They contribute approxImately 75 percent of the total wastewater flow attributable to
industrial sources (6). EPA has established categorical discharge standards for major industrial
users.
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Estimated Relative Toxics Contribution to POTWs from
Major/Secondary Industrial and Domestic Sources
ilillV.i1
:: ::: : : ::h: I
A’
r: /
: /
/
BEFORE PSES
AFTER PSES
Source: EPA Domestic Sewage Study, 1986
45%••..
SOURCE KEY
0
z
m
m
z
0
m
z
C )
m
Major Industrial
Domest
Secondary Industrial
2!
C)
C
m
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General wastewater characterization data for each major industrial category are available
in EPA documents and have been compiled In the EPA Treatability Manual (7). These documents
present typical priority and common pollutant concentrations for wastewaters discharged by
industries Included In each of the 26 specific industrial categories. Priority pollutants include 126
toxic metallic and organic compounds that are regLiated by categorical pretreatment standards for
specific industries. For POIWs which have implemented pretreatment programs, data developed
during the industrial waste survey (IWS) stage is an additional source of toxics information from
major industrial users (14).
Based on data collected during the Domestic Sewage Study , major industrial users-
contributing the greatest loading of toxic metals to POTWs are the electroplating, metal finishing
and organic chemical manufacturing categories (11). The major Industrial users contributing the
greatest Loadings of toxic priority pollutant organics to POIWs are the pharmaceutical
manufacturing, petroleum refining, pulp and paper and organic chemical manufacturing categories
(11). The implementation of proposed and promulgated Industrial pretreatment standards for
existing sources (PSES) may shift the relative contributions of priority pollutants from all industrial
categories (11). Compliance with PSES Is projected to result In a 95 percent decrease in priority
pollutant discharge by categorical industries (11).
2.1.2 Secondary Industrial and Commercial Users.
Secondary industrial and commercial users comprise a wide range of activities includIng
equipment manufacturing operations, laboratories, hospitals, laundries, and motor vehicle service
operations. While some larger users in this grouping may be included In a PO1Ws pretreatment
program, smaller users are typically excluded from pretreatment programs because of their size
and limited flows. Wastewater characterization data regarding secondary industrial and
commercial users Is therefore generally limited.
Due to their great numbers and exclusion from pretreatment requirements, secondary
industrial and commercial users can contribute significant toxIcity to PO1Ws. For example,
laundries were identified as being major dlschargers of both toxic metal and organic compounds
and the equipment manufacturing category was identified as having the greatest mass loading of
toxic organic compounds for secondary industrial and commercial users (11).
Secondary Industrial and commercial users have been identified as problematic industries
by PO1Ws due to the discharge of spent solvents and other chemIcals (11). For example,
hospitals and laboratories have been identified as sources of toxic metals (e:g., silver and copper);
solvents (e.g., toluene, methylene chloride, and 1 ,2-dlchloroethane) and disinfectants (e.g., phenol)
(11). In one specific Instance, a wood furniture manufacturer and refinishing facility was identified
as discharging wastewater with methanol and meth 1ene chloride concentrations in excess of
5,000 and 1,400 mg/I, respectively (11).
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2.1.3 RCRA and CERCLA Users
Discharges from RCRA treatment, storage and disposal facilities (TSDFs) and CERCIA
sites can contribute to the toxicity of wastewater at POTWs. There are an estima’ed 4900 RCRA
TSDFs that store r treat hazardous wastes (11). These facilities may discharge leachate,
contaminated runoff, treatment system effluent, air pollution scrubber wastewater, and other
aqueous wastestreams to POTWs. These facilities will continue to be a potential source of toxicity
to POTWs and they may become more significant sources in the future, since the number of
facilities is increasing. In addition, since they are not presently subject to categorical pretreatment
standards, their proportional contribution may increase due to the decrease in discharges from
other facilities which are presently subject to categorical pretreatment standards.
Hazardous waste site clean-ups initiated under CERCLA can contribute to POTW Influent
wastewater toxicity in a number of ways. Of the estimated 20,000 hazardous waste sites in the
USA. it is predicted that 10% will utilIze POTWs for some portion of the waste treatment (11). This
may include treatment of landfill leachate, contaminated groundwater. stored aqueous wastes,
treatment sludges, stormwater runoff, decontamination waters, and/or remedial wastewater
treatment system effluents.
2.1.4 Domestic Users
The results of several EPA studies have demonstrated that domestic users contribute a
small but significant toxicity loading to POTWs (6,11). The findings indicated that residential users
contribute toxic metals (e.g., lead, chromium, nickel), inorganics (e.g., cyanide), and organic
compounds (e.g., chlorinated solvents, aromatic hydrocarbons, and phthalate esters). As
previously discussed, the relative contribution of metal and priority pollutant organic constituents
from domestic users is expected to increase in the future as the contribution from other sources
declines (Figure 2-1) (11).
2.1.5 In-Plant Toxics Sources
A major in-plant source of effluent toxicity is the disinfection of P01W effluent with
chlorine. Chlorine combines with residual organic compounds In the treatment system effluent to
form toxic chlorine-substituted organics such as trihalomethanes (THMs) and chlorinated phenols.
Additional in-plant sources of toxicity include concentrated recycle streams from filtration, sludge
dewatering, incineration, and wet air oxidation processes. These streams may contain shock
loadings of toxic compounds or conventional poliutants which may decrease the biàlogical
treatment efficiency of conventional or toxic pollutant removal.
2.2 FATE OF TOXICS AND TOXICITY IN POTWS
The fate of toxicants in POTWs is dependent on the nature of the toxic constituents and on
the treatment processes used. The overall potential pathways and environmental impacts
associated with toxics and toxicity are illustrated in Figure 2-2. The primary focus of toxics
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ColiICtIOfl Syslem
Eifittrat’Ofl
Indusuy
Hazard
WOr SV
Air
Ri i• s
Pass ThrouQh
I , ’
Grounøwtsi
Comama suon
FIGURE 2.2 POTENTIAL PAThWAYS AND ENViRONMENTAL IMPACTS
ASSOCIATED WITH TOXICS/TOXICITY
(REF. EPA 1986)
I c von
2 -6
ENGINEERING-SCIENCE
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management is the overall removal from the wastewater of toxic constituents and hence toxicity.
There is also a need to consider the fate of the toxicants and toxicity within the POTW. While many
toxicants are degraded to non-toxic constituents, others are only partially degraded, retaining
some toxicity, or re partitioned to the sludge or air (Table 2-1 ). This partitioning can result in the
toxic problem being transferred to a different medium.
2.2.1 Treatment
2.2.1.1 BIodegradation
Aerobic biological treatment of toxlcants has been used for industrial wastes for many
years. Under optimum conditions, it Is usually more effective than physical-chemical treatment
options for many toxlcants, and can result In their destruction (6). In this respect, it is preferable to
other removal processes which may transfer toxic compounds to other media such as the air or
sludge. Aerobic biodegradation of toxicants is most likely to occur as a fortuitous reaction in
biological reactors (e.g., activated sludge and trickling filter units) designed for the biodegradation
of non-toxic compounds. For the purpose of this booklet, biodegradation is defined as the
complete conversion of an organic compound to carbon dioxide and water. Optimum
biodegradation is achieved under steady-state loading conditions with a biomass that is
acclimated to the toxic constituents. Under these conditions 90 percent or greater removal can be
achieved for a majority of toxic organics (10). In POTWs a much lower performance level is
generally achieved due to non steady-state conditions which prevent the establishment of an
acclimated blomass (10).
