15th International Symposium on Wastewater Treatment and Drinking Water,
Montreal, Canada, November 17-19, 1992.
"The Impact of Ozonation and Biological Treatment on Disinfection By-Products."
THE IMPACT OF OZONATION AND BIOLOGICAL TREATMENT ON
DISINFECTION BY-PRODUCTS
Hiba M. Shukairy, R. Scott Summers
Civil and Environmental Engineering Department
University of Cincinnati
Cincinnati, Ohio 45221-0071
and
Richard J. Miltner
Drinking Water Research Division
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
INTRODUCTION
Disinfection of drinking water leads to the formation
of disinfection by-products (DBFs). Organic and inorganic
DBFS are formed by the reaction of the disinfectant with
natural organic matter (NOW) and with inorganic compounds,
respectively. Some of these DBFs are .regulated or are
being considered for regulation because of the health
concern associated with them. In the seventies,
trihalomethanes (THMs) were the first group of DBFs that
were regulated with a maximum contaminant level (MCL) of
100 M9/L- This MCL may be reduced in the near future and
MCLs may be set for the individual species.
In an effort to minimize DBF formation while still
providing microbially safe water, modifications in drinking
water treatment have become necessary. These include the
use of alternative disinfectants and more efficient DBF
precursor removal.
Microbial regrowth in the distribution system can be
controlled by limiting nutrient availability and by the
presence of residual disinfectant. Ozonation often
increases the biodegradable organic carbon in the water
which would serve as a nutrient for the microorganisms.
(Langlais et al., 1991). Aldehydes and other oxidation by-
products are among these biodegradable ozone DBFs. Ozone
also reacts with bromide and generates bromate, an
inorganic DBF that may be regulated in the future.
In the presence of bromide, the halogenated DBFs are
a mixture of brominated and chlorinated products. Ozone or
chlorine can oxidize bromide, to form free bromine which
can react with NOM. Typically, the speciation shifts to
the more brominated DBFs (Amy et al., 1991) as the rate of
bromine substitution is believed to be faster than chlorine
substitution (Symons et al., 1987). Bromate is formed by
the further oxidation of hypobromite.
Ozonation used in drinking water treatment does not
seem to significantly affect the organic carbon
concentration, but does change the nature of the precursor
compounds. The concentration of halogenated DBFs formed
by subsequent chlorination is often decreased when compared
-------
to that formed with no pretreatment (Reckhow and Singer,
1984, Shukairy and Summers, 1992a, Miltner et al., 1992).
Upon ozonation, the bromide concentration decreases because
of the formation of bromate, and consequently the decrease
in the ratio of bromide to organic matter leads to a shift
in DBF speciation to the more chlorinated products.
The use of biotreatment in United States drinking
water treatment plants is very limited. Biological
treatment affects the nature of NOM. The dissolved organic
carbon (DOC) is decreased and the reactivity to subsequent
chlorination may be decreased as a consequence of the.
oxidation of the precursor compounds. Biotreatment
downstream of ozonation may biodegrade some of the ozone
DBFs and chlorine DBF precursors and minimize substrate
availability for regrowth (Miltner and Summers, 1992). A
review of the use of biotreatment for the control of DBFs
is given by Shukairy and Summers (1992b).
Biotreatment reduces the DOC concentration, while the
bromide concentration remains constant, resulting in an
increase in the bromide to DOC (Br/DOC) ratio. An increase
in Br/DOC has been shown to shift the speciation to the
more brominated DBFs (Amy et al., 1991). Upon subsequent
chlorination, DBF formation and speciation seem to be a
function of: DOC, oxidation of the precursor compounds,
bromide concentration and the chlorination conditions that
are used, i.e. pH, temperature, holding time and the
chlorine dose. At high chlorine to bromide ratios, the
speciation shifts to the more chlorinated byproducts.
OBJECTIVES ' . ,. „ _ 4.h_
This paper summarizes several recent studies on the
impact of ozonation and biological treatment on DBF
formation. Ozonation was characterized by the format ion
.
of ozonation DBFs such as aldehydes, •••1»ll«££no^gg"'
carbon (AOC) , biodegradable dissolved organic carbon (BDOC)
and the oxidation of bromide to bromate. The oxidation of
the DBF precursor compounds and the effectiveness of
biotreatment for the control of DBFs were monitored by the
formation potential (FP) for total organic halogen (TOX),
total THMs (TTHMs) and total measured haloacetic acid
(THAAs) . Special attention was also given to the impact
of bromide concentration on the speciation of the DBPs.
