ROBERT A. TAFT WATER RESEARCH CENTER
REPORT NO. TWRC-3
AN INVESTIGATION
OF LIGHT-CATALYZED CHLORINE OXIDATION
FOR TREATMENT OF WASTEWATER
ADVANCED WASTE TREATMENT RESEARCH LABORATORY III
U.S. DEPARTMENT OF THE INTERIOR
FEDERAL WATER POLLUTION CONTROL ADMINISTRATION
OHIO BASIN REGION
Cincinnati, Ohio
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AN INVESTIGATION OF LIGHT-CATALYZED CHLORINE
OXIDATION FOR TREATMENT OF WASTEWATER
by
Alfred F. Meiners, Elizabeth A. Lawler,
Mary E. Whitehead, and John I. Morrison
for
The Advanced Waste Treatment Research Laboratory
Robert A. Taft Water Research Center
This report is submitted in
fulfillment of Contract No.
14-12-72 between the Federal
Water Pollution Control Ad-
ministration and the Midwest
Research Institute.
U. S. Department of the Interior
Federal Water Pollution Control Administration
Cincinnati, Ohio
December 1968
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FOREWORD
In its assigned function as the Nation's principal
natural resource agency, the United States Department of the
Interior bears a special obligation to ensure that our expend-
able resources are conserved, that renewable resources are
managed to produce optimum yields, and that all resources con-
tribute their full measure to the progress, prosperity, and
security of America -- now and in the future.
This series of reports has been established to present
the results of intramural and contract research carried out under
the guidance of the technical staff of the FWPCA's Robert A. Taft
Water Research Center for the purpose of developing new or im-
proved wastewater treatment methods. Included is work conducted
under cooperative and contractual agreements with Federal, state,
and local agencies, research institutions, and industrial organi-
zations. The reports are published essentially as submitted by
the investigators. The ideas and conclusions presented are,
therefore, those of the investigators and not necessarily those of
the FWPCA.
Reports in this series will be distributed as supplies
permit. Requests should be sent to the Office of Information, Ohio
Basin Region, Federal Water Pollution Control Administration, 4676
Columbia Parkway, Cincinnati, Ohio 45226.
ii
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TABLE OF CONTENTS
Page Mo.
Abstract ................... ป ฐ ....... v
Summary: Wastewater Oxidation Studies - The Effects o
pH and Irradiation Time
Introduction . ......................... 4
First Series of Wastewater Oxidation Experiments ........ 5
Second Series of Wastevater Oxidation Experiments ........ 18
Reaction in the Dark ..................... 20
Reaction During Irradiation .................. 23
Effect of Irradiation Alone .................. 26
Third Series of Wastewater Oxidation Experiments . ....... 27
Further Investigation of the Effect of pH ........... 31
Effect of Chlorine Concentration ............... 32
Effect of Nitrate Concentration ................ 33
Effect of Temperature ............... - ..... 34
Ultraviolet-Catalyzed Chlorine Oxidation of
High-Ammonia Effluents .................... 49
Reactions of Aqueous Ammonia with Chlorine ........... 54
Ammonia-Chloramine Determinations. . . . ......... . . 57
Effect of Irradiation on the Ammonia-Chlorine Reaction ....
57
Comparison of UV Radiation Sources .... 59
Ultraviolet-Catalyzed Chlorine Oxidation of Pure Compounds ... 67
Investigation of the Effect of Ultraviolet Radiation, Plus Other
Oxidizing Agent? 77
Process Costs 80
Commercially Available, Ultraviolet Sources 81
General Design Considerations 81
iii
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TABLE OF CONTENTS (Concluded)
Page No.
Transmission of UV Radiation by Wastewater 85
Cost of Lamps, Power and Structure 85
Total Process Costs 8?
Experimental 89
Photochemical Reactor 89
Ultraviolet Radiation Sources .... 89
Analytical Methods 92
Sources of Wastewater 92
Laboratory-Scale, Sewage-Treatment Apparatus 96
Effluent Analyses 96
General Procedure 96
Effect of Ultraviolet Radiation on Chlorine Water 99
First Series of Wastewater Oxidation Experiments 99
Second Series of Effluent Oxidation Experiments 100
Third Series of Effluent Oxidation Experiments 104
Extent of Organic Oxidation Produced by Chlorine in the Dark . . 108
Extent of COD and TOC Elimination Produced by Irradiation
at pH 5 109
Ultraviolet-Catalyzed Chlorine Oxidation of High-Ammonia
Effluents 110
Ultraviolet-Catalyzed Chlorine Oxidation of Ammonia 114
Comparison of UV Radiation Sources 116
UV-Catalyzed Chlorine Oxidation of Pure Compounds 117
Investigation of the Effect of UV Radiation, Plus Other Oxidiz-
ing Agents 117
Ultraviolet Absorbance of Treated and Untreated Wastewater
Samples 118
References 121
IV
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ABSTRACT
A study was made of the effect of ultraviolet radiation on the
rate and extent of chlorine oxidation of organic material in highly nitrified
effluents from biological sewage treatment plants. Ultraviolet radiation
will very significantly increase the rate of this reaction. Also, the
extent of oxidation which can be achieved by chlorine combined with UV radia-
tion is usually much greater than that which can be achieved by chlorine
alone.
The rate of the catalytic oxidation is dependent upon pH, and the
most rapid rate of oxidation and most efficient use of chlorine are obtained
at pH 5. In seven different experiments performed at pH 5, the average COD
decrease was 67% in 5 min., 79fa in 10 min. and 95% in 15 min.
The rate of organic oxidation is not proportional to the chlorine
concentration; however, the rate of chlorine consumption is. Large ex-
cesses of chlorine do not increase the reaction rate but simply increase
the amount of chlorine required to eliminate a given amount of organic mat-
ter.
The rate and extent of the catalytic organic oxidation at pH 5
are not significantly affected by temperature. However, both the rate and
extent of catalytic oxidation are substantially reduced by the presence of
ammonia in an effluent.
A brief investigation of the scope of the UV-catalyzed chlorine
oxidation indicated that phenol, 2,4-dinitrophenol, glycine, formic acid,
and o-dinitrobenzene are oxidized rapidly and extensively.
On the basis of organic oxidation rate produced per watt of UV
output, high-pressure mercury arcs are about 2.7 times more efficient than
low-pressure mercury arcs.
Process costs of 7.2^ to 11.1^/1000 gal. were estimated, based
on several types of commercially available lamps.
v
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SUMMARY
WASTEWATER OXIDATION STUDIES - THE EFFECTS OF
pH AMD IRRADIATION TIME
Ultraviolet radiation will very significantly increase the rate
at which chlorine will oxidize the organic material in highly nitrified
wastewater. Also, the extent of oxidation which can be achieved by chlorine
and UV radiation is usually much greater than that which can be achieved by
chlorine alone; 5 to 8 times more TOG and COD could be eliminated in 10 min.
by chlorine plus UV radiation than could be eliminated in 6 days by chlorine
in the dark.
The rate of the catalytic organic oxidation is dependent upon
pH, and the most rapid rate of oxidation and most efficient use of chlorine
are obtained at pH 5. The rate of organic oxidation at pH 6.5 is not as
fast as at pH 5, but is faster than at pH 8.5. The organic oxidation rate
is much slower at pH 3 and at pH 10.
Ultraviolet radiation alone will produce reduction in the COD
and TOC of an effluent; however, UV radiation plus chlorine is 3 to 10
times faster, depending upon pH; at pH 5, COD is eliminated more than 8
times faster, and TOC is eliminated 4.5 times faster.
The wastewaters examined contained variable quantities of readily
oxidizable organic material. The chemical oxygen demand (COD) which could
be eliminated within 10 min. by chlorine in the dark averaged 12% (range
0.8-20$). The extent of total organic carbon (TOC) elimination during
this time averaged 6$ (range 0-15$).-
The oxidations of four different effluents were investigated at
pH 5. In seven different experiments, the average COD decrease was 67$ in
5 min. (range 51-84$), 79$ in 10 min. (range 66-100$), and 95$ in 15 min.
(range 88-100$). The average TOC decrease was 33$ in 5 min. (range 15-50$),
52$ in 10 min. (range 44-60$), and 75$ in 15 min. (range 70-81$).
The rate of COD elimination at pH 5 is most rapid during the first
5 min. and decreases as the oxidation proceeds. The rate of TOC elimina-
tion, however, is nearly linear over a 15-min. period.
1
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Effect of Chlorine Concentration
The rate of COD and TOC elimination is not proportional to the
chlorine concentration; however, the rate of chlorine consumption is. Large
excesses of chlorine do not increase the reaction rate but simply increase
the amount of chlorine required to eliminate a given amount of organic
matter. Most efficient use of chlorine is obtained when the chlorine is
added gradually during the irradiation period.
Effect of Temperature
The rate and extent of the catalytic organic oxidation at pH 5
are not significantly affected by temperature. The rate of COD elimination
at 25ฐC (77ฐF) is only slightly greater than it is at 5ฐC (41ฐF). The
rates of TOC elimination are about the same at both temperatures.
Effect of Ammonia
The presence of ammonia in an effluent drastically reduces the
rate and extent of the UV-catalyzed chlorine oxidation of organic matter.
For example, the addition of 23 ppm of ammonia nitrogen to a highly nitrified
effluent reduces the organic oxidation rate by more than tenfold. The
amount of chlorine actually required to eliminate 1 ppm of ammonia is about
four times the theoretical amount required to eliminate 1 ppm of COD. Also,
the oxidation of organic matter is greatly inhibited until all the ammonia
is oxidized.
In water, ammonia reacts with chlorine to form mono-, di- and
trichloramine in various proportions, depending upon pH and ratio of reactants,
At pH 5, an excess of chlorine rapidly converts most of the ammonia to
trichloramine which is relatively stable in the presence of excess chlorine.
Irradiation of an ammonia-chlorine reaction-mixture rapidly accelerates the
conversion of trichloramine to nitrate and other oxidation products of
ammonia including, presumably, nitrogen gas.
Oxidation of Pure Compounds
A brief investigation was made of the effect of UV-catalyzed
chlorine oxidation on the TOC of water containing eight pure organic com-
pounds. The following compounds'are oxidized rapidly and extensively:
phenol (61$, 8 min.), 2,4-dinitrophenol (55%, 10 min.), glycine (61$, 4 min.),
formic acid (90$, 4 min.)? and o-dinitrobenzene (65$, 10 min.). Benzoic
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acid is also oxidized (45%, 10 min.), t>u"t no~t as fast as the other compounds.
Acetic acid and ethanol are oxidized at a much slower rate (less than 10%,
10 min.).
Other Oxidizing Agents
A very brief study was made of the extent of organic oxidation
produced when wastewater was treated with UV radiation plus (l) molecular
oxygen and (2) hydrogen peroxide. No significant decrease in TOG was
detected after oxygen had been bubbled through an irradiated reaction
mixture for 20 min. Hydrogen peroxide produced no significant decrease
in TOG after 30 minป in the dark; irradiation of this reaction mixture for
another 30 min. produced only a slight decrease in TOC.
Ultraviolet Sources
At the present time, mercury-arc lamps are probably the most prac-
tical sources of UV radiation for the catalytic chlorine oxidation of organic
material in wastewater. On the basis of organic oxidation rate produced
per watt of UV output, high-pressure mercury arcs, which emit a broad spec-
trum of wavelengths (220 - 366 mp,), are about 2.7 times more efficient than
low-pressure mercury arcs which emit almost exclusively at one wavelength
(253.7 mj, ).
Process Costs
Process cost estimates were made for large-scale application of
UV-catalyzed chlorine oxidation to wastewater. Costs of 7.20 to 11.10/1000
gal. were estimated employing commercially available UV lamps. The assump-
tions made were that a contact time of 10 min. is required for effective
organic oxidation and that the catalytic process requires the application
of 15 times more radiant energy than that required for UV sterilization.
Process costs could be lowered substantially if any one of the
following factors could be reduced: (l) the amount of radiant energy per
unit volume required for effective oxidation, (2) the contact time and
(3) the cost of the radiation source. The precise determination of these
factors will require a study designed to determine exactly how much waste-
water can be treated effectively using each radiant energy source.
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INTRODUCTION
Earlier studies at Midwest Research Institute had demonstrated
that ultraviolet radiation strongly accelerates the rate at which aqueous
chlorine oxidizes starch and other organic compounds .-21 Chlorine is
widely used for the disinfection of water. However, in the absence of
ultraviolet radiation, chlorine will oxidize only a small fraction of the
*Z A I
organic material in wastewater. ?.,,/
The purpose of the present work was to determine the usefulness
of ultraviolet-catalyzed chlorine oxidation in producing more extensive, and
more rapid, removal of the organic material in highly nitrified wastewater.
Another objective was to estimate the cost of large-scale application of this
process. The results of this research are presented in nine major sections.
The first series of wastewater oxidation experiments was a gen-
eral investigation of the effect of pH, and a comparison of the rate and
extent of organic oxidation which could be achieved by chlorine plus UV
radiation, by chlorine alone, and by UV radiation alone.
The second series of wastewater oxidation experiments was designed
to determine the effect of variation in the amount of chlorine applied,
variation in irradiation time, and the effect of relatively small differences
in pH.
The third series of wastewater oxidation experiments was designed
to. clarify further the effects of pH and chlorine concentration, and to
determine whether or not the catalytic oxidation was subject to a tempera-
ture effect.
The fourth section discusses the problems which arise if relatively
large amounts of ammonia (15-30 ppm) are present in the effluent.
The fifth section discusses the results of a direct investigation
of the ammonia-chlorine reaction.
The relative effectiveness of two major types of UV sources is
discussed in a sixth section.
The various factors which influence the cost of large-scale
application of this process are discussed in a seventh section.
The eighth section describes briefly the application of
UV-catalyzed chlorine oxidation to pure organic compounds.
The final section discusses the effect of W radiation on the
oxidizing action of oxygen and hydrogen peroxide.
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FIRST SERIES OF WASTEWATER OXIDATION EXPERIMENTS
Summary
Experiments in this series showed that the oxidation of organic
matter in wastewater by chlorine is much faster when the reaction mixture
is irradiated than when the reaction mixture is kept in the dark. The
extent of COD elimination in the catalytic process is always greater than
the extent of TOG elimination.
Chlorine plus UV radiation produces organic oxidation 3 to 10
times faster than UV radiation alone, depending upon pH.
Considerable portions of ammonia in wastewater are converted
to nitrate by the UV-catalyzed chlorine oxidation process.
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First Series of Wastewater Oxidation Experiments
The first series of experiments was designed to compare (l) the
effects of two pH levels (pH 5 and pH 10), (2) the difference between
reaction in the dark and reaction when irradiated, and (3) the difference
between radiation alone and radiation plus chlorine. The design of this
series of experiments is shown in Table I.
TABLE I
EXPERIMENTAL DESIGN,
FIRST SERIES OF EXPERIMENTS
Experiment Number
pH 5 pH 10
Chlorine, plus irradiation 3 4
Irradiation, no chlorine 5 6
Chlorine, no irradiation 7 8
The pH levels of 5 and 10 were chosen because, at pH 5, the active
chlorine in solution is 100$ hypochlorous acid; while, at pH 10, the active
chlorine is 100$ hypochlorite^/ (Figure l).* These two reagents would be
expected to react differently in the catalyzed oxidation because of their
distinctly different ultraviolet spectra (Figure 2).
The procedures used in this series were slightly different from
those used subsequently. The effluent in this series was acidified at
the point of collection (4 ml. H2S04/gal), and the pH was adjusted prior
to each experiment using 40$ sodium hydroxide. In subsequent experiments,
acidification at the point of collection was omitted. Also, contrary
to subsequent procedures, the UV lamp in this series was not allowed to
reach maximum irradiation intensity before being inserted into the reactor.
The analytical results obtained for chlorine concentration, COD
and TOC (which are presented in Figures 3-8) are summarized in Tables II
and III.
The first conclusion derived from this series of exploratory ex-
periments is that the oxidation proceeds many times faster upon irradia-
tion than it does in the dark. Thus, the indicated rate of oxidation
at pH 5, as measured by the rate of TOC elimination and the rate of chlorine
consumption, is 60 to 100 times faster upon irradiation than it is in the dark.
Figures in this report are inserted at the end of the section to which
they apply.
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TABLE II
RATES OF DECREASE IN CHLORINE CONCENTRATION,
TOC AND COD IN FIRST SERIES OF EXPERIMENTS
Average Rate Average Rate
Reaction Conditions
Exp.
No.
3
4
5
6
7
8
Initial Cl2
Concn. (ppm)
150
150
0
0
150
150
pH
5
10
5
10
5
10
Types of
Irrad.
UV
UV
UV
UV
None
None
of Decrease in
Chlorine Concn.
(ppm/min)
8.82
6-22V
--
0.133k/
0.055^7
0=290^/
0.0177k/
of TOC
Decrease
(ppm/min)
0.237
0.22
0.051
0.073
0.0037
__
0.016
0.00066
Average Rate
of COD
Decrease
(ppm/min)
1.08
1.10
0.132
0.110
0.012
0.00033
a/ In this experiment the chlorine disappearance was very rapid, so that
this value could only be estimated.
p_/ In Experiments 7 and 8, the chlorine concentration apparently decreased
at a non-linear rate (see Figures 7 and 8) until it reached a certain
level (about 65 ppm); then it remained constant. The first values refer
to rates during the first few hours of the experiment. The second
values were calculated for the duration of the entire experiment
(1,340 min. for Experiment 7; 4,535 min. for Experiment 8).
TABLE III
EXTENT OF COD AND TOC DECREASE IN
FIRST SERIES
OF EXPERIMENTS
Reaction Conditions
Exp.
No.
3
4
5
6
7
8
Initial Cl2
Concn. (ppm)
150
150
0
0
150
150
pH
5
10
5
10
5
10
Types of
Irrad .
UV
UV
UV
UV
None
None
COD
(V
95
82
82
59
51
16
Decrease
(min.Ji/
27
20
170
145
1,341
4,535
TOC
ill
55
25
73
84
12
15
Decrease
(min.);
27
20
170
145
1,341
4,353
a/ Irradiation time or reaction time depending on the nature of
the experiment.
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However, these differences in reaction rates are somewhat exag-
gerated because the rate of oxidation in the dark is most rapid at the
beginning of the oxidation; and, in these experiments, the oxidation in
the dark was essentially complete long before the final COD and TOC samples
were taken. The gradual slowing of the oxidation rate in the dark is indi-
cated from the plot of chlorine consumption vs. time in Experiment 7
(Figure 7). Subsequent studies (see.the later section entitled "Second
Series of Experiments") have shown that there is wide variation in the
amount of organic material which can be oxidized in 10 min. in the dark.
