-------
Table 4-25. Classes of Organic Compounds Adsorbed on
Carbon (5)
Organic Chemical
Class
Examples of Chemical Class
Aromatic hydrocarbons Benzene, toluene, xylene
Polynudear aromattos Naphthalene, anthracenes, biphenyls
Chlorinated aromatics Chlorobenzene, polychlorinated
biphenyls, aldrin, endrin, toxaphene,
DDT
Phenol, cresol, resorcenol, polyphenyls
Trichlorophenol, pentachlorophenol
Gasoline, kerosene
Phenolics
Chlorinated phenolics
High molecular weight
aliphatic and branch-
chain hydrocarbons8
Chlorinated aliphatic
hydrocarbons
1,1,1 -Trichloroethane,
trichloroethylene, carbon tetrachloride,
perchloroethylene
Tar acids, benzoic acid
High molecular weight
aliphatic acids and
aromatic adds8
High molecular weight Aniline, toluene, diamine
aliphatic amines and
aromatic amines"
High molecular weight Hydroquinone, polyethylene glycol
ketones, esters, ethers,
and alcohols"
Surfactants
Soluble organic dyes
Alkyl benzene sulfonates
Methylene blue, indigo carmine
* High molecular weight includes compounds in the range of 4 to 20
carbon atoms.
basis. In addition to optimizing equipment selection and
chemical requirements, the pilot tests can be used to
identify potential operating problems. Examples include
scale buildup, sludge bulking, and postprecipitates. In
these cases, corrective action can be taken before full-
scale operations.
Field analysis kits are commonly used to analyze
treated samples for quick results to guide the tests;
however, these data are typically supported by labora-
tory analyses using EPA-approved methods. The labo-
ratory results serve as the basis for full-scale equipment
design and selection.
4.4.1.3 Vendor Treatability Tests
Vendors commonly agree to perform treatability tests
with their equipment at the project site or in their labo-
ratories. By sending samples of ground water or
leachate to multiple equipment vendors for treatability
tests, the best vendor of a selected technology can be
chosen. The advantages of proprietary chemicals and
design show up in the test results. Vendors may be
subcontracted to perform the treatability tests, or they
can be requested to test their products at their own
expense as a prequalification for bidding. Duplicate
samples are usually submitted to an unbiased labora-
tory for a confirming analysis at the owner's expense.
4.4.1.4 independent Treatability Tests
Many qualified consultants and laboratories can perform
independent treatability tests under contract. In these
circumstances, there is less bias toward process selec-
tion of a specific equipment design or proprietary tech-
nology. Combination processes can be incorporated into
treatment trains that result in improved contaminant re-
moval over single processes. Although independent
treatability testing does not benefit from the advantages
of proprietary processes and chemical compounds, the
results are unbiased. The technology recommendations
are based on performance, economics, reliability, and
true client needs.
4.4.2 Treatability Testing Strategies
4.4.2.1 Technology Screening
The objectives of the initial technology screening are to:
• Verify the suitability and effectiveness of candidate
treatment technologies in meeting treatment objec-
tives.
• Identify the treatment process steps and the order in
which these steps are performed.
• Obtain treatment process data (e.g., chemicals
needed, dosages, reaction times, separation rates)
and preliminary cost information.
The first step is to develop a test plan. A testing plan may
be developed to present a detailed description of the
processes to be tested and to show how the tests will
be conducted. Because the tests are only valid if the
samples are representative, flow and concentration data
must be collected over as long a period as possible. The
testing plan should contain specific information on:
• A sampling strategy that addresses variation with
time.
• The numbers and types of experiments proposed.
• The volume of ground water or leachate required for
each test.
• A list of parameters that will be chosen to optimize
operation of the treatment arrangement.
• The sampling and analytical requirements for each
test series.
• A basis for selecting the numbers and types of
experiments.
Health and safety plans and quality assurance project
plans may also need to be developed before testing
begins.
64
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Table 4-26. Summary of Carbon Adsorption Capacities (5)
Compound
Acenaphthene
Acenaphthylene
Acetophenone
2-Acetylaminofluorene
Acridine orange
Acridine yellow*
Acrolein
Acrylonitrile
Adenine"
Aldrin
4-Aminobiphenyl
Anethole"
o-Anisidineb
Anthracene
Aroclor 1221
Aroclor 1232
Benzene
alpha-Benzene hexachloride (alpha-BHC)
beta-Benzene hexachloride (beta-BHC)
gamma-Benzene hexachloride
Adsorption
Capacity
(mg/g)a
190
115
74
318
180
230
1.2
1.4
71
651
200
300
50
376
242
630
1.0
303
220
256
Compound
Adsorption
Capacity
(mg/g)a
(gamma-BHC) (Lindane)
Benzidine dihydrochloride
Benzo(k)fluoranthene
3,4-Benzofluoranthene
Benzole acid
Benzo(g,h,i)perylene
Benzo(a)pyrene
Benzothiazole"
Bis(2-chloroethoxy)methane
Bis(2-chloroisopropyl)ether
Bis(2-ethylhexyl)phthalate
Bromoform
4-Bromophenyl phenyl ether
5-Bromouracil
Butylbenzyl phthalate
N-Butylphthalate
Carbon tetrachloride
Chlordane
Chlorobenzene
p-Chloro-m-cresol
Chloroethane
2-Chloroethyl vinyl ether
Chloroform
2-Chloronaphthalene
1 -Chloro-2-nitrobenzene
2-Chlorophenol
4-Chlorophenyl phenyl ether
5-Chlorouracllb
Cyclohexanoneb
220
181
57
0.76
11
34
120
11
24
11,300
20
144
44
1,520
220
11
245
91
124
0.59
3.9
2.6
280
130
51
111
25
6.2
Cytosineb
Dibenzo(a,h)anthracene
Dibromochloromethane
1,2-Dibromo-3-chloropropane
1,2-Dichlorobenzene
1,3-Dichlorobenzene
1,4-Dichlorobenzene
3,3-Dichlorobenzidine
Dichlorobromomethane
Dichlorodiphenyldichloro-
ethylene (DDE)
Dichlorodiphenyltrichloroethane (DDT)
1,1-Dichloroethane
1,2-Dichloroethane
1,2-trans-Dichloroethene
1,1 -Dichloroethylene
2,4-Dichlorophenol
1,2-Dichloropropane
1,2-Dichloropropene
Dieldrin
Diethyl phthalate
4-Dimethylaminoazobenzene
N-Dimethylnitrosamine
2,4-Dimethylphenol
Dimethylphenylcarbinol5
Dimethyl phthalate
4,6-Dinitro-o-cresol ,
2,4-Dinitrophenol
2,4-Dinitrotoluene
2,6-Dinitrotoluene
Diphenylamine
1,1 -Diphenylhydrazine
alpha-Endosulfan
beta-Endosulfan
Endosulfan sulfate
Endrin
Ethylbenzene
Ethylenediaminetetraacetic acid
Fluoranthene
Fluorene
5-Fluorouracilb
Guanineb
Heptachlor
Heptachlor epoxide
Hexachlorobenzene
Hexachlorobutadiene
Hexachloroethane
Isophorone
1.1
69
4.8
53
129
118
121
300
7.9
232
322
1.8
3.'6
3.1
4.9
157
5.9
8.2
606
110
249
6.8 x10"5
78
210
97
169
33
146
145
120
135
194
615
686
666
53
0.86
664
330
5.5
120
1,220
1,038
450
258
97
32
65
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Table 4-26. Summary of Carbon Adsorption Capacities (5) (Continued)
Compound
4,4'-Methylene-bis-(2-chloroaniline)
Methylene chloride
Naphthalene
alpha-NaphthoI
beta-Naphtholb
alpha-Naphthylamlne
beta-Naphthylamlne
p-Nitroanlllneb
Nitrobenzene
4-NitrobiphenyI
2-Nilrophenol
4-Nitrophenol
N-Nitrosodlphenylamlne
N-Nitrosodl-n-propylamine
p-Nonylphenol
Pentachlorophenol
Phenanthrene
Phenol
Phenylmercuric acetate
Styrene
1 ,1 ,2,2-Tetrachloroethane
Tetrachloroethene
1 ,2,3,4-Tetrahydronaphthaiene
Adsorption
Capacity
(mg/g)a
190
1.3
.132
180
200
160
150
140
68 ,
370
99
76
220
24
250
150
215
21
270
120
11
51
74
Compound
Thymineb
Toluene
1 ,2,4-Trichlorobenzene
1 ,1 ,1-Trichloroethane
1 ,1 ,2-Trichloroethane
Trichloroethene
Trichlorofluoromethane
2,4,6-Trichlorophenol
Uracil"
p-Xylene
Not Adsorbed
Acetone cyanohydrin
Adipic acid
Butylamine
Choline chloride
Cyclohexylamine
Diethylene glycol
Ethanol
Hexamethylenediamine
Hyclroquinone
Molpholine
Triethanolamine
Adsorption
Capacity
(mg/g/
27
26
157
2.5
5.8
28
5.6
155
11
85
* Adsorption capacities are calculated for an equilibrium concentration of 1.0 mg/L at neutral pH.
b Compounds prepared in "mineralized" distilled water containing the following composition:
Ion
Ca**
K*
Mg4*
Na+
Cone. (mg/L)
100
12.6
25.3
92
Ion
cr
SO4--
Alkalinity
PO4--
Conc. (mg/L)
177
100
200
10
After the test plan has been developed, bench-scale jar
tests should be .performed in accordance with the test
plan. Consideration should be given to technology se-
lection and proper treatment sequence after a review of
the characterization data is complete.
For most treatment steps, a series of small-scale j'ar
tests can be performed to select effective treatment
chemicals and to determine an appropriate range of
dosages and reaction times for further tests. Stand-
ardized bench tests are then performed on larger vol-
umes (usually 1 L) to obtain design factors that are
effective in the planning and design of pilot plant and
full-scale treatment equipment. Based on these test re-
sults, a larger sample is commonly treated to provide
sufficient sample for the next treatment step. Prepara-
tion of treated samples for the performance of a stand-
ardized bench test always starts with raw sample, and
the preliminary treatment tests are performed in such a
manner as to minimize the inadvertent loss of sample
components important for the evaluation of data from
the bench test.
4.4.2.2 Optimization Testing
In-depth optimization testing on the selected processes
or treatment trains should be provided before the equip-
ment is selected. This additional test sequence provides
further insights into how the technology will react under
vaiying water characteristics and flow rates. Also, oper-
ating parameters can be evaluated to improve perform-
ance and/or reduce costs. To achieve this level of
testing, it may be necessary to initiate pilot plant testing.
4.4.2.3 Design Verification
Data derived from treatability studies are very useful for
full-scale treatment system design. Chemical doses, pH,
settling rates, oxygen requirements, air-to-water ratios,
66
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sludge production, and retention times are examples of
process parameters that can be determined directly
from treatability testing. Full-scale equipment can be
sized after applying the appropriate scaleup factors.
Space requirements can then be accurately determined.
Capital cost estimates of full-scale treatment systems
based on well-performed treatability tests should be
within 20 to 30 percent of actual cost. Operating cost
estimates should also be reasonably accurate because
chemical and power needs will scale up directly. If per-
formed properly, the treatability study should lay a solid
foundation to minimize the risks involved in meeting
established cleanup goals.
4.4.3 Advantages of Treatability Testing
In the absence of literature or database performance
statistics, treatability testing provides the remediation
designer with preliminary information on whether or not
the selected process(es) will meet expected removal
goals. Acandidate process can be evaluated with regard
to size and operating parameters. New or innovative
processes of interest can be applied to the ground water
or leachate without excessive risk of time or funds. The
time element of treatment for many processes can be
estimated in a shorter period than if full-scale tests are
performed. Examples would be GAC and ion exchange,
where a small amount of medium would be depleted
quickly to establish breakthrough time.
4.4.4 Limitations of Treatability Tests
Experienced and skilled personnel are required to per-
form treatability tests. These personnel typically have
treated water matrices for many years and can select
proper chemical dosages, sequences, and treatment
trains to meet the project objectives. Samples resulting
from treatment must be preserved and sent to qualified
laboratories for analysis. Shipment and analysis require
a few days to several weeks before the treatability re-
sults are known. The time and cost of performing the
testing and laboratory analysis must be considered. The
collection of representative treatability test samples is
critical. Samples that are too dilute or too concentrated
could result in a treatment system that is undersized or
oversized. Long periods of bench or pilot testing may
also be required for those sites with matrix charac-
teristics that vary significantly.
Bench-scale treatability tests can be used to provide
preliminary guidance on technology selection. They also
may prove useful in the initial identification of pretreat-
ment requirements and in estimation of the expected
magnitude of treatment efficiency, effluent quality, and
chemical dosages. Selection of basic design criteria for
more comprehensive pilot plant testing should also be
achievable. When evaluating the data from a treatability
test, however, it must be remembered that the samples
collected to perform the tests usually represent only a
single point in time. Because the treatment system de-
sign may operate for years, even decades, long-term
sampling changes must be considered. Usually, no al-
lowance is made in the sample collection methodology
for such factors as seasonal variations in ground water
or leachate strength or the impact of runoff or rainfall.
Furthermore, the appropriate scaleup factors must be
applied to the bench test results so that the results can
be correctly interpreted. Thus, readers are cautioned not
to rely solely on the results of the bench-scale treatability
study to provide sufficient technical information for a
successful engineering design. Rather, the bench test
results should be used in combination with subsequent
continuous flow-through pilot plant tests, other available
site data, and related experience to ensure that a well-
operating, full-scale system is designed and constructed
consistent with the goals of the project.
4.5 References
1. U.S. EPA. 1990. Land disposal restrictions for third third scheduled
wastes; rule. Fed. Reg. 55:22,624-22,625. June 1.
2. U.S. EPA. 1994. RREL Treatability Database, Version 5.0. Risk
Reduction Engineering Laboratory, Cincinnati, OH.
3. U.S. EPA. 1990. Basics of pump and treat ground-water remedia-
tion technology. EPA/600/8-90/003. Ada, OK.
4. U.S. EPA. 1980. Carbon adsorption isotherms for toxic organics.
EPA/600/8-80/023. Cincinnati, OH.
5. U.S. EPA. 1987. Development document for effluent limitations
guidelines and standards for the organic chemicals, plastics, and
synthetic fibers. EPA/440/1-87/009. Washington, DC.
6. Adams, J., and R. Clark. 1991. Evaluation of packed tower aera-
tion and granular activated carbon for controlling selected or-
ganics. J. Am. Waterworks Assoc. 83(1):49-57.
67
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Chapters
Case Studies
In this chapter, examples of ground-water or leachate
problems at four sites illustrate how treatment technolo-
gies were evaluated, selected, designed, and imple-
mented. Each case study covers the following topics:
• Background information about the site
• Evaluation of treatment alternatives
• Project design
• Results and summary
The purpose of these selected case studies is to show
that many factors play a role in a decision. Site-specific
factors, including regulatory issues, are part of the
evaluation and selection process. For example, in Case
Study 1 air is allowed to be discharged directly to the
atmosphere, while in Case Study 4 the state required air
emissions controls. In Case Study 1, the state required
a temporary treatment system. Case Study 3 illustrates
the importance of treatability studies for process selec-
Case Study 1: Ground-Water and Landfill
Leachate Treatment
Physical/chemical treatment to remove
metals, volatile organic compounds (VOCs),
and ammonia
Case Study 2: Ground-Water Treatment
Biological fluidized bed reactor to
remove organics
Case Study 3: Landfill Leachate Treatment
Chemical pretreatment and biological
treatment to remove metals and organics
Case Study 4: Ground-Water Treatment
High-temperature air stripping to
remove VOCs
Figure 5-1. Case studies in Chapter 5.
tion. Figure 5-1 presents a brief description of each case
study.
5.1 Case Study 1: Ground-Water and
Landfill Leachate Treatment—
Physical/Chemical Treatment To
Remove Metals, VOCs, and Ammonia
5.1.1 Background
This project involved a 75-acre (30.4-hectare) landfill
that was developed in the early 1940s. A 21-acre (8.5-
hectare) double-lined expansion area was permitted
and placed in operation in the eastern portion of the site
during the summer of 1987; however, the older, western
portion of the facility was unlined. Leachate from this
unlined portion of the landfill had affected the ground
water in the immediate vicinity. The landfill had recently
been sold, but the previous owner, under a Consent
Agreement with the state, was required to extract and
treat the leachate/ground-water mixture from the west-
ern portion of the site. The method of treatment selected
was lime pH adjustment and biological oxidation in an
aerated lagoon.
Later, a leachate and ground-water extraction system
for the eastern portion of the site was installed. Lime
addition was unnecessary due to the self-neutralizing
character of leachate volatile acids; however, the exist-
ing aerated lagoon treatment system was grossly under-
sized to treat the additional water effectively. The new
owner contracted with a consulting engineer to design a
new physical/chemical treatment system to remove
metals, VOCs, and ammonia from the extracted
ground water and leachate. The projected ground-
water/leachate flow rate for design was 350 gal/min (0.5
million gal/day) (1,325 L/min). Effluent from the landfill
leachate treatment system flowed into a small creek that
was classified for warm water fishery, recreation, water
supply, and aquatic life. Stringent effluent limits were
set, and a rigid schedule for compliance was made part
of the Consent Agreement with the previous owner.
Leachate/ground-water analysis data collected from the
eastern site indicated that samples from the landfill wells
had biochemical oxygen demand (BOD) concentrations
69
-------
ranging from 300 to 400 mg/L. Therefore, the state
required the owner to include biological treatment, in
addition to physical/chemical treatment, to meet the ef-
fluent limits (see Table 5-1). The state threatened to
close the landfill if the effluent limits were not met on
schedule.
Toblo 5-1. Comparison of Temporary System Effluent With
Consent Agreement Discharge Limits
Analysis
The following parameters except
pH are In mg/L:
PH
BOD5
Suspended solids
NH4-N. summer
NH4-N, winter
Total phosphorus
Iron
Manganese
Zinc
Copper
Lead
Nickel
System
Effluent
6.45
<2
<1
—
<1
2.35
0.10
0.02
0.15
0.02
<0.1
<0.1
Limit
(Monthly
Average)
6-9
10
10
1
3
2
1.5
1.0
0.3
0.07
0.03
0.013
The following parameters are
In
trans-1 ,2-Dtehloroethylene
Trichloroethylene
1,1-Dtehloroelhylene
Methyleno chloride
Carbon tetrachloride
Totrachloroethylene
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
0.05
27.0
3.0
1.9
4.0
8.0
Because the state would not grant an extension for the
design and construction of the new leachate/ground
water treatment system, the owner proposed to install
and operate a 200-gal/min (757-L/min) temporary treat-
ment system. A plan was submitted to the state for
approval with a fast-track design and construction
schedule for the biological treatment system and com-
pletion of the physical/chemical treatment system. Op-
eration of the temporary treatment system to maintain
compliance with the Consent Agreement during con-
struction was the key to state approval of the plan.
Together with the consulting engineer, the new owner
met with state regulators to explain the plan and the
temporary system. Treatability studies were performed
to convince the regulators that the temporary treatment
system would meet effluent limits. The new owner, the
consulting engineer, and regulators continued to meet
to expedite approval of the biological treatment system
design and permitting for construction and operation.
5.1,2 Evaluation of Treatment Alternatives
The owner was presented with three alternatives to
maintain the quality of water in the stream flowing past
the landfill.
• Close the landfill.
• Haul leachate/ground water to a distant landfill with
a leachate treatment system or to a municipal waste-
water treatment system.
• Install the 200-gal/min (757-L/min) temporary treat-
ment system and operate it until the 350-gal/min
(1,325-L/min) permanent system could be completed.
Obviously, the owner wished to remain in business, so
closing the landfill, even temporarily, was not an option.
The daily revenue was necessary to pay for improve-
ments and meet the payroll.
Hauling leachate/ground water for treatment elsewhere
was impractical due to the large volume and expense
of trucking. Treatment elsewhere also presented tech-
nical problems due to the metals content of the
leachate/ground water.
By installing a temporary treatment system, the new
owner could comply with the terms of the Consent
Agreement. Treatment and effluent quality would be
under the owner's control. The consultant's engineers
would hire and train new treatment system operators
while operating the temporary system. This experience
would be useful when the new 350-gal/min (1,325-
L/min) system was finally completed.
The capital and operating costs of the temporary treat-
ment system were minor compared with going out of
business or hauling the ground water/leachate for treat-
ment elsewhere. The owner and consultant, after some
negotiation, were able to convince the state to approve
the temporary treatment plan.
5.1.3 Project Design
The consulting engineer was contracted to design, build,
and operate a temporary ground-water/leachate treat-
ment system that would meet the following objectives:
• Design and construction must be complete and the
system ready to operate in 1 month.
• The system must operate at the lowest cost possible
due to its short life span, scheduled to be 6 months.
• The system must meet discharge limits for BOD,
VOCs, and metals as defined in the Consent Agree-
ment (see Table 5-1).
• Operation must be easy and similar to the 350-
gal/min (1,325-L/min) system.