A specific objective of this paper was to compare DBF
control by batch biological treatment at the bench-scale to
that by a continuous flow sand filter at the pilot-scale.
was used in both the bench. and
pilot-scale biotreatment studies. Ozone was applied ma
pilot-scale countercurrent reactor in both studies. For
the bench-scale biotreatment, the experimental design was
set un as a 6 by 3 by 2 matrix. Ozone was dosed at five
lelectellevelsand a^ontrol. Three bromide levels 5C ).7
ug/L (ambient), 258, 550 M9/L, were selected. Each ozone -
bromide combiAation was run with a ^without b^otreat ment
Biotreatment was carried out in mixed batch reactors. The
water quality parameters examined were: chlorine demand,
-------
DOC, BDOC, AOC, spectral absorption coefficient (SAC),
bromide and brornate, aldehydes, TOX , THMs and HAAs.
In comparison, for the pilot-scale biotreatment, raw
Ohio River water was, ozo^ati|d ;a§ an ozone to DOC ratio of
0.7 mg/mg. After coagulation"^•%locculation and settling,
the flow was split to eignt parallel filters. (Miltner and
Summers, 1992). The results from a fixed bed single-pass
filter with sand will be reported in this paper.
MATERIALS AND METHODS
Raw Ohio River water was trucked from the Cincinnati
Water Works to the USEPA facility. Ozonation was conducted
at room temperature in a 15 cm (6 in.) diameter
countercurrent flow-through contactor. The transfer
efficiency was greater than 94 percent. This ozonation
system has been described in detail (Miltner et al., 1990).
After each change in ozone dose, samples were collected
after steady state conditions were reached, which was
conservatively chosen at two times the T10p time based on
tracer studies. Applied gas to the contactor and off-gas
from the contactor were measured by UV. Dissolved ozone
from the contactor was measured spectrophotometrically
using the indigo trisulfonate method (Bader and Hoigne,
1981). For the bromide spike, a concentrated stock
potassium bromide solution was added to the raw water
before ozonation. To provide the required concentration as
bromide, the rate of flow of the stock solution was varied.
Samples were collected before and after contact with ozone.
For the pilot-scale system, ozonation, alum
coagulation, flocculation, sedimentation and sand
filtration were used. The sand filter (Filter 5), was a
3.8 cm (1.5 in.) diameter glass column containing 76 cm (30
in.) of sand (ES= 0.45 mm) supported by 20 cm (8 in.) of
gravel and 10 cm (4 in) of coarse sand.
For the bench-scale biotreatment, batch reactors were
used. The reactor is a modification of the Joret-Levi
reactor (Joret et al., 1988). To provide enough sample for
formation potential determination, a 2 L Erlenmeyer flask
containing 300 ml of Ohio-River-water-acclimated-sand was
used with a sample volume of 1 L. Vacuum was applied to
the reactor forcing the incoming air through two water
traps for scrubbing and humification. This air was to
provide enough oxygen for the bacterial growth and for
mixingV The samples were kept in the bioreactors for five
days, and before formation potential tests, were filtered
using prewashed 0.45 /m pore diameter (Millipore HV)
membrane filters. Biodegradation was measured by the
difference between the DOC before and after biotreatment.
DOC was measured by EPA Method 415.1 and UV absorbance
was measured at 254 nm and reported as SAC. AOC was
measured using the methods of van der Kooij et al.
(1982,1987). Two strains of heterotrophs, Pseudomonas
fluorescens P17 and Spirillum NOX, were employed in AOC
determinations. Bromide and bromate concentrations were
measured by ion chromatography by the method of Hautman and
Bolyard (1991). The minimum detection level for bromate
was approximately 7 ^g/~L. Aldehyde concentrations were
-------
measured by a modification of the PFBOA derivitization
method described by Miltner et al. (1991).
Samples were collected for formation potential tests
before and after ozonation and after biotreatment. For
formation potential determination, a 12 mg/L chlorine dose
was used, at ambient pH (7.5-8.0), at 20 °C and held
headspace-free in the dark for seven days. After
quenching, samples were collected for DBF analyses that
were based on USEPA methods: THMs were measured by EPA
Method 551; TOX by EPA Method 450.1 and HAAs by EPA Method
552.
