6EPA
United States
Environmental Protection
Agency
Office of Water July 1984
Program Operations (WH-546)
Washington DC 20460
Independent
Physical-Chemical (IPC)
Treatment of
Municipal Wastewater
Design and Operations
Feedback
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INDEPENDENT PHYSICAL-CHEMICAL (IPO TREATMENT
OF MUNICIPAL MASTEWATER
FEEDBACK TO DESIGN/OPERATIONS
BY
ROY F, !''ESTON, INC,
HESTON !-'AY
WEST CHESTER, PENNSYLVANIA 19380
PROJECT MANAGER
JOYCE E, LEMMON
CONTRACT No, 68-01-6737
JULY 1984
U,S, ENVIRONMENTAL PROTECTION AGENCY
MUNICIPAL CONSTRUCTION DIVISION
WASHINGTON, D,C, 20460
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TABLE OF CONTENTS
Section Title Page
SUMMARY S-l
1.0 INTRODUCTION 1
2.0 PROCESS DESCRIPTION 2
2.1 Process Components 2
2.2 Problems with IPC Treatment Plants 2
3.0 PROBLEMS AND REMEDIAL MEASURES ASSOCIATED WITH
THE LIME HANDLING SYSTEM 6
3.1 Lime Loading and unloading 6
3.1.1 Problems 6
3.1.2 Remedial Measures 7
3.2 Lime Storage and Dry Feeders 7
3.2.1 Problems 7
3.2.2 Remedial Measures 8
3.3 Lime Slaking 8
3.3.1 Problems 8
3.3.2 Remedial Measures 9
3.4 Lime Slurrying 10
3.4.1 Problems 10
3.4.2 Remedial Measures 10
3.5 Lime Slurry Transport 11
3.5.1 Problems 11
3.5.2 Remedial Measures 12
3.6 Lime Slurry peed 13
3.6.1 Problems 13
3.6.2 Remedial Measures 14
4.0 PROBLEMS AND REMEDIAL MEASURES ASSOCIATED WITH
THE TERTIARY FILTRATION SYSTEM 15
4.1 Filtration Cycle 15
4.1.1 Problems 15
4.1.2 Remedial Measures 16
4.2 Backwash Cycle 17
4.2.1 Problems 17
4.2.2 Remedial Measures 18
11
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TABLE OF CONTENTS
(continued)
Section Title Page
5.0 PROBLEMS AND REMEDIAL MEASURES ASSOCIATED WITH
GRANULAR ACTIVATED CARBON SYSTEM 20
5.1 Adsorption Process 23
5.1.1 Problems 23
5.1.2 Remedial Measures 24
5.2 Carbon Contactor 26
5.2.1 Problems 26
5.2.2 Remedial Measures 27
5.3 Carbon Transport System 29
5.3.1 Problems 29
5.3.2 Remedial Measures 29
5.4 Backwash System 30
5.4.1 problems 30
5.4.2 Remedial Measures 30
5.5 Regeneration System 30
5.5.1 Problems • 30
5.5.2 Remedial Measures 30
5.6 Instrumentation and Control System 31
5.6.1 Problems 31
5.6.2 Remedial Measures 31
6.0 SUMMARY OF FINDINGS AND CONCLUSIONS 32
REFERENCES 35
APPENDIX A UNIT PROCESSES AND TREATMENT PERFORMANCE
OF IPC PLANTS A-l-
APPENDIX B LIME HANDLING SYSTEMS: IDENTIFIED PROBLEMS
AND SUGGESTED REMEDIAL MEASURES B-l
APPENDIX C FILTRATION SYSTEM: IDENTIFIED PROBLEMS
AND SUGGESTED REMEDIAL MEASURES C-l
APPENDIX D GRANULAR ACTIVATED CARBON SYSTEM: IDENTI-
FIED PROBLEMS AND SUGGESTED REMEDIAL
MEASURES D-l
iii
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LIST OF TABLES
Table No. Title
1 Problem Summary of independent Physical-
Chemical (IPC) Treatment Plants Visited
During the AWT Effectiveness Project 4
2 summary of IPC Facility Performance 21
LIST OF FIGURES
Figure No. Title Page
1 Typical Advanced IPC System Flow schematic 3
IV
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SUMMARY
This report presents the results of an investigation of 11 inde-
pendent Physical-Chemical (IPC) Treatment Plants, conducted as
part of a nationwide advanced waste treatment (AWT) effective-
ness evaluation sponsored by the U.S. Environmental Protection
Agency (U.S. EPA). The results of the investigation indicated
that virtually all of these plants are experiencing difficulties
with one or more of their treatment processes.
IPC treatment, as the name implies, involves the utilization of
only physical and chemical treatment processes (e.g., clarifica-
tion, filtration, carbon adsorption, ion-exchange, etc.) for the
treatment of wastewater. This document briefly outlines the
problems encountered at IPC plants and provides a limited dis-
cussion of the impacts of these problems on the plant's perform-
ance.
Problems associated with chemical treatment of wastewater, spe-
cifically with lime, are related to handling and feeding of this
material, and result in poor process performance that adversely
affects the downstream processes. The granular activated carbon
(GAC) process, commonly used in IPC plants, has been afflicted
with odor and corrosion problems associated with hydrogen sul-
fide formation, in some instances, the process has not attained
the degree of soluble organic material removal anticipated. In
addition, the granular tertiary filtration process has not met
design performance criteria. This latter problem has occurred
due to the inability of this process to cope with inconsistent
effluent quality from upstream processes, and the lack of ade-
quate flexibility in handling varying flow and solids loadings.
Potential remedies to the problems identified by this investi-
gation are also outlined in this document. These remedies should
be applied only after an engineer experienced with the design
and operation of IPC processes has thoroughly evaluated a facil-
ity to determine which solutions are practical and cost-effec-
tive.
S-l
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EPA has identified 14 IPC publicly owned treatment plants
(POTW's) operating in the united states (22). This report exam-
ines the performance of 11 of these 14 IPC facilities, and ex-
plores the capabilities and limitations of the IPC process. Des-
criptions of the unit processes, discharge requirements, and
performance characteristics for each plant are included in Ap-
pendix A.
The goals of this report are to:
• Identify design deficiencies, equipment performance de-
ficiencies, and operating problems relating to the IPC
process based on information from site visits.
• Suggest methods of improvement (as related to design,
equipment, and plant operations) so that they may be
used as feedback to the operators of existing facili-
ties.
Performance data for this feedback report were collected during
an investigation of advanced waste treatment (AWT) technologies,
as part of a U.S. Environmental Protection Agency (U.S. EPA) AWT
effectiveness evaluation. Eleven of the 14 identified IPC plants
in the united states were visited, and their treatment process-
es, performance, deficiencies, and problems documented. This in-
formation, supplemented with published data and other available
information, provided the basis for this report.
S-2
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1.0 INTRODUCTION
Independent Physical-Chemical (IPC) wastewater treatment systems
typically include preliminary treatment (such as bar screens,
comminutor, and/or grit chamber), chemical precipitation, clar-
ification, granular media filtration, activated carbon adsorp-
tion, and effluent disinfection (chlorination). Not every IPC
plant contains all of these processes; however, these are the
most common components, and will usually be found in some combi-
nation.
The IPC approach gained widespread interest in the early 1970's
as an alternative to conventional biological treatment process-
es. At that time the eutrophication of receiving waters was
identified as a serious problem caused by the presence of phos-
phorus in synthetic detergents commonly found in domestic waste-
waters. The IPC process using lime precipitation was considered
one of the methods of wastewater treatment for phosphorus remov-
al. The perceived advantages of the IPC process over biological
processes are summarized as follows:
• • More readily adaptable to variations in wastewater flow
and composition.
• Less susceptible to upsets from industrial wastes.
• Efficient removal of heavy metals by chemical precipi-
tation.
• Does not require treatment for stabilization of sludge.
Sludge is dewatered easily and can be disposed of in
landfills.
• Less space requirements.
• Removes phosphorus from the effluent, thus mitigating
the eutrophication problem.
Based on the observation of several IPC plants, it appears that
the plants are having problems meeting effluent discharge re-
quirements (17) and are also faced with the high cost of dispos-
ing of large quantities of chemical sludge (11). It is evident
that some of the process units in IPC plants, particularly the
granular activated carbon process, are not performing as expect-
ed due to design deficiencies and improper operation and mainte-
nance.