The processes required to duplicate the 350-gal/min
(1,325-L/min) system included aeration pretreatment to
70
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oxidize iron, chemical precipitation and filtration for met-
als removal, air stripping for VOC removal, and sludge
dewatering. Due to lenient air emission standards in that
part of the state, no air stripper off-gas treatment was
required. Aqueous-phase carbon was added to the tem-
porary system as an effluent polishing step to assure the
state that effluent would meet the discharge limits.
Wastewater treatment engineers assigned to the project
met the challenging design objectives in the following
manner:
• Rolloff boxes were used as tanks for clarification,
sludge thickening, and filter backwash water storage.
The boxes had reuse value later for trash pickup.
• Sketches replaced formal drawings to detail the de-
sign for shop fabrication and field assembly. Valuable
time was saved for earlier fabrication of equipment,
piping, and site preparation.
• Carbon canisters and an air stripper package unit
were rented for the temporary system to reduce capi-
tal cost and design time. An option to buy/lease was
arranged but was never exercised.
• The consultant's technicians procured and mounted
package filters on a ,skid. PVC. piping was quickly
installed in the shop and was ready for field deploy-
ment in 2 weeks.
• All connections were made with hoses and quick-
couplings to eliminate field piping.
• Controls were rudimentary. All pumps and motors
were operated with simple on-off manual switches.
Some plug-in float switches were used to energize
alarms on high or low tank level. A pH meter with
on/off control/alarm switches operated the caustic
soda pump, the only automatic subsystem.
• A package precoat vacuum filter was rented to de-
water the metal hydroxide sludge. Precoating the fil-
ter with diatomaceous earth eliminated iron fouling of
the filter media.
• The site was prepared by leveling and paving with
crushed limestone. Railroad ties supported the equip-
ment. Terraces cut into the hillside where the tanks
were installed provided the hydraulic gradient re-
quired for gravity flow of water from one process to
another, eliminating transfer pumps.
• An inexpensive pole barn was erected over the
equipment for cold weather operation after the sys-
tem proved to operate satisfactorily without any modi-
fications. Kerosene-fueled space heaters provided
ample heat during winter operation.
• Special tanks (rapid mix tank and flocculator) were
constructed of carbon steel. To reduce costs and
Oi It{••?••- j'iSVMi,'-'",'•,"'. • . . . , ',.. . ,
save time, only the outside surfaces of the tanks were
painted, because the tanks would have little salvage
value at the conclusion of the project.
A layout of the temporary system is shown in Figure 5-2.
The 200-gal/min (757-L/min) temporary treatment sys-
tem was operated for 6 months at a cost of approxi-,
mately $500,000. The flow rate during operation
averaged 120 gal/min (454 L/min). At the end of the
project, the temporary system was dismantled and the
rental package units returned. The consultant claimed
the equipment with salvage value, and the rolloff boxes
were given to the landfill owner.
5.1.4 Results and Summary
Effluent samples from the temporary ground-water/
leachate treatment system were analyzed weekly and
compared with the discharge limits set forth in the Con-
sent Agreement. The results of the effluent sampling and
analysis program are shown in Table 5-1, along with the
state discharge standards for this landfill. The outfall
monthly averages met the discharge limits.
The use of a temporary system enabled the landfill
owner to complete the construction of a new, permanent
350-gal/min (1,325-L/min) ground-water/leachate treat-
ment system that had already been designed. A new,
additional biological (activated sludge) system was de-
signed and constructed during the operation of the tem-
porary system. The full-scale treatment system diagram
is shown in Figure 5-3. The temporary treatment system
provided training for the new operators while they be-
came familiar with the new treatment system being con-
structed nearby. Although the owner did not have to
address air quality, the water quality in the creek was
preserved. (In other states, air stripper off-gas treatment
would have been required.)
5.7.5 Source
Blenk, J.P., and R.A. Kormanik. 1987. Full-scale treat-
ment of leachate and ground water at a sanitary landfill:
A case study. Presented at the Water Pollution Control
Federation Annual Conference (October).
5.2 Case Study 2: Ground-Water
Treatment—Biological Fluidized Bed
Reactor To Remove Organ ics
5.2.1 Background
A chemical manufacturer had contaminated ground
water under a retention pond used as a cooling water
source. It was determined, however, that this system
would be unable to meet stringent water quality dis-
charge standards proposed by the state. The company
undertook development of a biological treatment system!
71
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Spare
/ JF-i
Cii&on Cittoon
Cokvnn Column , ,
l'X^8 5'X1S'
1
Carbon
Column
5'xlff
I I
~I
Air Stripper
10'x12' ' —
Clarifier#3 ,e,
8' x 25' r
'-- ^rJJ
c —
Add -k
Sldd y
i hJff
To ^ Effluent Holding Tank ? L
Creek 81 x 23'
Filter
Backwash
Figure 5-2. Layout of temporary system.
Rocoulati
Neutralization
500.000 Gal/Day /^~^**\ " '
350 Gal/Min.
Leachate
and
Ground Water
\
Lim
Physic
Sup
^
e Polyme
al/Chemical
ematant
Physical/Chemical
Supernatant
Filter
Cake .
To Landfill"
Disposal
Dif. Skid s*P
^d L^
— = — rfi
Clarifier#4 I L
8' x 25' *^
on
Gravity Co
> Plate ..__
Separator /^
I ~{
Gravity * V
. Plate S V
Separator f
r
Sludqe ,
Thickener
i
Sludge
Dewatering
'• . .
Sludge
Biological Sludge
Filtrate
Leachate _>
Blower From -»
Backwash S~< We||S Ij
From V-/
Filter s;
, \ ?Air
Clarifier#1
8' x 25'
•*A Equalization Tank
\ 8'x23'
fl ^A-^ 1 -r-,
v Sludge
N siudge Thickener
^ Sludge *J»
*,
r1
Clarifier#2
8' x 25'
pH
ntroller s — >.
~v r°"
-/• k>
AcM .. sS%
Filters
Biological Leachate
Treatment System
rv^T1^
I J -^Dta. N.
VVFtea*it«\J rUl
-V< 6'Dla' PoS^M* l^J
f \ -S-Dla.
D.E. Rlter
*" Skid
rxio'
Dewatered
Sludge
VOCs
Ammonia
t
r
-O -» To
V.^/ Discharge
^ V
Air
Air
Stripping
Figure 5-3. The Integrated physical/chemical and biological treatment system.
The regulated chemicals of most concern included
methanol (CAS number 67-56-1), acetone (67-64-1),
methylene chloride (75-09-2), tert-butyl alcohol (75-65-
0), chlorobenzene (108-90-7), 1,2-dichloroethane (107-
06-2), tetrahydrofuran (109-99-9), and toluene (108-88-3).
A bench-scale treatability study indicated that a biologi-
cal fluidized bed reactor (FBR) showed promise for
treating these compounds. This encouraged the chemi-
cal manufacturer to commission a pilot-scale unit, which
was used to finalize process design parameters for a
full-scale system,
5.2.2 Evaluation of Treatment Alternatives
Three alternative systems were initially evaluated on a
bench-scale:
• An FBR with sand as the support medium
• An FBR with GAG as the support medium
72
-------
• A submerged fixed-media biofilter
The bench-scale studies compared these systems' abil-
ity to handle startup, steady-state operation, and shock
loads.
During startup, it was found that the sand and carbon
fluidized bed reactors performed similarly with regard to
maximum hydraulic and organic loading rates, with both
over five times better than the biofilter. During steady-
state operation, the sand and carbon FBRs performed
equally well, with the biofilter found to be inferior due to
a significantly lower hydraulic/organic loading rate. Dur-
ing a spike event, reactors operating at steady state
were subjected to shock loads of the chemicals listed
previously. All reactors responded well to the shock
loads of the degradable compounds (e.g., methanol,
acetone, and toluene), but the carbon FBR was clearly
superior for the less readily degradable compounds
(e.g., tert-butyl alcohol, tetrahydrofuran, and 1,2-dichlo-
roethane). Stripping was clearly the lowest in the carbon
FBR compared with those that had no adsorptive capa-
bilities. The conclusion was to proceed with pilot-scale
testing of a carbon fluidized bed reactor.
5.2.3 Project Design and Pilot-Scale Test
The carbon FBR pilot system used in this test is shown
in Figure 5-4. The system included:
Steady-State
Feed Solution
Spike
Feed Solution
Chemical
Feed
Pumps
Influent Flow
Valve
• Means for separately delivering a steady feed, influ-
ent water, and nutrients.
• Recirculation through the reactor to maintain fluidiz-
ing flux.
• Oxygen dissolution to the feed.
• An agitator to aid sloughing of excess microorgan-
isms from the activated carbon.
The FBR unit was designed and constructed as a pro-
totype of a full-scale reactor. The reactor was 20 in. (50.8
cm) in diameter and 14 ft (4.3 m) tall, providing 32 ft3
(0.9 m3) empty bed volume. The recirculation flow was
set to maintain fluidization and was provided by a cen-
trifugal pump. Oxygen was supplied in a somewhat
purified state by passing a compressed air stream
through a molecular sieve. Injecting the gas followed by
trapping and reinjecting the bubbles enabled the influent
to be oxygenated to levels four to five times greater than
normal atmospheric saturation levels.
The test used three feed solutions. Two of these com-
bined a base organic feed with a nutrient solution, both
of which were needed to maintain a microbial population
capable of handling shock loads. The base organic mix-
ture included methanol, acetone, and methylene chlo-
ride, standard components of the wastewater. The third
solution was another organic feed that was used to
simulate shock loads. This feed contained projected
peak levels of tert-butanol, 1,2-dichloroethane, tetrahy-
Effluent DO
Probe and
Controller
Influent
Feed Pumps
Effluent
pH Probe
Recirculation
Pumps
r
t Influent
-Tj DO
J Recirculation Probe
Flow Valve O
-r, T
"?
-1
o
3
Carbon
FBR
Reactor
Air
Purifk
System
Effluent
(to sanitary
sewer)
Air
Puffier Compressor
Nutrient
Solution
Trap
System Influent
(from retention pond)
Figure 5-4. Carbon FBR pilot system.
Oxygen
Control
Valve
Nutrient Ł
Feed Pump
73
-------
drofuran, toluene, methanol, acetone, and methyiene
chloride.
The test included three phases: startup, verification of
operating point, and a general performance assess-
ment.
The startup phase involved the cultivation of appropriate
bacteria in a seed tank. The initial population was ob-
tained from sediment in the retention pond, supple-
mented with activated sludge from a municipal
wastewater treatment plant. The culture was fed a mix
of all targeted compounds and nutrients and was aer-
ated. After seed was added to the system, infinite recir-
culation was implemented for several hours to provide
time for microbial attachment to the activated carbon
granules.
After the reactor was seeded, continuous operation was
initiated. The initial goals were development of a viable
biomass in the system and verification of the steady-
state operating conditions determined in the bench-
scale studies. The steady-state conditions included an
organic loading rate (OLR) of 120 Ib COD/1000 tf'-day
(1,922 kg COD/1,000 m3-day), an influent COD of 25
mg/L, and an empty bed contact time (EBCT) of 18.7
min, with a reactor volume of 32 ft3 (0.9 m3) and an
influent flow rate of 12.8 gal/min (48.4 L/min). The influ-
ent COD and flow rate represented a blend of the feed
solution and retention pond water. After steady-state
conditions were established, the reactor was peri-
odically given a shock load to simulate the effects of
rainfall events and subsequent release of additional
compounds to the system.
The purpose of the performance assessment was to
optimize the design for full-scale operation. This was
carried out by incrementally increasing the steady-state
load, followed by a shock load. The OLR was scheduled
to be increased stepwise from 120 Ib COD/1,000 tf'-day
(1,922 kg COD/1,000 m3-day) to 150, 180, and 210 Ib
COD/1,000 ft3-day (2,403, 2,883, and 3,364 kg
COD/1,000 m3-day) based on a recommendation from
Envirex. The EBCT and flow rate were then modified to
maintain an influent COD concentration of 25 mg/L.
Gases were also collected and analyzed during this
phase to determine whether air emissions could be a
problem for a full-scale unit.
5.2.4 Results
Specific results are summarized' in Table 5-2. The
startup of the pilot-scale unit took approximately 6
weeks to complete. The steady-state operating parame-
ters were verified successfully. Under the conditions
outlined earlier, average influent and effluent COD val-
ues of 28 and 2.3 mg/L, respectively, were obtained,
producing an overall COD removal efficiency of 92 per-
cent. The bed height increased during the steady-state
Table 5-2. Results of Pilot-Scale Tests
Influent Effluent Removal
Steady-State Parameter:
COD (mg/L)
Methanol (mg/L)
Methyiene chloride (ng/L)
Shock Loading Parameter:
Methanol (mg/L)
Acetone (ng/L)
Methyiene chloride (ng/L)
t-Butyl alcohol (ng/L)
1 ,2-Dichloroethane (ng/L)
Tetrahydrofuran (|ig/L)
Toluene (ng/L)
28
11.6
33
28
350
160
200
30
120
27
2.3
<0.5
12. •
<1
, 20
15
36
3
25 .
1
92
>96
64
>99
96'
91
82
90
92
96 ..
operation and stabilized near 11 ft (3.3 m), representing
a bed expansion of 30 percent. This indicated that the
populations in the reactor were healthy and viable. The
oxygen utilization rate confirmed this observation.
The shock load performance of the system was excel-
lent. On a mass basis, methanol and toluene were
removed to the greatest extent (greater than 95 per-
cent), followed by acetone, 1,2-dichloroethane, tetrariy-
drofuran, and methyiene chloride (90 to 95 percent).
Tert-butyl alcohol was removed to the least extent (80
percent).
Difficulties were encountered at the outset of the next
performance assessment. When the OLR was in-
creased to 150 Ib COD/1000 ft3-day (2,403 .kg
COD/1,000 m3-day), the bed depth rose to the system
design maximum of 11.5 ft (3.5 m). This indicated that
the bed was fully loaded; thus, while treatment could
continue, additional food would only produce wasted
cells. The ability of the system to handle shock loads
was also generally better at the 120 Ib COD/1,000
ft3-day rather than 150 Ib COD/1,000 ft3-day (1,922
rather than 2,403 kg COD/1,000 m3-day), especially
with regard to less degradable compounds such as
tert-butyl alcohol. The OLR of 120 Ib COD/1,000 ft3-day
(1,922 kg COD/1,000 m3-day) was finally deemed to be
optimal because it produced a good balance between
biomass growth and sloughing.
The off-gas analysis also produced good results.'All
seven target compounds were below detection levels in
the gas phase during a shock load test.
5.2.5 Summary
Activated carbon treatment is well suited for removing
low concentrations of organic compounds from water. In
combination with biological destruction, the process has
the potential to be extremely useful in situations such as
this. The key element in the procedure was the initial
74
-------
treatability study. That study established that microor-
ganisms likely to thrive in the system were able to
degrade wastes such as tetrahydrofuran that were not
previously described in the literature as biodegradable.
Had the treatability results indicated potential difficulties
with such treatment, one or more pretreatment proc-
esses would have been required, or use of microorgan-
isms would have been abandoned. Because the initial
treatability study was successful, moving on to pilot-
scale studies followed standard chemical and environ-
mental engineering design procedures.
5.2.6 Source
Kang, S.J., C.J. Englert, T.J. Astfalk, and M.A. Young.
1990. Treatment of leachate from a hazardous waste
landfill. In: Proceedings of the 44th Purdue Industrial
Waste Conference. Chelsea, Ml: Lewis Publishers.
5.3 Case Study 3: Landfill Leachate
Treatment—Chemical Pretreatment
and Biological Treatment To Remove
Metals and Organics
5.3.7 Background
A hazardous waste landfill had historically received both
domestic refuse and industrial wastes. Pretreatment of
the landfill leachate before discharge to the local publicly
owned treatment works was required to meet the local
sewer use ordinance. The pretreatment could use a
combination of biological and physical-chemical proc-
esses. Analysis of the leachate indicated significant con-
centrations of pollutants as measured by COD, BOD,
total Kjeldahl nitrogen (TKN), ammonia nitrogen, phe-
nol, cyanide, methylene chloride, arsenic, and nickel.
5.3.2 Evaluation of Treatment Alternatives
Bench-scale treatability tests were performed on the
leachate to identify processes suitable for reducing its
strength and toxicity. The processes evaluated included
activated carbon adsorption, ammonia stripping, metals
removal, and aerobic and anaerobic biological treat-
ment. All tests proved to be successful except for an-
aerobic treatment.
Based on what had to be removed from the waste, it was
determined that a chemical pretreatment step was re-
quired before biological treatment. The purpose of
chemical pretreatment was to reduce metals and other
toxicants that could potentially interfere with biological
activity and to prevent discharge exceeding the sewer
use ordinance limits. Chemical treatment consisted of
metals precipitation with subsequent settling of the met-
al sludge and addition of growth nutrients. Two biological
systems were selected for pilot testing: conventional
activated sludge and activated sludge containing pow-
dered activated carbon. The last pretreatment step was
activated carbon adsorption to polish the remaining low
concentration of organics. The effluent from the carbon
system was of sufficient quality to be discharged directly
to the sanitary sewer.
5.3.3 Project Design
Leachate from several cells was collected into separate
tanks. This provided equalization before feeding to the
treatment system. The equalized feed was processed
through the metals removal system, then transferred to
the biological system.
The chemical treatment step consisted of three mix
tanks, where pH was adjusted, metal precipitate parti-
cles were coagulated and flocculated, and nutrients
were added to encourage microbial growth. This chemi-
cal treatment step resulted in nickel removal of 15 to 75
percent, depending on the chemicals selected. Use of
ferrous and ferric hydroxides as sweep coagulants gave
the best removal but generated large quantities of slow-
settling sludge. Use of oxidants such as hydrogen per-
oxide or potassium permanganate also gave high
removals but made the leachate foam. Simple pH ad-
justment with sodium hydroxide generated small quan-
tities of nonfoaming sludge and was the preferred
method operationally, despite the fact that it removed
only about 40 percent of the nickel.
The biological reactor pilot tests examined two treat-
ment methods: conventional activated sludge and the
powdered activated carbon process. The systems were
set up as two-stage operations, with the second stage
designed to test reactor performance when much of the
possible high-strength loading was removed. (Staging
has other operational advantages for both leachate and
ground-water treatment, as outlined below). The re-
moval performances of these two systems are com-
pared in Table 5-3. Overall, the pilot results indicated
that both BOD and COD removals in excess of 90
percent were possible with either of these techniques.
This indicated that the leachate test samples had little
toxicity for activated sludge bacteria and that little non-
degradable adsorbable material was present in the feed.
The full-scale system used the conventional activated
sludge process with necessary features to add pow-
dered activated carbon. The treatment plant was de-
signed for 30,000 gal/day (113,562 L/day) and is shown
in Figure 5-5. The system featured flexibility in adding
powdered activated carbon when needed; the effluent
was also routed through carbon columns when polishing
was required for compliance.
5.3.4 Results and Summary
Operating data for the system, which was installed in
1990, demonstrate its effectiveness. These data are
75
-------
Table 5-3. Comparison of Conventional Activated Sludge and Powdered Activated Carbon Reactor Performance
Conventional A.S. Effluent
Powdered Activated Carbon
Process Effluent
Parameter Influent Stage 1 Stage 2 %a
HRT (days) — 20 10 —
SRT(days) — 20 20 —
Carbon dose (mg/L) — — — . —
OLR(lb COD/1 03fl?-d) —75 32 —
COD (mg/L) 24,000 2,750 2,120 91
BODs(mg/L) 12,700 576 478 96
MLSS (mg/L) — 5,810 5,000 —
MLVSS (mg/L) — 3,100 2,550 —
TKN(mfl/L) 880 663 623 29
Ammonla-N (mg/L) 345 257 131 62
Ortho-phosphate (mg/L) 43 2 4 91
Nickel (mg/L) 16 7.95 7.6 53
Phenol (mg/L) 290 0.85 0.29. >99
Cyanide (mg/L) 10.7 6.1 5.1 52
8 Overall removal efficiency
HRT s hydraulic retention time
MLSS = mixed liquor suspended solids
MLVSS » mixed liquor volatile suspended sol ds
SRT = solids retention time
1 nnrhntn T fl"0*
* I 11 r^<
Contact _ __ *-» , . . , (ST.. ^1
Water No. 1 No. 2 t^ ~^l f^ 1 (^ ^\ 1 EqUf "
Tanks (500,000 (200,000 ffifc jjgj jj&j °^ (50.™
Gal) _____ Gal) W | *Wl | la'S>° *
Master Cell Holding Tanks ' L^«
Waste Fc
— n PumDS
L03—
' (°lr Carbon
_ ^r^ Column
Transfer Pumps (3)
,1 l| Treated
J Water ^
Treated Eff
Sampler . Pumps (
„,, Effluent
IP Meter
f -^ Municipal
"M?~ Treatment
Plant
Stage 1 Stage 2 %a
20 10 —
20 20 —
7,500 0 . —
75 21 —
1,750 1,670 93
703 432 97
13,800 10,400 —
8,470 6,840 —
637 517 41
213 181 48
4 11 74
8.7 8.4 48
0.36 0.06 >99
4.1 2.1 80
I J"~T r~T Chemicals
Btion I Metals Treatment
)Gal) — -
« t
~T_ I Powdered Activated
r^f r Carb0" Slud9e
-H it-1 (C -A Thickener
— 1 «38SU V'-1^
Biological Treatment f
System -•_*,
\s
Effluent ,<• ^_ f ,.