2.2.1.2 TransformatIon
Transformation is the partial degradation of a toxicant which occurs during biological and
chemical treatment processes. Toxic organic compounds can be transformed Into compounds
which may exhibit toxicity different than the original compound. The transformed compound may
be more or less toxic than the origInal compound or it may be non-toxic. An example of the
biological transformation of a toxicant is the conversion of trichloroethene (TCE) to 1,2-
dichioroethene by an incomplete bIological pathway.
2.2.2 Volatilization
VolatHizatlon may occur in P01W units that are aerated (e.g., aerated grit chambers and
activated sludge tanks) or that have a large surface area (e.g., trickling filters and clariflers).
Volatile organic compounds, although partially treated by biodegradation, are also subject to
removal in both primary and secondary treatment processes by volatilization.
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TABLE 2-1
PREDOMINANT FATES OF TOXIC POLLUTANTS IN POTWS
Toxic ConstItuent Category
Example
ConstItuents Biodegradation
Fate
of Toxic_Constituents
Volatilization
Sedimentation
Sorption
Onto
Solids
Pass Through
Volatile Organics
Tr lchloroethene x
x
x
Semi-Volatile Base Neutral Organics
Dleth IphthaIates x
x
x
Semi-Volatile Acid Extractable Organics
2-chiorophenol x
x
x
Toxic Metals
Mercuiy
x
x
x
Non-Metal Inorganics
Cyanide
x
x
x
Conventional Pollutants
Ammonia x
x
x
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The main factors influencing volatilization are the concentration, physlcochemical
characteristics, and the rate of biodegradation of each compounds. The physicochemical
properties affecting volatility are water solubility and the equilibrium distribution between air and
water as measured by Henrys Law Con ar , (KH), which is viewed as the most important
indicator of volatility for specific compounds.
2.2.3 Sedimentation and Sorption on Solids
Sedimentation is the primary removal mechanism for metals and inorganics. Up to 50
percent of these toxic constituents can be removed by sedImentation (16). Elevated levels-of-the
toxic Inorganics may accumulate In the settled sludge since these compounds are neither volatile
nor readily biodegradable. Concentration of excessive levels of metals and other Inorganics may
cause operational problems in digestion processes and may restrict land disposal of sludge.
Additionally, sludge incinerators may require additional controls to prevent the release of toxIc
constituents to the air.
Sorption of organic compounds onto particulates and biomass us also a significant
removai mechanism for low volatility toxic organIc compounds (5). Compounds with a high affinity
for sorption include pesticides, phthalates and other low solubllity, low volatility organics. As with
sedimentation, sorptIon results in the concentration of toxic constituents in the sludge.
2.2.4 Pass-Through
Toxic constituents which are not treated through biodegradation or transformation,
volatilized, or subject to accumulation in settled sludge due to sedImentatIon and sorption will pass
through the P01W and be discharged with the effluent to the receiving water. These constituents
potentially impact aquatic life and/or human health depending on toxic constituent concentrations
and exposure pathways.
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SECTION 3
REMOVAL OF TOXICS AND TOXICITY IN POTWS
3.1 INTRODUCTION
This section presents a review of the toxicant removal capabilities of P01W unit
processes. Conventional wastewater treatment processes can partially or completely remove
many toxicants and can be a valuable tool for the management of effluent toxicity by POTWs.
Removal mechanisms include biodegradation, volatilization and incorporation into settled sludge
(sorption). It should be noted, however, that although volatilization and sorption may result in a
reduction in effluent toxicity, the removed toxicants are not destroyed and are transferred to the
atmosphere or the settled sludge.
3.2 REMOVAL CAPABILITIES IN P01W TREATMENT SYSTEMS
Although POTWs have only recently begun to systematically monitor toxicants in their
influent and effluent, several studies have been conducted by the EPA to determine the treatability
of toxic compounds in conventional wastewater treatment facilities (6, 11). EPA research Indicates
that a typical wastewater treatment process employing primary settling and biological treatment
can achieve a high degree of removal of certain toxicants from wastewater. A well-operated
wastewater treatment process train consisting of primary settling and biological treatment with an
acclimated biomass can achieve over 95 percent removal of volatile organic compounds, 98
percent removal of semI-volatile organic compounds, and from 20 to 90 percent removal of metals,
respectively (20). However, these removal levels may not be achieved at all PO1Ws since they
were achieved under steady state conditions with an acclimated blomass.
To assess the occurrence and fate of toxic pollutants in full-scale operating POTWs, EPA
studied 50 PO1Ws at 40 cities in 1978 and 1979. This study, known as the 40 City Study, provides
a baseline indication of the capabilities of POTWs to treat toxic metals and organics (6). The
majority of the 50 facilities studied employed primary sedimentation followed by activated sludge
biological treatment. However, a number of facilities employed activated sludge/tricklIng filter
combinatIons (7 facilities), trickling filters alone (7 facilities), rotating biological contactors (1
facility), pure oxygen activated sludge (2 facilities), or aerated lagoons (2 facilities) -(6).
Additionally, 9 facilities employed advanced wastewater treatment technologies such as
nitrificatlon. A summary of the volatile organic, semi-volatile organic, and metallic prlortty pollutant
compounds detected in at least 20 percent of the collected samples in that study is presented in
Tables 3-1 through 3-3. In general, the study found that activated sludge, trickling filter, rotating
biological contactor, and pure oxygen activated sludge processes were approximately equally
MAC/FA8OI/00004
3-1
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effective in removing toxic priority pollutants. The data presented in Tables 3-1 through 3-3 only
represents POTWs where the indicated compound was detected.
Eleven priority pollutant volatile organic compounds (VOCs) were co’ sistently detected In
POTW Influent samples (Table 3-1) at concentrations ranging from 1 to 49,000 ugh. Removal of
VOCs by the POTWs was generally consistent with that found by research studies. The median
removals were 85 percent or greater for a majority of the measured VOCs. Meth ,1ene chloride and
toluene were not as effectively removed by the POTWs as the other detected priority pollutant
VOCs. However, it Is also evident that elevated levels (> 1000 ug/l) of several VOCs passed
through to effluents from specific POTWs during the survey (Table 3-1), indIcating that site specific
removal efficiency may vary greatly from the median.
PrIority pollutant semi-volatile organic compounds that were consistently detected in the
POTW influent wastewater during the 40 City Study are presented in Table 3-2. Influent
concentrations of the detected semi-volatile organics were generally lower than those detected for
the VOCs (Table 3-2). Median influent concentrations were generally below 10 ug/l, although
maximum influent levels were much greater. Excellent removal was typically observed for phenol;
naphthalene and butylbenzylpthalate. BIs (2 ethylhex!y1)pthalate and dl-n-butylpthalate appeared
to be more resistant to degradation (Table 3-2) or other removal processes.
Heavy metals and cyanide were regularly detected in the POTW Influent wastewater (Table
3-3). Median removal efficIencies for metals ranged from 35 percent (nickel) to 97 percent (lead).
Maximum effluent concentrations reported In Table 3-3 IndIcate that pass through of metals and
cyanide did occur, potentially contributing to the toxicity of the POTW effluent.