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2.0 PROCESS DESCRIPTION
2.1 PROCESS COMPONENTS
IPC treatment plants are comprised of a combination of different
physical and chemical treatment processes, the selection and or-
der of which usually depends on wastewater influent character-
istics and the effluent discharge requirements. There is no
standard unit process sequence for IPC plants. However, based on
the information from the plants surveyed, the typical process
units used in IPC plants are the following:
Screening.
Comminuting.
Grit chamber.
Chemical precipitation.
Clarification.
Tertiary filtration.
Granular activated carbon with carbon regeneration.
Chlorination.
in addition, dechlorination ion exchange and post-aeration are
also used in some plants to meet the site-specific effluent re-
quirements. The IPC treatment process relies to a great extent
on chemical coagulation and sedimentation to remove suspended
and colloidal solids. Filtration is commonly utilized as a proc-
ess to remove the residual suspended solids in the effluent af-
ter the clarification process. The granular activated carbon
system is used in place of a biological process for the removal
of soluble organics. When exhausted, the carbon with its ad-
sorbed organics is incinerated in a carbon regeneration furnace.
Of the eleven plants evaluated for performance, six of the
plants have filtration before carbon adsorption; three do not
have any filtration systems; one plant has filtration after car-
bon adsorption; and one plant has filtration both before and
after carbon adsorption. A typical schematic flow diagram of an
IPC plant is shown in Figure 1.
2.2 PROBLEMS WITH IPC TREATMENT PLANTS
The results of the AWT effectiveness evaluation (18) indicated
that there are many problems associated with the IPC treatment
technology that adversely affect its performance. Table 1 pres-
ents a summary of these problems as they relate to the major
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RAW SEWAGE
PLANT
SANITARY SEWER
ENTRANCE
MANHOLE
ENTRANCE STRUCTURE
COMMINUTORS. BAR SCREEN
PLANT
DRAINAGE
GRIT CHAMBER S PARSHALL FLUME
CLARI
FLOCCULATOR
RECARBONATION TANK
PRE CHLORINATION FEED
BYPASS ANY
OR ALL UNITS
MULTI MEDIA FILTER
FILTER WET WELL
FILTER EFFLUENT
PUMPS
BYPASS ANY
OR ALL UNITS
CARBON
AOSOR6TION
VESSELS
SODIUM HYDROXIDE FEED
CHLORINE BLENDER
BREAK POINT
CHLORINATION FEED
BYPASS ANY
OR ALL UNITS
OUTFALL SEWER
Source: Lozier Engineers, Rochester, New York
Figure 1. Typical advanced IPC system flow schematic.
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Table 1
Problem Summary of independent physical-Chemical (IPC)
Treatment Plants Visited During the AWT Effectiveness Project-1-
Unit
process Component
Lime feed system
Other chemical feed
system
GAC system
Filtration system
Process linkages2
Total
Number
of Plants
8
9
11
6
11
Number
of
Plants
with
Problems
5
3
10
3
5
Percent
of
Plants
with
Problems
63
33
91
50
45
leased on 11 operating IPC POTW's in the united states that
were visited.
2process linkages refer to the interdependence of unit process-
es in a treatment system.
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component process units in the system. As illustrated in Table
1, almost all of the plants had problems with their granular
activated carbon systems. Three major problem areas at IPC
plants have been identified, as follows:
• Lime handling system.
• Granular activated carbon system (GAC).
• Tertiary filtration system.
in each of these systems, problems are identified, and the caus-
es of the problems and the impacts of these problems on the per-
formance of the IPC plant are discussed. Remedies are suggested
for mitigating the deficiencies noted. Special consideration has
been given to remedies that facilitate improvement of existing
IPC treatment facilities.
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3.0 PROBLEMS AND REMEDIAL MEASURES ASSOCIATED WITH THE LIME
HANDLING SYSTEM
This section discusses the problems and remedial measures asso-
ciated with lime handling systems. The specific components of
lime handling systems discussed are the following:
Lime loading and unloading.
Lime storage and dry feeders.
Lime slaking.
Lime slurrying.
Lime slurry transport.
Lime slurry feed.
A summary of the problems and remedies are given in Appendix B.
3.1 LIME LOADING AND UNLOADING
3.1.1 Problems
Problems that occur while loading and unloading lime are the
following:
• One of the major problems experienced with loading and
unloading lime is the generation of lime dust. Manual
handling of bagged lime is a source of dust in the
loading/unloading area, in the case of bulk lime handl-
ing, the problem of dust is primarily attributed to
the malfunctioning of baghouses installed on top of
lime storage bins. If the baghouse filters are not
emptied frequently, they are unable to collect the
dust, thereby causing dissipation of dust in the load-
ing/unloading area.
• Sharp elbows and bends in lime transport piping to the
storage bin are subject to severe damage caused by
abrasion, depending on the type of lime used (hydrated
lime is generally less abrasive than quicklime).
• Maintenance and repair of lime transport piping is dif-
ficult if the piping is located at high elevations or
is otherwise inaccessible.
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3.1.2 Remedial Measures
Remedial actions that may be taken to alleviate these problems
are the following:
• An efficient dust collection system is essential for a
bulk lime storage bin. A hood and baghouse installed on
the top of the storage bin should be manually checked
after every loading operation to ensure that the con-
tents of the dust collection bag are discharged back
into the storage bin. shaking the bag helps to dis-
charge the contents easily. The bag should be replaced
periodically.
• A safety valve should be provided on the top of the
lime storage bin to prevent rupture of the bin in case
of buildup of excessive pressure due to malfunctioning
of the baghouse.
• sharp elbows and bends in dry lime transport piping
should be avoided. Piping with sweep turns of a mini-
mum 3 to 4 foot radius is recommended to reduce mechan-
ical wear and decrease resistance to flow. Piping
should be reinforced with additional plates at bends
to minimize excessive wear by abrasion, use of mate-
rials with high abrasion resistance should be consid-
ered for bends.
• The top of the lime storage bin and transport piping
should be easily accessible for maintenance purposes.
3.2 LIME STORAGE AND DRY FEEDERS
3.2.1 Problems
Problems involving lime storage and dry feeders are the follow-
ing:
• in lime storage bins, the flow of lime to the feeders
is interrupted by "arching" or "bridging" above the
hopper opening. Sudden "flooding" of the feed hopper
occurs when the arch breaks. This problem is particu-
larly common when lime in the form of fine powder is
used. Granular and pebble lime are generally free-flow-
ing materials.
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• Clogging of the feed hopper opening and feeder valve in
the storage bin. This problem occurs due to the entry
of moisture into the storage bin which causes the lime
powder to "cake," thereby preventing free-flowing con-
ditions.
3.2.2 Remedial Measures
Remedial measures to overcome these problems include the follow-
ing:
• The lime storage bin should have a conical bottom with
a 60° slope to facilitate easy flow of material into
the feed hopper.
• A "live bin" system or bin vibrator at the bottom of
the storage bin will prevent arching and bridging of
lime above the feed hopper opening.
• A volumetric type of feeder is preferred over the
gravimetric type, since the former is more reliable
and easier to operate and maintain.
• A rotary valve may be installed between the feeder and
lime slaker to prevent the entry of moisture into the
feeder.
3.3 LIME SLAKING
3.3.1 Problems
The following problems can occur in the lime slaking operation:
• Excessive mechanical wear of grit conveyors in deten-
tion- and paste-type slakers.
• Maintaining airtight conditions in a slaking system
and operating it under negative pressure is difficult.
Thus, moisture from the slaker travels back to the lime
storage bin causing "caking" of lime and resulting in
clogging of feed hoppers.
• Probes used for indicating slurry levels in slakers
malfunction due to encrustation and scaling.
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• Cleaning of slakers for maintenance is a labor-inten-
sive operation; encrustations of lime on tank walls,
valves, and orifices normally have to be manually
chipped, scraped, and removed from the slaker. This
cleaning problem is further aggravated if some parts
of the slaker are not easily accessible.
• instrumentation panels located on or adjacent to the
slaker are often covered with dust and grit. This con-
tributes greatly to malfunctioning of lime control
systems.
3.3.2 Remedial Measures
Measures to resolve these problems include the following:
• The lime slaker should be sufficiently offset from the
lime storage bin and feeder to prevent the steam and
moist lime vapors from the slaking operation traveling
backwards to the storage bin. This measure will help
to avoid the problem of "caking" of lime in the feeder
and storage bin.
