United States
                   Environmental Protection
                   Agency
 Risk Reduction
 Engineering Laboratory
 Cincinnati, OH 45268
                   Research and Development
 EPA/600/S2-90/012  Aug. 1990
&EPA         Project Summary
                   Performance of  Activated
                   Sludge - Powered  Activated
                   Carbon - Wet  Air Regeneration
                   Systems

                   Kevin J. Deeny, James A. Heidman, and Arthur J. Condren
                    The investigation summarized  in
                  this  report was undertaken  to
                  evaluate  the  performance  of
                  powdered activated  carbon (PAC)
                  technology used in conjunction with
                  wet air  regeneration (WAR)  at
                  municipal  wastewater treatment
                  plants. Excessive ash concentrations
                  accumulated in the  mixed liquor
                  suspended  solids (MLSS) at all
                  facilities that relied on the WAR unit
                  blowdown for ash  control. A variety
                  of ash control methods have been
                  implemented and  are documented.
                  The nitric acid test for PAC  was
                  shown to  substantially overestimate
                  PAC concentrations. Previous claims
                  that PAC losses through WAR are 5%
                  or less were based on selected use
                  of the nitric acid  test. PAC losses
                  across WAR or  the desirability and
                  economics of recovering the volatile
                  suspended  solids.  (VSS) exiting the
                  WAR reactor could not be quantified.
                  Other areas covered  in the report
                  include adsorptive capacity of the
                  recycled material,  tertiary filter  per-
                  formance,  metals accumulation,
                  oxygen transfer, operation  and
                  maintenance concerns and economic
                  considerations. The report  includes
                  Appendices submitted  by the system
                  manufacturer that  dispute many  of
                  the report conclusions and  provide
                  alternative explanations for some  of
                  the data obtained.
                     This  Project  Summary was
                  developed  by ERA'S Risk Reduction
                  Engineering  Laboratory,  Cincinnati,
OH, to announce key findings of the
research  project that is  fully
documented in a  separate report of
the same title (see Project Report
ordering information at back).

Introduction
   Addition of PAC to activated sludge
systems is a  proven  technology for
wastewater treatment. The use of wet air
oxidation for  the treatment  of non-PAC
sludges, such as primary and secondary
sludges,  is  also  an established
technology. Eleven municipal facilities in
the United States have been built using
these combined technologies, with the
wet air oxidation  process, which is
commonly  called  WAR,  used for
oxidation of excess biological solids and
regeneration of spent PAC.
   Nearly all municipal systems designed
for PAC addition in  the United States
have included WAR. A majority  of these
systems received Federal funding  under
the innovative technology program. The
evaluation summarized in this report was
undertaken to document the performance
of the PAC/WAR technology  at municipal
plants. The information on plant operation
and performance reflects data available
on or before August 1988.

Technology Description
   Figure 1 illustrates a flow diagram for
a typical municipal system incorporating
the PAC/WAR technology. Virgin PAC is
added  to the activated sludge  system
influent as a  make-up dosage. A slip
stream from the the secondary clarifier

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underflow,  which is composed of  an
activated  sludge/PAC  mixture,  is
thickened before being pumped to WAR.
Effluent filters,  at one  time  considered
optional (1), were installed in nearly all of
the municipal systems.
   The purposes  of the WAR systems
are  to  destroy excess  biomass,
regenerate PAC and provide  a means of
controlling ash build-up.
   High pressure feed pumps are used to
pump the activated sludge/PAC  mixture
to the WAR system and  to sustain an
operating pressure of approximately 800
psi.  Air is injected into the  sludge/PAC
stream by means of multiple-stage high-
pressure compressors.  Heat exchangers
are included for the mutual  functions of
reducing  the temperature of the treated
material and increasing the temperature
of  the  incoming  material.  The
air/sludge/PAC rrjixture reacts in a vessel
(reactor)  for a period of 25 to  50  min
before being discharged through the heat
exchangers. Steam boilers are used at he
beginning of each operating  cycle to
raise the  system temperature.  The
oxidation reaction  generally  provides
most of the heat required to sustain the
reaction  temperature between  230 °C to
245°C. Material exiting the WAR system
consists  of a mixture of PAC, other VSS,
nonvolatile  suspended  solids (NVSS),
and  a  large  component  of  soluble
organics  (which are formed in the for the
process). In accordance with  the claims
process (2),  the WAR reactor blowdown
stream was the only means of controlling
ash in the original design approach. This
stream  was  to  be  mixed  with  plant
effluent and a return stream  from  a
parallel  plate settler  underflow, before
flowing to the settler for separation of the
PAC  and ash  materials.  The  settler
overflow, containing recovered PAC, was
to be returned to the  process. A portion
of the settler underflow, containing settled
ash, was to be wasted.

