United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-048 Aug. 1983
Project Summary
Removing Organics from
Philadelphia Drinking Water by
Combined Ozonation and
Adsorption
Howard M. Neukrug, Matthew G. Smith, James T. Coyle, James P. Santo,
Jeanne McElhaney, Irwin H. Suffet, Steven W. Maloney, Paul C. Chrostowski,
Wesley Pipes, Jacob Gibs, and Keith Bancroft
Laboratory and pilot scale studies
were conducted to investigate the
combined unit processes of oxidation
by ozonation and adsorption by granu-
lar activated carbon (GAC). In addition,
the effect of chlorine and chlorine by-
products on the ozone and GAC pro-
cesses was investigated.
The study used Delaware River water
that was treated by two coagulation/
filtration plants: a full-scale plant op-
erating with a 2 mg/L free chlorine
residual and a 30,000 gpd pilot plant
operating without any disinfection.
The rapid sand filter effluents from
each were applied to parallel GAC and
O3/GAC systems. The GAC beds re-
mained in service between 360 and
500 days.
The removal of trace organics sub-
stances at the ng/L to jug/L level and
the removal of TOC at the mg/L level
were carefully monitored along with
microbial parameters of biological spe-
ciation and growth rates. System com-
parisons were made using estimated
total costs of each unit process, as
determined by the carbon regenera-
tion rate needed to maintain various
effluent criteria.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search 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
Removing trace organics from drinking
water by adsorption onto granular acti-
vated carbon (GAC) has been repeatedly
demonstrated during pilot plant research
studies in Philadelphia, Pennsylvania.
Though GAC systems are both technically
feasible and operationally manageable,
the substantial operating and maintenance
costs associated with frequent carbon
regeneration could place a severe economic
burden on the water utility. Thus the
primary concern for the practical use of
GAC is to increase its useful bed life for
removing trace organic compounds of
potential health concern.
This study examines whether ozonation
used as a pretreatment to GAC adsorption
can increase the useful bed life of GAC
sufficiently to justify its cost The project is
based on the fact that ozonation will trans-
form some of the higher-molecular-weight
humic substances into more readily bio-
degradable forms. These lower-molecular-
weight organic compounds are then po-
tentially available as a food source for
microbes already present on the GAC bed.
Preozonation may thus make available
more adsorptive sites on the carbon for the
less biodegradable, more harmful organic
compounds that are poorly oxidized (e.g.,
chloroform and 1,2-dichloropropane). Pre-
ozonation may also help prolong GAC bed
life by stripping volatile organic com-
pounds from the process strea'm.
The present project was conducted on
both a pilot and laboratory scale to investi-
-------
gate the technical and economic feasibility
of incorporating an ozonation and/or a
GAC unit process into a conventional
water treatment train to remove trace
organics of health concern. The relation-
ship between adsorption and biological
activity during water treatment with ozone
and GAC was carefully evaluated, as were
the effects of prechlorination on these
mechanisms. The removal of trace organic
substances of health concern at the ng/L
to ju.g/L level and the removal of TOC at
the mg/L level were monitored along with
microbial paramenters of biological speci-
ation and growth rates. The engineering
and economic analyses of the combined
treatment systems were made in terms of
the following health effects priorities:
Group I. Carcinogens and Suspected
Carcinogens listed by
(1) National Academy of
Sciences (3,9)
(2) National Cancer Institute
(10)
Group IA. Mutagens, Teratogens and
Promoters listed by
(1) National Cancer Institute
(10)
Group II. Priority Pollutants listed in
(1) NRDCvs Train (11)
Group III. Other Compounds of Potential
Health Effect listed by
(1) National Academy of
Sciences (9)
Group IV. Precursors -- those organic
compounds that react with a
disinfectant to produce a by-
product that falls into groups I -
III.
Group V. Humic Substances and Non-
Health-Effect Compounds in
High Concentration that can
compete with.compounds of
Groups I through III and cause
earlier breakthrough of these
compounds on GAC columns.