For quality assurance ten percent duplication was
used. Error bars in the figures represent the range of
results from the duplicate biotreatment or ozonation tests.
Error bars for biotreated samples represent the range of
results from two separate reactors.
RESULTS AND DISCUSSION
The experimental matrix of the bench-scale
biotreatment study is summarized by the DOC results in
Figure 1 which show the impact of ozonation and biological
treatment on DOC concentration. For all bromide levels,
ozonation did not have a significant impact on the DOC
concentration. Biological treatment of the raw water
(O3/DOC ratio equal to 0 mg/mg) resulted in a 13 to 14
percent removal of DOC. With ozonation followed by
biotreatment, a range of 20 to 40 percent DOC removal was
observed, with the majority of the effect occurring at
O3/DOC ratios less than 0.8 mg/mg.
2.0
OZONATION
cn
E
1.2
8 0.8
Q
0.4
0.0
OZONATION + BIOTREATMENT
BROMIDE = 50.7 fj.g/L
BROMIDE = 258 fj.q/1
BROMIDE = 550 /ug/L
0
1 2
TRANSFERRED OZONE/DOC (mg/mg)
Figure 1. BENCH-SCALE BIOTREATMENT: IMPACT OF OZONATION
AND BIOTREATMENT ON DOC CONCENTRATION AT THREE
BROMIDE LEVELS.
-------
Biological treatment not only removed the DOC but also
seemed to lower the chlorine demand (Figure 2). In this
case, ozonation alone enhanced chlorine demand removal,
biotreatment alone decreased the demand by 43 percent, and
the combination of ozonation and biotreatment decreased the
demand by a range of 60 to 70 percent.
7
OZONATION
OZONATION + BIOTREATMENT
DOC0 = 1.68 mg/L
BROMIDE = 258 /j,g/l
0
1 2
TRANSFERRED OZONE/DOC (mg/mg)
Figure 2. BENCH-SCALE BIOTREATMENT: IMPACT OF OZONATION
AND BIOTREATMENT ON CHLORINE DEMAND.
The halogenated DBFs were also decreased by ozonation
and by biotreatment. The total THM formation potential
results are presented in Figure 3. Ozonation decreased the
TTHMFP by a range of 27 to 46 percent, and a 28 percent
reduction in TTHMFP was observed by biotreatment alone. In
comparison, at all ozone doses, the effect of biotreatment
was another reduction of 12 to 19 percent. TOXFP and
total measured HAAFP results from this study, though not
shown, were also decreased by ozonation and by biotreatment
(Shukairy et al., I992b).
Ozonation DBPs
BDOC and AOC: The formation of biodegradable organic
matter by ozonation is shown in Figures 4 to 7. The BDOC
increased with increasing ozone doses at all bromide
levels, Figure 4. The most significant increase in BDOC
was at O,/DOC ratios less than 0.8 mg/mg. At higher ozone
doses, the increase in BDOC was minimal. Similar site
specific BDOC behavior at higher ozone doses have been
reported (Langlais et al., 1991). AOC measured by both
strains NOX and P17 increased with increasing ozone dose as
-------
350
50
0
OZONATION
OZONATION -1- BIOTREATMENT
- DOC0 = 1.68 mg/L
BROMIDE0 = 550 /j.g/1
0
1 2
TRANSFERRED OZONE/DOC (mg/mg)
Figure 3. BENCH-SCALE BIOTREATMENT: IMPACT OF OZONATION AND
BIOTREATMENT ON TOTAL THM FORMATION POTENTIAL.
O BROMIDE = 50.7
A BROMIDE = 258 M9/L
D BROMIDE = 550
0.0
1 2-
TRANSFERRED OZONE / DOC (mg/mg)
Figure 4. BENCH-SCALE BIOTREATMENT: IMPACT OF OZONATION ON
BDOC AT THREE BROMIDE LEVELS.
-------
shown in Figure 5. Most of
O3/DOC ratios below 1.2 mg/mg.
increases were minimal.
this increase occurred at
At higher ozone doses, AOC
1000
LJ
X
o
I
O
CP 400 -
X
O
-z.