Study Procedures
   Initially, discussions  were held with
personnel at the operating facilities, U.  S.
Environmental Protection Agency (EPA)
regional  offices, and the  process
 From
 Primary
 Clartfiers
                                                        lTo Tertiary Filters
                                                        i  Cake Disposal
  Figure 1.  Flow Diagram of Typical System with PAC/WAR.

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 manufacturer (Zimpro  Inc.)  to   gather
 background  information. Typical process
 data were collected  from the various
 facilities and reviewed. Site visits to five
 facilities  were  made  to  review  the
 intended versus the actual operation, and
 the types of  plant records maintained and
 analyses  performed;  a thorough plant
 inspection  documented  locations  of
 sampling  points and  sidestreams.
 Following  a  preliminary  analysis of the
 data and  assessment of the  PAC/WAR
 process,  an interim meeting  was  held
 (12/87) with  personnel  from Zimpro, EPA
 and the assessing contractor to review
 and discuss the preliminary  findings.
 Information  and  discussions  from this
 meeting were used by EPA to determine
 steps needed to complete the evaluation.
 Subsequently, two more facilities were
 visited  to  gather  additional data.
 Supplemental conversations  were then
 held with  people  at the various operating
 plants to  confirm information or secure
 missing  data.  This  information  was
 analyzed along with other published data
 to complete the technology evaluation.
   A  summary  of the results was
 presented  and  discussed during a  final
 meeting   (8/88)  with  several  EPA
 personnel, Zimpro personnel,  and the
 contractor  team.  Discussions  during the
 final  review meeting  and subsequent
 communications with  Zimpro Inc., have
 clearly indicated  a difference of opinion
 as  to  the  appropriate  interpretation of
 much  of the assembled data.  For  this
 reason, comments from Zimpro Inc., are
 provided in two appendices to  the final
 report so that their viewpoints will also be
 available to the reader.

 Plant Summary
   The municipal  PAC/WAR facilities that
 were reviewed are summarized  in Table
 1. Color reduction, nitrification,  limited
 space  availability and toxics  removal
 were the predominant  factors given for
 selecting this technology. Effluent permit
 limits range from  typical  30/30 mg/L for
 BOD5 and  total suspended solids (TSS)
 (with and without  nitrification) to  summer
 limits at Kalamazoo of  7/20/2/1 mg/L for
 BOD5/TSS/NH3-N/Total  Phosphorus. The
 current status  of municipal facilities
 indicates that all  have,  in some way,
 modified the  original design  and/or  of
 their systems.