Transter S|udge 1 "
Tank ConditioninglSA
uent ±=± <2-500Gal) —
21 Sludge Filter Press
2) r-, 20Ft3 n ^
D [H^
u ttttt1-1
Sludge >^^ ToWDI
Cake S"^* Landfill
Figure 5-5. Full-scale system using the conventional activated sludge process.
76
-------
summarized in Table 5-4. The COD and BOD removals
were generally excellent in the full-scale system.
Table 5-4. Full-Scale Operating Data
Parameter Influent Effluent % Removal
COD (mg/L)
BOD (mg/L)
Ammonia-N (mg/L)
Ortho-P (mg/L)
3,571
715
261
2.99
420
32
44
1.64
88
96
83
45
The leachate in this case study was typical of many
leachates emanating from hazardous waste facilities:
very high strength with a mixture of metals and organic
compounds. Initial treatability studies were critical in
determining what processes would work in this case.
Other systems may not need the same combination of
processes. For example, a nonhazardous waste
leachate may not need metals removal. Another point
that the treatability studies showed was that anaerobic
treatment was unworkable. Because some conventional
wisdom would suggest that anaerobic treatment should
be used for high-strength wastes, proceeding to pilot
scale with an anaerobic system in this case would have
produced unacceptable results. Once the necessary
processes had been identified, standard environmental
and chemical engineering design techniques were used
to produce the pilot-scale tests and the full-scale design.
5.3.5 Source
Kiiljian, A.H., Jr., RA. Van Meter, C.D. Fifield, J. O.
Thaler, and T.-P. Chen. 1994. Remedial biodegradation
of low organic strength cooling water using carbon
fluidized bed reactor. In: Proceedings of the 49th Annual
Purdue Industrial Waste Conference (May).
5.4 Case Study 4: Ground-Water
Treatment—High-Temperature Air
Stripping To Remove VOCs
5.4.7 Background
The ground water beneath McClellan Air Force Base in
Sacramento, California, was contaminated with fuel and
solvents from spills and storage tank leaks. Volatile and
semivolatile organics, such as acetone and methyl ethyl
ketone, had been reported at ppm levels. A treatment
system consisting of air stripping and liquid-phase carb-
on adsorption was installed to eliminate these com-
pounds from the ground water. (Blaney and Branscome,
1988). This system is described briefly below.
5.4.2 Project Design
The air stripping system employed at McClellan Air
Force Base is a high-temperature process. The facility
was built in 1986 for a cost of approximately $3.1 million.
The process is diagrammed in Figure 5-6. The contami-
nated ground water is pumped to a storage tank which
provides flow and waste strength equalization. Water
from the storage tank is then fed to a series of heat
exchangers. Heating increases the air stripping effi-
ciency for the VOCs. In this case, the ground water is
pumped through a water-to-water plate and frame, sin-
gle-pass heat exchanger, which raises the temperature
from about 65°F (18.3°C) to approximately 95°F (35°C).
The water temperature is elevated an additional 7 to
10°F (3.8°C to 5.5°C) in a single-pass fin-tube air-to-
water heat exchanger. The ground water is then pumped
to the stripping tower.
The water flow rate to the air stripper is approximately
270 gal/min (1,021 L/min) with an air-to-water ratio of
30:1. The packing materials consist of 2-in. (5-cm) plas-
tic balls. The height of the packing media is 25 ft (7.6
m). The tower effluent contains trace concentrations of
the VOC pollutants. For example, concentrations of
1,2-dichloroethane, cis-1,2-dichloroethene, 1,1,1-tri-
chloroethane, and trichloroethene are nearly equal to
the practical quantitation limits (PQLs) of 0.5 u.g/L. The
liquid effluent enters a wet well, where it is subsequently
pumped to two GAG units in series. The purpose of the
GAG is to remove the trace quantities of other organic
pollutants that are not amenable to air stripping. The
effluent from the GAC is finally discharged to a nearby
creek.
The stripper off-gas is preheated in two air-to-air heat
exchangers in series, where its temperature is brought
to approximately 1,200°F (649°C) before being inciner-
ated. The temperature inside the incinerator is main-
tained at 1,815°F (990.5°C). The incinerator gases are
recycled to preheat both the stripper off-gas and the
ground-water stream fed to the stripper. Once the heat-
ing value of the waste gases is recovered, the gas is fed
to a caustic scrubber to neutralize hydrochloric acid
before being discharged into the atmosphere.
5.4.3 Results and Summary
One of the major operating problems encountered was
the potential for calcium and magnesium carbonate pre-
cipitation to foul the packing material. The original 1-in.
(2.5-cm) packing material was replaced with 2-in. (5-cm)
balls to decrease the likelihood of fouling. Corrosion
within the incinerator is also a problem because of the
extreme off-gas temperature combined with the pres-
ence of hydrochloric acid. Mechanical failures resulting
from corrosion are common. As parts wear out, they are
replaced with new components constructed using spe-
cial metals and alloys.
The facility is continually undergoing design modifica-
tions. An early corrective action was to equalize plant
flows in an attempt to eliminate downtime when the
77
-------
Incinerator
Off-Gas
Ground Water •
Water to Water
Heat Exchanger
Air to Water
Heat Exchanger
Air to Air
Heat Exchanger
Air to Air
Heat Exchanger
Effluent
„„„, „ „_ __
Recycle
Air Stripper
HCI
Scrubber
i
Cleaned Gas
Figure 5-6. Ground-water treatment system, McClellan Air Force Base.
influent flow control valve and the stripper level control
valve failed. Each valve works independently, but each
one senses changes in plant flow and makes the
changes necessary to maintain its preset operating level
either by opening or closing the valve.
Over time, the facility staff have fine-tuned the control-
lers operating the level control valves until the range and
span were set in tune with the flow of the plant.
As far as polishing the stripper effluent is concerned, the
efficiency and economics of the GAG may need to be
re-evaluated against an alternative process, such as
chemical oxidation.
78
-------
Appendix A
Compendium of Ground-Water and Leachate Treatment Technologies
This appendix presents information about the most
common technologies for treating contaminated ground-
water and landfill leachates. Figure A-1 lists the tech-
nologies that are described. Each treatment technology
summary addresses the following topics:
• A brief technology description
• A process flow diagram
• PretreatmenVchemical requirements
• Parameters of interest
• Key design considerations and criteria
• Residuals generation
• Major cost elements
The technology descriptions that follow discuss percent-
age removal for gross waste parameters such as COD,
BOD, and nitrogen, as well as organics not included in
the list of 20 compounds frequently found at hazardous
Biological
• Activated sludge system
• Sequencing batch reactor
• Powdered activated carbon
• Rotating biological contactor
• Aerobic fluidized bed biological reactor
Physical/Chemical
• Air stripping
• Activated carbon
• Ion exchange
• Reverse osmosis
• Chemical precipitation of metals
• Chemical oxidation
• Chemically assisted clarification (polymer only)
• Filtration
Radiation
• Ultraviolet radiation
waste sites. For specific contaminant removal data for
these 20 compounds, the reader should consult Tables
4-3 through 4-22. The ranges listed for the design crite-
ria are keyed to the specific references cited and not to
the process.
Note that because cost data are difficult to obtain, cost
units or cost figures may vary from summary to sum-
mary. The cost data are not presented in any uniform
fashion, such as cost per unit mass of contaminant
removed. The cost data are presented as they are re-
ported in the literature or as available from vendors. In
most instances, no adjustments using an index value
have been made from the years reported in the refer-
ences. Therefore, direct comparisons using these cost
data are discouraged. The reader is encouraged to con-
sult the original references. Abbreviations used through-
out the Appendix are defined on page ix.
Conversion from nonmetric to metric units can be ac-
complished using the following conversion factors:
Figure A-1. Compendium of ground-water and leachate treat-
ment technologies.
To convert from:
gal
gal/ft2
gal/ft3
gal/min
gal/min
ft
ft2
ft3
Ib
Ib/ft2
Ib/ft3
in.
ac
To:
L
L/m2
Urn3
rrrVhr
L/sec
m
m2
m3
kg
kg/m2
kg/m3
cm
km2
Multiply by:
3.785412
42.1
139.8
0.227
0.06309
0.3048
0.0929
0.0283
0.4536
4.8824
16.0184
2.54
4.0468 x 10"3
79
-------
Biological
A.1 Activated Sludge System
A. 1.1 Technology Description
The activated sludge process is a suspended-growth,
biological treatment system that uses aerobic microor-
ganisms to biodegrade organic contaminants. Influent is
introduced into an aeration tank, where a mixed culture
of bacteria is maintained in suspension. In the presence
of oxygen, nutrients, organic compounds, and accli-
mated biomass, a series of biochemical reactions is
carried out in the reactor that degrades the organics and
generates new biomass. Diffused or mechanical aera-
tion is used to maintain aerobic conditions and good
mixing in the reactor. After a specified period, the mix-
ture of new cells and old cells is passed into a settling
tank, where the cells are separated from the treated
water. A portion of the settled cells is recycled to main-
tain the desired concentration of organisms in the reac-
tor, and the remainder is wasted and sent to sludge
handling facilities.
Variations in the conventional activated sludge process
have been developed to provide greater, tolerance for
shock loadings, to improve sludge settling charac-
teristics, to achieve higher BOD5 removals, and to
achieve integrated biological nutrients removal.
A.1.2 Common Modifications
Complete mixing, plug flow, step aeration, modified
aeration, extended aeration, contact stabilization, pure
oxygen aeration, and anoxic/aerobic sequential reactors.
A. 1.3 Technology Status
The activated sludge process was developed in England
in 1914 and was so named because it involved the
production of an activated mass of microorganisms ca-
pable of stabilizing a waste aerobically. Activated sludge
has been widely used for municipal and industrial waste-
water treatment but not for ground-water treatment.
A.1.4 Applications
Most suitable for soluble organics, adequate for nutrient
removal. Easily degrades alkanes, alkenes, and most
aromatics. Widely tested for leachate treatment.
A.1.5 Process Limitations
Limited BOD loading capacity. Equalization may be re-
quired for extreme fluctuating flow and loading condi-
tions. VOCs may be driven off to a certain extent during
aeration. Relatively high sludge production. May not be
suitable for low-strength ground-water treatment. Some
contaminants are known to be nonbiodegradable aero-
bically, such as TCE, PCE, carbon tetrachloride, and
chloroform.
A.1.6 Typical Equipment
General: aeration tank, air diffuser or mechanical aera-
tor, mixer, air blowers, submersible or screw sludge
pumps, aeration basin, clarifier, sludge dewatering
equipment.
A.1.7 Flow Diagram
Figure A-2.
A.1.8 Chemical Requirements
Nutrients (N or P) if they are not sufficient in the
leachate; polymer if required for sludge settling.
A.1.9 Design Criteria
Parameter Range Reference
MLSS (mg/L)
MLVSS (mg/L)
FYM (Ib BOD/lb MLVSS/day)
Maximum volumetric COD
loading (Ib COD/1,000 tfVday)
SRT (days)
RT (days)
3,000-6,000
2,500-4,000
0.01-1.0
10-30
2-40
0.1-20
1
1
2
2
1,2
1-4
A.1.10 Performance
Compound
COD
Influent
(mg/L)
23,900
1,296
Removal %
89-91
93+
Reference
1
2
BOD5
12,700
95-96
NH4-N
TKN
564
387
345
880
98+
99
25-97
25-29
2
3
1
1
A.1.11 Residuals Generated
Aerobic process: 01-0.6 Ib sludge/lb COD removed, at
about 1.0% solids concentration.
80
-------
Nutrients
Aerator
Aeration Tank
Recycled Sludge
Effluent
Secondary
Clarifier
Recycle Pump
Waste Sludge
Figure A-2. Activated sludge system.
A. 1.12 Process and Mechanical Reliability
Expected to have high process and mechanical reliabil-
ity. Single or dual reactor design provides on-line reli-
ability and flexibility.
A.1.13 Environmental Impact
Reactor can be enclosed to minimize gas release, and
an off-gas treatment can be installed where needed.
A. 1.14 Major Cost Elements
Capital costs for the activated sludge process for
leachate treatment are estimated to be $2.5 to $5.1
million per million gal/day treatment capacity; O&M
costs are estimated to be $0.33 to $0,5 million per
million gal/day capacity (5). The aeration basin design
assumes a detention time of 6 hours based on an aera-
tor power input of 0.1 hp per 1,000 gal. The clarifier
design is based on an operation of 600 gal/day/ft2.
Breakdown of Capital Costs
Aeration basin
Clarifier
Aerators
Pumps and piping
Residuals management
Breakdown of O&M Costs
Power
Labor
Chemicals
Residuals management
28%
29%
1%
12%
30%
9%
12%
19%
60%
A packaged activated sludge reactor with 0.02 million
gal/day design capacity had a capital cost of $150,000,
which includes equalization tank, feed tank, system con-
trol, pumps and pipings, and installation. This applica-
tion was for high-strength ground-water treatment, with
1,296 mg/L and 546 mg/L average influent COD and
BOD5, respectively (2).
A.1.15 References
1. Kang J.S., J.C. Englert, J.T. Astfalk, and A.M. Young. 1990. Treat-
ment of leachate from a hazardous waste landfill. 44th Purdue Ind.
Waste Conf. Proc. 44:573-579.
2. Molchan, A.G., and S.J. Kang. 1992. Onsite portable bioremedia-
tion unit. Presented at the Air and Waste Management Association
85th Annual Meeting and Exhibition, Kansas City, MO.
3. Brouns, M.T., S.S. Koegler, K.J. Fredrickson, P.S. Luttrell, and A.K.
Borgeson. 1991. Biological treatment of Hanford ground water:
Development of an ex situ treatment process. In: Hinchee and
Olfenbuttel, eds. Onsite bioremediation. Butterworth-Heinemann.
4. Mueller, G.J., E.S. Lantz, D. Ross, J.R. Colvin, P.O. Middaugh, and
H.P. Pritchard. 1993. Strategy using bioreactor and specially se-
lected microorganisms for bioremediation of ground water contami-
nated with creosote and pentachlorophenol. Environ. Sci. Technol.
27:691-698.
5. McArdle, J.L., M.M. Arozarena, and E.W. Gallagher. 1987. Hand-
book on treatment of hazardous waste leachate. EPA/600/8-
87/006.
A.1.16 Additional Source
1. Flathman, E.P., E.D. Jerger, and M.P. Woodhull. 1992. Remedia-
tion of dichloromethane (DCM) contaminated ground water. Envi-
ron. Prog. 11(3):202-209.
81
-------
A.2 Sequencing Batch Reactor
A.2.1 Technology Description
The sequencing batch reactor (SBR) is a periodically
operated, suspended growth, activated sludge.process.
The only conceptual difference between the SBR and
the conventional continuous-flow activated sludge sys-
tem is that each SBR tank carries out functions such as
equalization, biological treatment, and sedimentation in
a time rather than in a space sequence. Because of the
flexibility associated with working in time rather than in
space, the SBR can be operated as either a labor-
intensive, low-energy, high-sludge-yield system or a
minimal-labor, high-energy, low-sludge-yield system for
essentially the same physical plant. The actual operat-
ing policy can be adjusted in accordance with prevailing
economic conditions by simply modifying.the settings of
the control mechanism. Labor, energy, and sludge yield
can also be traded off with initial capital costs. The cycle
for each tank in a typical SBR is divided into five discrete
periods: FILL, REACT, SETTLE, DRAW, and IDLE, as
shown in Figure A-3. Each tank in the SBR system is
filled during a distinct period. During this FILL period,
organism selection can be controlled by manipulating
the actual specific growth rates of the microbes and by
regulating the oxygen tension in the reactor (e.g., from
anaerobic to aerobic). After a tank is filled, treatment
continues with the SBR operating as a batch reactor.
During this REACT period, further organism selection is
achieved by controlling the length of time the organisms
are subjected to starvation conditions. After treatment,
the microbes are allowed to separate by sedimentation
during a period called SETTLE. The treated effluent is
subsequently drawn from the reactor during an addi-
tional, distinct DRAW period. The time between FILL
periods for a given tank is called IDLE. Sludge wasting
may take place near the end of REACT or during SET-
TLE, DRAW, and IDLE. FILL and REACT may have
several possible different phases based on aeration and
mixing policies. Overall control of the system is accom-
plished with level sensors an a timing device or micro-
processor. A floating mixer and/or motored decanter is
used, as well as submerged diffusers.
By using a single tank, SBR not only saves the land
requirement (no return activated sludge [RAS] pump
station or clarifiers); it also provides exceptional flexibil-
ity in the readily changeable time and mode of aeration
in each stage. SBR is flexible enough to tolerate load-
ing/flow fluctuations as well as to achieve complete
nitrification/denitrification and phosphorus removal.
A.2.2 Common Modifications
Different operating strategies, multiple-stage SBRs.
A.2.3 Technology Status
Aerated f ill-and-draw reactor technology was developed in
the 1920s. In the 1970s, the latest wave of re-discovering
the fill-and-draw treatment technology was initiated at the
University of Notre Dame. The first full-scale SBR for the
treatment of leachates from a hazardous waste disposal
site was initiated in 1980 (1). Since then, it has become a
well-established technology for a variety of wastewater
and leachate treatment applications. Over 800 full-scale
SBRs have been designed and constructed worldwide.
A.2.4 Applications
Widely used for leachate treatment. Most suitable for
soluble organics and nutrient removal. Treatment of
leachate contaminated with phenols, benzoic acids,
chlorobenzoic acids, other aromatics, halogenated
aliphatics, aliphatics, or general BOD and COD reduc-
tion. This technology has not been widely applied to
low-strength ground-water treatment.
A.2.5 Process Limitations
During FILL, the SBR has the same dilution advantage
as a continuous-flow activated sludge system. As a
result, it is subject to toxic interferences only if it is not
designed properly. Equalization may be required under
highly variable flow and loading conditions, or for treat-
ment of continuous flow with single reactor installation.
A.2.6 Typical Equipment
SBR tank, microprocessor-based control system, float-
ing mixer, floating/motorized decanter, diffused/jet aera-
tion system, air blowers, submersible sludge pumps.
Tank insulation and a supplemental heat source may be
required for winter operation.
-4.2.7 Flow Diagram
Figure A-3.
A.2.8 Chemical Requirements
Nutrients (N or P) if they are not sufficient in the
leachate; polymer may be required for sludge settling.
A.2.9 Design Criteria
Parameter
Range
Reference
Cycles/tank (d'1)
MLSS (mg/L)
SRT (days)
F/M (Ib COD/lb MLVSS/day)
Volumetric COD loading
(Ib COD/1, 000 tfVday)
1-3
3,500-10,000
10-30
0.05-0.54
30-135
2-4
2-4
3, 4
3, 4
2,3
HRT (days)
1-10
2-4
82
-------
Influent and Nutrients
r\
FILL
REACT
SETTLE
Effluent
DRAW
IDLE
_ Waste
** Sludge
Figure A-3. Sequencing batch reactor.
A.2.10 Performance
Compound
COD
SCOD
BODg
SBOD5
TOC
TOX
TSS
NH4-N
NO3-N
TKN
Influent
Strength
(mg/L)
1,000-5,300
8,000
818-6,000
5,200
2,500
325
155-1,500
7-310
332
5-250
Removal
Percentage
(%)
85-92
94
95-99
95-99+
90-95+
28-66
70-99+
74-99+
97+
96-98
Reference
2-4
4
2-4
4
4
2
3
3,4
3
3
A.2.11 Residuals Generated
Aerobic process: 0.1-0.6 Ib sludge/lb COD removed at
about 1.0 percent solids concentration.
A.2.12 Process and Mechanical Reliability
Expected to have high process and mechanical reliabil-
ity; loading/flow fluctuations are generally tolerable.
A.2.13 Environmental Impact
Reactor can be enclosed to minimize venting gas re-
lease. Sludge yield is relatively low.
A.2.14 Energy Notes
For SBR, the aerator and mixer are the major power-
consuming items. The sludge pump and water pump
may add 10 to 20 percent extra. From 0.014 million
, gal/day to 0.167 million gal/day SBR, 500-1,000 hp
power consumption per million gal/day capacity is typi-
cal, but these devices do not run 24 hr/day (3).
A.2.15 Major Cost Elements
For capital costs, see the table on page 84.
Routine O&M includes daily check of equipment status,
sampling and analysis for process parameters and the
effluent, dewatering where applicable, and periodic
maintenance. In all cases, these duties require less than
one full-time operator. Chemical costs are additional.
A.2.16 References
1. Herzbrun, P.A., R.L. Irvine, and K.C. Malinowski. 1985. Biological
treatment of hazardous waste in the SBR. J. Water Poll. Control
Fed. 57:1,163.
2. Ying, W.C., J. Wnukowski, D. Wilde, and D. McLeod. 1992. Suc-
cessful leachate treatment in SBR-adsorption system. 47»i Purdue
Indus. Waste Conf. Proc. 47:502-518.
3. Aqua-Aerobic Systems, Inc. 1994. Design report of recent instal-
lation. Rockford, IL.
