Wastewater Dechlorination State-of-the-Art
Field Survey and Pilot Studies
Los Angeles County Sanitation Districts
Whittier, CA
Prepared for
Municipal Environmental Research Lab
Cincinnati, OH
See 81
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
PBS2-102336
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EPA-600/2-81- 169
September 1981
PBS2-102336
WASTEWATER DECHLORINATION
STATE-OF-THE-ART FIELD SURVEY AND PILOT STUDIES
by
Ching-lin Chen
Henry B. Gan
Sanitation Districts of Los Angeles County
Whittier, California 90607
Contract Nos. 14-12-150 and 68-03-2745
Project Officers
Albert D. Venosa
Irwin J. Kugelman
Wastewater Research Division
Municipal Environmental Research Laboratory
Cincinnati, Ohio 45268
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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TECHNICAL REPORT DATA
(Please read Instructions on [he reverse before completing)
1. REPORT NO.
EPA-600/2-81-169
2.
ORD Report
3. RECIPIENT'S ACCESSION ISO.
1-0233
4. TITLE AND SUBTITLE
Wastewater Dechlorination State-of-the-Art Field Survey
and Pilot Studies
5. REPORT DATE
September 1981
6. PERFORMING ORGANIZATION COOS
7. AUTHOHIS)
8. PERFORMING ORGANIZATION REPORT NO
Ching-lin Chen and Henry B. Gan
9. PERFORMING ORGANIZATION NAME AND ADDRESS
County Sanitation Districts of Los Angeles County
Whittier, California 90607
10. PROGRAM ELEMENT NO.
AZB1B DIJ B-m Ta^k A/13
11. CONTRACT/GRANT NO.
14-12-150 and
68-03-2745
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory _
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
OH
13. TYPE OF REPORT AND PERIOD COVERED
Final Rpnnrt, fi/7"3-o/7Q
=a
FIN
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officers: Albert D. Venosa (513)684-7668
Irwin J. Kuqelman (513)684-7633
18. A8STI
XCT
A study of dechlorination was conducted in the County Sanitation Districts of Los
ftngeles County to determine the utility and efficiency of the sulfur dioxide methbd-
a£ ^to Proyidf.a cost-effectiveness comparison of sulfur dioxide and two other methods
of dechlonnation, namely, activated carbon and holding tank processes. Study objectives
toere accomplished through three main phases of work: literature review pilot-scale
testing, and full-scale evaluation in the field. '
The pilot-scale testing indicated that no degradation of physical and chemical water
Duality occurred in the dechlonnated effluents from any of the three dechlorination
Drocesses investigated. However, a one to two order of magnitude increase in total
2 th de[|STty in the 10-minute samples following dechlorination was commonly observed
among the three dechlonnation processes. The increase seemed to originate from con-
tamination by the existing microorganism communities in the dechlorinated effluent
rather than from the reactivation of injured bacterial cells
The field survey involved the canvassing of 55 operating plants in California by
iiail telephone, and site visits to selected facilities. Although overdosing of sulfur
loxide was frequently necessary to meet the residual chlorine discharge standards,
ost installations found pH adjustment and reaeration of the dechlorinated effluent
nnecessary. Process cost estimates indicate that sulfur dioxide process is the most
ost-effective method for dechlorination.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lOENTIFIERS/OPEN ENDED TERMS
c. OQSATt Fieid/Gtoup
3. DISTRIBUTION STATEMENT
For Public Release
19. SECURITY CLASS (This Report)
Unclassified
20.SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220*1 (9-73)
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
ii
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FOREWORD
The U.S. Environmental Protection Agency was created because of Increas-
ing public and government concern about the dangers of pollution to the
health and welfare of the American people. Noxious air, foul water, and
spoiled land are tragic testimonies to the deterioration of our natural en-
vironment. The complexity of that environment and the interplay of its com-
ponents require a concentrated and integrated attack on the problem .
Research and development is that necessary first step in problem solu-
tion; it involves defining the problem, measuring its impact, and searching
for solutions. The Municipal Environmental Research Laboratory develops new
and improved technology and systems to prevent, treat, and manage wastewater
and solid and hazardous waste pollutant discharges from municipal and com-
munity sources, to preserve and treat public drinking water supplies, and to
minimize the adverse economic, social, health, and aesthetic effects of
pollution. This publication is one of the products of that reserch and
provides a most vital communications link between the researcher and the user
community.
This report describes the efficiency and cost-effectiveness of the
sulfur dioxide dechlorination process required to minimize the toxic effects
of chlorine and chloramines of the chlorinated effluents from municipal
wastewater treatment facilities upon the aquatic environment.
Francis T. Mayo, Director
Municipal Environmental Research
Laboratory
ill
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ABSTRACT
A study of dechlorination was conducted in the Los Angeles County
Sanitation Districts to determine the utility and efficiency of the sulfur
dioxide method and to provide a cost-effectiveness comparison of sulfur
dioxide and two other methods of dechlorinationactivated carbon and holding
tank processes. Study objectives were accomplished through three main
phases of work: A literature review, pilot-scale testing, and full-scale
evaluation in the field.
The literature review involved an extensive search on the practice of
dechlorination in the United States and abroad, an assessment of the need
for reaeration and pH adjustment in the dechlorinated effluent, and an
examination of the extent of bacteriological aftergrowth in outfall pipelines
and receiving waters.
The pilot-scale testing indicated that no degradation of physical and
chemical water qualities occurred for the dechlorinated effluents from any
of the three dechlorination processes investigated. However, a 1 to 2 orders
of magnitude increase in total coliform density in the 10-minute samples
following dechlorination was commonly observed among the three dechlorina-
tion processes. The increase seemed to originate from the contamination by
the existing microorganism communities in the dechlorinated effluent rather
than from the reactivation of injured bacterial cells.
The field survey involved the canvassing of 55 operating plants in
California by mail, telephone, and site visits to selected facilities.
The feed forward method of sulfur dioxide dosage control with signals re-
ceived from both a flow and residual chlorine controller appeared to be the
most commonly employed method. Although overdosing of sulfur dioxide was
frequently necesssary to meet the residual chlorine discharge standards, most
installations found pH adjustment and reaeration of the dechlorinated efflu-
ent unnecessary.
Process cost estimates based on the field survey and pilot plant study
have been prepared for all three dechlorination processes. The sulfur diox-
ide process seems to be the most cost-effective method for dechlorination.
This report was submitted by the Sanitation Districts of Los Angeles
County, Whittier, California, in fulfillment of Contract Nos. 14-12-150
and 68-03-2745 under the partial sponsorship of the U.S. Environmental
Protection Agency. This report covers the period from June 1973 to September
1979, and work was completed as of January 1980.
iv
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CONTENTS
Foreword iii
Abstract iv
Figures vi
Tables viii
Acknowledgments x
1. Introduction 1
2. Conclusions 3
3. Recommendations 5
4. Literature Review 6
General
Dechlorination standards
Dechlorination processes
Dechlorination instrumentation
Dechlorination experience
5. Field Survey 14
General
Questionnaire responses
Site visits
6. Pilot Plant Studies 29
General
Dechlorination with sulfur dioxide
Dechlorination with holding-tank impoundment
Dechlorination with activated carbon adsorption
7. Process Cost Estimates 68
General
Sulfur dioxide dechlorination
Holding pond dechlorination
Carbon adsorption dechlorination
Cost comparisons
References 86
Appendix 89
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FIGURES
Number Page
1 Map of California Regional Water Quality Control
Boards 15
2 Distributin of dechlorination facilities included in
survey results analyses 17
3 Feed control system most commonly employed in sulfur
dioxide dechlorination facilities in California 24
4 Feed control systems used in dechlorination facilities
to avoid excessive SOj overdose 25
5 Critical components of a chlorine residual analyzer 27
6 Flow diagram of dechlorination pilot plant systems
at Pomona, California 30
7 Schematic diagram of chlorine contactor used in
pilot studies 31
8 Chlorination of Pomona Water Reclamation Plant secondary
effluent laboratory jar tests 33
9 Pilot plant observation of total coliform before and after
dechlorination with S02 38
10 Rate of contamination after initial startup in clean
dechlorination pilot plant systems 41
11 Bacterial responses in dechlorinated effluents of pilot
plant studies 42
12 Dissipation of free chlorine in distilled water and
secondary effluent 47
13 Dissipation of chlorine residual in secondary effluent 49
14 Impoundment time required for dissipation of
chlorine residual 51
vi
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Number Page
15 Carbon dechlorination flow scheme 52
16 Schematic diagram of carbon contactor used in
pilot study 54
17 Chlorine profile in dechlorination carbon contactor 59
18 Chlorine residual of carbon - dechlorinated effluent 66
19 Process cost curves for sulfur dioxide dechlorination 73
20 Process cost comparison among different dechlorination
processes 84
21 Cost comparison between sulfur dioxide and holding
pond dechlorination processes under different
cost assumptions as described in Table 19 85
vn
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TABLES
Number Page
1 Profile of Dechlorination Facilities in Survey (1977) 18
2 Engineering Design Information of Dechlorination
Facilities in Survey (1977) 19
3 Operational Information of Dechlorination Facilities
in Survey (1977) 20
4 Dechlorination Facilities Visited in Survey (1978) 23
5 Average Water Qualities During Pilot Sulfur Dioxide
Dechlorination Study 35
6 Jar Test Results of Bacterial Aftergrowth after
Dechlorination 39
7 Salmonella Isolations in Effluents of Pilot Plant
Studies with Known Salmonella in Unchlorinated
Secondary Effluent 44
8 Quantitative Analyses for Salmonella in Effluents of
Pilot Plant Studies 45
9 Effects of Holding Time on Residual Chlorine and
Remaining Organisms 50
10 Virgin Carbon Characteristics of Activated Carbon Used
in Pilot Study 55
11 Average Water Qualities During Carbon Dechlorination
Study 57
12 Chlorine Profiles in Carbon Bed for Dechlorination 60
13 Regeneration of Dechlorination Carbon-
(Calgon Filtrasorb 400) 67
14 Summary of Sulfur Dioxide Dechlorination Costs - Plant
Size = 43.8 I/sec (1 mgd) 69
viii
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Number Page
15 Summary of Sulfur Dioxide Dechlorlnatlon Costs - Plant
Size = 219 I/sec (5 mgd) 70
16 Summary of Sulfur Dioxide Dechlorination Costs - Plant
Size = 438 I/sec (10 mgd) 71
17 Process Cost Estimates for Holding Pond Dechlorination .... 74
18 Unit Costs for Operation and Maintenance Cost Estimates .... 75
19 Effects of Cost Parameters on Capital Amortization for
Holding Pond Dechlorination Process 76
20 Summary of Carbon Adsorpton Dechlorination Costs - Plant
Size = 43.8 I/sec (1 mgd) 78
21 Summary of Carbon Adsorption Dechlorination Costs -
Plant Size = 219 I/sec (5 mgd) 79
22 Summary of Carbon Adsorption Dechlorination Costs -
Plant Size = 438 I/sec (10 mgd) 80
23 Summary of Dechlorination Process Cost Estimates 81
ix
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ACKNOWLEDGMENTS
This study was undertaken through a cooperative effort of the U.S.
Environmental Protection Agency and the Sanitation Districts of Los Angeles
County. The pilot plant study was performed at the Sanitation Districts'
Advanced Wastewater Treatment Research Facility, Pomona, California..
The cooperation of various treatment plant personnel involved in field
visits and the mail questionnaire survey is greatly appreciated.
Mr. George C. White gave invaluable assistance in the field survey.
Credits for this research project are extended to staff of the Pomona
Research Laboratory and the San Jose Creek Microbiology Laboratory, both
of the Sanitation Districts.
Special thanks are also expressed to Ms. Vicki Rice and Mr. John Cussen
for their assistance in preparing this report.
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SECTION 1
INTRODUCTION
Because of growing concern over the effects of chlorine and chloramines
on the aquatic environment, dech1orination has become an important unit
process to be considered as part of a wastewater treatment system employing
chlorination as its disinfection process. The chlorine residuals, either
free chlorine or chloramines have been well demonstrated to be toxic to
fish and other aquatic organisms (1, 2, 3, 4). Therefore, the regulatory
agencies have already or are in the process of establishing residual chlorine
effluent standards for wastewater discharges (5, 6, 7). These established
standards or proposed criteria for chlorine residuals are normally dictated
by the residual chlorine detection limits.
The Sanitation Districts of Los Angeles County are required by the
California Regional Water Quality Control Board (Los Angeles Region) to pro-
vide dechlorination facilities at their water reclamation plants for chlorine
residual control. The total chlorine residuals allowed in these plant
effluents, which are discharged into nearby creeks or rivers, are equal to or
less than 0.1 mg/1. This study was initiated as a result of the need for
dechlorination in the Sanitation Districts' facilities. The study had three
main objectives as follows:
1. To establish on a pilot scale the utility and efficiency of sulfur dioxide
(SO?) for dechlorinating chlorinated secondary municipal wastewater
effTuent.
2. To demonstrate on a full scale the cost effectiveness of SO? dechlori-
nation under actual operating conditions.
3. To examine and ascertain the cost effectiveness of other methods of
dechlorination (i.e., activated carbon and holding tank processes).
The study objectives have been accomplished through three main phases of
work: (1) a literature review, (2) pilot scale testing, and (3) full scale
evaluation.
The literature review was performed with an extensive search on the
practice of dechlorination in the United States and other countries, the
assessment of the need for reaeration and pH adjustment in the dechlorinated
effluent, and the extent of bacteriological "aftergrowth" in outfall pipe-
lines and receiving waters.
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The pilot scale testing was conducted at the Sanitation Districts'
Advanced Wastewater Treatment Research Facility, Pomona, California. The
three methods of dechlorination evaluated were sulfur dioxide (SO?), granular
activated carbon, and water impoundment. Emphasis was placed on the sulfur
dioxide process because of its potential for being the most cost effective
method for dechlorination. The granular carbon method had been investigated
previously at the same research facility, and the results are included in
this report. The water impoundment method was evaluated concurrently with
the sulfur dioxide method.
The full scale evaluation was conducted by means of a field survey of
all California treatment plants that practiced dechlorination by any means.
The primary objectives of the field survey were to assess the effectiveness
and reliability of actual full scale dechlorination installations. Infor-
mation on the methods of control for the sulfonation system, cost effective-
ness, and the bacteriological aftergrowth in the dechlorinated effluent were
also requested through the field survey, which was conducted with both
questionnaire correspondence and site visit followup.
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SECTION 2
CONCLUSIONS
1. The sulfur dioxide process Is considered to be the most cost effective
method for dechlorination, particularly in the State of California.
2. The feed forward method of control, with flow as the primary signal and
residual chlorine as the secondary signal, is most commonly used in
sulfur dioxide dechlorination facilities.
3. Overdosing the chlorinated wastewater effluents with sulfur dioxide is
essential to accomplish consistent dechlorination.
4. Excessive overdose of sulfur dioxide can be avoided by using discrete
instruments and alternate methods of feed.
5. The reliability of the sulfur dioxide feed forward control system is
generally good.
6. The residual chlorine analyzer is the weakest link in a sulfur dioxide
feed system. Most analyzers manufactured today are not capable of main-
taining accurate calibration in the absence of minimal amount of
chlorine.
7. No significant physical-chemical degradation of the effluent was found
after dechlorination with sulfur dioxide. Depletion of dissolved oxygen
or reduction in pH was not observed in the pilot plant studies at a
sulfur dioxide to residual chlorine dosage ratio of 2 to 1.
8. Bacteriological aftergrowth in some microorganism populations was found
after dechlorination. This was observed predominantly in the total
coliform group. Some increases in fecal coliforms and other bacteria
(as detected in the total plate count) were also found in the dechlori-
nated effluents. Salmonella was not detected in most of the samples.
Fecal streptococci in the effluent remained relatively unchanged after
dechlorination.
9. The bacterial increases in the dechlorinated effluents seem to be attri-
buted to contamination by the microorganism communities existing in the
dechlorinated effluent rather than reactivation of injured bacterial
cells.
