United States
Environmental Protection
Agency
Municipal Environmental Research,
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-020 May 1982
Project Summary
Biological Processes in the
Treatment of Municipal
Water Supplies
R. G. Rice, C. M. Robson, G. W. Miller, J. C. Clark, and W. Kuhn
Studies were conducted of a Euro-
pean water treatment technique that
appears to produce high quality drink-
ing water without the synthesis of hal-
ogenated organic materials during the
water treatment process. This biologi-
cal treatment technique involves the
sequential application of chemical
oxidation (usually by means of ozone),
rapid media filtration, optional reaera-
tion, and granular activated carbon
(GAC) adsorption.
The use of this biologically
enhanced, granular activated carbon
(BEGAC) technology was studied in
several European water treatment
plants to determine its advantages
and disadvantages for use in the Uni-
ted States. Seven European water
works were visited where chemical
preoxidation is followed by rapid
media filtration and GAC adsorption.
The process is still under develop-
ment in these European water works,
but results to date are positive. They
indicate that in those water works
using GAC adsorption of dissolved
organic materials, incorporation of
chemical preoxidation with small
amounts of ozone (1 to 2 mg/L) can
result in extending the life of GAC
adsorbers by factors of 4 to 6 before
reactivation is required. The process
can be used for the biological removal
of ammonia from raw water supplies
and has replaced breakpoint chlorina-
tion in several European plants. Such
replacement eliminates the prechlori-
nation step, which in turn eliminates
the formation of significant quantities
of halogenated organics.
Results to date indicate that after
biological equilibrium is attained in
GAC adsorbers, 25 to 35 percent of
the influent dissolved organic carbon
is removed from solution biologically.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory,
Cincinnati, OH, to announce key find-
ings of the research project that is
fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
This project resulted from the current
need to learn as much as possible about
methods for controlling organic con-
taminants in drinking water. The pres-
ent project is an outgrowth of an earlier
study on the state of the art of ozone and
chlorine dioxide technologies in munici-
pal water treatment (Public Technology,
Inc. 1976. An Assessment of Ozone and
Chlorine Dioxide Technologies for
Treatment of Municipal Water Supp-
lies. EPA-600/2-78-147. U.S. Environ-
mental Protection Agency, Cincinnati,
Ohio). During the course of this 4-week,
onsite survey of European water treat-
ment facilities, the site team observed
the use of a biological treatment tech-
nique in France, the Federal Republic of
Germany, and Switzerland that is not
-------
currently practiced in the United States.
This technique involves the deliberate
promotion of aerobic biological growths
on filter media (sand, anthracite) and
GAC media (columns or beds) for pur-
poses of nitrification and of removing
organic chemicals. The aerobic biologi-
cal activity appears to be enhanced by
an oxidation step applied before the
activated carbon treatment. Such
preoxidation steps frequently involve
the addition of ozone.
Evidence obtained from numerous
European pilot-plant studies and from
several full-scale operating plants in
Europe supported the claim that a prop-
erly designed and operated combina-
tion of ozone and GAC unit processes
enhances the removal of some types of
organic chemicals and can reduce the
frequency of regeneration of the acti-
vated carbon media, depending on the
reactivation criteria. The latter charac-
teristic is vital, since one of the primary
concerns of public water supply sys-
tems regarding the use of GAC (in addi-
tion to the high capital cost) is the
relatively high cost associated with fre-
quent reactivation. Furthermore, this
biological process replaces breakpoint
chlorination and eliminates the genera-
tion of chlorinated organic materials
during the early stages of the water
treatment processes.
Some experiences with the BEGAC
process were described briefly in the
earlier report (EPA-600/2-78-147), but
additional details were required to
establish this method as a viable means
of enhancing treatment effectiveness
and reducing operating costs. This
study was therefore undertaken to
acquire information on the following
specific subject areas:
Determining design criteria used
for BEGAC systems in Europe;
Determining mechanisms by
which BEGAC systems operate;
Determining microbiological as-
pects of BEGAC systems;
Gathering field operational and
cost data on BEGAC systems;
Quantification of technical and
cost benefits of BEGAC systems;
Determining changes in U.S. treat-
ment plant designs required for
retrofitting BEGAC systems into
existing plants.
