United States
Environmental Protection
Municipal Environmental Research
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-051  August 1982
Project Summary
Chlorine  Dioxide
Disinfection and Granular
Activated  Carbon  Adsorption
Ben W. Lykins, Jr., and Mark Griese
  A pilot plant study was designed to
evaluate chlorine dioxide disinfection
as an alternative to chlorine for drasti-
cally reducing or preventing the pro-
duction of trihalomethanes. Also in-
vestigated was the effectiveness of
post-treatment adsorption by virgin
and reactivated granulated activated
carbon (GAC) for removal of organic
compounds that were either present in
the source water or formed after dis-
  The performance of a 0.38 m3/ min
(100 gpm) pilot plant using chlorine
dioxide disinfection for both raw and
treated water was compared with that
of a full-scale plant applying chlorine
disinfection at similar locations. Two
parallel post-filtration adsorber con-
tactors consisting of virgin in one
contactor and reactivated GAC in the
other were continuously operated and
evaluated until  exhaustion.  After
about 90 days of operation, the GAC
was educted and reactivated offsite by
an infrared furnace.
  Composite  samples of spent and
reactivated GAC were collected during
each run, and a representative virgin
GAC sample was taken directly from
the shipping bags for characterization.
Various properties were determined
on these samples to ensure that the
spent  GAC had been reactivated to
essentially virgin conditions and  to
provide an opportunity to compare the
performances of virgin and reactivated
  Analyses performed during the pro-
ject consisted of the quantification of
14 volatile and 8 extractable organic
compounds along with qualitative
(detected/nondetected) determina-
tions by mass spectrometer scans of
32 additional volatiles and 54 extrac-
table organics. Additional data were
collected for 9 inorganic metals, total
organic carbon (TOC), and other pa-
rameters such as turbidity, standard
plate count (S PC), and total colif orms.
  This Project Summary was develop-
ed by EPA's Municipal Environmental
Research Laboratory, Cincinnati. OH,
to announce key findings of the re-
search project that is fully documented
in a separate report of the same title
(see Project Report ordering informa-
tion at back).

  An experimental study was initiated
at the waterworks facility in Evansville,
Indiana, to help satisfy a basic need
within the water treatment and supply
industry for producing drinking water
relatively free of organics. This location
provided insight into the feasibility of
implementing an alternative method of
disinfection in a typical surface water
plant. The specific objectives estab-
lished for this project included:

   to  develop a water treatment
    process using chlorine dioxide as
    a disinfectant and to compare its

Table 1.    Experimental Modes of Operation for Pilot Plant
Chlorine   Dioxide   Alum   Polymer    Mix
Filter   Carbon  Chlorine  Dioxide


     production of trihalomethanes
     with those produced during chlo-
     rine disinfection.
   to determine whether any organic
     byproducts are formed when using
     chlorine  dioxide as  opposed to
     chlorine as a disinfectant.
   to determine the disinfection ef-
     ficiency of chlorine dioxide and its
     ability to provide residual neces-
     sary for full-scale distribution use.
   to determine the effectiveness of
     virgin  and  reactivated GAC for
     removing organic compounds that
     were either present in the filtered
     water  or formed after chlorine
     dioxide disinfection.
Treatment Method Selection
  The initial phase of the project con-
sisted  of a  control study and  three
experimental modes of operation (Table
1). Forthe control study (Run 1), the pilot
plant was operated for 2 weeks using
pre- and  post-treatment chlorine disin-
fection  and  bypassing  the GAC
contactors to allow a performance com-
parison with the full-scale plant. This
study revealed that the average concen-
trations of the two plant effluents were
comparable. In  addition  to average
values, the data for total instantaneous
trihalomethanes (THM's) and TOC were
subjected to the  t-test at a 95 percent
confidence level. This test showed no
significant difference for either param-
eter when data from the pilot plant were
compared with those for the full-scale
plant; the full-scale plant could thus be
used as a control for subsequent experi-
  The other three runs were 3  weeks
long and were evaluated to determine
which treatment method would be used
during the long-term operating  phase.
The method of disinfection used for Run
2 consisted  of chlorine addition to the
raw water and to the GAC effluent just
before it  entered the clearwell. For this
and subsequent runs, the GAC con-
tactors were placed in operation.