4. Harty, M.D., P.G. Hurta, H.P. Werthman, and A.J. Konsella. 1993.
Sequencing batch reactor treatment of high-strength leachate: A
pilot-scale study. In: Proceedings of the Water Environment Fed-
eration 66th Annual Conference and Exposition, Vol. 5. Hazardous
wastes and ground water, pp. 21-31.
83
-------
Capital Costs (2)
Design
ROW S1»d9e
(million Level of treatment (mg/L) Metals De-
gat/day) Removal watering
0.014
0.0167
0.0288
0.043
0.053
0.085
Inf.
Eff.
Inf.
Eff.
Inf.
Eff.
Inf.
Eff.
Inf.
Eff.
Inf.
Eff.
COD BODS
850
10
4,500
200
1,000 500
150 20
5,000
60
4,730 2,350
764 <30
820
<10
TSS
1,500
10
1.000
200
100
20
200
60
-
<200
155
<15
TKN P
332a - N N
10a
300b - N Y
20" -
5 Y Y
-
250 - Y Y
5
552" - N Y
<5» -
yb 4 N Y
<2b <2
Total SBR No.
Building Holding Capital Capital of
Enclosure Tank ($Million) ($Mlllion) Units
N Y 1.0 0.13 1
N Y 7.2 - 2
Y N 1.6 0.16 2
N Y 2.8
Y Y 3.1
N N 1.6 0.36 2
»AsN03-N
"AsNHrN
+ s Plus sludge conditioning and oil/water separation.
[] > Required by state to have 30-day influent and effluent storage capacity.
84
-------
A.3 Powdered Activated Carbon,
Biological (Biophysical)
A.3.1 Technology Description
This biophysical system involves the controlled addition
of powdered activated carbon to an activated sludge
system. The mixture of influent, activated sludge, and
powdered carbon is held in the aeration basin for a
hydraulic detention time adequate for the desired bio-
logical treatment. After aeration, the mixture flows to a
clarifier. Settled solids are fed back to the aeration tank
to maintain the necessary concentrations of microorgan-
isms and carbon, and the clear supernatant is dis-
charged. Fresh carbon is added to the aeration basin at
a rate dependent on influent characteristics and desired
effluent quality. Excess solids are wasted directly from
the recycle stream. Wasted solids can be processed by
simple dewatering and disposal or by wet-air oxidation,
or for destruction of organics and regeneration of the
activated carbon. For small installations, however, car-
bon regeneration is typically handled off site. The pow-
dered activated carbon system is also operated in
fill-and-draw mode, similar to SBR operation.
The powdered activated carbon system combines
physical adsorption with biological treatment, achieving
a higher degree of treatment than possible by either
mode alone. The presence of carbon in the aeration
basin removes some refractory organics that are difficult
for microorganism to attack, enhances solids settling,
and buffers the system against loading fluctuation and
toxic shocks.
By using the fill-and-draw operating mode, the system
provides exceptional flexibility because of the readily
adjustable time and aeration mode in each stage, which
is important for treatment of leachate with variable com-
position and strength.
A.3.2 Common Modifications
Different operating strategies, continuous or batch sys-
tems, multiple-stage powdered activated carbon, aero-
bic/anaerobic powdered activated carbon. Pretreatment
units of metal precipitation, oil/water separation, and
postcarbon adsorption.
A.3.3 Technology Status
The practice of adding powdered carbon into the acti-
vated sludge process was started during the early
1970s. Applications in leachate treatment started in the
1980s.
A.3.4 Applications
Widely used for leachate treatment and high-strength
ground water (particularly with low BOD to COD ratio).
Most suitable for soluble organics and nutrient removal.
Better color and refractive organics removal than con-
ventional process. Treatment of leachate contaminated
with phenols, other aromatics, volatile acids, halogen-
ated aliphatics, aliphatics, color removal, or general
BOD and COD reduction.
A.3.5 Process Limitations
Metals removal may require pretreatment. Other appli-
cations may require equalization tank, oil/water separa-
tor, sludge dewatering, postcarbon adsorption or filter.
Certain applications may require off-gas control system.
May be unsuitable for low-strength ground water (COD
<40 mg/L).
A.3.6 Typical Equipment
Aeration contact tank, hydraulic carbon delivery system,
microprocessor-based control center, aeration blower,
decanter (for batch reactor) or clarifier (for continuous
reactor), air diffuser and internal air piping, submersible
or other type sludge pumps.
A.3.7 Flow Diagram
Figure A-4.
A.3.8 Chemical Requirements
Nutrients (N or P) if they are not sufficient in the
leachate; chemicals if metal precipitation is required.
A.3.9 Design Criteria
Leachate
Parameter
Carbon dosage (mg/L)
MLSS (mg/L)
SRT (days)
F/M (Ib BOD/lb MLVSS/day)
Maximum COD loading
(Ib/1,000ft3/day)
Maximum cycle (days)3
Minimum cycle time (hr)a
HRT (days)
Maximum clarifier overflow
rate (gal/day/ft2)''
Range
50-10,000
2,000-11,000
10-20
0.05-0.3
200
2-5
4.8
1-16
480-520
Reference
1-5
1
1-3,5-6
7
2,7
7 '
1,2,5-7
6
3 Batch operation mode parameters
Continuous operation mode parameter
85
-------
Virgin
Carbon
Storage
V n
\A/i"tn w T ^^ I 1
Waste ^ * ^-1 : .; ; .; { { .; { •
A U 1 ::••::::
I 1 •* ' •* •' *' •* * *
Contact-Aer
Tank
Carbon F
|"""^"| Polyelectrolyte
1 1 Storage
VvX Settling Tank Filtration
| Q (Optional)
T I ^1 II 1 ^
4^ l^^^J -^-:
ation &$$Ł
Recycle 1 '
i_^
Thickener
O ««
^ • 1 1^
< \- ir
^5&
t- 1
3*
To regeneration
Figure A-4. Powdered activated carbon system general process.
Ground Water Ground Water
Parameter Range Reference _^_ •— Remova, ^^
Carbon dosage (mg/L) 10-100
MLSS (mg/L) 4,000-20,000
SRT(days) 10-30
F/M (Ib BOO/lb MLVSS/day) 0.1-0.7
Maximum COD volumetric 200
loading (Ib COD/1,000 ftVday)
HRT (days) 0.5-2
Maximum cycle (days)8 5
Minimum cycle time (hr)a 4.8
COD 364-11,500 72-99% 8, 10-14
BODS 130-8,260 83-99% 8,11,13,14
Total BTEX 0.75-9.9 93-99%+ 11
NH4-N 200 75-94% 10-12
, o
8 A.3.11 Residuals Generated
9 Aerobic process: about 0.24-0.3 Ib sludge/lb COD
g removed (8)
» Batch mode operating parameters ^ 3 ^ process and Mechanical Reliability
A.3.10 Performance EExpected to have high process and mechanical reliabil-
ity. Unit has some tolerance to loading and flow fluctua-
Leachate tions.
Influent Removal
Compound (mg/L) (%) Reference ^ ff ^ Fnvir^nm9nffll |m/,a/,f
COD 870-3,237 67-99%+ 1-3,5-7,9 The presence of carbon may reduce stripping of VOCs.
BODS 53-1 ,600 90-99%+ 1 , 2, 5-7, 9 Aeration tank can be enclosed and off-gas treated, when
NH4-N 26-315 82-99%+ 3,5,6,9 needed.
on and grease so 93% 1 ^3M Major Cost Elements
Volatile organic acids 20 99% 1
„„„. H See tables on page 87.
Volatile orqanlc >3 99% 1 K M
compounds
86
-------
Leachate
Design
Flow
(million/
gal/day)
0.035a
Inf
Eff.
0.040" Inf.
Eff.
0.033° Inf
Eff.
Metals Sludge
Level of Treatment (mg/L) Removal Dewatei
COD
843
600
COD
1,812
75
COD
1,150
400
BODS
406
300
BODg
916
<10
BODS
600
<10
TSS
62
50
VGA
20
0.02
TSS
300
<20
O&G
150
5
O&G
30
2
O&G
30
<1
unit Ing
Phenolics
1.42
0.05 No Yes
VOC
>3
0.02 Yes Yes
NH3-N
80
<1 No No
O&M O&M
r- System Capital ($1,000 ($1,000 Refer-
Mode ($Million) IbCOD) gal) ence
Batch 0.37 28 4.3 15
Con- - 1.7-2.0 25-30 1,2
tinuous
Bateh 0.27 0.13 1 2 15
i o,,o*=^ „!.,,»„«» V I-;;' —--»•«•»«»- w,^,, ay*mi,, ^uuiiutyo, uiuwers, pumps, insiruments/contro s, MCC, e.
mentTnd Ss dewatering ' ^^ ^^ ^^ *"* ™™9 S8tViCeS' "° building' ™e °&M cost °overs the l
No capital cost information is available. All tanks are covered
«"» carb°" feed •»*"". °&M manuals, startup and training
Ground Water
Design
Flow
(million/
gal/day)
Level of Treatment (mg/L)
Sludge
De- Carbon
water- Solids Regener- Capital
ing Disposal ation ($Million)
O&M O&M
($/lb ($1,000 Refer-
COD) gal) ence
1-8a COD NH3-N OCA DCB
Inf. 6,000 200 53 12
Eff. <100 <10 <0.01 0.002
No
Yes Yes -b (Con- 0.04- 2-3 10, 12
tinuous) 0.6
uu,,uu»ueauiioin,
87
-------
A3.75 References
1. Lebel, A., R. Meeden, and B. Stirrat. 1988. Biophysical treatment
facility for hazardous waste landfill leachates. Presented ait the
Water Pollution Control Federation Conference, Dallas, TX.
2. McShane, F.S., A. Lebel, E.T. Pollock, and A.B. Stirrat. 1986.
Biophysical treatment of landfill leachate containing organic com-
pounds. 41st Purdue Indus. Waste Conf. Proc.
3. Zimpro Report 1991. Landfill leachate treatment: Innovations in
South Valley (Burlington County Case). Reactor.
4. Depuydt, T.K., A. Higgins, and R. Simpkins. 1991. Innovation
technologies for solid waste management and leachate treatment
at the Burlington County, New Jersey, resource recovery facilities
complex. Presented at the Canadian Waste Management/Waste
Technology '91 Conference.
5. Copa, M.W., and A.J. Meidl. 1986. Powdered carbon effectively
treats toxic leachate. Poll. Engin. 7.
6. Zimpro Brochure. 1985. Package PACT system.
7. Zimpro Brochure. 1986. Factory assembled batch PACT system.
8. Su, Y.B., K.J. Berrigan, and A.A. Shayer. 1991. Treatment of
ground water contaminated with organics at an adhesives pro-
duction facility. Presented at the Superfund '91 Conference,
Washington, DC.
9. Zimpro Brochure. 1991. Leachate treatment system. Bulletin LL-
100.
10. Zimpro Brochure. 1989. PACT system for ground-water treat-
ment. Bulletin HT-302.
11. Zimpro Technical Report. Contaminated ground-water project.
12. Meidl, A.J., and L.R. Peterson. 1987. The treatment of contami-
nated ground water and RCRA wastewater. Presented at the 4th
National RCRA Conference on HMCRI, Washington, DC.
13. Zimpro Report. 1992. Ground-water remediation. Reactor.
14. HAZMAT World. 1993. Biophysical system treats ground water.
HAZMAT World, p. 84
15. Zimpro Technical Report. Recent cost comparison (unpublished).
A.3.16 Additional Sources
1. Zimpro Report 1992. Bostik PACT system. Reactor.
2. Zimpro Report. 1983. Bofors-Nobel landfill leachate treatment
Reactor.
3. Zimpro Report 1992. Landfill leachate treatment. Reactor.
88
-------
A.4 Rotating Biological Contactor
A.4.1 Technology Description
The rotating biological contactor (RBC) is an aerobic
fixed-film biological treatment process. The RBC con-
sists of a series of closely spaced plastic (polystyrene,
polyvinyl chloride, or polyethylene) disks on a horizontal
shaft. The assemblage is mounted in a contoured-
bottom tank to partially immerse (about 40 percent) the
disks in the waste stream. The disks, which develop a
slime layer over the entire wetted surface, rotate slowly
through the wastewater and alternately contact the
biomass with the organic matter in the waste stream and
then with the atmosphere for absorption of oxygen. Ex-
cess biomass on the media is stripped off by rotational
shear forces, and the stripped solids are held in suspen-
sion with the wastewater by the mixing action of the
disks. The sloughed solids are carried with the effluent
to a clarifier, where they are settled and separated from
the treated waste. Staging, which employs a number of
RBCs in series, enhances biological treatment effi-
ciency, improves shock-handling ability, and could aid in
achieving nitrification.
RBCs provide a greater degree of flexibility for meeting
the changing needs of a leachate treatment plant than
do trickling filters. The modular construction of RBCs
permits their multiple staging to meet increases or de-
creases in treatment demands.
Factors affecting the treatment efficiency of RBC sys-
tems include the type and concentration of organics
present, hydraulic residence time, rotational speed, me-
dia surface area exposed and submerged, and pre- and
posttreatment activities.
A.4.2 Common Modifications
Multiple staging; use of dense media for latter stages in
train; use of molded covers or housing of units; various
methods of pretreatment and posttreatment of waste-
water; use of air-driven system in lieu of mechanically
driven system; addition of air to tanks; addition of chemi-
cals for pH control; and sludge recycle to enhance
nitrification.
A.4.3 Technology Status
RBCs were first developed in Europe in the 1950s.
Commercial applications in the United States did not
occur until the late 1960s, mostly for municipal and
industrial wastewater. EPA sponsored several treatabil-
ity studies for RBC treating leachate in the 1980s. There
have been rare applications since then.
A.4.4 Applications
Widely tested for leachate treatment but with few instal-
lations. Suitable only for soluble organics, and adequate
for nitrification. Effective for treating solvents, halogen-
ated organics, acetone, alcohols, phenols, phthalates,
cyanides, ammonia, and petroleum products. No appli-
cations for ground-water treatment have been identified.
A.4.5 Process Limitations
Low-rate system, limited loading capacity, and not effi-
cient for degrading refractory compounds or removing
metals. Toxic constituents (such as heavy metals, pes-
ticides, etc.) may require pretreatment. Use of dense
media in earlier stages can result in media clogging.
Off-gas treatment may be required if aeration is pro-
vided. May require supplemental aeration and alkalinity
addition. Vulnerable to climate changes and low tem-
perature if not housed or covered. Not suitable for treat-
ment of low-strength ground water (less than 40 mg/L
BOD5).
A.4.6 Typical Equipment
Rotating disk system, tank, clarifier, hydraulic delivery
system, water pumps, sludge pumps.
A.4.7 Flow Diagram
Figure A-5.
A.4.8 Chemical Requirements
Nutrients (N or P) if they are not sufficient in the leachate
or ground water; alkalinity adjustment chemicals.
A.4.9 Design Criteria
Parameter
MLVSS (mg/L)
MLVSS (mg/L)
F/M (Ib BOD/lb MLVSS/day)
Maximum BOD volumetric
loading (Ib BOD/1,000 flrVday)
Maximum BOD surface
loading (Ib BOD/1,000 ft2/day)
Number of stages per train
Range
3,000-4,000
1,500-3,000
0.05-0.3
15-60
0.05-0.7
1-4
Reference
11
1
2
1
2
Hydraulic surface loading
(gal/day/ft2)
HRT (days)
0.3-1.5
1.5-10
89
-------
Shaft Drive
Primaiy Effluent
Shaft Orientation*
To Secondary Clarifier
'Alternative shaft orientation is parallel to direction of flow with a
common drive for all the stages in a single train.
Figure A-5. Typical staged rotating biological contactor configuration.
A.4.10 Performance
Compound
SCOD
SBODS
TBODs
TOO
DOC
NH4-N
Influent
(mg/L)
800-5,200
100-2,700
3,000
2,100
300-2,000
100
Removal
(%)
55-99
95-99+
99+
99
63-99
80-99
Reference
1,3-5
1, 3-5
3
3
3-5
1, 2
A.4.11 Residuals Generated
Aerobic process: 0.2-0.5 Ib/lb COD removed at about
2.0 percent solids concentration.
A.4.12 Process and Mechanical Reliability
Expected to have high process and mechanical reli-
ability.
A.4.13 Environmental Impact
Reactor can be enclosed to minimize off-gas release.
A.4.14 Major Cost Elements
The construction cost of RBC is estimated to be about
$0.6 million per million gal/day capacity (using ENR
index of 2,475). Costs include RBC disks, RBC shafts
(standard media, 100,000 ft2/shaft), motor drives (5
hp/shaft), molded fiberglass covers, and reinforced con-
crete basins; clarifiers are not included, assuming a
surface loading rate of 1.0 gal/day/ft2 and carbonaceous
oxidation only. O&M costs are estimated at $0-01 to $0.1
million per million gal/day capacity (using ENR index of
2,475). Specific applications to leachate or ground-
water treatment will yield different costs, but no such
data are available at present.
A.4.15 References
1. Lugowski, A., D. Haycock, R. Poisson, and S. Beszedits. 1990.
Biological treatment of landfill leachate. 44th Purdue Indus. Waste
Conf. Proc. 44:565-571.
2. U.S. EPA. 1990. Innovative and alternative technology assess-
ment manual. EPA/430/9-78/009.
3. Opatken, J.E., K.H. Howard, and J.J. Bond. 1989. Biological treat-
ment of leachate from a Superfund site. Environ. Progress 8(1):12-
18.
4. Opatken, J.E., K.H. Howard, and J.J. Bond. 1988. Stringfellow
leachate treatment with RBC. Environ. Prog. 7(1).
5. U.S. EPA. 1988. Stringfellow leachate treatment with RBC.
EPA/600/D-88/013.
A.4.16 Additional Sources
1. U.S. EPA. 1987. Handbook on treatment of hazardous waste
leachate. EPA/600/8-87/006.
2. U.S. EPA. 1992. Rotating biological contactors. Engineering Bul-
letin. EPA/540/S-92/007.
90
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A.5 Aerobic Fluidized Bed Biological
Reactor
A.5.1 Technology Description
An aerobic fluidized bed biological reactor (FBR) is a
fixed-film biological treatment technology. The microor-
ganisms are grown on either granular activated carbon
(GAG) or sand media. Dedicated pumps provide desired
fluidization and control the reactor internal flux. Influent
enters the bottom of the reactor through a distributor,
which is designed to provide uniform fluidization of the
media and to prevent short-circuiting or plugging. The
media bed expands farther as the biofilm grows in thick-
ness and reduces the media density. An internal growth
control system intercepts the rising bed at a desired
height, removes the bulk of biomass from the particle,
and returns the media back to the reactor. The aero-
bic/GAC FBR is most widely used for ground-water
treatment. In a proprietary system design, an oxygen
preparation unit enriches the oxygen in the air supply to
about 90 percent, and the oxygen-enriched air is then
predissolved in the influent.
Using GAC media integrates biological removal and
carbon adsorption, which has the advantage of tolerat-
ing loading or flow fluctuations, and may speed system
startup, compared with other types of media. The fluidi-
zation and high oxygen transfer capacity in the aero:
bic/GAC FBR make the process extremely efficient. The
high surface area of the media supports a reactor
biomass concentration three to 10 times greater than in
conventional suspended growth processes. The vertical
installation and high loading capacity reduce the land
requirement. The short hydraulic retention time makes
this process suitable for low to moderate levels of con-
taminated ground-water treatment. Typically, GAC offers
easier/faster startup than the sand media.
A.5.2 Common Modifications
Anoxic, anaerobic process; combination of aerobic/an-
oxic; sand/GAC media.
A.5.3 Technology Status
The technology was developed in the 1970s.
A.5.4 Applications
Most suitable for soluble organics. Aerobic/GAC FBR
has been widely used for treatment of ground water
contaminated with BTEX, other aromatics, halogenated
aliphatics, aliphatics, or general BOD and COD reduc-
tion. This technology has not been widely applied to
leachate treatment.
A.5.5 Process Limitations
Free products may simply pass through or cover the
biofilm surface. Iron levels above 20 mg/L may require
pretreatment to avoid plugging problems. Calcium and
magnesium may cause scaling problems. Not designed
for TSS removal; pretreatment is required for influent
containing high solids content. GAC FBR is not efficient
for low-yield, nonbiodegradable organics because it is
often operated as a high loading system and has very
short retention time.
A.5.6 Typical Equipment
General: fluidization reactor and internals, reactor hy-
draulic distribution system, internal growth control sys-
tem, weir/baffle, and nutrient feed system. Aerobic mode
addition: oxygen source or preparation unit, pressurized
bubble contactor, and dilution chamber. Anoxic: supple-
mental carbon source feed system as needed.
A.5.7 Flow Diagram
Figure A-6.
A.5.8 Aerobic/GAC FBR Reactor Sizing
Figure A-7 provides a general sizing curve for BTEX
treatment in GAC/FBR based on flow rate, at 35 mg/L
influent COD and 14-foot design bed height. The curve
would be different for other contaminants or COD levels.
A.5.9 Chemical Requirements
Aerobic process: nutrients (N or P) if not sufficient in the
ground water.
Anoxic process: external carbon source if needed.