• Maintaining the required slaking temperature is essen-
tial for complete hydration of quicklime. The optimum
slaking temperature range is 175°F to 185°F.
• Water-to-lime ratio for slaking should normally range
between 3:1 and 4:1 for detention-type slakers. How-
ever, recommendations for optimum slaking conditions
for the type of lime used should be obtained from the
vendor supplying the slaker.
• Lime slakers should be airtight and operate under nega-
tive pressure in order to prevent moisture and dust
from entering the work area or working backwards into
the lime feed system or lime storage bin. Aspirators,
though often used, have not always been successful in
maintaining a negative pressure. It is suggested that
a fan be used to draw vapors from the slaker and help
maintain a negative pressure in the slaker.
• Sonic-type level sensor systems can be used to avoid
encrustation problems commonly experienced with probes.
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• instrumentation panels and electrical control systems
should be located away from slakers and preferably be
housed separately to avoid entry of dust and moisture
from the slakers.
• Slakers should be located so that they are easily ac-
cessible for maintenance.
• Spare screw conveyor parts should be stored or readily
available as replacements because screw conveyors for
grit removal are prone to abrasive mechanical wear.
3.4 LIME SLURRYING
3.4.1 Problems
in most treatment process applications, lime is introduced as a
slurry. In the slurrying operation, slaked quicklime or hydrated
lime is mixed with water and agitated in a covered tank to form
a slurry of a concentration suitable for feeding (usually 5 to
10 percent by weight). Problems associated with lime slurrying
operations are as follows:
• Probes used for level control in slurry tanks are coat-
ed with scale and rendered ineffective.
• Maintenance of agitator motors, level controllers, etc.
in elevated slurry tanks is a problem due to poor ac-
cessibility.
• severe abrasion of the tank can occur if fiber-rein-
forced plastic (FRP) tanks are used for lime slurry
preparation, especially when quicklime is used; hydrat-
ed lime tends to be less abrasive.
3.4.2 Remedial Measures
Measures to alleviate problems in the lime slurrying operation
include the following:
• Sonic-type slurry level sensor systems are preferable
to conventional probes that become encrusted frequent-
ly.
10
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• Lime slurry tanks should be covered to prevent splash-
ing of slurry. For the slurrying of powdered hydrated
lime, a vent with a dust collection bag is required to
trap the dust generated. The bag should be located away
from the point where the lime enters the slurry tank
and should be checked and cleaned regularly.
• Lime slurry tanks should be constructed of corrosion-
resistant metal and not of fiber-reinforced plastic
(FRP) to prevent abrasion problems, particularly if
quicklime is used.
• Access should be provided for the maintenance of agi-
tators, level controllers, and other equipment in the
slurry tank.
• Water used for preparing lime slurry should not contain
excessive levels of carbonates, sulfates, or any other
ingredients that could react with the lime to cause
precipitation and scaling.
3.5 LIME SLURRY TRANSPORT
3.5.1 Problems
Transportation of lime slurry presents one of the most difficult
problems in a lime handling system, as noted below:
• Scaling of pipes is a severe problem common in most
lime slurry transport systems. Scaling may be due to
the following:
Leakage of air into pipes around the pump seals
or through other appurtenances, carbon dioxide in
the air reacts with lime to precipitate calcium
carbonate as scale on the inner walls of pipes.
Settling of solids from the lime slurry during
off cycles.
• Scaling and deposition of solids in sharp bends and el-
bows is very common in lime slurry transport lines.
Right angle bends at the bottom of vertical pipes are
extremely prone to the deposition of lime solids.
11
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• Small diameter piping is reported to be one of the maj-
or causes of frequent clogging of lime slurry transport
pipes in many wastewater treatment plants.
• Cleaning of scale accumulated in lime transport lines
is extremely difficult and labor-intensive, partic-
ularly when long lengths of metal pipes are used with-
out cleanouts.
3.5.2 Remedial Measures
Measures that may be employed to overcome these problems are as
follows:
• Lime transport piping should be at least 1-1/2 to 2 in-
ches in diameter to avoid frequent clogging problems.
• Flexible hoses should be used for lime slurry transport
piping wherever possible. Long straight lengths can be
of rigid piping. Flexible hoses have the major advan-
tage of being easier to maintain when clogging occurs.
Agitation of a flexible hose can release plugs caused
by an air lock or solids deposition in a lime transport
line. Scale accumulated on the inner walls of a flex-
ible lime transport pipe can be removed by flexing the
hose, which is not possible with rigid pipe. Flexible
hoses are also easier to replace than rigid pipes.
Transparent/translucent type flexible hoses help to
locate plugs in the line faster. However, flexible
hoses require more supports than rigid piping.
• Lime transport lines should be installed with minimum
bends. Sharp elbows and vertical runs should be avoid-
ed, "cleanouts" should be provided in lime slurry
transport lines as often as possible, particularly at
the bottom of vertical runs to facilitate cleaning of
lime deposits.
• Periodic cleaning of lime slurry pipelines using de-
vices called "pigs" would help to maintain a clean
slurry transport system. "Pigs" are plastic-rubber
products with abrasives spirally embedded in the sur-
face. It is moved by water pressure through the pipe
and removes the scale by a scouring or augering action.
12
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• It is recommended that lime transport lines be operated
continuously. Deposition of solids and scaling occur
when the line is out of service for only a few hours. A
recycling loop is one of the methods used successfully
to maintain continuous operation of a lime transport
system during off cycles.
• Provision for flushing lime slurry transport lines is
essential to prevent excessive build-up of scale in
pipes, valves, and other parts of the conveying system.
If the lime transport system does not have a recircu-
lating loop, automatic devices should be installed to
flush the line with water immediately after each opera-
tional cycle. If a loop system is not used, provision
should be made to manually flush the loop with water
after each lime feed operation. Periodic flushing of
the lines with corrosion inhibited dilute hydrochloric
acid to clean the residual scale is desirable to main-
tain a trouble-free lime transport system.
3.6 LIME SLURRY FEED
3.6.1 Problems
The controlled addition of lime slurry to a treatment process is
generally carried out using feed pumps and control valves. Prob-
lems experienced with lime slurry feed systems are as follows:
• Scaling and clogging of pumps and metering valves.
Clogging is particularly common when the feed system
is used intermittently.
• in pH-controlled lime slurry feed systems, encrusta-
tion of the pH probe (with lime solids and calcium car-
bonate scales) results in erroneous pH readings and
thus improper dosage of lime to the process.
• Progressive cavity-type metering pumps have high main-
tenance requirements due to stator wear.
• slurry feed metering valves with variable flow rate
control are easily clogged due to lime deposits in the
constricted areas of the valves.
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3.6.2 Remedial Measures
Measures to alleviate problems in the lime slurry feed system
are as follows:
• Take-off points for lime slurry feed should be located
on the vertical portion of transport loops and as close
as possible to the point of application. Provision
should be made for backflushing the take-off assembly
for cleaning purposes.
• Feed control valves should be operated in a fully
opened or fully-closed mode. Pinch valves are prefer-
able for this operation. Constricted valve openings
tend to clog due to scaling and deposition with lime
solids.
• The problem of malfunctioning pH probes due to scaling
can be solved by alternate use of two pH probes. One
probe can be cleaned and calibrated while the other is
being used. pH probes are to be cleaned frequently
with dilute acid and rinsed with-water.
• Diaphragm-type metering pumps provide better control
of feed than progressive cavity or other types of
pumps, and are less expensive to maintain.
• Rotary cup-type feeder or similar slurry feed systems
are preferable, wherever possible, over chemical feed
pumps because the latter are susceptible to clogging
problems.
14
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4.0 PROBLEMS AND REMEDIAL MEASURES ASSOCIATED WITH THE TERTI-
ARY FILTRATION SYSTEM
This section discusses the problems and remedial measures asso-
ciated with the tertiary filtration system in an IPC wastewater
treatment plant. The filtration system is divided into two oper-
ations, namely, the filtration cycle and the backwash cycle, in
order to separately address the problems and remedies for each
operation. A summary of the problems and remedies is given in
Appendix C.
4.1 FILTRATION CYCLE
4.1.1 Problems
Problems that occur during the filtration cycle are as follows:
• Media clogging is a widespread filtration problem that
results in increased head loss through the bed and
thus decreases the length of the filter run. Media
clogging can result from the following:
Microbial growth in the filter bed.