I
o
o
800 -
600 -
200
V P17
O NOX
200
UJ
150 O
CT
-------
2.0
1.6
1.2
O
O 0.8
CD
0.4
0.0
OGC0- (1.5 - 52) mg/L
O OZONATEO
* SETTLED
a FILTER 5 (SAND FILTERED)
50
100
DAY
150
200
Figuire 6. PILOT-SCALE BIOTREATMENT: IMPACT OF OZONATION AND
SAND FILTRATION ON BDOC.
800
SETTLED
FILTER 4
O FILTER 5
O FILTER 6
D FILTER 7
A FILTER 8
50
100
150
200
250
RUN TIME, days
Figure 7. PILOT-SCALE BIOTREATMENT: CONTROL OF AOC-NOX IN
BIOLOGICAL FILTERS.
8
-------
Aldehydes: An increase in aldehyde concentrations
with ozonation of Ohio River water is shown in Figure 8.
All aldehydes detected, methyl glyoxal, propanal, pent anal,
acetaldehyde and methyl glyoxal, were subsequently reduced
by biotreatment, at all ozone doses, to concentrations less
than that in the raw water. Similar decreases in aldehyde
concentrations attributed to biotreatment have been
reported (Shukairy et al., 1992a; Miltner et al., 1990),
indicating that these simpler molecules are very
biodegradable.
UJ
CJ
-z.
a
o
Ld
Q
>-
X
LU
Q
_J
DOC. = 1.68 mg/L
O • METHYL GLYOXAL
V T PROPANAL
O • PENTANAL
A A ACETALDEHYDE
O * GLYOXAL
OZONATION + BIOTREATMENT
1 2
TRANSFERRED OZONE/DOC (mg/mg)
Figure 8. BENCH-SCALE BIOTREATMENT: IMPACT OF OZONATION AND
BIOTREATMENT ON THE FORMATION AND CONTROL OF
ALDEHYDES.
The biodegradability of aldehydes in the pilot-plant is
also apparent from the behavior of these compounds in the
sand filter (Filter 5) . Figure 9 shows the results for
methyl glyoxal. For the control of this aldehyde, little
or no time was required to bioacclimate these filters as
removal was near 100 percent in the first week of
operation. The other aldehydes examined but not shown,
formaldehyde, glyoxal and acetaldehyde, were not as
biodegradable as methyl glyoxal but the trends in their
control were similar to that of methyl glyoxal.
-------
CH
_J
<
X
a
o
_j
X
I—
Ld
° r
12
8
A
V
•-i
o
50
100
150
200
250
RUN TIME, days
Figure 9. PILOT-SCALE BIOTREATMENT: CONTROL OF METHYL
GLYOXAL IN BIOLOGICAL FILTERS.
Bromata: In the presence of bromide, ozone oxidizes
the bromide to hypobromite ion and then to bromate. At
ambient bromide concentrations, 50.7 M9/L, bromate was not
detected at O3/DOC ratios less than 0.8 mg/mg. Increasing
ozone doses caused bromate levels to increase while the
bromide concentration decreased simultaneously (Figure 10).
At the highest O,/DOC ratio studied, 2.54 mg/mg, 50 percent
of the initial bromide concentration had reacted to form
bromate. At the highest bromide level investigated, 550
/ig/L, bromate was detected at the lowest ozone dose in this
study and showed continued increase with increasing ozone
dose to 300 Mg/L, Figure 11. At this highest dose studied,
34 percent of the initial bromide concentration had reacted
to form bromate.
DBF Speciation
The presence of bromide in the water affects the
speciation of the DBFs. Upon ozonation, the bromide
concentration decreased due to bromate formation (Figures
10 and 11) . The DOC of the water was not significantly
altered however (Figure 1). This led to a significant
decrease in the Br/DOC ratio. Figure 12 shows the impact
of ozonation and biotreatment on the Br/DOC ratio. At all
bromide levels, the ratio decreased by ozonation compared
to the raw water by as much as 50 percent.
10
-------
AMBIENT BROMIDE
DOC = 1.68 mg/L
1 2 3
TRANSFERRED OZONE/DOC (mg/mg)
Figure 10. CONVERSION OF BROMIDE TO BROMATE WITH OZONATION
AT THE AMBIENT BROMIDE LEVEL.