Site Visits
After consulting with leading Euro-
pean water treatment authorities dur-
ing early 1978, the site visit team
conducted visits to selected European
facilities during June 1978. The prim-
ary questions to be answered were:
1. Is BEGAC effective for removal of
organic chemicals, and if so,
under what conditions?
2. Is BEGAC an effective replace-
ment process for ammonia remo-
val by breakpoint chlorination,
and if so, under what conditions?
3. How and why does the BEGAC
process achieve its effectiveness?
4. Is a preoxidation step necessary?
If so, must the preoxidant always
be ozone?
5. Can the added capital and operat-
ing costs of an ozonation or other
preoxidant system be offset by the
increase in operating time before
the GAC must be regenerated?
6. Is BEGAC bacteriologically safe to
use for drinking water treatment?
7. What pretreatment and post-
treatment steps are made neces-
sary when BEGAC is incorporated
into a drinking water treatment
system?
8. Does biological regeneration of
the GAC truly occur, and if so, to
what extent?
Not all of these questions were an-
swered, since the BEGAC process still is
being studied and developed by Euro-
pean water treatment specialists. But
answers to some of these questions
were obtained by conducting a review
of the published literature and a 3-week
site visitation of the following facilities:
1. Operational drinking water treat-
ment plants using granular acti-
vated carbon facilities designed to
promote biological growth,
2. Research institutes and universi-
ties conducting studies on the
BEGAC process, and
3. Activated carbon and ozone sys-
tems manufacturers in Western
Europe during June 1978.
The scope of this report could not be
confined to ozone/GAC treatment sys-
tems alone, however. Early in the study,
it became apparent that Europeans use
many biological processes in the treat-
ment of drinking water and that BEGAC
appeared to be a more advanced treat-
ment system based on earlier operating
experiences with other biological pro-
cesses. The scope of this final report
was thus extended to include discus-
sion of other European biological drink-
ing water treatment methods. But
because of the complex problems of
removing organic chemicals, our pri-
mary emphasis during the study phase
remained on ozone and GAC systems.
Seven European drinking water treat-
ment plants were visited that currently
use ozone/GAC processing. Tabfe 1
summarizes pertinent parameters deal-
ing with the status of BEGAC process-
ing at each plant. In most of these
plants, criteria for reactivating the GAC
have not yet been specified.
Literature Search and Review
Many papers were obtained from per-
sons and institutions visited during the
June 1978 survey. In addition, two
technical conferences contributed
timely, pertinent papers. One confer-
ence (Oxidation Techniques in Water
Treatment) was held in Karlsruhe, Fed-
eral Republic of Germany during Sep-
tember 1978, and the other (Adsorption
From the Aqueous Phase) was part of
the 176th Annual Meeting of the Amer-
ican Chemical Society held in Miami
Beach, Florida, also in September 1978.
A search of the published literature
yielded many applicable papers. Results
of this literature review are interwoven
throughout the report.
Results
1. The primary responsibility of a
drinking water producer is to provide
drinking water safe from harmful
pathogenic microorganisms. To this
end, water supply utilities of the United
States have sought to preclude the
growth of all types of microorganisms
within the water treatment system. But
in other countries, some water utilities
intentionally incorporate biological pro-
cesses into their water treatment sys-
tems to reduce the levels of dissolved
organics and still maintain the microbi-
ologically safe quality of the finished
waters
2. The treatment of drinking water by
the application of biological processes
is not new. Biological activity is one of
the processes in the slow sand filter,
which was a key treatment step of early
water treatment facilities, but which is
generally considered obsolete in con-
temporary U.S. practice. But biological
treatment in many forms is an impor-
tant process in many European drinking
water treatment systems. Examples of
biological treatment of drinking water
include the following.