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10. Similar effects on the chemical, physical and bacteriological qualities
of the dechlorinated effluents were found for the carbon adsorption and
holding tank dech1 orination processes as with the sulfur dioxide de-
chlorination process.
11. The carbon adsorption dechlorination process is substantially more
expensive than the other two processes investigated. It is not
economically feasible to use the carbon adsorption process solely for
dechlorination purpose.
12. The holding pond process may become more cost-effective than the sulfur
dioxide process for dechlorination where inexpensive land is available
and simpler pond construction is acceptable.
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SECTION 3
RECOMMENDATIONS
1. More reliable chlorine analyzer should be developed to perfect the auto-
mation of the sulfur dioxide feed control system.
2. The effects of organic loading on the carbon capacity for dechlorination
should be thoroughly evaluated.
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SECTION 4
LITERATURE REVIEW
GENERAL
As part of this wastewater dechlorination study, a literature review has
been conducted to address the following subjects:
1. The practice of dechlorination with respect to types of processes and
their control and monitoring Instrumentation.
2. An assessment of the extent to which reaeration and pH adjustment Is
necessary following dechlorination, particularly, the sulfur dioxide
dechlorination.
3. The extent of bacteriological aftergrowth in outfall pipelines and
receiving waters.
Dechlorination has been practiced for quite some time in the field of
water treatment(8»9). The practice is usually associated with a superchlori-
nation for destruction of odors, tastes and other chlorine demand causing
substances in addition to bacteria and viruses(10). The excess chlorine re-
siduals are first removed by dechlorination process from the superchlorinated
effluents, and appropriate amounts of chlorine are then added into the
dechlorinated effluents to maintain desirable levels of chlorine residuals in
the final effluents. Such practice has been found to be satisfactory for
maintaining a necessary level of chlorine residual to provide bacteriologi-
cal ly safe water.
The application of dechlorination to wastewater treatment is rather a
new practice in the field. It has been employed recently to protect
aquatic life from the toxicity of the chlorine residuals in the discharging
effluents. Therefore, the sources of information regarding this practice
are very limited. Nevertheless, this section is intended to summarize these
pertinent information in both fields of water and wastewater treatment.
OECHLORINATION STANDARDS
Chlorination has been commonly employed to achieve various disinfection
standards for wastewaters discharging into natural water streams or lakes.
These disinfection standards usually require certain levels of chlorine
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residuals to ensure the necessary destruction of bacteria and viruses.
The remaining chlorine residuals have been found to be toxic to aquatic
life, especially fishf3'4.11*12).
Depending on the type of chlorine discharge (i.e., continuous or inter-
mittent), the toxicity limits of total chlorine residuals for the protection
of various aquatic species may vary widely, from less than 0.002 mg/1 for
continuous discharge to 0.4 mg/1 for intermittent discharge, as proposed by
Brungs(3), and Basch and Truchan(^).
Having recognized the problem of residual chlorine, the regulatory
agencies have already or are in the process of establishing residual chlorine
standards for wastewater discharges. For example, the State of Maryland has
set 0.02 and 0.5 mg/1 total chlorine residual standards, respectively, for
trout and other waters(^); the State of California has set slightly different
chlorine residual limits, mostly at the levels of 0.1 mg/1 or less, for
waste water discharges into different receiving water systems within each
individual basin under Regional Water Quality Control Board.
Any standards with total chlorine residuals less than 0.05 mg/1 are
essentially requiring that no chlorine residuals should be detectable in the
discharged effluents. This is based on the current capabilities of instru-
mentation and analytical procedures for detecting the chlorine residuals
DECHLORINATION PROCESSES
There are basically three types of dechlorination processes in the field
of practice. They are:
1. Dechlorination with chemical solutions.
(a) Sulfur compounds, such as sulfur dioxide, sodium sulfite, sodium
bisulfite and sodium thiosulfate.
(b) Hydrogen peroxide.
(c) Ammonia.
2. Dechlorination with granular activated carbon.
3. Dechlorination by dissipation in holding lagoons.
Among the above processes, the sulfur dioxide dechlorination process
seems to be the most popular one because of its low cost and its readily
available supply.
Dechlorination with Sulfur Compounds
Sulfur Dioxide
The various chemical reactions involved in sulfur dioxide dechlorination
process are shown as follows:
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S02 + H20 H2S03
HOC1 + H2S03 HC1 + H2S04
NH2C1 + H2S03 + H20 - -NH4C1 + H2$04
NHC12+ 2H2S03+ 2H20 - »NH4C1 + HC1 + 2H2S04
NC13 + 3H2S03 + 3H20 -NH4C1 + 2HC1 + 3H2S04
The above equations Indicate that acids are produced during the sul-
fur dioxide dechlorination reactions. These acids may cause substantial
pH reduction In low alkalinity waters and make It necessary to adjust pH
after dechlorlnatlon. The equations also show that both free chlorine and
ch lor amines can be dechlorlnated with sulfur dioxide.
Usually a slight excess amount of sulfur dioxide is added to ensure the
complete removal of the chlorine residual. However, the excess amount of
sulfur dioxide may exist in the water as sulfite (S03=) or react with the
dissolved oxygen in the water as indicated by the following reactions:
S02 + H20 -H2S03
Excessive sulfite (i.e., >10 mg/1) has been reported to be partially
responsible for the mortality of some fish species(4). The excess sulfite
will cause the depletion of dissolved oxygen in the receiving streams, which
may endanger the aquatic lives. The reaction of excessive sulfur dioxide
with water may also cause further pH reduction in the dechlorinated water.
The reaction between sulfur dioxide and chlorine residual is instan-
taneous^'. Therefore, a contact tank other than the initial sulfur dioxide
mixing and sparging compartment is usually not needed for a sulfur dioxide
dechlorination system.
Other Sulfur Compounds
Similar reactions can readily occur between other sulfur compounds, such
as sodium sulfite, sodium bisulfite and sodium thiosulfate, and residual
chlorine to produce essentially the same end products as those of sulfur
dioxide dechlorination. Sodium thiosulfate is not commonly used as a
dechlorinating agent because of its relatively slower reaction and the re-
ported odor nuisance associated with its reaction^).
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Dechlorination with Hydrogen Peroxide
The use of hydrogen peroxide (HgO?) as a dechlorinating agent Is not
well documented. The chemical Is believed to react with free residual
chlorine only and not with residual chloramines. The reaction is as follows:
HOC1 +
Because of the production of oxygen in its reaction, it is possible that
a closed loop control on the basis of dissolved oxygen can be used to adjust
the feed of hydrogen peroxide in the dechlorination operation. Furthermore,
no additonal pollutants may result from the overdosing of hydrogen peroxide.
Dechlorination with Ammonia
The residual free chlorine can be effectively removed by ammonia accord-
ing to the following reaction:
3C12 + 2NH3 -N2(gas) + 6HCL
The stoichiometric relationship is 6.3 mg chlorine to 1 mg ammonia. The
field practice indicated that 0.17 mg/1 of NH3 could dechlorinate 1 mg/1 of
HOClO4). This low NH3 dosage requirement is considered to be the chief
benefit of using ammonia for dechlorination. However, the reaction time
required to complete the ammonia dechlorination is rather lengthy with a
minimum of 20 minutest). Furthermore, it is extremely difficult to hit
exactly the proper location on the breakpoint curve to produce the above
reaction for complete removal of free chlorine residual. Usually, the
resulting residuals may be a mixture of monochloramine and dichloramine.
Dechlorination with Granular Activated Carbon
Use of granular activated carbon as a means for dechlorination following
superchlorination in a municipal water treatment plant was practiced as early
as 1910 in Reading, England(^). However, this kind of practice is considered
to be too expensive for municipal operations, and thus its application has
been limited to special water treatment problems.
Cassel et al.O^) reported that the activated carbon dechlorination pro-
cess could effectively remove the soluble organics, free chlorine residuals
and chlorinated organics from the effluents treated with breakpoint chlorina-
tion for ammonia removal. Bauer and Snoeyink(17) also employed activated
carbon for removing ammonia after being chlorinated with dosages less than
the requirement of a breakpoint chlorination.
The reaction equations proposed for the various activated carbon de-
chlorination applications may be summarized in the following:
C + HOC1 "CO + HC1
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where £ represents the clean state activated carbon and CO represents the
oxidized state activated carbon. Some of the surface oxTcTes may decompose to
CO or C02.
According to Bauer and Snoeyinlo^), dichloramine may react with
activated carbon and be converted to nitrogen gas and hydrochloric acid as
follows:
2NHC12 + H20 + £-N2 (gas) + 4HC1 + CO
The above reaction 1s believed to occur much more rapidly than the
following reactions of monochloramine with activated carbon and no evidence
of reconversion to NH3 has been obtained.
NH2C1 + H20 + £ -NH3 + HC1 + CO
2NH2C1 + CO-N2(gas) + 2HC1 + C
The acid produced by the above reactions may necessitate a pH adjustment
step after dechlorination, as in the case with sulfur compounds.
According to the above reactions, activated carbon dechlorination can be
employed to produce any desired degree of ammonia removal in addition to de-
chlorinating the water. This dual removal function is important for protect-
ing aquatic life from the toxicity of ammonia and chlorine residual.
However, the dual function can be accomplished only with proper pH control to
ensure the predominant form of chloramine is dichloramine. This is further
supported by the results obtained by Atkins et al.08) in their pilot plant
studies at Owasso, Michigan.
The oxidation of the activated carbon surface by the chlorine residuals
during dechlorination may reduce the carbon adsorption capacity for aromatic
compounds 09«20). The reduction may be attributed to the decrease of sur-
face area and the increase in surface acidity. Although Magee^21) reported
that some surface oxides may be decomposed, as indicated above, to CO and C02,
the carbon surface eventually becomes saturated with oxides. It is not known
if the buildup of oxides may result in the decrease of dechlorination
efficiency.
It has been shown that the carbon adsorption capacity for dechlorination
can be effectively restored with thermal regeneration processes^!,22).
Dechlorination with Holding Lagoons
The technical information regarding chlorine dissipation in holding
lagoons is not well documented. The scarcely available data were mostly
developed from laboratory or small scale pilot plant observations.
10
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Snoeyink and Markus(23) found that free chlorine in a secondary efflu-
ent exposed to bright sunlight decayed from 2.0 to 0.2 mg/1 in approximately
30 minutes, while monochloramine decayed far more slowly. Katz(24) demon-
strated in his laboratory studies that the rates of chlorine dissipation
can be altered by the presence of nitrogenous compounds, sunlight and high
salinity.
DECHLORINATION INSTRUMENTATION
Depending on types of processes being employed for dechlorination, the
process control instrumentation may range from a simple effluent chlorine
residual monitoring system to a more sophisticated combination system con-
sisting of a dechlorinating chemical and a chlorine residual monitor. The
latter system is usually required for a dechlorination process with chemical
solutions, such as sulfur dioxide and sodium sulfite.
Since current residual chlorine standards are beyond the control abili-
ties of commercially available chlorine residual analyzers, an improvement of
the accuracy, sensitivity and reliability of the chlorine residual analyzer
is vital to effective dechlorination process control for aquatic life
protection.
A feed forward control mode, using a flow signal and a predechlorination
chlorine residual signal, is presently considered as the most practical
control mechanism for sulfur dioxide dechlorination. However, the actual
chlorine residual in the dechlorinated effluent is not automatically recorded
in a feed forward control system. A feedback system can be used to control
the effluent residual chlorine only if a reliable, sensitive and accurate
chlorine residual analyzer for measuring trace amounts of chlorine is avail-
able.
DECHLORINATION EXPERIENCE
pH Adjustment
According to the various chemical reactions described previously, the
dechlorination processes usually result in the production of acids in the
dechlorinated effluent, i.e., hydrochloric and/or sulfuric acid. The extent
of the pH effects of these acids on the effluents depends greatly on the
buffer capacities of the dechlorinated waters.
The alkalinity of chlorinated wastewater effluents is normally in the
range of 150 to 200 mg/1 as CaC03- This range of alkalinity provides a
moderate level of buffer capacity for maintaining an acceptable pH in the
dechlorinated effluent. Therefore, there is usually no need for pH adjust-
ment for a well operated dechlorination plant.
Post-Aeration
The potential of dissolved oxygen depletion associated with dechlorina-
tion processes may be attributed to the following factors:
11
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1. The oxidation of excess dechlorinating chemicals by the dissolved
oxygen, as the oxidation of residual sulfite in the sulfur dioxide de-
ch1 orination system.
2. The consumption of dissolved oxygen by the biological oxidations taking
place in the dechlorination systems, such as in the case of activated
carbon dechlorination.
Consequently, the need for post aeration after dechlorination is depen-
dent on the following parameters:
1. The concentration of dissolved oxygen in the water stream ahead of the
dechlorination system.
2. The amount of excess dechlorinating chemicals in the dechlorinated
effluent.
3. The potential of biological growth in the dechlorination system.
Under normal operating conditions, the sparging and rapid mixing chamber
in a sulfur dioxide dechlorination system is able to provide adequate dis-
solved oxygen to compensate for the oxygen depletion caused by the oxidation
of the limited amount of excess sulfite in the dechlorinated effluent.
Therefore, post-aeration is not normally needed with a well-designed mixing
system.
Bacteriological Aftergrowth
The bacteriological aftergrowth is defined in this study as the rapid in-
crease of bacterial population in the disinfected wastewater immediately
following the removal of bactericidal effects. The remaining nutrients and
organics in the biologically oxidized and disinfected wastewaters are gen-
erally believed to be adequate for sustaining bacteriological growth after
the removal of bactericidal effects. Therefore, a rapid increase of bac-
terial population can be developed in the wastewaters by the following
mechanisms.
1. Contamination
Gan (25) had observed an increase of total coliforms from a level of 2.2
MPN or less per 100 ml of sample to a level of approximately 1,000 MPN or
more per 100 ml of sample in his carbon-dechlorination pilot plant studies.
Since the residual chlorine could be effectively removed by the top layer of
the granular activated carbon bed in the carbon-dechlorination system, the
carbon bed below the active dechlorination layer would become an excellent
environment for bacteriological growth. Such growth area is thus believed to
be a natural source of bacterial contamination for dechlorinated wastewaters.
Slime build-up in outfall channels or conduits immediately following the
dechlorination plants may be also responsible for the bacteriological after-
growth in the dechlorinated wastewaters.
12
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2. Photoreactivation
Scheible et al (26) had noted a 0.6 to 1.0 order of magnitude increase
in fecal coliform levels after exposure of ultraviolet light irradiated"
_samples to visible light. Such aftergrowth_isjbelieved"to b"e caused~by cell
"repair as a result of photorcactivation.
3. Loss of Harboring or Sheltering Effects
The Crustacea or the suspended solids in the wastewaters may harbor or
shelter the bacteria during the disinfection process and prevent them from
being destroyed by the bactericidal effects. Tracy et al (27) believed that
the harbored coliform bacteria could be released into the disinfected water
after the damage of the Crustacea and the removal of the residual chlorine.
Similar effects are expected from the suspended solids.
Other types of bacteriological aftergrowth have also been observed Jjy
many investigators (28, 29, 30) down stream from effluentjJischarges or
storm overflows. These types of aftergrowth are primariTy attributed to the
changes in nutrient levels and in the balances between bacteria and bacteria
predators. The toxic bacterial metabolic products may play a role similar
to that of the predators.
13
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SECTION 5
FIELD SURVEY
GENERAL
An extensive survey of all treatment plants in the State of California
practicing dechlorination was conducted during the study period. The
dechlorination requirement for wastewaters in the State varies from one
region to another. There are nine Regional Water Quality Control Boards in
the State as indicated in Figure 1. Each Board sets and enforces the water
quality requirements for the region under its jurisdiction. The chlorine
discharge limits are set primarily according to the existing qualities and
beneficial uses of the receiving waters.