600
500 /ig/L BROMIDE ADDED
DOCQ = 1.68 mg/L
TRANSFERRED OZONE/DOC (mg/mg)'
Figure 11. CONVERSION OF BROMIDE TO BROMATE BY OZONATION AT
A TOTAL INITIAL BROMIDE CONCENTRATION OF 550jLig/L.
11
-------
With biotreatment alone, the DOC decreased significantly
(Figure 1), while the bromide concentration remained
unchanged. Therefore the Br/DOC ratio increased as shown
in Figure 12. The impact of bromate formation at high
ozone doses was also apparent in the biotreated samples.
The Br/DOC ratio decreased with increasing ozone dose as
compared to the raw biotreated water. In both ozonated and
unozonated samples, biotreatment increased the Br/DOC ratio
in comparison to the nonbiotreated sample.
o.o
0.0
OZONATION
O
OZONATION +
BIOTREATMENT
BROMIDEQ
50.7 M9/L
258 M9/L -
550
0.5 1.0 1.5 2.0 2.5
TRANSFERRED OZONE/DOC (mg/mg)
3.0
Figure 12. BENCH-SCALE BIOTREATMENT: IMPACT OF OZONATION
AND BIOTREATMENT ON THE BROMIDE TO DOC RATIO.
The change in Br/DOC ratio is very important as it
affects the speciation of the DBFs. As the ratio
increases, a shift to the more highly brominated species
occurs. Figure 13 and 14 show the impact of bromide
addition on THM and HAA speciation, respectively, for the
raw untreated Ohio River water. Chloro-substituted species
formation decreased as the Br/DOC ratio increased, while
the more bromo-substituted species increased. At the
lowest Br/DOC ratio (50.7 M9/L Br), chloroform was the
dominant species and was decreased by 80 percent at the
highest bromide concentration studied. At the highest
Br/DOC ratio, the dibromochloromethane (CHClBr2) became the
most dominant species, and chloroform the least. Bromoform
increased significantly with increasing Br/DOC (Figure 13) .
For HAA species, Figure 14, diehloroacetic acid (DCAA) was
the most dominant species at low Br/DOC ratios and
decreased by 71 percent as the ratio increased. At the
12
-------
^
-z.
o
<
LU
O.
o
Q_
O
a:
O
200
150
100
50
RAW OHIO RIVER WATER ""'.
0.0
0.1
0.2
A CHCIjFP
Q CHCI2BrFP
O CHCIBr2FP
O CHBr-jFP
= 1.6S mg/L
0.3
0.4
BROMIDE/DOC (mg/mg)
Figure 13. IMPACT OF BROMIDE ADDITION ON THM SPECIATION OF
UNTREATED WATER.
60
CT>
40
UJ
o
Q_
O
!< 20
o
0.0
RAW OHIO RIVER WATER
OOCQ= 1.68 mg/L.
A OCAAFP
Q TCAAFP
O BCAAFP
O OBAAFP
0.1 0.2 0.3
BROMIDE / DOC (mg/mg)
0.4
Figure 14. IMPACT OF BROMIDE ADDITION ON HAA SPECIATION FOR
UNTREATED WATER.
13
-------
highest Br/DOC ratio, bromochloroacetic acid (BCAA) became
the most dominant species.
This shift in speciation would also be more
significant in full distribution systems or in simulated
distribution system studies where the chlorine dose would
be much lower than in these FP studies . At low chlorine to
bromide ratios the speciation is more shifted to the bromo-
substituted species.
The impact of the change in Br/DOC ratio by ozonation
and biotreatment on DBF speciation can also be inferred
from the individual species behavior. Figure 15 shows the
control of formation potential by ozonation and
biotreatment of chloroform (CHC13) and bromodichloromethane
(CHClpBr) at ambient bromide. The percent removal is
calculated relative to the concentration of the particular
species in the control sample, i.e. the raw water. For
this study, chloroform represents 80 percent of the TTHMs
and its behavior is similar to that of the TTHMs.
Oxidation of the precursor compounds by ozonation resulted
in 22 percent removal of CHC13FP. This removal was not
enhanced by increasing ozone dose. Similar behavior upon
ozonation was observed for CHCl-BrFP. With biotreatment,
DOC removal and biological oxidation
resulted in improved removal of CHC13FP,
raw water and up to 50 percent
biotreatment .
of the precursors
30 percent for the
by ozonation and
UJ
O
CE
LU
a.