A.5.10 Design Criteria
Maximum loading Aerobic process: 400 Ib COD/1,000 ff/day
Anoxic process: 300-500 Ib NO3-N/1,000 ff/day
Minimum HRT 5-10 minutes
A.5.11 Performance
Compound
Total BTEX
Total volatile
hydrocarbons
Influent
Range
(mg/L)
2.0-7.8
9.42
Removal
Range (%)
99-99+
99+
Reference
2-7
7
A.5.12 Residuals Generated
Aerobic process: 0.3-0.5 Ib sludge/lb COD removed at
about 1 to 2 percent solids concentration.
91
-------
Water Level
Nutrient
Feed
Equalization
Tank
-R-
Fluidization
Basket Fluidization Flow
Strainer pumps Contro1
Valve
0
Produced
Ground-Water
Wells
Figure A-6. Aerobic fluldized bed biological reactor (1).
10,000 •
9,000 •
<2»
*g 8,000 •
^8j 7,000 •
j| 6,000 •
•g 5,OOO •
&
u. 4,000 •
5 3,000 '
1,000 •
n .
X
s
X
/
/
s
/
/
/
y
/
/
/
/
/
2
Reactor Diameter (ft)
Figure A-7. Fluid bed sizing curve, ground-water aerobic
application (1).
Anoxic process: 0.6-0.8 Ib sludge/lb nitrate nitrogen re-
moved at about 1 to 2 percent solids concentration.
A.5.13 Process and Mechanical Reliability
Expected to have high process and mechanical reliabil-
ity. Single or dual reactor design provides on-line reli-
ability and flexibility. GAG FBR offers the advantage of
stable performance under fluctuating loading conditions.
Effluent
A.5.14 Environmental Impact
Applying oxygen enriching and predissolving mecha-
nism, GAC/FBR minimizes off-gas generation. In low-
strength ground-water application, only nominal carbon
replacement is needed to compensate for physical loss.
A.5.15 Major Cost Elements
Capital costs (as shown in Figure A-8) include all gen-
eral equipment listed above plus carbon media, general
engineering, and startup cost. The costs do not include
intake and discharge piping, sludge dewatering, and
building. Estimation is based on 35 mg/L influent COD
and bed height of 14 feet (4.3 m).
Energy cost (as shown in Figure A-9) is based on the
electrical power consumption for fluidization pumps, in-
ternal growth control system, air compressor and prepa-
ration systems, and control system.
Labor cost is estimated at 0.5 to 1.5 full-time operator
and chemist. Duties include daily maintenance checkup,
sampling, and routine analysis.
A.5.16 References
1. Envirex Design Criteria. 1994.
92
-------
10.00.
1.00
0.10
100
1,000
Feed Flow Rate (gal/min)
10,000
Figure A-8. Granular activated carbon/fluid bed budgetary price,
ground-water aerobic application (1).
1,000.
,100
LU
"a
10
100
1,000
Influent Flow (gal/min)
10,000
Figure A-9. Granular activated carbon/fluid bed energy require-
ment, influent flow versus operational energy (1).
2. Mueller, R.G., T.R. Sun, and W.G. Edmunds. 1990. Treatment of
ground waters containing aromatic hydrocarbon in a GAG fluidized
bed biological reactor. Presented at AlChE Summer National Meet-
ing, San Diego, CA.
3. Hickey, F.R., D. Wagner, and G. Mazewski. 1990. Combined bio-
logical fluid bed-carbon adsorption system for BTEX-contaminated
ground-water remediation. Presented at the 4th National Outdoor
Action Conference on Aquifer Restoration, Ground-Water Monitor-
ing, and Geophysical Methods, Las Vegas, NV.
4. Perpich, W., Jr., and R. Laubacher R. 1992. Implementation of
GAC fluidized bed reactor (GAC-FBR) for treatment of petroleum
hydrocarbons in ground water at two BP oil distribution terminals,
pilot and full scale. Presented at the International Symposium on
the Implementation of Biotechnology and Industrial Waste Treat-
ment and Bioremediation, Grand Rapids, Ml.
5. Gerbasi, J.P., J.K. Smith, and J. Fillos. 1991. Biological treatment
of petroleum hydrocarbons. Presented at the NWWA/API Petro-
leum Hydrocarbons and Organic Chemicals in Ground Water Con-
ference, Houston, TX.
6. Laubacher, C.R., E.B. Blackburn, L. Rogozinski, and W. Perpich,
Jr. 1993. Emissionless ground-water treatment using a biological
fluidized bed reactor (FBR). Presented at the API/National Ground
Water Association Petroleum Hydrocarbon Conference, Houston,
TX.
7. Hickey, R., A. Sunday, D. Wagner, B. Heine, V. Grshko, D.T. Hayes,
and G. Mazewski. 1993. Applications of the GAC-FBR to gas in-
dustry wastestreams. Presented at the 6th International IGT Sym-
posium on Gas, Oil, and Environmental Biotechnology, Colorado
Springs, CO.
A.5.17 Additional Sources
1. Envirex Report. 1992. GAC fluid bed skid-mounted systems.
2. Mazewski, G., J. Tiffany, and S. Hanson. 1992. Experiences with
GAC-fluid bed biorestoration of BTEX-contaminated ground wa-
ters. Presented at the International Symposium on the Implemen-
tation of Biotechnology and Industrial Waste Treatment and
Bioremediation, Grand Rapids, Ml.
3. McSherry, P.M., M.G. Davis, and J.R. Falco. 1992. Measurement
of VOC emissions from wastewater treatability units. Presented at
the Air and Waste Management Association 85th Annual Meeting
and Exhibition, Kansas City, MO.
93
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Physical/Chemical
A.6 Air Stripping
A.6.1 Technology Description
Stripping occurs when a gas, such as air or steam, is
introduced into a water containing volatile constituents.
Volatile organic compounds (VOCs) are released from
the water phase to the gas phase, proportional to the
differential in concentration of the volatile constituent
between the two phases. The interphase transfer of a
VOC will continue until equilibrium is established. At
equilibrium, the concentration (or partial pressure) of, a
substance in the gas phase is proportional to its concen-
tration in the liquid phase. This relationship is known as
Henry's Law, and is unique for each compound. Air
stripping involves optimization of Henry's Law to transfer
aqueous contaminants into an air phase. The contami-
nated air may be released or can be treated by flaring
or other oxidation method, by activated carbon adsorp-
tion or by scrubbing. The air stream must be reduced to
between 40 and 50 percent humidity before entering the
carbon adsorption system.
The residual concentrations of volatile contaminants
that remain in the water phase depend in part on system
temperature, total pressure, and molecular interactions
occurring between the dissolved contaminants) and water.
The rate of transfer of VOCs can be modeled using
Pick's Law:
TVOC = ~Ki.avoc (C-Cs)i (')
where
rvoc = rate of VOC mass transfer (ng/ft3 • h)
Ki.a = overall VOC mass transfer coefficient (h'1)
C = concentration of VOC in liquid dig/ft3)
Cs = saturation concentration of VOC in
liquid (ug/ft3)
Values for KLa can be found in the literature for many
specific compounds.
The saturation concentration of the VOC, Cs, is a func-
tion of the partial pressure of the VOC in the gas phase
in contact with the wastewater. This relationship is given
by Henry's Law as
Typically, Henry's Law constants (H) are tabulated in
units of volume x pressure/mole. A value of H0 is then
calculated from
7^ = no.
Cs
where
Cg = concentration of VOC in gas phase (u.g/ft3)
HO = Henry's Law constant (unitless)
(2)
LJ _ ' j_
HC-RT,
(3)
where R is the ideal gas law constant and T is the
absolute temperature.
A.6.2 Process Flow Diagram
A schematic of an air stripper is shown in Figure A-10.
Contaminated water is pumped to a storage tank (Point
1) along with any recycle from the air stripper. Water
from the storage tank is then fed to the air stripper (Point
3) at ambient temperature, although in some cases the
feed stream may be heated in a heat exchanger (Point
2). If required, the liquid effluent from the air stripping
tower is further treated (Point 4) with carbon adsorption
or other appropriate technologies. The off-gas can also
be treated (Points), using gas phase carbon adsorption,
thermal incineration, or catalytic oxidation (1).
A.6.3 Pretreatment Requirements
To avoid fouling column packing, obtain uniform flow,
and maintain evenly distributed contaminant concentra-
tions, influent ground water or leachate may be pre-
treated using the following unit operations:
• Hydraulic and/or waste strength equalization, to ad-
just for variable flow and contaminant concentrations
(2).
• TSS removal by settling, filtration, skimming, etc.
« Separation of immiscible liquids (LNAPL, DNAPL) by
gravity separation or flotation.
• Iron/manganese or hardness removal by precipitation
or ion exchange.
• Dissolved heavy metals removal by precipitation or
ion exchange.
• pH adjustment to minimize precipitation of dissolved
metals, biological fouling, and corrosion, and possibly
enhance system performance.
• Disposal of TSS and chemical precipitation treatment
sludges, LNAPL, DNAPL, and any other waste pre-
treatment residuals.
A.6.4 Parameters of Interest
Several significant parameters for design and process
control, in addition to flow, are listed in Table A-1.
94
-------
Off-Gas Treatment
(5)
| Stripper
I Off-Gas
Gas
Liquid
Inlet Water
Contaminated
Ground Water
or .
Surface Water
Pre-
treatment
Storage
Tanks
.(1)
Feed
Heat
Exchangers
(Optional)
Support
ci naie
Air
Stripper
(3)
MMpflJtl — Water
JKfelM Distribution
\ / Packing
/\ ~| — Media
JB^JI Air
[ Effluent Water
Recycle (Optional)
Treated Liquid
Figure A-10. Air stripping system.
Table A-1. Significant Treatment Parameters for Design of Air
Stripping Units
Parameter
Rationale
Contaminants Only VOCs and some SVOCs with
present H^O.003 can be removed by air stripping.
Other dissolved chemicals can degrade
effectiveness of stripper by fouling or
precipitating on packing material.
Contaminant For given operating conditions, an air
concentration stripper provides a fixed chemical-
dependent removal efficiency. The variation
in the influent concentration must be known
to determine the maximum target removal
efficiency for the chemical chosen.
Temperature Temperature is an important determinant of
removal efficiency. Henry's Law constants
depend on the water temperature. Freezing
conditions may foul packing.
Composition Some naturally occurring constituents, such
as iron or calcium carbonate, can foul or
plug air stripper media.
Water pH Precipitation of certain metals depends
strongly on the solution pH.
Target effluent For this technology, a suitable VOC with a
concentration target removal efficiency can be selected as
the basis for designing an air stripper.
A.6.5 Applications and Design Considerations
The design of air strippers is based on the type of
contaminant present, the contaminant concentration,
the required effluent concentration, water temperature,
and water flow rate. Major design variables include gas
pressure drop, air-to-water ratio, hydraulic loading rate,
and type of packing (1). Example design parameters (3)
are listed in Table A-2 for several common ground-water
organic contaminants.
Goodrich et al. (4) have presented several example
applications of air stripping for ground water using a
packed tower (see Table A-3). Table A-3 compares influ-
ent concentrations versus several design parameters.
Air stripping applications for leachates that contain high
VOC concentrations have also been recommended (5).
A second type of stripping device is a "low profile"
stripping unit. Low profile tray air strippers have
smaller dimensions than the conventional packed
tower. One example configuration is a modular design
in. which the trays are inside a fitted rectangular
shaped tower, shown schematically in Figure A-11.
The trays are made of sheet metal (aluminum or
steel). The tower itself is less than 6 feet tall. Low
profile strippers have been used with liquid flow rates
of 600 to 1,600 ft3/min. Because these systems use
high air-to-water ratios, they are best suited for treat-
ment of water containing highly volatile organic com-
pounds. Several advantages include lower pressure
pumps, better liquid distribution characteristics, low
maintenance, resistance to fouling, lower buildings for
enclosure, increased retention time, and portability.
One disadvantage may be the higher operating costs
associated with the high blower power needed to
overcome the high static head of moving air through
layers of water.
A.6.6 Major Cost Elements
Figures A-12 and A-13 present estimated capital costs
and annual O&M costs associated with 99 percent re-
moval of several VOCs and radon using packed tower
air stripping. The costs presented are a function of daily
flow, in millions of gallons per day.
A.6.7 Residuals Generated
The primary residual generated by an air stripping
process itself is the contaminated off-gas stream. VOC
95
-------
Table A-2. Typical Air Stripping Design Parameters for Removal of 12 Commonly Occurring
Volatile Organic Chemicals9 (3)
Henrv's Law Air-to-Water
Compound
Benzene
Carbon tetrachloride
Chlorobenzene
1 ,2-Dichlorobenzene
1,2-DIchloroethylene
cls-1 ,2-Dtohloroethylene
Dichloromethane
Tetrachloroethylene
Toluene
1,1,1 -Trichloroethane
Trichloroethylene
m-Xylene
Constant
0.106
0.556
0.069
0.090
0.023
0.093
0.048
0.295
0.117
0.172
0.116
0.093
Ratio
32.7
6.2
50.3
38.7
150.6
37.1
71.6
11.8
29.6
20.1
29.9
37.3
Air Stripper
Height ft (m)
36.2 (10.9)
44.9 (13.5)
37.6 (11.3)
40.4 (12.1)
33.5 (10.0)
34.9 (10.5)
28.6 (8.6)
43.8 (13.1)
39.0 (11.7)
40.1 (12.0)
38.0 (11.4)
40.5 (12.1)
a Water flow rate, 2.16 million gal/day (8.17 x 106 L/day); inlet water concentration,
treatment objective, 1.0 ng/L; air stripper temperature, 50°F (10°C); air stripper
drop, 50.0 (N/m2)/m packing; air stripper packing, 3-in. plastic saddles.
Diameter of
Packed
Column ft (m)
8.4 (2.5)
5.0(1.5)
22.7 (6.8)
8.9 (2.7)
14.9 (4.5)
8.7 (2.6)
11.1 (3.3)
6.0(1.8)
8.1 (2.4)
7.1 (2.1)
8.1 (2.4)
18.3 (5.5)
100.0 ng/L; water
packing pressure
Table A-3. Applications of Packed Tower Aeration (4)
Location
(Number of
Towers)
Hartland, Wl (1)
Schoefield, Wl (1)
Rothschild, Wl (2)
Wausau, Wla (2)
Elkhart. IN* (3)
Total Influent
Flow (million
gal/day)
1.4
1.1
4
8
10
Contaminants
TCE, PCE, DOE
TCE, PCE, DOE,
TCA
TCE, PCE, DCE,
benzene
TCE, PCE, DCE
TCE, carbon
tetrachloride
Concentration
(H9/L)
170
100
100
200
100
Tower Air-
to-Water
Ratio
50:1
28:1
40:1
35:1
30:1
Tower
Height (ft)
35
40
55
25
55
*Superfund site
emissions from a stripping tower are calculated with the
formula (3)
Emission rate (Ib/hr) = (C1-C2) * V * (5E-7), (4)
where
C1 = influent concentration of the VOC (ug/L)
C2 3 effluent concentration of the VOC (ug/L)
V = water flow rate (gal/min)
Often, off-gas treatment, such as by dehumidification
followed by gas-phase carbon adsorption, is employed
to segregate contaminants from the off-gas stream. Al-
ternatively, if the gas has a high BTU content, it may be
piped to a flare or incinerated, if properly permitted.
Other options include catalytic oxidation and scrubbing.
A.6.8 References
1. U.S. EPA. 1991. Air stripping of aqueous solutions. EPA/540/2-
91/022. Washington, DC.
2. Patterson, J.W., and J.P. Menez. 1984. Simultaneous wastewater
concentration and flow rate equalization. Environ. Prog. 3:81-87.
3.' U.S. EPA. 1990. Technologies for upgrading existing or designing
new drinking water treatment facilities. EPA/625/4-89/023. Cincin-
nati, OH.
4. Goodrich, J.A., B.W. Lykins, Jr., R.M. Clark, and E. Timothy Oppelt.
1991. Is remediated groundwater meeting SDWA requirements?
JAWWA 83:55-62.
5. Eckenfelder, W.W., Jr., and J.L Musterman. 1994. Leachate treat-
ment technologies to meet alternative discharge requirements.
Nashville, TN: Eckenfelder, Inc.
96
-------
Influent.
Off-gas
Air
Figure A-11. Low-profile tray-type air stripper.
100
10
to
O
0.1
0.01
Trichlorethylene
Vinyl Chloride/Radon
0.1 1 10
System Capacity (million gal/day)
Effluent
100
Rgure A-12. Capital cost curve for 99-percent removal of sev-
eral VOCs and radon using packed tower aeration,
in 1989 dollars (3).
1,000
I 100
J
5.
•a
8
I 10
Trichloroethylene
Vinyl Chloride/Radon
.' X
X
.'
,'' X
X
0.1
1 10
System Capacity (million gal/day)
100
Figure A-13. O&M cost curve for 99-percent removal of several
VOCs and radon using packed tower aeration, in
1989 dollars (3).
97
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A.7 Activated Carbon
A.7.1 Technology Description
Activated carbon is effective in removing many contami-
nants from leachate and ground water. Removal is ac-
complished by adsorption, which is a phenomenon of
physical attraction of molecules to the surface of the
carbon. Activated carbon is made from coal, wood, coke,
or coconuts, and has over 100 m2 of surface area per
gram. Adsorption capacities of 0.5 to 10 percent by
weight are typical, and the carbon can be regenerated
for reuse.
Activated carbon purifies ground water or leachate di-
rectly when the water is pumped through containers of
liquid-phase carbon. If air stripping or soil vapor extrac-
tion is used as the primary means of water purification,
activated carbon may be used to remove the contami-
nants from the air discharge. In this case, the off-gases
are passed through vapor-phase carbon.
Permanent carbon treatment systems use carbon steel
vessels that are epoxy lined. Disposable carbon canis-
ters are also available. Drum sizes can contain from 150
to 2,400 Ib of carbon for liquid- or vapor-phase use. The
canisters are suitable for shipment and disposal, and are
easily handled by fork truck. Other types of containers
are available with hopper bottoms for removal of the
carbon for regeneration. Carbon vendors will exchange
spent carbon with fresh carbon. Large carbon vessels
are drained and refilled with bulk carbon from tank trucks
or on-site carbon storage silos. On-site regeneration
may be cost-effective for large users of carbon.
A.7.2 Process Flow Diagram
Carbon canisters can be piped for upflow, downflow,
parallel, or series operation. A typical carbon process
flow diagram is presented in Figure A-14.
A. 7.3 Application
Many organic compounds and some metals are re-
moved from contaminated ground water and leachate
by activated carbon.
Contaminated
Ground Watar or
Loachata
4
Sample
Valve
igr
To
Discharge
A. 7A Pretreatment Requirements
Water high in suspended solids (>50 mg/L) should be
filtered before activated carbon treatment (1). The car-
bon surface provides an ideal condition for bacterial
growth. Jn some cases, growth of bacteria may become
excessive. In these cases, pretreatment is necessary to
minimize operating problems.
A. 7.5 Parameters of Interest
Some parameters of interest that may assist in the
selection of activated carbon systems are shown below.
Contaminant data Type and concentration of pollutants to be
removed; required removal efficiency;
suspended solids in feed stream.
Iodine number Quantity of iodine adsorbed (mg) by 1 g of
carbon, usually 900-1,100.
Carbon isotherm data Lab tests that predict the amount of
specific contaminant adsorbed per gram of
carbon.
Carbon selection Bituminous, lignite, coconut, wood, etc.
A. 7.6 Design Considerations and Criteria
Breakthrough is defined as the volume of water that has
passed through the carbon bed before the maximum
allowable concentration appears in the effluent. Provide
sample valves in the piping along the carbon vessels to
monitor for breakthrough. For canister applications, ar-
range piping, valves, and connections to allow replace-
ment of the primary canister with the secondary canister
in a series arrangement. New canisters should always
replace the secondary canister. Allow space to store
fresh and spent carbon, and for fork truck access. Other
design considerations are (2, 3):
Pressure drop
Total pressure
Empty bed contact
time (EBCT)
Volume of carbon
Hydraulic loading
rate
Adsorption capacity
Pump Filler
Figure A-14. Uquld-phase granular activated carbon process.
Impurity loading rate
2 to 15 in. H^Q per canister (air); 0.1 to
1 psi per canister (water).
Sum of strainers, cartridge filters,
canisters, piping; typically 5 to 15 psi
15 to 60 min typical for liquid systems;
determined from pilot tests or from carbon
supplier. Contact with vapor-phase carbon
results in nearly instantaneous removal.
Calculated from EBCT and flow rate.
Vol = flow rate x EBCT.
2-8 gal/min/ft2 common; used to
calculate area of carbon vessels.
Area required = flow rate divided by
loading rate (gal/min/fl?)
X/M = KC1/n, where
X = amount contaminant adsorbed (mg)
M = unit weight of carbon (g)
K, n = empirical constants
C = concentration of contaminant (mg/L)
Note: The above equation applies to
liquid- and vapor-phase carbon. Different
constants must be inserted.
Amount of contaminant adsorbed per
gram of carbon.
98
-------
Humidity
Temperature
Row direction
Backwash
Safety
Material of
construction
Decreases vapor-phase carbon
effectiveness. Curves available.
Decreases vapor-phase carbon
effectiveness, but will offset negative effect
of humidity if air is preheated, for a net
gain of carbon effectiveness. See supplier
performance curves.