No comparable data base describes whole effluent toxicity removal by PO1Ws. However,
a number of toxicity reductIon evaluatIons (TREs) have been conducted to date, with many
currently in progress. In a study of six Ohio PO1Ws there was a measurable reduction in toxicity In
four of the plants studied following treatment in the P01W (4). No whole effluent toxicity reductIon
was observed In the remaining two plants. A significant reductIon In toxicity was observed when
segregated wastestreams were treated In batch activated sludge reactors at the Buckman WWTP
in Jacksonville, Florida (3). AlternatIvely, a TRE conducted at the Patapsco WWTP In Baltimore,
Maryland Indicated substantial toxIcity pass-through even though the WWTP achieved consistent
conventional pollutant control (17).
3.3 TOXICS REMOVAL CAPABIUTY OF POTW UNIT PROCESSES
Toxics removal capabilities of IndIvidual P01W treatment processes are a function of the
toxic components and the physical/chemical or biological removal mechanisms occurring within
specific unit processes. The toxics removal capabilitIes of primary, secondary and advanced
treatment technologies are reviewed below. In order to determine typical removal capabilities of
various treatment technologies, several studies and the EPA Risk Reduction Engineering
Laboratory (RREL) treatability database were reviewed (6, 11, 1. 15). For each treatment
MAC/FASO1/00004
3-2
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TABLE 3-1
VOLATILE ORGANIC COMPOUNDS IN POTW(’)
INFLUENTS AND EFFLUENTS
Constituent
mu
uen& Concentration
(ua/fl
Median
Removal (%)
Effluent Con
cenirprion (un/fl
Median
Minimum
Maximum
Minimum
Maximum
Benzene
2
1
1.560
99 +
1
72
1 ,1,1-Tr lchiorethane
29
1
30.000
94
1
3.500
Chloroform
7
1
430
62
1
87
I ,2-trans-Dlchloroethene
2
1
200
99 +
1
17
Ethy lbenzene
8
1
730
99 +
1
49
Methytene Chloilde
38
1
49,000
56
1
62.000
Tetrachloroethylene
23
1
5,700
85
1
1.200
Toluene
27
1
13,000
40
1
1,100
Tr lchioroethylene
28
1
1.800
97
1
230
1.1 -Dichloroethane
--
1
24
--
--
--
1,1-Dichioroethylene
-
1
243
--
--
Note: (1) Data presented (or!constltuents present> 20% of the time.
Source: Reference (6).
MAC/FMOI/00000
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TABLE 3-2
SEMI-VOLATILE ORGANIC COMPOUNDS IN POTW(’)
INFLUENTS AND EFFLUENTS
Constituent
Inif
uent Concentration
luau)
Median
Removal (%)
Effluent Con
centration (ua/ii
Median
Minimum
Maximum
Minimum
Maximum
Phenol
7
1
1400
99
1
89
Pentach lorophenol
3
1
640
--
1
440
Naph thalene
3
1
150
99+
1
24(2)
Bis(2-ethyl hex p1)pthaIate
27
2
670
58
1
370
But 4 Benzyi Phthalate
3
2
560
99 +
1
34(2)
DI-N-But 1 Phthalate
4
1
140
51
1
97
12-Dlchlorobenzene
--
1
440
--
1
27(2)
Phenanthrene
—
1
93
--
1
32(2)
Note: (1) Data presented for constituents present > 20% of the time.
Note: (2) Present in effluent <20% of time.
Source: Reference (6).
MAC./FARO1 /flflflfl6
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TABLE 3-3
TOXIC METALS IN POTW(’)
INFLUENTS AND EFFLUENTS
Constituent
Infi
uent Concentration
lao/fl
Median
Removal (%)
Effluent Con
centration 4 Lll
Median
Minimum
Maximum
Minimum
Maximum
METALS
NIckel
54
22
9.250
35
7
67P
CadmIum
3
1
1800
93
2
82
Chromium
105
8
2.300
76
2
759
Lead
53
16
2.540
97
20
217
Mercury
0.517
0.200
40
86
0.200
1 200
SAver
8
2
320
95
1
30
Copper
132
7
2,300
82
3
255
Zinc
273
22
9,250
77
18
3.150
Cyanide
249
3
7.580
59
2
2.140
Note: (1) Data presented for constituents present > 20% of the time.
Source: Reference (6).
MAC/FA8OI/0000a
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technology, the references were evaluated to determine the removal range for various toxic
compound fractions (e.g.. volatile organic compounds, semi-volatile organic compounds, heavy
metals) and representative percent removal for each toxic compound fraction.
3.3.1 Removal During Primary Treatment
Primary treatment in POTWs is intended to remove settleable and floatable solids from the
wastewater prior to secondary treatment. Primary treatment provides a limited degree of
wastewater equalization which tends to reduce shock loading to secondary treatment operations.
To improve process efficiency, chemical addition and flocculation are sometimes used prior to
primary sedimentation.
A summary of toxic organic and toxic metal removal performance of primary
sedimentation data indicates a 46 percent representative removal of volatile organic compounds
(removal range = 0 to 87 percent) and a 46 percent representative removal of toxic metals and
cyanide (removal range = 14 to 90 percent) (6). Insufficient data exists to present removal
percentages for semi-volatile organic and pesticide compounds.
The primary toxics removal mechanisms occurring during typically employed
sedimentation processes are settling of Insoluble toxicants, sorption of toxicants onto suspended
solids, and volatilization. The degree of removal of soluble toxicants will depend on the compound
solubility, volatility, and tendency to sorb onto suspended organic and inorganic partldes.
Additionally, density, size and concentration of the suspended solids as well as the clarifier
hydraulic loading and surface area affect the removal of both soluble and insoluble toxics during
primary sedimentation. Shock hydraulic or solids loadings to primary clarifiers can oveiload the
process and result in reduced removals due to increased solids carry over. Process performance
can also be hindered by the presence of surfactants or oil and grease which decrease the rate of
volatilization and hinder settling.
3.3.2 Removal During Secondary Treatment
Secondary biological treatment technologies employed at PO1Ws utilize a viable bacterial
community to convert degradable influent constituents into biomass. For the purpose of this
booklet, only aerobic secondary treatment systems are discussed since they are most commonly
used in POTWs.
Two process configurations commonly used for secondary treatment are suspended
growth systems (activated sludge and aerobic lagoons) and attached growth systems (trickling
filters and rotating biological contactors). The actIvated sludge process is currently the most
widely used secondary treatment option. In this process, the wastewater contacts biomass in an
aeration tank supplied with sufficient dissolved oxygen to maintain aerobic conditions. Following
this treatment step, the biological solids are separated from the treated wastewater In a settling
tank and then returned to the aeration tank.
MAC/FA8OI/00004
3-6
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Trickling filters are commonly used secondary treatment options at small PO1Ws because
of their economic operation and relatively consistent performance. The trickling filter consists of a
fixed film medium (rock, wood or plastic) which acts as an attachment site for the biomass.
Wastewater applied to the packing at a controlled rate allows wastewater con ct .dith the attached
micro-organisms. Excess sludge sioughed from the medium is then separated from the treated
wastewater in a sedimentation tank following the trickling filter.