River sand bank filtration
Surface storage (reservoirs)
Gravity clarification
Coarse media biological reactors
Fluidized bed nitrification
Biologically active filter media
-------
Table 1. Water Treatment Plants Visited That Use Ozone/GAC Treatment
Plant
la Chapelle
Morsang-sur-
Seine
Kralingen
Dohne
Holthausen
& Flehe
Hardhof
(Lengg &
Moos)
Location
Rouen,
France
Villabe,
France
Rotter-
dam, The
Nether-
lands
Miilheim,
FRG
Dussel-
dorf.
FRG
Zurich,
Switzer-
land
Type of Date Ozone Primary Purpose Date GAC
Plant Installed of Ozone Installed
Municipally
owned.
privately
operated
Privately
owned &
operated
Municipal
waterworks
Municipal
waterworks
Municipal
waterworks
Municipal
waterworks
1977 Preozonation for
Mn + organics
oxidation; post-
GAC ozonation
for disinfection
1970 Organics oxida-
tion + disinfec-
tion
1977 Disinfection +
organics oxida-
tion
April Preozonation for
1977 flocculation aid;
secondary ozona-
tion for disinfec-
tion
1954 Fe & Mn oxidation
+ organics oxida-
tion
1975 Disinfection/,
viruses, organics
oxidation
1977
ca. 1975
1977
Nov.
1977
mid-
1960's
1975
Frequency of
Reactivation
BEG AC operating
since Jan. 1977
without reacti-
vation
BE GAC pilot unit
in operation since
1977. Ran 1 yr
w/o reactivation
GAC had not
operated long
enough to have
developed bio-
logical activity
BEG AC system
operating since
Nov. 1977 with-
out reactiva-
tion
5 to 6 months
every 2 to 3
years
GAC
Reactivation
Criteria
Not yet
defined
Not yet
defined
Breakthrough
of THM's
Not yet established.
Old process (which
included breakpoint
chlorination): break-
through of roc/.
When TOC1 adsorption
front reaches lower
GAC quadrants
When COD levels in
GAC effluents
increase
Biologically enhanced granular
activated carbon (BEGAC)
Ground passage of treated water
3. The incorporation of biological
treatment steps into water treatment
processes offers the following prospec-
tive benefits in water treatment:
Reduction in the level of dissolved
organic materials
Lower oxidant (chlorine, chlorine
dioxide, or ozone) demand
Reduced operational costs
Reduced levels of bacterial re-
growths in distribution systems
4. BEGAC can be defined as the
sequential unit processes (Figure 1)
consisting of:
a. Oxygenation by aeration, oxygen
injection, or chemical oxidation
b. Sand, anthracite, or multi-media
filtration
c. Optional reoxygenationorreaera-
tion and
d. GAC adsorption
This combination of three pro-
cesses (chemical oxidation,
adsorption, and biochemical oxi-
dation) can remove ammonia and
some (but not all) soluble organic
substances from drinking water.
5. Dissolved organic materials in drink-
ing water can be classified as follows:
1. Biodegradable, adsorbable by
GAC
2. Biodegradable, nonadsorbable
by GAC
3. Nonbiodegradable, adsorbable
by GAC
4. Nonbiodegradable, nonadsor-
bable by GAC
Although these categories are simpli-
fied for the purpose of discussing treat-
ment of dilute water streams, they
provide a framework for postulating
mechanisms by which BEGAC probably
functions.
6. Both the filtration media and GAC
provide supports for the biomass, which
uses soluble organics and ammonia as
substrates. The application of strong
oxidants such as ozone to a raw water
stream being treated can change the
chemical nature of the dissolved
organic materials. Strong oxidants can
convert some (but rarely all) nonbiode-
gradable materials into biodegradable
materials. Biochemical decomposition
of organic nutrients adsorbed by the
high surface area in GAC has been
claimed to restore a portion of the sites
to again become available for adsorp-
tion. Thus one objective of preoxidation
is to couple adsorption with biological
degradation.