 Ash Accumulation  and Control
  Mixed liquor  ash accumulation was a
common  problem at  all full scale
 PAC/WAR  facilities listed  in Table  1.
when they  were operated as originally
designed. The size and specific gravity of
 the ash and PAC particles were found  to
 be similar, and effective separation would
 not occur. As a result, ash  was returned
 to the process from the  Lamelle settler
 along  with the PAC.  Mixed  liquor ash
 levels  of  from  60%  to  80%  were
 observed at facilities that relied solely on
 WAR unit blowdown for ash control. This
 led to the loss of excess TSS from the
 secondary loadings on the tertiary filters.
    A variety of methods were initiated for
 ash  control. Vernon discontinued  PAC
 addition for several months at a time, but
 continued  to  run   the WAR  system.
 Mixed liquor was occasionally purged  to
 the primary clarifiers for disposal with the
 primary sludge.  PAC addition  was
 recently reinitiated to control  effluent
 color. Mount Holly discharges a portion of
 the WAR  unit effluent to  the  primary
 sludge dewatering  system  for disposal.
 East  Burlington  practices   direct
 dewatering of a WAR reactor effluent slip
 stream. PAC addition at South Burlington
 has  been  discontinued, and  the  plant
 currently operates  as  a conventional
 activated  sludge  facility.  Kalamazoo
 purged  mixed  liquor  for ash  control
 before  constructing  a  differential
 sedimentation  and elutriation  (DSE)
 system to separate  ash. Bedford Heights
 switched to  addition of a nonactivated
 carbon (NAG), which is used on a throw-
 away basis (no WAR system operation).
 The NAC costs $0.16/lb, which is roughly
 half the cost of a  typical  PAC,  and is
 maintained at the minimum concentration
 needed  for satisfactory plant  operation.
 Medina  County  is operating a modified
 DSE  system and is dewatering the ash
 with the primary sludge. North Olmsted
 experimented  with  several operating
 modes,  with and  without WAR  unit
 operation and with  and without PAC or
 NAC  addition. They recently switched to
 conventional  activated sludge  operation
 but plan to convert  back  to the use of
 NAC. Sauget added PAC during start-up,
 but  a catastrophic  failure  of a heat
 exchanger made it impossible to operate
 their WAR  system.  The initial PAC dose
 has since been  wasted from the plant. El
 Paso  is wasting a slip-stream  of sludge
 upstream from  their WAR  reactor to
 anaerobic digesters.

 Differential Sedimentation and
 Elutriation (DSE)
   Zimpro Inc.,  conducted a number of
 standardized  pilot plant  studies  of the
 DSE   process  to estimate   the
requirements for full-scale ash  removal
facilities.  On  average,  the  results
indicated that 37% ash removal and 90%
VSS  recovery  would  be reasonable
 expectations. Four  of the  PAC/WAR
 systems either have or are in the process
 of installing DSE systems.
    A slip-stream of the WAR unit effluent
 is blended with softened water in an ap-
 proximately  1:4  volumetric  ratio.
 Dispersants, such as  sodium hexameta-
 phosphate or metasilicate, and an anionic
 polymer are  then added before an up-
 flow elutriation tank. VSS (including  PAC)
 are concentrated and removed in the
 underflow,  and  the  ash  fraction  is
 concentrated  and exits in the overflow.
 Cationic polymer addition flocculates the
 ash, and this  stream is sent to a clarifier
 for separation. A filter press is the normal
 mode for dewatering  the  concentrated
 ash underflow. East Burlington has  a full
 scale  DSE system but,  because of the
 low PAC dosage required for satisfactory
 wastewater treatment,  does  not consider
 it cost  effective to operate.   Instead  a
 slip stream of WAR reactor  effluent is
 sent to  a dedicated  filter  press for
 dewatering. The system  at Jessup, MD,
 was not  in operation  at  the time this
 technology evaluation was conducted. A
 full  scale system  at Kalamazoo  was
 brought  on line in June 1988. Data  from
 the modified DSE system at Medina  were
 unavailable  for  incorporation  in  this
 evaluation.

 Ash Balances and Accumulation

   East   Burlington  and   Kalamazoo
 maintain extensive plant records and also
 monitor  internal  sidestreams. Material
 balances  for several  parameters  (e.g.,
 TSS,  VSS, and NVSS)  around  their
 aeration  basins and  WAR units  were
 developed from the operating records at
 these  plants. An  excellent TSS  balance
 was developed for 1 yr of record at the
 East Burlington plant. The recycled ash
 (NVSS) from the WAR unit  constituted
 83% of  the ash entering the aeration
 basins.
   Figure  2 illustrates the  buildup of
 various  MLSS components  that  was
 experienced over a 273-day period at the
 Kalamazoo facility. This operating period
 was selected because it does not include
 the removal of 4 million gallons of mixed
 liquor  from  the aeration  basins  for
 temporary ash reduction, which occurred
 in  the  last quarter of  1986,  nor  does  it
 include the period of  sustained  high
effluent TSS, which occurred  in the  last
quarter of 1987. The mixed liquor carbon
volatile   suspended   solids  (PAC)
concentration was measured by  a nitric
acid digestion procedure discussed in the
next section of this summary.  During the
periods  when effluent quality  was
reasonably satisfactory (April  through