Downflow mode is most common for liquid
flow. Upflow variation used for high
suspended solids waters. Series or
parallel selection based on characteristics
of adsorption wave front.
Permanent carbon installations are
normally equipped with a backwash
system to purge entrapped suspended
solids from the carbon bed. Air scour may
be included to detach foulants or
biological growth from the carbon.
Consider dust when handling bulk carbon.
Spontaneous combustion is possible at
certain conditions of temperature and
humidity.
Use carbon steel vessels with epoxy
coating.
A.7.7 Treatment Ranges
The effectiveness of activated carbon to adsorb con-
taminants varies inversely with contact time, contami-
nant concentration, temperature, and humidity. See
Tables 4-3 to 4-22 for ranges of contaminant removal.
A.7.8 Major Cost Elements
Estimated costs for liquid-phase carbon and vapor-
phase carbon adsorption are listed as follows:
Liquid-Phase Carbon Costs
Nominal Flow Rate
Gal/Min
Million
Gal/Day
Capital
Cost8
Annual
O&M
Cost"
Cost per
1,000 Gal
10
50
100
300
0.014
0.072
0.144
0.288
$5,000
$13,000
$20,000
$39,000
$7,100
$15,100
$22,300
$53,300
$1.40
$0.60
$0.40
$0.35
Vapor-Phase Carbon Costs
Nominal Flow Rate
Ft3/Min
100
500
1,000
3,000
Capital
Cost0
$6,000
$18,000
$36,000
$58,000
O&M
Cost11
$2.700
$9,800
$19,200
$47,800
Cost per
1,000 Gal8
$0.55
$0.40
$0.35
$0.30
a Capital cost estimated on the basis of two pressure vessels on a
prepiped, prewired skid, no installation included.
Based on $0.08/kWh power, $10/hour labor for 1 hour per day, 360
days annual operation, 1 mg/L contaminant and 5 percent adsorp-
tion by weight, $1.00/pound carbon, 5 percent of capital for main-
tenance, and 5-yr life at 8 percent interest.
0 Capital cost basis is 2 to 4 skid-mounted, reusable carbon vessels
with hose connections, initial fill of carbon, sizes of 400 Ib, 2,000 Ib,
and 10,000 Ib as required for rated flow at 5-in, H2O pressure drop
or less. .
Operating cost based on 99+ percent removal of all VOCs from
water with 1 mg/L VOC, 75:t air water ratio (volume based), 5
percent adsorbency, $10.00/hr operator, 40 hr/yr changeover time,
no power, no freight, 5-yr life at 8 percent interest, 5 percent of
capital for maintenance, and $1.00/lb regeneration or replacement
carbon.
9 Costs per 1,000 gal correspond to flow rates for liquid-phase carbon,
fr/min divided by 10 (i.e., 1,000 fr/min 10 = 100 gal/min).
A.7.9 Residuals Generated
Residuals consist of bulk spent carbon, disposable can-
isters (including spent carbon), or reusable vessels con-
taining spent carbon. If cartridge pre- and postfilters are
used, spent cartridge filter elements will be generated.
Carbon fines and backwash water are generated at
startup.
A.7.10 References
1. Hagar, D.G., J.L. Rizzo, and R.H. Zanistch. Advanced waste treat-
ment design seminar: Experience with activated carbon in treat-
ment of textile industry wastewaters. U.S. EPA Technology Transfer
Seminar Series.
2. Calgon Carbon Corporation. Adsorption handbook. Pittsburgh, PA.
3. U.S. EPA. No date. Process design manual for carbon adsorption.
Technology Transfer Series.
A.7.11 Additional Source
1. Carbtrol Corporation. 1990. Technical information data sheets.
Westport, CT.
99
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A.8 Ion Exchange
A.8.1 Technology Description
Ion exchange is an adsorption process that uses a resin
media to remove contaminants from ground water or
leachate. Cation resins adsorb metals, while anion res-
ins adsorb such contaminants as nitrate and sulfate.
Some resins are designed to adsorb only specific metals
and are used for the recovery of metals in electroplating
and metal finishing operations. Chelating resins are se-
lective in adsorbing toxic metals such as copper, nickel,
mercury, and lead.
Ion exchange systems consist of pressure vessels con-
taining beds of resin pellets and strainer systems to
retain the pellets. The most common mode of operation
is continuous downflow using a fixed bed. Other operat-
ing modes include batch and fluidized bed. The method
of resin bed regeneration can be cocurrent or counter-
current. In cocurrent regeneration, the regeneration so-
lution flows downward through the resin bed, in a similar
manner as the liquid being treated. In countercurrent
regeneration, solution flows upward, opposite the direc-
tion of water flow, which scours the bed and regenerates
the resin with less solution.
A single batch mode ion exchange vessel may be ade-
quate for contaminant removal if continuous operation
is not required. Regeneration will, however, require tem-
porary interruption of water treatment. A process flow
diagram for a single ion exchange system is shown in
Figure A-15. Additional tanks and pumps are required
Feed to System
10-mm
Cartridge
Filter
for regeneration, chemical feed, and collection of spent
solution. Clean water is also required to flush the regen-
eration solution from the resin bed before resuming
operation.
Ion exchange equipment configurations include parallel
and series vessel arrangements. In a parallel ion ex-
change system, two or more vessels each treat a frac-
tion of the total flow. Any one of the parallel flow vessels
may be regenerated while the others remain on line.
Series configuration systems have two vessels, each
sized for 100 percent of the flow. After the lead vessel is
regenerated, it becomes the lag vessel. The series con-
figuration assures passage of contaminated water
through at least one bed of freshly regenerated resin.
A.8.2 Application
Ion exchange is useful for removing and recovering
metals. This process can also remove sulfates, nitrates,
and radionuclides from water.
A.8,3 Pretreatment Requirements
Minimum pretreatment is 10-(j.m cartridge filtration.
Other pretreatment may be required, including:
Carbon adsorption Removes large organic molecules that foul
strong base resins.
Dechlorination
Avoid prechlorination or neutralize chlorine.
Aeration, Remove iron and manganese, which coat
precipitation, filtration resin pellets.
Cocurrent >
Ion
Exchange
Vessel
Backwash Water
Effluent to Discharge
Strong Acid
Regenerate
Feed Tank
To Further
Processing
or Disposal
Figure A-15. Typical cocurrent ion exchange system.
100
-------
A.8.4 Parameters of Interest
The following parameters are important for successful
ion exchange operation:
Parameter of Basis of Interest
Interest
Type of contaminant Basis for selection of resin.
Determines equipment size and frequency
of regeneration.
Determines materials of construction,
regeneration chemicals.
Volume of bed and area of vessel(s)
depend on flow rate. Bed depth ranges from
2 to 5 feet.
Breakthrough curves for water with single
metal contamination are available from
vendors. Complex matrices require bench or
pilot breakthrough test to determine impact
of other contaminants.
Sufficient to flush suspended solids from
resin bed. Depends on resin density.
Provide flow adjustment or consult resin
supplier.
Volume required, contact time, flow rate,
storage capacity.
IDS, conductivity, pH, flow rate.
Concentration of
contaminant
Resin selection
(acid or base resin)
Row rate
Capacity of resin
Backwash rate
Regeneration
Instrumentation
Resin volume
Cross-sectional area
A.8.5 Design Considerations and Criteria
The following design information serves as a guide for
evaluation and preliminary ion exchange design (1):
Provide resin bed volume that will result in
a service flow of 2 to 4 gal/min/ft3.
Pressure vessel diameter should provide a
cross-sectional area resulting in 5 to 8
gal/min/ft2.
Backwash rate Needs to be sufficient to fluidize bed to 50
to 75 percent more than original depth.
Regeneration Acid or caustic, as required, 1-5N solution:
Contact t'me: 30 min
Flow rate (volume based): 0.25 to 0.5
gal/min/ft4
Flow rate (area based): 1 to 2 gal/min/ft2
Rinse Flush at rapid rate. Provide storage for 50
to 100 gal/ft3 resin volume.
Materials of Tanks—Epoxy coating or rubber lined
construction Pipes—PVC for water, stainless steel or
plastic lined steel for acids
Pumps—316 stainless steel for acid,
carbon steel for caustic, cast iron or plastic
for water
A.8.6 Treatment Ranges
Many contaminants, especially metals, can be removed
by ion exchange. High concentrations of contaminants
result in shorter runs before regeneration is required.
Treatment ranges for many contaminants are listed in
Chapter 4.
A.8.7 Major Cost Elements
Nominal Flow Rate
Gal/Min
10
50
100
300
Million
Gal/Day
0.014
0.072
0.144
0.432
Capital
Cost3
$31,000
$81,000
$123,000
$237,000
Annual
O&M
Cost"
$26,000
$75,000
$128,000
$330,000
Cost per
1,000 Galc
$5.20
$3.00
$2.60
$2.20
a Based on quotation for dual-bed system (anion and cation ex-
change), completely assembled on a skid, no site work included.
Single-bed systems cost approximately one-third as much.
Cost based on one regeneration per day, 2 hours operator attention
per day @ $10/hour, 5 percent of capital cost for maintenance,
$0.08 per kWh power, and 5-year life at 8 percent capital recovery
factor. Acid and caustic use at 5N, 30 minutes' detention time in
resin bed. Annual operation of 360 days.
0 Cost based on annual operation of 360 days, 23 hours per day.
A.8.8 Residuals Generated
The rate of generating residuals is,proportional to the
concentration of contaminants in the Jeachate or ground
water. Residuals generated by ion exchange include:
• Spent chemicals: acid and/or caustic soda
• Backwash water: dilute acid or basic solution
• Filters: spent cartridges
• Resin: fouled resin granules
A.8.9 Reference
1. Rohm and Haas Company. Technical bulletins: Ion exchange and
fluid process. Philadelphia, PA.
101
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A.9 Reverse Osmosis
A.9.1 Technology Description
Reverse osmosis (RO) is a separation process that uses
selective semipermeable membranes to remove dis-
solved solids, such as metal salts, from water. A high-
pressure pump forces the water through a membrane,
overcoming the natural osmotic pressure, to divide the
water into a dilute (product) stream and a concentrated
(brine) stream. Molecules of water pass through the
membrane while contaminants are flushed along the
surface of the membrane and exit as brine.
The most commonly used materials for membranes are
cellulose acetate, aromatic poiyamide, and thin-film
composites. RO membranes (or modules) are config-
ured into tubular, spiral wound, hollow fiber, pr plate-
and-frame modules. The modules are inserted into long
pressure vessels that can contain one or more modules.
RO systems consist of a pretreatment pump, a high-
pressure feed pump, one or more pressure vessels,
controls, and instrumentation.
Membranes have a limited life of approximately 2 years.
When product water production declines, the mem-
branes must be restored with a cleaning solution. Tubu-
lar and plate and frame membranes can be physically
scrubbed with a brush. All membranes can be cleaned
chemically by recirculating the cleaning solution through
the membranes to restore performance. Membranes
can also be removed from the RO system and sent to
cleaning centers for flushing and rejuvenation. When
cleaning is no longer effective, the membranes must be
replaced.
Theoretically, 100 percent of the water pumped into a
RO system could be recovered as product water, but the
module would soon be fouled beyond restoration. Some
brine must flow out of the module to remove concen-
trated contaminants. This rejected flow may be signifi-
cant (15 to 25 percent of the feed flow). This is one of
the disadvantages of the RO process. To ensure ade-
quate flow of brine over the membrane surface and
reduce the volume of the reject, RO modules are ar-
ranged in stages. As the raw water is converted to
product, brine flow is reduced. Fewer modules in down-
stream stages maintain the minimum flow necessary for
flushing. A typical multistage RO system is shown in
Figure A-16.
A.9.2 Applications
Reverse osmosis is widely used for desalination of
brackish water as a potable water source. Special mem-
branes have been developed for industrial uses and for
purifying wastewater. Metal compounds are readily re-
moved. Reverse osmosis is a commercially mature
process available for many special applications.
A.9.3 Pretreatment Requirements
Typical RO membrane pore sizes range from 5 to 20
Angstrom units (0.0005 to 0.002 u.m), while pressures
of 300 to 400 psi are usually encountered. Therefore,
RO feed water needs to be very low in turbidity (gener-
ally, less than 1.0 NTU). Pretreatment may be neces-
sary, including chemical addition, clarification, and
filtration. Final cartridge filtration using 5-u.m filters is
standard practice. Some RO membranes are sensitive
to chlorine. Activated carbon pretreatment is used when
needed to remove chlorine. Biofouling can be prevented
by chlorination and dechlorination of the feed water. Use
stainless steel and/or plastic piping to prevent iron foul-
ing from contact with steel pipes. Perform a Langelier
Index calculation to determine if the water tends to
corrode ferrous piping or if deposits and scale may form.
Adjust the pH with acid, if necessary, to maintain solu-
bility of metals such as calcium, magnesium, and iron.
Chemical requirements are:
pH adjustment
Baotericide
Dechlorination
Chelating agents
Sulfuric acid, hydrochloric acid.
Chlorine, sodium hypochlorite.
Activated carbon.
EDTA, proprietary solutions.
A.9.4 Membrane Maintenance
When RO membranes are not in use, they must not be
allowed to dry out or freeze. Fill with recommended
preservative solution. Flush before using RO system.
When cleaning becomes necessary, cleaning solution is
normally recycled through the RO system at high flow
with the bypass valve open.
Cleaning solution
Storage
EDTA, tripolyphosphate, citric acid,
acetic acid, proprietary cleaners.
Formaldehyde, glutahyde, sodium
metabisulphite, proprietary solutions.
A.9.5 Parameters of Interest
A thorough analysis of the water is necessary to deter-
mine the pretreatment requirements and values of oper-
ating parameters, which are:
Flux Flow rate of product (permeate) per unit
of membrane area, gal/f^/day.
Product recovery Ratio of product flow rate to feed flow rate.
Rejection Percent removal of contaminant(s).
A.9.6 Design Considerations and Criteria
Membrane fouling can be reduced by proper design,
based on analysis of ground water or leachate samples.
102
-------
Cleaning
Solution
Activated-
Carbon
(If Required)
pH
Adjust Tank
(If Required)
Booster
Pump
Cartridge
Filter
Throttle
Feed Valve
Pump
RO Module
Bypass Valve
—»f RO Module
Figure A-16. Reverse osmosis process.
Typical design parameters are (1):
•M RO Module
RO Module
s
J
1
' 1
: J
7
Brine Reject
I Flow Meter
Valve
Product Manifold
Product
Nominal Flow Rate
Feed water quality
Suspended solids
Temperature
Product water flow
Recovery
Pressure
Rejection
Waste stream
Less than 50,000 mg/L total dissolved
solids. Minimum levels of iron, magnesium
sulfates, calcium carbonate, silicates,
chlorine, and biological organisms.
Remove colloids, silt with 5- to 10-um filters.
85°F to 120°F.
1 to 10 gal/ft/Vday.
5 to 6 percent per module; 50 to 90 percent
per system.
400 to 600 psi.
70 to 97 percent sodium chloride solution.
Brine flow rate of 10 to 50 percent of feed
flow rate.
Gal/Min
10
50
100
300
Million
Gal/Day
0.014
0.072
0.144
0.432
Capital
Cost
$20,000
$80,000
$175,000
$450,000
Annual
O&M
Cost
$15,100
$61,600
$112,500
$310,600
Cost per
1,000 Gal
$2.90
$2.40
$2.20
$2.00
A.9.7 Treatment Ranges
Treatment efficiency of RO is most sensitive to fouling
factors. Pressure, temperature, flow rate, and mem-
brane age also affect removals. See Tables 4-3 to 4-22
for a list of treatment ranges.
A.9.8 Major Cost Elements
Estimated costs for RO systems of various sizes are:
A.9.9 Residuals Generated
Brine is the primary residual, with concentrations of
dissolved solids and contaminants approaching 10
times that of the feed water. Flow rate of brine ranges
from 10 to 50 percent of feed. Spent carbon and filter
cartridges are solid wastes. Batches of cleaning solu-
tion, 30 to 50 gal per cleaning event. Spent modules,
2-year life expectancy.
A.9.10 Reference
1. E.I. duPont de Nemours and Co. Permasep engineering manual.
Permasep Products, Wilmington, DE.
A.9.11 Additional Source
1. UOP, Inc. Product bulletins. Fluid Systems Division, San Diego,
CA.
103
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A.10 Chemical Precipitation of Metals
A10.1 Technology Description
Chemical precipitation is a principle technology for re-
moving metals contaminants from contaminated ground
water.
In general, metals can be precipitated to insoluble metal
hydroxides, suifides, carbonates, or other salts. The
chemical precipitation process involves several principle
mechanisms, including formation of the metal precipi-
tate species, and coprecipitation or adsorption. The
major process variables that influence precipitation re-
actions are treatment pH; type of treatment chemical(s)
and dosage; types of ligands present; wastewater vol-
ume and temperature; the number of treatment stages;
and the chemical speciation(s) of the pollutant(s) to be
precipitated. Each variable can directly influence the
degree of treatment performance and cost. Cost factors
to be considered include the type of treatment chemicals
employed and the volume of sludge generated. If the
residual waste (sludge) is deemed hazardous, the cost
of disposal can increase by an order of magnitude or
more (1).
Precipitation in the most narrow sense involves a shift
in chemical conditions to force a soluble species to form
an insoluble (or precipitated) salt. This could result, for
example, by the addition of sodium sulfide to a cadmium
wastewater to precipitate cadmium sulfide. Classically,
precipitation for heavy metals treatment is perceived to
result through pH adjustment and consequent precipita-
tion of the metal hydroxide. "Precipitation," however, is
now recognized to encompass a much broader range of
phenomena, including formation of mixed or transient
salts and adsorptive coprecipitation. The latter results
from adsorption of one metal species onto the highly
reactive surface of a solid phase, typically formed in situ.
Coprecipitation may be induced, for example, by the
addition of an iron or alum coagulant, or incidental due
to the precipitation of a secondary species already pre-
sent within the wastewater. The consequence of this
broader range of chemical behavior is that residual met-
al solubility levels far below the theoretical solubility
limits of simple metal salts are commonly achieved.
Treatability studies are often needed to optimize treat-
ment variables, such that effluent limits are achieved
cost effectively. Volumes and handling characteristics of
precipitation treatment sludges frequently override other
economic factors in selection or optimization of precipi-
tation treatment variables.
A. 10.2 Process Flow Diagram
Example precipitation sequences are shown in Figures
A-17 and A-18. The physical/chemical system in Figure
A-17 includes the following unit processes: equalization,
coarse filtration, chemical oxidation, coprecipitation with
lime and ferric chloride, clarification (flocculation and
sedimentation), polishing filtration for clarifier super-
natant, and sludge dewatering. This sequence may be
representative of treatment for arsenic, where prepara-
tory oxidation of arsenite to arsenate enhances copre-
cipitation treatment efficiency. Chemical reduction, for
example, of hexavalent chromate anion to the trivalent
chromic cation, may be substituted in this treatment
scheme. Figure A-18 shows a treatment sequence em-
ploying simple direct precipitation, flocculation, and
sedimentation.
A. 10.3 Pretreatment Requirements
Design data are needed for each stage of a precipitation
treatment sequence. A listing of sequence design ele-
ments is given in Table A-4.
Table A-4. Design
Treatment Stage
Elements for Precipitation Treatment
Design Elements
Equalization Waste strength, flow, separate immiscible
liquids (LNAPL, DNAPL)
Chemical addition pH control, type of chemicals used,
coprecipitant/adsorbent, reactor
design-rapid mix
Flocculation Flow, flocculent aids, mixing regime,
flocculation basin residence time
Sedimentation Flow, basin configuration, hydraulic loading,
precipitate settling characteristics
Effluent filtration Flow, filter media, filter aids, number of
filter units
Sludge thickening Sludge volume, conditioning chemicals,
and/or dewatering dewatering unit type and size
Precipitation processes have been identified for the ef-
fective removal of various metals contaminants in
ground water (3, 4). Several example processes are
given in Table A-5. The effectiveness of chemical pre-
cipitation treatment is limited. Nyer. (5) suggested that at
low influent heavy metals concentration, ion exchange
could be a more cost-effective treatment technique. This
is especially true at metals concentrations having dis-
charge limits below the solubility limit. The impact of
competing nontoxic ions such as calcium on ion ex-
change process efficiency and cost-effectiveness must
be evaluated.
A. 10.4 Parameters of Interest
Significant parameters for design and process control
are given in Table A-6.
A. 10.5 Major Cost Elements
Figures A-19 and A-20 present example construction
costs and operation and maintenance costs curves,
104
-------
Tertiary Treatment
i Reverse Osmosis
Well
Pump
Caustic +
Oxidant
Lime +
Ferric Chloride
Equalization
Pump
'
r
Filter
H
Coarse
Filter
*
Oxidation
Discharge
Activated
Carbon
Ion Exchange
Discharge
Dischi
Solids
Figure A-17. Physical chemical treatment process.
Precipitating Precipation Flocculation
Chemicals
Flocculating
Agents
Inlet Liquid __
Stream
Sedimentation
..A
•>
"•
C
c
LP
I C
^ <
-0 Q-
l
-0
m~~zz***~-~- —
Outlet Liquid
Stream
1 Sedimentation Basin
Figure A-18. Representative configuration employing precipitation, flocculation, and sedimentation (2).
respectively, for a package water treatment plant for
precipitation, flocculation, sedimentation, and filtration.