                             The instantaneous average data for
                           the second run showed an increase in
                           the total trihalomethane(TTHM) concen-
                           tration from 1.3/ug/Lintherawwaterto
                           31.3 ;ug/L in the GAC influent. After
                           passing through the GAC contactors,
                           the total instantaneousTHM concentra-
                           tion decreased to 0.1 fjg/L. The average
                           TOC concentration decreased from 2.6
                           mg/Lintherawwaterto2.1 mg/Lafter
                           mixed media filtration, and it was further
                           reduced to 0.3 mg/L by the  GAC con-
                             Total coliform  counts were reduced
                           from an average of 4,800/100 ml in the
                           second run raw  water to <1/100 mL
                           after pre-treatment disinfection.  Very
                           little regrowth occurred  through the
                           carbon, with the  average  GAC effluent
                           containing 1/100 mL. Subsequent disin-
                           fection reduced  the total coliforms to
                             Mass spectrometer scans of both the
                           volatiles and extractables showed only
                           those instantaneous compounds previ-
                           ously identified by gas chromatography
                           (GC) evaluation and verified the removal
                           of these compounds by GAC treatment.
                             The third run consisted of a treatment
                           method using no pre-GAC disinfection.
                           Chlorine dioxide  disinfection  was  used
                           only after  the GAC contactors.  This
                           method of treatment permitted the study
                           of organic removal with GAC and with-
                           out interference from those organic
                           compounds attributed to disinfection; it
                           could also be used to determine whether
                           any  byproducts were formed when
                           chlorine dioxide  was used after  GAC
                             The TOC concentrations were reduced
                           by almost 40 percent (4.2 to 2.5 mg/L)
                           after  pilot  plant treatment.  Complete
                           treatment, including GAC, reduced TOC
                           concentrations by 80 percent (4.2 to 0.8
                           mg/L). Breakthrough occurred in TOC
                           concentrations in about 1 week at GAC
                           depths of 6 and 18 in. At  30 and 78 in.
                           (with 7.7 min of empty bed contact time
                           at 78 in.), no breakthrough was detected
                           during the run.
                       Various samples were  stored for 3
                     days with chlorine and chlorine dioxide.
                     The average concentrations showed a
                     large increase in  the raw water THM
                     level when stored with chlorine (1.2 to
                     247jug/L)and a slight increase in those
                     samples  stored with chlorine dioxide
                     (1.2 to 2.9 jug/L). The slight increase
                     with chlorine dioxide is attributed to a
                     small amount of unreacted chlorine
                     present after generation. The final THM
                     concentration after 78 in. of GAC was
                     38//g/L and 0.7/ug/L, respectively,  for
                     chlorine and  chlorine dioxide  storage.
                     Although chlorine dioxide disinfection
                     after the GAC contactors reduced the
                     total coliform and SPC to acceptable
                     values, slime growths were a problem in
                     the treatment plant because no disinfec-
                     tant was added to the raw water.
                       The objectives of the fourth run were
                     to determine whether any byproducts
                     were formed when chlorine dioxide was
                     used as a  pre-treatment  disinfectant,
                     and to evaluate  GAC removal of any
                     organic compounds present or formed.
                       Average concentrations for the instan-
                     taneous THM's showed the raw water
                     value of 3.6 fjg/L being reduced to 0.2
                     //g/L through the pilot plant clearwell.
                     Very similar values were  noted for the
                     THM's produced  when stored with a
                     chlorine dioxide residual  (3.7 //g/L for
                     the raw water and 1.1 //g/L for the
                     clearwell effluent).
                       As in previous  runs,  the qualitative
                     mass spectrometer scans did not indi-
                     cate  the formation of any byproducts
                     relative to this mode of treatment. Also,
                     no increase  in the concentration of
                     metals occurred after passage through
                     the activated carbon contactors.