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                 Table 1. Summary of Municipal PAC/WAR Facilities Reviewed
                                                                              Permit Limits
Facility
Vernon, CT
Mt. Holly. NJ
E, Burlington, NC
S. Burlington, NC
Kalamazoo, Ml
Bedford Hts., OH
Medina Co., OH
N. Olmsted, OH*
SaugetlL
EIPaso.TX
Flow, mgd
Current/
Design
4.2/6.5
2.4/5.0
7.0112.0
6.8/9.5
25/54
3.4/3.5
7/10
6/7
16/27
4.5/10
PAC/WAR
Status' i
MA [
MA l
MA '•
AS
MA :
NAC '•
MA S
AS I
AS i
MA ,
i-ieason
for
PAC"
C
C,S
C.N.T
C,N,T
C,N,T
N,S
N
N.S
T
A/,0
BODg,
mg/L
~W
30
72-24
12-24
7-30
10
10
10
20
SD##
rss,
mg/L
20
30
30
30
20-30
12
12
30
25
SD
NH3-N,
mg/L

20
4.0-8.0
4.0-8.0
2.0-10.0
5.1
1.5-8.0
2.3-6,9
""*
SD
                  *MA = Modified operation and/or design for ash pontrol.
                  AS  = Converted to conventional activated sludge.
                  NAC = Converted to the use of nonactivated carbon without regeneration.
                  -C  - Color Removal, S = Space, N = Nitrification, T = Toxics, O = Organics.
                  *Plan to convert to NAC without regeneration.
                  ##SD - Secondary Drinking Water Standards.
mid-September), there was a continuous
increase in ash concentrations.
PAC Measurements and Loss

Analytical Procedures
   Attempts  to construct mass balances
for PAC from  plant  records  were
unsuccessful. Determination of the PAC
content  in  the mixed  liquor  is  an
important process control parameter, and
the inability to perform PAC  balances
was deemed significant.  This  led to a
review of the nitric acid test method used
to determine the  PAC  fraction of the
MLSS in PAC/WAR systems.
   The MLVSS measured in PAC/WAR
system aeration tanks may be presumed
to  include active biomass,  residue,
nondegradeable VSS in  the  entering
wastewater, recycled and  virgin  PAC,
organics bound  to  the PAC  (which  are
measured as VSS), and any inert  VSS
formed in  and/or  not  oxidized or
solubilized in the WAR process.
 PAC/WAR  plants have traditionally
classified all VSS in the aeration basin as
 either PAC or biomass,  with  the  PAC
 concentrations measured on an ash free
 basis. The analytical method provided to
 the facilities to differentiate  between
 these two  classes of VSS assumes that
 all non-PAC VSS are dissolved by  nitric
 acid digestion.
    According to Zimpro personnel (3), the
 nitric  acid digestion  technique  was
 developed  at  Zimpro  to attempt to
 quantitatively determine the biomass and
 powdered carbon in a mixture.  A number
 of claims  concerning the accuracy and
appropriateness of the test are  doc-
umented in the Report.
Plant Operating Results