A.10.6 Residuals Generated
The quantity of sludge produced depends on the quality
of the water being treated and the type of treatment
chemical used (e.g., lime, alum, or iron containing
sludges). The amount of sludge produced can be ap-
proximated from the chemistry and raw water quality
(i.e., adding the suspended solids removed to the co-
agulant added). Better estimates, however, are obtained
by treatability studies using the actual ground water or
leachate to be treated.
A.10.7 References
1. Patterson, J.W. 1985. Industrial wastewater treatment technology,
2nd ed. Boston, MA: Butterworth Publishers.
2. U.S. EPA. 1982. Handbook for remedial action at waste disposal
sites. EPA/625/6-82/006. Cincinnati, OH.
3. U.S. EPA. 1990. Technologies for upgrading existing or designing
new drinking water treatment facilities. EPA/625/4-89/023. Cincin-
nati, OH.
4. American Society of Civil Engineers (ASCE) and American Water
Works Association (AWWA). 1990. Water treatment plant design,
2nd ed. New York, NY: McGraw-Hill.
5. Nyer, E.K. 1992. Ground-water treatment technology. New York,
NY: Van Nostrand Reinhold Company.
6. U.S. EPA. 1978. Estimating costs for water treatment as a function
of size and treatment plant efficiency. EPA/600/2-78/182. Cincin-
nati, OH.
A.10.8 Additional Sources
1. Dentel, S.K., B.M. Gucciardi, T.A. Sober, P.V. Shetty, and J.J. Re-
sta. 1989. Procedures manual for polymer selection in water treat-
ment plants. Prepared for AWWA Research Foundation, Denver,
CO.
2. Eckenfelder, W.W., Jr. 1989. Industrial water pollution control. New
York, NY: McGraw-Hill.
105
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Table A-5. Example Precipitation Treatment Methods for Metal Contaminants (1,4)
Contaminant Process pH Range
Comments.
Arsente (+5)
Arsenic (+3)
Cadmium
Chromium (+3)
Chromium (+6)
Lead
Inorganic mercury
Selenium
Silver
Ferric sulfate coprecipitation
Alum coprecipitation
Lime softening
Ferric sulfate coprecipitation
Alum coprecipitation
Ume softening
"Hydroxide" precipitation
Ferric sulfate coprecipitation
Ume softening
"Hydroxide" precipitation
Ferric sulfate coprecipitation
Alum coprecipitation
Ume softening
Ferrous sulfate coprecipitation
"Hydroxide" precipitation
Ferric sulfate coprecipitation
Alum coprecipitation
Ume softening
Ferric sulfate coprecipitation
Ferric sulfate coprecipitation
Ferric sulfate coprecipitation
Alum coprecipitation
Ume softening
6-8
6-7
>10.5
6-8
6-7
>10.5
Varies
7-8
Varies
6-9
6-7
>10.5
7-9.5
Varies
6-9
5-7
7-8
6-7
7-9
6.2-6.4
— ' ;
Oxidation to As5+ by
chlorination required
before coprecipitation
Effective over full
lime-softening range
—
—
Effective over full
lime-softening range
—
—
•Effective over full
lime-softening range
108
104
2 gal/min/ft2
5 gal/min/ft2
LlL.
r •< > * ' * •'
100 101 1Q2 1Q3
Capacity (gal/min)
104
105
104
2 gal/min/ft2
5 gal/min/ft2
100 1Q1 1Q2 ' 1Q3
Capacity (gal/min)
104
Figure A-19. Construction cost curves for package complete Figure A-20. O&M cost curves for package complete treatment
treatment plants, In 1978 dollars (6). plants, in 1978 dollars (6).
106
-------
Table A-6. Significant Treatment Variables for Precipitation
Treatment Variable Potential Effect(s)
Optimum pH
Treatment
chemical/dosage
Treatment chemical
coprecipitant/adsorbent
used
Wastewater volume
Treatment stages
Pollutant chemical
speciation
Other ions present
Wastewater temperature
Settling velocity and
settled sludge volume
Effectiveness of polymers
To achieve the necessary effluent limits, the optimal pH must be determined. pH control is a
function of the chemical(s) used to precipitate metals in the ground water. The treatment pH can
also affect the amount of sludge generated and its settieability. Figure A-21 shows the solubility of
various metal hydroxides as a function of pH.
The cost and type of treatment chemical used influences both the amount and type of sludge
produced. The use of sulfide, for example, may achieve the lowest effluent residual metals
concentrations but make sludge generated hazardous (because of reactivity). Sodium hydroxide,
on the other hand, may generate less sludge, but the sludge can have poor settieability. Sodium
hydroxide is also expensive. Lime is relatively inexpensive, and the sludge generated has
generally good settling characteristics. Lime usually generates a large volume of sludge, however,
which affects the cost of disposal.
Typically, ferric iron salts are used to effect coprecipitation/adsorption of trace metals from solution.
Ferrous iron salts and alum, however, have also been investigated and are widely used (1).
The volume of water to be treated affects the amount of chemical used and sludge produced.
Patterson (1) reported that approximately 4 percent of the wastewater volume treated becomes
sludge.
Often multiple^stage precipitation processes.enhance metals removals. Dividing precipitation,
coprecipitation, and adsorption into several discrete processes allows each to be optimized for a
given pollutant(s). This could reduce the amount of sludge produced because each pollutant is
removed at its "optimal" chemical dosage, chemical type, and pH. Further, the sludge produced in
each step may have reclamation possibilities versus disposal, and sludge volume versus
settieability.
The chemical speciation of the pollutant to be removed directly affects the degree of removal. For
example, arsenate is readily coprecipitated by lime-ferric chloride addition, but arsenite is not (1).
Hence additional treatment steps are required. In this case, chemical oxidation could be used to
convert arsenite to arsenate.
The presence of other ions may or may not enhance the precipitation, coprecipitation, and
adsorption process. Ions such as sulfate and carbonate may increase chemical demand by
reacting with the treatment chemical(s). Ions such as chloride may compete with metals for surface
sites on the precipitate or may form other, more soluble metal complexes. Hardness also
influences the treatment effectiveness.
High lime plus ferric chloride could be required to coprecipitate or adsorb the micropollutant
concentrations of metals present to achieve water quality based effluent limits (WQBEL). Hardness
as CaCO3 could offset the quantity of lime (CaO) required, for example. The quantity of sludge
produced, however, would remain constant.
Wastewater temperature may affect the minimum solubility of the metals present. Generally, as the
temperature is increased, the solubility is increased and the soluble metals in the wastewater are
not precipitated to their optimal residual concentrations.
A design criteria in the design of sedimentation tank is for the overflow rate to be less than the
settling velocity of the feed solids. The manner in which the suspended solids settle depends on
the nature of the solids present. The settling of activated sludge and flocculated chemical
suspensions usually takes place in the hindered settling regime (6).
This type of settling is characterized by the formation of a distinct interface between the clear
water (supernatant) and the particles in the settling region. Discrete, flocculant, and hindered
settling have different settling characteristics and require different methods of settling velocity
determination. The settled sludge volume is the volume of sludge collected at the bottom of a test
cylinder after quiescent settling for a given period, normally 30 minutes to 1 hour. It provides
information on the expected volume of sludge that will be generated in a settling basin.
Polymers act to promote particle aggregation by either reducing charge, bridging, or
coagulation-bridging. Polymers may be used either as primary coagulants, in which case they are
typically low molecular weight or positively charged, or as coagulant aids, in which case they have
a higher molecular weight and a positive, negative, or neutral charge (7). Chemical characteristics
of polymers and laboratory (jar) test of polymer performance provide the information that
determines the best polymer to use and the optimal dosage level.
107
-------
0.001
50.0005 -
"4 6 8 10 12
Figure A-21. Solubilities of metal hydroxides at various phis.
108
-------
A.11 Chemical Oxidation
A. 11.1 Technology Description
Oxidation—reduction or "redox" reactions—can play an
important role in the treatment of a contaminated ground
water. The chemical behavior of compounds containing
carbon, nitrogen, sulfur, iron, and manganese, for exam-
ple, are largely influenced by redox reactions. Often,
redox reactions are employed to facilitate the removal
of a pollutant from a given wastewater. For instance, the
reduction of hexavalent chromium to the trivalent ion
facilitates the removal of chromium by precipitation. Oxi-
dation of arsenite to arsenate can enhance the efficiency
of certain arsenic treatment technologies. Similarly, cya-
nide can be oxidized, using sodium hypochlorite, to
carbon dioxide and nitrogen at elevated pH (1).
Chemical oxidation involves the loss of one or more
electrons by the element oxidized. The electron ac-
ceptor may be another element, including an oxygen
molecule, or it may be a chemical species containing
oxygen, such as hydrogen peroxide and chlorine dioxide
or some other electron acceptor. Oxidation processes
for some organic compounds may be too slow to com-
pletely oxidize the constituents to CO2 and water. Weber
and Smith (2) categorized organic compounds' amena-
bility to oxidation. For example, high reactivity com-
pounds include phenols, aldehydes, aromatic amines,
certain organic sulfur compounds; medium reactivity
compounds include alcohols, alkyl-substituted aromat-
ics, nitro-substituted aromatics, unsaturated alkyl
groups, carbohydrates, aliphatic ketones, acids, esters,
and amines; and low reactivity compounds include ha-
logenated hydrocarbons, saturated aliphatic com-
pounds, and benzene.
Chemical oxidation is a potential treatment option for the
removal of certain organic pollutants from a ground
water or leachate. The amount of oxidant required in
practice is generally greater than the theoretical mass
calculated. The reasons for this are numerous and in-
clude incomplete oxidant consumption and oxidant de-
mand caused by other species in solution. Often,
oxidation reactions are pH dependent, hence pH control
may be an important design variable. Economics of
treatment and treatability of a specific pollutant also
govern the degree of oxidation. For example, partial
oxidation of dichlorophenol in a contaminated ground
water may be employed to facilitate subsequent removal
by activated carbon. Partial oxidation followed by addi-
tional treatment options may be more efficient and cost
effective than using a complete oxidation treatment
scheme alone. An increase in the biodegradability of
refractory organics due to chemical oxidation has been
reported (3). Examples of common oxidants include
ozone, chlorine, hydrogen peroxide, and UV radiation.
The use of chlorine to oxidize organic compounds must
be closely evaluated due to the potential formation of
toxic chlorinated reaction byproducts.
A. 11.2 Process Flow Diagram
A simple oxidation treatment schematic, which might be
applicable to arsenic, is shown in Figure A-22. This
treatment sequence consists of equalization, coarse fil-
tration, the oxidation step, coprecipitation, flocculation,
and a polishing step using filtration.
A. 11.3 Design Considerations and Criteria
Chemical oxidants such as hydrogen peroxide, chlorine,
and ozone are commonly employed in ground-water
and leachate treatment. The use of these chemicals is
briefly described below.
A.11.3.1 Ozonation Systems
Ozone is an allotrope of oxygen. It is relatively unstable,
having a half-life of less than 30 minutes in distilled
water at 20°C (4). Ozonation systems have four major
components: air preparation or pure oxygen feed,
ozone generation, ozone contacting, and off-gas de-
struction (5).
Ozone is produced by passing air between oppositely
charged plates or through tubes in which a core and the
tube walls serve as the oppositely charged surfaces. Air
is refrigerated to below the dew point to condense out
atmospheric humidity. The air is then passed through a
silica gel or activated alumina to further lower the dew
point to minus 40 to 60°C. The use of dry, clean air
results in lower ozone generator maintenance require-
ments, long-life units, and more ozone produced per unit
of power added.
If pure oxygen gas is used as the feed to the ozonator,
it should have a purity greater than 95 percent and a
dew point lower than -60°C. Oxygen feed can also be
produced on site by either pressure swing adsorption of
oxygen from air or cryogenic production from air. Pure
oxygen feed is generally more cost effective than air for
ozonation systems that generate more than 3,500 Ib/day
of ozone.
Once produced, ozone is bubbled through the ground
water or leachate using a diffusion system, such as
two-chamber porous plate diffusers, with a 15- to 24-ft
water column. Ozone transfer occurs as fine bubbles
containing ozone and air (or oxygen) rise slowly inside
the column, contacting the contaminated water phase.
The correct ozone dose to achieve oxidation must be
determined by treatability studies. There are many site
specific variables, such as ozone production efficiency
and wastewater quality, that must be determined to
correlate ozone dosage and contaminant oxidation effi-
ciency. Table A-7 lists some example removal efficien-
cies obtained by ozone treatment.
109
-------
Caustic +
Oxidant
Lime +
Ferric Chloride
WeH
Pump
Effluent
Polymer
Figure A-22. Simple oxidation process.
Table A-7. Removal Efficiencies by Ozone Oxidation (6)
Removal Efficiency
Organic Compounds
Ozone Oxidation at 2 to 6 ppm
AHcanas
Alkenes
Aromatfcs
Pesticides
0-30
30-100
30-100
30-100
Any ozone remaining in the off-gas from the diffusion
system must be destroyed before release to the atmos-
phere. It should be noted, however, that the ozone con-
tactor can be designed for 100 percent absorption. The
destruction of excess ozone from ozone contactor ex-
haust gases can be accomplished thermally by heating
the off-gases to 300°C to 350°C for 3 seconds; catalyti-
cally by using metal catalysts or metal oxides; or by
employing a combination of thermal and catalytic de-
struction (7). It is generally more cost effective to destroy
ozone in exhaust gases than to recycle the gases
through the feed air preparation and ozone generation
systems.
Capital and O&M costs associated with ozone treatment
are given in Figures A-23 and A-24, respectively.
A.11.3.2 Hydrogen Peroxide
EPA (7) has reported design criteria for a full-scale
ozone/hydrogen peroxide plant treating a ground water
contaminated with TCE and PCE. The design parame-
ters for this system are presented in Table A-8. One
economic advantage of oxidation over the use of packed
tower stripping for this ground water was the absence of
off-gas controls because the contaminants were oxi-
dized, not merely stripped from the water phase. An-
other process for generating hydroxyl radical is the
catalyzed decomposition of hydrogen peroxide by iron
(II), known as Fenton's reagent. The optimal pH range
for the reaction is 3 to 5 (9).
Solids
Table A-8. Design Parameters for Hydrogen Peroxide-Ozone
Treatment Plant (7)
Parameter
Value
Plant flow (gal/min)
TCE concentration (ug/L)
PCE concentration (u.g/L)
Reaction tank capacity (gal)
Hydraulic detention time (min)
Reaction tank stages (number)
Ozone dosage (mg/L)
Ozone generator capacity (Ib/day)
Peroxide dosage (mg/L)
Peroxide storage (gal at 50-percent
concentration)
2,000
200
20
6,000
3
1
4
100
2
1,000
A. 11.3.3 Chlorine
Chlorination is widely used in waste treatment for disin-
fection. Aqueous chlorine owes its oxidizing power to
two chemical species: the hypochlorite ion (OCI") and
hypochlorous acid (HOCI). Chlorine can oxidize both
inorganic and organic substances.
The destruction of cyanide can be accomplished by
alkaline Chlorination. In this process, cyanide is oxidized
rapidly by hypochlorite (either as sodium hypochlorite or
produced by the reaction of chlorine with sodium hydrox-
ide) to cyanate at pH greater than 10 (1). Further oxida-
tion of cyanate by hypochlorite or chlorine results in the
formation of CO2 and N2. The recommended pH for this
second stage is 8.5. The reaction is complete within 1
hour(1).
The use of chlorine for oxidizing organic compounds can
result in the formation of toxic chlorinated byproducts,
such as trihalomethanes. Thus, the use of alternative
oxidants such as ozone, hydrogen peroxide, and chlo-
rine dioxide may be preferred.
110
-------
107
106
8
c
o
t3
"55
I 105
104
' ' ' ""'
10°
101
102
103
10"
105
Generation Rate (Ib/day)
Figure A-23. Construction cost curve for ozone generation sys-
tems, updated to 1992 dollars (8).
A. 11.4 References
1. Patterson, J.W. 1985. Industrial wastewater treatment technology.
Boston, MA: Butterworth Publishers.
2. Weber, W.J., Jr., and E.H. Smith. 1986. Removing dissolved or-
ganic contaminants from water. ES&T 20:970-979.
3. Bowers, A.R., F.H. Cho, and A. Singh. 1992. Chemical oxidation
of aromatic compounds: Comparison of HaOa, KMnO4, and Oa for
toxicity reduction and improvements in biodegradability. In: Eck-
enfelder, W.W., A.R. Bowers, and J.A. Roth, eds. Chemical oxida-
tion. Lancaster, PA: Technomic Publishing Co. pp. 11-25.
4. Reynolds, T.D. 1982. Unit operations and processes in environ-
mental engineering. Monterey, CA: Brooks/Cole Engineering Divi-
sion.
5. Ferguson, D.W., J.T. Gramith, and M.J. McGuire. 1991. Applying
ozone for organics control and disinfection: A utility perspective
JAWWA 83:32-39.
107
106
105
104
103
10° 101 102 1Q3
Generation Rate (Ib/day)
104
105
Figure A-24. O&M cost curve for ozone generation systems
updated to 1992 dollars (8).
6. Goodrich, J.A., B.W. Lykins, Jr., R.M. Clark, and E. Timothy Oppelt:
1991. Is remedial ground water meeting SWDA requirements?
JAWWA 83:55-62.
7. U.S. EPA, 1990. Technologies for upgrading existing or designing
new drinking water treatment facilities. EPA/625/4-89/023 Cincin-
nati, OH.
8. U.S. EPA. 1978. Estimating costs for water treatment as a function
of size and treatment plant efficiency. EPA/600/2-78/182 Cincin-
nati, OH.
9. Robinson, S.F., and R.M. Monsen. 1992. Hydrogen peroxide and
environmental immediate response. In: Eckenfelder, W.W,, A.R.
Bowers, and J.A. Roth, eds. Chemical oxidation. Lancaster, PA:
Technomic Publishing Co. pp. 51-67.
4,71.5 Additional Source
1. Eckenfelder, W.W., Jr. 1989. Industrial water pollution control. New
York, NY: McGraw-Hill.
111
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A.12 Chemically Assisted Clarification
(Polymer Only)
A.12.1 Technology Description
Polyelectrolytes (polymers) are low or high molecular
weight organic compounds that are added to water as a
flocculant/coagulant solution to enhance the gravity set-
tling of colloids and suspended solids. Polymers are
available as anionic, cationic, and nonionic types in
liquid and dry powder form. The effectiveness of
polyelectrolytes in water treatment can be quite variable.
Polymers are effective in flocculating suspensions of
inorganic materials (clays, soil, colloids, metal salts,
etc.); however, they are usually not effective alone for
flocculating organic suspensions. Rather, they can be
used to improve the performance of alum or ferric salts
in treating organic suspensions. Dry polymers cost less
to ship, but liquid polymers are easier to mix with water.
Polymer solutions are viscous and sticky. Special mixing
techniques and equipment are necessary to prepare
polymer solutions in the field.
Package polymer mixing systems are available with
mixers, tanks, dry polymer hoppers, dry feeders, and
controls to automatically mix dry polymer with water.
Other automatic package systems continuously mix liq-
uid polymer with water in static mixers. The solution is
stored in a day tank for use until another batch is re-
quired. All polymer systems require a wetting mecha-
nism, batch mix tank, mixer, holding tank, and metering
pump. Atypical polymer mixing system diagram is pre-
sented in Figure A-25. Electrical power and clean water
supplies are necessary for polymer solution preparation.
A.12.2 Application
Polymers are used with chemical precipitation and filtra-
tion treatment processes. Refer to Tables 4-3 to 4-22 for
compounds that are removed by the above processes.
Treatability studies should be performed to select the
proper type and dosage of polymer, or, at a minimum,
the manufacturer should be consulted for recommenda-
tions.
A. 12.3 Pretreatment Requirements
The polymer manufacturer's instructions should be fol-
lowed closely for best results. An accurate scale and
graduated mix tank are required for proportioning poly-
mer and water. The mixer should be of the low speed
type to minimize shear while mixing. An eductor and
pressurized water supply efficiently wet dry polymer
before mixing. Dry polymer can also be added manually
to water in a mix tank by slowly sprinkling the dry powder
into the mixer vortex until all powder is dissolved. A
separate feed tank is required only if the treatment
process cannot be interrupted while polymer is mixing.
A.12.4 Parameters of Interest
The following parameters should be given consideration
for a successful polymer application:
Type of polymer Select anionic, cationic, or nonionic based on a
treatability study or vendor recommendations.
Dose Jar tests will show by visual comparison which
dose is appropriate. Poor settling can occur if
polymer is overdosed or underdosed.
Temperature Some polymers mix well in cold water, others
require warm water for disoejsal. Nevor freeze
polymer.
Polymer
Preweighed
Dry Polymer
Water
1
^*^AZ*~+Z*^*~**~
J
%
To
Rocculatton
Basin
Polymer
Mix Tank
Transfer
Pump
Polymer
Holding (Day)
Tank
Polymer
Metering
Pump
Figure A-25. Polymer mixing and feed system.