However, when irradiation is begun after 10 min. in the dark, the rate of
organic oxidation is increased up to 15-fold.
The second general conclusion drawn from this series of experi-
ments was that the extent of COD elimination is significantly greater than
the extent of TOC elimination. This conclusion was shown to be valid for
all subsequent experiments.
In the initial series of experiments, there appeared to be little
difference between pH 5 and pH 10 in respect to the rate of TOC and COD
elimination. However, this similarity was the result of inopportune sam-
pling times (see Figures 3 and 4), and subsequent experiments indicated that
the rate of organic oxidation is considerably greater at pH 5 than at pH 10.
A third conclusion from this series of experiments was that chlo-
rine plus UV radiation produces more rapid decreases in TOC and COD than UV
radiation alone. Comparing rates produced by chlorine plus UV radiation
at pH 5 with rates produced by UV radiation alone at pH 5, COD is eliminated
8.2 times faster, and TOC is eliminated 4.5 times faster; at pH 10, COD is
eliminated 10 times faster, and TOC is eliminated 3 times faster. Subsequent
experiments (see "Second Series of Experiments", p. 18) indicated that, at
pH 6.5, chlorine plus UV radiation eliminates COD about 7 times faster than
radiation alone.
The effluent used in this first series contained considerable
amounts of ammonia (2-6 ppm N) . 'Some difficulties in precision were encount-
ered in these ammonia determinations because of turbidity, which was prob-
ably the result of required adjustments in pH. Ammonia concentrations
determined for the first series of experiments are shown in Table IV. In
every experiment in which chlorine was present, there were very significant
decreases in ammonia concentration. (The ammonia-chlorine reaction is
examined in greater detail in the section concerning the oxidation of high-
ammonia effluents, p. 49, and the section concerning the ammonia-chlorine
reaction, p. 54).
Ultraviolet radiation alone (Experiments 5 and 6) had almost no
effect on ammonia concentration. This conclusion was verified in a sub-
sequent experiment (Experiment 15, p. 115).
a
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TABLE IV
AMMONIA CONCENTRATIONS
(First Series of Experiments)
Reaction Conditions
Exp.
No.
3
4
5
6
7
8
Initial C12 Types of
Concn. (ppm) pH Irrad.
150
150
0
0
150
150
5
10
5
10
5
10
uv
uv
uv
uv
None
None
Ammonia (ppm li)
Reaction Time
(min.)
27
20
171
145
1,341
01 R ^b/
ri-L > ซJI
4,535
a/ These gTmnon-ia values were obtained using a relatively fresh sample of
effluent.
b/ Considerable turbidity was noticed in these samples.
Initial
4.0
2.1
6.4^
6.^a
Final
2.8
7.2
6.6
2.7
2.9
In this first series of experiments, the observation was made that
significant quantities of ammonia were oxidized to nitrate in the experiments
in which the effluent was exposed to UV radiation and chlorine (Experiments
3 and 4); there were substantial increases in nitrate concentration (Table V)
Chlorine in the dark also produced an increase in nitrate concentration
(Experiments 7 and 8), but this increase was not as great as that produced
by chlorine plus irradiation. UV radiation alone actually decreased the
nitrate concentration. This observation was confirmed in Experiment 15,
p. 115. The formation of nitrate in the ammonia-chlorine reaction was in-
vestigated further in subsequent experiments (see the two sections of this
report concerned with the oxidation of high-ammonia effluents, p. 49, and
the section concerned with the ammonia-chlorine reaction, p. 54).
TABLE V
3
4
5
6
7
8
NITRATE CONCENTRATIONS
(First Series of Experiments)
Reaction Conditions
Initial C12 Types of
Concn. (ppm) pH Irrad.
150
150
0
0
150
150
5
10
5
10
5
10
UV
UV
UV
UV
None
None
Reaction Time
(min.)
27
20
196
145
1,341
4,535
Nitrate (ppm H)
Initial Final
0.50
0.50
0.26
2.44
2.85
0.20
0.09
1.95
1.27
-------
100
90
90
100
Figure 1 - Relative Amounts of HOC1 and OC1"
at Various pH Levels
10
-------
I I I I 1 I I I I II
240 260 280 300
WAVELENGTH (millimicrons)
Figure 2 - Ultraviolet Spec.tra of Hypฐchlorous
Acid and Hypochlorite Ion
-------
Time (min.)
Figure 3 - UV-Catalyzed Chlorine Oxidation of Effluent
Cr-1 at pH 5 (Experiment 3)
-------
I 100
_o
-C
L
30
15
20
Q_
c
:
.
E
Q.
10 <ฃ
u
:
10
20
Time (min.)
Figure 4 - UV-Catalyzed Chlorine Oxidation of Effluent
G-l at pH 10 (Experiment 4)
-------
Time (min.)
Figure 5 - Ultraviolet Irradiation of Effluent
G-l at pH 5 (Experiment 5)
E
D.
c
0
- 10
0
14
-------
15 -
a
U
0
Time (min.)
Figure 6 - Ultraviolet Irradiation of Effluent
G-l at pH 10 (Experiment 6)
O
0
U
- 10
15
-------
COD
30
20
I
Q.
8
L
a.
(.
50
10
;
500
Time (min.)
,000
]
,500
Figure 7 - Chlorination of Effluent G-l
at pH 5 (Experiment 7)
16
-------
COD
30 -
a
Q-
20 ~H
0
I
10
E
..:.
1.
u
0
50
10 -
500
1,000
Time (min.)
L
4,335
0
Figure 8 - Chlorination of Effluent G-l
at pH 10 (Experiment 8)
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SECOND SERIES OF WASTEWATER OXIDATION EXPERIMENTS
Summary
Experiments performed in this series indicated that, in the UV-
catalyzed process, the extent of organic oxidation is proportional to the
irradiation time, but not to chlorine concentration. The catalytic oxida-
tion rate is faster at pH 6.5 than at pH 8.5; the average extent of COD
decrease produced in 10 min. was 60.0$ at pH 6.5 and 45.6$ at pH 8.5.
(The organic oxidation rate is fastest at pH 5, and experiments performed
at pH 5 are described in the third series of wastewater oxidation experi-
ments.)
Experiments performed in this series and in the third series
have indicated that considerable variation exists in the amount of organic
oxidation which can be achieved when wastewater samples are treated for
10 min. with chlorine in the dark. In 13 experiments employing six dif-
ferent effluents, the extent of COD elimination during 10 min. in the dark
averaged 12% (range 0.8-20$) and the extent of TOG elimination during
this time averaged 6$ (range 0-15.3$).
18
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Second Series of Wastewater Oxidation Experiments
The low-ammonia effluents used in the second series of experi-
ments were obtained from two sources. First, a laboratory-scale activated
sludge apparatus was constructed and used to reduce the ammonia content of
high-ammonia municipal effluents. (This apparatus is described in the
Experimental Section.) Second, a reliable source of the desired type of
highly nitrified effluent was located. This source was a sewage treatment
plant of the activated sludge, extended aeration type. The plant was of
novel design and was operated on an experimental basis by the Smith and
Loveless Corporation.
Our experimental work continued using effluents obtained from
both of these sources.
A series of nine, effluent, oxidation experiments was designed to
investigate simultaneously the effect on COD and TOG of two levels, each,
of chlorine concentration, irradiation time and pH.
The chlorine concentrations investigated consisted of (l) a
slight excess over the theoretical amount of chlorine, and (2) a large
(75$) excess over the theoretical value.
Irradiation times of 10 and 15 min. were examined to determine
whether or not significant differences in COD and TOC elimination are
caused by differences in irradiation time of this magnitude. In these
experiments the UV lamp was allowed to warm up and was emitting maxisium-
intensity radiation when inserted into the reactor.
The pH levels of 6.5 and 8.5 were selected for study. These
values are only about 1 pH unit different from the pH of the untreated
effluent, but variations of this magnitude could have a large effect on
the oxidation reaction; at pH 6.5 about 90% of the available chlorine is
present as undissociated hypochlorous acid and, at pH 8.5, about 90$ of
the available chlorine exists as hypochlorite ion (see Figure l).
A complete factorial experiment was designed, and the order of
experiments was randomized. The design and randomization of the experiments
are shown in Table VI. The numbers refer to actual experiment numbers; that
is, Experiment 39 was run first, and Experiment 47 was run last in this
series.
In Experiment 41, no chlorine was used, no pH adjustment was made,
and the effluent was exposed to UV radiation for 10 and 15 min.
19
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TABLE VI
EXPERIMENTAL DESIGN
(Experiments 39 - 47)
_ pH 6.5 PH 8.5
High Cl2 Low Cla High C12 Low C12
(175 ppm) (102 ppm) (175 ppm) (102 ppm)
Short irradiation time (10 min.) 43ง/ 46 47 40
Long irradiation time (15 min.) 44 45 39 42
a/ The numbers 39-47 refer to experiment numbers. The experiments were
performed in random order and are numbered in the order in which
they were performed.
The effluent (S&L-5) used in these experiments was obtained
from the Smith and Loveless, experimental, sewage-treatment plant. This
effluent was very highly nitrified; the ammonia content was less than 1 ppm
(N), and the nitrate content was 10.6 ppm (N). The average COD was 22.0 ppm.
The results of this series of experiments are presented in the
following tables. Table VTI shows the extent of COD elimination produced
in the dark and upon subsequent irradiation.
Reaction in the dark - The results shown in Table VII indicate
that substantial elimination of COD occurred during the initial period of
chlorination in the dark. In some of the experiments, the indicated
decrease in COD was equal toor even greater thanthe subsequent COD
decrease which occurred upon irradiation. Although not all the experiments
show large COD decreases during this period,, (in fact, some ,show slight
increases), there appears to be a statistically significant difference
between the analytical figures obtained before and after chlorination in
the dark; the average COD before chlorination was 20.8, the average after
chlorination was 16.2. The difference between these figures represents
a 22$ average decrease in COD. A comparison of these averages is prob-
ably valid because it is not possible to correlate the individual COD
decreases with differences in pH or differences in chlorine concentration.
20
-------
TABLE VII
EXTENT OF COD ELIMINATION
Initial
Chlorine
Expt.
No.
39
40
41
41
42
43
44
45
46
47
Concentration
pH
8.5
8.5
7.5
7.5
8.5
6.5
6.5
6.5
6.5
8.5
(ppm)
175
102
0
0
102
175
175
102
102
175
Ultraviolet
Irradiation
Time
(min.)
15
10
10
15
15
10
15
15
10
10
Extent
of COD
Elimination
in Darkฃ/
Extent of COD
Elimination After
Treatment in the
Dark and After
Irradiation^/
-5.23
M
27.1
33.3
49.5
43.2
+0.61
-2.70
+0.29
-1.84
+0.70
-1.98
-6.35
-5.55
^J
cj
O^/
10.3
oV
9.4
30.1
29.9
13.0
35.7
52.0
59.6
68.8
59.5
53.8
a/ The percentages were calculated after adjusting the initial COD
values to account for the dilution which occurs when chlorine
water is added.
b/ In these experiments, the slight increase in COD which was detected is
within the range of experimental error.
c/ No "reaction in the dark" preceded irradiation.
However, we do not believe that the extent of oxidation in the
dark was as great as these figures indicate. The main reason for doubt
is that the amount of chlorine consumed during the same period is not
sufficient to produce COD decreases of this magnitude. The elimination of
1 ppm of COD requires 4.43 ppm of chlorine. Inspection of the data
presented in Table VIII clearly shows that the apparent COD elimination in
this series of experiments was far greater than that which could be produced
by the amount of chlorine consumed.
The apparent loss of COD in the dark was probably caused by a
loss of volatile organic matter during the nitrogen purge. Except for the
first sample (which obviously does not require dechlorination) and the
final sample (which usually contained only traces of chlorine), each sample
was acidified and purged with nitrogen in order to remove chlorine. We
believe-that this particular effluent was unique in that it contained rela-
tively large quantities of volatile organic products.
21
-------
TABLE VIII
COMPARISON OF COD ELIMINATION WITH CHLORINE
CONSUMPTION IN THE DARK
Theoretical COD Elimination
Chlorine Equivalent to Observed
Expt. Consumption Chlorine Consumption COD Elimination^/
Mo- (ppm) (ppm) (ppm)
39 7 1.58 5.23
40 10 2.26 7.55
42 3 0.68 {ฃ/
43 8 1.81 1.84
44 3 0.68 oV
45 7 1.58 1.98
46 7 1.58 6.35
47 5 1.13 5.55
a/ Initial COD values were adjusted to account for the dilution which
occurs when chlorine water is added.
b/ In these experiments, the slight increase in COD which was detected
is within the range of experimental error.
In general, the TOG analyses (Table IX) also show significant de-
creases during the 10-min. period in the dark. (Unfortunately, some of the
TOG analyses in this series were obviously too high and had to be discarded.)
However, the TOG samples were taken at the same time as the COD samples, and
the two samples were subjected simultaneously to the dechlorination proce-
dure. Therefore, the TOG data are subject to the same errors as the COD
data.
In subsequent experiments, the TOC samples were taken separately
and dechlorinated by acidification (to pH 1 with 1^304), followed by treat-
ment with excess sodium bisulfite. This procedure could not be used for
the COD samples because excess bisulfite would interfere with the COD
determination.
These subsequent experiments provided considerable information
concerning the extent of oxidation which takes place during a 10-min. period
of chlorination in the dark. From a total of 13 experiments with six dif-
ferent effluents, the following observations were made: (l) during the 10-
min. period of chlorination in the dark, the extent of COD reduction averaged
12$ and ranged from 0.6-20$; (2) the extent of TOC reduction during this
time was, in general, less than the extent of COD reduction. The TOC reduc-
tion averaged 6$_ and ranged from 0-15.3$.
22
-------
TABLE IX
fi/
EXTENT OF TOG ELIMINATION IN THE DARK AND
UPON IRRADIATION
Initial
Chlorine
Concentration
(ppm)
175
102
0
0
102
175
175
102
102
175
Ultraviolet
Irradiation
Time
(min. )
15
10
10
15
15
10
15
15
10
10
Extent of
TOG Elimination
in Dark
(*)
-8
-33
-
-
-4
+3 /
-eฃ/
+9
+14
-22
Extent of
TOC Elimination
on Irradiation
(*)
V
V
-10
-19
-35
-25
-soฃ/
+12
-17
-26
39 8.5
40 8.5
41 7.5
41 7.5
42 8.5
43 6.5
44 6.5
45 6.5
46 6.5
47 8.5
~^JInitial TOC values were adjusted to account for the dilution vhich
occurs when chlorine water is added.
b/ The calculations for these experiments could not "be made "because the
~~ TOC results were obviously in error.
c/ These values were calculated assuming that the actual initial TOC in
Experiment 44 was equal to average initial TOC value (9.11 ppm).
A summary of data concerning the extent of oxidation in the
dark is presented in the Experimental section (see- "Extent of Oxidation
Produced by Chlorine in the Dark," p. 107).
Reaction during irradiation - When the UV lamp was 'placed in
the immersion well, the chlorine concentration began to decrease rapidly
(Table X). By far the greatest percentage of available chlorine was con-
sumed during the" first 5 min. Almost all the remaining chlorine was con-
sumed during the second 5 min.; and, in almost every case, the small amount
of residual chlorine was consumed during the final 5 min. of irradiation.
The extent of chlorine consumption during the first 5 min.
(Table XI) was directly proportional to the chlorine concentration and was
not related to the difference in pH. The extent of chlorine consumption
during the second 5 min. was likewise directly related to the amount of
chlorine present.
23
-------
TABLE X
CHLORINE CONSUMPTION IN THE DARK
AND DURING IRRADIATION
Expt.
No.
39
40
42
43
44
45
46
47
Initial Chlorine
Concentration
(ppm)
175
102
102
175
175
102
102
175
Chlorine Consumption (ppm)^'
In the Dark
(10 Bin.)
7
10
3
8
3
7
7
5
0-5 min
112
70
72
95
114
72
63
118
Upon Irradiation
5-10 min. 10-15 min.
31 6
24
24 3
60
54 7
14 1
30
47
"aT In experiments in which the chlorine concentrations were not determined
~~ exactly at 5-min. intervals, the chlorine consumption during these
periods was estimated.
TABLE XI
CHLORINE CONSUMPTION (PPM) DURING FIRST
FIVE MINUTES OF IRRADIATION
(Experiments 39-47) a/
At pH 6.5
At pH 8.5
175 ppm Cl2 102 ppm Cl2
95 (43)
114 (44)
63 (46)
72 (45)
175 ppm Cl2
118 (47)
112 (39)
102 ppm Cl2
70 (40)
72 (42)
a/ The individual experiment numbers are shown in parentheses.
24
-------
Since practically all the chlorine was consumed during the first
10 min., the extent of organic oxidation during the 10-min. experiments
would be expected to be similar to that which occurred during the 15-min.
experiment. (As discussed below, the extent of organic oxidation produced
by UV-radiation alone during the third 5-min. period would not be significant.)
This postulation is confirmed by the results shown in Table XII.
Also indicated by the results presented in Table XII is the con-
clusion that no particular benefit is derived by the presence of a large
excess of chlorine. This is perhaps the most important conclusion derived
from this series of experiments.
Another conclusion drawn from the results shown in Table XII is
that the oxidation is more effective at pH 6.5 than at pH 8.5; the average
COD decrease at pH 6.5 was 60.0%, the average COD decrease at pH 8,5 was
45.6$. For these calculations, the results of both the 10-min. and the
15-mino experiments were combined. The results, 60.0% and 45.6$, are the
approximate amount of COD elimination produced in 10 min. because, as indi-
cated in Table X (p. 24), the chlorine had been almost completely consumed
at the end of 10 min. As discussed below, an insignificant amount of
COD elimination would be expected during the final 5 min.
TABLE XII
PERCENT ELIMINATION OF COD DURING IRRADIATION
(Experiments 39-47)
Total
Irradiation At pH 6.5 At pH 8.5
Time, min. 175 ppm Gig 102 ppm Clg 175 ppm Clg 102 ppm Cl2
10 52.0 59.5 53.8 43.2
15 59.6 68.8 49.5 35.7
25
-------
Effect of irradiation alone - In Experiment 41, the effluent was
irradiated as in the other experiments, but no chlorine was added. After
10 min., there was no detectable decrease in COD (the analytical results
actually indicated 2.9$ increase in COD which is considered to be within
the range of experimental error). However, the TOC decrease was
10.4$. After 15 min., the COD decrease amounted to 13.0$ and the TOC
decrease was 18.8$. (Since the TOC decrease cannot theoretically exceed
the COD decrease, one of these analytical results is obviously inaccurate.)