Dechlorination is employed mostly in the urban areas, such as
San Francisco (Region 2), Sacramento (Region 5), and Los Angeles (Region
4). The threat to fish and wildlife is most prevalent in these areas be-
cause of the voluminous amount of wastewater discharges. Receiving streams
and rivers are incapable of assimilating the chlorine discharge from the
treatment plants without endangering fish lives and other aquatic organisms.
Region 2 decnlorinates approximately 3x106 m3 (800 million gallons) of
wastewater daily to protect the fish and wildlife habitat in the
San Francisco Bay estuaries. The Bay is one of the most important coastal
estuaries in the State. Myriads of fish and wildlife species utilize the
Bay habitats for feeding and nursery ground. The Bay also functions as the
major drainage outlet for wastewaters in the region. Dechlorination is thus
necessary for wastewater discharges in the Bay.
Region 5 dechlorinates its wastewaters to protect the fish and water-
fowl habitat in the rivers. Region 4 dechlorinates only the wastewater
discharges from its inland plants to protect the fish in the low flowing
rivers.
The North Coast (Region 1) had only three facilities dechlorinating
their effluents during the field survey. However, rapid growth in the
region has generated sufficient chlorinated wastewater to threaten the
fish life in the area.
The Central Coast (Region 3) and San Diego (Region 9) regions utilized
submarine ocean outfall to disperse their wastewater discharges. There-
fore, no dechlorination was practiced in these areas.
14
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!North Coast Region (1) Los Angeles Region(4)
>
o
i Santa Rosa
[ ' San Francisco Bay
Region (2)
Oakland
Central Coast
Region (3)
San Luis Obispo
Los Angeles
Central Valley
Region (5)
Sacramento
Lahontan Region (6)
South Lake Tahoe
Colorado River Basin
Region (7)
Indio
Santa Ana Region (8)
Riverside
San Diego Region (9)
San Diego
Figure 1. Map of California Regional Water Quality Control Boards
15
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The Colorado River Basin (Region 7) and Santa Ana (Region 8) are
water scarce regions. Wastewater effluents are normally discharged Into
ephemeral streams which contained virtually no fish life. Consequently,
no dech1 or1nation is required in these regions.
The Lahontan Region (Region 6) disposes its wastewater via land dis-
posal and, therefore, has no dechloriantion facility.
The various Caifornia Regional Water Quality Control Boards were con-
tacted in May 1977 for information regarding the dechlorinatin installa-
tions in their specific regions. From the list of treatment plants pro-
vided by the Boards, superintendents of the treatment plants were contacted
by telephone in early June 1977 to inquire if dechlorination was practiced
at their plants. A total of 35 plants out of the 55 facilities contacted
already used sulfur dioxide dechlorination in their plants. The remaining
20 plants were divided into three different situations: (1) five plants
were under construction; (2) five plants were still in design stages; and
(3) ten plants used holding lagoons or long pipe lines as interim means for
dechlorination.
The survey-questionnaires were mailed to all 55 treatment plants in
June 1977 and requests were made to return the completed questionnaires to
the Sanitation Districts of Los Angeles County by the end of July 1977.
However, only 31 of the 35 plants practicing sulfur dioxide dechlorination
had returned their completed questionnaires in time for statistical analy-
ses. The distribution of these 31 dechlorination facilities is shown in
Figure 2.
QUESTIONNAIRE RESPONSES
A copy of the blank survey-questionnaire which covers general, en-
gineering design and operational information inquiries is included in
Appendix A of this report for reference. Responses to the questionnaires
from the 31 dechlorination facilities are summarized in Tables 1, 2, and 3
with respect to three different categories of information. These results
are expressed in terms of percent of total responses.
As indicated in Table 1, about 61 percent of the dechlorination
facilities in the State of California had their initial startup operation
in January, 1976 or later. This was about the time when the stringent
water quality requirements were imposed on wastewater treatment facilities
in California. The table also indicates that about 84 percent of the
treatment plants employed secondary treatment processes ahead of their
dechlorination facilities. The remaining plants either had primary or
tertiary treatment processes as pretreatment units for dechlorination.
Furthermore, the table indicates that 68 percent of the sulfur dioxide
dechlorination facilities surveyed had an average flow of 2.3x10^ m^/day
(6 mgd) or less.
The total chlorine residuals before dechlorination were in the range
of 2 to 10 mg/1. These levels of chlorine residuals were required for
16
-------
NOTES:
. Numbers in parentheses denote
dechlorination facilities included in
survey result analyses.
2. Other numbers denote regions
of the State Water Quality
Control Board.
Figure 2. Distribution of dechlorination facilities included in survey
results analyses.
17
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TABLE 1. PROFILE OF DECHLORINATION FACILITIES IN SURVEY (1977)
Percent of total
Description responses
(a) Startup date of dechlorination facilities
Before January 1976 39
After January 1976 61
(b) Type of treatment preceding dechlorination
Primary 10
Secondary 84
Tertiary 6
(c) Average daily plant flow
Less than 2.3xl04rn3/d (6 mgd) 68
2.3xl04 to S.SxlO^/d 16
(6-10 mgd)
Greater than 3.8xlQ4m3/d (10 mgd) 16
(d) Sulfur dioxide capacity
0 to 45.4 kg/d (0 to 100 Ibs/day) 13
45.8 to 227 kg/d (101 to 500 Ibs/day) 35
Greater than 227 kg/d (500 Ibs/day) 52
(e) Total coliform discharge standard
Less than or equal to 2.2/100 ml 22
Less than or equal to 23/100 ml 16
Less than or equal to 100/100 ml 10
Less than or equal to 240/100 ml 42
Others 10
(f) Total residual chlorine discharge standard
0 58
Less than or equal to 0.1 mg/1 29
Greater than 2 mg/1 13
18
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TABLE 2. ENGINEERING DESIGN INFORMATION OF DECHLORINATION
FACILITIES IN SURVEY (1977)
Percent of total
Description responses
(a) Type of feed control system
Feedforward 87
Feedback 10
Feedforward and feedback 3
Flow paced 27
Residual control 27
Flow and residual controls 46
Pneumatic flow signal 7
Electronic flow signal 93
Pneumatic dosage signal 10
Electronic dosage signal 90
Gap residual controller 16
Proportional and reset controller 26
None 58
Multiplier 35
Without multiplier 65
With adjustable slope factor 10
Without adjustable slope factor 90
(b) Contacting method
S02 injected in mixing chamber 32
S02 injected in outfall pipe 68
Reaeration provided after dechlorination 3
Reaeration not necessary after dechlorination 97
pH adjustment provided after dechlorination 3
Others 97
19
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TABLE 3. OPERATIONAL INFORMATION OF DECHLORINATION FACILITIES
IN SURVEY (1977)
Percent of total
Description responses
(a) Is dechlorination system operated 24-hrs daily?
Yes 94
No 6
(b) What is the desirable S02 : Cl£ ratio employed?
1 or less 74
Greater than 1 26
(c) Is overdosing necessary to meet standard?
Yes 87
No 13
(d) Is S02 feed control system reliable?
Yes 58
No 42
(e) Will system handle drastic fluctuation of
residual chlorine?
Yes 50
No 50
(f) Is biological aftergrowth observed after
dechlorination?
Yes 6
No 94
20
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meeting the various disinfection goals shown in Table 1. The disinfection
requirement of most wastewater treatment facilities was to meet either a
2.2 or less total coliform MPN per 100 ml or 240 or less total coliform MPN
per 100 ml. The limit of 2.2 or less MPN/100 ml was required for facili-
ties which discharged their effluents into water streams for non-restricted
recreation usage, while the limit of 240 or less MPN/100 ml was for facili-
ties which discharged their effluents into shellfish harvesting areas.
The limits of chlorine residuals for most wastewater discharges were
generally 0.1 mg/1 or less. Several dechlorination facilities reported
total chlorine residuals of 2 to 6 mg/1 in their dechlorinated effluents.
In these facilities, the discharge requirement for chlorine was not
monitored until several kilometers downstream. Consequently, the plant
can discharge a higher level of chlorine residual at the plant site. Due to
normal chlorine dissipation along the channel, virtually all the chlorine
residuals were found to be reduced by the time they reached the required
monitoring point.
Table 2 summarizes the engineering design information gathered in the
field survey. Most responses to the survey-questionnaires showed that a
feed-forward type, with primary control based on flow and secondary control
based on chlorine residual levels at the chlorine contact chamber effluent,
was a preferred control system for S02 feed. The secondary control signal
on chlorine residuals must be fed forward instead of being fed backward,
since currently available residual chlorine analyzers are not capable of
monitoring and controlling the trace amount of chlorine residual in the de-
chlorination effluent. The analyzers will lose their sensitivities and
accuracies after extended periods of measuring trace or zero amount of
chlorine residuals. The survey results also indicate that both the flow and
dose signals are transmitted electronically rather than pneumatically, thus
reflecting the modernization of the control equipment. However, controllers,
multipliers, and adjustable slope factors are not used in most install-
ations. These devices have been used to fine-tune the sulfur dioxide
requirement for dechlorination.
The survey results on the operational information of the dechlori-
nation facilities are summarized in Table 3. Approximately 94 percent of
the facilities surveyed operated their dechlorination systems continuously
on a 24 hour basis. The remaining 6 percent operated their systems inter-
mittently, turning on the sulfonators only at high chlorine residual
levels. Seventy-four percent of the facilities surveyed attempted to
operate their dechlorination systems with the theoretical sulfur dioxide/
chlorine residual ratio of 0.9. However, most (87 percent) found it
necessary to overdose sulfur dioxide in order to achieve the stringent
chlorine residual standard. Approximately 97 percent of the dechlorination
facilities surveyed reported that it was not necessary to adjust pH and
perform reaeration of their dechlorinated effluents. Biological after-
growth was not observed in 94 percent of the dechlorination plant
effluents. Only about 68 percent of the correspondents of dechlori-
nation facilities believed that their S02 feed control systems were
reliable.
21
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SITE VISITS
Of the 55 dechlorination facilities surveyed, 17 plants were selected
for site visits to obtain further information regarding the operation of
dechlorination systems. These plants, as listed in Table 4, are generally
located in the San Francisco, Sacramento, San Jose, Santa Rosa, and
Los Angeles areas of the State of California. The specific objectives of
the site visits were to study various S02 feed control methods and inter-
view plant operators regarding operations of their systems. All the treat-
ment facilities visited were secondary treatment systems. The plant flow
capacities ranged from 1.1x10* to 3.0x105 m3/day (3 to 80 mgd). The
sulfonator capacities ranged from 200 to 6,900 kg/day (450 to 15,200
Ib/day).
The most common layout of sulfur dioxide dechlorination system em-
ployed in the plants visited is shown in Figure 3. As indicated in the
figure, a feed forward residual signal and a feed forward flow signal were
fed to the sulfonator. These two signals were sometimes combined into a
product signal through an electronic multiplier before feeding to the
sulfonator. This was done to avoid having to excessively overdose the
chlorinated effluent with S02-
In order to improve the control system further, an electronic ratio
controller was adopted after the multiplier in some facilities. The ratio
station maintained the desired ratio between the flow and residual signals
combined in the multiplier. This seemed to provide a more precise control
on the sulfur dioxide dosage requirement for dechlorination.
Two alternate methods have been devised to overcome the inability of
the chlorine analyzer in providing a feedback signal to the sulfonator.
Figure 4 shows a schematic of such a system.
In alternate No. 1, a two-stage method of dechlorination is used. One
chlorine analyzer is used to instruct sulfonator No. 1 to dechlorinate to a
10:1 ratio of the chlorine residual discharge limit. The analyzer seems to
perform best within a 10 to 1 setting. Calibration is maintained very well
because of the continuous presence of chlorine residual in the first-stage
dechlorinated effluent. Sulfonator No. 2 is then used to remove the re-
maining residual chlorine. Because the residual chlorine has been reduced
to approximately 1 mg/1 level in the first-stage dechlorinated effluent,
excessive overdose of the sulfur dioxide with sulfonator No. 2 is thus
avoided.
In alternate No. 2, a biased residual chlorine signal is transmitted
through the analyzer to keep it in calibration. A feedback residual signal
from the dechlorinated effluent greater than the biased signal signifies
incomplete dechlorination. The sulfur dioxide is programmed to dose pro-
portional to any signal greater than the biased signal.
The simple feed forward sulfur dioxide feed control system is in-
adequate for most dechlorination installations. It requires a small
22
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TABLE 4. DECHLORINATION FACILITIES VISITED IN SURVEY (1978)
Dechlorination
facilities
Operated
By
S02Capacity
kg/day
Daily avg.
flow m3/d
City Main WTP
San Jose/Santa Clara
WPCP
Northeast MRP
Arden WTP
San Pablo San. WPCP
Main Treatment Plant
Hayward WTP
Pomona URP
Harold May WQCP
Laguna WTP
Valencia WRP
Cordova WTP
Richmond WPCP
Irvington WTP
Newark WTP
Alvarado WTP
West College WTP
City of Sacramento
City of San Jose
County of Sacramento
County of Sacramento
San Pablo San. Dist.
San Rafael San. Dist.
City of Hayward
L.A. Co. San. Dist.
City of Palo Alto
City of Santa Rosa
L.A. Co. San. Dist.
County of Sacramento
City of Richmond
Union Sanitary Dist.
Union Sanitary Dist.
Union Sanitary Dist.
City of Santa Rosa
6,900
3,450
2,724
1,725
908
908
908
908
863
454
454
431
409
227
227
227
204
l.SxlO5
S.OxlO5
5.0x10"
1.9x10"
3.0x10*
1.1x10*
4.5x10*
2.3xl03
l.lxlO5
1.1x10*
1.1x10*
7.6xl03
2.7x10*
2.3x10*
1.9x10*
1.1x10*
1.5x10*
Notes: 1 kg/day =2.2 Ibs/day; 1 m3/d = 2.64x10"* mgd
23
-------
CHLORINE
CHLORINATED
...._._.. _..fc
ANALYZER
|
DRAIN
SAMPLE
SOLUTION
EFFLUENT
NOTE:
FEED FORWARD
RESIDUAL SIGNAL
... T _>
1
SULFONATOR
> t
1 ' '
I CJsTATION !
t*\. JFEEO FORWARD
MULTIPLIER l^°7 SISNAL
1
IFLOWMETER
*fS
S02 SOLUTION
, DECHLORINATED^
"Vy EFFLUENT
ELECTRICAL SIGNAL
i innin FI nun
Figure 3. Feed control system most commonly employed in sulfur dioxide dechlorination
facilities in California.
-------
NOTE:
ELECTRICAL SIGNAL
LIQUID FLOW
ALTERNATE_NO_I
| SET POINT I
I ANALYZER TO
I 10:1 RATIO OF
I DISCHARGE
\ LIMIT J
I
ALTERNATE NO. 2
ro
in
CHLORINAT
SULFONATOR
FEED BACK
^RESIDUAL SIGNAL
t
i
i
!
{FEEDFORWARD
j FLOW SIGNAL
1
1
1
ED ^/^FLOWMETER ,
|
CHLORINE
ANALYZER
DRAIN
S02 SOLUTION
r
I BIASED
. I RESIDUAL
*" | CHLORINE
SIGNAL
l_ _l
i
SAMPLE SOLUTION
DECHLORINATED
EFFLUENT
EFFLUENT
Figure 4. Feed control systems used in dechlorination facilities to avoid excessive SO2 overdose.
-------
capital investment and offers simplicity of control. However, the feed
forward control system requires an overdosing of sulfur dioxide to accom-
plish the stringent dechlorination goals. Such an overdosing cost may
become a significant factor in large dechlorination installations.
Alternate sulfur dioxide control systems discussed previously seem to be
more economical for large dechlorination installations. They reduce the
sulfur dioxide overdose requirement and hence the operating chemical
cost.
According to the field operators contacted, the weakest link in a
sulfur dioxide feed control system was the chlorine residual analyzer. The
measuring electrode of the chlorine analyzer lost its sensitivity rapidly
in a dechlorination effluent. The presence of some amount of chlorine
residual seemed to help prevent oxidation of the electrode. The abrasive
grits in the measuring cell block were found not able to prevent oxides
from forming on the electrode in the absence of chlorine residual.