The specific criteria chosen for GAC regen-
eration are listed in Table 1. Except for the
criteria based on the cumulative break-
through of 50% of the dissolved organic
carbon (DOC) and trihalomethane forma-
tion potential (THMFP), all of the criteria
investigated are based on the effluent of a
single filter, and not on the average effluent
of a multiple-filter operation.
The following questions are addressed
in this report:
1. Can enhanced TOC removal before
GAC treatment increase the capacity
of the GAC for the trace organics of
health concern?
2. Can ozonation as a pretreatment to
GAC adsorption increase the useful
Table 1. Organic Criteria for GAC Regeneration
Parameter Criteria Investigated
DOC
DOC, THMFP
Chloroform
1,2-Dichloropropane
All volatile organic
compounds with average
concentration >0.1 ng/L
Effluent levels of: 0.5, 1.0, 1.5, and ZO mg/L
50% cumulative breakthrough
Effluent levels of: 1, 10, and 100 (uj/L
Effluent levels of: 1 and 5 fig/L
Average time to: Initial breakthrough
100% breakthrough
bed life of GAC sufficiently to justify
its cost?
3. How does prechlorination affect the
ozonation process and the GAC ad-
sorption capacity for chlorinated or-
ganics and other volatile organics?
4. Can a conventional treatment sys-
tem be maintained without predisin-
fection? Can the bacterial integrity of
the distribution system be maintained
with only post-chlorination?
Process Description
This report provides a detailed analysis
of the unit operations of ozonation and
GAC treatment when used in combina-
tions of O,/GAC, 03/SAND, CI./GAC,
CI2-03/GAC, and no disinfection/GAC
following the conventional treatment pro-
cesses of raw water settling, coagulation,
flocculation, sedimentation, and rapid sand
filtration. Figure 1 presents a schematic of
the five advance water treatment (AWT)
systems evaluated in this study. Two of
these systems received their water from
the chlorinated rapid-sand-filter effluent
of the Torresdale Water Treatment Plant, a
conventional coagulation/filtration plant
that supplies the City of Philadelphia with
half of its daily water requirements. The
remaining three AWT systems received
the nonchlorinated rapid-sand-filter efflu-
ent of a 30,000 gpd pilot plant The
primary difference between the operations
of the plants is the fact that only the
Torresdale plant chlorinates its process
water; the pilot plant does not practice
disinfection of any kind. The purpose of
using the two plants was to determine the
effects of chlorination and chlorine by-
Torresdale Plant
Marginal
Delaware River
1
Pilot Plant
Breakpoint Clz •*• t
FeCla/CafOHh . i-
FeC/3/NaOH
GAC
Figure 1. Schematic of the five advanced water treatment systems evaluated
GAC
-------
products on the AWT systems investi-
gated. Following conventional treatment
the rapid-sand-filter effluents of the Torres-
dale and pilot plants were applied to the
ozone and the carbon contactors.
Both ozone systems used cocurrent
flow, in which both the ozone gas and
water enter the contactors from the bot-
tom. For the diffusion of the ozone gas into
water, a porous dome diffuser was used.
The contactors were constructed of 316 L
stainless steel pipe that was 13 feet high
and had an inside diameter of 10 in. To the
extent possible, the two contacting sys-
tems were operated under identical con-
ditions. Following ozonation, stainless
steel retention tanks provided the ozonated
water with sufficient contact time to yield
an ozone residual below detectable limits.
These tanks maximize the ozone/water
contact time and minimize the possibility
of oxidizing the carbon granules. A cen-
trifugal pumping system then transfers
the water from the retention tanks to the
03/GAC and the 03/SAND systems.
Conventional Treatment
Significant differences were observed
in the DOC and THMPF effluent levels
from the two conventional treatment sys-
tems. In fact by postponing chlorination
until after rapid sand filtration, the pilot
plant conventional treatment processes
reduced THMFP by a third during the 1-
year period of study.
Two factors appear to have been pri-
mary influences. First the two clarification
systems varied greatly in their ability to
remove DOC from their process streams.