A comparison of the average COD decrease produced in 10 min. at
pH 6.5 (60.0$) with the COD decrease produced by UV radiation alone during
this time (2/3 x 13.0$ = 8.66$) indicates that chlorine plus UV radiation
is about seven times more effective than radiation alone. This result is
consistent with the results of the first series of exploratory experiments,
which indicated that chlorine plus UV radiation eliminated COD 10 times
faster than radiation alone at pH 10, and more than eight times faster
than UV radiation alone at pH 5.
26
-------
THIRD SERIES OF WASTEWATER OXIDATION EXPERIMENTS
Summary
In the UV-catalyzed chlorine oxidation of wastewater, the organic
oxidation rate is faster at pH 6.5 than at pH 3; and is faster at pH 5 than at
pH 3 or pH 10.
Large excesses of chlorine do not increase the organic oxidation
rate, except at pH 10. Most efficient use of chlorine was obtained when
chlorine was added gradually during the irradiation period.
At pH 5 and pH 6.5, the rate of COD elimination is most rapid
during the first 5 min. and decreases as the reaction proceeds. The elimi-
nation of TOC is approximately linear over a 15-min. irradiation period.
At pH 5, the average COD elimination was 67$ in 5 min. (range
51-84$), 79$ in 10 min. (range 66-100$), and 94.5$ in 15 min. (range 88-
100$). The average TOC decrease was 33$ in 5 min. (range 15-50$), 52$ in
10 min. (range 44-60$) and 75$ in 15 min. (range 70-81$).
In the UV-catalyzed chlorine oxidation process, the rate and ex-
tent of organic oxidation is not affected by temperature within the range
5ฐ-25ฐC (41ฐ-77ฐF).
27
-------
Third Series of Wastewater Oxidation Experiments
Some important questions were generated by the preceding series
of experiments. Perhaps the most important question was "What extent of
COD and TOG elimination occurs during the first 5-min. period of irradiation,
the time during which the largest amount of chlorine is consumed?" Two
other related questions were "Is the amount of organic material oxidized
proportional to the amount of chlorine consumed?" and "Given a large excess
of chlorine and an extended period of illumination, can all the organic
material "be eliminated?" Another important question was "Since pH 6.5 ap-
pears more effective than pH 8.5, would a further decrease in pH be even
more effective?"
Experiments 48 and 49 - These experiments were designed to answer
the above questions. Both experiments were performed using an effluent
(S&L-6) which was obtained from the same source as the effluent used in Ex-
periments 39-47. In Experiment 48 the pH level was maintained near 3.0,
and samples were withdrawn at 5-min. intervals. Samples for TOG determin-
ation were not dechlorinated by nitrogen purge, but were treated with ex-
cess sodium bisulfite and acidified to pH 1 with HgSO^ Experiment 49 was
similar, except that the pH was maintained at 6.5.
The results of these experiments are shown in Figures 9 and 10.
The effect of pH on COD and TOG elimination was very marked. At pH 3.0,
there was a 33$ drop in COD and a 12$ drop in TOG after 10-min. illu-
mination. However, at pH 6.5, the COD elimination amounted to 72%, and the
TOC elimination amounted to 54$ during the same length of time.
Moreover, after only 5 min. at pH 6.5, the COD elimination amounted
to 44$ and the TOC elimination amounted to 38$. These results clearly show
that the oxidation is much more effective at pH 6.5 than at pH 3.0.
The role of excess chlorine was further clarified by these ex-
periments. After all the initial chlorine had been consumed, an additional
amount of chlorine approximately equal to the initial chlorine dose was added
to the reaction mixture. As is evident in Figures 9 and 10, no significant
acceleration of either the COD or TOC elimination was caused by this addi-
tion of excess chlorine.
The results of these two experiments and the preceding series of
experiments (Experiments 39 - 47) indicate clearly that the presence of ex-
cess chlorine is of no particular value.
Experiment 49 indicates that, at pH 6.5, the rate of oxidation of
organic matter, as measured by both COD and TOC, decreases as the reaction
progresses. In subsequent experiments at pH 5, the rate of COD elimination
28
-------
also decreased with time, tut the rate of TOG elimination was approximately
linear. Apparently, the organic constituents in a particular effluent vary
widely in regard to the rate at which they are oxidized. Thus, the overall
rate of oxidation decreases as the more-easily-oxidized material is consumed.
Also clarified by these experiments is the role of pH; decreasing
the pH from 6.5 to 3.0 (Experiments 48 and 49), or raising the pH from 6.5
to 8.5, (Experiments 39 - 47) produces significant decreases in the oxida-
tion rate. These conclusions were further substantiated in Experiments 52 -
54, described below.
Experiment 50 - The primary objective of Experiment 50 was to
confirm the results of Experiment 49 using a municipal effluent which had
been further processed in our laboratory-scale, extended-aeration apparatus.
The results (Figure 11) confirm that a very large proportion of
the total COD and TOG elimination does occur during the first 5 min. of
irradiation. Tables XIII and XIV present the results of experiments
49 and 50.
TABLE XIII
UV- CATALYZED CHLORINE OXIDATION OF AH EFELUEKT
OBTAINED FROM A LAEGE, SEWAGE -TREATMENT PLANT
("Effluent S&L-6, pH 6.5, Experiment 49)
Chlorine COD TOG
Consumption Elimination Elimination
Reaction Period (ppm) (ppm) TJ- (ppm)
During 10 min.
in dark 10 0.2 0.8 0.04 0.5
During first 5-min.
irradiation 80 11.1 44.0 2.8 37.7
During second 5-min.
irradiation 55 7.0 27.7 1.2 16.1
Totals after
20 min. 125 18.3 72.5 4.04 54.3
a/ The percent figures were calculated by dividing the amount of COD
.(or TOG) eliminated during each 5-min. interval by the original
COD (or TOG) value (corrected for the dilution effect caused by
added chlorine).
29
-------
TABLE XIV
UV-CATALYZED CHLORINE OXIDATION OF AN EFFLUENT FROM
A LABORATORY-SCALE, SEWAGE-TREATMENT APPARATUS"
(Effluent MRI-428, pH 6.5, Experiment 50)
Chlorine COD TOC
Consumption Elimination Elimination
Reaction Period (ppm) (ppm) ($)*/ (ppm) (%)ฃ./
During 10 min.
jn dark 6 0.76 2.9
During first 5-min.
irradiation 137 19.43 73.5
During second 5-min.
irradiation 21 2.72 10.2
Totals after
20 min. 164 22.91 86.6 7.2 68.1
a/ The percent figures were calculated "by dividing the amount of COD
~ (or TOC) elimination during each 5-min. interval by the original
COD (or TOC) value (corrected for the dilution effect caused "by
added chlorine).
Three important observations were made, based on the results of
Experiments 49 and 50.
(l) There was very little consumption of chlorine or elimination
of COD or TOC during the 10-min. period of chlorination in the dark. Thus,
these two effluents contained relatively small amounts of organic material
which could be oxidized in the dark. As discussed in the previous section,
the average amount of TOC and COD elimination produced during the 10-min.
period of chlorination in the dark was 10$. (See Experimental Section,
"Extent of Organic Oxidation Produced by Chlorine in the Dark", p. 108.)
(2) Large amounts of TOC and COD elimination were produced dur-
ing the initial 5-min. period of irradiation. For the Smith and Loveless
effluent, 44$ COD elimination and 38$ TOO elimination occurred during this
time. For the effluent produced in the laboratory-scale, activated-sludge
apparatus, 74$ COD elimination and 44$ TOC elimination was produced
during this initial 5-min. period of irradiation.
30
-------
(3) Less COD and TOG elimination is produced during the second
5-min. period of irradiation. Elimination of COD during the second 5-min.
period was 27.7$ for the Smith and Loveless effluent, and 10.2$ for the
laboratory-produced effluent. Elimination of TOC during this time was
16.1$ for the Smith and Loveless effluent, and 18.9$ for the laboratory-
produced effluent.
Further investigation of the effect of pH - Three experiments
(Experiments 52 - 54) were designed to investigate the rate and extent of
W-catalyzed chlorine oxidation at pH 3, pH 5 and pH 10. The effluent
(MRI-512) used in these experiments contained 33.8 mg/liter COD, 13.2 mg/
liter TOC, 2.5 mg/liter ammonia nitrogen and 4.0 mg/liter nitrate nitro- ,
gen (average values). It had been produced in our laboratory by passing
high-ammonia municipal wastewater through the laboratory-scale, activated-
sludge apparatus. In each experiment the effluent was treated with chlorine
water to provide an initial chlorine concentration of about 200 ppm. This
concentration represents a 33$ excess over the theoretical amount of chlo-
rine required to oxidize all of the organic material to C02 and HgO. The
results of a second addition of chlorine will be discussed in the next sec-
tion, "Effect of Chlorine Concentration", p. 32.
The experiments were performed at room temperature and were iden-
tical, except that each was performed at a different pH (pH 3, pH 5, and pH
10). 'During the 10-min. period of chlorination in the dark, the average
chlorine concentration decreased about 26 ppm. During this time, there was
an average decrease in COD of 3.6 mg/liter (12$) and an average decrease in
TOC of 0.3 mg/liter (3$). These results in the dark were about the same in
each experiment, except that the chlorine consumption and the extent of TOC
decrease were somewhat greater at pH 10.
The results of these experiments are shown in Figures 12 - 14,
and the data are summarized in Figures 15 and 16. The results presented in
Figure 15 indicate that the rate of COD elimination upon irradiation is the
fastest at pH 5; approximately 70$ of the COD present after treatment with
chlorine in the dark was eliminated during 5 min. of irradiation, and 80$ was
eliminated within 10 min.
The extent of TOC elimination in these experiments is shown in
Figure 16. These results are in agreement with the COD data; more rapid
TOC elimination is produced at pH 5 than at pH 3 or at pH 10. However, the
extent of TOC elimination is not as great as the extent of COD elimination.
A curious fact is that the TOC plots are almost linear, while the rate of
COD elimination decreases as the oxidation proceeds.
31
-------
In these three experiments, the rate of chlorine consumption was
about the same at all pH values; about two-thirds of the initial chlorine
was consumed after 5 min. of irradiation, and practically all the initial
chlori-e was consumed after 10 min. of irradiation. Obviously, because of
the large extent of organic oxidation, the most efficient utilization of
chlorine was obtained at pH 5.
Subsequent experiments have confirmed that pH 5 is the optimum
pH for the most efficient chlorine utilization and organic oxidation. These
experiments are described in detail later in this report, and a summary of
the data concerning the extent of organic oxidation is presented in the
Experimental section (see "Extent of COD and TOC Elimination Produced
by Irradiation at pH 5", p. 109). Seven experiments, using four different
effluents, are compared. The data are presented graphically in Figures 17
and 18.
These figures show that the average COD elimination at pH 5 is
67% in 5 min., 79% in 10 min. and 95$ in 15 min. The concurrent TOC elimina-
tion is 55% in 5 min., 52% in 10 min. and 75% in 15 min.
The data presented in these figures (Figures 17 and 18) confirm
the observations of Experiments 52 - 54 that the rate of COD elimination
decreases as the oxidation proceeds, but that the rate of TOC elimination
is linear.
Effect of chlorine concentration - In general, the elimina-
tion of COD and TOC and the consumption of chlorine are most rapid at the
beginning of the UV-catalyzed oxidation. However, the rate of organic oxi-
dation is not directly proportional to the chlorine concentration; in the
second series of eight experiments described in the preceding section, a
75$ excess of chlorine produced no more organic oxidation in 10 min. than
did a stoichiometric amount of chlorine.
The results of other experiments in this series have indicated
that large increases in the initial chlorine concentration do not produce
correspondingly large increases in organic oxidation rates. In Experiments
48 and 49, a second addition of chlorine approximately equal to the origi-
nal amount of chlorine was added to the reaction mixtures after the reac-
tion mixtures had been irradiated for about 10 min. No significant increase
in organic oxidation rate was observed.
In Experiments 52 - 54, a second addition of chlorine was made,
and the results at pH 5 (Experiment 54) and at pH 3 (Experiment 52) were
similar to the results of Experiments 48 (pH 3.0) and 49 (pH 6.5). How-
ever, at pH 10 (Experiment 53), the second addition of chlorine actually
did increase the rate of COD elimination. The rate of TOC elimination,
however, was not affected.
32
-------
Analysis of the above results indicates that, at pH values between
5.0 and 8.5, (l) only a certain minimum concentration of chlorine is re-
quired for maximum oxidation rate, and (2) concentrations of chlorine above
this minimum are wasteful.
These conclusions are substantiated by an experiment (Experiment
78) in which the chlorine water was not added in one portion, but was added
gradually in increments during the irradiation period. The results, pre-
sented in Figure 19, show conclusively that extensive elimination of COD
(88$ in 15 min.) and TOG (70% in 15 min.) can be achieved even when the con-
centration of chlorine does not exceed 36 ppm. The amount of chlorine con-
sumed in this reaction was equivalent to approximately 89$ of the total
amount added. This amount of chlorine is only slightly in excess of the
theoretical amount of chlorine (145 ppm) required to eliminate all of the
original COD (32.9 ppm).
Thus, for the most efficient use of chlorine, a gradual addition of
chlorine during irradiation is necessary.
The chlorine consumed, but yet not accounted for by an equivalent
amount of organic oxidation, is most probably consumed by auto-decomposition
reactions. The fact that chlorine is decomposed by ultraviolet radiation is
well known, and the products are known to be chloric acid, hydrochloric acid
and oxygen.ฃ/ The extent to which chlorine alone is decomposed in our reac-
tor is shown in Figure 20. Note that the decomposition is very much faster
at pH 10 than at pH 5.
Effect of nitrate concentration - Because effluents contain
varying concentrations of nitrate, it was important to learn whether or not
variations in nitrate concentration could be responsible for observed vari-
ations in the rates of COD and TOC elimination. In one experiment (Experi-
ment 77, Figure 21), 20 ppm of nitrate nitrogen (as potassium nitrate) was
added to an effluent prior to treatment with chlorine. The effluent (S&L
624A) was the same as the one used in Experiment 75 (Figure 22). A com-
parison of Figures 21 and 22 shows that the rate of COD elimination and the
rate of chlorine consumption are practically the same in each experiment.
Therefore, within the range of 4-20 ppm, nitrate concentration has no effect
on the rate or extent of the UV-catalyzed chlorine oxidation.
33
-------
Effect of temperature - Two effluent oxidation experiments
(Experiments 58 and 59) were performed in exactly the same manner, except
that in one the temperature was held near 5ฐC (41ฐF) and in the other the
tempera "cure was held near 25ฐC (?7ฐF). The results are shown in Figures
23 anc1 24. These figures show that the rate of chlorine consumption, rate
of COD elimination, and rate of TOG elimination are practically the
same at "both temperatures. The temperatures of most effluents from extended
aeration processes would be within the temperature range investigated.
Therefore, in actual operation, ordinary temperature changes should have
no effect on the rate of effluent oxidation.
34
-------
140 -
Additional
Chlorine
Lamp Off
10
15
30
35
40
20 25
Time (min.)
Figure 9 - UV-Catalyzed Chlorine Oxidation of Effluent S&L-6-A at pH 3.0 (Experiment 48)
-------
Additional
Chlorine Added
Lamp Off
1
-
-
-
,_
_
1
JU
28
26
24
22
20
18
16 ฃ -
o.
Q.
14o -
O
12 < -
10
8
6
4
2 -
7
6
5
A
EL
u
O
3 ป-
2
1
20 25
Time (min.)
30
35
40
Figure 10 - UV-Catalyzed Chlorine Oxidation of Effluent S&L-6-A at pH 6.5 (Experiment 49)
-------
(,,
I
I
160
140
1
120
3 10ฐ
c
_0
U 80
60
40
20
Lamp Inserted Lamp Off
l
\ Chlorine
|\
1 \
COD 1 \
1 Dl\
\\
TOC \\
^ \ \
" ฐ^ \\
\\\
\ \\
\\
\\
\\
V
\\
\\\
V ^^o-I2L
V^^^
\ "\s. COD
v n ^ l
A "*D
^"V^ Chlorine
| | | I^A . ป^ A 1 1 I
5 10 15 20 25 30 35 40
30 -
28 -
26 -
24 -
22 -
20 -
18 -
< .
16 J-
. Q
14 Q
u
12 -
10 -
8
6
4 -
2
18
16
14
12
11
10
9
**ป*.
E
8 o.
a.
,.
7 Q
i
6
5
4
3
2
1
Figure 11 -
Time (min.)
UV-Catalyzed Chlorine Oxidation of Effluent MRI-428 at pH 6.5 (Experiment 50)
-------
i,,
'.
Additional
Chlorine
- 2
0
15
30
35
40
20 25
Time (min.)
Figure 12 - UV-Catalyzed Chlorine Oxidation of Effluent MRI-512 at pH '6 (Experiment 52)
-------
,
320 -
Lamp Inserted
Additional
Chlorine
10
15
40
0
15 20 25
Time (min.)
Figure 13 - UV-Catalyzed Chlorine Oxidation of Effluent MRI-512 at pH 10 (Experiment 53)
-------
320
280 -
Additional
Chlorine
10
20
25 30
Time (min.)
40
-32 -
- 28 -
U>
14
10
T
8 *
0
Figure 14 - UV-Catalyzed Chlorine Oxidation of Effluent MRI-512 at pH 5 (Experiment 54)
-------
c
g
t:
i
c
6
Q
'
0
u
'
D
o
< '
1)
u
80 -
B
^
"5
C
(U
I
4 8
Time (min.)
80 .
I
4 8
Time (min.)
Figure 15 -
Extent of Chemical Oxygen Demand
(COD) Elimination Produced by UV-
Catalyzed Chlorine Oxidation
Figure 16 - Extent of Total Organic Carbon (lOC)
Elimination Produced by UV-Catalyzed
Chlorine Oxidation
-------
I
r i
C
01
0
o
5 10
Time (min.)
20
40
c
II
U
0)
ฐ- 60
80
100
T 1 T T" ~T T
0
PH5
I I I I I
5 10
Time (min.)