Figure 5 shows a schematic of a residual chlorine sampling cell.
Measuring of the chlorine residual takes place in the measuring cell block.
The platinum is the reference electrode and the copper is the measuring
electrode. A small D.C. current is produced in the presence of free
chlorine or iodine proportional to its concentration. This current is
measured by a recording ammeter in terms of mg/1 of chlorine. The
efficient operation of the analyzer is dependent upon several factors, all
of which are equally important. The cell block and electrodes have to be
free from biological or chemical fouling. Continuous mixing with abrasive
grit or filtration have been successful to some extent in preventing
contamination of the electrodes. The buffer solution must be maintained
since the analyzer is calibrated to read accurately at a specific pH. The
flow and pressure of the sample water must be fairly constant, since they
affect cell currant production. A malfunction in any of the above con-
ditions will give a false reading and result in underdosing or overdosing
of the sulfur dioxide.
During the site visit, it was learned that poor performance was ex-
perienced with the chlorine analyzer when the plant received a high propor-
tion of industrial wastes. Plugging of the measuring cell block frequently
occurred. Installation of filters preceding the cell block did not seem to
improve the reliability of the chlorine analyzer. However, the operators
of the sulfonation systems were generally satisfied with the reliability of
their sulfonators. Most of the operators visited felt a slight overdose of
the sulfur dioxide was necessary to meet the discharge requirement of 0.1
mg/1 or less chlorine residual consistently.
Biological growth in the dechlorinated effluents was not visually ob-
servable in most plants since the effluents were usually discharged in a
submerged outfall pipe or intermingled with the receiving waters containing
natural fresh water slime growth. However, laboratory analytical results
from these plants indicated an increase in total coliforms after dechlori-
nation. As a result, coliform discharge limitations were usually exceeded
at the point of discharge. The California Regional Water Quality Control
26
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BUFFER
SOLUTION, pH
WATER
FLOW
REGULATOR
MEASURING
CELL
BLOCK
Pt Cu
WASTE
SAMPLE WATER,
FLOW a PRESSURE
Figure 5. Critical components of a chlorine residual analyzer.
27
-------
Boards have allowed the treatment plants to monitor coliform results before
dechlorination.
A continuous monitoring of the dechlorinated effluent was previously
required in some cases for compliance with the discharge standards of
California Regional Water Quality Control Boards. However, since a con-
tinuous recording of zero chlorine residual on the recorder chart is not
possible because of the limitation of the chlorine analyzer, the California
Regional Water Quality Control Baords have modified their requirements for
monitoring of the dechlorinated effluents for chlorine residuals from a
continuous basis to an hourly basis. The analyzer monitoring the chlori-
nated effluent is temporarily used to monitor the dechlorinated effluent
for residual chlorine once every hour. Such a special arrangement can keep
the chlorine analyzer in line with calibration.
28
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SECTION 6
PILOT PLANT STUDIES
GENERAL
The dechlorination pilot plant studies were conducted at the Los Angeles
County Sanitation Districts' Pomona Research Facility, Pomona, California.
The systems investigated included sulfur dioxide, holding-tank impoundment,
and activated carbon adsorption dechlorination processes. The pilot plant
systems which are depicted schematically in Figure 6 were comparatively large
scale ranging from 95 to 760 1/min (25 to 200 gpm) in flow rate.
The unchlorinated secondary effluent water used in these pilot plant
studies was obtained from the nearby Pomona Water Reclamation Plant, which is
owned and operated by the Sanitation Districts. The Pomona Water Reclamation
Plant consists of primary sedimentation, activated sludge biological oxida-
tion, secondary sedimentation, granular activated carbon adsorption, chlori-
nation, and sulfur dioxide dechlorination unit processes in series. The
plant receives mostly domestic wastewater from the neighboring communities.
The plant has an average flow of 3.8xl04 m3/day (10 mgd). The unchlorinated
secondary effluent was pumped from the outlet of the secondary sedimentation
system through a 15 cm (6 in) steel pipe to the holding tank at the research
facility. The pumping rate was maintained at 35 I/sec (550 gpm). The
secondary effluent was pumped from the holding tank to the chlorination pilot
plant systems before being fed to the dechlorination pilot plants.
The sulfur dioxide and holding-tank impoundment dechlorination processes
were investigated during this pilot plant study period, while the activated
carbon adsorption dechlorination process was evaluated previously as a part
of other research projects. The results of all three dechlorination pilot
plant studies are presented together in this report.
DECHLORINATION WITH SULFUR DIOXIDE
Description of Pilot Plant
The pilot plant consisted of a chlorination and a dechlorination system
in series. Two identical chlorine and sulfur dioxide contact tanks such as
that shown in Figure 7 were used for this study. The contact tank had the
flexibility of providing a two hour theoretical contact time (tank volume
divided by flow rate) for either a 95 1/min (25 gpm) or a 190 1/min (50 gpm)
flow. The tank had an adequate inlet flow distribution and a proper length
29
-------
CHLORINATED
EFFLUENT
SULFUR DIOXIDE
ANALYZER
JDRAIN
SULFONATOR
J
CONTACT CHAMBER
DECHLORINATED
EFFLUENT
MIXING
CHAMBER
ACTIVATED CARBON
CHLORINATED
EFFLUENT
DECHLORINATED
EFFLUENT
CHLORINATED T
EFFLUENT
NOTE:
HOLDING TANK
HOLDING TANK
T DECHLORINATED
EFFLUENT
ELECTRICAL SIGNAL
LIQUID FLOW
Figure 6. Flow diagram of dechlorination pilot plant systems at
Pomona, California.
30
-------
MIXING COMPARTMENTS
\
1
c
"c
1
.1
~e
0
\
q
\
\
J 1
J
n
1
i-
;
V,
s
\
f .
[I
!
^
« ^ i »
"T^ "~^
n ^ t
.. u t
i>H r
v y L
\H r
i*W ^
Be
ttv ^ K
""--^____ ^
1
~H3 -
1 fc
*
x 25gpm FLOW PATH
r ^
J^
.^ ^
1 . ^^
1 * ^
-*tKrURArtlJ BArrLtb
REMOVABLE GATE
^^^^ C/"\ _ Cl Oli/ DAT~LJ
OU gpm rLOW PAFI
"~^v
\
V
)
~x.
/ 1
^/
(TANK DEPTH = 2*8")
I1 =12"= 30.48cm
Igpm = 3.8 l/min.
Figure 7. Schematic diagram of chlorine contactor used In pilot studies.
-------
to width ratio (40:1) to approximate plug-flow. However, a tracer study con-
ducted with ponticyl pink dye indicated the time for initial dye detection
was approximately 52 minutes and the model time was 98 minutes.
As indicated in Figure 7, two perforated baffles were installed 28 cm
(11 in) downstream from the inlet of the contact tank. These baffles were
used to form 28 cm x 66 cm x 66 cm (11 in x 26 in x 26 in) compartments for
chlorine or sulfur dioxide sparging and mixing. A 0.25 kW (0.33 hp) mixer
equipped with a 1.6 cm (0.6 in) shaft and a 7.6 cm (3 in) diameter propeller
was installed at an inclined angle in each of the compartments to provide an
energy density of 2 kW per cubic meter (1 hp per 100 gallons) for chlorine or
sulfur dioxide mixing. Both chlorine and sulfur dioxide solutions were made
with tap water and were sparged through perforated PVC pipes at the bottom of
each mixing compartment. Two additional perforated baffles were installed
1.5 m (5 ft) downstream from the inlets of the contact tank, as shown in
Figure 7, to promote uniform flow in the tank.
A Fischer and Porter chlorine control system was used in the chlorina-
tion pilot plant, while a modified Wallace and Tiernan chlorinator was used
as sulfonator for the dech1orination pilot plant. The chlorine controller
was provided with a 3 to 500 percent proportional band adjustment mechanism
and an automatic reset. A compound loop control was incorporated into the
chlorine control system to compensate for flow variation.
Operation of Pilot Plant
Prior to the pilot plan* operation, laboratory jar tests were first con-
ducted with unchlorinated secondary effluent to determine the chlorine
residual necessary to meet the 2.2 per 100 ml MPN total coliform standard of
California for non-restricted recreational water reuse. The results are
shown in Figure 8. As indicated in the figure, a chlorine residual of 6 mg/1
seemed to be sufficient to meet the total coliform bacteria standard with a
contact time of 120 minutes. However, the actual chlorine dosage was found
to vary from approximately 8 mg/1 to 14 mg/1 in the daily pilot plant
operations to meet the bacterial standard. The variations of chlorine dosage
in response to the water quality changes had resulted in a wide range of
chlorine residuals in the chlorinated effluent. The average residual
chlorine in the chlorinated effluent was about 6 mg/1.
The sulfur dioxide feed control system employed only a feed forward
chlorine residual signal to dechlorinate the chlorinated effluent. The
sulfur dioxide was dosed in proportion to the chlorine measured in the
chlorinated effluent, which fed into the dechlorination system. The residual
chlorine was continuously monitored by a chlorine analyzer and a recorder.
An electronic signal was sent from the analyzer to the sulfonator to control
sulfur dioxide dosage based on chlorine residual. The sulfonator was read-
justed to feed sulfur dioxide in direct proportion to the measured chlorine
residual in the effluent feeding the dechlorination system.
The automatic mechanisms of the sulfonator system did not function suc-
.cessfully because of some malfunctions developed in the sulfur dioxide
32
-------
CHLORINE DEMAND 2mg/l
FEEDWATER: SEC. EFFL.
4 6 8 10
CHLORINE RESIDUAL, mg/l
Figure 8. Chlorination of Pomona Water Reclamation Plant secondary
effluent laboratory jar tests.
33
-------
dispensing control. Therefore, the sulfonator was operated manually through-
out most part of the dechlorination study. The sulfur dioxide dosage was
manually preset to remove a specific chlorine residual in the chlorinated
effluent, which was fed into the dechlorination system. Since the flow and
residual chlorine were both very constant in the pilot plant testing, the
removal of residual chlorine with a preset sulfur dioxide dosage could be
reliably achieved. However, in a full scale plant operation where both flow
and chlorine residual may vary substantially, a multiplier/ratio station for
effectively monitoring the sulfonator may have to be employed.
A chlorine residual analyzer/recorder system was used in the pilot plant
to monitor the residual chlorine in the dechlorinated effluent. However, the
analyzer was found to be incapable of measuring chlorine residual after a
brief period of non-chlorine detection in the dechlorinated effluent.
Similar problems are expected in full-scale systems. Monitoring of the
dechlorinated effluent to ensure the absence of residual chlorine, therefore,
had to be done manually with grab samples collected several times a day. The
residual chlorine was measured by the DPD ferrous ion titration method (31).
During the pilot plant study, the sulfur dioxide was added to the
chlorinated effluent in the mixing chamber of the dechlorination system at
ratios ranging from 1 to 2 mg/1 of sulfur dioxide to 1 mg/1 of residual
chlorine. From the mixing chamber, the dechlorinated effluent was fed
through the sulfur dioxide contact chamber to study bacterial aftergrowth and
physical/chemical degradation of the dechlorinated effluent. The theoretical
contact time in the contact chamber was about two hours.
Grab samples for bacteriological and water quality analyses before and
after dechlorination were collected once to twice a day, while composite
samples were also collected daily for total and dissolved chemical oxygen
demand (TCOO and DCOD, respectively) and total dissolved solids (TDS)
analyses. Both chlorination and dechlorination pilot plants were operated
continuously from Monday to Friday every week.
Experimental Results and Discussion
Effects of Dechlorination on Effluent Quality Characteristics --
During the dechlorination study, a total of 177 sets of samples was col-
lected under rather steady conditions during the period of October, 1977
through June, 1978. The average results of these analytical data are pre-
sented in Table 5.
As indicated in Table 5, effluent quality after dechlorination was
generally improved. The total chlorine residual in the dechlorinated effluent
was maintained consistently below detection limit. An average of 4 mg/1
sulfite was detected in the dechlorinated effluent under the complete
dechlorination conditions. Stoichiometrically, this excessive amount of
sulfite may ultimately cause about one milligram of dissolved oxygen (DO)
demand per liter of dechlorinated effluent discharged.
34
-------
TABLE 5. AVERAGE WATER QUALITIES DURING PILOT SULFUR DIOXIDE DECHLORINATION STUDY
Water quality
parameter
Total chlorine residual, mg/1
Dissolved oxygen, mg/1
Sulflte, mg/1 SO,
Median pH
Ammonia, mg/1 N
TDS, mg/1
Sulfate, mg/1 S0=
Total COD, mg/1
Dissolved COD, mg/1
Turbidity, FTU
Suspended sol Ids, mg/1
Temperature, °C
Alkalinity, mg/1 CaC03
Secondary
effluent
--
1.7
--
7.3
12.3
519
108
37
22
2.3
5
23.7
215
Chlorinated
effluent
(2 hr-
contact)
6.2
4.1
7.2
11.7
509
106
35
22
2.6
5
23.6
191
Dechlorinated
ef f 1 uent
(10 min-
contact)
ND
6.0
4.8
7.1
9.7
474
100
30
19
2.4
4
23.4
175
Dechlorinated
effluent
(2 hr-
contact)
ND
6.1
3.4
7.1
9.9
475
100
30
19
2.4
4
23.4
178
Notes: (1) The averages were based on 177 sets of samples.
(2) ND = not detectable (detection limit = 0.05 mg/1).
-------
The dissolved oxygen was increased from a level of 4 mg/1 in the chlori-
nated effluent to a level of 6 mg/1 in the dechlorinated effluent through
the sulfur dioxide dechlorination system. This improvement was attributed
to the vigorous mixing provided in the sulfur dioxide mixing compartment
of the dechlorination system. No further reaeration of the dechlorinated
effluent was found necessary in the pilot plant study.
The hydrogen ions released during the sulfur dioxide dechlorination pro-
cess caused a decrease of the alkalinity in the dechlorinated effluent. The
limited amount of alkalinity reduction only slightly reduced the pH from
7.2 in the chlorinated effluent to 7.1 in the dechlorinated effluent. There-
fore, it was not necessary to make any pH adjustment for the dechlorinated
effluent during the pilot plant, study . The average of the total dissolved
solids was also slightly decreased from approximately 510 mg/1 to 475 mg/1
through the dechlorination process.
The other quality parameters, such as ammonia nitrogen, sulfate, total
and dissolved COD, turbidity and suspended solids, were also reduced slightly
through the dechlorination process. However, the reductions were not
considered significant enough to warrant further explanation.
Effects of SOg Overdose on DO and pH
Dissolved oxygen depletion and pH reduction after sulfur dioxide de-
chlorination were generally anticipated because of the reducing property of
sulfur dioxide and the release of hydrogen ions in its reactions with water
and residual chlorine. However, due to the moderate dosing of sulfur dioxide
generally added in the dechlorination process, the effects of DO depletion
and pH reduction were found insignificant in both full-scale plant survey and
pilot plant study. These effects can be further minimized by the provision
of a vigorous sulfur dioxide mixing and the availability of moderate level of
alkalinity in the wastewater.
A brief study during the pilot plant operations showed an overdose of 50
mg/1 of sulfur dioxide was necessary to produce any significant effects of
DO depletion and pH reduction. Therefore, reaeration and pH adjustment may
not be necessary for controlling DO depletion and pH reduction except when
conditions such as high chlorine residual, low alkalinity, and poor sulfur
dioxide control prevail in the operations.
Sulfur Dioxide/Chlorine Ratio --
According to the sulfur dioxide dechlorination reactions, a stoichio-
metric addition of 0.9 parts of sulfur dioxide per part of residual chlorine
is adequate to achieve complete neutralization of residual chlorine. How-
ever, maintaining this ratio is often difficult because of equipment limita-
tions. Moreover, the ratio does not assure complete removal of residual
chlorine if other sulfur dioxide demand exists in the chlorinated effluent.
Consequently, an overdosing of sulfur dioxide is generally practiced to
comply consistently with the chlorine residual standard.