Reported toxics removal performances of activated sludge and trickling filter systems are
presented in Table 3-4. Both activated sludge systems and trickling filters can typically achieve 50
percent or greater removal of toxics for both organics and metals. --
Toxics removal In secondary treatment results primarily from the biodegradation or
transformation of volatile and semi-volatile organics and the adsorption of semi-volatile organics,
pestlcides/PCBs, and metals onto the biological floc. Volatilization Is also a significant removal
mechanism in aerated systems, resulting In the transfer of toxic constituents to the air. Sludge
age, hydraulic residence time, and the type and concentration of the toxic organics in the
wastewater affect organic biodegradation in activated sludge systems. inhibition of secondary
treatment systems by toxic metals and organics can be a significant problem and has been studied
extensively. Detailed information on process inhibition by toxic constituents is provided in EPA’s
Guidance Manual for Prevention of interference at POTWs (15).
The extent of toxlcs removal during secondary treatment Is largely dependent on the
biodegradability of the constituents. Non-biodegradable constituents such as metals, pesticides,
and PCBs tend to accumulate in the biological solids. While many semi-volatile organics are
biodegradable, others such as chlorinated phenols and phthaiates tend to accumulate in biological
solids since they require ideal reactor conditions for complete biodegradation.
3.3.3 Removal During Advanced Treatment
Advanced treatment processes are utilized when effluent criteria cannot be met by
secondary treatment alone. The most commonly used P01W advanced treatment processes are
coagulation/flocculation/sedimentation and filtration. Activated carbon adsorption has also been
occasionally used by POTWs when effluent criteria are especially stringent. Toxics removal data
for these processes by PO1Ws are limited, but all three have been used extensively by industrial
discharges for toxics temoval.
3.3.3.1 Coagulatlon/Floccuiatlon/Sed lmentatlon
Ferric chloride, aluminum sulfate, and various polymers are chemical coaguiants
commonly added to wastewater to promote additIonal removal of suspended solids and
phosphorus. The process consists of an initial mixing of the coagulant with the wastewater
followed by a slow mixing (flocculation) to Increase the size of the resulting tioc. Lime is often
Mi*C/FABO1 /00004
3-7
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TABLE 3-4
TOXIC REMOVAL PERFORMANCE
SECONDARY TREATMENT PROCESSES
Trickling Filter Activated Sludge
Toxic Representative Removal Representative Removal
Category Removal (%) Range (%) Removal (%) - Range
Volatile Organics
57
14-99
76
25->99
Semi-volatile Base Neutral Organics
65
25-98
71
11-99
Semi-volatile Acid Extractable Organlcs
46
12-98
78
17-> 99
Pesticides and PCBs
ID
ID
ID
ID
Toxic Metals and Cyanide
50
4-97
54
1-99
Note:
Sources:
ID = insufficient Data.
References (6, 11, 14, 1).
MAC/FA8O I/00004
3-8
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added with coagSarns to facilitate the precipitation of metal hydroxides which are removed during
the sedimentation process. Solids are then removed from the wastewater in a sedimentation tank.
Reported toxics removal performance of the coagulation/Ilocculatlon/sedimeritatlon
process Is summarized In Table 3.5. The data for Table 3-5 are based on coagulatlon/
flocculatIon/sedimentatIon treatment without prior treatment of the wastewater. Nevertheless, the
ability of the process to remove toxic constituents not readily removed by secondary treatment,
partlculady semi-volatile organics, pestickles, PCBs, and metals, is clearly shown. The toxic
constituents removed by coagulation/if occuiatlon/sedimentatlon accumulates in the sludge
produced by the process.
Coagulatlon/flocculation/sedimentatlon promotes the precipitation of dissolved metals
and the removal of colloidal size particles 1 which may contain sorbed toxic pollutants. Coagulant
type and dosage are crftlcal in ensuring good flocculation and solids removal. AdditIonally,
maintaining the proper flow rate to the sedimentation lank is critical for optimal removal of solids.
3.3.3.2 Fi)tration
Filtration removes residual suspended matter from the waslewater. It can be employed
directly after secondary treatment or following coagulation/flocculation/sedimentation. Reported
toxic removal during filtration is summarized In Table 3-5.
Filtration may remove toxic compounds sorbed onto suspended particles too light or small
to have settled out during previous sedimentation steps. The degree of removal of toxic
compounds sorbed onto particulates In a rapid sand filter Is dependent on a number of
mechanisms including particulate straining. Interception on sand grain surfaces, sedimentation In
void spaces formed by sand grains and attachment mechanisms that occur on a molecular level.
Filtration efficiency is not affected by toxic loading, but Is affected by high solids loadings
and by variations In hflaulic loadings. Both can reduce solids capture by the filter. While
filtration Is capable of removing a wide range of toxic constituents, the removal range Is highly
variable, since toxic constituent removal Is ultimately dependent on the removal of the non-toxic
solids on which toxic constituents are sorbed. Accordingly, filter backwash can contain high
concentrations of toxic compounds. Filter backwash should be reintroduced Into the treatment
plant Influent at a low rate to prevent shock loading of the system.
3.3.3 3 ActIvated Carbon Adsorption
Activated carbon removes contaminants in the wastewater through adsorption onto its
macro- and micro-pore sttuctures. Higher molecdar weight organic molecules such as PCBs are
preferentially adsorbed over lower molecular weIght compounds such as VOCs.
Activated carbon Is utilized in either the granular actIvated carbon (GAC) or powdered
activated carbon (PAC) forms. Wastewater treatment by GAC takes p lace in a flow through
MPCJFAso IJOXO4
3.9
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TABLE 3 5
TOXIC REMOVAL PERFORMANCE
OF COAGULATION/FLOCCULATION/SEDIMENTATION
AND FILTRATION
CoagulatIon/Flocculation/Sedimentation FiltraHon
Toxic Representative Removal Representative Removal
Category Removal (%) Range (%) Removal (%) Range
Volatile Organlcs
76
0-99
60
0->99
Semi-volatile Base Neutral Organics
85
27-99
61
230->99
Semi-volatile Acid Extractable Organics
66
21-99
56
22->99
Pesticides and PCBs
28
16-77
ID
ID
Toxic Metals and Cyanide
52
0-99
46
0->99
ID - Insufficient Data.
Sources: References (6, 11, 14, 1).
MAC/FA8O1/0 0004
3-10
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column or bed. Treatment by PAC is typically achieved by adding the activated carbon directly to
the activated sludge aeration basin. The exhausted carbon is either regenerated or disposed.
Reported removal percentages of toxic organics by activated carbon adsorption are
summarized in Table 3-6. Granular and powdered activated carbon, when employed under Ideal
conditions, may remove significant amounts of most toxics. However, performance may be
hindered In some instances by the effects of competitive adsorption, which occurs when mixtures
of organic compounds compete for carbon adsorption sites.
Activated carbon removes toxics either by adsorption onto the carbon or, to a lesser
degree, by filtration of solids. Most dissolved organics can be adsorbed by carbon. Thus,
activated carbon can remove organics that are not completely removed by biological treatment.
Activated carbon is also capable of removing some Inorganic toxics including cyanide, chromium,
and mercury. However, most metal species are not effectively adsorbed by activated carbon.
Granular activated carbon systems are sensitive to clogging due to high loadings of solids
or fouling due to biological growth. Where high concentrations of non-toxic organics are present,
the carbon can be rapidly saturated, requiring frequent carbon regeneration to prevent
breakthrough of toxic organic constituents.
3.4 SUMMARY
PO1Ws employing primary settling and biological treatment can achieve varying degrees
of toxicant removal. Major removal mechanisms in typical PO1Ws Include sedimentation of toxics
sorbed onto particulate matter, volatilization, and treatment through biodegradation or
transformation. Advanced treatment technologies Induding coagulation/flocculatIon/sediment-
ation, filtration, and activated carbon adsorption can also enhance overall P01W toxic compounds
removal.