   In addition to using  the nitric acid test
procedures forf process control,  several
operating facilities also use the nitric acid
techniques to measure the  PAC losses
across  the  WAR  unit. The individual
measurement results from  three facilities
where these  data were  available are
summarized in Table 2.
   Nine months of data from both East
Burlington and tKalamazoo were analyzed
in attempts to establish PAC balances for
these facilities.   The results of  this
analysis are presented in Table 3. These
material balances  show that Kalamazoo
measures daily losses and accumulations
of PAC that exceed the PAC addition rate
by a factor of four. East  Burlington
measures daily PAC losses that are five
times higher than the  mass of daily PAC
addition. Since measurement of the PAC
addition rate does not depend on  the
nitric acid  procedure and has  been
verified through comparison  with plant
purchase  and [use records, the  average
 rate of PAC addition is known. Therefore,
the nitric acid procedure substantially
 overestimates PAC concentrations,
 making the  measured  value  of this
 parameter of no quantitative significance.
    A steady  state mass balance was also
 developed for East Burlington to evaluate
 aerator PAC concentrations as a function
 of PAC loss in WAR  and in  effluent and
 waste  solids. JThe results  indicated  that
 the PAC  concentrations measured in the
 aerator with ihe  nitric  acid test were
higher  than  could  be  present.  A
comparison of the measure value with
computed values  for  various assumed
oxidation  losses in  the  WAR unit
indicated that even with no  PAC oxidation
in  WAR,  the  measurement  error
[(measured value-true value) true  value]
would be 67%.
   Results  of previous VSS destruction
studies  on wet air oxidation of sludges
not containing PAC  are summarized in
the report and show that most, but  not all,
of the  VSS are oxidized or solubilized. A
small portion of VSS does  not go into
solution and, as shown  in  Figure 1,
nondegradeable VSS entering the plant
that are neither oxidized nor solubilized
by WAR must cycle  in the system until
escaping  in  the  plant effluent or until
being removed in  a waste stream.  Part or
all of the gradual buildup in MLVSS at
Kalamazoo, as shown in Figure 2,  can be
attributed to this  type  of  material.
Biomass  destruction through   WAR
(measured by the  nitric  acid test)  at
Kalamazoo decreased from  greater than
96% shortly  after start-up in  1985 to an
average of 83% during the first 5 mos. of
 1988.
    The  characterization  of  the VSS
existing WAR (as measured by the nitric
 acid test) at three  facilities  are sum-
 marized in Table 4.  The accumulation of
 this "biomass" material contributes to the
 falsely  high values for the  measured PAC
 concentrations.
    The absence of a correlation between
 PAC  addition   and  PAC  levels  (as
 measured by the nitric acid procedure)  at
 Kalamazoo is apparent in Figure  3. Ten-

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day moving averages of PAC  addition
minus the estimated daily PAC  loss
calculated from the effluent VSS values
and the measured PAC percentage in the
aeration basins) are shown along with the
measured 10-day moving average values
of mixed liquor PAC concentrations in the
aeration basins. There is  a gradual rise in
the measured  PAC concentrations  that,
on  a  long term basis,  is  independent of
the PAC addition rate.

PAC Loss by WAR
   The data summarized  in  Table 2
indicate PAC losses across WAR units to
be  in the range  of 30% to  40%  per
regeneration.  As shown in  Table  3,
however, the magnitude of the PAC loss
exceeds by four to five  fold the amount of
PAC added; this shows that the absolute
values  of the PAC  concentration
measured by the nitric  acid  digestion
technique are meaningless.  Whether or
not the  relative change of 30%  to 40%
represents the actual percentage  loss per
WAR  cycle cannot be determined from
the data available.
   In  previous  pilot  studies  of  PAC
systems with WAR, Zimpro reported  low
PAC  losses  through  WAR.   For
example.results reported from Back River
(4)  stated that the WAR unit operated
with PAC recovery efficiencies in excess
of 95%.  In an attempt to ascertain  the
reason for the large variations  between
the Back  River  results  and  those
observed  at  the three  facilities
summarized  in Table  2,  a detailed
analysis of the  Back  River report  was
 undertaken. The reasons for the apparent
 differences are  related to the  selected
 use of the nitric acid procedure and are
 detailed in the final report.

 Tertiary Filtration
   Tertiary filters were installed in nearly
 all  of the municipal  PAC/WAR facilities
 even though  several facilities have  an
 effluent TSS limit of only 30  mg/l. Solids
 capture in secondary clarification was not
 adequate at  East Burlington or Kala-
 mazoo to consistently meet the discharge
 permit indicating the key  role played  by
 the tertiary filters at these locations. In
 addition, polymer  assisted  clarification
 was normally   used  at  the  various
 facilities.  Typical  polymer  costs were
 estimated at  $21,000/yr/MGD based  on
 an applied dosage of 2.75 mg/l and a unit
 costs of $2.50/dry Ib.