36
-------
During the pilot plant study, the sulfur dioxide was manually adjusted
to achieve complete dechlorination. It was found the S02/C12 ratio varied
from 1 to 2 in the pilot plant operations. The additional S02 demand of the
chlorinated effluent was not easily identified. However, there was no dif-
ficulty in obtaining complete dechlorination as long as an excess of approxi-
mately 4 mg/1 of sulfite was maintained in the dechlorinated effluent.
Bacteriological Aftergrowth
Bacteria measured for this phase of work included total and fecal coli-
forms, total aerobic plate count at 35 °C, fecal streptococci, and Salmonella.
All tests were performed in accordance with Standard Methods (31) except for
the Salmonella spp. which were isolated using the methods of Kenner and
Clark (32), as modified by Venosa e£ a± (33), and recommended by Van Sluis
and Yanko (34).
Figure 9 shows typical total coliform results for the chlorination and
dechlorination pilot plant operations. An increase in total coliforms shortly
after dechlorination was consistently observed in the dechlorinated effluent.
It was presumed that the increase of total coliform bacteria after dechlori-
nation might be due to either a recovery of the bacteria injured during
chlorination or contamination during the detention period in the sulfur diox-
ide contact chamber. Contamination from the air was not considered likely
since the sulfur dioxide contact chamber was covered with a plastic sheet
throughout the pilot plant operations.
A special study conducted with filtered secondary effluent, instead of
the unfiltered effluent employed during the routine pilot plant operations,
was performed to determine if bacteriological aftergrowth would still occur
after the removal of most suspended solids. These solids were suspected as a
possible source of recontamination since they might shelter bacteria and thus
prevent bacteria from being killed by chlorine. The filter employed in this
study was a dual-media pressure filter, which reduced suspended solids from
an average level of 5 mg/1 in the secondary effluent to an average level of 2
mg/1 in the filtered effluent. The results indicated that the same bacterial
aftergrowth phenomenon was also observed in the filtered secondary effluent.
Therefore, the limited amount of suspended solids in the pilot plant second-
ary effluent was disregarded as a significant contaminant responsible for the
increased total coliform count after dechlorination.
Jar tests were performed in the laboratory to determine if the total
coliform increase could be attributed to the recovery of the injured bac-
terial cells. A chlorinated secondary effluent sample from the chlorination
pilot plant was collected in a sterilized bottle and then dechlorinated with
sulfur dioxide solution (sulfurous acid). The results are summarized in
Table 6. As indicated in the table, samples collected from the chlorination
chamber in sterilized bottles containing a dechlorinating agent showed no
increase in total coliform bacteria when held for the appropriate time.
This indicated that the aftergrowth phenomenon was not due to revival of
injured coliforms to any significant extent.
37
-------
10'
I05
8'°4
I
10
CHLORINE DOSAGE = I3mg/l
CI2 RES. BEFORE DE CI2 = 9.8mq/l
CI2 RES. AFTER DE CI2 = Omg/l
APPROX. S02! CI2 RATIO =1 = 1
ING CHLORINATION
AFTER
DECHLORINATIO
CALIFORNIA
I
STANDARD
I
0 I
PERIOD
AFTER
CHLORI NATION!
(hours)
PERIOD
AFTER
SO,
DECHLOR1NATION
(hours)
Figure 9. Pilot plant observation of total coHform before and
after dechloMnation with S02-
38
-------
TABLE 6. JAR TEST RESULTS OF BACTERIAL AFTERGROWTH AFTER DECHLORINATION
10
vo
Experiment
number
1
2
3
4
5
6
7
Chlorinated
ef f 1 uent
(2 hrs)
2
<2
5
2
2
2
2
Dechlorinated In
sample bottle
(10 min)
2
<2
2
2
2
<2
<2
Dechlorinated 1n
pilot plant tank
(10 min)
49
79
33
49
33
49
490
Note: All results expressed as total coliform MPN per 100 ml.
-------
The sulfur dioxide dechlorination pilot system was subsequently used for
further aftergrowth studies. The sulfur dioxide contact chamber and mixing
compartment were thoroughly cleaned and disinfected. The disinfection was
performed with an impoundment of chlorinated water (with chlorine residual of
approximatley 10 mg/1) in the contact chamber for a period of about 64 hours.
The system was then put in operation and the dechlorinated effluent samples
were collected at 1, 2, 3, and 4 day intervals after startup. The typical
results are presented in Figure 10. Total coliforms increased by about two
orders of magnitude (100-fold) within the first three days. The increase
seemed to level off after the initial three day period.
The gradual increase in total' coliforms suggested that the source of
contamination might be attributed to a buildup of bacterial growth in the
sulfur dioxide contact chamber. Slime and scum buildup were consistently
observed in the contact chamber a few days after startup.
Samples of slime and scum collected from the sulfur dioxide contact
chamber contained very high concentrations of coliforms. The following
samples were collected and tested on June 30, 1978:
1. Scum buildup on the side of the sulfur dioxide contact chamber at the
water-air interface. Total and fecal coliforms, expressed as MPN per
gram of dry scum material, were 1.9 x 108 and 2.8 x 106, respectively.
2. Dead insects and scum entrapped in foam floating on surface of contact
chamber. Total and fecal coliforms were 6.0 x 106 and 6.0 x 105 MPN per
gram of dry materials, respectively.
3. Final portion of the contact chamber before discharge point. Very
light slime growth on all chamber surfaces. The slime could not be
sampled directly, so the slime materials were stirred into the water and
the mixed water from the chamber was sampled. Total and fecal coliforms
were 39 and 23 MPN per 100 ml, respectively.
The above data seemed to indicate that the recontami nation by the com-
munities of microorganisms growing inside the sulfur dioxide contact chamber
was primarily responsible for the bacterial aftergrowth in the dechlorinated
effluent. In an experimental situation, like the pilot plant study, very
strict control measures could control the growth of these communities of
microorganisms and subsequent coliform contamination of the dechlorinated
effluents. In actual practice, however, this type of control would not be
possible.
Besides the total and fecal coliform analyses, other bacteriological
analyses were performed. These results were presented graphically in Figure
11. Increases were found in the total plate count populations as well as the
fecal coliforms. These increases (less than 0.5 log unit) were significantly
lower than those found for the total coliforms. No significant change in the
fecal streptococci counts was observed after dechlorination.
40
-------
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o>
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0.5
(0
5 0.4
ul
CO
UJ
tr
0.3
cc
UJ
O 0.2
<
CD
O.I
LOG AVERAGE OF 19 SAMPLES
-
_
_
evj
O
UJ
Q
(T
UJ
h-
Lu
^
CO
UJ
13
~
2
O
esi
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i-
u_
CO
cc
D
O
x
CM
O
Q
CC
UJ
1
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^
UJ
1-
z
-------
In addition to the above bacteriological tests, Salmonella analyses were
also performed. Two enrichment media were employed to isolate the Salmonella:
namely, dulcitol selenite broth (DSE) and tetrathionate broth (TB). Both
have been shown to be effective for enriching Salmonella. Following enrich-
ment, isolation and confirmation of Salmonella colonies were carried out.
Isolation media used were Xylose Lysine Desoxycholate (XLD) and Bismuth
Sulfite (BS). Confirmation of typical colonies was performed biochemically
using Lysine Iron Agar, Triple Sugar Iron Agar, and Urea Broth, and serologi-
cally using Salmonella polyvalent-0 antiserum. A total of 26 tests was
conducted. All were qualitative tests since low numbers of Salmonella were
anticipated due to chlorine disinfection of the water sampleT!The results
provided an estimate of sampling volume size for the quantitative tests
performed later.
Table 7 summarizes the qualitative results of the Salmonella tests.
Only results where Salmonella were isolated in the unchlorinated secondary
effluent are presented.Of the 26 unchlorinated secondary effluent samples,
Salmonella were isolated in 15. Of these 15 samples, only three, or 20
percent of the 15 samples, showed the presence of Salmonella after dechlori-
nation.
Table 8 shows the quantitative results for Salmonella tests. The pro-
cedure used was the same as the qualitative method except that 16 to 24 liter
samples were filtered through a Whatman GF/F filter and diatomaceous earth
under pressure; the filtrates were placed in 10 ml enrichment broth (both DSE
and TB were used) and homogenized in a blender. The resulting homogenates
were tested by the MPN Procedure, using tetrathionate broth at 37°C. No
Salmonella were detected (detection limit = 0.05 Salmonella/1) in the de-
chlorinated effluent even though positives were found in the unchlorinated
secondary effluent. The Salmonella counts for the unchlorinated secondary
effluent ranged from 8 to 40 per liter of sample.
The results of the bacteriological aftergrowth study indicated that pre-
vention of slime growth in the dechlorination system was not feasible. The
growth appeared to be similar to that found in natural streams. The slime
growth in dechlorinated effluent may be enhanced by the available nutrients
in wastewater, the moderate ambient temperature, and the lack of toxic
chlorine residuals. It is believed that the presence of chlorine residuals
is an important factor in deterring the growth of microorganisms in the
effluent and receiving waters.
Reliability of Process Instrumentation
The chlorine residual was controlled automatically at an averaged level
of 6 mg/1 by a feedback sampling control system. The average chlorine dosage
required to achieve this residual was about 10 mg/1. The chlorine analyzer
was found to require a regular cleaning of the electrodes and weekly calibra-
tion. Periodic bleeding of the buffer solution lines was also necessary as
part of the maintenance required of the analyzer. The buffer solution was
added to maintain the pH of the sample within 4.0 to 4.5.
43
-------
TABLE 7. SALMONELLA ISOLATIONS IN EFFLUENTS OF PILOT PLANT STUDIES
WITH KNOWN SALMONELLA IN UNCHLORINATED SECONDARY EFFLUENT
Unchlorlnated
Sampling secondary Dechlorinated
date eff1uent eff1uent
3/29/78
4/ 5/78
5/ 8/78
5/31/78
6/19/78
6/28/78
7/ 6/78
7/10/78
7/12/78
7/17/78
7/24/78
7/28/78
8/ 2/78
8/23/78
8/25/78
44
-------
TABLE 8. QUANTITATIVE ANALYSES FOR SALMONELLA IN EFFLUENTS
OF PILOT PLANT STUDIES '
Sampling
date
Unchlorinated
secondary
effluent
(Salmonella/liter)
Dechlorinated
eff1uent
(Salmonella/1 iter)
8/15/78
8/16/78
8/17/78
10
8
40
<0.05
<0.05
<0.06
45
-------
It was demonstrated in this pilot study that the dechlorination system
would be best controlled by operating in manual mode. The sulfur dioxide
dosage was manually preset to remove a specific chlorine residual in the
chlorinated secondary effluent. This mode of operation was proved to be very
successfull and reliable in the pilot plant study where both chlorine re-
sidual and flow were kept constant. Since the automatic sulfur dioxide feed
control system did not function successfully, the system was bypassed in the
early stage of the study and was never fully evaluated during this dechlori-
nation pilot plant study.
As discussed previously, the chlorine analyzer was not functional for
continuous monitoring of the trace amount of chlorine residual in the de-
chlorinated effluent. Laboratory titration methods are still believed to be
the most reliable techniques for monitoring the efficiencies of dechlorina-
tion processes. However, it is very important to have a reliable on-stream
chlorine monitoring system to constantly maintain the chlorine residuals
below the allowable limits. Before such a system can be developed, an
overdosing of sulfur dioxide to assure complete dechlorination seems to be an
effective alternate solution.
DECHLORINATION WITH HOLDING-TANK IMPOUNDMENT
Description of Pilot Plant
As shown in Figure 7, the 95 1/min (25 gpm) pilot plant flow would only
occupy one-half of the chlorine contactor for a two hour theoretical contact
time. Therefore, the other half of the chlorine contactor was used as a
holding tank for this phase of the dechlorination study. The holding tank
was open to the air without any cover to simulate the natural pond situation.
The same chlorination pilot plant system used in the sulfur dioxide dechlori-
nation pilot plant study was employed to provide chlorinated secondary
effluent for this study.
Operation of Pilot Plant
Chlorinated secondary effluent from the pilot plant was diverted into
the holding tank for dechlorination by impoundment (i.e., dissipation of
residual chlorine by volatilization, sunlight destruction, etc.). Samples
were collected from the holding tank periodically and tested for residual
chlorine and coliforms. The batch experiment was repeated to see if the
results could be reproduced under similar operating conditions.
Experimental Results and Discussion
The dissipation of free chlorine in the absence of sulfur dioxide addi-
tion was briefly investigated in the laboratory. Jars containing chlorinated
nitrified-secondary effluent and chlorinated distilled water were allowed
to stand for 72 hours. The initial chlorine residuals for both types of
waters were about 1.5 mg/1 as free chlorine. Figure 12 shows the dissipation
of chlorine in both types of waters. As shown, no chlorine residual was
detected in the chlorinated nitrified-secondary effluent after two hours of
standing. By comparison, it took about 72 hours for the residual chlorine to
46
-------
I I
Ce = l.5mg/l AS FREE CI2
TEMPERATURE s26°C
20 40 60
DISSIPATION TIME, hrs.
Figure 12. Dissipation of free chlorine in distilled water
and secondary effluent.
47
-------
dissipate in distilled water. The more rapid dissipation rate of chlorine in
the nitrified-secondary effluent was attributed to the presence of more
chlorine demand substances.
The dissipation of chlorine residual in its various forms was also in-
vestigated in the laboratory. Jars of chlorinated nitrified-secondary
effluent containing approximately 1.4 mg/1 of free chlorine, 0.6 mg/1 of
monochloramine, 1.4 mg/1 of dichloramine, and 0.8 mg/1 of nitrogen trichlor-
ide were allowed to stand for 72 hours. All forms of chlorine residuals were
determined by DPD titration method (31). Figure 13 shows the dissipation
results for free chlorine, monochloramine, dichloramine, and nitrogen tri-
chloride. As shown in the figure, the free chlorine and nitrogen trichloride
exhibited almost similar dissipation rate with virtually no detectable
concentration after two hours of standing. The dissipation rates of these
two forms were much faster than those of monochloramine and dichloramine.
The monochloramine and dichloramine were still measured in the secondary
effluent after 72 hours of standing under laboratory conditions. The rela-
tive rates shown in Figure 13 may be influenced by differences in initial
concentrations of various chlorine forms, but the trend seems to be clear
that both monochloramine and dichloramine forms are dissipated slowly.
The pilot plant holding-tank dechlorination results are summarized in
Table 9. By extrapolating, the data, the holdina_times reauired for. comolete
dechlorination by natural dissipation were estimated to be about 68 and 56
hours, respectively, for initial total chlorine residuals of 3.7 mg/1 and 2.7
mg/1. Using data from Figure 13 as well as Table 9, a relationship between
period of impoundment and initial total chlorine residual for complete
dechlorination in a holding tank can be derived as shown in Figure 14. Based
on Figure 14, the total impoundment time for dechlorinating a chlorinated
effluent with 5 mg/i of total chlorine residual is approximately 96 hours.
As indicated in Table 9, the initial total coliform density was slightly
increased during the initial 43 hour period but the fecal coliforms remained
relatively unchanged. As soon as the total chlorine residual had completely
dissipated, a significant increase in the total and fecal coliforms was
found. The degree of increase in total coliforms was quite similar to that
found with sulfur dioxide dechlorination. Approximately two orders of
magnitude of total coliform increase were observed in the dechlorinated
effluent. The fecal coliform increase was about 1 log unit. No other water
quality data are presented for these holding tank pilot plant studies since
no significant changes other than chlorine residual and coliforms were
observed during the study.
DECHLORINATION WITH ACTIVATED CARBON ADSORPTION
Description of Pilot Plant
In early 1972, the Sanitation Districts of Los Angeles County initiated
a pilot plant study at their Pomona Research Facility to evaluate the flow
scheme, shown in Figure 15, for their proposed Malibu Water Reclamation
Plant. The objectives of the treatment were to produce a treated effluent
48
-------
Co VALUES, mg/l
FREE CHLORINE = 1.36
MONOCHLORAMINE = 0.58
DICHLORAMINE = 1.36
NITROGEN TRICHLORIDE = 0.78
MONOCHLORAMINE
DICHLORAMINE
FREE CHLORINE
NITROGEN TRICHLORIDE
20 40 60
DISSIPATION TIME, hrs.