MAC/FA8OI/00004
3-11
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TABLE 3-6
TOXIC REMOVAL PERFORMANCE
OF GRANULAR ACTIVATED AND POWDERED ACTIVATED CARBON
GAC PAC
Toxic Representative Removal Representative Removal
Category Removal (%) Range (%) Removal (%) Range
Volatile Organlcs
76
0->99
73
23->99
Semi-volatile Base Neutral Organics
71
0->99
63
20->99
Semi-volatile Acid Extractable Organics
78
10->99
40
2-99
Pesticides and PCBs
ID
ID
78
23->99
Toxic Metals and Cyanide
46
0->99
63
60-80
Sources: References (6, 11, 14, 1).
MACfFA SOI/00004
3-12
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SECTION 4
ENHANCED REMOVAL OF TOXICS AND TOXICITY
The majority of POIWs are designed for the control of conventional wastewater pollutants
such as biochemical oxygen demand (BOD) and total suspended solids (TSS). Nevertheless,
typical P01W unit processes have been observed to provide varying degrees of toxicant control.
This section presents a review of the methods available to enhance toxic compound removal in a
P01W. A combination of controls Including influent wastewater equalIzatIon/diversion and
biological process optImization (e.g. adjustment of operating parameters, chemical addition,
nutrient addition, etc.) can be used to enhance the intrinsic toxicant removal capabilities of P01W
unit processes. Moreover, add-on treatment technologies can be utilized to remove toxicity or
specific groups of toxicants. Table 4.1 presents a summary of the primary methods of enhancing
toxicant removal.
4.1 CORRECTION OF PERFORMANCE UMITING PROBLEMS
P01W performance problems can result from both desIgn limitations and from institutional
problems (whether administrative, operational, or maintenance related). EPA has developed a
comprehensive program called the Composite CorrectIon Program (CCP) which utilizes a
systematic methodology to identify and eliminate performance limiting problems at PO1Ws for
conventional pollutants (9). Although this methodology Is dIrected at operational problems
associated with the control of conventional pollutants, it may also be effective at improving the
treatment of toxicants in inefficiently operated POTWs. By identifying and correcting problems
related to conventional pollutant removal, an overall increase in treatment efficiency for
conventional as well as toxic pollutants is likely to occur.
4.2 PROCESS OPTIMIZATION
The most economic method for enhancing the removal of toxicants from P01W
wastewater Is the opfimization of existIng unit processes. On-line controls or treatment additives
(e.g., nutrients, coagulants, adsorbents, etc.) are most often used to optimize the toxicant removal
efficiency of existIng unit processes.
4.2.1. On-Une Monitoring With Diversion Control
On-line monitoring for toxic metals coupled with wastewater diversion is currently
practiced by a few PO1Ws. The pH and conductivity of the Influent wastewater is measured and
recorded continuously In the Influent. When the pH drops or conductivity rises drastically, possibly
indicating an Increased heavy metal level, the influent flow Is diverted to a holding basin until the
MAC/FA8 O1/ 00004
4 -1
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TABLE 4.1
METHODS OF ENHANCING TOXIC COMPOUND/TOXICITY REMOVAL IN P01W EFFLUENT
Method Description Advantages Disadvantages
1) On-Une Monitoring
with Diversion
Control.
Divert influent wastewater to a
holding basin when monitors
Indicate abrupt changes in pH,
specific conductMty. TOC. etc.
• Protects biological unit
processes from shock loadings
ot toxics.
Monitoring
equipment and
holding basin add
capital and O8M
costs.
2) Biological Process
Control
Operate activated sludge systems
at Increased sludge age and solids
concentration.
• System is less subject to toxic
inhibition and is more likely to
increase toxic compound
biodegradation efficiency
• Siudge settling
characteristics
degrade at a sludge
age In excess of 15
days.
3) Modification of
Biological Reactor
Configuration
a) Completely
Mixed Activated
Sludge (CMAS)
Operate activated sludge system in
the completely mixed reactor
configuration.
Dilution of Influent wastewater
may enhance toxics removal
and helps dampen shock loads.
Reactor contents more easily
monitored and controlled due to
homogeneity.
• Many existing
POTWs have plug
flow reactors
Expensive to convert
to CMAS.
• Less desireable
sludge settling
characteristics than
with tapered air
activated sludge
systems.
MAC/FABO1/00008
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TABLE 4.1, CONTINUED
Method Descilption Advantages Disadvantages
b) Step Aeration
Activated
Sludge (SMS)
Influent wastewater is introduced at
several points along the length of a
plug flow reactor.
• Minimizes the maximum
concentration of toxics in the
reactor.
• Can convert tapered air
activated siudge system to this
configuration without major
construction.
• Less desireable
sludge settling
characteristics than
with tapered air
activated sludge
systems.
4) Treatment Process
Additives
a) Nutrients
Phosphorous, nitrogen, or
micronutrient addition to biological
systems.
• May increase treatment
efficiency by providing required
limiting nutrients
• Problematic when
added In excess (e g.
many POTWs have P
effluent limitations)
b) pH adjustment
Adjust wastewater pH to
appropriate level with lime, caustic
or acid.
• Ume or caustic addition
enhance metals precipitation.
• pH adjustment may be required
to facilitate biological treatment.
• Chemical feed
equipment could be
costly.
MAC/FA8O1/00008
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TABLE 4.1, CONTINUED
Method Description Advantages Disadvantages
c) Coagulants
Addition
Add polymers or inorganic
coagulants to Improve toxic metals
removal during primary
sedImentation. Could also use
coagulants to enhance settling of
biological solids.
• Enhancement of toxic metals
removal during primary
sedimentation may protect
biological treatment unit
processes from upsets.
Can be used to enhance
settleability of secondary sludge
from systems operated at high
MCRTs.
Could increase the
toxicity of return
activated sludge
when used In
secondary settlers
d) Powdered
Activated
Carbon (PAC)
Addition
Add PAC to biological aeration
basin.
• Provides protection against
shock loads of toxic organic
compounds.
Improves the removal of poorly
degraded and nondegradable
organic compounds.
• Enhances sludge dewaterablity.
PAC is costly, and is
not easily
regenerated.
May increase toxic
loading to sludge If
toxics laden PAC is
wasted with
biological solids.
5) Disinfection Process
Optimization /
Alternatives
a) Breakpoint
Chlorination
Process
Optimization
Conduct chlorination at lower
chlorine dose. pH. temperature
and/or contact time when possible.
Reduce formation of THMs
Only applicable
when chlorinaton is
significant
contributor to
effluent toxicity.
IIAC’JFAPJII ft
-------
TABLE 4.1, CONTINUED
Method Description Advantages Disadvantages
b) Alternate Disinfect by UV oxidation, Ozone, or Reduce the formation of THMs UV oxidation and
Disinfection chloride dioxide application, and other chlorinated organics Ozone do not
Methods provide a chlorine
Chlorine dioxide creates a residual.
chlorine residual.
Ozone is associated
with the formation of
toxic compounds
which contribute to
effluent toxicity.
6) Influent flow Influent passes through an online • Protects unit processes Additional cost for
Equalization storage tank to provide equalization (especially biological treatment basin installation and
of wastewater quality and quantity. systems) from shock loadings of maintenance.
toxic compounds.