15
Figure 17 - Average Percent of COD Eliminated
Upon Irradiation at pH 5
Figure 18 - Average Percent of TOG Eliminated
Upon Irradiation at pH 5
-------
Lamp
Inserted
1C
15
Time (min,)
25
24
20
a.
a_
16 0 I
o
u
12 H
0
12
10
a
8 .*
U
30
35
Figure 19 - UV-Catalyzed Chlorine Oxidation : Effluent S&L-624-A at
pH 5 With Continuous Adc:' "ion of Chlorine
(Experiment 78)
43
-------
10
15 20
Time (min.)
25
Figure 20 - Rates of Chlorine Decomposition During Irradiation at
pH 5 and at pH 10
44
-------
i
i ii
180
160
Lamp Inserted
Additional
Chlorine
10
15
30
Figure 21 -
20
Time (min.)
UV-Jatalyzed Chlorine 0;:idatiori of Effluent G&L-S24-A, C
20 ppm of Added Hitrate Hitro^rii, at pfl ,5 (Experiment 11')
H 14
- 12
- 10
!
' '
Q_
I '
0
- 6
- 4
- 2
-------
!
180 r-
Additional
Chlorine
20 -
30
H 28
35
15 20 25
Time (min,)
: n - italyzed Chlorine 0> ; , ! i-A at pit 5 (Experiment 75
-------
Lamp Inserted
260
220
1
28
24
20
16 ~ -
CL
CL
.Q
o
12 U ~
8
4
30
14
12
10
a !
Jl
6 *"
ซ
2
0
15 20 25
Time (min.)
Figure 23 - UY-Catalyzed Chlorine Oxidation of Effluent MRI-525 at pH 5 and 5ฐC (Experiment 58,
-------
0
1
28
24
20
16 ฃ-
Q.
Q
12 u-
8
4
14
12
10
8 -ฃ
0-
U
O
6 *-
4
2
n
20 25 30
Time (min.)
Figure 24 - UV-Catalyzed Chlorine Oxidation-of Effluent MRI-525 at pH 5 and 20ฐ-25ฐ (Experiment 59)
-------
ULTRAVIOLET-CATALYZED CHLORINE OXIDATION
OF HIGH-AMMDNIA EFFLUENTS
Summary
The presence of ammonia in an effluent drastically reduces the
rate and extent of UV-catalyzed chlorine oxidation of organic matter.
For example, the addition of 23 ppm of ammonia nitrogen to a highly nitri-
fied effluent reduced the organic oxidation rate "by more than tenfold.
The amount of chlorine actually required to eliminate 1 ppm of ammonia
in the UV-catalyzed process is about four times the theoretical amount
required to eliminate 1 ppm of COD.
4-9
-------
Ultraviolet-Catalyzed Chlorine Oxidation of High-Ammonia Effluents
Municipal, sewage-treatment plants are frequently overloaded
and. often produce effluents which contain relatively high concentrations
of amronia (15-30 ppm N) . Although it was known in advance that the treat-
ment of effluents of this kind would not be economical, several
oxidation experiments were perf ormed with high-ammonia effluents for the
purpose of determining: (l) the effect of relatively high, ammonia con-
centrations (15-30 ppm N) on the elimination of COD and TOG; and (2) the
technical feasibility of using chlorine to produce a low-ammonia effluent
for use in the laboratory.
When wastewater containing about 15 ppm ammonia nitrogen and
having a COD of about 50 ppm is treated with about 180 ppm of chlorine in
the dark, the concentration of "free" chlorine decreases rapidly, ammonia
is simultaneously converted to chloramines, and a gradual increase in nitrate
concentration begins. Irradiation produces a further rapid decrease in
the chlorine concentration and a rapid increase in the nitrate concentra-
tion. These results were observed both at pH 5 (Experiment 20) and at pH 10
(Experiment 21). In these experiments, only about a 50$ decrease in COD
was produced after about 15 min. irradiation.
The elimination of 1 ppm of COD requires 4.43 ppm of chlorine,
assuming complete conversion of the organic matter to carbon dioxide. If
it is assumed that ammonia is oxidized to nitrogen gas, 1 ppm of ammonia
nitrogen requires 7.6 ppm of chlorine. The oxidation of 1 ppm ammonia
nitrogen to nitrate requires 20.3 ppm of chlorine.
Thus, the calculated chlorine "demand" for the effluent used
in these experiments was 114 ppm of chlorine for the ammonia and 222 ppm
for the COD. However, only about one-half (180 ppm) of the theoretical
amount of chlorine was applied. Since about 60% of the chlorine consumed
was theoretically required for the COD elimination, presumably the remainder
was consumed in the oxidation of ammonia and by autodecomposition.
Similar results were obtained with other effluents. In Experiment
23, after 15 min. in the dark followed by 15 min. of irradiation, the
decreases in ammonia (down 76$) and COD (down 30$) accounted for 95$ of
the chlorine consumed.
The undesirable effect of ammonia on the elimination of COD is
apparent in all three of these experiments: in order to' eliminate 1 ppm
of COD, approximately 7.5 ppm of chlorine was required; this was about 170$
more than the theoretical amount.
50
-------
Even poorer efficiency of COD elimination was achieved in Experi-
ments 27 and 30; elimination of 1 ppm of COD required about 11 ppm of
chlorine, or 2.5 times the theoretical amount. In these two experiments,
only about 40$ of the chlorine was used for COD elimination; the remainder
was consumed in ammonia oxidation.
Subsequent experiments were designed for the purpose of removing
ammonia from the effluents by means of treatment with chlorine. The objec-
tive was not to find an economical process for removing ammonia, but to
producein the laboratorya low-ammonia effluent for further investigation.
Experiment 27 showed that very poor elimination of ammonia is
achieved during a 15-min. period of chlorination in the dark. This result
was confirmed by experiments with pure ammonia which will be discussed in
the next section. The experiments with pure ammonia had also indicated
that ammonia elimination would be favored by avoiding large excesses of
chlorine and by operating at pH levels above 6.5.
In Experiments 28 and 29, longer periods of chlorination in the
dark were employed. Two samples of a high-ammonia effluent (21 ppm N) were
treated in the dark with identical quantities of chlorine while the pH was
maintained above 6.5. In Experiment 28 5 the chlorine was added gradually
during 1 hr.; and, in Experiment 29, the chlorine was added all at once.
The gradual addition of chlorine produced a greater decrease in ammonia
concentration (an 86$ decrease compared to a 70$ decrease), and less
chlorine was required to eliminate a given amount of ammonia. (The amount
of chlorine consumed for each ppm of ammonia eliminated was 13.7 ppm for
Experiment 28 and 14.9 ppm for Experiment 29.) These differences, although
significant, are probably not large enough to warrant the extra effort
required to add chlorine gradually.
In subsequent experimental work, after conditions had been estab-
lished for highly effective oxidation of organic matter in effluents, the
rate of oxidation of a low-ammonia effluent was compared with the rate of
oxidation of the same effluent when ammonia was added. The effluent used
in Experiment 75 (Figure 22, p. 46) was low in ammonia content (1.9 ppm
ammonia nitrogen), and the rate of COD elimination (58$ after 5 min. of
irradiation and 67$ after 10 min. of irradiation) was within the range of
that observed for other low-ammonia effluents. In Experiment 76 (Figure
25, p. 53), 23 ppm ammonia nitrogen, as ammonium chloride, was added to
the effluent. The inhibiting effect on the rate of COD elimination was
pronounced; instead of 58$ elimination in 5 min., only 4.5$ of the COD was
eliminated in 5 min.
51
-------
After about 12 min. in the dark, and about 6 mln. irradiation,
the chlorine concentration had been severely depleted. Therefore, a second
addition of chlorineabout equal to the firstwas made. This second
addition of chlorine evidently was sufficient to overcome the inhibiting
effefc of the ammonia, because a distinct increase in the rate of COD elimina-
tion was observed (Figure 25). After a total of 13 min. irradiation, the
decrease in COD amounted to 64$. The amount of chlorine required to pro-
duce this decrease in COD amounted to 21.6 ppm of chlorine for each ppm of
COD; this was almost five times the theoretical amount (4.43 ppm). If
the assumption is made that the actual amount of chlorine required to
eliminate the COD was equal to the theoretical amount, then the oxidation
oi 1 ppm of ammonia nitrogen required 17.5 ppm of chlorine; this was al-
most four times the chlorine demand of 1 ppm of COD.
52
-------
Additional
Chlorine
10
15 20
Time (min.)
25
30
Figure 25 - UV-Catalyzed Chlorine Oxidation of Effluent S&L-624-A Containing
23 ppm of Added Ammonia Nitrogen at pH 5 (Experiment 76)
53
-------
REACTIONS OF AQUEOUS AMMONIA WITH CHLORINE
Summary
In water, ammonia reacts with chlorine to form mono-, di- and
trichloramine in various proportions depending upon pH and ratio of react ants
At pH 5, an excess of chlorine rapidly converts most of the ammonia to
trichloramine which is relatively stable in the presence of excess chlo-
rine. Irradiation of an ammonia-chlorine reaction mixture rapidly acceler-
ates the conversion of trichloramine to nitrate and other oxidation products
of ammonia including, presumably, nitrogen gas.
54
-------
The Reaction of Aqueous Ammonia with Chlorine
In order to clarify some of the observations made during the
studies of high-ammonia effluents, a number of chlorine oxidation experi-
ments were performed using a dilute solution of ammonium chloride.
The general experimental observations are similar to those made
with high-ammonia effluents. When chlorine is added to ammonia in the dark,
(l) the concentration of chlorine decreases rapidly, (2) the concentration
of ammonia decreases rapidly, (3) chloramines are formed rapidly and in
varying proportions depending upon pH and reactant ratio, and (4) a slow
build-up in nitrate concentration begins. Irradiation of an ammonia-chlo-
rine reaction mixture appears to rapidly accelerate the decomposition of
chloramines to products containing nitrogen in higher oxidation states.
A. T. Palin has written a series of three authoritative articles
on the ammonia-chlorine interaction in water.!/ Of particular interest to
this work are his investigations concerning the products formed from
ammonia and chlorine interacting at various pH levels. For example, his
studies at pH 5 indicate that, when chlorine (6.0 ppm) interacts with
ammonia (0.5 ppm), the solution contains the following products:
After 10 min. After 2.0_hr.
Free chlorine 2.7 ppm 2.9 ppm
Trichloramine 0.9 ppm 1.0 ppm
Dichloramine 3.0 ppm 0.0 ppm
Monochloramine 0.0 ppm 0.0 ppm
Palin observed that monochloramine is fairly stable in the pres-
ence of excess ammonia, but is decomposed by excess chlorine.
2KH2C1 + HOC1-ปN2 + 3HC1 +
He also observed that dichloramine will decompose to nitrogen, HC1 and
chlorine, but that a solution of trichloramine and excess chlorine is com-
paratively stable.
55
-------
Our observations of the ammonia-chlorine reaction in the dark are
consistent with these observations, even though our experiments were per-
formed it higher concentrations.
In all of our ammonia-chlorine experiments, rapid and large ini-
tial decreases in chlorine concentration were observed (Table XV).
TABLE XV
INITIAL DECREASES IN CHLORINE COHGERTRAIIOH PRODUCED BY AMM3KIA
Observed
Initial Initial Decrease in Chlorine
Ammonia Goncn. Chlorine Concn. Concentration
Experiment No. (ppm N) (ppm) (ppm) (min.)
13 12.8 148 105 2.7
17 13.5 408 160 8.5
26 28.8 304 167 2.3
Evidently, this rapid initial reaction is a result of the forma-
tion of chloramines, predominantly trichloramine. Chlorine concentrations.
were determined by the iodide-thiosulfate procedure; and, using this method,
only a small proportion of trichloramine will titrate as free chlorine./
During the rapid initial reaction, there is some oxidation of
ammonia as evidenced by a rapid, but small, development of nitrate concentra-
tion in every case.
The initial rapid decrease in chlorine concentration is followed
by a very slow decrease in chlorine concentration. In Experiment 17, the
initial decrease in chlorine concentration amounted to 160 ppm within 8.5
min.; but 4 days were required for an additional decrease of 119 ppm.
As the second slow decrease in chlorine concentration proceeds,
there is a parallel slow increase in nitrate concentration.
8/ Standard Methods-Water and Wastewater, 12th Ed., 1965, p. 90, American
Public Health Association.
56
-------
Ammonia-chloramine determinations -In all our experiments,
ammonia was determined "by the direct Nesslerization procedure. However,
in Experiment 26, ammonia determinations after 15 min. varied markedly,
depending upon the manner in which the sample was treated. When sodium
bisulfite was used to remove residual chlorine, only a slight decrease in
ammonia concentration was detected (from 28.8 ppm to 24.4 ppm). When resid-
ual chlorine was removed by acidification followed by nitrogen purge, the
ammonia content had apparently decreased by 68% (to 9.1 ppm).
We believe that the difference between the high ammonia value
obtained when one sample was treated with bisulfite and the low value
obtained when a duplicate sample was purged with nitrogen represents the
amount of ammonia present as chloramines. Thus, at this point of the reac-
tion, the amount of ammonia present as chloramines was approximately
24.4 - 9.1 = 15.3 ppm H. Reduction with bisulfite converted chloramines back
to ammonia, but the nitrogen purge caused ammonia nitrogen to be lost from
the solution. This ammonia loss could occur as simple volatilization of the
chloramines or by partial hydrolysis of the relatively stable trichloramine
to mono- and dichloramines which decomposed to nitrogen (and other products).
Effect of irradiation on the ammonia-chlorine reaction - When
an ammonia-chlorine solution is irradiated after standing in the dark for
about 15 min., there is a very rapid and extensive decrease in the chlor-
amine concentration, a rapid and substantial additional decrease in the
ammonia concentration and a rapid increase in the nitrate concentration.
In Experiment 26, the results were as shown in Table XVI.
TABIE XVI
EFFECT OF IRRADIATION ON THE AMMONIA-CHLORINE REACTION
Ammonia
(ppm N)
Chlorine
(ppm)
Chloramines
(ppm N)
Nitrate
(ppm W)
Initial
Concentrations
28.8
304
0
0
After 15 Min.
in the Dark
9.1
177
15.32'
0.25
After 15 Min.
Irradiation
4.0
36.8
6.35
_a/ The difference between the high ammonia value obtained when one sample was
treated with bisulfite, and the low value obtained when a duplicate sample
was purged with nitrogen, provides an approximation of the chloramine
concentration.
57
-------
The results obtained upon irradiation were similar, even after the
ammonia-chlorine solution had been allowed to stand for 4 days in the dark
(Experiment 17, Table XVII).
TABLE XVII
EFFECT OF IRRADIATION OM AN AMMONIA-CHLORINE SOLUTION
THAT HAD BEEN ALLOWED TO STAND IN THE DARK FOR 4 DAYS
Initial After 4 Days After 30 Min.
Concentrations in the Dark Irradiation
Ammonia
(ppm H) 13.5 1.6 0
Chlorine
(ppm) 408 229 0
Nitrate
(ppm N) 0.02 4.0 9.0
These results indicate that chloramines are very rapidly decom-
posed by UV radiation to products other than ammonia. Nitrate appears to
be the major product, but other oxidation products of ammonia are also
formed.
58
-------
COMPARISON OF UV RADIATION SOURCES
Summary
At the present time, mercury-arc lamps are probably the most
practical sources of W radiation for the catalytic chlorine oxidation of
organic material in wastewater. On the basis of organic oxidation rate
produced per watt of W output, high-pressure mercury arcs, which emit a
broad spectrum of wavelengths (220 - 366 mp,), are about 2.7 times more
efficient than low-pressure mercury arcs which emit almost exclusively at
one wavelength (253.7 up).
59
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A Comparison of UV Radiation Sources
Lewis R. Roller in his text, ultraviolet Radiation,?/ discusses
in considerable detail the various sources of W radiation. Other than _
sunlight, the two most-useful W sources are arcs and incandescent materials.
The most efficient and most useful of these are the arcs. For a number of
practical reasons, mercury arcs have been the most-widely-used UV sources.
in our opinion, mercury-arc lamps are, at the present time, the most prac-
tical source of UV radiation for use in the catalyzed chlorine oxidation
process.
There are basically two kinds of mercury-arc lamps: the high-
pressure arc and the low-pressure arc.
The source of ultraviolet radiation in all of our experiments
thus far described has been a high-pressure mercury-arc lamp. Lamps of
this kind emit a broad spectrum of wavelengths between 220 np, and 366 np,.
(For a description of this spectrum, see Figure 26). Low-pressure, mercury-
arc lamps.emit radiation almost exclusively at 253.7 mi. High-pressure
mercury arcs generally emit much-more-intense radiation than low-pressure
mercury arcs of about the same size. However, the useful life of high-
pressure lamps is usually much shorter, and the cost of high-pressure
lamps is considerably greater, than that of low-pressure lamps of the same
size. Also, low-pressure lamps convert electrical energy to radiant energy
more efficiently. A disadvantage of the low-pressure lamps is that the
253.7-iqjt-wavelength is not transmitted by water or wastewater to the ex-
tent that longer wavelengths are. All these factors--intensity, wave-
length, catalytic efficiency, lamp cost, lamp life, and electrical effi-
ciencymust be considered in determining the most useful, UV source for
the catalytic chlorine oxidation.
The catalytic efficiency of radiation from low-pressure lamps
in promoting the catalytic oxidation was unknown, and could only be deter-
mined experimentally.
The low-pressure lamp which we used was manufactured by the
Nester/Faust Manufacturing Corporation and is probably the most intense,
short-wavelength source available commercially which will fit in the photo-
chemical reactor. The electrical output and electrical efficiency charac-
teristics of this lamp are compared with those of the high-pressure lamp
in Table XVIII.
60
-------
TABLE XVIII
COMPARISON OF LABORATORY-SCALE, MERCURY-AEG LAMPS
High-Pressure Low-Pressure
Lampg/ Lampfr/
Input 450 w. 50 w.
UV output 83.7 w. 40 w.
Electrical efficiency ฑ8.6% 80%
~jj These figures were obtained from Hanovia Lamp Division, Engelhard
Hanovia, Inc., Research Laboratory Bulletin, 5-1-59.
b/ These figures were supplied by Mr. Conman of Nester/Faust Manufacturing
Corporation.
Using the low-pressure lamp, effluent oxidation experiments were
conducted at pH 5 and at pH 10; and the same effluent was treated in the
same manner using the high-pressure source. The results of these experi-
ments (Experiments 55-57) are presented in Figures 27-29.
As expected, the rate of the oxidation is greater at pH 5
(Figure 27) than at pH 10 (Figure 29); COD was eliminated about three
times faster at PH 5 than at PH 10, and TOG was eliminated more than
seven times faster at pH 5 than at pH 10.