100
75
50
-25
-50
DOCQ = 1.68 mg/L
BROMIDE
50.7
0
OZONATION +
OZONATION BIOTREATMENT
A
cr
CHCI-jFP CQ = 150
CHBrCI2FP CQ = 27.7
1 2
TRANSFERRED OZONE/DOC (mg/mg)
Figure 15. BENCH-SCALE BIOTREATMENT: PERCENT REMOVAL OF THM
SPECIES BY OZONATION AND BIOTREATMENT.
14
-------
The behavior of bromodichloromethane upon biotreatment
was slightly different however. An increase in the Br/DOC
ratio due to the decrease in DOC with biotreatment resulted
in 17 percent increased formation of CHCl2Br. As the
bromide concentration decreased, with increasing ozone
dose, because of bromate formation (Figure 10) , the Br/DOC
ratio decreased resulting in removal of CHCl,BrFP.
The more highly brominated DBF species displayed
behavioral trends very different from that of the
chlorinated DBFs. For dibromochloromethane, at the ambient
bromide concentration and at an O3/DOC ratio of 0.53 mg/mg,
there was an increase of 26 percent in formation as shown
in Figure 16. Bromate was not detected at this ozone dose
(Figure 10) , hence the bromide was oxidized to form free
bromine and react with the organic matter upon
chlorination. As the ozone doses increased, bromate
concentrations increased, bromide decreased, the Br/DOC
ratio decreased and the speciation shifted to the more
chloro-substituted species (59 percent decrease in the
CHBr2ClFP at an O3/DOC ratio of 2.54 mg/mg).
With biotreatment at ambient bromide levels, the
Br/DOC ratio was even higher than in the raw water leading
to the formation of CHBr2Cl. The trend upon
ozonation/biotreatment was similar to the trend observed
for ozonation only. A 25 percent increase in the formation
of CHBr2Cl was observed at an O3/DOC ratio of 1.78 mg/mg.
For bromoform, the behavior was similar to that of
CHBr2Cl upon ozonation. With biotreatment however,
bromoform was removed at all ozone doses. As the organic
matter concentration was significantly decreased by
biotreatment bromoform was no longer detected.
100
DOCQ = 1.68 mg/L
75 (- 8ROWIDE0 = 50.7 /j.g/L
o
s
UJ
UJ
o
ct:
UJ
CL
-25
-50
-75
-100
OZONATION 4-
OZONATION BIOTREATMENT
O •
O *
CHCI8r2FP CQ = 6.91 /j.g/1:
CHBr^FP CQ = 2.05 /J.g/1
0 1.2 3
TRANSFERRED OZONE/DOC (rng/mg)
Figure 16. BENCH-SCALE BIOTREATMENT: PERCENT REMOVAL OF THM
SPECIES BY OZONATION AND BIOTREATMENT.
15
-------
HAA speciation trends, similar to those of the THMs,
were observed at all bromide levels. Figure 17 shows the
percent control of DCAAFP and DBAAFP at ambient bromide.
Similar behavior was also observed for TCAAFP. The highly
chlorinated HAA species responded to ozonation and
biotreatment in a manner similar to those of the highly
chlorinated THM species.
Low ozone doses resulted in 16 to 18 percent removal
of DCAAFP, and biotreatment, with and without ozonation,
resulted in improved removal (50 to 70 percent). For the
DBAA species, at a low O3/DOC ratio there was 35 percent
increase in formation. As the ozone dose increased
however, the bromide concentration decreased and a 100
percent removal of DBAAFP was observed at an O3/DOC ratio
of 2.54 mg/mg. This effect was even more pronounced with
biotreatment.
In comparison, on a pilot-scale for Filter 5, the
behavior of DCAAFP is shown in Figure 18. Filter 5
averaged 41 percent removal of DCAAFP when steady state
conditions were reached. It took near 50 days to establish
steady state removal of DCAAFP in this sand filter.
Generally it took one and a half to two and a half months
to establish steady state biodegradation of precursors for
THMs, HAAs and TOX. This is longer than the time required
to establish control of aldehydes (only days) or AOC-NOX
(one month). Precursors of halogenated compounds are
larger molecules than the smaller, more biodegradable ozone
DBP molecules.