 Recycle Loadings

   PAC systems  have  a  high mass  of
 organics, nitrogen and phosphorus in the
 WAR reactor effluent. The WAR  return
 stream can represent a significant portion
 of the  loading applied to  the secondary
 process.  Organic (BOD5) recycle loading
 at E. Burlington  and  Kalamazoo  ranged
 from 11 % to 29% of the primary effluent
 loading  and the NH3-N loading  ranged
 from 54% to 120%.
   Kalamazoo monitors  total  phosphorus
 in  the  WAR  return  stream. The
concentration  is  high  and  represents
730%  of the  mass  loading from the
primary  clarifier. This facility  has  a
phosphorus limitation and adds  alum  to
 the  secondary system for  its precipi-
 tation.  The  precipitated  phosphorus
 compounds  and those  resulting  from
 cellular destruction  by  WAR  have
 concentrated as  an  insoluble,  inert
 recycled material.

 Adsorptive Capacity of
 Recycled PAC
   It  is  difficult to  characterize  the
 adsorptive capacity of the material exiting
 the   WAR  system.  Attempts  to
 characterize the  regenerated PAC from
 the Sauget pilot study (5) showed that the
 COD adsorption  capacity was too  low to
 measure. That  study concluded that
 comparison  of virgin and  regenerated
 PACS was not an appropriate indicator of
 performance.
   Recktenwalt (6)  reported that  PAC
 subjected to multiple regenerations does
 not  retain  significant  capacity  for
 adsorption  of low  molecular weight
 compounds such as 2,4-dinitrophenol. On
 the  other  hand,   methylene  blue
 adsorption after  regeneration  was
 essentially  the same  as  that for  virgin
 PAC. Materials  that have  adsorptive
 properties  similar  to methylene  blue
 should adsorb as well to the recycled
 VSS as to virgin PAC.

 Metals Accumulation

   Activated carbon  will  adsorb  some
 heavy metals.  This removal  mechanism
could  help  reduce the  toxicity to
biological functions  in  PAC/activated
sludge systems.  One facility  (Bedford
Heights) experienced operating  and
  Table 2.  Measured PAC Losses Across WAR by Nitric
          Acid Digestion
                       Measured PAC
                       Loss per WAR   Number
  Location       Period     Cycle, %     of Samples
                                                        Table 3.  PAC Balances
  Kalamazoo   2/88-5/88      40.6

  £ Burlington 1/87-2/88      30.8

  Mt. Holly     1/87-7/87      32.1
46

31

48
Parameter
Input
PAC Added'
Kalamazoo,
Ib/day
3,704
Total 3,704
East
Burlington,
Ib/day
404
404
                                                        Loss + Accumulation
                                                           PAC Accumulation'                      1,277         0
                                                           PAC in Final Effluent"                   1,056       232
                                                           PAC Destroyed in WAR"                11,452       1,596
                                                           PAC Removed in Filter Press Solids"1          0         344

                                                        	Total	73,785	2,172

                                                        "Reported on an ash-free basis.
                                                        "Based on nitric acid test procedure.