Prevents hydraulic overloading
of system.
7) Effluent Equalization Effluent passes through an on4lne May lower the maximum effluent Additional cost for
storage basin to provide concentrations of toxic basin installation and
equalization of effluent quality, constituents below the toxicity maintenance.
threshold of the receiving water.
MAC/FA8O1/00008
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TABLE 4.1, CONTINUED
Method Description Advantages Disadvantages
8) Physical/Chemical
Treatment
a) Coagulation / Rapid mixing of polymers or Helps remove toxics sorbed Sludge disposal
Flocculation inorganic coagulants followed by onto colloidal particles (PCBs, required.
slow mixed flocculation and metals, pesticides).
quiescent settling. • Additional capital
and O&M cost
b) Filtration Deep-bed filtratIon with single or - Helps remove particulates not Filter backwash may
multimedIa filter, removed during primary or be toxic.
socondary clarification
Partlculates may contain sorbed Additional capital
toxics. and O&M cost.
c) Granular Wastewater is passed through - Adsorbs many toxic organic Very expensive
Activated columns packed with GAC. compounds that could pass capital and 0&M
Carbon (GAC) through traditional P01W unit costs.
processes.
IAh( IcAnn1 lrv-vyig
-------
pH and conductivity In the Influent return to normal. At that time, the diverted wastewater can be
bled back to the influent wastestream at a controlled rate so that metal concentrations are diluted.
This reduces waste load fluctuations and provides a more stable environment for biological
treatment.
This technique has also been used by industries to control shock loads of organic wastes.
In this case, on-line total organic carbon ( OC) monitors are used to Initiate wastewater diversion if
the organic loading becomes too high. Diverted wastewater Is bled back into the system a a rate
which allows dilutIon and acclimation of the biomass.
4.2.2 Biological Process Control
Biological process control is most applicable to activated sludge systems, although some
modifications to fixed film processes (e.g., trickling filters) are also applicable to toxics removal
enhancement. The most significant activated sludge operational control parameters are mean cell
residence ttme (MCRT) and mixed liquor suspended solids (MLSS). Many engineers and
operators also utilize the food to microorganism ratio (F/M) as a system control parameter. The
F/M is defined as the mass of food used over a finite amount of time divided by the mass of
organisms contained in the reactor. By varying these inter-related process parameters the
biomass can be acclimated and be made more resistant to toxic slug loadings as well as amenable
to the biodegradation of toxic organics which are otherwise resãstant to biodegradation.
The MCRT (sludge age) is defined as the ratio of the mass of viable bacteria in a reactor to
the mass of viable bacteria lost per unit time. The MCRT Is inversely proportional to the bacterial
growth rate and food utilization rate. Increasing the MCRT results in an environment where
organisms are in great competitIon for available food sources. As a result bacterial metabolic
control mechanisms will be more likely to initiate the production of enzymes needed to break down
food sources. This is analogous to operating at a low F/M. Activated sludge systems operated at
a high MCRT are less subject to inhibition by toxicants and are more effective at acclimatIng to and
degrading toxic organic compounds. Many industrial activated sludge systems are operated at
long MCRTs (in excess of 15 days) in order to accommodate high levels of toxicants present in
their wastewater. A disadvantage to operating at a longer sludge age is a deterioration of sludge
seWing characteristics for MCRTs In excess of approximately 15 days. As a result, many of these
systems add coagulants prior to secondary clarification to Improve settling.
In addition to promoting an acclimated biomass, increasing the MCRT typically results In
an increase in the MLSS concentration. Systems operated at a high MLSS are less affected by
shock loadings of toxics since the additional biomass may offset some of the toxic effects.
For a fixed film process, the biomass characteristics cannot be as easily controlled.
Nevertheless, varying the amount and point of recirculation in a trIcklIng filter can increase the
removal of Industrial pollutants. Recirculating secondary clarifier effluent can achieve the greatest
dilution effect, which may be desirable for high-strength organic waste or toxics. Additionally,
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recircutation of unclarified effluent may be beneficial since it would increase the biomass available
for degradation of the toxic substances.
4.2.3 ModifIcation of Biological Reactor Coniguretlon
The reactor configuration of an activated sludge system can have a significant effect on
the systems susceptibility to treatment interference by toxicants and its ability to degrade them.
Activated sludge systems generally Include either a completely mixed or plug flow aeration basin.
Completely mixed aeration basins are most often employed in industrial wastewater treatment
systems. Influent wastewater is Instantaneously diluted within the entire volume of the aeration
basin by intense mixing. This type of system is most suitable to treating vartable strength
wastewater with elevated toxics concentrations because the dilution effect helps protect the
biomass from contacting high concentrations of toxicants. A disadvantage of the completely
mixed activated sludge system is its tendency to produce a sludge which settles more slowly than
sludge from treatment process which employes a concentration gradient across the system, such
as tapered air activated sludge (discussed below).
Many POTWs employ tapered aeration activated sludge (T AS) which utilizes a plug flow
reactor with all influent wastewater entering the head of the basin. Influent wastewater passes
through the basin as a slug, with a substrate concentration gradient forming across the reactor.
This type of system is particularly susceptible to upset since the biomass at the influent end of the
basin contacts the maximum concentration of toxic substances. An improvement in toxics
removal capacity and a decrease in process upsets may be achieved by converting the TAAS
system to a step aeration activated sludge system (SAAS). in this system influent wastewater Is
split into several portions and introduced into the plug flow reactor at several points. This allows a
more even distribution of the toxicants and minimizes the maximum concentration that will come in
contact with the biomass. Again, this system produces a sludge which settles more slowly than
sludge from a TMS system due to the lack of a concentration gradient In the SAAS system.
4.2.4 ChemIcal Addition
Addition of chemicals or nutrients to various unit processes have often Improved the
removal of toxicants in Industrial wastewater treatment facilities. The following are examples of
chemicals or additives that can improve industrial wastestream treatabiiity or biological process
stability:
nutrients;
lime or caustic;
organic polymers;
inorganic coagulants;
powdered activated carbon.
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4.2.4.1 NutrIents
Phosphorus and, to a lesser extent, sulfur and nitrogen addition, occasionally improve
biological treatment and sludge settleability of Industrial wastewaters with high crb ..iaceous
content. In general, better treatment and settleablifty are attributed to correcting a nutrient
deficient condition resulting from a high Industrial/domestic wastewater ratio.
4.2.4.2 pH Adjustment
- Ume and caustic addition prior to primary treatment raises the pH and improves
precipitation of some heavy metals in primary clariflers. While optimum pH ranges exist for
precipitation of metals from solution, actual removals are affected by many factors and are
therefore system dependent. Ume can also be used for pH adjustment of an acidic wastewater
prior to aeration to provide a more favorable environment for biodegradation. Conversely, acid
neutralization can be used for highly alkaline wastewaters.
4.2.4.3 Coagulants
Polymers and inorganic coagulants such as alum and ten-ic chloride can be introduced to
P01W wastestreams to help remove Insoluble pollutants. Added prior to primary treatment, the
coagulants Improve primary sedimentation and may Increase the removal of oxlcants before they
reach the aeration basins or secondary treatment units. Added after the aeration basins, the
coagulant aids can assist In controlling bulking sludge and reducing effluent suspended solids. Jar
testing Is an important part of any chemical addition program because it can determine optimum
dosages. It should also be noted that chemical coagulants can affect the characteristics of the
sludge and thus change ultimate disposal methods. If added after secondary treatment, they
could Increase the toxicity of the recycle sludge. Therefore, their use should be carefully evaluated
and contamination potentIal should be investigated.