The difference in organic oxidation rate produced by the two
sources was also about as expected. A comparison of Figure 27 with Figure
28 shows that the less-intense low-pressure lamp produces COD elimination
and TOC elimination at about a fivefold slower rate than the high-pressure
lamp.
The efficiency of chlorine utilization was about the same in
each of these experiments: the low-pressure lamp produced a COD elimina-
tion of 0.122 ppm for each ppm of chlorine consumed; the high-pressure lamp
produced a COD elimination of 0.126 ppm for each ppm of chlorine consumed.
Although the high-pressure lamp produces a fivefold greater
oxidation rate, its catalytic efficiency-expressed as the rate of COD
elimination per watt of UV output-is not five times as great as that of
the low-pressure lamp. The rate of COD removal produced by the low-pressure
source was 0.447 ppm/min; the rate of COD removal produced by the high-
pressure source was 2.51 PPm/min. Dividing these rates by UV output of
61
-------
each lamp (40 w. for the low-pressure lamp; 83.7 w. for the high-pressure
lamp) yields a figure which represents the catalytic efficiency of COD
elimination based on radiant energy (Table XIX).
TABLE XIX
CATALYTIC EFFICIENCY OF COD ELIMINATION
BASED ON RADIANT ENERGY
Low-Pressure Lamp 0.0112 ppm/min/watt of UV output
High-Pressure Lamp 0.0300 ppm/min/watt of UV output
Thus, the high-pressure mercury arc produces COD elimination
more than five times faster than the low-pressure arc, and the catalytic
efficiency of the high-pressure radiation is about 2.7 times greater than
radiation from the low-pressure arc.
Overall process costs for both kinds of lamps have been esti-
mated based on this information, and are presented in a separate section
of this report. (See "Process Costs", p. 80)
62
-------
.
13
12
11
10
o 9
>- 8
CXL
LLJ
Z 7
LLJ
Q
ฃ 6
Q c
< 5
o;
4
3
2
-
-
-
-
-
1 1
)0 220 240
1
1 1 1
1
1
1 1 1 1
-
-
-
-
1-
1 I
260 280 300 320 340 361
WAVELENGTH (millimicrons)
Figure 26 - Ultraviolet Spectral Energy Distribution of the Emission from a 450-w.,
Quartz, Mercury-Vapor Lamp (Excluding the 25.6-w. Line at 366 iru)
-------
200 -
50
Figure 27 - UV-Catalyzed Chlorine Oxidation of Effluent MRI-516 at i
Using a Low-Pressure UV Source (Experiment 55)
-------
280
10
20 25
Time (min.)
30
35
-28 -
-24 -
- 20 -
- 16 "?-
i
CL
2U-
- 8
- 4
0
14
12
10
I I
'
I
40
Figure 28 UV-Catalyzed Chlorine Oxidation or Effluent MRI-bl6 at pH 5 Using the High-Prujjure UV Source (Experiment
-------
Lamp Inserted
I
Chlorine
25
Time (min.)
30
35
40
28
24
20 7
a.
a.
i i
O
16 U
12
8
14
a.
' I
4
Figure 29 - !JV-Catalyzed Chlorine Oxidation of Effluent MRI-516 at pH 10
U;;ing a Low-Pre, IV Sour'"- (Experiment 57)
-------
ULTRAVIOLET-CATALYZED CHLORINE OXIDATIOK
OF PURE COMPOUNDS
Summary
A brief investigation was made of the effect of UV-catalyzed
chlorine oxidation on the TOC of water containing eight pure organic com-
pounds. The following compounds are oxidized rapidly and extensively:
phenol (61$, 8 min.), 2,4-dinitrophenol (55%, 10 min.), glycine (61$, 4 min.),
formic acid (90$, 4 min.), and o_-dinitrobenzene (65$, 10 min.). Benzoic
acid is also oxidized (45$, 10 min.), but not as fast as the other com-
pounds. Acetic acid and ethanol are oxidized at a much slower rate (less
than 10$, 10 min.)
67
-------
Ultraviolet-Catalyzed Chlorine Oxidation of Pure Compounds
In order to provide information concerning the types of chemical
compounds that can be oxidized by the UV-catalyzed chlorine oxidation, eight
pure compounds were subjected to conditions approximating those of the
effluent oxidation experiments.
The oxidation of pure organic compounds -was of low priority and
of secondary interest during the present research contract. Therefore,
these experiments were designed so that they could be performed rapidly
and with only a minimum of analytical work.
Only the rate and extent of compound destruction were measured,
usually by TOG determinations or ultraviolet spectra analyses; and no
attempt was made to determine the number or kinds of products formed. In
all of these experiments, the pH was maintained near 5.0; this was the pH range
found to be optimum in the effluent oxidation studies.*
Phenol - The rate of oxidation of phenol was followed by means
of TOG analyses (Figure 30) and appears to be quite rapid (61$ after 8 min.
of irradiation). The rate of TOC elimination appears to level off after
about 61$ of the TOC has been eliminated, but this decrease in rate may
have been caused by the depletion of chlorine.
2,4-Dinitrophenol - Also shown in Figure 30 are the results
of the 2,4-dinitrophenol oxidation. The rate of oxidation of this com-
pound is also very rapid, as indicated by the rapid decrease in ultraviolet
absorbance at 256 mu, (practically 100$ elimination in 8 min.) and the
fairly rapid decrease in TOC (53$ in 10 min.).
Acetic acid '- Acetic acid is apparently not oxidized rapidly
under these conditions (Figure 31). The results of the TOC analyses are
somewhat erratic, probably because of loss of volatile organics during
the oxygen-gas purge of the sample prior to TOC determination. However,
the results are sufficiently conclusive to indicate that no large decrease
in TOC occurred during the 10-min. period of irradiation. Chemical oxygen
demand (COD) analyses were also made on samples from this reaction. The
COD results indicate that only about 29$ of the COD was eliminated during the
10-min. period of irradiation. However, the results of the COD analyses
are lower than the theoretical values because acetic acid is not completely
oxidized by dichromate during the COD determinations.
* There is no reason to believe that pH 5 would be the optimum pH for the
oxidation of every kind of organic compound.
68
-------
Our COD analytical prodecure calls for 50 ml. of sample. The
refluxing mixture of sample and acidic dichromate is concentrated by allow-
ing 25 ml. of distillate to accumulate in a Dean Stark Trr:p. In the COD
determinations, the first acetic acid sample was analyzed in triplicate;
and in one of the determinations, the distillate was submitted for TOC
determination. A comparison of the TOC value (10.6 mg/litor) of the
distillate with that of the starting material (14.2 rag/liter) shows that
37$ of the acetic acid collects in the distillate receiver during the COD
determinations.
The procedure of concentrating a large COD sample is recommended
by Standard Methods^/ for dilute samples, even though the unavoidable loss
of volatile acids is recognized.
In spite of the analytical difficulties, it may be concluded
that only a relatively small fraction of the acetic acid was oxidized by
the UV-catalyzed chlorine oxidation.
Ethanol - The TOC data from the ethanol oxidation experiment
(Experiment 62, Figure 31) indicate that the oxidation of ethanol does not
proceed to a very great extent in 10 min. (Again there appear to be
inaccuracies in the TOC data, probably because of loss of volatile products
prior to the determination.) Probably the alcohol is oxidized rapidly by
the UV-catalyzed reaction to acetic acid (no loss in TOC) which is subse-
quently oxidized at a much lower rate. The more rapid decrease of chlorine
concentration in the ethanol oxidation (compared to the acetic acid oxida-
tion, Experiment 61, Figure 31) is an indication that the ethanol was
being at least partially oxidized.
Triplicate COD determinations were made on the original ethanol
sample; and, as in the acetic acid determinations, a significant (18$) loss
of volatile material from the refluxing COD mixture was detected.
Glycine - The oxidation of glycine is apparently quite rapid
compared to acetic acid. The observed TOC decrease amounted to 61$ in 4 min.
(Figure 32), but the rate of TOC decrease appeared to level off after it
had decreased "by about 78$. ฅe have no explanation for the apparent tem-
porary decrease in TOC which occurred in the dark.
69
-------
Benzole acid - The oxidation of benzoic acid proceeds at a
fairly rapid rate according to the TOC figures: 45% in 10 min. (Figure 33).
This oridation of benzoic acid does not occur in the dark since no signi-
fican"1" consumption of chlorine nor decrease in TOC occurred during a
10-min. period of chlorination in the dark.
Formic acid - Formic acid is very rapidly oxidized by the UV-cata-
lyzed reaction (Figure 34). The extent of TOC decrease amounted to 90$
within 4 min. Practically no oxidation occurred during an initial 10-min.
per:"od of chlorination in the dark. It is not difficult to explain why a
residual of TOC was not eliminated. TOC values of 1.2-1.4 mg/liter are not
significantly different from zero; and, therefore, the actual amount of TOC
elimination achieved was perhaps 100$.
ฃ-Dinitrobenzene - The rate and extent to which p_-dinitroben-
zene can be oxidized came as a surprise (Figure 35). The extent of
oxidation was followed both by UV absorbance and by TOC determinations.
Both analytical techniques indicated that rapid and extensive oxidation
occurred upon irradiation. Almost all the chlorine had been consumed
after 10 min. irradiation; and the TOC decrease amounted to 19$ in 5 min.,
65$ in 10 min. and 73$ in 15 min. At the end of 16 min., practically all
the UV absorbance at 255 mi had been eliminated. However, the actual time
required for this elimination was probably much less than 16 min. because
only a relatively small amount of oxidation is required to destroy the
aromatic ring which is predominantly responsible for the UV absorbance.
In the dark, no significant oxidation occurred during 10 min.;
as determined in a separate experiment (Experiment 74), UV radiation in
the absence of chlorine produces no decrease in absorbance during 20 min.
radiation.
70
-------
Lamp Inserted
160 -
A
I Absorbance
140 -
120 -
i
Q.
(
100 -
80 -
60
40 -
20 -
1
1
1
0.7
0.6
0.5
0.4
D
V
0.3
0.2
0.
0.0
14
12
10
8 I
0
20
10 15 20 05
Time (min.) Time (min.)
Figure '60 - UV-Catalyzed Chlorine Oxidation of (a) Phenol (Experiment 60) and (b) 2,4-Dinitrophenol (Experiment 63)
-------
Lamp Inserted
Lamp Inserted
280 -
i
10
15
-
20
0
20
-
5 10 15
Time (min.) Time (min.)
UV-c Chloriii-,- Oxidation of (a) A /Void (Experiment 61) and (b) Ethanol (ExperinK.it 62)
-------
.
0
180 r
160 -
Lamp Inserted
Additional
Chlorine
5 10 15 20 25 30 35
Time (min.)
Figure 32 UV-Catalyzed Chlorine Oxidation of Glycine (Experiment 68)
- 14
0
-------
280
Lamp Inserted
15 20
Time (min.)
25
_
--
1
14
10
8 7
U
O
6 ป-
4
2
ซ 1
30 35
Fig'>.:; - UV-C Chloriii' 0; idation of B'jnzoic Acid (Experiment 69)
-------
I
Lamp Inserted Additional
Chlorine
10
30
35
- 16
- 14
- 12
- 10
- 8
- 6
- 4
- 2
a
< >
0
0
15 20 25
Time (min.)
Figure 34 - UV-Catalyzed Chlorine Oxidation of Formic Acid (Experiment 70)
-------
30
35 40
20 25
Time (min.)
Figure ', UV-Catalyzed Chi- rine Oxidation of ^-Dinitrobenzene (Experiment 75)
-------
INVESTIGATION OF THE EFFECT OF ULTRAVIOLET KADI.Vn f
PLUS OTHER OXIDIZING AOHTTS
Summar;
A very brief study was made of the extent of organic oxidation
produced when wastewater was treated with TJV radiation plus (l) molecular
oxygen, and (2) hydrogen peroxide. No significant redaction in TOC was
detected after oxygen had been bubbled through an irradiated reaction
mixture for 20 min. Hydrogen peroxide produced no significant decrease in
TOC after 30 min. in the dark; irradiation of this reaction mixture for
another 30 min. produced only a slight decrease in TOC.
77
-------
Investigation of the_Effect_ of Ultraviolet Radiation, Plus Other
Oxidizing Agents
Two reagents, oxygen and hydrogen peroxide, were investigated
for the purpose of determining whether or not the oxidizing action of
these reagents could be accelerated by UV radiation. Both reagents are
possible intermediates in UV-catalyzed chlorine oxidation. Therefore,
the purpose of these experiments was to provide results useful for the
interpretation of UV-catalyzed chlorine oxidation, as well as to explore
possibilities for novel UV-catalyzed oxidations.
Because of the relatively low priority of these experiments,
no elaborate analytical studies were made.
Treatment of wastewater with oxygen and UV radiation - In
Experiment 80, pure oxygen gas was continuously bubbled through an effluent
while the reaction mixture was irradiated. (No adjustment of pH was made
prior to, or during, the experiment.) The results of this experiment were
compared with a similar experiment in which nitrogen gas was bubbled through
the irradiated reaction mixture. In neither experiment was there a signi-
ficant decrease in TOC in 20 man.
UV radiation alone had no detectable effect on the TOC content
of this effluent within a period of 45 min. In prior experiments, UV-
catalyzed chlorine oxidation of this effluent had produced large decreases
in both TOC and COD (Experiments 75, 77, 78; Figures 19, 21, 22; pp. 43, 45, 46)
The results of these experiments showed conclusively that (l) molec-
ular oxygen cannot be an intermediate in the UV-catalysed chlorine oxida-
tion, and (2) UV radiation plus oxygen do not produce much organic oxida-
tion compared to UV radiation plus chlorine.
Treatment of wastewater with hydrogen peroxide and UV radi-
tion - The same effluent used in the above series of experiments was
treated in the dark with hydrogen peroxide in excess of the amount required
to oxidize all the organic material in the effluent to C00 (Figure 36).
After 30 min. in the dark, no significant decrease in TOC was observed, ai.u
there was only a slight decrease in the hydrogen peroxide concentration.
The reaction mixture was then irradiated for 30 min. The irradiation pro-
duced only a very slight acceleration in the rate of decrease in hydrogen
peroxide concentration. There was also a small (2Q%] decrease in TOC
during the 30-min. irradiation period.
The results of this experiment indicated that (l) hydrogen per-
oxide cannot be an intermediate in the UV-catalyzed chlorine oxidation, and
(2) hydrogen peroxide plus UV radiation produces only a slight amount of
effluent oxidation compared to UV radiation plus chlorine.
78
-------
I
160
140
120
100
Lamp Inserted
A Hft
* A-""" "~~'~^--A-A^ -A__
---o O-
.ซ> O~"^^~ ~ ""ฐvซj~~ ~~* *~- ^-^^*""" TOG
H
^Q.
,-fN 80
\J
:n
60
40
20
0
~u
1 1 1 1 1 1
0 5 10 15 20 25 30
_
-
-A 0
u^O-^-AX
^**^"**A^ ^-*"^*^*ป-
U^^^^ "^^^^^^
"^^^^a-
_
_
i i i i i i
14
12
*E"
a_
in ^
u
O
i
8
6
4
2
35 40 45 50 55 60
Time (min.)
Figure 36 - Treatment of Effluent S&L-624 With Hydrogen Peroxide and Ultraviolet Radiation (Experiment 81)
-------
PROCESS COSTS
Summary
Preliminary, process-cost estimates were made for the application
of the UV-catalyzed chlorine oxidation to the treatment of wastewater on a
large scale. Costs of 7.2$zf to 11.1^/1,000 gal. were estimated for a plant
producing 10-million gal/day. Because of the nature of this process, costs
would not increase significantly for plants producing 1-million gal/day.
In determining process costs, the major factors considered were
(1) the commercial availability of UV-radiation sources, (2) the design
and efficiency of the reactor system, (3) the transmission of UV radiation
by wastewater, and (4) the costs of chlorine, lamps, power and structure.
The assumptions made were that a contact time of 10 min. is
required for effective organic oxidation and that the catalytic process
requires the application of 15 times more radiant energy than that required
for UV sterilization.
Process costs could be lowered substantially if any one of the
following factors could be reduced: (l) the amount of radiant energ^ per
unit volume required for effective oxidation, (2) the contact time, and
(3) the cost of the radiation source. The precise determination of these
factors can only be achieved by a study designed to determine exactly how
much wastewater can be trea^ed effectively using each radiant energy source.
80
-------
Process Costs
There are four important factors to consider In estimating the
cost of UV-catalyzed chlorine oxidation -:: a large scale. These are (l) the
cost of chlorine, (2) the cost of the ultraviolet lamps, (5) the power cost,
and (4) the cost of structure which includes land, labor, maintenance, capital,
and interest charges.
The cost of chlorine is the only simple factor to calculate.
Assuming that the average, highly nitrified (less than 4 ppm NH3) effluent
will possess a COD of 30 ppm, the theoretical amount of chlorine which must
be applied is 133 ppm. The application of 135 ppm of chlorine will cost
4.10^/1,000 gal. (taking the price of chlorine as 3.65$f/lb)-ฃr/
As will be subsequently shown, all the other costs are directly
related to the amount of water which can be treated by an individual W
lamp.
Commercially available., ultraviolet sources - Earlier in this
report, the opinion was stated that mercury-arc lamps are--at the p?-esent
time--the most practical source of UV radiation for this application. Two
types of mercury-arc lamps were also discussed earlier. (Both of these
topics are discussed in the section concerning UV sources, p. 59.) Some
characteristics of several, commercially available, UV lamps are shown in
Tables XX and XXI.
These lamps represent only a small fraction of the mercury-arc
lamps that are commercially available and were selected to provide repre-
sentative examples.
The ideal lamp for this process may not be presently available
commercially. Most of the lamps that are available were evidently designed
for specific uses. Perhaps a special lamp design could be devised which
would provide the particular characteristics (e.g., long life, intense
output of highly effective wavelengths, etc.) which would be best suited to
this process. Perhaps cheaper lamps, similar to those used for visual il-
lumination purposes, could be employed with no large offsetting decrease in
reaction-promoting efficiency. However, a consideration of the lamps de-
scribed in Tables XX and XXI will permit an estimate of the lamp costs which
would be encountered in large-scale processes using currently available,
mercury-arc lamps.
funeral design considerations - In determining process costs,
the most difficult factor to estimate is the amount of water which can be
treated with a given amount of UV energy. Obviously, a given volume and type
of water will require the application of a certain specific amount of UV
energy for a certain specific time in order to achieve a pre-determined, prod-
uct-water quality.
81
-------
TABLE XX
COMMERCIALLY AVAILABLE, MERCURY-ARC
Lamp
(G. E. Ordering Length
Abbreviation) Type]?/ (in.)