100
LU
UJ
O
OH
UJ
Q_
-100
OZONATION
+
OZONATION BIOTREATMENT
• DCAAFP 50.0 M9/L
DBAAFP 0.40 /j.g/1
TRANSFERRED OZONE / DOC (mg/mg)
Figure 17. BENCH-SCALE BIOTREATMENT: PERCENT REMOVAL OF HAA
SPECIES BY OZONATION AND BIOTREATMENT.
-------
60
O1
=1
cr
I_L_
<
<
O
Q
O FILTER 5
O FILTER 6
D FILTER 7
A FILTER 8
20
10 -
0
50
100
150
200
250
RUN TIME, days
Figure 18. PILOT-SCALE BIOTREATMENT: CONTROL OP DCAAFP IN
BIOLOGICAL FILTERS.
Bench-Scale versus Pilot-Scale Biodearadation
The bench-scale bioreactors used in this study provide
five day of contact time at 20 °C for water and
bioacclimated sand surfaces. Mogren et al. (1990) and
Joret et al. (1988) found five days sufficient to provide
optimum biodegradation. In these studies that provided
greater than 95 percent biodegradation of aldehydes and 30
to 76 percent of DBF precursors, as seen in Table 1. These
levels of control were not found in the pilot-scale
biological sand filter having 10 minutes contact time and
temperatures ranging from 17° to 27 °C. Table 1 shows for
smaller molecules like aldehydes the bench and pilot scale
systems were comparable, but for more complex molecules
like DBF precursors poorer control was observed under the
pilot-scale real world conditions.
17
-------
Table l.
Control of Drinking Water Parameters by
Biologically Active Sand
Parameter
Methyl Glyoxal
Forma Idehyde
AOC-NOX
DOC
THMFP
CHC1,FP
HAAFP
DCAAFP
TOXFP
Percent Removal"
Bench-Scale
Bioreactorse'f
99,99
96, d
d
8,31
36,20
58,32
65,68
76,51
43,39
Pilot Plant
Filter 5b'c-9
97 +/- 2
88 +/- 7
47 -I-/- 14
16 +/- 9
17 +/- 5
25 +./- 5
37 +/- 6
41 +/- 6
26 +/- 7
a O3/DOC approximately 0.7 mg/mg
b after steady-state control established
c based on 163 days of operation
d no data
e based on Miltner, Shukairy and Summers (1992)
f based on Shukairy, Summers and Miltner (1992b)
g based on Miltner and summers (1992)
SUMMARY
Ozonation of organic matter leads to the formation of
more biodegradable compounds and to ozonation DBFs. In the
presence of bromide, ozonation also leads to significant
formation of bromate. For a source water that has a high
bromide concentration, the use of ozonation must be
carefully considered because of the high bromate
concentrations that could be generated.
Aldehydes, ozonation DBFs, are very biodegradable and
can be controlled by biof iltration at both bench and pilot-
scales.
Ozonation and biotreatment provide good control for
halogenated DBF precursors.* There seems to be no
improvement in the control by ozonation above a certain
ozone to DOC ratio. For Ohio River water, the ratio is
between 0.7 and 1.0 mg/mg. For the individual THM and HAA
species, biotreatment is less effective for the control of
the bromo-substituted compounds because of the increase in
bromide to DOC ratio and this effect is even more
pronounced at lower chlorine doses.
The batch-scale bioreactors using sand, with 5 days
residence time, represent ultimate biodegradation. Similar
control by biotreatment was attainable for easily
biodegradable aldehydes in pilot-scale sand filters where
residence times are in the order of minutes. However, for
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the more complex compounds like DBF precursors, poorer
control was observed in pilot-scale biological filters than
in bench scale bioreactor?.
On a pilot-scale, :,biqdegradation of aldehydes was
established in a matter of days, AOC-NOX in about a month
and DBF precursors in 1.5'to 2; 5 months.
*• *
ACKNOWLEDGEMENTS
The authors thank the staff of the Cincinnati Water
Works, without whom this study would not have been
possible. The authors also appreciate the efforts of all
the staff at the USEPA pilot plant. This work was funded
by USEPA in-house funds and by a Cooperative Agreement CR-
816700 between the USEPA and the University of Cincinnati.
Although the research described was funded by USEPA, it has
not been subjected to agency review and therefore does not
necessarily reflect the view of 'the agency.
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