Figure 13. Dissipation of chlorine residual in secondary effluent.
49
-------
TABLE 9. EFFECTS OF HOLDING TIME ON RESIDUAL CHLORINE AND REMAINING ORGANISMS
U1
o
Sampling
date
6/27/78
6/28/78
6/28/78
6/29/78
6/30/78
7/ 3/78
11 5/78
7/ 5/78
11 6/78
Accumul ated
holding
time
(hrs)
0
19
24
43
67
0
42
48
66
Free
0
0
0
0
0
0
0
0
0
Residual chlorine
(mg/1)
Mono D1 Trl
3.5 0.2 0
2.4 2.2 0
1.1 0.1 0
0.5 0 0
0 0.1 0
2.6 0.1 0
0.2 0 0
0.1 0.1 0
000
Remaining
organisms
(MPN/ 100ml)
Total
3.7
2.6
1.2
0.5
0.1
2.7
0.2
0.2
0
Total
col 1 forms
5
2_
2_
23
7.9xl02
<2
17
49
3.3xl02
Fecal
conforms
<2
±2
li
2_
33
<2
i
13
49
Notes: 1. Temperature-30°C.
2. Underlined numbers show coliform count is still within the 95 percent confidence
limit of the coliform count at zero holding time.
3. Weather condition - sunny.
-------
140
120
100
Q
Id
a:
S 80
a:
LU
60
UJ
a
o
Q.
40
20
Effluent Chlorine Residual <0.05mg/l
I i i
246
CHLORINE RESIDUAL, mg/l
8
Figure 14. Impoundment time required for dissipation of chlorine residual
51
-------
CHEMICAL
PRETREATMENT
CHLORINATION
U1
ro
SECONDARY \
EFFLUENT
L.
CARBON
CONTACTOR
1
-oJ
LO*
CHLORINE
CONTACT
CHAMBER
CARBON
CONTACTOR
2
-O
DECHLORINATED
EFFLUENT
O SAMPLING POINT
Figure 15. Carbon dechlorination flow scheme.
-------
free of viruses and chlorine residual and to meet the water quality standards
for non-restricted recreational water reuse. The pilot plant study was
completed in December, 1974.
The pilot plant consisted of first-stage carbon contactor, chlorine
contact tank, and second-stage carbon contactor in series. The first-stage
carbon contactor was to remove most of the suspended solids, organic con-
stituents and possibly viruses to enhance the efficiency of the disinfection
process. Chlorine was used as the disinfectant for the kill of viruses and
bacteria to meet the disinfection standards. Finally, the chlorinated
effluent was dechlorinated by the second-stage carbon contactor. The second-
stage carbon contactor was also designed to provide additional removal of
organics and viruses to assure the effluent free of viruses.
An identical design was used for both first-stage and second-stage car-
bon contactors. As shown in Figure 16, the carbon contactor was a steel tank
measuring 1.8 m (6 ft) in diameter and 4.9 m (16 ft) in height. Carbon depth
in the contactor was about 2.9 m (9.5 ft). Sampling taps were provided at
various depths of the contactor. Both contactors were coated with corrosion-
inhibiting bitumastic coal-tar epoxy coating. The Calgon Filtrasorb 300,
with 8 x 30 mesh size, granular activated carbon was used in the first-stage
carbon contactor, while the finer Calgon Filtrasorb 400, with 12 x 40 mesh
size, granular activated carbon was used in the second-stage carbon contac-
tor. Table 10 shows the average characteristics of the virgin Filtrasorb 300
and Filtrasorb 400 granular activated carbons.
A Wallace and Tiernan chlorinator was used to control the chlorine dos-
age. The chlorine was carried by tap water and the solution was mixed with
the first-stage carbon effluent through a Venturi device. The chlorinated
water was then directed into a 45 m3 (12,000 gallons) steel chlorine contact
tank. The tank was well baffled to provide an actual detention time as close
to the theoretical detention time as possible. The tank was covered during
the pilot plant study.
Pilot Plant Operation
The pilot plant was operated continuously at an average flow of 12.6
I/sec (200 gpm). At this flow rate, the empty-bed detention time for both
first-stage and second-stage carbon contactors was approximately 10 minutes
each. The modal detention time in the chlorine contact tank was determined
to be about 45 minutes in a special dye tracer study.
The secondary effluent from the Pomona Water Reclamation Plant was first
pretreated with alum in the dosage range of 5 to 10 mg/1 and 0.1 mg/1 of
Calgon WT-3000 anionic polymer before being fed into the first-stage carbon
contactor. The carbon contactors were operated in a down-flow and pres-
surized mode. The chlorine dosage was maintained within the range of 10 to
20 mg/1 to provide an average total chlorine residual of 10 mg/1 to meet the
disinfection standards. The effluent of the second-stage carbon contactor
was monitored for the breakthrough of chlorine residual. At such time when
the chlorine breakthrough was detected, both contactor carbon media were
53
-------
FULL OPEN COVER
WITH 15" PORTHOLE
f
3WIWJ^_j.^Jt-J_fc.J W *-J lt "^'^^^
nnnnnnnnnnnn n^
ro o£} c» o o o
20-I" HOLES E
WASH
WATER
^ft
-
SURFACE WASH-
_____Q. :\
CARBON BED SURFACE-^y
;^|^::|KP'.i5|5x^5x?:?!x!x
iAMPLTNGl
NEVA CLO
CREEN
t-
6 FT
BOLT RING
INFLUENT
*- BACKWASH
CARBON
"CHARGE
CARBON
^DISCHARGE
-EFFLUENT
'BACKWASH
NOTE:
l'= 12"= 30.48cm
Figure 16. Schematic diagram of carbon contactor used In pilot study.
54
-------
TABLE 10. VIRGIN CARBON CHARACTERISTICS OF ACTIVATED CARBON USED IN PILOT STUDY
en
en
Carbon
characteristics
Iodine number, mg/g
Molasses number
Methylene blue no., mg/g
Apparent density, g/cm3
Ash, %
Mean particle dia., mm
Sieve analysis:
% retained on no.
8
10
12
14
16
18
20
30
40
Pan
Calgon Filtrasorb 300
(8 x 30 mesh)
984
222
271
0.484
5.5
1.6
4.2
16.3
25.7
18.7
16.8
10.2
4.9
2.6
0.6
Calgon Filtrasorb 400
(12 x 40 mesh)
1062
237
275
0.463
5.8
1.0
1.8
10.3
24.9
20.8
14.8
20.6
6.0
0.8
-------
thermally regenerated with a multiple hearth carbon regeneration system at
the Pomona Research Facility. The description and operation of the carbon
regeneration system were presented elsewhere (34).
The first-stage carbon contactor was equipped with an automatic flow and
backwash control. The interval of backwashing was controlled by a preset
total headloss of 138 kN/m2 (20 psi) in the contactor, and it was found to
vary between 10 and 18 hours, depending on the quality of secondary effluent.
The second-stage carbon contactor was backwashed manually once every two
weeks of operation.
Composite samples were collected daily at various process monitoring
points, as indicated in Figure 15, for general water quality analyses.
Special grab samples were also taken as often as necessary for the analyses
of chlorine residuals, total and fecal coliforms. All analyses were per-
formed according to the Standard Methods procedures. In addition, some virus
samples were also collected for monitoring the efficiency of virus removal
under this mode of treatment operation. The virus results are presented
elsewhere (35).
Results and Discussion
Water Quality Effects --
The average water qualities of the samples collected at various sampling
points during the study are presented in Table 11. The averages of the
total chlorine residuals and total coliforms were calculated with data ob-
tained from those sampling days when the total coliforms in the chlorinated
effluent were equal to or less than 2.2 MPN per 100 ml. Since the carbon
regeneration was conducted whenever the chlorine residual was detected in
the dechlorinated effluent, no chlorine residual was detected during normal
operations of the carbon dechlorination pilot plant. The other water quality
averages in Table 11 were based on data collected during the entire dechlori-
nation study.
As indicated in Table 11, the chemical and physical properties of the
dechlorinated effluent were substantially improved after the carbon adsorp-
tion process. The chlorine residuals were also effectively removed by the
activated carbon. The pH values of the dechlorinated effluent were only
slightly lower than those of pre-chlorination samples, and thus no pH adjust-
ment was found necessary to correct any unfavorable pH conditions.
Bacteriological Aftergrowth
As shown in Table 11 and Figure 10, total coliforms increased by about
two orders of magnitude in the carbon dechlorinated effluent. The pattern
of the gradual increase of total coliforms in the dechlorinated effluent with
respect to the carbon operation time seemed to be responsive to the buildup
of microorganisms in the carbon bed. Therefore, the bacteriological after-
growth observed in the carbon dechlorinated effluent was believed to be the
result of contamination by the growth of microorganisms in the carbon bed.
56
-------
TABLE 11. AVERAGE WATER QUALITIES DURING CARBON DECHLORINATION STUDY
Water quality
parameter
Median pH
Total COD, mg/1
Dissolved COD, mg/1
Color, units
Turbidity, FTU
Suspended solids, mg/1
Total chlorine residual, mg/1
Total coli forms, MPN/100 ml
Secondary
effluent
7.6
39
25
33
8.1
13
-_
First-
stage
carbon
effluent
7.4
20
16
15
2.3
3
--
3.04xlOs
Second-
Chlorinated stage
ef f 1 uent carbon
ef f 1 uent
7.3
13
10
4
2.1
2
10.7 ND
< 2.2 310
Notes: (1) ND = not detected (detection limit = 0.05 mg/1),
(2)
Based on 54 sets of data.
-------
Based on some limited amount of data on the fate of fecal conforms
through the carbon dechlorination contactor, similar aftergrowth of fecal
conforms was observed In the dechlorinated effluent.. The extent of after-
growth was about one order of magnitude Increase, which was about one-tenth
of the increase of total conforms.
Carbon Capacity for Dechlorination
Dechlorination by granular activated carbon was found to be very effec-
tive with respect to either free chlorine or chloramine residuals. The
removal seemed to be controlled primarily by the accumulated dosage of
total chlorine residual, instead of the instant loading level of total
chlorine residual. This would simplify the monitoring of residual chlorine
in the dechlorinated effluent. The detection of chlorine breakthrough seems
to be adequate for process monitoring.
The carbon capacity for dechlorination with 0.1 mg/1 residual chlorine
as control limit was found to vary between 0.19 kg and 0.22 kg of total
chlorine residual applied per kg of activated carbon in the dechlorination
contactor. The capacity was increased to approximately 0.27 kg of total
chlorine residual per kg of carbon when 0.5 mg/1 of chlorine residual was
used as a control limit for dechlorination. The regeneration of carbon did
not seem to create any significant effects on the carbon capacity for de-
chlorination. The dechlorination function of the carbon was not shown to
interfere with the functions of chemical oxygen demand and color removals by
the carbon.
With very limited data obtained with a small scale carbon dechlorination
system prior to this 12.6 I/sec (200 gpm) large scale study, the carbon
capacity was found to be slightly increased from an average of 0.17 kg to
0.21 kg of total chlorine residual applied per kg of activated carbon, if
carbon particle size was decreased from 8 x 30 mesh (Calgon Filtrasorb 300)
to 12 x 40 mesh (Calgon Filtrasorb 400). This finding was the reason for
selection of Filtrasorb 400 for this large scale carbon dechlorination pilot
plant study.
Chlorine Profile in Carbon Bed"
Figure 17 shows some typical chlorine residual profiles for the de-
chlorination carbon contactor on a semi-log plot. To a first approximation
each 30 cm (1 ft) of carbon bed near the upstream end removed about 20
percent of the total chlorine residuals from the water entering it. The
removal rate was increased to approximately 30 percent every 30 cm (1 ft) of
carbon bed near the downstream end of the contactor.
Table 12 compares chlorine residual profiles taken when free chlorine
was detected in the influent to the chlorine contactor with similar profiles
taken on two days (9/24/74 and 10/1/74) when the influent showed only
a combined chlorine residual. As indicated in Table 12, the "monochloramine
residual" was removed more rapidly than the "dichloramine residual" on those
"free chlorine day" profiles. The "dichloramine residual" was found to
decline slowly with no sharp drop to zero. This seems to support the theory
58
-------
50.00
10.00 -
0"
E
LU
z
cc
3
o
o
en
UJ
cc
5.00 -
3 3/5/74 - Ib. Cl/lb. C = 0.09
A 3/19/74- Ib. Cl/ Ib. C = 0.1 8
3/26/74- Ib.CI/ Ib. C - 0.2 I
Iff. = 0.305m
Mb. CI/lb.C= IkgCI/kgC
ZERO CHLORINE RESIDUAL
0.10
234567
DEPTH IN CARBON BED, ft.
Figure 17. Chlorine profile in dechlorination carbon contactor
59
-------
TABLE 12. CHLORINE PROFILES IN CARBON BED FOR DECHLORINATION
(Ti
O
Sampl 1 ng
date
8/27
9/ 3
Type of residual
chlorine (mg/1)
Free
Monochloramine
Dlchloramine
Trichloramine
Free
Monochloramine
Dlchloramine
Trichloramine
ChloMne
contactor
Inf.
9.2
0
2.4
0
5.2
0
2.0
4.6
Eff.
1.4
0
1.4
0
4.0
0
1.5
0.6
Depth
0
0
5.3
1.8
0
0
3.6
1.4
0
below top of carbon (ft)
1
0
0.4
0.6
0
0
0
0.5
0
3579
0000
0000
0.1 0.1 0.1 0.1
0000
0000
0000
0.4 0.3 0.2 0.1
0000
Second stage
carbon
ef f 1 uent
0
0
0.1
0
0
0
0.3
0
-------
TABLE 12. CHLORINE PROFILES IN CARBON BED FOR DECHLORINATION (Cont)
Sampling
date
10/ 8
10/29
Type of residual
chlorine (mg/1 )
Free
Monochloramine
Dichloramine
Trichloramine
Free
Monochloramine
Dichloramine
Trichloramine
Chlorine
contactor
Inf
8
1
1
10
1
1
0
.0
-
.9
.4
.5
.1
.2
. Eff.
0
7.2
1.8
0
0
1.2
1.2
0
Depth
0
0
7.2
0.3
0.7
3.9
0
1.6
0
below top of
1 3
0 0
1.1 0.3
0.6 0
0 0
0 0
0.2 0.1
0.8 0.5
0 0
5
0
0
0.2
0
0
0
0.3
0
carbon (ft)
7
0
0
0.2
0
0
0
0.1
0
9
0
0
0
0
0
0
0.1
0
Second stage
carbon
effluent
0
0
0
0
0
0
0.1
0
-------
TABLE 12. CHLORINE PROFILES IN CARBON BED FOR DECHLORINATION (Cont.)
01
r\>
Sampl 1 ng
date
ll/ 6
11/12
Type of residual
chlorine (mg/1)
Free
Monochloramine
Dichloramlne
Trichloramine
Free
Monochloramine
Dichloramine
Trichloramine
Chlorine
contactor
Inf.
7.3
0.5
1.9
2.1
6.4
0.4
2.4
0
Eff.
8.2
0.4
1.9
0
5.4
0.3
2.2
1.8
Depth
0
3.3
0.5
1.6
0
9.1
0.4
2.5
0.6
below top of carbon
1 3
0 0
0.5 0.1
1.0 0.7
0 0
0.7 0
0.1 0.1
1.5 1.3
0 0
5
0
0.1
0.4
0
0
0
0.9
0
7
0
0
0.4
0
0
0
0.1
0
(ft)
9
0
0
0.3
0
0
0
0.5
0
Second stage
carbon
effluent
0
0
0.3
0
0
0
0.5
0
-------
TABLE 12. CHLORINE PROFILES IN CARBON BED FOR DECHLORINATION (Cont)
CO
Sampling Type of residual
date chlorine (mg/1 )
11/20 Free
Monochloramine
Dichloramine
Trichloramine
9/24 Free
Monochloramine
Dichloramine
Trichloramine
Chlorine
contactor
Inf.