                       Because a pre-disinfectant is required
                     to control slime growth in the treatment
                     plant. Run  3 was  eliminated from con-
                     sideration for further study. The second
                     and fourth runs were evaluated based
                     on an estimate of what the consumer
                     might receive from each of the treatment
                     modes. In both of these modes, adequate

 disinfection was accomplished and
 mass spectrometer sea ns of the priority
 pollutants did not showthe formation of
 any byproducts relative to the disinfec-
 tant used other than the THM's. There-
 fore, a desire to adhere to the original
 study objectives  resulted in selecting
 chlorine dioxide  as a pre- and post-
 treatment disinfectant for long-term
 Pilot Plant Operation
  After the pre- and post-chlorine diox-
 ide disinfection operational  mode was
 selected for long-term studies, four
 additional runs were  completed. Each
 run was approximately 3 months. For all
 runs, the performance of the pilot plant
 through  GAC treatment was compared
 with the performance of the full-scale
 plant under normal operation (pre- and
 post-treatment chlorine disinfection).
 Also, two parallel contactors were used
 with one always containing virgin GAC,
 and the other one containing virgin GAC
 during the first run and once, twice, and
 thrice reactivated GAC for the remaining
 three runs.
  The  effect of  using  pre-treatment
chlorine  dioxide disinfection for main-
tenance  of bacterial water quality and
the reduction of THM's was evaluated
by comparing the sand filter effluent's of
both plants. Terminal THM reduction
through  coagulation and settling was
determined by storing all samples for 3
days (estimated residence time in the
Evansville distribution system) at am-
bient temperature with a free chlorine
  The  use of pre-treatment chlorine
dioxide disinfection allowed substanti-
ally more of the THM  precursors to be
removed by  coagulation and  settling
than with  pre-treatment chlorination.
This was caused by less  precursors
being converted to THM's in the pres-
ence of chlorine dioxide thereby allow-
ing  more to be available for removal by
coagulation and settling. Therefore, the
THM's formed  during post-treatment
chlorination and  subsequently  in the
distribution system would be reduced. A
comparison of the average terminal
THM concentration for all runs of both
disinfectants showed about 60 percent
less concentration of THM's when chlo-
rine dioxide was used for pre-treatment
disinfection. Though THM  precursors
were reduced by using  pre-treatment
chlorine dioxide,  no  difference was
noted in the averageTOC concentration,
regardless of the type of pre-treatment
disinfectant used.
   Because of the THM reductions noted
 by the use  of pre-treatment chlorine
 dioxide disinfection, an additional study
 was completed to determine the feasi-
 bility  and benefits of  using chlorine
 dioxide in Evansville's full-scale plant.
 Although chlorine dioxide could be used
 as a pre-treatment disinfectant, chlorine
 was desired  as the post-treatment dis-
 infectant because of the size of Evans-
 ville's distribution system and the need
 to maintain a sufficient disinfectant level
 throughout this system. Data generated
 from previous runs indicated that main-
 tenance of a chlorine dioxide residual
 over  an extended period  of time was
   The pilot plant GAC contactors were
 bypassed to simulate the full-scale plant
 as closely as possible. Chlorine dioxide
 was introduced  into the raw water in
 sufficient quantities to maintain a slight
 residual through mixed media filtration
 (an average addition was 1.1 mg/L, and
 the average residual after filtration was
 0.1 mg/L). An attempt was made to
 keep the total oxidant  level below 0.5
 mg/L.  During this run, the  average
 concentration of chlorine  dioxide plus
 chlorite was  0.7 mg/L.  The instantan-
 eous  THM data after  filtration  again
 showed a reduction inTHM's when pre-
 treatment chlorine dioxide disinfection
 was used. No difference in the bacterio-
 logical quality of the two plant effluents
 was noticed when chlorinated effluents
 were compared.
   Each of the parallel  contactors con-
 tained 545 to 590 kg (1,200 and 1,300
 Ib) of a lignite-based GAC. During each
 of the four runs, one contactor always
 contained virgin GAC  and the  other
 contained reactivated GAC. Analysis of
 the GAC showed that the spent carbon
 in each reactivation was  restored at
 least to its virgin state.
   Cumulative surface area  distribution
 curves indicated that reactivated GAC
 for all runs  had  a  total surface  area
 greater than the virgin GAC. This addi-
 tional surface area was developed pri-
 marily in  the small pore  region (less
 than 30 Angstroms). Also, the iodine
 number and  cumulative surface area
 correlated almost exactly indicating that
 the pores were open and  maintained.