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                                                  uillllilinjiiiui^iiliNiNlilllliiiiimun.lllNllllil-uiuu
                              i  16  31  46  61  76 91  106 121 136 151166 181 196 211 226 241 256 271
                                                Jan 1 to Sept 30, 1987
                       o MLSS  mg/l              + MLVSS, mg/l               « MLCVSS, mg/l
                    figure 2. Aeration basin suspended sdjids components at Kalamazoo, Ml.
effluent  quality  problems  that  were
attributed to heavy metals  accumulation.
This facility later controlled ash and  ash
associated heavy metal accumulations by
substituting  NAG  for PAC   and
abandoning attempts at media recovery.
   The Vernon facility noted high metals
concentrations in the blend  of  primary
and  waste  secondary sludge fed to the
vacuum  filters and conducted an EP
Toxicity  Extraction to  determine  the
Resources  Conservation Recovery  Act
(RCRA) status of the sludge.  Results of
the  EP  Toxicity  Extraction analyses
indicated that the metals  did not leach
appreciably under conditions of the test.
Operations  and  Maintenance
Considerations
   A WAR  unit  is composed  of high
temperature and  high pressure compo-
nents. Operating temperature/ pressure
conditions  require that repairs (such as
welding) be  performed  by  certified
craftsmen  and  that   all repairs  be
completed in such a manner  that the
pressure  and  temperature  rating
certifications are maintained.
   Operations of a WAR system requires
a working  knowledge  of boiler  water
chemistry. Several facilities experienced
coil failures in their WAR system boilers
that  were reported to  be the result of
inadequate deoxygenation of boiler feed
water. Othei" facilities  experienced
frequent  failure of high pressure valves
that  required I replacement of trims  and
seats.  A design  modification  to utilize
ceramic components has decreased the
failure rate at] some facilities.  Kalamazoo
and  Mount Holly have located alternative
suppliers  which has  resulted in valve
component  increased  service  life  and
reduced  co:St.  North  Olmsted   had
difficulty in! obtaining  replacement
components, borne of which had a 52-wk
delivery schedule because of the special
nature of the alloys specified  by the
system manufacturer.
   Scale formation in  the WAR reactor
reported by  several  facilities.  Formation
was severe at  some plants, resulting  in
limited   throughput  capacity   and
decreased operating temperature. Scale
formation continued  to occur in some
plants that  regularly acid cleaned  their
WAR systems. Manual  removal of  scale
with  water lasers has been  required  at
some facilitieb-
   Significant scum accumulation on the
surface of  secondary clarifiers  was
experienced  at three facilities. The cause
(s) for these  accumulations has not been
determined.
   Additional  O &  M  considerations  in-
cluded frequent maintenance on the last
stage of multi-stage air compressors, ab-
rasion-related repairs  to slurry  transfer
pumps, and  check valve  problems  on
high pressure feed pumps.
Economic Considerations

   A few  facilities  maintained separate
records of the costs associated with WAR
system, O & M. Average monthly O & M
costs in  1986 (parts,  electricity,fuel  oil
cleaning  and labor) for one facility that
processed an average  of  42,000  gpd,
containing 26,300  Ib/d of  TSS,  through
their WAR unit averaged $21.86/1,000  gal
or  $35.13/1,000 Ib of TSS  processed
through the  WAR unit. Another plant that
also maintained separate  cost records
computed 1986 WAR processing  costs
(fuel, water,  electric @ $.07/Kwh, repairs,
and labor)  to be  $27.68/1,000 gal or
50.88/1,000  Ib of TSS.
    Bedford  Heights maintained detailed
records of WAR operating  costs. For an

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2 -


 7 -


0


-7 -


-2 -


-3-


-4-
            -5
                         +\
                                           +  Carbon In-Out, LB/D
                                           D  10-day MLCVSS, mg/l
 	I	I	
7    76    37
	I1""
 46
T"
 67
""I '"
76
                                             97
 I
706
                                                  I
                                                 736

                                          Jan-Sept. 1987
                                                                  151   166
                                                                             I     I     I     I     I
                                                                            787   796   277   226  247
                     I
                    256
 I
277
Figure 3.  Ten day moving average ofPAC addition less loss and measured aeration basin levels at Kalamazoo, Ml.
11-mo  period  in  1986, the WAR  unit
processed 2.58 million gal at an average
cost $42.00/1,000  gal (labor, natural gas,
electricity, water lubricants, and repairs).
The cost was  equivalent to  $75.58 per
1,000 Ib processed. Bedford Heights also
operates a  low pressure oxidation (LPO)
unit for primary sludge  conditioning. The
1986 LPO operating costs (labor, utilities,
repairs)  were  $15.00/1,000  gal  con-
ditioned in this unit.
   Bedford  Heights considered  installing
a  DSE  system  during  their  cost
effectiveness  analysis of  options to
address ash buildup problems.  Instead,
they chose to  substitute NAG  for PAC
and waste the excess  biomass/NAC
mixture to  the primary clarifiers.  The
combined sludge is  now conditioned in
the  LPO unit  and the  WAR  unit is no
longer  operated  as such. They  have
proposed to convert the WAR unit to an
additional LPO unit.
   The economic  analysis performed  for
the  retrofit DSE  system at  Kalamazoo
                             assumed that all VSS  that exited the
                             WAR system were PAC (7). Based on the
                             nitric acid procedure, the PAC  content is
                             only 68% of the total  VSS  (Table 4).
                             Based  on the mass balances  presented
                             earlier, however, it is clear that the actual
                             PAC concentration is substantially  less
                             than that  measured  by  this  testing
                             procedure. Since there  is  no analytical
                             procedure available for the determination
                             of  true  PAC  content,   the  cost
                             effectiveness of the  Kalamazoo DSE
                             system cannot be accurately determined
                             on the basis of the reported value of the
                             PAC that is recovered by the system.