10.4
0.6
2.2
1.5
0
13.6
0.5
0
Eff.
8.9
0.6
2.0
1.8
0
12.8
0.4
0
Depth
0
8.9
0.4
1.7
1.2
0
12.4
0.4
0
below top of carbon (ft)
1
0
0.8
1.1
0
0
5.1
0
0
3
0
0.2
0.8
0
0
0
0
0
5
0
0.8
0.6
0
0
0
0.1
0
7
0
0
0.1
0
0
0
0
0
9
0
0
0.4
0
0
0
0
0
Second stage
carbon
effluent
0
0
0.2
0
0
0
0
0
-------
TABLE 12. CHLORINE PROFILES IN CARBON BED FOR DECHLORINATION (Cont)
Chlorine
Sampling
date
10/ 1
Type of residual
chlorine (mg/1)
Free
Monochloramine
Dichloramine
Trichloramine
contactor
Inf.
0
10.8
0.5
0
Eff.
0
11.3
0.5
0
Depth
0
0
11.3
0.6
0
below
1
0
4.4
0
0
top
3
0
0
0
0
of
5
0
0
0
0
carbon
7
0
0
0
0
(ft)
9
0
0
0
0
Second stage
carbon
effluent
0
0
0
0
Notes:
1) 1 ft = 0.305m
Sampling dates of 9/25 and 10/1 were for normal operating conditions without free
chlorine residual in the chlorine contactor Influent sample.
-------
of the formation of the persistent N-chlororganic nuisance residuals by the
free chlorine and the organic nitrogen compounds in the water. According to
White (13), the free chlorine could react with the organic nitrogen compounds
such as creatinine, and the product of such reaction would cause a false
"dichloramine" reading by the standard analytical procedure. Therefore,
premature chlorine breakthrough may occur in the presence of free chlorine
residual and organic nitrogen compounds. The bactericidal and toxic effects
of such nuisance residuals are still unknown.
Process Reliability
The variation of the total chlorine residuals for chlorinated and de-
chlorinated effluents during the first sequence of this pilot plant study are
illustrated in Figure 18. As indicated in the figure, the total chlorine
residuals of the chlorinated effluent fluctuated within a rather wide range
of 2.6 mg/1 to 15.1 mg/1. However, the chlorine residuals in the dechlori-
nated effluent appeared to remain consistently under the detection limit of
0.05 mg/1 throughout the entire sequence of operation. The sequence was
terminated after two consecutive samples showing detectable chlorine re-
siduals. Similar reliability was repeatedly demonstrated in other sequences
of pilot plant operations. Therefore, the carbon dechlorination process is
believed to be a very reliable process. The operation and monitoring of the
system were also observed to be quite straightforward.
Regeneration of Oech1 orination Carbon --
Typical results for the regeneration of the dechlorination carbon with
a multiple hearth furnace system are presented in Table 13. The operating
conditions of the furnace were maintained at the similar conditions normally
used for the regeneration of carbon for wastewater treatment. It is clear
from the results of the analyses of carbon characteristics that the dechlori-
nation carbon was effectively reactivated to its virgin qualities. This was
further supported by the fact that each sequence of operation produced a
similar carbon capacity for dechlorination. Therefore, it is believed that
the dechlorination carbon can be effectively regenerated with conventional
thermal processes, such as multiple hearth furnace, under normal operating
conditions.
65
-------
01
20
18
16
14
o»
E
ID
O
£ 12
to
UJ
o:
UJ
2
a:
3
O
8
r i i i
FIRST SEQUENCE OF OPERATIONS 6-1-73 TO 9-21-73
-CARBON EMPTY-BED CONTACT TIME5 10MINUTES
CHLORINATED EFFLUENT
8
L
-CARBON-DECHLORINATED EFFLUENT
16 24 32 40
CONSECUTIVE SAMPLING RUN, days
48
56
Figure 18. Chlorine residual of carbon-dechlon'nated effluent.
-------
TABLE 13. REGENERATION OF DECHLORINATION CARBON (CALGON FILTRASORB 400)
Carbon Characteristics
Iodine number, mg/9
Apparent density, g/cm3
Molasses number
Methylene blue no., mg/9
Ash, %
Sieve analysis:
% Retained on sieve No.
8
12
14
16
18
20
30
40
Pan
Virgin
carbon
723
0.456
206
358
8.1
0.1
2.0
34.3
21.4
13.0
19.8
8.4
1.0
Spent
carbon
composite
sample
625
0.512
287
142
12.9
1.2
5.7
24.7
23.6
17.4
22.6
4.4
0.4
Regenerated carbon composite sample
Dry
711
0.473
321
201
12.8
1.3
3.6
13.9
21.1
27.3
25.8
6.3
O.B
Quenched
695
0.458
375
163
12.9
1.1
5.1
21.7
22.9
17.6
24.3
6.8
0.5
-------
SECTION 7
PROCESS COST ESTIMATES
GENERAL
Cost estimates for three different dechlorination systems were prepared
using the information gathered in the study. These were the sulfur dioxide,
holding pond (estimate was made for pond instead of tank for practical
application), and activated carbon adsorption dechlorination systems. In
deriving the cost estimates, three levels of total chlorine residuals were
used to cover a wider spectrum for meeting different disinfection standards
in the nation. All the costs were based on meeting the 0.05 mg/1 or less
dechlorination requirement for maximizing the protection of aquatic life.
Three plant sizes of 43.8 I/sec (1 mgd), 219 I/sec (5 mgd) and 438 I/sec
(10 mgd) were used in preparing the cost estimates for the various dechlori-
nation processes. The process cost based on unit volume of processed water
is believed to approach a leveling off value with plant size larger than 438
I/sec (10 mgd). Therefore, tne three plant sizes used in these cost esti-
mates may provide a general picture of the cost ranges for the three de-
chlorination processes investigated in this study.
An 8 percent interest rate was used for calculating the capital amortiza-
tion cost for all three decMorination processes. However, different amor-
tization periods were used for different processes. The specific amortiza-
tion periods used for the sulfur dioxide, holding pond and activated carbon
adsorption dechlorination processes are 15, 30, and 20 years, respectively.
The types and durabilities of the different structures normally used for the
different dechlorination process plants have been considered in making the
selection of an appropriate amortization period for each process cost es-
timate.
SULFUR DIOXIDE DECHLORINATION
Cost estimates for the sulfur dioxide dechlorination process under
various operating and design conditions are summarized in Tables 14, 15, and
16. The sulfur dioxide to residual chlorine (SO? : Cl?) dosage ratio was
assumed to be 2 to 1 in the preparation of the cost estimates. No costs for
pH adjustment and post dechlorination aeration were included in the process
cost estimates, since these were not considered necessary for the dechlori-
nation of domestic wastewater effluent.
68
-------
TABLE 14. SUMMARY OF SULFUR DIOXIDE DECHLORINATION COSTS
PLANT SIZE = 43.8 I/sec (1 mgd)
Cost Parameter
Capital costs ($)
SOa mixing & contact system
SOa feeding & control system
SOa handling & storage system
Sub- total
Electrical (10%)
Sub- total
Contingencies (20%)
Sub- total
Engineering (15%)
Total capital
Capital amortization U/m3)
O&M costs (t/m3)
S02 supply
Power
Labor
Maintenance materials
Water for S02 solution
Total O&M
Total process cost U/m3)
Influent residual chlorine
0.5
2,000
12,000
5.000
19.000
1,900
20,900
4.180
25,080
3.760
28.840
0.24
0.03
0.05
0.53
0.08
0.03
0.72
0.96
5
2,000
20,000
5.000
27,000
2.700
29,700
5,940
35,640
5.350
40,990
0.35
0.26
0.05
0.53
0.11
0.03
0.98
1.33
, mg/1
10
2,000
25,000
30.000
57,000
5,700
62,700
12,540
75,240
11,290
86,530
0.73
0.55
0.05
0.53
0.24
0.03
1.40
2.13
69
-------
TABLE 15. SUMMARY OF SULFUR DIOXIDE OECHLORINATION COSTS
PLANT SIZE = 219 I/sec (5 mgd)
Cost parameter
Capital costs ($)
SO: mixing & contact system
SOz feeding & control system
S02 handling & storage system
Sub- total
Electrical (10%)
Sub- total
Contingencies (20%)
Sub- total
Engineering (15%)
Total capital
Capital amortization (4/m3)
Q&M costs (
-------
TABLE 16. SUMMARY OF SULFUR DIOXIDE DECHLORINATION COSTS
PLANT SIZE = 438 I/sec (10 mgd)
Cost parameter
Capital costs ($)
502 mixing & contact system
SOz feeding & control system
SOz handling & storage system
Sub- total
Electrical (10%)
Sub-total
Contingencies (20%)
Sub-total
Engineering (15%)
Total capital
Capital amortization U/m3)
O&M costs (
-------
A detention time of 10 seconds was provided In the sulfur dioxide mixing
and contact system to facilitate the complete reactions between sulfur
dioxide and chlorine residual species. A mixer to provide an average of 2.0
kW (2.7 hp) per cubic meter of mixing volume was included in the cost es-
timate. A minimal labor of 2 hours per day was assumed for the operation and
maintenance of the dechlorination system for all three sizes of plants.
As indicated in Tables 14 through 16, the total process cost estimates
range from 0.23 cents/m3 (0.87 cents/1000 gal) to 2.13 cents/m3 (8.06 cents/
1000 gal), depending on the size of plant and concentration of influent
chlorine residual. The effects of these factors on the process cost esti-
mates are illustrated in Figure 19. The cost curves indicate that the
process costs for sulfur dioxide dechlorination approach minimum levels when
the plant sizes are larger than 438 I/sec (10 mgd).
HOLDING POND DECHLORINATION
According to Figure 14, the necessary detention times for dissipation of
0.5, 5 and 10 mg/1 total influent chlorine residuals in a holding pond are
approximately 9.6, 96 and 192 hours, respectively. In the cost estimates, a
water depth of 1.83 m (6 ft) was assumed for the pond construction. A layer
of 10 cm (4 in) gravel lining was provided for the holding pond. Table 17
summarizes the cost estimates for various operating conditions for the
holding pond dechlorination process. The associated unit costs for operation
and maintenance are listed in Table 18. The daily labor required for opera-
tion and maintenance was assumed to be 2 hours for 43.8 I/sec (1 mgd) plant
and 4 hours for both 219 I/sec (5 mgd) and 438 I/sec (10 mgd) plants.
As indicated in Table 17, the total process costs for holding pond de-
chlorination process range from 0.22 cents/m3 (0.83 cents/1000 gal) to 2.58
cents/m3 (9.77 cents/1000 gal). The proportion of the capital amortization
cost to the total process cost is as high as 95 percent for the case of 10
mg/1 chlorine residual in a 438 I/sec (10 mgd) plant. Table 19 was prepared
to demonstrate the effects of major capital items, such as land, excavation
and lining costs, on the capital amortization costs. The table indicates
that the total capital amortization cost for a 438 I/sec (10 mgd) plant with
10 mg/1 influent chlorine residual can be reduced from 2.02 cents/m3 (7.65
cents/1000 gal) to 0.30 cents/m3 (1.14 cents/1000 gal), an 85 percent reduc-
tion, depending on land and construction conditions.
CARBON ADSORPTION DECHLORINATION
The following general operating conditions were assumed in making the
various cost estimates for the carbon adsorption dechlorination process:
1. Carbon capacity for dechlorination = 0.2 kg chlorine residual per kg
of carbon (0.2 Ib Cl2/lb carbon).
2. Carbon regeneration loss = 7 percent per regeneration.
72
-------
CO
2.5
10
E2.0
§
1.5
U
en
8 '-°
cc
Q.
PLANT SIZE, mgd
456
8
EFFLUENT CHLORINE RESIDUAL
58 0.05 mg/l
INFLUENT CHLORINE RESIDUAL
10.0 mg/l
* - 5.0 mg/l
« 0.5 mg/l
10
I
I
L
I
I-
L
9.0
IA
8.01
o
7.0§
o
5.0 §
4.0
3-0 g
u
50 100 150 200 250 300
PLANT SIZE, I/sec.
350
400
450
2.0
1.0 <
o
O1"
Figure 19. Process cost curves for sulfur dioxide dechlorination.
-------
TABLE 17. PROCESS COST ESTIMATES FOR HOLDING POND DECHLORINATION
Plant
size
(mgd)
1
s
10
Residual
chlorine
(ng/0
0 5
5
10
0 5
S
10
0.5
S
10
Pond
VOllBB
(1000 ft')
53
533
1.067
267
2.672
5.329
533
5 .329
10.672
Land
area
(acre)
0 4
4.1
8.4
2.1
20.8
41.6
4.1
41.6
83.3
Land
cost
(1000$)
B
82
168
42
416
832
82
832
1.666
Excavation
a
hauling
cost
(IOOOS)
3.5
31.7
63.3
17.8
158.0
296.5
31.6
296.5
592.8
Lining
cost
(1000$)
4.4
43.6
87.1
21.8
217.7
435.4
43 6
435.4
870.6
Piping
I
other
cost
(1000$)
5.0
5.0
5.0
10.0
10 0
10.0
15.0
15 0
15.0
Total
capital
cost
(1000$)
20.9
162.3
318.4
81.6
801.7
1.573.9
172.2
1.573.9
3.144.4
Capital
anrtt-
zatlon
0.13
1.04
2.05
0.10
1.03
2.02
0.11
1.01
2.02
Process cost estlwte
«/')
Operation
I
nalnte nance
0.53
0.53
0.53
0.21
0.21
0.21
0.11
0.11
0.11
Total
process
cost
0.66
1.57
2.56
0.31
1.24
2.23
0.22
1.12
2.13
Notes. 1 ugd = 43.3 I/sec; 1.000 ft1 - 28.3 '; 1 acre - 0.405 ha.
-------
TABLE 18. UNIT COSTS FOR OPERATION AND MAINTENANCE COST ESTIMATES
Sulfur dioxide
Activated carbon
$/lb
$/lb
0.13
0.75
Power
Fuel
Backwash water
Water supply
Labor
Excavation & hauling
Lining cost (gravel)
4/kWh 5.0
4/therm 18.0
,000 gallons 3.0
,000 gallons 60.0
$/hr 10.0
$/yd3
<1,000 yd3 2.0
1,000 ^ 10,000 yd3 1.8
10,000 * 100,000 yd3 1.6
<100,000 yd3 1.5
4/ft2 20.0
Notes: 1 Ib = 0.454 kg;
1 gal = 3.785 1;
1 yd3 = 0.765 m3;
1 therm = 105,500 kJ;
1 acre = 0.405 ha;
1 ft2 = 0.093 m2;
75
-------
TABLE 19. EFFECTS OF COST PARAMETERS ON CAPITAL AMORTIZATION
FOR HOLDING POND DECHLORINATION PROCESS
Plant
size
(mgd)
1
5
10
Residual
chlorine
(mg/1)
0.5
5
10
0.5
5
10
0.5
5
10
Capital
Case 1
0.13
1.04
2.05
0.10
1.03
2.02
0.11
1.01
2.02
Amortization
cost,
Case 2 Case 3
0.09
0.56
1.12
0.07
0.54
1.06
0.06
0.52
1.06
0.06
0.28
0.55
0.03
0.26
0.51
0.04
0.24
0.49
-------
3. Fuel consumption In carbon regeneration = 9,280 kJ per kg of carbon
regenerated (4,000 BTU/lb carbon).
4. Power consumption = 80 kWh Per 1,000 m3 (300 kWh per million gallons).
5. Carbon empty-bed contact time = 10 minutes.
6. A multiple hearth furnace with afterburner and Venturi wet scrubber
air pollution control system was used as carbon regeneration system.
7. Gravity concrete tank was used as carbon contact system.
8. The annual labor ranges from 4,360 hours to 7,240 hours depending
on the operating conditions.