4.2.4.4 Powdered Activated Carbon
Powdered activated carbon (PAC) can be added to the aeration basin of an activated
sludge system to provide protection against shock loading of toxic organic compounds or
enhanced removal of baseline influent levels of toxic organics. Studies have indicated that the
addition of PAC can significantly Improve the removal of some poorly degradable and non-
degradable organic compounds (21). AdditIonally, PAC provides a dense Ii oc nucleation surface
which improves sludge settleability and sludge dewatering characteristics.
4.2.5 DisinfectIon Process OptImIzatIon/Alternatives
Disinfection of most P01W effluents is normally accomplished by the breakpoint
chlorination method. This technique leads to the formation of trihalomethane compounds (THMs)
which contribute to effluent toxicity. The formation of ThMs can be reduced by adjusting the
chlorination procedure or through the use of alternative disInfection methods.
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In general, THM formation can be reduced by decreasing chlorine dosage, pH, reaction
time and/or reaction temperature. Additionally, upstream enhancement of organic carbon removal
will also help minimize the formation of THMs.
Alternative disinfection methods employing ultraviolet (UV) oxidation, ozone, or chlorine
dioxide may also be utilized to minimize the production of halogenated organics. These methods
are all effective for dIsinfection of P01W effluent. However, UV oxidation and ozone do not leave a
chlorine residual which is required in many NPDES discharge permits. Additionally, ozone has
been associated with the production of carbonyi compounds (e.g. Formaldehyde) which may also
contribute to effluent toxIcity (2). — -
4.3 ADDITIONAL TREATMENT
The most permanent type of toxics control effort that can be undertaken is a physical
addition to, or modification of. the P01W. Possible modification to PO1Ws could include flow
equalization prior to treatment, effluent equalization, or addition of physical/chemical treatment
unit processes.
4.3.1 Influent Flow Equalization
Equalization of Influent wastewater helps to dampen slug or diurnal loads of high-strength
contaminants entering a treatment plant. Slug loads of high strength wastewater can cause
breakthrough of toxicants in both suspended and fixed film biological treatment systems.
Slug loadings of toxicants can cause breakthrough if the biomass is not acclimated to the
toxic compounds. Shock loadings of non-toxic compounds can cause toxics breakthrough by
overloading the biomass and causing a general loss of treatment efficiency for all compounds,
Including any toxics that may be present.
4.3.2 Effluent EqualIzatIon
Equalization of treated wastewater prior to discharge can be utilized to dampen
fluctuations In effluent quality. Fluctuations In effluent toxlcant levels can occur because of diurnal
variations or slug loadings of toxicants to the POTW. Additionally, in biological treatment systems,
single compound effluent varlablltty can be caused by fluctuations In bacterial populations or as a
result of microbial control mechanisms. Effluent equalization may work to reduce toxicant
discharge levels below their receMng water toxicity threshold limit.
4.3.3 PhysIcal/Chemical Treatment
For PO1Ws with only primary and secondary treatment, additional removal of toxics can
be achieved by adding advanced wastewater treatment process such as coagulation/flocculation
and sedimentation, filtration, or granular activated carbon adsorption. Each process, described
previously, can provide enhanced removal of certain toxlcants.
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4.4 SUMMARY
Several toxlcant removal enhancement techniques are available for POTWs. In general.
these techniques stress process optimization through modification of treatment system or
disinfection process procedures, augmentation of existing treatment processes with chemical
additives, and modification of the biological reactor configuration. Employment of alternate
disinfection techniques such as UV oxidation and ozonatlon may reduce the formation of THMs
and other chlorinated organic compounds. FinalIi, advanced wastewater treatment processes
such as coagulatIon/flocculatIon/sedimentation, filtration, and carbon adsorption may be effective
in providing enhanced toxicant treatment. - -
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SECTION 5
SOURCE CONTROL OF TOXICS AND TOXICITY
5.1 INTRODUCTION
Source control of toxics can be an effective method of reducing P01W effluent toxicity.
PO1Ws with a large number and variety of indirect dlschargers (Industrial, RCRA or CERCLA
users) or a limited pretreatment data base generally need to conduct monitoring to locate potential
toxic sources. EPA has developed a procedure for monitoring and characterizing toxic sewer
dischargers called Toxicity Source EvaIuatlon which Is described in the Municloal Toxicity
Reduction Evaluation (TRE Protocol (17). The data gathered from implementing this procedure
can be used to evaluate options for pretreatment control of toxics/toxicity. In situations where
existing pretreatment regulations (general, specific or categorical) are insufficient for the P01W to
achieve compliance with its toxics/toxlcity limitations, the municipality can develop local limits for
sewer users (14).
5.2 TOXICITY SOURCE EVALUATION - TiER I
Using the data gathered In a pretreatment program review and P01W effluent toxicity
identification evaluation tests, Indirect dlschargers whose discharge potentially contains refractory
toxicants can be Identified and selected for Tier I evaluation. Tier I testing involves samplIng the
selected dischargers and analyzing these samples for toxics and/or toxicity (16). Chemical-
specific analysis for toxics may provide useful Information when the number of indirect dlschargers
is small enough to allow comprehensive sampling and analysis. In situations where the number of
indirect dlschar9ers Is large, however, It Is difficult to develop sufficient data to achieve chemical-
specific identification of the toxicants. In this case, the Identification of toxic sources can be
accomplished by measuring wastewater toxicity at selected locations in the sewer collection
system or by testing wastewater toxicity at the points of indirect discharge.
The data base developed from the Tier I evaluation provides Information on the potential
sources of toxics and toxicity entering sewer collection system. This Information may be sufficient
to Identify the major toxic wastewater contributors, so that the evaluation may proceed to the
selection of options for controlling the toxlcs/toxlcity. If the informatIon Is not adequate to Identify
the toxic dlschargers, a Tier II - Toxicity Source Evaluation can be Implemented.
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5.3 TOXICITY SOURCE EVALUATION - TIER ii
A Tier II evaluation gathers additional information on the Indirect dischargers to the P01W
to confirm the suspected sources of toxlcs/toxirity entified In the Tier I evaluation. Based on the
Tier I data, indirect potentially toxic dischargers are Identified and their wastewaters are sampled
and analyzed using the Refractory Toxicity Assessment (RTA) procedure (17). The RTA estimates
the influent toxicity that would be expected to pass through the POTW (I.e. refractory toxicity).
The results of the Tier ii testing rank indirect discharges in terms of their potential to
contribute Inhibitory material or refractory toxicity to the P01W. These data aid In the identification
of the major toxic dischargers and can be utilized In the development of local pretreatment limits.
5.4 DEVELOPMENT OF LOCAL UMITS
The P01W can develop local limits to control the pass-through of toxics and toxicity, and
the treatment interferences that are caused by indirect discharges. As part of the Initial process,
the P01W should identity the issues of concern related to achieving compliance with federal, state
or regional requirements, including water quality protection, sludge quality protection, treatment
operations safeguards, worker health and safety, or air quality protection. The EPA Guidance
Manual on the Development and Imp!ementation of Local Discharge Umitations Under the
Pretreatment Program (14) describes several technical approaches to developing local limits.