 Thus it was  unlikely that  any gradual
 degradation of adsorptive capacity would
occur after subsequent reactivations.
 Ratios for Brunauer-Emmett-Teller (BET)
surface area/iodine  number for an
average of two virgin samples and each
 of the three reactivation cycles  were
 1.08,1.06,1.08, and 1.03, respectively.
   Organic  loading on the GAC was
 evaluated  for TOC by comparing the
 sum of TOC removed to the sum of TOC
 applied per unit weight of carbon. This
 loading indicated that the virgin and
 subsequently  reactivated GAC per-
 formed essentially the same (see Figure
 1). The average TOC carbon use rate for
 both the virgin and the reactivated GAC
 was about 0.05  kg/m3 at the steady-
 state conditions that occurred  after
 about 60 days of operation.
  Pilot-plant evaluation of chlorine di-
oxide disinfection and GAC treatment
have provided some  insight into this
treatment scheme.  The use of either
chlorine dioxide or chlorine in raw water
provides similar disinfection qualities
through conventional treatment. Also,
because chlorine dioxide has less de-
mand  and possibly  strong  oxidative
properties, smaller concentrations were
needed to produce effective disinfection.
By using less applied chlorine dioxide,
some of the difference between the cost
of chlorine dioxide and chlorine can
probably be recouped.
  Application of chlorine dioxide to the
raw water produced less concentration
of THMS'sinthefinished water than did
chlorine addition (average of 51 //g/Las
opposed to 130 fjg/L for all runs).
Furthermore, chlorine dioxide disinfec-
tion  produced no organic  byproducts
other than those noted with chlorine
disinfection (i.e., among priority pollu-
  GAC was spent and reactivated three
successive times and essentially re-
stored to  virgin  state as indicated by
several GAC properties and perform-
ance comparisons  with virgin GAC.
Gross  estimates of volumetric  losses
during GAC offsite reactivation were
about  5 percent, and overall system
losses (eduction, handling, transport,
and  reactivation)  averaged  about 8
  Production of chlorine dioxide did not
proceed stoichiometrically, and thus
some chlorite  and chlorine were  pro-
duced. Out of the  generator, on  the
average, the percentage of chlorine
dioxide, free chlorine, and chlorite pro-
duced was 64, 6, and 30, respectively.
Both chlorine and chlorine dioxide were
effectively removed by the GAC and the
chlorite concentration was lowered.
                                                                                     > US GOVERNMENT PRINTING OFFICE 1882-559-017/0751

         o.o r
                          Virgin GAC
                          Reactivated GAC
             0.0            0.02           0.04            0.06
                               Sum of TOO applied, mg/kg GAC
   Figure 1.  Comparison of virgin and once reactivated GAC for TOC removed
             vs TOC applied.
      In some situations, the use of chlorine
    dioxide as the primary raw water disin-
    fectant is a viable alternative to chlorine
    disinfection when the THM concentra-
    tions must be reduced to meet promul-
    gated drinking water standards.
      The full report was submitted in ful-
    fillment of Cooperative Agreement No.
    CR804902  by the  City of  Evansville,
    Indiana, under the  sponsorship of the
    U.S. Environmental  Protection Agency.
                                    The EPA author Ben W. Lykins, Jr. (also the EPA Project Officer, see below) is
                                     with the Municipal Environmental Research Laboratory, Cincinnati,  OH
                                     45268; Mark Griese is with the Evansville Waterworks Department, Evans-
                                     ville, IN 47740.
                                    The complete report,  entitled "Chlorine Dioxide Disinfection and Granular
                                     Activated Carbon Adsorption," (Order No.  PB 82-227  737; Cost: $10.50,
                                     subject to change) will be available only from:
                                           National Technical Information Service
                                           5285 Port Royal Road
                                           Springfield, VA22161
                                           Telephone: 703-487-4650
                                    The EPA Project Officer can be contacted at:
                                           Municipal Environmental Research Laboratory
                                           U.S. Environmental Protection Agency
                                           Cincinnati, OH 45268
United States
Environmental Protection
                          Center for Environmental Research
                          Cincinnati OH 45268
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