Solids carryover from prior treatment processes,
especially when process upsets occur.
Oil and grease carryover from prior treatment
processes.
Precipitation of calcium carbonate, calcium sul-
fate, calcium hydroxide, etc. on the filter bed
due to malfunctioning of a prior unit treatment
process.
• Hydraulic surges in influent flow to filters caused by
a lack of flow equalization facilities result in
operating difficulties and poor effluent quality.
• Uneven spacing of wash water troughs on the filter bed
creates differential velocity gradients, causing carry-
over of sand media during backwashing.
• improper design of the filter underdrain system causes
migration of filter media to the underdrains and clog-
ging of backwash nozzles.
15
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• Many operators have little or no training in the oper-
ation of filtration systems. This lack of knowledge and
training can cause ineffective filtration and inhibit
operators from making the alterations necessary to im-
prove filtration operations. This inflexibility can
compound problems during periods of process upsets.
4.1.2 Remedial Measures
Measures that may be employed to alleviate these problems are
as follows:
• The problem of frequent clogging of media and buildup
of head loss can be reduced by considering the follow-
ing measures:
Judicious selection of the type of filter media.
Multimedia filters normally perform better than
conventional single media sand filters in tertiary
wastewatef applications.
Applying a disinfectant, usually chlorine, to the
filter influent to control microbial growth in the
filter bed. The disinfectant should be applied on
a periodic basis or whenever microbial growth is
detected.
The treatment processes ahead of the filter should
be designed to provide better removal of suspended
solids. Removal of high concentrations of carry-
over solids by filtration systems is not cost ef-
fective. The preceding treatment process should
also remove oil and grease prior to the filtration
system. Once coated on the filter media, oil and
grease cannot be removed by normal backwash
methods.
• The problem of poor effluent quality due to hydraulic
surges in the influent to the filter can be mitigated
by incorporating the following measures:
influent flow to filters should be recorded and an
automatic controller should be provided to ensure
an even flow distribution among filters, in cases
where flow exceeds the design hydraulic capacity
of the filters, diverting the additional flow to
a surge tank should be considered in the design
of the system.
16
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Designing the filter system with the option to
operate filters in a parallel or series mode, in
case of increased suspended solids loading to the
filter due to sudden process upsets, series opera-
tion could help to meet the requirements for ef-
fluent quality. However, additional filters would
have to be provided to enable operating filters in
series.
• wash water troughs should be spaced uniformly over the
filter bed. Leveling of the troughs is critical to fil-
ter operation and troughs should be checked and adjust-
ed regularly.
• Clogging of backwashing nozzles due to media migration
can be minimized by utilizing nozzles fitted with a
protective plate on top.
• All operator(s) who work with the filtration process
must be familiar with filtration technology and the
operation of their system, pull knowledge of the sys-
tem will permit the operator to make operational modi-
fications necessary to improve the performance of the
system. This technical skill will be especially helpful
during periods of upsets in preceding treatment proc-
esses. The operator(s) must be able to assess the sit-
uation, modify the filtration system operating proto-
col, and, if necessary, decide when and what part of
the flow should bypass the filtration system.
4.2 BACKWASH CYCLE
4.2.1 Problems
Problems associated with the backwash cycle are the following:
• Backwash systems designed to operate on the basis of a
single criterion, either a fixed time interval or a
predetermined head loss, sometimes result in improper
frequency of backwash. For example, the backwash cycle
may not be initiated until the preset time interval
although the filter may require backwashing due to
high head loss that may have built up.
17
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• if the backwash rate and/or duration is not sufficient,
the bed will not be thoroughly cleaned, conversely, too
high a backwash rate because of an incorrect setting on
a backwash system with no rate-limiting control can re-
sult in media loss, gravel mounding, or gravel dis-
placement.
• incorrect operation of the auxiliary backwashing sys-
tems, such as surface-water wash, air scour, or subsur-
face agitation, can cause the following problems:
incomplete backwashing resulting in reduced filter
run times. This problem could occur if the auxil-
iary backwash system is not operative during the
initial fluidization stage of backwashing, thus
causing insufficient removal of foreign material
from the bed.
Loss of filter media. If the auxiliary air scour
is operated during the second stage of
backwashing when the wash water is flowing into
the troughs, the filter media would be carried
over with 'the wash water.
• Upstream process upsets can occur because of excessive
hydraulic loading on treatment units that receive back-
wash wastewater from tertiary filters.
• improper selection of the material of construction for
backwash nozzles results in corrosion and dislodging
from their support structures causing inadequate back-
washing.
4.2.2 Remedial Measures
Measures that may be taken to alleviate these problems include
the following:
• Backwash frequency should be controlled on the basis of
both head loss and a fixed time interval, whichever is
needed first. Effluent quality should be monitored and
a provision for manual override for backwashing should
be available to overcome upset conditions in the filter
operation.
18
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• Maintaining the correct operational sequencing is im-
portant for effective backwashing. The operator(s)
should observe the filter instrumentation during each
backwashing cycle to ensure that the correct operation-
al sequence occurs. At a minimum, a monthly visual
check should be made of each filter cell for a complete
backwash cycle to ascertain that all systems are oper-
ating correctly.
• The correct rate and duration of backwashing are essen-
tial for good filter system operation. The operator(s)
should frequently check all of the settings of the rate
and timer controls to ensure that they are appropriate.
The controls and instrumentation should be recalibrated
as required to ensure that the system is functioning
properly. The operator(s) should adjust the rate of the
backwash flow to compensate for the change in water
viscosity because of changing temperatures. The rate
should be decreased during the cooler part of the year
and increased during periods of warmer weather so that
a comparable degree of bed expansion is achieved
throughout the year during backwash.
• Timer systems used for controlling the duration of
backwash should be adjustable for the total duration
as well as the duration of high and low rate cycles in
backwashing. This design feature builds an additional
flexibility into the operation of the filter, which is
often very helpful in mitigating problems.
• An interlock control system is recommended to ensure
that the designed maximum number of filters to be
backwashed at any given time is not exceeded.
• It is recommended that backwash wastewater be collected
in a surge tank and recycled to other process units at
a controlled rate. This will help to minimize problems
created by significant hydraulic surges due to dis-
charge of backwash wastewater from the tertiary fil-
ters.
• Materials of construction used for backwash nozzles,
underdrains and their support structure, and the filter
walls must be compatible with each other to avoid cor-
rosion problems caused by galvanic action and electrol-
ysis. Backwash nozzles should be securely mounted on
the supporting structure.
19
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5.0 PROBLEMS AND REMEDIAL MEASURES ASSOCIATED WITH THE GRANU-
LAR ACTIVATED CARBON SYSTEM
IPC treatment plants were designed and built to provide a sec-
ondary or higher level of treatment of wastewaters without the
use of biological treatment processes, secondary treatment typ-
ically required not less than 85 percent removal of BODs and
total suspended solids (TSS) and monthly average effluent
BODs and TSS concentrations not to exceed 30 and 30 mg/L,
respectively (2). GAG systems were intended to provide suffi-
cient soluble BOD removal to meet these secondary treatment
requirements. Some engineers and researchers have expressed
doubt over the ability of GAC systems to remove sufficient
soluble BOD to meet these secondary effluent requirements, and
the more stringent advanced effluent requirements that some IPC
treatment plants must meet (6).
Appendix A provides a summary of the effluent BOD and SS re-
quirements and treatment plant performance of the IPC plants
visited. An evaluation of the information given in Appendix A
is presented in Table 2. It should be noted that out of the
eleven IPC plants visited, five plants had taken the GAC unit
off-line, in order to make a realistic assessment of the per-
formance of the IPC plants, this evaluation is based on the
information from the six fully operational plants. Based on
Table 2, the following observations on the performance of IPC
plants are made:
• Only 33 percent of the plants met all BOD and SS re-
quirements.
• 80 percent of the plants met the BOD concentration re-
quirements, but only 33 percent could meet the percent
removal criterion for BOD.
• 80 percent of the plants met the SS concentration re-
quirements, and 83 percent met the percent removal cri-
terion for SS.
It was observed that only two out of the four plants designed
for secondary treatment met the effluent requirements. The two
plants designed for tertiary effluent requirements did not meet
the effluent standards.