Once the local limits have been developed, several planning Issues regarding their
Implementation must be addressed. These Issues Include the selection of an effectIve mechanism
for Imposing local limits (permit, ordinance, order, etc.), public participation, on-going compliance
monitoring, and provisions for recovery of costs associated with local limits development.
5.5 SUMMARY
Source control of toxlcants and toxicity Is one of the most desirable methods of toxics
management since It promotes waste minimization and is typically more economical than the use
of add-on technologies. The tiered approach of toxicity source Identification in conjunction with
the enforcement of categorical pretreatment standards and the Implementation of local
pretreatment standards are effective, systematic methods of source control.
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SECTION 6
SUMMARY
Successful management of toxicants and toxicity requires an integrated approach
employing strategies such as source control, categorical and local pretreatment regulations,
optimization of existing P01W unit operations, and utilization of add-oi treatment technologies.
Because each toxicant displays a different set of characteristics, a single strategy will generally not
solve all of the toxicity problems -at every P01W. This booklet reviewed several treatment
technologies which may be used In treating toxicants at POTWs. Although the treatment of
concentrated Industrial wastes has been practiced for many years, experience with the removal of
low concentration of toxicants at POIWs is still very limited.
The material presented in this booklet is based on sound engineering principles but limited
research and field experience. In the next few years many POTWs will further develop and test
many Ideas described here at full scale plants. This booklet will be followed by reports on full and
pilot scale demonstration projects, technology transfer manuals on new and innovative treatment
technologies, and protocols which can be used to evaluate the extent to which existing treatment
facilities can be expected to remove toxic pollutants.
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APPENDIX A
REFERENCES
1. Dostal, K.A., USEPA. Treatablllty Data Base, USEPA Risk Reduction Engineering
Laboratory, Cincinnati, OH (September, 1989).
2. Glaze, W. H., Koga, M., and Dr. Lamcilla, Ozonation Byproducts 2. “improvement of an
Aqueous-Phase Derivatization Method for the Detection of Formaldehyde and Other
Carbonyl Compounds Formed by the Ozonatlon of Drinking Water”, Environmental
Science & Technoloav , Vol. 23, No. 7, pps 838-847, 1989.
3. Logue, C. L; Koopman, B.; Brown, G. K.; and G. Bitton, “Toxicity Screening in a Large,
Municipal Wastewater System”, Journal of the Water PollutIon Control Federation , Vol. 61,
No. 5, pp. 632-640, 1989.
4. Neiheisel, 1. W., W. B. Homing. II, B. M. Austem, D. F. Bishop, T. T. Reed, and J. F.
Esteurk, “Toxicity Reduction at Municipal Wastewater Treatment Plants In Ohio”, Journal
Water Pr,Ilutlon Control Federation , Vol 60, No. 1, pp. 57-67, 1988.
5. Petrasek, A. C., I. Kugelman, B. M. Austem, T. A. Pressly, L A. Winslow, and R. H. Wise,
“Fate of Toxic Organic Compounds in Wastewater Treatment Plants”, Journal Water
Pollution Control Federation , Vol. 55, No. 10. pp. 1286-1296, 1983.
6. USEPA, Fate of Priority Pollutants In Publicly Owned Treatment Works, EPA 440/1-82/303,
PB-83, 122788, Effluent Guidelines DMsion, Washington, DC, September 1982.
7. USEPA, Treatability Manual, EPA-600/2-82-00i, Office of Research and Development,
Washington, DC, August 1982.
8. USEPA, Methods for Organic Chemical Analysis of Municipal and Industrial Wastewater,
EPA 600/4-82-057, Environmental Monitoring and Support Laboratory, Cincinnati, OH,
July 1982.
9. USEPA, Handbook: Improving P01W Performance Using the Composite Correction
Program Approach, EPA-625/6-84-008, Center for Environmental Research Information,
Cincinnati, OH, October 1984.
10. USEPA, Organic Chemical Fate Prediction In ActIvated Sludge Treatment Processes, EPA
600/2-85/102, PB85-247674, Water Engineering Research Laboratory, Cincinnati, OH,
August 1985.
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11. USEPA, Report to Congress on the Discharge of Hazardous Wastes to Publicly Owned
Treatment Works, EPA 530-SW-86-004, PB-86-1 84017, Office of Water Regulations and
Standards, Washington, DC, February 1987.
12. USEPA, Test Methods For Evaluating Solid Waste, SW-846, Office of Solid Waste and
Emergency Response, Washington, DC, November 1986.
13. USEPA, Permrt Writer’s Guide to Water Quality-Based Permitting for Toxic Pollutants, EPA
440/4-87-005, Office of Water, Washington, DC, July 1987.
14. USEPA, Guidance Manual on the Development and Implementation of Local Discharge
Umitatlons Under the Pretreatment Program, Office of Water Enforcement and Permits,
Washington. DC, December 1987.
15. USEPA, Guidance Manual For Preventing Interference at PQTWs, Permits DMsion EN-36,
Washington, DC, September 1987.
16. USEPA, Methods for Aquatic Toxicity Identification Evaluations: Phase 1 ToxIcity
Characterization Procedures, EPA/600/3-88/034, Environmental Research Laboratory,
Duluth, MN, September 1988.
17. USEPA, Toxicity Reduction Evaluation Protocol for Municipal Wastewater Treatment
Plants, EPA/600/2-88/062, Risk Reduction Engineering Laboratory, Cincinnati, OH, April
1989.
18. USEPA, Generalized Methodology for Conducting industrial Toxicity Reduction
Evaluations (I ’REs), EPA/600/2-88/70, Risk Reduction Engineering Laboratory, Cincinnati,
OH, March 1989.
19. USEPA, Overview of Selected EPA Regulations and Guidance Affecting P01W
Management, Office of Water, Washington, DC, September 1989.
20. Proceedings of the International Conference on Innovative Biological Treatment of Toxic
Wastewaters, Arlington, VA, June 1986.
21. Weber, W. J., and B. E. Jones, Toxic Substance Removal in Actrvated Sludge and PAC
Treatment Systems, EPA/600/52-96/045, EPA Water Engineering Research Laboratory.
Cincinnati, OH, June, 1986.
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APPENDIX B
LIST OF ABBREVIATIONS AND ACRONYMS
SOD Biochemical Oxygen Demand
CCP Composite Correction Progrdm
CERCLA Comprehensive Environmental Response, Compensation, and Liability Act
CMAS Completely Mixed Activated Sludge
CWA Clean Water Act
EPA Environmental Protection Agency
F/M Food to Microorganism Ratio
IWS Industrial Waste Survey
LEL Lower Explosive Limit
MCRT Mean Cell Residence Time
MLSS Milligrams Per Liter Suspended Solids
NPDES National Pollutant Discharge Elimination System
0&M Operations and Maintenance
Phosphorous
PAC Powdered Activated Carbon
PCB Polychlonnated Biphenyl
P01W Pubflcly Owned Treatment Works
PSES Pretreatment Standards For ExistIng Sources
RCRA Resource Conservation and Recovery Act
RREL Risk Reduction Engineering Laboratory
RTA Refractory Toxicity Assessment
SAAS Step Aeration Activated Sludge
TAAS Tapered Aeration Activated Sludge
THM Thha lomethane
TOC Total Organic Carbon
TRE Toxicity Reduction Evaluation
TSDF Treatment, Storage or Disposal Facility
TSS Total Suspended Solids
UV Ultra Violet
VOC Volatile Organic Compound
WWTP Wastewater Treatment Plant
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