UA-11 HP 22
UA-37 HP 52
G64T6 LP 64
G36T6 LP 36
G30T8 LP 36
H1500-A23 MP 12
H 400-A33-1 FL 2ฃ/
Electrical
Input
(watts)
1,200
3,000
65
35
30
1,500
400
UV
Output
(watts)
Life
(hr.)
255
782
18.5
13.7
8.8
486
22
1,000
1,000
7,500
7,500
7,500
6,000
24,000
a/ The data in this table were obtained from General Electric.
b/ HP = High pressure, LP = Low pressure, MP = Medium pressure, FL - Flood-
lamp
c/ The arc length of this lamp is about 2 in.; however, the lamp itself
is about 8 in. long.
TABLE XXI
DISTRIBUTION (IN TRAITS)
OF SELECTED MERCURY-ARC
SPECTRAL ENERGY
Lamp
(G. E. Ordering
Abbreviation )
UA-37
G64T6
H1500-A23
H 400-A33-1
Y
HP
J-i..K
Mr
FL
Far UV
'/ (220-280 mti)
250(22$)
18(90$)
189(26$)
0(0$)
Middle UV
(280-320 mu)
279(25$)
0.4(2$)
157(22$)
1.5(2$)
Near UV
(320-400 nu)
252(22$)
0.3(1.5$)
140(20$)
20.5(26$)
Visible
(400-700 nu)
347(31$)
1.3(6.5$)
227(32$)
55.7(72$)
T/The data in this table were obtained from General Electric.
b/ HP = High pressure, LP = Low pressure, MP = Medium pressure, FL = Floodlamp
-------
TABLE XXII
REPLACEMENT COSTS OF MERCURY-ARC
Lamp
(G. E. Ordering
Abbreviation)
UA-11
UA-37
G64T6
G36T6
G30T8
H1500-A23
H 400-A33-1
Lamp
Cost*?/
Daily /
Costฃ/
2.33
3.68
0.0448
0.0400
0.0112
0.450
0.0124
Daily Cost of 100
Watts of UV Output
($)
0.914
0.470
0.242
0.292
0.128
0.0927
0.0564
a/ The data in this table were obtained from General Electric.
b/ These figures are the replacement costs of the individual lamps if the
lamps are purchased in large quantities.
ฃ/ The daily cost is the replacement cost divided by the lamp life in
days.
The General Electric brochure on germicidal lamps (TP-122) states
that a device, such as the one shown in Figure 37, "will provide 90$. dis-
infection (with a 100$ factor of safety) of drinkable water, transmitting
2537 A effectively to a depth of at least 5 in., if these rates of flow
are not exceeded: (lamp) G-30T8, 500 gallons per hr." In this apparatus,
the amount of water treated at one time is 36 x 5 x 8 = 1440 in =6.24 gal.
At a flow rate of 500 gal/hr, the average "contact time" is 0.748 min.,
and the UV energy applied is 1.06 w. -min/ gal.*
Our studies have Indicated that a contact time of approximately
10 min. will be required for substantial elimination of COD and TOC. A
10-min. contact time in a reactor such as the one described in Figure 37
would reduce the flow rate to 37.4 gal/hr, and the UV energy applied would
be 14.1 w. -min/ gal. Therefore, in our cost estimation, we have assumed
that effective organic removal can be achieved by the application of 15 w.-
min/gal .
*
The G-30T8 lamp emits 8.8 w. of UV energy (8.8 x 0.748) -r 6.64 = 1.06 w.
min/gal .
83
-------
ALZAK
ALUMINUM
REFLECTOR
LET
Figure 37 - Suggested Dimensions and Ratings of a Small, Gravity-Type
Water Disinfector*
This is the simplest of four designs proposed by General Electric
their brochure on Germicidal Lamps (TP-122). The designations
T8 and G30T8 refer to lamps produced by GE.
84
-------
Transmission of UV radiation by wastewater - Another factor which
will influence the amount of water which can "be treated at one time is the
UV transmission characteristics of the water. The General Electric Com-
pany has used the term "Effective depth of penetration" (EDP) which is the
depth at which 90$> of the UV energy has been absorbed. This value is simple
to determine for a single wavelength such as that used in germicidal applica-
tions, and it varies from 2 to 5 in. for a typical wastewater.* However,
for high-pressure, mercury-arc irradiation the EDP is more difficult to
determine because of the spectrum of wavelengths emitted by these lamps.
Since most of the energy emitted by high-pressure lamps is of longer wave-
length, a considerable increase in EDP would be expected. For example,
examination of the UV spectrum of a typical wastewater shows that the EDP
at 366 n^, (the most prominent wavelength emitted from a high-pressure
mercury arc) is at least six times as great as the EDP at 253.7 m^. Further-
more, our studies have shown that, as the UV-catalyzed chlorine oxidation
proceeds, the UV transmission of the wastewater increases greatly (see
Experimental, p. 118).
In germicidal operations, the EDP cannot be exceeded without
decreasing the effectiveness of the process. However, the UV-catalyzed
oxidation process is not subject to this limitation. In germicidal opera-
tions, it is required that no portion of the water receive less than a
sterilizing dose of radiation. However, in the oxidation process, even the
smallest amount of UV energy will contribute to the extent of oxidation.
In germicidal operations, UV energy must be wasted to insure sterilization;
in the oxidation process, maximum utilization of UV energy is desired.
Thus, for maximum efficiency, the oxidation process must treat water at
depths which substantially exceed the EDP for sterilization applications.
Cost of lamps, power and structure - The above discussion indicates
that many factors must be considered in selecting the most effective, UV
source and reactor design for large-scale water treatment. However, based
upon the assumption that 15 w.-min/gal of UV energy will be required for
the catalyzed chlorine oxidation, some estimates of the cost of presently
available lamps, power, and structure can be made.
Personal communication, Dr. R. B. Dean, Cincinnati Water Research
Laboratory.
85
-------
Lamp costs - The UA-37 lamp (Tables XX and XXI ) is representative
of high-pressure mercury arcs. The 782-w. UV output of this lamp would
permit the treatment of 52.2 gal/min., or 75,100 gal/day. Considering the
daily lamp replacement cost of $3.68 (Table XXI), the lamp cost would be
4.
Our laboratory studies have shown that the catalytic efficiency
of high-pressure lamps is 2.7 times greater than that of the low-pressure
lamps (Table XIX ). Therefore, for performance comparable to that of the
high-pressure lamps (which are assumed to be capable of operating effectively
with an application of 15.0 w . -min/gal ) , the amount of energy required from
low-pressure lamps would have to be 40.0 w. -min/gal.
The G64T6 lamp (Tables XX and XXI ) is typical of low-pressure
mercury arcs. This lamp emits only 18.5 w. of UV energy which would per-
mit the treatment of only 0.46 gal/min, or 665 gal/ day. Considering the
daily replacement cost (Table XXI ), the lamp cost would amount to 6.74^/1,000
gal.
The relatively high costs of both types of these lamps suggest
that other radiation sources be considered. Since the relative efficiency
of longer wavelengths is not known, perhaps cheaper lamps which provide
irradiation in the near ultraviolet (340-400 mj, ) or short -wavelength visible
(400-450 ma) might be developed especially for this application.
Two other types of mercury-arc lamps are described in Tables XX
through XXII. One of these is a 1,500 w. medium-pressure lamp (G. E.
ordering abbreviation H1500-A23) and the other is a 400 w. mercury-arc lamp
for floodlighting applications (G. E. ordering abbreviation H400-A33-1).
These lamps have been designed to provide exceptionally long lifetimes. The
longer life of these lamps plus the fact that they are marketed in large
vo-unie, results in significantly lower daily costs per 100 w. of UV output
(Tacle XXII).
Power costs - The high-pressure lamp (UA-37) requires 3,000 w.
of input electrical energy. The daily cost of this energy would be 57. 6^/
lamp, assuming that power costs 0.80jf/kw-hr. Since our calculations
indicate that each lamp will treat 75,100 gal/day, power cost would be
0.77^/1,000 gal. of water treated.
The low-pressure lamp (G64T6) requires only 65 w. of input elec-
trical energy, or a daily cost per lamp of 1.25^. Assuming that each lamp
treats 1,400 gal/day, the power cost would be 0.89^/1,000 gal.
On a similar basis, power cuts for the medium-pressure lamp
(H1500-A23) would be 0.62^/1,000 gal.; for the floodlamp (H400-A33-1), 0.35yf/
1,000 gal.
86
-------
Structure costs - If each high-pressure lamp (UA-37) will treat
75,100 gal. of water per day, then 133 lamps are required for a plant proc-
essing 10-million gal/day. The size of this plant can "be estimated at 2,310
sq. ft., based on the length of the lamps and by assuming that the total
width required for the channel is 4 ft. At $10/sq. ft., the estimated cost of
structure would be $23,100. Straight-line depreciation (20 years) places
the daily contribution of structure cost at $3.21. Maintenance (at 11$ of
structure cost) is estimated at 36^/day. The daily labor cost (one man,
24 hr/day) of $120/day would be the most significant factor in structure
cost.
Thus, for the high-pressure lamps, the total cost of structure,
land, maintenance, labor, capital and interest is estimated at $125/day, or
1.25^/1,000 gal.
Structure costs are considerably higher for the low-pressure
lamps because of the greater number of lamps required. Each low-pressure
lamp (G64T6) will presumably treat 665 gal. of water per day. This means
that 15,000 lamps are required for a 10-million gal/day plant. In order
to hold the size of the plant to a reasonable figure, we have assumed that
five lamps can be used in each unit cell. We have further assumed that
no loss of radiant energy is produced by this grouping of the lamps.
Making the same assumptions as were made for the high-pressure lamps, a
plant size of 30,600 sq. ft. and costing $306,000 is obtained. Straight-
line depreciation (20 years) leads to a daily structure cost of $42.50.
Maintenance would be $4.67, and labor (two men, 24 hr/day) is estimated at
$240/day.
Thus, for the low-pressure lamps, the total cost of structure, land,
labor, capital, and interest is estimated at $290/day, or 2.900/1,000 gal.
Structure costs cannot be estimated on a similar basis for the
medium-pressure lamp or the floodlamp because of their considerably shorter
arc-lengths. However, using the above estimates and assuming that structure
costs will be inversely proportional to the amount of water treated per
lamp, the structure cost for the medium-pressure lamp would be 1.50^/1,000 gal.,
structure cost for the floodlamp would be 2.70^/1,000 gal.
Total process costs - Total estimated process costs are shown in
Table XXIII. Process costs for the high-pressure and low-pressure lamps are
approximately the same, and there is an obvious "trade-off" between these two
kinds of lamps; the low-pressure lamps are cheaper, but require higher
structure costs.
Total process costs for the medium-pressure (H1500-A23) and flood-
lamp (H400-A33-1) are significantly lower because of the lower cost of
producing ultraviolet energy using these lamps.
87
-------
Each of these estimated total process costs could be lowered
considerably if any one of the following factors could be reduced: (l) the
amount of radiant energy per unit volume required for effective oxidation,
(2) the contact time, and (3) the cost of the radiation source. The precise
determination of these factors can only be achieved by a study designed to
determine exactly how much wastewater can be treated effectively using each
radiant energy source.
TABLE XXIII
ESTIMATED PROCESS COSTSg/ (CEHTS/1,000 GAL)
High-Pressure Low-Pressure Medium-Pressure
Lamps Lamps Lamps Floodlamp
Chlorine 4.10 4.10 4.10 4.10
Lamps 4.90 3.20 0.97 0.59
Power 0.77 0.89 0.62 0.36
Structure 1.25 2.90 1.50 2.70
11.02 11.09 7.19 7.75
a/ Costs were calculated assuming: (l) that a contact time of 10 min.
was required; (2) that the ultraviolet energy required is 15.0 w.-min/gal,
for the high-pressure lamps and 40.0 w.-min/gal. for the low-pressure
lamps; and (3) that the low-pressure lamps could be operated in clusters
of five with no significant loss in radiant energy.
88
-------
EXPERIMENTAL
Photochemical Reactor
All of the effluent oxidation experiments were performed in the
photochemical reactor shown in Figure 38. The reactor consisted of a
typical laboratory apparatus for the investigation of UV-catalyzed reac-
tions and was suitably equipped to permit thermal control, rapid sampling,
continuous monitoring of pH and the addition of aqueous alkali to control
pH as the oxidation proceeded. The reactor vessel was a 5-liter, four-
necked flask equipped with a quartz immersion well. The immersion well
(Hanovia Lamp Division, Engelhard Hanovia, Inc.) contained the ultraviolet
source, and was equipped with an outer jacket through which cooling water
was circulated. This well was located in the large center neck of the flask.
A combination pH electrode was placed in one of the side-necks.
Into another side-neck was placed a thermometer, thermocouple well, and a
glass tube which led to a syringe-type sampling device (Manostat Corpora-
tion). The third side-neck was equipped with a 500-ml., pressure-equalizing,
addition funnel.
The contents of the flask were stirred by a magnetic stirrer.
Temperature was controlled by a "Gardsman" controller (West Instrument
Corporation) which was activated by the thermocouple. The controller
activated an off-on switch which regulated the flow of cooling water to
the immersion well. A regulator was used to maintain the pressure of the
cooling water at about 5 psi. If additional cooling was required, the
cooling water was passed through a coil of aluminum tubing immersed in
ice-water. Reactions "in the dark" were performed by wrapping the reactor
in aluminum, foil.
Ultraviolet Radiation Sources
The ultraviolet source for almost all the oxidation experiments
was a 450-w., high-pressure,mercury-vapor lamp powered by a 285-v. trans-
former (radiated energy, 175.8 w.). The lamp and transformer are products
of the Hanovia Lamp Division, Engelhard Hanovia, Inc. The spectral output
of this lamp is typical of high-pressure, mercury-arc lamps and is shown in
detail in Table XXIV and graphically in Figure 26 (p. 63).
89
-------
.re 38 - r. for
Shlori . Qxic at i
90
-------
TABLE XXIV
SPECTRAL-ENERGY DISTRIBUTION OF HIGH-PRESSURE,
MERCURY-ABC LAMP
Mercury Lines
(millimicrons)
1367.3 (infrared)
1128 7
1014.0
578.0 (yellow)
546.1 (green)
435.8 (blue)
404.5 (violet)
366.0 (UV)
334.1
313.0
302.5
296.7
289.4
280.4
275.3
270.0
265 . 2
257.1
253.7 (reversed)*
248.2
240 oO
238.0
236.0
232.0
222 4
Total watts
Radiated Energy
(watts)
2.6
3.3
10.5
20.0
24.5
20.2
11.0
25.6
2.4
13.2
7.2
4.3
1.6
2.4
0.7
1.0
4.0
1.5
5.8
2.3
1.9
2.3
2.3
1.5
3.7
175.8
253.7 line is reversed in high-pressure lamps
91
-------
An alternate ultraviolet source was a low-pressure, mercury-arc
lamp manufactured by Nester/Faust Manufacturing Corporation and specially
modified to fit in our reactor. This lamp was selected because it is prob-
ably the most intense, short-wavelength source available commercially which
would fit within the immersion well. The electrical output and electrical
efficiency characteristics of this lamp are compared with those of the high-
pressure lamp in Table XVIII (p. 61). Data supplied by the manufacturer
indicated that 96$ of the UV output of this lamp is between 245 n^ and 260 iqj,
Analytical Methods
All analytical determinations were performed as described in
Standard Methods.i^/ Total organic carbon (TOC) determinations were per-
formed at the Cincinnati Water Research Laboratory by means of a Beckman
carbonaceous analyser; the brucine method was used for nitrate determina-
tions; ammonia was determined by direct Nesslerization; chlorine was deter-
mined using the iodometric procedure. All analytical samples were imme-
diately acidified to pH 1 with concentrated sulfuric acid in order to
stabilise the samples for COD and TOC analyses.
The acidified (pH l) samples for COD analysis were dechlorinated
by purging the sample with nitrogen gas until no chlorine could be detected
by means cf starch-iodide paper. The removal of chlorine by this method
is facilitated by low pH values (Figure 39), and this step usually required
about 15-20 nin. Longer periods of time were required when the effluent
contained more than 4 ppm of ammonia. The TOC sample was dechlorinated
with excess, solid, sodium bisulfite, and was similarly acidified.
Sources of Waste-water
The primary sources of wastewater x^ere local, municipal, sewage-
treatment plants of the extended aeration type. Another source of waste-
wator was an experimental sewage-treatment plant operated by the Smith &
Loveless Corporation, Lenexa, Kansas. This plant is also of the extended
aeration type and treats sewage from the city of Lenexa, Kansas. Apparently,
the design of this plant is to be patented, and the company cannot release
details of the process. The Smith & Loveless plant proved to be a very
reiiable source of highly nitrified effluent.
92
-------
200
Figure 39 -
Time (min.)
Effect of pH or. the Rate of Chlorine Removal
From an Aqueous Solution During Nitrogen-
Gas Purge
-------
Since ammonia concentrations above 3-4 ppm could not be oxidized
economically, effluents containing more than 4 ppm of ammonia nitrogen were
further nitrified by means of the laboratory-scale, activated-sludge appa-
ratus. (See p. 96.)
On arrival, the effluents were filtered through a cylindrical plug
(1-1/4 in. diameter x 4 in.) of Pyrex, glass-wool, filtering fiber. This
procedure removed 99% or more of the total suspended matter in the effluents.
The filtered effluents were stored in a cold, room (9ฐC) and were ordinarily
used the same week that they were obtained. Each 5-gal. sample of effluent
was filtered and analyzed on arrival for COD, TOG, ammonia, nitrate and (occa-
sionally) nitrite. The COD and TOC determinations were repeated immediately
before the oxidation experiments.
The Zinzer plant - The equipment used in this plant was manu-
factured by the Smith & Loveless Corporation. It has a capacity of 17,000
gal/day with a BOD loading of 34 Ib/day. At the time it was sampled, this
plant was loaded at a rate of 7,200 gal/day, and 15.3 Ib. of BOD/day, during
the summer months. During the remainder of the year, the load is increased
to 15,855 gal/day and 38.38 Ib. of BOD/day. The increased loading is
caused by operation of an elementary school.
Some characteristics of the Zinzer plant are presented in Table
XXV.
TABLE XXV
CHABACTERISTICS OF THE ZIMZER PLANT
Jfodel No. (Smith & Loveless) 12C17
Aeration tank
Capacity (gal.) 17,000
Normal BOD capacity (lb/day)2/ 34
Blowers
Recommended capacity (cfm) 72
Settling tank
Total capacity (gal.) 3,949
Overflow rate (gal/sq. ft./day) 135
a/ Based on 15 Ib. of 5-day BOD/1,000 cu. ft. of aeration tank capacity.