It is evident that a large fraction of the plants are unable to
meet the percent removal criterion for BOD although most meet
the effluent concentration limits. One possible explanation for
20
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Table 2
Summary of IPC Facility Performance1
Effluent Requirement
All BODs and SS effluent
requirements
BODs limit
Percent BODs removal
requirement
Suspended solids limit
Total
Number
of
Plants
with
Requirement
6
5
6
5
Percent SS removal requirement 6
Number
of
Plants
Not
Meeting
Requirement
4
1
4
1
1
Percent
of Plants
Not
Meeting
Requirement
67
20
67
20
17
iflased on operating data from six fully operational IPC facil-
ities; five of the 11 plants visited had taken their GAG units
off-line.
21
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the failure to meet the percent removal criterion could relate
to influent strength. A weak influent (BOD and SS <160 mg/L)
makes it more difficult to achieve a given percent removal cri-
terion since relatively lower absolute effluent concentrations
must be produced. Of the plants that failed to meet the percent
removal criterion, all but one had influent BOD concentrations
of 160 mg/L or less.
Although 80 percent of the fully operational plants satisfied
effluent BOD concentration requirements, two facts must be
noted. First, all of the plants meeting this criterion were
operating well below design flow capacity. Secondly, in all but
one case, the influent strength was relatively weak (BOD and
SS <160 mg/L). It is impossible to project performance for full
strength, design flow conditions given the available operating
data.
Although the evaluation just discussed considers performance
data only from the six fully operational plants, the reasons
for the other five plants not being fully operational must also
be considered. The GAG units in these plants had severe problems
and had to be taken out of service. Some of these problems re-
lated to operational difficulties (e.g., plugging of the- carbon
bed, odor generation, corrosion of contactors, excessive costs
due to frequent regeneration of the carbon, etc.). In other cas-
es, the GAG unit simply could not achieve the treatment levels
required, and the expense of keeping the unit on-line could not
be justified. In all five cases the GAG unit, which is primarily
responsible for soluble BOD removal, did not function as intend-
ed. This raises a question as to the capability of the GAG proc-
ess to meet the appropriate effluent requirements for BOD remov-
al.
The following discussion of problems and suggested remedial
measures for GAG systems has been subdivided according to the
different components of a,typical GAG system. A specific section
is included on the carbon adsorption process itself. The effec-
tiveness, or ineffectiveness, of the carbon adsorption process
in removing soluble organics is a key issue. The process compon-
ents discussed include the following:
Adsorption process.
Carbon contactor.
Backwash system.
Carbon regeneration system.
Instrumentation and control system.
22
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Appendix D includes a summary of problems and suggested remedies
for the different components of the GAC system.
5.1 ADSORPTION PROCESS
5.1.1 Problems
The major operational process problem with the GAC system is the
inadequate removal of soluble BODs in the treated effluent.
This single problem significantly affects the overall perform-
ance of IPC plants and is considered a major deficiency of the
IPC process. The following discussion focuses on the carbon
adsorption process itself and its ability to remove soluble BOD.
According to theory, activated carbon removes soluble organics
from solution in three steps. The first step is the transport of
the solute through a surface film to the interior of the carbon.
The next step is the diffusion of the solute within the pores of
the activated carbon. The third step is the adsorption of the
solute on the interior surfaces bounding the pore and capillary
spaces of the activated carbon. Several factors can affect the
effectiveness of soluble organic matter adsorption by activated
carbon. These factors include the following (21, 22):
• The characteristics of the material to be adsorbed in-
cluding molecular weight, molecular size, and polarity.
Activated carbon is not effective for the removal of
low molecular weight soluble organic compounds. A
wastewater with a high percentage of these compounds is
a poor candidate for activated carbon treatment.
• The nature of the carbon itself (adsorptive capacity,
regeneration characteristics, structural properties,
and physical condition). All activated carbons do not
have the same properties; these properties vary depend-
ing on the type of carbon, utilizing an inappropriate
activated carbon can significantly reduce GAC system
performance.
• Wastewater characteristics such as temperature and pH.
• Performance of prior treatment processes and the BOD
and suspended solids loadings to the GAC system.
23
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Biological activity within a GAG system may signifi-
cantly enhance the removal of soluble organics and non-
adsorbable (e.g., nonpolar and low molecular weight)
compounds, but can also cause physical fouling and re-
duction in active surface of the carbon bed. The most
prevalent explanation is that adsorption causes in-
creased biological removal through a substrate concen-
tration effect on the reaction rate (1, 8). This bio-
logical activity has been postulated as the mechanism
responsible for the constant, long-term removals
observed in activated carbon systems (8, 16). However,
some researchers have hypothesized that slow mass
transfer into micropore regions accounts for the con-
stant removal of organic substances over extended time
periods (10, 13, 14, 15). At this time, it is not pos-
sible to conclude which mechanism is responsible for
the constant, long-term soluble organic removals. It is
important to recognize that this mechanism, although
not well understood, has the potential to enhance
removal in IPC systems(4).
5.1.2 Remedial Measures
Remedial measures to improve the efficiency of the GAG system
for soluble BOD removal are discussed in this section.
• Plant modifications to improve BOD removal include the
following:
Possible changes to the chemical precipitation and
clarification systems including improvements to
upgrade the current system and switching from lime
to a different chemical that may prove more effec-
tive.
Revising the order of the treatment processes to
decrease the pollutant loading to the GAG system,
such as placing the filtration system ahead of the
carbon contactors, may improve the BOD removal
performance of the GAG system, thus enabling the
plant to meet its BOD discharge objective.
24
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Chemical additions to enhance soluble BOD removal (3,
4, 5). Peroxide, oxygen, ozone, or sodium nitrate can
potentially improve carbon system performance by con-
trolling microbial growth in GAC systems. The control
of microbial growth includes both the enhancement and
elimination of microbial activity. Anaerobic micro-
organisms, when established in a carbon contactor, can
cause the generation of hydrogen sulfides. Addition of
sodium nitrate has been very effective in preventing
microbial reduction of sulfates to hydrogen sulfides
under anaerobic conditions (4). Aerobic microbial
growth can have either a positive or negative effect
on the GAC system effluent. Aerobic microbial activity
can lead to the biological assimilation of organics by
microorganisms in the contactor and prevent sulfide
formation. This biological assimilation can help to
reduce the BODs in the GAC system effluent. However,
aerobic microbial growth can interfere with adsorption
capability of the carbon bed and increase backwash and/
or regeneration requirements.
An aerobic condition can be created in the carbon con-
tactor by adding air, oxygen, etc. to the carbon system
influent which, in turn, can ensure the growth of
aerobic microorganisms in the contactors (3, 5). Chemi-
cals have also been added to decrease the wastewater
pH to slightly below neutral levels to increase the ad-
sorptive characteristics of the activated carbon (21).
25
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• The carbon should be regenerated at required intervals
to ensure a fresh, readily adsorbing carbon. It is
important that any carbon lost during regeneration be
replaced. The type of activated carbon installed with
the system should also be studied. Carbon structural
properties, performance, and cost are not necessarily
related. Sometimes a structurally sound and inexpensive
carbon is selected at the sacrifice of performance. The
plant operators may have to change the specific acti-
vated carbon type, at possibly greater cost, to meet
effluent requirements.
• Pretreatment of selected wastewater sources for the
removal or alteration of nonadsorbable compounds. This
procedure may require an industrial or combined waste-
water testing program to:
Determine by isotherm testing if activated carbon
can still effectively treat the wastewater as
originally designed, and to determine if the non-
adsorbable compounds are entering the treatment
plant.
Determine by gas chromatography/mass spectrometry
testing which compound(s) are not adsorbed by the
activated carbon system.
Determine industrial source(s) of nonadsorbable
compound(s).
Develop a treatment or pretreatment program to re-
move or alter the nonadsorbable compound(s). Ap-
propriate regulations must be available or enacted
to enforce the pretreatment program.
5.2 CARBON CONTACTOR
5.2.1 Problems
The following problems are associated with the carbon contactor:
• Corrosion of carbon contactors has been observed in a
number of POTW's. Dry carbon is not corrosive. However,
partially dewatered carbon is extremely corrosive, un-
der conditions of continuous exposure, it may produce
pitting in unprotected mild steel plate by electrolytic
corrosion at a rate as high as 250 mils per year.