                              Table 4. Characterization of VSS from
                                      WAR
                              Facility          % PAC'   % Biomas"
E. Burlington
Kalamazoo
Mt. Holly
79.0
67.7
79.2
21.0
32.3
20.8
                               "As measured by the nitric acid procedure
   Operating costs for  DSE systems
include those  associated  with water,
water  softening,  dispersant and  dual
polymer  application, power and  labor.
Manufacturer pilot  studies were used  to
project these costs to  be approximately
$20/1,000  gal  of  material  processed.
Given the inaccuracy of the estimates  of
PAC content, it is difficult to determine
the benefit of a DSE  system operation
over that of direct wasting of a fraction  of
the material, as is practiced  by several
facilities.
   The  full report was submitted  in
fulfillment of EPA contract  No. 68-03-
3429  by  James  M.  Montgomery
Consulting  Engineers,  Inc.  under the
sponsorship of   the U.S. Environmental
Protection Agency.

References
1.  "Powdered Carbon: Right Combination
   at Tight Times", Reactor, 57, Zimpro,
   Inc. , June 1986.

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2. Bendt, C. L, Wet Air Regeneration of
   PAC, presented  at  the International
   Conference  on  Application   of
   Adsorption  to Wastewater Treatment,
   Vanderbilt University, February, 1981.
3. Knopp. P.  V.,  et a!., "Wet Oxidation
   Regeneration", in Carbon Adsorption
   Handbook,   edited  by  P.  N.
   Cheremisinoff and F. Ellerbusch, Ann
   Arbor Science  Publishers, Ann Arbor,
   Ml, (1978).
        4. Pilot Activated Sludge and Powdered
           Carbon Enhanced Activated Sludge
           Study at Baltimore, Maryland's Back
           River  WWTP, prepared  by Zimpro
           Inc. , Rothschild, Wisconsin.
        5. Vollstedt,  T  J. and Berrigan.,  J. K.,
           "Evaluation 'of Ash Removal from  a
           PACT/WAR^  pilot  System at  the
           American  Bottoms RWWTP", Zimpro
           Inc.,  Rothschild, Wisconsin,  July
           (1987).    ;
6.  Recktenwalt  M.A.,  fWet  Air
   Regeneration  of  PAC.   in  the
   PAC/Activated Sludge Prgcess", M.
   S. thesis, Environmental Engineering
   in Civil  Engineering, University  of
   Illinois, Urbana, IL(1986).
7.  "Ash Removal  Carbon Recovery
   System Testing and Proposed  Full-
   Scale  Design  for  the  Water
   Reclamation  Plant,   Kalamazoo
   Michigan",  Zimpro  Inc.,  August
   (1986).
   Kevin J. Deeny is with Jumkins Engineering, Inc., Morgahtown, PA 19543-0368;
        James A. Heldman  (also the EPA Project Officer, see below) is with the
        Risk Reduction Engineering Laboratory, Cincinnati, OH 45268; and Arthur
        J.  Condron is with  James M.  Montgomery  Consulting Engineers, Inc.,
        Pasadena, CA 91109-7009.
   The complete report, entitled "Performance  of Activated  Sludge-Powered
        Activated Carbon-Wet  Air Regeneration  Systems,"  (Order No. PB 90-
        188889IAS; Cost: $17.00, subject to change) will be available only from:
            National Technical Information Service
            5285 Port Royal Road
            Springfield, VA 22161                     i
            Telephone: 703-487-4650
   The EPA Project Officer can be contacted at:          :
            Risk Reduction Engineering Laboratory
            U.S Environmental Protection Agency
            Cincfncinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental! Research
Information
Cincinnati OH 45268
               BULK RATE
          POSTAGE & FEES PAID
                   EPA
             PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-90/012

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