For example, the pilot plant clarifier (an
upflow sludge contactor without clarifi-
cation) removed nearly three times the
DOC removed through the Torresdale clar-
ification system (transverse flow-through
paddle flocculators and sedimentation
basins with chlorination). Second, a por-
tion of the DOC normally found in the
Delaware River Estuary was readily de-
graded by the bacteria present in the pilot
plant conventional treatment train. Bac-
terial degradation of organics was only a
factor in the pilot plant system, since the
Torresdale plant inhibited bacterial growth
through prechlorination.
In addition to THMFP and DOC reduc-
tions, postponing the chlorination process
should be considered for another reason:
Prechlorination at Torresdale appears to
produce many more nonpolar compounds
(both chlorinated and nonchlorinated), as
observed from the broad spectrum anal-
ysis of extracts from macroreticular resin
accumulators. These compounds could
arise from oxidation and/or substitution of
low-molecular-weight organics and high-
molecular-weight humics by chlorine.
The operational integrity of the pilot
plant was maintained continuously for
more than 2 years without any predis-
infection. With a covered raw water basin,
clarifier, and rapid sand filters, no large
algae blooms or filter-clogging bacteria
were noted. But bacterial levels were high
throughout the system, and higher forms
of animal life (e.g., fresh water shrimp)
were occasionally observed in the rapid
sand filters during the summer months.
Bench-scale testing indicated that satis-
factory disinfection of the pilot plant water
could be achieved with post-chlorination.
Ozonation Systems
The ozonation process affected the level
of organic compounds (both natural and
synthetic) in the Delaware River water
through two mechanisms: oxidation and
volatilization. To monitor this removal,
TOC, UV adsorbance at 254 nm (A254),
THMFP, and specific-compound chroma-
tography were used. Stripping was the
dominant mechanism for removing the
specific volatile organic compounds be-
low a C-8 hydrocarbon (as determined by
the purge and trap method for both chlor-
inated and nonchlorinated water). Above
the C-8 hydrocarbons, stripping still pre-
dominated for the chlorinated influent but
oxidation was the predominant mechan-
ism for removing organics in the non-
chlorinated influent (as determined by the
XAD resin isolation method).
Many of the more hazardous organic
substances found in the water supply are
low-molecular-weight organic compounds
that remain stable upon ozonation. Typ-
ically, these compounds have Henry's law
coefficients greater than 1 x 10"3 atm-
m3/mole and may thus be easily stripped
from the water. A good example of this
class of volatile compound is chloroform.
Although volatilization plays a major role
in removing the lower-molecular-weight
organic compounds, it was of little sig-
nificance to overall DOC removal. Only a
small percentage (<1%) of the DOC reduc-
tions may be accounted for by the volatili-
zation of chloroform and other easily
stripped organics, as determined by per-
forming mass balances across the con-
tactors. Most DOC removal observed
during ozonation resulted from the com-
plete oxidation of organics to carbon
dioxide.
GC profiles of volatile and semi-volatile
organics provided evidence of the pro-
duction of many organic compounds of
unknown identity and unknown health
concern during ozonation. Acetone was
the only organic compound confirmed by
GC/MS to be produced at detectable
levels during the ozonation process. Since
acetone is both highly volatile and bio-
degradable, it was not found in high con-
centrations in the 03/GAC or 03/SAND
system effluents.
Prechlorination appeared to produce
compounds that were more resistant to
further oxidation by ozone (as measured
by DOC, A254, and THMFP). This fact was
most notable for THMFP. Although THMFP
levels were consistently reduced when
nonchlorinated water was ozonated, the
ozonation of prechlorinated water caused
both increases and decreases in THMFP.
Averaged through the study period, ozon-
ation increased the THMFP levels of pre-
chlorinated water. Thus to oxidize organics
by means of ozone, the applied water
should not be predisinfected with chlorine.