7. The porous structure of GAC pre-
sents an ideal medium for proliferation
of attached biological growth (fixed film
biological growth). Both biomass and
substrate are retained by the GACthe
biomass on the outer surface, and
adsorbed organics in the micropores.
8. Bacteria are too large to fit into
the micropores; thus they become at-
tached to GAC media only on the outer
surfaces and in the larger macropores
near the outer surface that are suffi-
ciently large to house them. As a result,
only 1 to 2 percent of the total surface
area available for adsorption of dis-
solved organics is used by the bacteria.
This amount of bacterial growth is not
sufficient to interfere with normal
adsorption processes unless it becomes
too dense and physically blocks the pas-
sages from the outer surfaces into the
micropores.
9. Bacterial growths build up rapidly
in GAC media. Those species that con-
sume mainly carbonaceous organic
materials appear to attain their maxi-
mum concentrations within 24 to 48 hr
after virgin or reactivated GAC is placed
in service. Nitrogen-converting bacteria
take longer to build up to their equili-
brium concentrations (30 to 90 days),
-------
Water or
Wastewater
Aeration,
Oxygenation
or Oxidation
Inert Medium
Filtration
Aeration or
Oxygenation
GAC
Contactor
Post-Treatment
Figure 1. Block diagram of the Bio-
logic a I Activated Carbon
Process.
but low levels of ammonia are con-
verted to nitrate within a few days after
fresh or reactivated GAC is placed into
service.
10. Operational water treatment
plants using BEGAC processes demon-
strate that regeneration cycles of GAC
adsorbers can be extended if a large
proportion of the soluble organics
entering the GAC system are biode-
gradable and if essential conditions (like
minimum dissolved oxygen levels) are
maintained. No single BEGAC system
design is as yet universally accepted. So
even though data exist from a number
of plants, the design engineer will still
have to establish design criteria for
BEGAC processing in pilot plant stud-
ies. Clearly, however, designs can be
developed under certain conditions to
take advantage of extended GAC opera-
tional life by enhanced biological activ-
ity on both the filter media and the GAC.
11. Extension of the operational life
of GAC adsorbers depends on the crite-
ria set for reactivation. In European
drinking water treatment plants using
chemical preoxidation followed by GAC
adsorption, these reactivation criteria
have not yet been standaidized from
plant to plant. In those plants that have
been in operation the longest using
ozone followed by GAC (the three Dus-
setdorf plants), GAC is reactivated
when the chlorinated organics adsorp-
tion front (measured as dissolved
organic chlorine) reaches the lower
quadrant of the GAC. Other European
plants monitor levels of dissolved
organic carbon, permanganate
demand, UV absorption, turbidity, and
taste and odor m the GAC effluents. If
any of these levels increase suddenly
and significantly, the GAC may be
reactivated.
12. Several microbiological studies
have demonstrated that the predomi-
nant microorganisms in the GAC media
and in the water leaving the BEGAC
system are typical soil and water bacte-
ria. Pathogenic bacteria entering a
properly designed and operated BEGAC
system have been shown to be unable
to compete with the predominant
microorganisms present, and therefore
the pathogenic species die off. Further
study is required to confirm the pres-
ence or absence of harmful endotoxins.
Only low dosages of post-disinfectant
have been shown to be necessary to
achieve the prerequisite levels of bacte-
riological quality of the treated water
being discharged to the water distribu-
tion system.
13. Decisions to install GAC should
not be based solely on the benefits to be
gained from BEGAC. Rather, the deci-
sion to use GAC to remove specific
organic materials should be made first.
Once the decision to install GAC has
been made, careful consideration
should be given to extending the opera-
tional life and improving the overall
organic removal process performance
of the GAC by enhancing biological
activity in this medium.
14. Reactivation criteria for BEGAC
should be the same as those for GAC,
and they should be based on the partic-
ular dissolved organic materials pres-
ent in the raw water.