26
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Corrosion can also be caused by hydrogen sulfide. Hy-
drogen sulfide gas develops when sulfates present in
the influent wastewater are biochemically reduced by
sulfate-reducing bacteria, conditions promoting or ac-
celerating hydrogen sulfide production in GAC contac-
tors include (17, 21):
Anaerobic conditions, i.e., the absence of oxygen
in the GAC system influent.
High concentrations of BOD and sulfates in the GAC
system influent.
Long detention times.
• Media clogging occurs in GAC systems in the IPC plants.
It is primarily caused by development of microbial
growth in the carbon bed. Media clogging increases the
head loss through the carbon bed and thus decreases the
length of the operating cycle. Some clogging problems
are the result of backwashing deficiencies, including:
Lack of backwashing facilities.
Design of an ineffective backwash system (no aux-
iliary wash or scour systems provided).
Backwash rate and/or duration are not sufficient
to thoroughly clean the bed.
5.2.2 Remedial Measures
Measures that may be employed to alleviate problems associated
with the carbon contactor are as follows:
• Carbon contactors, when constructed of mild steel,
should be covered with protective coatings of suffi-
cient thickness, such as coal-tar epoxy paint. The con-
tactor surface should be prepared prior to applying any
coating, to ensure that the coating will adhere to the
contactor surface. This preparation should include re-
pairing any defects found on the contactor surface,
cleaning the contactor interior, and surface prepara-
tion appropriate for the coating to be applied. Dewa-
tering bins, wash tanks, and quench tanks should also
receive a protective coating. Fiberglass tankage may
also be acceptable from a design standpoint.
27
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Potential remedies for controlling hydrogen sulfide
generation can be made by either chemical additions or
operating modifications. Chemical additions have been
used with limited success to control anaerobic micro-
bial growth/ which is the principal cause of hydrogen
sulfide generation. A better approach is to maintain
aerobic conditions in the column, thus limiting the
growth of hydrogen sulfide-producing bacteria (because
they require anaerobic conditions to grow).
Operating modifications can also be used to control hy-
drogen sulfide production in GAC systems, such as:
Increase the frequency of backwash, as needed.
Backwash GAC columns more thoroughly by use of
surface wash, if available. The plant should con-
sider installing this equipment if not already in
place.
Reduce the GAC system detention time by removing
certain carbon contactors from service if the de-
tention time is too long.
Preaerate the influent wastewater to the GAC sys-
tem utilizing a mechanical system.
Addition of sodium nitrate (NaNO3) to the in-
fluent of the GAC system.
These measures will aid in maintaining aerobic condi-
tions in the GAC contactor, which, in turn, will de-
crease hydrogen sulfide generation (4, 21, 22).
Media clogging can be limited by the proper operation
of the backwash system. Processing the correct rate
and duration of backwashing is mandatory for good GAC
system operation. Considerations should be given to
modifying the system to include an auxiliary wash sys-
tem if none is provided. Microbial growth can be con-
trolled by applying the above methods for hydrogen sul-
fide control.
28
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5.3 CARBON TRANSPORT SYSTEM
5.3.1 Problems
Problems that occur in the carbon transport system are as fol-
lows:
• Clogging of the carbon transport system pipes occurs
with GAC systems at many plants. The causes of this
problem are primarily design related and include the
following:
Undersizing of carbon slurry lines.
Poor carbon transport system design, i.e., use of
short radius and 90° elbows or insufficient
fluid velocity.
Lack of cleanouts in the carbon transport system.
• Clogging of the carbon slurry pumps used in GAC sys-
tems. The use of the wrong type of pump and/or small
diameter influent and effluent piping causes pump clog-
ging problems.
• Abrasion wear of carbon slurry pipes. The use of un-
lined mild steel pipe and short radius, right angle
bends in the slurry transport system result in exces-
sive wear.
5.3.2 Remedial Measures
Measures that may be taken to alleviate these problems are as
follows:
• coated cast iron steel pipe or glass-lined or rubber-
lined steel pipe are preferred for carbon transport
systems. Mild steel or FRP pipe should never be uti-
lized as a carbon transport pipe. Abrasion is greatest
at bends. Long radius fittings at changes in direction
of flow, along with extra heavy elbows and tees are
recommended. Rubber or ceramic-lined impellers are also
recommended for carbon slurry pumps (21).
29
-------
• Several improvements can be made to alleviate clogging
of the carbon transport pipes, increasing the transport
line size (a minimum pipe diameter of 2 inches is rec-
ommended) and decreasing the carbon-to-water slurry ra-
tio can help to prevent clogging in carbon slurry pipe-
lines.
5.4 BACKWASH SYSTEM
5.4.1 Problems
Clogging of the backwash and/or surface wash nozzles is a prob-
lem in the carbon contactor. Carbon media and/or solids that
leave the contactor are responsible for clogging nozzles and
wash mechanisms. The carbon migrates to the contactor under-
drains due to structural failures in the media support system,
where it is picked up by the incoming backwash water and causes
clogging of the distribution nozzles.
5.4.2 Remedial Measures
Preventing carbon loss can remedy the clogging of backwash and/
or surface wash nozzles that is caused by solids and media mi-
gration through the underdrain and into the backwash system.
Screens can be added to critical locations to prevent media and
solids migration. Cleanouts should be placed in order to permit
the screens to be cleaned. Frequent backwashing (especially af-
ter loading the carbon) will remove carbon fines from the bed
and decrease carbon clogs. These preventative measures should
also decrease carbon losses within a GAC system, thus reducing
operating costs.
5.5 REGENERATION SYSTEM
5.5.1 Problems
The regeneration system is a source of carbon loss during opera-
tion. Some carbon loss is expected during regeneration opera-
tions, but incorrect furnace operating conditions can result in
excessive carbon loss.
5.5.2 Remedial Measures
Preventing excess furnace operating temperatures, timely removal
of the regenerated carbon from the furnace, and proper handling
of the regenerated carbon can keep carbon loss during regenera-
tion to a minimum.
30
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5.6 INSTRUMENTATION AND CONTROL SYSTEM
5 .6 .1 Problems
Maintenance operations at many treatment plants are not adequate
to keep the system functioning properly, insufficient mainte-
nance can result in nonfunctioning or ineffective instrumenta-
tion systems, inoperable valves, pumps that do not work, etc.
These systems can impact on operations and cause the system to
discharge a poor quality effluent.
5.6.2 Remedial Measures
An adequate maintenance program should be established to ensure
that the instrumentation and control systems function properly.
It is especially important that these systems function properly.
These systems allow the plant operator(s) to control and monitor
the GAC process.
31
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6.0 SUMMARY OF FINDINGS AND CONCLUSIONS
Based on the previous discussion, the following conclusions on
the overall performance of IPC treatment systems may be made:
• The performance evaluation of IPC plants indicates that
most of the plants have numerous operational problems
with various process units. Chemical feed systems, par-
ticularly lime handling systems, have been especially
difficult to operate and maintain. The operation and
maintenance costs of the IPC plants have been very high
due to the high costs of chemicals, and excessive main-
tenance requirements. The survey showed that 6 out of
the eleven IPC plants evaluated had decommissioned one
or more of their process units due to severe operation-
al problems or excessively high costs of operation.
• From the standpoint of effluent quality, only two out
of the six fully operational IPC plants meet their
specified effluent discharge limitations. Both of
these plants were designed for secondary treatment
levels. The two operational plants designed for ter-
tiary treatment • levels did not meet the discharge
standards. Many IPC plants have problems attaining per-
cent removal requirements, while meeting the effluent
concentration requirements for 8005 and SS. This may
be attributed to weak influent strength (BOD5 of 160
mg/L or less), which was observed at most plants
visited.
• One possible explanation for the lower than expected
BOD removals in many IPC plants appears to be because
carbon adsorption may not be effective for removal of
low molecular weight soluble organics which exist in
domestic, as well as industrial wastewaters. Air or
oxygen-containing compounds may be fed to the carbon
adsorbers to enhance aerobic biological activity and
consequent removal of low molecular weight biodegrad-
able organic material. However, increased levels of
biological growth within the carbon bed can also re-
quire more frequent carbon regeneration requirements.
32
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• The operation of IPC plants requires qualified operat-
ing personnel trained specifically for dealing with
physical-chemical processes. This type of training is
significantly different from the training and experi-
ence commonly received from operating biological treat-
ment processes. This deficiency has been observed in
several of the IPC plants visited.