94
-------
The Nance plant - This plant is of the extended aeration type and
was built in place. Only one of the two aeration tanks is presently in
operation. The influent is aerated for 24 hr. at 1-2 ppm dissolved oxy-
gen and passes to the settling tank where it is retained for 4 hr. Other
characteristics of this plant are presented in Table XXVI.
TAILS XXVI
CHARACTERISTICS OF THE NANCE PLANT
Aeration Tanks
Capacity, Each (gal.) 40,250
Retention Time (hr0) 24
Settling Tanks (2)
Capacity, Each (gal.) 6,700
Retention Time (hr.) 4
Estimated BOD Load (ib/day) 68
The Randolph Corners plant - This plant serves 79 homes repre-
senting an inflow of 22,120 gal/day. The plant is very similar to the
Zinzer plant, except that there are two units of 17,500-gal. capacity each.
The Gracemore plant - This plant uses a relatively new "Oxigest"
design by Smith & Loveless. The process is more sophisticated than simple
"Extended Aeration" and is a modification of conventional activated-
sludge treatment known as "Contact Stabilization." A feature of this proc-
ess is a re-aeration of the activated sludge.
The Gracemore plant is much larger than the other municipal
sewage-treatment plants. During normal dry weather, the plant receives
195,300 gal/day. This figure increases to 500,000 gal/day during wet
weather. The flow is divided, about half going to the Model R Oxigest
facility and half going to an Imhoff-Tank, Trickling Filter. The Oxigest
facility has a design, BOD-load capacity of 425 Ib/day. During wet weather,
the design flow is exceeded substantially.
95
-------
Laboratory-Scale, Sewage-Treatment Apparatus
The apparatus was similar to the one described by Ludzackiz/, and it
incorporated most of the features of similar apparatus at the Cincinnati
Water Research Laboratories (personal communications, E. F. Earth and C. E.
Ehines). A photograph of the apparatus is presented in Figure 40.
The aerator compartment consists of a 9-liter, Pyrex, glass bottle
with the bottom cut off and a 3/4-in. hole drilled in the side. The vol-
ume of this compartment, when filled to the overflow point, is 7.6 liters.
The aerator compartment was placed in a specially designed hood equipped
with Plexiglas doors and an exhaust fan which conducts air to an adjoining
exhaust hood. Influent to the aerator flows from the bottom of a 5-gal.
jug situated on top of the hood. Effluent from the aerator flows to a
5-gal. plastic carboy located under the hood.
The starting material used in this apparatus consisted of effluent
obtained from a municipal plant (Gracemore). Control over the rate at
which this material flows into the aerator compartment is maintained by an
air bleed, through a needle valve (Nupro 4 M Fine Metering Valve), into the
reservoir. The rate^ of flow was allowed to vary from about 4 to 8 liters/day.
Effluent Analyses
A summary of the characteristics of effluents obtained from var-
ious sewage treatment plants is presented in Table XXVII.
General Procedure
Filtered effluent (4.0 liters) was placed in the reactor, and
samples of the untreated effluent were analyzed for total organic carbon
(TOG), chemical oxygen demand (COD), ammonia and nitrate.
The pH of the effluent was adjusted to the desired value using
concentrated sulfuric acid or 40$ aqueous sodium hydroxide. Chlorine water
was placed in the addition funnel, and an aliquot was taken for analysis.
The volume of chlorine water in the funnel was adjusted to provide the
desired initial chlorine concentration in the reactor. The chlorine water
was added rapidly to the reactor, and the pH was readjustedif necessary
96
-------
Figure 40 - Laboratory-Scale, Sewage-Treatment Apparatus
-------
Effluent*
z-i
TABIE XXVII
AMLYSES OF EFFEUEHTS USED IN THIS STUDY
Amonia (ppm gj. Nitrate (ppm ง]
22.06
G-l
G-2
G-3
G-4
G-5
RC-2
G-5 A
RC-3
0-6
S&L-l
S&L-3
S&L-5
S&L-6
G-59C
MRI-428
MRI-512
mi-516
G-5 28
MRI-61
S&L-619
S&L-625
3.8 (avg.
13.9 (avg.
30.5
30.2
"1 f* Q
|_Q 53
23.7, 25.7
20
21.8
32.0
1.8 (avg.
2.1
)
)
.)
0.9 (avg.)
1.6
14.38, 14.80
2.2
2.52
1.33
19.98
4.33
22.6, 23.0
1.94, 2.60
7.8
(avg.)
11.0 (avg.)
11.5
10.6 (avg.)
13.4
0.05
35.8
3.08
11.50, 10.38
0.15
24.00
0.15, 0.15
3.74, 3.60
29.4 (avg.)
49.7
35 (avg..
24 avg.
22.0 (avg.)
18-9, 21.5
51.65, 43.43
31.2, 3S.3
35.76, 34.54
29.51, 29.66
207.3
23.74
26.53, 24.73
31.34, 31.41
The first code letter, or letters, refer to the effluent source (G = Grace-
more subdivision sewage treatment plant; Z = the Zinzer plant, N =
the Nance plant; EC = Randolph Corners plant; S&L <= Smith & loveless
Corporation, experimental plant, Lenexa, Kansas; VSH. = effluent from
laboratory- scale, sewage -treatment apparatus at Midwest Research Insti-
tute). The number after the code letter refers either to the sample
number or to the date obtained (for example, 59 represents May 9th).
Usually, the chlorine-treated effluent was allowed to stand in the dark
for about 10 min. During this time, the chlorine concentration was deter
mined at various intervals; at the end of this period, samples were with-
drawn for COD and TOC analyses.
98
-------
The ultraviolet lamp, which was omitting at maximum intensity,
was then placed within the immersion well. Samples for COD and TOG analyses
were taken at about 5-min. intervals and were treated as before. The
chlorine concentration was determined frequently during the irradiation
period. In almost all the experiments, the pH of the reaction mixture was
adjusted from time to time using 40% aqueous sodium hydroxide.
The acidified (pH l) samples for COD analyses were dechlorinated
"by purging the sample with nitrogen gas until no chlorine could be detected
by means of starch-iodide paper. The removal of chlorine by this method
is facilitated by low pH values, and this step usually required 15-20 min.
(longer periods of time were required when the effluent contained more
than 4-5 ppm of ammonia). The TOC sample was taken separately, dechlorin-
ated with excess solid sodium bisulfite, and similarly acidified.
Effect of Ultraviolet Radiation on Chlorine Water
The reactor was charged with tap water and chlorine water to
provide 4,300 ml. of water containing about 200 ppm C12- The pH was
adjusted to the desired level (with concentrated HC1 or 10$ NaOH), the
chlorine concentration was determined, and the UV lamp was turned on. Tempera-
ture of the contents of the flask was maintained by passing ice-water
through the cooling jacket of the immersion well. The rates of decomposi-
tion at pH 5 and pH 10 are shown in Figure 20 (p. 44).
First Series of Wastewater Oxidation Experiments (Experiments 5-8)
The first series of six experiments was designed to investigate
two levels of pH (5 and 10). Control experiments were run to determine the
effect of chlorine in the dark and the effect of UV radiation in the
absence of chlorine. The experimental design is shown in Table I (p. 5).
In this series of experiments, the UV lamp was placed in the
reactor and turned on at the time indicated. In experiments to be per-
formed in the dark, the reactor was covered with aluminum foil; and, of
course, the lamp remained off.
The effluent used in the first series of experiments was obtained
from the Gracemore sewage treatment plant (G-l). It was treated with sul-
fur ic acid (4 ml/gal.) at the point of collection.
The analytical results for chlorine concentration, TOC and COD
(plotted vs. time) are shown in Figures 3-8 (pp. 12-17).
99
-------
In Experiments 3 and 4 (Figures 3 and 4), the final TOG and COD
samples were taken at 27 and at 20 min., respectively. However, the chlo-
rine was gone after about 17 min. and 8 min., respectively. Because of
this inopportune sampling time, oxidation rates at pH 5 and pH 10 could not
validly be compared with these data.
Second. Series of Effluent Oxidation Experiments (Experiments 59-47)
The effluent used in this series was obtained from the Smith &
Loveless,experimental,sewage-treatment plant (S&L-5). The experimental
design is presented in Table VI (p. 20). The GOD and TCC samples were taken
simultaneously; the samples were acidified (pH l) with sulfuric acid and then
purged with nitrogen until no chlorine could be detected using starch-
iodide paper. Part of each sample was sent to Cincinnati for TOG deter-
mination, and the remainder was analyzed for COD.
at ion
Time
(min.)
0
0
2.2
5.0
9.5
9.9
21.2
26.2
31.2
36.2
Experiment 59: High chlorine (175 ppm), pH 6.5, 15 min. irradi-
Sample
39A
C12 added*
39B
Lamp inserted
39C
Chlorine
(ppn)
171
119.7
166.0
185.5
43.5,
12.0
6.9
COD
TOG
20.7, 20.9
10.2
13.6, 14.7
9.1, 11.8
8.8
21.5
* 290 ml. chlorine water (containing 2,530 ppm chlorine).
100
-------
Experiment 40: Low chlorine (102 ppm), pH 8.5, 10 min. irradia-
tion
Time
(min.)
0
0
3.9
6.5
9.2
10.0
10.5
15.5
20.5
Chlorine
COD
TOG
Sample
40A
C12 added*
40B
Lamp Inserted
40C
102
93.1
98.4
93.9
21.8
6.9
24.1, 23.3
16.6, 13.7
12.9
9.6
6.0
21.0
175 ml. chlorine water (containing 2,430 ppm chlorine).
Experiment 41: No chlorine, 10 and 15 min. irradiation
Time
(min. )
0
10.4
15.8
Sample
Lamp inserted
41A
41B
pH
7.5
7.4
7.4
Experiment 42: Low chlorine (102 ppm),
Time
(min. )
0
0
2.3
5.0
9.2
9.8
10.6
15.7
20.6
25.6
Sample
42A
Gig added*
--
42B
Lamp inserted
42C
Chlorine
(ppm)
__
102
92.7
99.6
98.5
25.9
2.3
0.0
COD TOC
(ppm) (ppm)
20.4, 21.2 "9.6
24.8, 18.1 8.6
18.1 7.8
pH 8.5, 15 min. irradiation
COD TOC
(ppm.) ( ppm )
19.7, 18.9 12.4
19.4, 18.1 11.4
--
__
11.9, 11.9 7.8
101
-------
ฃ
Time
(min.)
0
0
2.1
5.1
9.2
10.2
12.9
17.9
22.9
Sample
43A
Clg added*
__
43B
Lamp inserted
__
43C
Chlorine COD
(ppml (ppgl
20.6, 17.8
178.0
160.3
171.3
171.7
14.0, 17.8
71.0
10.3 8.7, 8.4
\
TOC
(PPrc)
8.6
" ^
~"
8.2
ป
-
6.0
325 ml. chlorine water (containing 2,370 ppm chlorine).
Experiment 44: High chlorine (175 ppm), PH 6.5, 05 min. irradiation
Time Chlorine COD TOC
(min.) Sample (ppm) (PPm) (PF1)
0 444 ~ 17.5, 20.9 28.0
0 C12 added* 178
1.5 " 170.2
5.2 - 176.3
9>2 176.9
9]Q 44B 18.2, 18.7 8.4
10.8 Lamp inserted
15.8 60.7
20.8 " 6.2
25.8 44C ' 0.6 6.4, 8.0 4.6
* 325 ml. chlorine water (containing 2,370 ppm chlorine).
102
-------
Experiment 45; Low chlorine (102 ppm), pH 6.5, 15 min. irradiation
Time
(min. )
0
0
2.1
5.3
9.0
9.8
10.2
16.5
20.1
25.2
Sample
45A
C12 added*
--
45 B
Lamp inserted
--
--
45C
Chloric COD
(ppm) (ppm)
22.8, 21.8
104
93.9
97.0
97.0
18.7, 19.9
__
5.7
0.2
0.0 4.6, 8.7
\
TOG
(ppm)
9.0
--
~
--
--
9.4
--
--
--
9.8
* 190 ml. chlorine water (containing 2,290 ppm chlorine).
Experiment 46: Low chlorine (102 ppm), pH 6.5, 10 min. irradiation
COD TOG
(pffli) iฃpml
22.2 7.8
Time
(min.)
0
0
2.5
5.2
7.9
8.8
10.2
10.6
11.0
15.7
Sample
46A
C12 added*
46B
Lamp inserted
pH
7.7
--
-~
6.4
--
--
6.3
_
Chlorine
(ppm)
102
88.9
91.6
--
95.0
ซ.
28.6
15.2, 14.4 8.4
46C 6.2 0.6 7.1, 5.6 6.2
200 ml. chlorine water (containing 2,136 ppm chlorine).
103
-------
Experiment 47; High chlorine, (175 ppm), pH 8.5, 10 min. irradiation
Time
(min.)
0
0
2.4
4.6
4.9
8.9
9.8
10.1
10.4
15.2
18.8
20.4
Sample
47A
C12 added*
47B
Lamp inserted
47C
pH
7.7
8.5
8.85
8.25
Chlorine
(ppm)
174
162.3
168.3
168.9
45.8
COD
(PPn)
20.2
12.4, 13.7
2.1 8.2, 9.0
TOG
(ppm)
10.0
7.2
6.8
345 ml. chlorine water (containing 2,191 ppm chlorine).
Third Series of Effluent Oxidation Experiments (Experiments 48-50, 52-54,
and 77 and 78)
A major difference in procedure was followed in this series; TOG
and COD samples were taken separately. The TOC samples (30 ml.) were imme-
.diately treated with excess sodium bisulfite and acidified with concentrated
sulfuric acid (4 drops/30 ml. sample) to pH 1. The COD sample (120 ml.)
was acidified, as before, to pH 1 and purged with a stream of nitrogen until
no chlorine could be detected using starch-iodide paper. In a number of
these experiments, a second addition of chlorine approximately equal to the
first was made after most of the original chlorine had been consumed.
104
-------
addition
Experiment 48: pH 5.0, 26 min. irradiation, two-stage chlorine
Time
(min.)
0
0
0
2.2
3.6
5.1
9.6
9.7
10.2
11.2
15.6
15.9
16.1
16.9
20.9
21.0
21.5
25.8
26.5
27.4
29.2
29 .-5
32.1
37.4
37.4
Sample
48A*
48-1*
C10 added**
2
--
--
48-2
48B
Lamp inserted
.
48-3
48C
48-4
48D
48-5
48E
C12 added**
48F
48-6
pH
3.6
2.7
9.0
3.05
2.2
Chlorine
127
112.8
119.1
118.5
50.2
< 0.5
91.6
51.0
16.6
COD
(PPฐ0
19.3
15.0, 15.0
12.2, 13.5
13.5, 10.7
8.8, 10.7
4.2***
TOC
(ppฐ0
7.8
7.0
7.0
6o4
6.4
6.0***
Smith and Loveless, S&L-6-A.
** 275 ml. chlorine water (containing 1,957 ppm chlorine).
*** Adjusting for the second addition of chlorine, the following values
are obtained: 48-F, COD = 4.56; 48-6, TOC = 6.5.
105
-------
addition
Experiment 49: pH 6.5, 25 min. irradiation two-stage chlorine
Time
(min.)
0
0
0
0.8
2.0
4.8
9.2
9.3
9.8
10.6
11.1
13.2
15.6
15.8
16.2
18.2
20.4
20.7
21.1
23.3
23.9
25.3
27.2
27.7
28.2
36.8
36.8
Sample
49A*
49-1
C12 added**
49-2
49B
Lamp inserted
49-3
49C
49-4
49D
C12 added**
49-5
49E
49F
49-6
m
7.6
6.9
--
6.5
5.9
5.2
4.35
6.6
Chlorine COD TOC
'(ppm) jppm)
125
109.9
127.6
117.7
40.0
2.3
51.9
30.0
4.5
27.19
24.72, 25.52
13.55, 12.44
6.40, 6.60
8.0
7.4
4.6
3.4
2.2***
4.64, 4.75***
0,0
1.8***
* Smith and Loveless, S&L-6-A.
** 300 ml. chlorine water (containing 1,790 ppm chlorine).
*** Adjusting for the dilution produced by the second addition of chlorine,
the following values are obtained: 49E, COD =5.1; 49-5, TOO =2.4;
49-6, TOC = 1.96.
106
-------
Experiment 50; pH 6.5, 15 min. irradiation
Chlorine COD TOG
(ppm) (ppm)
Time
jjnin. )
0
0
0
1.1
1.9
4.3
4.8
5.3
9.3
10.4
10.5
11.0
14.0
16.1
16.3
17.0
19.4
20.9
22.1
22.2
25.7
26.2
26.2
Sample
50 A*
50-1
C12 added**
50-2
SOB
Lamp inserted
--
50-3
50C
50-4
SOD
50E
50-5
PJ
7.5
--
4.8
--
4.8
5.1
7.8
6.7
6.4
--
--
--
4.0
5.9
5.9
29.75
12
168
157.5
162.0
161.4
10
24.58, 26.71
75,9
5.4
6.44, 6.00
13.6
2.1
3.4
3.08, 2.92
0.5
2.92
3.2
Laboratory-produced effluent, MRI-428.
** 505 ml. chlorine water (containing 1,493 ppm chlorine).
Experiments 52-54 - Three experiments were designed to
investigate the rate and extent of UV-catalyzed chlorine oxidation at PH 3,
T>H 5 and PH 10. The effluent (MRI 512) used in these experiments contamed
33.8 mg/liter COD, 13.2 mg/liter TOG, 2.5 ing/liter of ammonia nitrogen
and 4.0 mg/liter nitrate nitrogen (average values). In each experiment,
the effluent was treated with chlorine water to provide an imtnal chlo-
rine concentration of about 200 ppm. This concentration represents a
33# excess over the theoretical amount of chlorine required to oxidize
all of the organic material to C02 and H20.
107
-------
The experiments were performed at room temperature and were
identical, except that each was performed at a different pH (pH 3, pH 5
and pH 10) . The experimental results are shown in Figures 12-14 (pp. 38-40).
The COD and TOC data are presented graphically in Figures 15-16 (p. 41).
Experiment 77, the effect of nitrate concentration - In Experi-
ment 77, 20 ppm of nitrate nitrogen (as potassium nitrate) was added to an
effluent prior to treatment with chlorine. The effluent (S&L 624A) was
the same as the one used in Experiment 75 (Figure 22). The results of the
experiment (Experiment 77) with the nitrate-containing effluent are shown
in Figure 21 (p. 45).