112
-------
Feed Most polymers must be diluted to 0.1 to 0.5
concentration percent at the injection point.
Time Mixing time (dilution) and flocculation detention
time are critical.
Mixing shear Overmixing and high speed mixers should be
avoided.
A.12.S Design Considerations and Criteria
Polymer mixing and feed systems should be designed
in accordance with the following considerations and
criteria (1-4):
Materials of Use stainless steel or fiberglass. Avoid
construction rubber. PVC pipe is suitable.
Storage volume Mix batches that will be used in 2 to 3 days.
Solution shelf life is limited. Storage tank
should be 1.5 times mix tank volume.
Stock mixer Low speed mixers are best. Power must be
selection sufficient to prevent motor overload. Vendors
can select the most efficient mixer for each
application. Provide tank size, power
available, type and concentration of polymer,
mixing time requirement.
Stock concentration Dilute with water'to 1 to 2 percent for
storage. Dilute to 0.1 to 0.5 percent in the
pipelines or in a tank before injection.
Stock mix time Mix for 15 to 30 minutes per manufacturer's
instructions. Let solution stand quietly 30 to
60 minutes until all polymer is dissolved.
Water Clean, under 50 psi pressure desirable.
Plentiful supply.
Polyelectrolyte addition
Safety
Eye protection required. See MSDS. Spillage
causes slippery floors, falls. Rinse thoroughly,
provide nonslip surfaces
Dosage
Addition sequence
Flocculation
Settling
For dilute suspensions (say <100 mg/L
suspended solids), try 1 to 10 mg/L cationic
polymer or 0.5 to 5 mg/L anionic or nonionic
polymer. For concentrated suspensions
(>1,000 mg/L), try 1 to 300 mg/L cationic
polymer or 1 to 100 mg/L anionic or nonionic
polymer.
Slowly add polymers in dilute solutions
(usually 0.1 to 0.5 percent) to the water while
vigorously agitating for 1 to 2 minutes to
ensure dispersal.
Only enough agitation should be applied to
keep the developing floe from settling.
Flocculate about 5 to 10 minutes. If more
flocculation time is needed, try using a higher
polymer dosage.
Polyelectrolytes produce a floe that settles
rapidly, usually 0.5 to 1.0 ft/min or more. If
the settling rate is less than 0.5 ft/min,
increase the polymer dosage. Minimum
settling tank detention time should be 4
minutes per foot of depth.
A. 12.6 Treatment Ranges
Polymer is used with chemical precipitation and filtra-
tion. Refer to Tables 4-3 to 4-22 for a range of chemicals
removed and the removal efficiencies for those two
processes.
A. 12.7 Major Cost Elements
Major cost elements for polymer mix systems are the
tanks, mixers, and pumps. Typical cost ranges are listed
below (5):
Nominal Flow Rate
Gal/Min
10
50
100
300
Million
Gal/Day
0.014
0.072
0.144
0.432
Capital
Cost3
$8,000
$9,000
$10,000
$16,000
Annual
O&M
Cost"
$4,400
$6,400
$8,900
$19,700
Cost per
1,000 Gal
$0.85
$0.25
$0.20
$0.15
Cost is based on catalog prices for mixers, tanks, metering pumps,
transfer pumps, and estimated assembly cost for each size.
Based on 1 hour operator attention per 3 days, $2/pound polymer
cost, $10/hour operator, 5 mg/L dose, $0.08/kWh, 360 days/year,
24 hours/day operation.
A.12.9 Residuals Generated
The only residual from polymer use is the empty ship-
ping container. The smallest commercial package is
25 Ib; therefore, one empty container is generated for
every 25 Ib of polymer used unless larger shipping
containers are ordered. Spillage and tank leftovers can
be drained to a sewer.
A.12.10 References
1. Allied Colloids, Inc. Polymer for water pollution control. Product
Bulletins. Suffolk, VA.
2. American Petroleum Institute. The chemistry and chemicals of
coagulation and flocculation. Committee on Refinery and Environ-
mental Control.
3. Stockhausen, Inc. Clean Water Clean Environment Product Bulle-
tins. Greensboro, NC.
4. U.S. EPA. 1979. Chemical aids manual for wastewater treatment
facilities. EPA/430/9-79/018.
5. McMaster-Carr Catalog No. 100. P.O. Box 4355, Chicago, IL
60680.
113
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A.13 Filtration
A.13.1 Technology Description
The filtration process consists of a fixed or moving bed
of media that traps and removes suspended solids from
water passing through the media. Monomedia filters
usually contain sand, while multimedia filters include
sand, anthracite, and possibly garnet. In multimedia
filters, a layer of granular anthracite (coal) is provided
above the sand to trap large particles that would quickly
blind the sand media. This results in extended runs
between backwash cycles. Garnet sand is very fine and
is commonly used as a final polishing media when ex-
tremely low turbidity effluent is required. The garnet
rests on the support media below the sand layer.
Two types of fixed bed filters are available. Pressure
filters contain media in an enclosed, watertight pressure
vessel and require a feed pump to force the water
through the media. A gravity filter operates on the basis
of differential pressure of a static head of water above
the media, which causes flow through the filter.
All fixed media filters have influent and effluent distribu-
tion systems consisting of pipes and fittings. Strainers
in the tank bottom are usually stainless steel screens.
Layers of uniformly sized gravel also serve as bottom
strainers and as a support for the sand. For both types
of filters, the bed builds up headless over time. When
the headloss becomes unacceptable, the filter needs to
be backwashed. Troughs are provided above the filter
media to collect filtered particles during backwashing.
Filters are backwashed by reversing the flow of water
(upward) from below the media. Sometimes air is dis-
persed into the sand bed to scour the media.
Fixed bed filters (see Figure A-26) can be automatically
backwashed when the differential pressure exceeds a
preset limit or when a timer starts the backwash cycle.
Powered valves and a backwash pump are activated
and controlled by adjustable cam timers or electronic
programmable logic controllers to perform the baclcwash
function. A supply of clean backwash water is required.
Backwash water and trapped particles are commonly
discharged to an equalization tank upstream of the
water treatment system's primary clarifier or screen for
removal. Backwash water may also be discharged to a
sanitary sewer if discharge criteria are met.
r
Moving bed filters (shown in Figure A-27) use an air lift
pump and draft tube to recirculate sand from the filter
bottom to the top of the filter vessel, which is usually
open at the top. Dirty water entering the filter at the
bottom must travel upward, countercurrently, through
the downward-moving fluidized sand bed. Particles are
strained from the rising water and carried downward with
the sand. Due to the difference in specific gravity, the
lighter particles are removed from the filter when the
sand is recycled through a separation box at the top of
the filter or in a remote location. The heavier sand falls
back into the filter, while the lighter particles flow over a
weir to waste. Moving bed filters are continuously back-
washed and have a constant rate of effluent flow.
For waters having less than 10 mg/L suspended solids,
cartridge filters may be cost effective. Cartridge filters
have very low capital cost and can remove particles of
1 urn or larger size. Using two-stage cartridge filters
(coarse and fine) in series extends the life of the fine
cartridge. Disposable or backwashable bag filters are
also available and may be quite cost effective for certain
applications. For applications with high concentrations
of suspended solids or a long duration, reusable filter
media should be investigated.
A.13.2 Applications
Filters are used to remove suspended solids from the
effluent upstream of processes such as secondary
clarifiers of biological systems or gravity separators of
physical/chemical treatment systems. Examples of
compounds that can be removed by filtration are listed
in Tables 4-3 to 4-22. Generally, only those compounds
that are associated with suspended solids or colloids
are removed by filtration; dissolved compounds are not
removed.
A.13.3 Pretreatment Requirements
Dissolved compounds should be pretreated by biologi-
cal or chemical precipitation processes to convert the
compound to a solid particle before filtration. Metal pre-
cipitates form at elevated pH; therefore, filters may con-
tain water of high pH that has been treated with lime
(CaO) or caustic soda (NaOH). Polymers may have to
be injected into the filter feed piping downstream of feed
pumps to enhance flocculation of "pin floes" that may
escape an upstream clarifier. Pretreatment for iron and
calcium may be required to prevent fouling and scaling.
A. 13.4 Parameters of Interest
The following' parameters apply to filtration:
• Suspended solids concentration: 20 to 200 mg/L typical.
• Particle size, distribution: 10 to 30 u,m typical.
• Particle characteristics: variable, from hard granular
to gelatinous possible.
• Pretreatment: high or low pH, temperature, corrosive-
ness, fouling, scaling tendency.
• Flow rate: consider transportable diameter, number
of units required.
• Type of feed water: oily, metal precipitate, biological,
algae, mill scale, etc.
114
-------
Influent Distributor
Backwash Trough
Spent Backwash
Anthracite
Sand Media
Gravel Under Drain
Backwash Inlet
-M-
Compressed
Air Scour
(Optional)
'YVVVYVYVYYV
JFiltered Effluent
*J^A~K^^K^^*~
Backwash
Storage Tank
^7
Efflu
Figure A-26. Fixed bed filter.
Backwash Pump
Flow Meter
Backwash Weir
Backwash With
. Suspended Solids
Filtered Effluent
Sand/Suspended Solids
Separation Chamber
Sand Return Port
Draft Tube
Air, Sand, Suspended
Solids Row Upward
Sand Flows Downward
Water Flows Upward
Suspended Solids
Sand
Air Bubbles
Figure A-27. Moving bed filter.
115
-------
The above information is necessary to determine the
hydraulic loading rate, type of filter, type of media, ma-
terials of construction, and need for air scour.
A. 13.5 Design Considerations and Criteria
The following design information serves as a guide for
evaluation and preliminary filtration design (1, 2):
Hydraulic loading 2 to 10 gal/min/ft2 range; 4 to 6 gal/min/ft2
rate typical.
Transportable size Limit diameter to 8 ft.
Backwash
requirement (fixed
bed)
Power
Bed depth
Rlter height
Pressure loss
—Use multiple filters for continuous flow
unless interruptable flow is acceptable.
—Backwash at 10 to 15 gal/min/ft2.
—Provide effluent storage for 10 min at
15 gal/min/ft2.
—Allow equalization tank size or disposal
capacity for backwash at 8- to 36-hour
intervals.
—Air scour, 5 tfVmin/ff2.
—Backwash flow 2 to 5 percent of feed
water typical.
—Air requirement, 0.05 to 0.15 frvrnin/ft2.
See Table 3-4 for typical power required.
Add extra power for air compressors;
gravity filters and moving bed filters need
less power for feed pump.
Sand, 1 to 2 ft; anthracite, 1 to 2 ft;
garnet, 4 to 6 in. Allow 25 to 50 percent
for bed expansion.
8 to 16 ft; allow for handrails and access
above filter vessel. For large flows,
pressure filters with horizontally mounted
cylindrical tanks are common.
Moving bed, 1 to 2 ft; gravity filter, 2 to 10
ft; pressure filter, 5 to 40 psi; cartridge
filter, 5 to 50 psi.
A. 13.6 Treatment Ranges
The removal efficiency of filters depends on paniculate
size, characteristics, loading rate, and media. Elffluent
quality deteriorates at high loading rates and long runs.
See Tables 4-3 to 4-22 for removal efficiencies of filters
for selected compounds.
A. 13.7 Major Cost Elements
Estimated costs for filtration systems of various sizes
are as follows:
Nominal Flow Rate
Gal/Min
10
50
100
300
Million
Gal/Day
0.014
0.072
0.144
0.432
Capital
Cost3
$5,000
$13,000
$20,000
$39,000
Annual
O&M Cost"
$4,300
$7,300
$10,400
$21,200
Cost per
1,000 Gal
$0.85
$0.30
$0.20
$0.15
a Price based on completely assembled dual vessel, prewired,
prepiped, skid-mounted system. Site work not included.
b Based on Va-hour operator per day at $10/hour, 5 percent of capital
cost for maintenance, $0.08/kWh, capital recovery of 8 percent for
5-year life, and 360 days of operation annually.
A.13.8 Residuals Generated
Residuals consist of backwash waste with suspended
solids:
Volume of backwash
Cartridge filters
Suspended solids
2 to 5 percent for fixed bed filter; 4 to 8
percent for moving bed filter.
Spent cartridges.
Calculate from removal efficiency.
A.13.9 References
1. U.S. EPA. 1975. Process design manual for suspended solids
removal. Technology Transfer. EPA/625/1-75/003a.
2. U.S. EPA. 1974. Wastewater filtration: Design considerations.
Technology Transfer. July.
116
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Radiation
A.14 Ultraviolet Radiation
A.14.1 Technology Description
Ultraviolet (UV) radiation technology can be used for
oxidizing organic contaminants. Peroxide is sometimes
used with UV radiation to catalyze the photolytic decom-
position reaction. In this case, a reactive hydroxyl radical
(OH°) is cleaved from the hydrogen peroxide molecule.
The hydroxyl radical is highly reactive and facilitates
oxidation. Ozone may also be used with UV.
Alkalinity is a key parameter in oxidation processes.
Carbonate and, to a lesser extent, bicarbonate ions are
excellent scavengers for free radicals (1, 2). Conse-
quently, influent pH control may be necessary to shift the
carbonate equilibrium toward carbonic acid (1, 3).
This system has four major components: the reactor
module, the air compressor/ozone generator module,
the hydrogen peroxide feed system, and the ozone de-
composer unit (4). Each system requires that pre-
treatment steps be employed to maximize treatment
efficiency.
Each major UV treatment application, i.e., UV/hydrogen
peroxide, UV/ozone, and UV/hydrogen peroxide/ozone
is described below.
A.14.2 Applications
A.14.2.1 UV/Hydrogen Peroxide/Ozone
UV/hydrogen peroxide technology has been used to
treat landfill leachate, ground water, and industrial
wastewater, all containing a variety of organic contami-
nants (3). The UV/hydrogen peroxide/ozone system
was also reported effective for volatile organic com-
pound oxidation, achieving removals of better than 90
percent.
A.14.2.2 UV/Hydrogen Peroxide
An evaluation of 70 full-scale UV/hydrogen peroxide
systems revealed that 30 percent were treating waste-
waters with organic concentrations between 10 ppm and
about 10,000 ppm, and 70 percent were being used to
treat ground water (5). These systems have the follow-
ing components: a chemical oxidation unit, a hydrogen
peroxide feed module, a UV lamp drive, and a control
panel (3). This system is shown in Figure A-28. The
UV/hydrogen peroxide system has been paired with
carbon adsorption, air stripping, or biological treatment,
depending on water quality and treatment objectives
(3,5).
The contaminated water is dosed with hydrogen perox-
ide before it enters the reactor. A splitter can be used,
however, to add hydrogen peroxide before any of the six
reactors within the oxidation unit. Acid may be added to
lower the pH. Water then flows through the six UV
reactors, which are separated by baffles to direct water
flow. Each UV reactor contains one high-intensity, me-
dium-pressure UV lamp mounted inside a quartz tube.
The lamp and tube assembly are positioned perpendicu-
lar to the side walls of the chamber. The combined UV
lamp power intensity for reactors ranges from 10 to 720
kW. Effluent pH adjustment, with sodium hydroxide, for
instance, may be required to meet the permitted pH
discharge criteria.
A.14.2.3 UWOzone
EPA (1) reported a typical contact time of 15 minutes for
UV/ozone oxidation systems. The use of ozone is de-
scribed in the technology summary on chemical oxidation.
A.14.3 Pretreatment Requirements
UV radiation works best when interferences, such as
suspended solids or iron, are absent from the water to
be treated. Typical pretreatment steps may include the
following unit operations:
• Equalization, storage, recirculation to adjust for vari-
able flow.
• Separate immiscible liquid (LNAPL, DNAPL) by grav-
ity separation or flotation.
• Remove suspended solids by sedimentation and/or
filtration.
• Remove iron by oxidation and precipitation (iron can
interfere with UV transmission).
• Remove as much of other nontarget dissolved
species as possible. Other oxidizable substances,
such as naturally present humic material, have an
associated demand that competes with contaminant
degradation.
• With hydrogen peroxide, adjust solution pH to be-
tween 4 and 6 if the influent carbonate plus bicarbon-
ate concentration is greater than about 400 mg/L as
equivalent calcium carbonate. (Low and high pH rap-
idly decrease destruction efficiencies.)
• Disposal of total suspended solids, chemically pre-
cipitated sludges, and LNAPL or DNAPL.
117
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To Discharge
or Disposal
Contaminated
Water
Hydrogen
Peroxide
Splitter
Static Mixer
Oxidation Unit
Rgure A-28. perox-pure UV oxidation treatment system (6).
A.14.4 Design Considerations
The UV reactor varies from 300 gal to 3,900 gal (7).
Ozone generators range from 10 to hundreds of pounds
per day. Hydrogen peroxide is either used in place of or
in combination with ozone. The optimal proportion of
oxidants for maximum removals, however, cannot be
predetermined, although the stoichiometry for hydroxyl
radical formation is predictable (4). Pilot-scale or treat-
ability tests, therefore, still need to be undertaken.
The performance of the Ultrox system is influenced by
waste characteristics, operating parameters (e.g., hy-
draulic retention time, ozone and hydrogen peroxide
dose, UV lamp intensity, influent pH level, and gas-to-
liquid flow rate ratio), and maintenance requirements.
An alternative chemical oxidation system typically con-
sists of a chemical oxidation unit (reactor chamber), a
hydrogen peroxide feed module, a UV lamp drive, and
a control panel unit. Systems capable of treating flow
rates varying from 5 gai/min to thousands of gallons per
minute have been built (3).
The principal operating parameters are hydrogen perox-
ide dose, influent pH, and flow rate. Although initial
values of these parameters can be estimated, treatabil-
ity studies are necessary to accurately establish their
design values.
A. 14.5 Major Cost Elements
Figures A-29 and A-30 present estimated capital and
O&M costs associated with the UV/hydrogen perox-
ide/ozone system. Figures A-31 and A-32 present esti-
mated capital costs and O&M costs for the UV/hydrogen
peroxide system.
A.14.6 Residuals Generated
UV/oxidation is claimed to be able to destroy organic
chemicals without creating a waste product. Oxidation
products include carbon dioxide, water, various salts, or
harmless organic acids. If the reactor off-gas contains
volatile compounds along with unreacted ozone, a cata-
lytic system can be employed to convert the organics to
mainly carbon dioxide, water, and salts (7).
A.14.7 References
1. U.S. EPA. 1990. Technologies for upgrading existing or designing
new drinking water treatment facilities. EPA/625/4-89/023. Cincin- '
nati, OH.
2. Glaze, W.H., J.-W. Kang, and D.H. Chapin. 1987. The chemistry
of water treatment processes involving ozone, hydrogen peroxide,
and ultraviolet radiation. Ozone Sci. Engin. 9:335-352.
3. U.S. EPA. 1993. perox-pure chemical oxidation technology. Appli-
cations analysis report. EPA/540/AR-93/501. Washington, DC.
4. U.S. EPA. 1990. Ultrox international ultraviolet radiation/oxidation
technology: Applications analysis report. EPA/540/A5-89/012. Cin-
cinnati, OH.
5. Froelich, E.M. 1992. Advanced chemical oxidation of organics us-
ing the perox-pure oxidation system. Wat. Poll. Res. J. Canada
27:169-183.
6. U.S. EPA. 1993. perox-pure chemical oxidation treatment.
EPA/540/MR-93/501. Washington, DC.
7. Ultrox. 1993. The Ultrox UV/oxidation process: On-site destruc-
tion of organics in water. Santa Ana, CA: Zimpro Environmental.
8. Schmidt, J.M. 1993. Pump and treat ground water. In:
NATO/CCMS. Demonstration of remedial action technologies for
contaminated land and ground water. Final Report. EPA/600/R-
930/012C. pp. 65-75.
A.14.8 Additional Source
1. Kearney, PC., M.T. Muldoon, and C.J. Somich. 1987. UV/ozona-
tion of eleven major pesticides as a waste disposal pretreatment.
Chemosphere 16:2,321-2,330.
118
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1,000
»
3
45
I
10
0.01
0.1
System Capacity (million gal/day)
Figure A-29. Capital cost curve for UV/hydrogen peroxide/
ozone technology, in 1990 dollars (8).
& 90,000
I
O
c
| 80,000
70,000
TCE at 1,070 ng/L
PCEat108ng/L
Hydrogen Peroxide Dose
of 60 mg/L
Hydraulic Retention Time -
of 30 sec
20 40 60 80 100
System Capacity (gal/min)
120
Figure A-31. Construction cost curve for perox-pure technol-
ogy, in 1993 dollars (3).
1,000 r
08
o
10
0.01
0.1
System Capacity (million gal/day)
Figure A-30. O&M cost curve for UV/hydrogen peroxide/ozone
technology, in 1990 dollars (8).
100,000
90,000
80,000
'• 70,000
60,000
50,000
40,000
30,000
TCE at 1,070 ng/L
PCEat108ng/L
Hydrogen Peroxide Dose
of 60 mg/L
Hydraulic Retention Time
of 30 sec
20 40 60 80 100
System Capacity (gal/min)
120
Figure A-32. O&M cost curve for perox-pure technology, in
1993 dollars (3). '
119
•A U.S. GOVERNMENT PRINTING OFFICE: 1996 760-001/41033
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