• it is recommended that the performance of IPC plants
should be evaluated by an engineer experienced in
physical/chemical treatment technology, and appropriate
remedial measures taken accordingly.
The following conclusions and recommendations are made for the
design and operation of specific unit processes in the IPC
plants:
• Frequent backwashing and maintaining aerobic conditions
in GAG contactors can minimize the hydrogen sulfide
generation problem.
• Lime handling systems are prone to problems of equip-
ment malfunction and, in general, require frequent
maintenance and operator attention due to the inherent
nature of the chemical and its limited solubility in
water. Lime slurry transport and feed systems are the
major problem areas in the lime handling system, scal-
ing and clogging of pipes is a chronic problem in the
lime handling system, problems of lime slurry transport
systems could be minimized by the following:
Maintaining continuous operation of the system
utilizing recirculation loops.
Using flexible hoses.
Periodically flushing the lines with water.
33
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Providing a minimum number of bends.
Using piping at least 2 inches in diameter.
• The design of a filtration system in IPC applications
should be based on the consideration that wastewater
filters require provisions for flexibility in operation
to handle process upsets and meet effluent discharge
criteria.
• The filtration system, if used at an IPC plant, should
be placed prior to the GAG system to decrease the pol-
lutant loading to the GAC system.
• incorrect backwashing protocol can cause media clog-
ging, media loss, gravel mounding and displacement, and
mudball formation in the tertiary filtration system.
In order to ensure that the filter is backwashed at the
appropriate time intervals, the frequency of backwash-
ing should be controlled on the basis of both head loss
and a fixed time interval, whichever occurs earlier.
Settings of the rate and timer controls for backwashing
should be checked regularly for correctness.
In the course of this study many design-, operational-, and
equipment-related problems have been observed at independent
physical-chemical treatment facilities, implementation of the
remedial measures recommended in this report should significant-
ly improve the performance and operational reliability of these
facilities. However, there is some question concerning the abil-
ity of IPC processes (specifically, the granular activated car-
bon process) to remove low molecular weight soluble organics to
the extent necessary to achieve advanced treatment design cri-
teria. It is recommended that this question be addressed in fur-
ther studies (i.e., pilot-scale studies and field studies).
34
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20. Roy F. Weston, inc. Feedback to Design/Operation - Granular
Activated Carbon Advanced wastewater Treatment (AWT) Task 5,
December 1983, Draft Report.
21. U.S. EPA Process Design Manual for Carbon Adsorption. Tech-
nology Transfer 1973.
22. U.S. EPA, Municipal Technology Branch, personal communica-
tion, January 1984.
23. Weber, W.J., Jr. Physiochemical Processes for Water Quality
Control. John Wiley and Sons, inc., New York, 1972.
36
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APPENDIX A
UNIT PROCESSES AND TREATMENT PERFORMANCE OF IPC PLANTS
-------
Unit processes and Treatment Performance of IPC Plants
present/
Treatment Design
Plant Plow
(mgd)
unit Process in Treatment Order
Parameter
influent
(rag/L)
Compliance with
Permit Effluent Requirements
Effluent Limit Percent2
(mg/L) (mg/L) concentration Removal
10/12.5 Preliminary treatment BOD5 211
cnemical (lime) precipitation SS 263
Kecarbonation-clarification (upflow)
Activated carbon adsorption
Cnlorination
Dual-media filtration
10.0/15.3 Preliminary treatment (municipal flow) BODj 135
Chlorination (municipal flow) SS 450
Primary sedimentation (municipal flow)
Cnemical (lime, alum, and polymer)
precipitation-clarification
(industrial and municipal flows)
Activated carbon adsorption (industrial
and municipal flows - downflow)
Post-aeration (industrial and municipal
flows)
3.75/6.0 Preliminary treatment BODs 160
Cnemical (ferric chloride and polymer) SS 220
precipitation-clarification
Horizontal pressure filtration
First stage activated carbon adsorption
(upflow)
Breakpoint Chlorination
Dechlorination (second stage activated
carcon adsorption upflow)
pH adjustment
50
30
40
20
30
30
8
8
No
yes
No
No
No
Yes
No
yes
la
10
10
20
No
Yes
NO
yes
^Activated carbon system not utilized.
2A11 plants are assumed to have a requirement to meet a minimum of 85 percent removal of BOD5 and SS unless specified otherwise.
-------
Unit Processes and Treatment Performance of IPC Plants
(continued)
present/
Treatment Design
Plant Plow
(mgd)
Unit Process in Treatment Order
Parameter
Compliance with
Permit Effluent Requirements
influent Effluent Limit Percent2
(mg/L) (mg/L) (mg/L) Concentration Removal
I
ro
0.31/0.60 Preliminary treatment BOD5
Chemical (lime and ferric chloride) SS
precipitation-clarification
Dual-media filtration
Activated carbon adsorption (downflow)
Dual-media filtration
Ion exchange columns
Cnlorination
0.05/0.05 Hydrosieve
Chemical (FeCla and polymer) BODg
precipitation-clarification SS
Activated carbon adsorption (upflow)
Chlorination
6.5/10.0 Preliminary treatment BOD5
Chemical (alum, PeCla, and polymer) SS
precipitation-clarification
Microstraining
Activated carbon adsorption (downflow)
Breakpoint chlonnation
Dechlorination
Post-aeration
0.5/1.0 Preliminary treatment BOD5
Chemical precipitation-clarification SS
Multimedia filtration
Activated carbon adsorption (downflow}
Breakpoint chlorination
Dechlorination
Post-aeration
8.1/13.0 Preliminary treatment BOD5
Chemical (alum, FeCl3, and polymer) SS
pieci Citation-clarification
Sand filtration
Activated carbon adsorption (upflow)
Chlorination
168
239
16
2
216
346
131
160
20
13
70
21
250
200
75
30
155
130
30
20
25
30
Ves
Yes
Yes
yes
95 percent
95 percent
30
30
No
Yes
No
Yes
No
Yes
10
10
No
No
No
Yes
30
30
Yes
Yes
NO
Yes
Activated carbon system not utilized.
2A11 plants are assumed to have a requirement to meet a minimum of 85 percent removal of BOD5 and SS unless specified otherwise.
-------
Unit Processes and Treatment Performance of IPC Plants
(continued)
n
Treatment
Plant
9
10
II1
Present/ Compliance witn
Design Permit Effluent Requirements
Flow Unit Process in Treatment Order Parameter Influent Effluent Limit Percent2
(mgd) (mg/L) (mg/L) (mg/L) Concentration Removal
0.35/0.5 Preliminary treatment BOD5 120 25 30 Yes No
Chemical (PeCl3 and lime) precipita- SS 150 75 30 No No -
tion-clarif ication
Activated carbon adsorption (downflow)
Chlorination
0.5/2.0 Preliminary treatment BOD5 137 11 30 Yes Yes
cnemical (Pecl3 and polymer) precipi- SS 145 7 30 Yes Yes
tat ion-clan ficat ion
Granular media filtration
Activated carbon adsorption (upflow)
Chlorination
11.0/16.0 Preliminary treatment BOU5 130 52 20 No No
Chemical (FeCla) precipitation- SS 121 33 20 No No
clarification
Activated carbon adsorption (downflow)
Chlorination
1 Activated carbon system not utilized.
2A11 plants are assumed to have a requirement to meet a minimum of 85 percent removal of BODs and SS unless specified otherwise.
AD-
D-0
BK-
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APPENDIX B
LIME HANDLING SYSTEMS: IDENTIFIED PROBLEMS AND SUGGESTED
REMEDIAL MEASURES
-------
Lime Handling System: Identified problems and Suggested
Remedial Measures
Identified Problem
Suggested Remedial Measures
Lime Loading and Unloading
Dust.
Mechanical weac of transport piping.
Delay in repair and maintenance of line
transport piping.
Lime Storage and Dry Feeders
Arching over hopper openings.
Clogging of feed hopper, valves, and
screw feeders.
Lime Slaking
Unreliable slaked lime delivery.
Mechanical wear of grit conveyors
and other moving parts.
Malfunctioning of probes used for
indicating levels of slurry.
Instrumentation for control systems
coated with lime dust.
Lime Slurryxng
Malfunctioning of liquid level control
systems in slurry tanks.
Inaccessibility of agitator drives and
other equipment located on slirry tanks.
Mechanical wear of FRP slurry tank
walls.