Experiment 78, the effect of chlorine concentration; Effluent
S&L 624A, pH 5, continuous addition of chlorine - In this experiment, the
chlorine water was not added all at once, but was added gradually during
the irradiation period. The results are shown in Figure 19 (p. 43).
The effect of temperature on the UV-catalyzed chlorine oxidation
of effluents - Two effluent oxidation experiments (Experiments 58 and 59)
were performed in exactly the same manner; except that, in one, the tempera-
ture was held near 5ฐC (41ฐF) and, in theother, the temperature was held
near 25ฐC (77ฐp). The results are shown in Figures 23 and 24 (pp. 47-48).
Extent of Organic Oxidation Produced by Chlorine in the Dark
A summary of the extent of COD and TOC decreases which occurred
during a 10-min. period of chlorination in the dark is presented in
Table XXVIII. In each of these experiments, the TOC sample was not sub-
mitted to the nitrogen purge; instead, it was dechlorinated by acidifica-
tion to pH 1 with sulfuric acid, followed by treatment with excess sodium
bisulfite.
108
-------
TABLE XXVIII
EXTENT OF COD AND TOG ELIMINATION PRODUCED BY A
10-MIW. PERIOD OF CHLORINATION IN THE DARK
Experiment
No.
48
49
50
52
53
54
55
56
57
58
59
75
77
Average
COD Elimination TOG Elimination
Effluent
S&L-6
S&L-6
MRI-428
MRI-512
MRI-512
MRI-512
MRI-516
MRI-516
MRI-516
MRI-525
MRI-525
S&L-624
S&L-624
a/
pH
3.0
6.5
6.5
3.0
10
5
5
5
10
5
5
5
5
16.7
0.8
3.3
11.8
12.1
11.3
14.7
15.4
20.0
14.4
16.4
2.0
16.4
11.94
a/ The significance of the effluent designation is explained at the
bottom of Table XXVII (p. 98).
b/ These TOG results are probably in error, because the extent of the TOO
elimination cannot be greater than the extent of COD elimination
(These TOG results were not included in the average).
c/ In this experiment, the TOG analysis indicated an increase in TOG.
Extent of COD and TOG Elimination Produced by Irradiation at pH 5
The following table (Table XXIX) presents a summary of the
experiments performed at pH 5 in which the COD and TOG samples were taken
separately. The average amount of COD and TOG eliminated was calculated,
and these values are plotted vs. time in Figures 17 and 18 (p. 42).
109
-------
TABLE XXIX
Experiment
No.
54
56
58ฃ/
59ฃ/
75
ffjQ./
Vftฎ/
Average!/
Effluent
No.
MBI-512
MRI-516
MRI-525
MRI-525
S&L-624
S&L-624
S&L-624
Extent
5 min.
70
84
69
80
60
51
52
66.6
of COD E
(
-------
Experiment 20: Effluent G-2, 180 ppm chlorine, pH 5, 15 min.
irradiation
Time
(min.) Sample pH
0 20A 7.1
0 Clp added
1.3 -- 9.2
8.5 Lamp on
11.9 6.4
15.3 20B
18.2
19.3 4.
20.3
21.3 20C 4.
* Solution was turbid.
Experiment 21:
irradiation
Time
(min . ) Sample pH
0 21A 7.05
0 C12 added
1.3 10.25
10.5 Lamp on
10.8
12.0 9.4
13.1
15.4 21B
17 .'2
19.0 21C
Chlorine Ammonia Nitrate COD
(ppm) (ppm N) (ppm N) (ppm)
0 15.1* 0 51.6
180
116
105
3.5 3.6
6,0
75
2.0
7 4.3 3.5 28.1
Effluent G-2, 170 ppm chlorine, pH 10, 8.5 min.
Chlorine Ammonia Nitrate COD
(ppm) (ppm N) (ppm N) (ppml
0 12.7* 0 47.7
170
93
92
88
1.6 2.5
9.0
0.6 2.5 3.4 22.3
* Solution was turbid.
Ill
-------
Experiment 25: Effluent RC-5, 589 ppm chlorine,
15 min
Time
(min. )
0
0
2.0
6.5
10.7
14.2
15.0
15.9
18.2
28.6
30.0
dark,
Time
(min. )
0
0
1.6
4.5
9.5
13.3
15.0
16.7
18.3
21.8
27.8
31.7
. in dark^ 15 min. irradiation
Sample p_H
23A 7 .4
Cl2 added
4.8
4.7
23B
Lamp inserted
__
3.9
2.4
23C
Experiment 27 :
15 min. irradiation
Sample pH
27A 7.2
Clp added
6.0
__ c cr
o <_/
27B
Lamp inserted
10.6*
27C
Chlorine Ammonia Nitrate COD
(ppm) (ppm W)' '(ppm N) (ppm)
0 21.4 1.65 159
389 --
275
268
263
262 18.5 1.80 130
43 5.0 6.80 112
Effluent RC-3, 375 ppm chlorine, pH 5, 15 min. in
Chlorine Ammonia Nitrate COD
(ppm) (ppm N) (ppm N) ipp^)
0 20.3 2.1 156
375
169.5
225.6
221.3
20.8 . 1.8 134.6
53.8
11.5
9.2 3.2 7.1 123.7
* Occasionally, an excess of sodium hydroxide was inadvertantly added.
The pH was adjusted downward as soon as possible using concentrated
sulfuric acid.
112
-------
Experiment 28: Effluent RC-5, 573 ppm chlorine (Added gradually),
60 min. in dark, pH maintained above 6.5
Tj_me Chlorine Ammonia
(min.) Sample pH (ppm) (PPm N)
0 28A 7.2 0 20.6
0 Start C12 373
addition
16.8 -- 6.8 49.2
26.9 -- 75.6
37.9 -- " 60.7
45.4 Complete C12
addition
46.7 -- " 99-6
60.0 28B 6.4 130.5 2ป9
Experiment 29; Effluent RC-5, 375 ppm chlorine (Added all at once),
60 min. in dark, pH maintained above 6.5
Time Chlorine Ammonia
(min.) Sample pH (ppm) (ppm N)
0 29A 7.2 0 22.4
0 Cl added 375
8.2 -- 6.9 151.1
12.6 6.9 162.6
25.6 6.85 161.4
38.0 6.75 155.7
60.0 29B 6.7 140.8 6.7
113
-------
Experiment 50: Effluent RC-5. 574 ppm chlorine (Added gradually),
60 min. in dark, 15-min. irradiation, pH 6.5
Time
(min.)
0
0
Sample
30A
Start dp
PH
7.2
Chlorine
(ppm)
M M
Ammonia
(ppm N)
22.9
Nitrate
(ppm N)
2.0
COD
(ppm)
126
--
addition
7.8 6.8
12.3 6.6
16.4
38.7 6.55
43.1 Complete Cl2
addition
58.6
60.8 30B
62.1 Lamp inserted
77.1 6.9
41.2
64.1
97.3
21.8
3.3
4.2
2.6
3.1
103
92
Experiments 75 and 76; The effect of adding ammonia to a highly
nitrified effluent - The effluent used in Experiment 75 was low in ammonia
content (1.9 ppm ammonia nitrogen). Experiment 76 was performed using
the same effluent to which 23 ppm ammonia nitrogen (as ammonium chloride)
was added. The results of these experiments are shown in Figures 22 and 25
(pp. 46 and 53).
Ultraviolet-Catalyzed Chlorine Oxidation of Ammonia
Experiments 13, 15, 17 and 26 were performed in accordance with
the general procedure, except that a solution of ammonium chloride was used
in place of an effluent. In some cases, as indicated, the lamp was not
turned on and allowed to warm up prior to insertion into the reactor. Except
as indicated, samples for ammonia and nitrate analyses were dechlorinated
by acidification to pH 1 with sulfuric acid, followed by nitrogen purge
until no chlorine could be detected with starch-iodide paper.
114
-------
irradiation
Time
(min. )
0
0
2.7
3.7
5.3
9.8
13.8
14.8
18.3
Sample
13A
C12 added
Lamp on
13B
--
13C
13D
Experiment 15:
Chlorine
(ppm)
0.0
148.0
43.0
--
12.5
3.5
Ammonium chloride,
Ammonia Nitrate
(ppm W) (ppm N)
12.8
--
0.2 0.8
__
0.1 2.2
2.0
no chlorine, pH 5, 182 min.
irradiation
Time
(min.)
0
93
182
Ammonia
Nitrate
Sample
15 B
15 C
15 D
12.7
13.0
10.8
0.50
0.05
Experiment 17: Ammonium chloride, 408 ppm chlorine, pH 5, 6 days
in dark, followed by 52 min. irradiation - This experiment was performed
in the dark using aluminum foil to cover the entire reactor. After 6 days,
the lamp was turned on.
Time
(min.)
0
0
5.7
8.5
44.1
0 (4 days
later)
0
4.3
9.6
17.5
20.0
31.0
32.0
Chlorine
Sample
17A
Cl added
17B
17 C
Lamp on
17D
0
408
348
293
229
213
138
48
32
9.5
115
Ammonia
(ppm N)
13.5
0.0
1.6
Nitrate
0.02
0.22
4.0
0.0
9.0
-------
Experiment 26: Ammonium chloride, 504 ppm chlorine> 15 min. in
dark^ 15 din, irradiation
Time Chlorine Ammonia Nitrate
Sample pJH (ppm) (ppm N) (ppm N)
6.4 0 28.8 0
304
5.6
137.4
5.3
171.8
177.5
4.9
24.4 0.25
9.1 0.05
2.5
36.8 4.6 6.35
4.0 6.95
Samples 26B and 26D (150 ml.) were acidified with concentrated sulfuric acid
(1 ml.) and treated with about 0.3 g. of sodium bisulfite (Reagent
grade, Merck). The solutions were then aerated until no odor of S02
could be detected. Prior to ammonia analysis, the solution was
adjusted to pH 10 with sodium hydroxide (40$ NaOH, followed by 5$ NaOH).
** Samples 26C and 26E (150 ml.) were acidified with concentrated sulfuric acid
(l ml.),- and nitrogen was bubbled through the resulting solutions until no
trace (or only a faint trace) of chlorine could be detected by starch-
iodide paper.
Comparison of uy Radiation Sources
Using the low-pressure, mercury-arc lamp, effluent oxidation experi-
ments were conducted at pH 5 and at pH 10; and the same effluent was treated
in the same manner using the high-pressure UV source. The results of these
experiments (Experiments 55-57) are presented in Figures 27-29 (pp. 64-66).
0
0
1.5
2.3
4.3
4.8
8.6
11.7
15.0
16.9
24.2
30.0
30.0
26A
Clp added
.
26B*
26C**
Lamp inserted
26D*
26E**
116
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UV-Catalyzed Chlorine Oxidation of Pure Compounds (Experiments 60-65, 68-70)
Aqueous solutions of eight pure compounds were subjected to condi-
tions approximating those of the effluent oxidation experiments.
Only the rate and extent of compound destruction were measured,
usually by TOG determinations or ultraviolet spectra analyses; and no
attempt was made to determine the number or kind of products formed. In
all of these experiments, the pH was maintained near 5.0. The results of
these experiments are shown in.Figures 30-35 (pp. 71-76).
Investigation of the Effect of UV Eadiation, Plus Other Oxidizing Agents
Treatment of wastewater with oxygen and UV radiation - In experi-
ment 80, pure oxygen gas was continuously bubbled through an effluent while
the reaction mixture was irradiated. (No adjustment of pH was made prior
to, or during, the experiment.) In Experiment 79, nitrogen gas was bubbled
through another sample of the same effluent while the solution was irradi-
ated. The results of these experiments are shown below:
Experiment 79: Effluent S&L-624B, nitrogen purge, no chlorine
Time TOC
(min.) Sample pH (ppnQ
0 79A 7.25 12.8
0 Lamp inserted;
N2 flow started
5.1 79C 7.40 12.0
10.0 79D 7.55 11.0
15.1 79E 7.70 10.0
20.0 79F 7.81
117
-------
19.9 min.
Time
(min.)
0
0
5.1
10.1
14.9
19.9
irradiation.
Sample
80A
Lamp inserted;
02 flow started
80C
SOD
80E
80F
PH
7.32
7.50
7.60
7.75
. 7.90
TOG
(ppm)
10.2
11.0
10.0
10.0
10.2
Treatment of wastewater with hydrogen peroxide and UV radiation -
The same effluent used in the above series of experiments was treated in
the dark with hydrogen peroxide in excess of the amount required to oxidize
all of the organic material in the effluent to COg. The reaction mixture
was kept in the dark for 30 min. and was then irradiated for 30 min. The
results of this experiment are shown in Figure 36 (p. 79).
Ultraviolet Absorbance of Treated and Untreated Wastewater Samples
Ultraviolet spectra of a number of treated and untreated waste-
water samples were obtained. A description of the samples is presented
in Table XXX, and the absorbance values at wavelengths between 230 mj, and
340 mj, are presented in Table XXXI.
The results of these determinations clearly show that large de-
creases in absorbance are produced by UV-catalyzed chlorine oxidation.
There are correspondingly large increases in the "Effective Depth of
Penetration" (EDp), a term which is defined on p. 85-
The EDP is equal to the reciprocal of the absorbance; thus, an
absorbance of zero is equivalent to an EDP of infinity, an absorbance of
0.01 is equivalent to an EDP of 100 cm., and an absorbance of 1.0 indicates
an EDP of 1 cm.
The data were obtained using a Beckman DK-2 spectrophotometer
and a cell of 1-cm. thickness. The indicated absorbances of some of the
treated samples are very nearly zero. Determination of more exact values
would require use of much longer cells.
118
-------
Note that decreases in absorbance are produced more rapidly
than decreases in COD or TOG. For example, with effluent MRI 516, a 31.51
decrease in COD (from the pure effluent to sample 55E) wrs accompanied by
a 51$ decrease in absorbance at 260 mj,
TABLE XXX
DESCRIPTION OF TREATED AND UNTREATED WASTEWATER SAMPLES
FOB WHICH UV ABSORBANCE DATA ARE AVAILABLE
Sample COD TOC NHs . Nitrate
Effluent No.* (ppm) (ppm) (ppm N) (ppm N) Treatment
MRI 428 (50A) 29.75 12.0 2.3 15.8 None
MRI 428 (50F) 2.92 3.2 - - 168 ppm C12, pH 6.5,
13 min. in the dark,
15 min. irrad. (Expt.
50, p. 37)
MRI 512 35.6 12.1 2.52 3.1 None
MRI 512 (54G) 0 1.6 - - 200 ppm Cl , pH 5, 13 min.
in the dark, 28 min.
irrad. (addn'l 200 ppm
dp added after 13 min.
irrad.) (Expt. 54, p. 40)
MRI 516 29.6 11.0 1.3 10.7 None
MRI 516 (55E) 9.3 7.0 - - 210 ppm Clg, pH 5, 10 min.
in the dark, 30 min.
irrad. with low pressure
source (Expt. 55, p. 64)
MRI 516 (56E) 0 3.2 - - 212 ppm C12, pH 5, 11 min.
in the dark, 12 min.
irrad. (Expt. 56, p. 65)
The sample number is the experiment number, plus a letter designating the
appropriate sample. This numbering system is identical to that used
elsewhere in the report.
119
-------
TABLE XXXI
ULTRAVIOLET ABSOHEANCE OF TREATED AND UIECREAJED WASTEWATER SAMPLES
Absorbance at Indicated Wavelength
Sample Wavelength (an) - > 250 240 250 260 270 280 290 500 510 520 550 540
MRI 428 (50A) Untreated >1.100 0.522 0.200 0.187 0.180 0.162 0.140 0.125 0.108 0.092 0.080 0.070
11 (SOP) Chlorinated* 0.720 0.080 0 0 0.002 0.007 0.012 0.017 0.017 0.017 0.016 0.017
o MRI 512 Untreated 0.600 0.510 0.245 0.232 0.218 0.190 0.160 0.153 0.115 0.100 0.090 0.075
(54G) Chlorinated* 0.2550 0 0 0 0 0 0 0 0 0 0
MRI 516 Untreated 0.940 0.500 0.200 0.192 0.180 0.160 0.155 0.115 0.100 0.087 0.078 0.068
(55E) Chlorinated* 0.760 0.240 0.140 0.095 0.075 0.070 0.072 0.070 0.064 0.055 0.047 0.040
(56) Chlorinated* 0.580 0.060 0 0 0 0 00 0 0 0 0
"
* Details of the chlorine treatment are presented in TABLE XXX.
-------
REFERENCES
1. Meiners, A. F., and F. V. Morriss, "The Light-Catalyzed Oxidation of
Starch with Aqueous Chlorine," J. Org. Chem., 29, 449 (1964).
2. Meiners, A. F., and F. V. Morriss, "Oxidized Starch Product and Method
of Making the Same," U. S. Patent 3,203,885 (August 31, 1965).
3. G-rigoropoulos, S. G., and D. W. Ryckman, "The Effect of Chlorine and
Chlorine Dioxide on Taste and Odor Causing Substances in Waters,"
Environmental and Sanitary Engineering Laboratories, Washington
University, St. Louis, Missouri, August 1961.
4. Summary Report, Advanced Waste Treatment Research, AWTR-14, U.S. Dept.
of Health, Education and Welfare, Division of Water Supply and
Pollution Control, April 1965, p. 79.
5. Moore, E. W., "Fundamentals of Chlorination of Sewage and Waste," Water
and Sewage Works, 98, 130 (1951).
6. Young, K. W., and A. J. Allmand, "Experiments on the Photolysis of Aqueous
Solutions of Chlorine," Can. J. Research, 27B, 318 (1949).
7. Palin, A. T., "A Study of the Chloro Derivatives of Ammonia and Related
Compounds", Water and Water Eng., 54 (10), 151; 54 (ll), 189; 54 (12),
248 (1950).
8. Standard Methods-Water and Wastewater, 12th Ed., 1965, p. 90, American
Public Health Association.
9. Roller, L. R., Ultraviolet Radiation, 2nd Edition, John Wiley & Sons,
Inc., New York, 1965.
10. Standard Methods-Water and Wastewater, 12th Ed., 1965, p. ,513, American
Public Health Association.
11. Chemical Week, September 24, 1968, p. 23.
12. Standard Methods-Water and Wastewater, 12th Ed., 1965, American Public
Health Association.
13. Ludzack, F. J., "Laboratory Model Activated Sludge Unit," Journal Water
Pollution Control Federation, 32, 605 (i960).
121
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