15. BEGAC processing will not pro-
vide any significant advantages over
GAC adsorption when the dissolved
organics to be removed are nonbiode-
gradable and cannot be made biode-
gradable even by chemical oxidation
with ozone. Exemplary materials of this
type include many of the halogenated
organic compounds produced prechlor-
ination of raw waters.
16. BEGAC systems have replaced
breakpoint chlorination processes in
several new and old European drinking
water treatment plants. This process
change has provided the advantage of
avoiding production of halogenated
organic materials during the early
stages of the treatment process. Once
halogenated organics have been syn-
thesized, they can be removed by GAC
adsorption, but only with short bed or
column lifetimes. In addition, replace-
ment of prechlorination with BEGAC
systems has also produced higher qual-
ity finished water with respect to dis-
solved organics, ammonia, turbidity
levels, and post-disinfectant (chlorine,
chlorine dioxide, or ozone) demands.
17. In European water treatment
plants, chemical preoxidation with
ozone applied before sand, anthracite,
or dual-media filtration units followed
by GAC adsorption has resulted in
extending the times between back-
washing in each medium by a factor of
about 2. Nevertheless, authorities at
the Dohne plant in Mulheim have found
it necessary to backwash biologically
operating filters and GAC adsorbers at
no greater intervals than 3 days to
ensure the absence of nematodes.
18. One older European plant (the
Dohne plant in Mulheim, Federal
Republic of Germany) replaced break-
point chlorination with BEGAC in 1977
at no increase in annual operating
costs, including allowances for annual-
ized capital costs.
19. When retrofitting BEGAC sys-
tems into existing drinking water treat-
ment plants as post-adsorbers (after
sand or other media filtration), provision
should be made to incorporate air
scouring into the backwash cycles of
both the filtration and GAC media.
20. Biodegradable organic" materials
generally are polar and less tightly held
by GAC upon adsorption. Nonbiode-
gradable organics tend to be nonpolar
(for example, many of the halogenated
organic compounds produced upon
prechlorination). Some of these nonpo-
lar, nonbiodegradable organic mate-
rials can be adsorbed to a higherdegree
and held more tightly by GAC. Because
of these differences, some halogenated
organic compounds are able to displace
less strongly adsorbed polar organic
materials from GAC surfaces by the
process of desorption. As a result, even
4
-------
though a BEGAC adsorber may be oper-
ating at biological equilibrium and may
appear to be saturated with respect to
adsorption of biodegradable organic
materials, it may still be capable of
adsorbing nonpolar, nonbiodegradable
organics that are present. In such
instances, reactivation could be delayed
until the nonpolar, nonbiodegradable
materials begin to break through the
GAC medium.
21. A screening test can be con-
ducted to determine whether BEGAC
adsorption will benefit a specific raw
water supply. This test shows the
amount of biodegradation that can
occur in the raw water supply. A sample
of the raw water is ozonized with low
utilized ozone dosages (1 to 10 mg/L),
and the amount of biodegradable mate-
rial present is compared with that of the
nonozonized raw water. If oxidation of
the organic materials with ozone does
not increase the rate of biodegradation,
then it can be concluded that BEGAC
wi 11 not show a ny adva ntages over GAC
for that water supply. On the other
hand, if the rate of biodegradation is
increased by low-level ozonation, bio-
logical enhancement of GAC should
provide performance advantages. The
extent of such improvements must be
determined for each raw water supply
to assess whether these process
improvements can justify the increased
costs for chemical preoxidation, preox-
ygenation, or preaeration.
22. Ozonation costs have been esti-
mated for a hypothetical 50-mgd drink-
ing water treatment plant that has
installed GAC columns with empty bed
contact times of 9 min and reactivation
times of once every 2 months. If preoxi-
dation with 2 mg/L of applied ozone
dosage will extend the GAC reactivation
time to 6 months, the costs associated
with installing the required ozonation
equipment are balanced by the savings
resulting from GAC reactivation.