Adsorption Systems
GAC systems remove both mg/L con-
centration of DOC and TH M FP and ng/L to
jmg/L concentrations of trace organics of
health concern. Within this framework,
each of the four adsorption systems op-
erated during the pilot-scale testing en-
countered varying levels of applied or-
ganic loads. In general, however, the fol-
lowing trend developed:
GAC(TP) > 03/GAC(TP) > GAC( PP) > 03/
GAC(PP)
where TP= Torresdale plant and PP= pilot
plant
The GAC(TP) system experienced the
highest organic loads, and the O3/GAC( PP)
system experienced the lowest This trend
was observed for all of the organic param-
eters measured, including DOC and the
volatile and semivolatile organics measured
by the purge and trap and the MRR
accumulator methods, respectively. The
pilot plant adsorption systems experienced
lower applied organic loads compared
with the Torresdale plant systems for the
reasons outline above for the conventional
treatment processes. Organic levels de-
creased through the ozonation systems
because of the production of carbon
dioxide, the subsequent biodegradation of
the partially oxidized products, and the
volatilization of trace organics. In general,
preozonation affected the concentration
and types of organics applies to the GAC
beds less than did the changes made in
conventional treatment processes.
Sand has been used in this study as an
inert medium control in which biological
TOC removal can be observed separately
from the combined adsorption/biological
TOC removal observed on GAC. The basis
for using sand beds in this manner was
-------
developed in bench- and pilot-scale test-
ing, which determined that the rate of
biological TOC removal on sand was
equivalent to that on GAC. Thus by com-
paring GAC, 03/GAC, and OVSAND sys-
tems during steady-state DOC removal
conditions, it was possible to estimate the
relative contributions of adsorption and
rapid biodegradation. It was thus deter-
mined that while preozonation increased
overall DOC removal, no synergistic re-
moval of DOC by the combined effects of
adsorption and biodegradation were ob-
served in the preozonated GAC systems.
The 03/GAC and the GAC systems all
proved capable of removing odoriferous
compounds from the process water. This
reduction was nearly complete and ap-
peared to be unaffected by the length of
time the carbon bed remained in service,
the type of water applied, or seasonal or
temporal changes. The use of ozone,
either alone or in conjunction with GAC
treatment, proved to be of little additional
benefit in reducing the odor threshold.
Preozonation did not significantly alter
the bed life of the adsorption systems
when bed life was based on limiting the
effluent levels of trihalomethanes, 1,2-
dichloropropane and 10 other volatile
organic compounds with average influent
concentrations greater then 0.1 /xg/L
The effect of preozonation on the time to
both initial and 100% breakthrough for
these compounds varied among com-
pounds and systems, but maintaining
GAC columns on line beyond 100% break-
through always resulted in a chromato-
graphic effect, in which the instantaneous
effluent concentrations exceeded the in-
fluent concentrations. The chromatographic
effect was frequently observed for chloro-
form through both the GAC and O3/GAC
systems. But the GAC systems retained
the chloroform adsorbed before bed ex-
haustion, whereas the net adsorption of
chloroform onto the O3/GAC systems
decreased nearly to zero following break-
through. This result may have been due to
the production of unidentified low-molec-
ular-weight organics through the ozona-
tion process; these organics then compete
for the available adsorptive sites.
Cost Considerations
Several advanced water treatment
schemes (Figure 2) were investigated to
determine the economic feasibility of each
to attain selected levels of organic removal
at the Torresdale Water Treatment Plant.
The results and operating parameters from
the pilot-scale investigations were used as
a basis for this economic feasibility study.
The treatment processes investigated were
Delaware River
I
Sedimentation
I
Clarification
Rapid Sand Filter [
Figure 2. Advanced water treatment alternatives
GAC alone, GAC preceded by ozone
(03/GAC), and ozone followed by sand
filtration (O3/SAND). Though both chlor-
inated and nonchlorinated systems were
investigated, no consideration was given
to any of the costs associated with modifi-
cations to the conventional treatment pro-
cesses of the Torresdale plant to allow for
a nonchlorinated treatment process. Table
2 lists the assumptions used in develop-
ing the costs.