Install and maintain a dust collection baghouse system
on lime storage silo/bin.
Avoid sharp elbows and bends in piping. Install addi-
tional plates at bends for reinforcement.
Install ladders, catwalks, and platforms for quick ac-
cess during maintenance work.
Install vibrating hoppers or 'live bin* systems.
Prevent entry of moisture into feeder by installing
rotary valve between feeder and slaker, or offset-
ting location of slaker from feeder.
Maintain proper temperature and water-to-lime ratio in
slaker. Operate slakers under negative pressure to
prevent entry of moisture into feeders. Periodic clean-
ing of slakers.
Use better quality lime with lower grit content:, if
possible. Spare screw conveyor should be available for
replacement.
Clean probes regularly. Consider use of sonic-type
level sensors.
Locate instrumentation panels away from high dust
areas. Enclose panels in housing.
Clean probes regularly. Consider use of sonic-type
level sensors. Provide overflow piping to handle
emergency conditions.
Install ladders, catwalks, and platforms to facilitate
access for maintenance.
Construct erosion-resistant steel slurry tanks to pre-
vent aorasion problems.
B-l
-------
Lime Handling System: Identified Problems and Suggested
Remedial Measures
(continued)
Identified Proolem Suggested Remedial Measures
Lime Slurry Transport
Clogging of lime slurry transport lines. Operate transport lines continuously. Install re-
circulation loops. Use flexible hoses for transport
piping. Minimize length of slurry transport lines.
Avoid sharp bends and elbows to prevent accumula-
tion. Provide cleanouts in piping. Use large diam-
eter piping to prevent frequent clogging. Plush
transport piping after each use with water, consid-
er use of covered troughs for lime slurry transport.
Lime Slurry Feed
Clogging of lime slurry feed piping, Locate take-off points for slurry feed as close to
pumps, and valves. point of application as possible. Use open/close-
type feed control valves — avoid variable flow
control valves. 'Rotodip' or similar type feed sys-
tems are preferable to progressive cavity-type feed
pumps.
Malfunctioning of pH meters used for Use two pH probes in cyclic order.
lime feed control.
B-2
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APPENDIX C
FILTRATION SYSTEM: IDENTIFIED PROBLEMS AND SUGGESTED
REMEDIAL MEASURES
-------
Filtration System: Identified Problems and Suggested
Remedial Measures
Identified Problem
Suggested Remedial Measures
Design Aspects
Frequent clogging of media and buildup
of excessive head loss.
Hydraulic surges in influent flow to
filters.
Improper frequency of backwashing.
Loss of media during backwashing.
Clogging of backwash nozzles due to
migration of media.
Corrosion of backwash nozzles.
Operating Aspects
A. Filtration Cycle
Media Clogging.
Excessive filtration system
downtime due to equipment
problems.
Incorrect operation of the filtration
system.
Multimedia filters should be considered. Design filters
to operate either in parallel or series. Improve qual-
ity of influent to filter by incorporating modifica-
tions to processes ahead of filter.
Provide equalization facilities ahead of filter.
Backwash frequency should be controlled on the basis of
predetermined head loss and a fixed time interval,
whichever is necessary earlier.
Wash water troughs should be uniformly distributed
over the entire area of the filter bed. A backwash rate
controller should be provided.
Use of nozzles fitted with a protective plate on top is
recommended.
Use of compatible materials of construction for noz-
zles, underdrain support structure, and filter bed to
avoid electrolysis and galvanic corrosion is recommend-
ed.
Microbial growth in filter bed ~ Add a disinfectant,
usually chlorine, to the filter influent periodical-
ly. Backwash to remove residual chlorine.
Solids carryover — The prior treatment process
should be modified to improve its performance. Removal
of these solids by filters is not effective.
Oil and grease carryover — The prior treatment proc-
esses should remove these constituents.
Chemical precipitation on filter — The chemical con-
ditions of the precipitation system should be adjust-
ed to ensure that all precipitation occurs in the pre-
cipitation system.
An adequate maintenance program should be established
and followed.
The operator(s) should receive training in filtration
theory and system operation. The operator(s) should be
aware of the system's capabilities so they can modify
it, especially during periods of prior treatment proc-
ess upsets, and in response to a change in conditions.
C-l
-------
Filtration System: 'Identified_Problems and Suggested
Remedial Measures
(continued)
Identified Problem
Suggested Remedial Measures
B. Backwashing Cycle
Incorrect operational sequencing
during filter bacfcwasning.
Incorrect rate and duration of
backwashing.
Incorrect operation of backwash
system.
Excessive backwash system downtime
due to equipment problems.
The operator(s) should observe the instrumentation dur-
ing backwashing to ensure that the correct operational
sequence occurs. A monthly visual check should also be
made of each filter cell for a complete backwash cycle
to ascertain that all systems are operating correctly.
A pole that rises above the media should be attached to
the arm of a submerged auxiliary wash or scour system
to aid in observing its operation.
Operators should be aware of correct backwashing rates
and duration. The settings of the rate and timer con-
trols should be checked regularly to ensure they are
correct. Operators should change backwash rates as
temperatures fluctuate to compensate for the change in
water viscosity with temperature.
Operators should be trained in the operation of the
backwash. They should be made aware of the system's
capabilities and how to modify its operation in re-
sponse to a change in conditions.
An adequate maintenance program should be established
and followed.
C-2
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APPENDIX D
GRANULAR ACTIVATED CARBON SYSTEM: IDENTIFIED PROBLEMS
AND SUGGESTED REMEDIAL MEASURES
-------
Granular Activated Carbon System: Identified Problems
and Suggested Remedial Measures
Identified Problem
Suggested Remedial Measures
Carbon Contactor
BOD removal goal not achieved.
Hydrogen sulCide generation in the
carbon contactor.
Corrosion of the carbon contactor.
Accumulation of solids in the carbon
contactor (media clogging).
Structural failure of the carbon
contactor underdrain and influent
piping.
Carbon Slurry Transport System
Clogging of the carbon slurry transport
pipeline.
Abrasion of the carbon slurry pipeline.
Clogging of the carbon slurry pumps.
The activated carbon should be tested for adsorptive
capacity; more frequent regeneration of the carbon; add
oxygen to the GAC influent.
Maintain aerobic conditions in the carbon contactor by
addition of oxygen, air, or peroxide to the GAC system
influent; add sodium nitrate to the influent to prevent
sulfide formation; increase the frequency of backwash-
ing; backwash GAC contactor more thoroughly by the use
of a surface wash; reduce the GAC system detention
time.
Spark test to determine defects in the contactor coat-
ing; patch defects in the contactor coating; reseal the
contactor with better coating material; use synthetic
connectors within the contactor; eliminate the poten-
tial for hydrogen sulfide generation.
Use surface washers and increase backwash frequency.
Modify underdrain and air grid system, redesign and re-
construct underdrain supports; replace defective piping
with pipe of increased wall thickness; specify a struc-
turally stronger grade of pipe; add additional pipe
supports.
Increase transport line size (minimum suggested
diameter is 2 inches); decrease carbon slurry concen-
tration; avoid the use of short radius right-angle
bonds.
Use black steel or lined steel pipe; long radius fit-
tings should be used at changes in direction of flow,
along with extra-heavy elbows and tees.
Decrease the carbon slurry concentration; modify the
carbon slurry pump (i.e., change the impeller or uti-
lize larger size intake or discharge piping); replace
the pump if the original cannot be modified to improve
its performanoe.
D-l
-------
Granular Activated Carbon System: Identified Problems
and Suggested Remedial Measures
(continued)
Identified pcoolem
Suggested Remedial Measures
Backwash System
Clogging of backwash and/or surface
wash nozzles.
Incorrect rate and/or duration of
backwasning.
Regeneration System
Excessive carbon loss.
Instrumentation and Control Systems
Nonfunctioning instrumentation and
control systems.
Prevent the carbon from leaving the contactor; add
screens to remove solids from the backwasn and surface
wash influent; provide cleanouts to permit cleaning of
the screens.
Operators should check rate and timer controls fre-
quently to ensure they are accurate; backwash controls
and instrumentation should be periodically recalibrat-
ed.
Operate the carbon regeneration furnace at the speci-
fied conditions; store enough spent carbon to permit
more continuous operation of the regeneration furnace.
An adequate maintenance program should be established
and followed.
L>-2
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