Further extension of the GAC reactiva-
tion time (to 2 and 3 years, as currently
occurs in some European drinking
water treatment plants using BAC pro-
cesses) will provide additional savings
in operating costs.
Recommendations
1. Various biological water treat-
ment processes should be investigated
as to their applicability for the treatment
of drinking water. Investigations should
include the use of GAC as well as other
adsorptive or inert media. Such studies
should be conducted on systems that do
not use initial breakpoint chlorination
and, ideally, on systems with no
prechlorination.
2. The nonpathogenic nature of bac-
teria should be confirmed in biologically
active GAC media and in the effluents
from such media.
3. The endotoxins produced by these
microorganisms should be identified,
and their toxicological significance
should be determined.
4. Studies should be conducted to
confirm the nature of the operative
mechanisms occurring with BEGAC
(i.e., adsorption/desorption versus
apparent biological regeneration).
5. More detailed operating informa-
tion should be obtained at selected
European plants, including the Rouen
plant in France, the Dohne, Dusseldorf,
and Schierstein plants in the Federal
Republic of Germany, and the Kralingen
plant in Rotterdam, the Netherlands.
Such information would include char-
acteristics of influent and BEGAC
media effluents about TOC, COD, DOC,
UV absorption, TOC1, ammonia, etc.
The specific parameters used at each
operating plant should be determined to
ascertain when the GAC must be
reactivated.
6. Determinations should be made of
the operational costs and treatment
consequences of doing away with
prechlorination in drinking water treat-
ment plants (for example, modification
of filter bottoms to allowforairscouring
and the necessity for more frequent
backwashing). Prototype U.S. plants
should be operated in both modes
(chlorination versus preoxidation by
other means) over a 1 -year cycle
(minimum).
7. A variety of raw water sources
should be screened to determine the
applicability of biological treatment pro-
cesses. Raw waters should be catego-
rized according to the biodegradability
of their organic components before and
after preoxidation.
8. European water treatment operat-
ing practices should be evaluated with-
out regard to the use of GAC with
preoxidation.
9. Biological processes for nitrifica-
tion of ammonia should be demon-
strated as possible replacements for
breakpoint chlorination.
10. The use of oxidants other than
ozone should be studied for the preoxi-
dation step. Candidate oxidants other
than ozone include H20z, KMn04, UV
(plus air or oxygen), C102 (free of excess
chlorine), and NHzC1 (free of excess
chlorine).
11. Studies should be made of fac-
tors affecting bacterial breakthrough
in BEGAC adsorbers. (Such break-
throughs have been reported in stud-
ies conducted at the Schierstein,
Federal Republic of Germany drinking
water treatment plant after 3 years of
use.) Bacterial monitoring should pos-
sibly be considered for BEGAC
systems.
The full report was submitted in ful-
fillment of Grant No. R-804385-01 by
Public Technology, Incorporated, under
the sponsorship of the U.S. Environ-
mental Protection Agency.
-------
R. G. Rice is with Jacobs Engineering Group, Washington, DC 20006; C. M.
Robson is with Purdue University. Lafayette, IN 47907; G. W. Miller is with
Public Technology, Inc., Washington, DC 20036; J. C. Clark is with Temple,
Barker & Sloan, Wellesley Hills, MA 02181; and W. Kuhn is with the
Universit'at Karlsruhe, Karlsruhe, Fed, Rep. Germany.
J. Keith Carswell is the EPA Project Officer (see below).
The complete report, entitled "Biological Processes in the Treatment of
Municipal Water Supplies,"(Order No. PB 82-199 704; Cost: $31.50, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati. OH 45268
1982-559-092/3410
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
RETURN POSTAGE GUARANTEED
PS 0000329
U S ENVIR PRUTECTION AGENCY
KEGIQN 5 LIBRARY
250 S DEARBORN STREET
CHICAGO IL 60604
------- |