Table 2. System Design Considerations
To calculate the total costs of each of the
treatment schemes, three unit processes
were examined separately to determine
the capital and operations and mainte-
nance (O&M) costs associated with each:
GAC postfiltration contactors, GAC filter/
adsorbers, and ozone generators and con-
tactors. In addition, the costs associated
with carbon regeneration and/or replace-
ment were examined. The economics of
each process were affected by the capital.
Flow
Peak
Average
GAC Contactors
480 mgd
282 mgd
EBCTfmin.)
Surface loading rate (gpm/ft2)
Contactor construction
Number of contactor pairs
GAC bed depth (ft.)
Post Filter
15
4.9
common wall
concrete
25
10
Filter/Adsorber
13.8
2.0
common wall
concrete (existing)
47
3.75
Ozone System
Ozone dose (Avg.)
Contact time (min.)
Contactor construction
Carbon
Cost
Loss/regeneration
Financing
Bond interest rate
Amortization period
Bond issue cost
Inflation for O&M
2mg/L
20
reinforced concrete
(18 ft deep, 2:1 length to width)
$0.7 O/Ib
7% (by weight)
12%
25 years
40% of capital
10% per year
-------
O&M, and financial costs. All costs inves-
tigated were based on the Torresdale plant
design flow of 282 mgd and an empty bed
contact time (EBCT) of 13.8 min. for sand
filter replacement (filter/adsorber mode)
and 15 and 30 min. for the post contactor
mode. Figure 3 presents the total first-
year costs for the advanced water treat-
ment systems at various carbon regenera-
tion frequencies. More specifically, total
first-year costs based on the bed life
necessary to maintain various DOC, THMFP,
chloroform, and DCP effluent criteria were
also developed.
Conclusions
• Enhanced TOC removal before treat-
ment does not appear to increase the
adsorptive capacity of the GAC for the
trace organics of health concern.
• The cost of preozonation is not suf-
ficiently offset by the lowered GAC
operating costs associated with less
frequent GAC regenerations, when the
removal of the halogenated, volatile
organic compounds is the controlling
criteria. For TOC reductions, preozon-
ation may be cost effective, depending
on the exact criteria chosen.
• Chlorination appears to produce com-
pounds resistant to further oxidation
by ozone and should thus be applied
only after ozonation.
• Chlorination and ozonation each affect
the adsorptive capacity of the specific
organic compounds differently.
• GAC effluents were effectively disin-
fected with chlorine. No bacterial re-
growth was found after 5 days.
• There were no operational problems
associated with maintaining a conven-
tional treatment system on line for
over 2 years without any type of pre-
disinfection.
The full report was submitted in ful-
fillment of Cooperative Agreement No.
CR806256 by the Philadelphia Water
Department under the sponsorship of the
U.S. Environmental Protection Agency.
60-r
Post Contactor (EBCT = 30 Min.)
o o
Post Contactor (EBCT = 15 Min.)
Sand Replacement (EBCT =13.8 Min.)
Ozonation
50
40
§,
30
20
•10
Figure 3.
3 6 9 12 15 18 21
Carbon Regeneration Frequency (Months)
Advanced water treatment total cost for first year
24
Howard M. Neukrug, Matthew G. Smith, James T. Coyle. James P. Santo, and
Jeanne McElhaney are with the Philadelphia Water Department, Philadelphia,
PA 19107;lrwinH. Suffet, Stephen W. Maloney, PaulC. Chrostowski, Wesley
Pipes, Jacob Gibs, and Keith Bancroft are with Drexel University. Philadelphia,
PA 19104.
J. Keith Cars well is the EPA Project Officer (see below).
The complete report, entitled "Removing Organics from Philadelphia Drinking
Water by Combined Ozonation and Adsorption," (Order No. PB 83-223 370;
Cost: $43.00, 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
-------
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
P6 0000329
U 3 fcNVIh PROTtCHUN
KtbiUN 5 LibRAKY
£30 S OEARBUKN SI«eET
CHICAGO IL 6060*4
3 1
------- |