9. Calgon Filtrasorb 400 granular activated carbon was used.
Tables 20 through 22 are the summaries of the cost estimates for carbon
adsorption dech1 orination process. The total process costs range from 2.91
cents/m3 (11.01 cents/1000 gal) to 11.10 cents/m3 (42.01 cents/1000 gal)
as indicated in the tables.
COST COMPARISONS
The cost estimates for sulfur dioxide, holding pond and carbon adsorp-
tion dechlorination processes are summarized in Table 23. As indicated in
both Table 23 and Figure 20, the carbon adsorption dechlorination process is
estimated to be substantially more expensive than the other two processes in
all cases. Therefore, the carbon adsorption process seems to be economically
unfeasible for being used solely for meeting a dechlorination requirement.
However, the carbon adsorption process may be considered as a potentially
cost-effective treatment process when removal of trace organics and dechlori-
nation are required at the same time.
The holding pond and sulfur dioxide dechlorination process are competi-
tive for various size plants with low influent chlorine residuals, as in-
dicated in Table 23. The holding pond dechlorination becomes more cost-
effective than sulfur dioxide dechlorination process when inexpensive land
can be obtained and simpler pond construction can be allowed. The presence
of good sunlight is also considered an important criterion for successful use
of holding pond dechlorination process. Considerable savings in operating
and maintenance costs are also obtainable with the holding pond dechlori-
nation process. Figure 21 compares the sulfur dioxide with the holding pond
dechlorination process under various cost alternatives as described in Table
19.
Under normal conditions, the sulfur dioxide dechlorination is believed
to be the most cost-effective process for meeting the effluent residual
chlorine standards. This is believed to be especially true for the State
of California where the land cost is very expensive and the bacterial
standards are very stringent.
77
-------
TABLE 20. SUMMARY OF CARBON ADSORPTION DECHLORINATION COSTS
PLANT SIZE = 43.8 I/sec (1 mgd)
Cost parameter
Capital costs ($)
Pumping & piping system
Initial carbon charge
Carbon contacting system
Carbon regeneration system
Sub- total
Electrical (10%)
Instrumentation (5%)
Sub-total
Contingencies (20%)
Sub- total
Engineering (15%)
Total capital
Capital amortization (
-------
TABLE 21. SUMMARY OF CARBON ADSORPTION DECHLORINATION COSTS
PLANT SIZE = 219 I/sec (5 mgd)
Cost parameter
Capital cost (S)
Pumping & piping system
Initial carbon charge
Carbon contacting system
Carbon regeneration system
Sub-total
Electrical (10%)
Instrumentation (5%)
Sub-total
Contingencies (20%)
Sub-total
Engineering (15%)
Total capital
Capital amortization (
-------
TABLE 22. SUMMARY OF CARBON ADSORPTION DECHLORINATION COSTS
PLANT SIZE = 438 I/sec (10 mgd)
Cost parameter
Capital costs ($)
Pumping & piping system
Initial carbon charge
Carbon contacting system
Carbon regeneration system
Sub- total
Electrical (1055)
Instrumentation (5%)
Sub- total
Contingencies (20%)
Sub-total
Engineering (155S)
Total capital
Capital amortization U/m3)
O&M costs (
-------
TABLE 23. SUMMARY OF DECHLORINATION PROCESS COST ESTIMATES
oo
Plant size Residual
chlorine Cost item
(mgd) mg/1
Capital
0.5 O&M
Total
Capital
1 5 O&M
Total
Capital
10 O&M
Total
Sulfur dioxide
U/m3)
0.24
0.72
0.96
0.35
0.98
1.33
0.73
1.40
2.13
Molding pond
U/m3)
0.13
0.53
0.66
1.04
0.53
1.57
2.05
0.53 -
2.58
Carbon adsorption
U/m3)
3.43
3.90
7.33
4.84
4.78
9.62
5.41
5.69
11.10
-------
TABLE 23. SUMMARY OF DECHLORINATION PROCESS COST ESTIMATES (Cont.)
r" 21*- size Residual
chlorine Cost Item
(mgd) mg/1
Capital
0.5 O&M
Total
Capital
5 5 O&M
Total
Capital
10 O&M
Total
Sulfur dioxide
U/m3)
0.08
0.25
0.33
0.15
0.50
0.65
0.17
0.79
0.96
Holding pond
U/m3)
0.10
0.21
0.31
1.03
0.21
1.24
2.02
0.21
2.23
Carbon adsorption
U/m3)
2.49
1.30
3.79
3.07
1.72
4.79
3.42
2.18
5.60
-------
TABLE 23. SUMMARY OF DECHLORINATION PROCESS COST ESTIMATES (Cont.)
oo
to
Plant size Residual
chlorine Cost item
(mgd) mg/1
Capital
0.5 O&M
Total
Capital
10 5 O&M
Total
Capital
10 O&M
Total
Sulfur dioxide
U/m3)
0.04
0.19
0.23
0.09
0.42
0.51
0.10
0.71
0.81
Holding pond
U/m3)
0.11
0.11
0.22
1.01
0.11
1.12
2.02
0.11
2.13
Carbon adsorption
U/m3)
1.92
0.99
2.91
2.15
1.35
3.50
2.27
1.78
4.05
Note: 1 mgd = 43.8 I/sec.
-------
10
0)
o
H3
CO
o
o
(O
o
PLANT SIZE = 488 I/sec. (10 mgd)
EFFLUENT CHLORINE RESIDUALS 0.05 mg/|
-CARBON ADSORPTION
HOLDING POND
-SULFUR DIOXIDE
468
INFLUENT CHLORINE RESIDUAL, mg/l
10
18
16
14 01
O
O
O
10 o
al
<
is
12
Figure 20. Process cost comparison among different dechlorination processes.
-------
2.5
oo
CJl
2.0
E
>K
(A
CO
8
1.5
UJ
8 i.o
0.5
PLANT SIZE= 438 I/sec. UOmgd)
EFFLUENT CHLORINE RESIDUAL
HOLDING POND
-« SULFUR DIOXIDE
O.O5mg/l
'CASE I
8.0
8
O
6.0
4.0
en
o
u
CO
CO
UJ
8
2.0 <
468
INFLUENT CHLORINE RESIDUAL, mg/l
10
12
Figure 21. Cost comparison between sulfur dioxide and holding pond dechlorination
processes under different cost assumptions as described in Table 19.
-------
REFERENCES
1. Zillich, J.A., "Toxicity of Combined Chlorine Residuals to Freshwater
Fish." Jour. WPCF, 44(2): 212 (1972).
2. Arthur, J.W., Andrew, R.W., Mattson, V.R., Olson, D.T., Glass, G.E.,
Halligan, B.J. and Walbridge, C.T., "Comparative Toxicity of Sewage
Effluent Disinfection to Freshwater Aquatic Life." EPA-600/3-75-012
(1975).
3. Brungs, W.A., "Effects of Residual Chlorine on Aquatic Life." Jour.
WPCF, 45: 2180 (1973).
4. Ward, R.W., Giffin, R.D., DeGraeve, G.M. and Stone, R.A., "Disinfection
Efficiency and Residual Toxicity of Several Wastewater Disinfectants.
Volume I Grandville, Michigan." EPA-600/2-76-156 (1976).
5. "Quality Criteria for Water." U.S. EPA (1976).
6. Robson, C.M., Hyatt, C.S., Jr., and Banerji, S.K., "We Must Improve
Chlorination Design." Water and Wastes Engineering, 12:61 (1975).
7. "Waste Discharge Requirements for County Sanitation Districts of
Los Angeles County (District 21-Pomona Water Renovation Plant)." Order
No. 76-78, Los Angeles Region, California Regional Water Quality
Control Board, Los Angeles, California 90012 (1976).
8. Howard, N.J. and Thompson, R.E., "Chlorine Studies on Taste Producing
Substances in Water and Factors Involved in Treatment by Super
Chlorination - Dechlorination Method." Jour. NEWWA, 40:276 (1976).
9. Olson, L.L. and Binning, C.D., "Design of Activated Carbon Adsorbers
for Aqueous Chlorine Removal Based on the Mechanism of Removal." Pre-
sented in ACS Meeting, Chicago, Illinois (August, 1973).
10. Baker, R.A., "Dechlorination and Sensory Control." Jour. AWWA, 56:1578
(1964).
11. Basch, R.E. and Truchan, J.G., "Calculated Residual Chlorine
Concentrations Safe for Fish." Interim Report, Michigan Water Resources
Commission, Department of Natural Resources, Lansing, Michigan (1973).
86
-------
REFERENCES (Cont.)
12. Brooks, A.S. and Seegert, G.L., "The Toxicity of Chlorine to Freshwater
Organisms under Varying Environmental Conditions." Proceedings of the
Conference on the Environmental Impact of Water Chlorination, Oak Ridge,
Tennessee (October, 1975).
13. White, G.C., Handbook of Chlorination, Van Nostrand Reinhold Co.,
New York (1972).
14. Williams, O.B., "Control of Free Residual Chlorine by Ammoniation."
Jour. AWWA, 55: 1195 (1963).
15. White, 6.C., "Chlorination and Dechlorination: A Scientific and
Practical Approach." Jour. AWWA, 60:540 (1968).
16. Cassel, A.F., Pressley, T.A., Schuk, W.W. and Bishop, D.F., "Physical -
Chemical Nitrogen Removal from Municipal Wastewater." Report prepared
for U.S. Environmental Protection Agency (1971).
17. Bauer, R.C. and Snoeyink, V.L., "Ammonia Removal by Chlorination
Followed by Contact with Activated Carbon." Central States Water
Pollution Control Association Meeting, Milwaukee, Wisconsin (1973).
18. Atkins, P.F., Jr., Scherger, O.A. and Barnes, R.A., "Ammonia Removal in
a Physical - Chemical Wastewater Treatment Plant." Presented at the
27th Purdue Industrial Waste Conference (1972).
19. Coughlin, R.W., Ezra, F. and Tan, R.N., "Influence of Chemisorbed
Oxygen in Adsorption onto Carbon from Aqueous Solution." Jour.
Colloid Interface Science, 28:386 (1968).
20. Puri, B.R., Singh, 0.0. Chandler, J. and Sharma, L.R., "Interaction
of Charcoal with Chlorine Water." Jour. Ind. Chem. Soc., 35:181 (1958).
21. Magee, V., "The Application of Granular Active Carbon for Oech1 orination
of Water Supplies." Proc.- Soc. Water Treat. Exam., 5:17(1956).
22. Beebe, R.D., "Malibu Plant Simulation Study." Technical Monthly Report,
Sanitation Districts of Los Angeles County, Whittier, California
(September, 1973).
23. Snoeyink, V.L. and Markus, F.I., "Chlorine Residuals in Treated
Effluents." Report to Illinois Institute for Environmental Quality,
Chicago, Illinois (August, 1973).
24. Katz, B.M., "Chlorine Dissipation and Toxicity Presence of Nitrogenous
Compounds." Jour. WPCF, 49:1627 (1977).
25. Gan, H., "Malibu Plant Simulation Study." Technical Monthly Report,
Sanitation Districts of Los Angeles County, Whittier, California
(August, 1972).
87
-------
REFERENCES (Cont.)
26. Schelble, O.K., Blnkowskl, G. and Mulligan, T.J., "Full Scale Evaluation
of Ultraviolet Disinfection of a Secondary Effluent," in "Progress in
Wastewater Disinfection Technology," A.D. Venosa, ed. EPA-600/9-79-018
(June 1979).
27. Tracy, H.W., Camarena, V.M. and Wing, F., "Coliform Persistence in
Highly Chlorinated Waters." Jour. AWWA, 58:1151 (1966).
28. Heufeelekian, H., "Disinfection of Sewage with Chlorine: IV Aftergrowth
of Coliform Organisms in Streams Receiving Chlorinated Sewage." Sewage
and Industrial Wastes, 23:273 (1951).
29. Eliassen, R., "Coliform Aftergrowths in Chlorinated Storm Overflows."
Journal of the Sanitary Engineering Division, Proceedings of ASCE,
94(SA2): 371 (1968).
30. Kittrell, F.W. and Furfari, S.A., "Observations of Coliform Bacteria
in Streams." Jour. WPCF, 35:1361 (1963).
31. "Standard Methods for the Examination of Water and Wastewater." 14th
ed., APHA, New York (1975).
32. Kenner, B.A., and Clark, H.P., "Detection and Enumeration of Salmonella
and Pseudomonas aeruginosa." Jour. WPCF, 46:2163 (1974).
33. Venosa, A.D., Opatken, E.J., and Meckes, M.C., "Comparison of Ozone
Contactors for Municipal Wastewater Effluent Disinfection." EPA-600/2-
79-098 (1979).
34. Van Sluis, R.J. and Ycmko, W.A., "The Fate of Salmonella sp Following
Dechlorination of Terttary Sewage Effluents." Interdepartmental Report,
County Sanitation Districts of Los Angeles County, Whittier, California
90607 (1978).
35. Directo, U.S., Chen, C. and Miele, R.P., "Two-Stage Granular Activated
Carbon Treatment." EPA-600/2-78-170 (1978).
36. Beebe, R.D., "Malibu Plant Simulation Study." Technical Monthly Report,
Sanitation Districts of Los Angeles County, Whittier, California (July,
1973).
88
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APPENDIX. DECHLORINATION FIELD SURVEY QUESTIONNAIRE
SULFUR DIOXIDE DECHLORINATION FIELD SURVEY
Conducted By
County Sanitation Districts of Los Angeles County
Under
U. S. EPA Contract No. 14-12-150
I. General Information:
(a) Name of Agency
Person Replying to Questionnaire .
Title Phone.
Address
(b) Name of Treatment Plant.
Address
Plant Type: Primary [ ] Secondary [ ] Tertiary [ ] Ponds [ )
Plant Flow (mgd). Minimum Daily Maximum Daily .
Average Daily Design Capacity .
(c) Discharge Standard: Total Coliform (MPN/100 ml)
Total Chlorine Residual (mg/l)
(d) Sulfur Dioxide Capacity (Ibs/day) No. of Sulfonators .
Startup Date Construction Cost
II. Engineering Design Information
(a) Firm Designing Dechlormation System.
Address
Design Engineer Phone
(b) SO2 Feed Control System (please provide drawings)
Equipment Manufacturer- W/T [ ] F/P [ ] Others (specify)
89
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APPENDIX. DECHLORINATION FIELD SURVEY QUESTIONNAIRE (CONT.)
II. (Continued)
(b) Feedforward [ 1 Feedback [ ) Others (specify)
Flow Paced [ ] Residual Control [ ]
Flow and Residual Control [ 1
Flow Signal: Pneumatic [ ] Electric ( ]
Dosage Signal: Pneumatic [ 1 Electric ( ]
Residual Controller: Gap [ ] Proportional and Reset [ ] None [ ]
Multiplier: Yes I ] No [ 1 Adiustable Slope Factor Yes [ ] No [ 1
No. of Analyzers Manufacturer
Analyzer Range (as mg/l C12 Residual)
Analyzer Sampling Points ^_^_^^^^^^^^^_^^^_^_^__^_^^^^
Lagtime (mms.) Flow Meter Location .
What is the most unique feature of your feed control design?
(c) S02 Mixing Chamber Yes [ I No [ ] Detention Time (mins.).
SO2 Injection Device: Diffuser I ] Others (specify)
S02 Mixer Type Mechanical [ ] Hydraulic Jump [ ]
Parshall Flume [ I None ( ]
Reaeration- Yes [ ] No [ 1 pH Adjustment- Yes [ 1 No [ ]
(d) Why did you decide on SO2 for dechlormation?
III. Operational Information
(a) Is dechlormation system operated daily (24 hours/day)'
Yes [) No ( ]
90
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APPENDIX. DECHLORINATION FIELD SURVEY QUESTIONNAIRE (CONT.)
III. (Continued)
(b) Is overdosing of SO, commonly employed to meet residual discharge standard?
Yes [ 1 No (I Please explain
(c) What is the SO2/C12 (Ib/lb) ratio requirement of the plant?.
(d) How much SO2 dbs) does your plant use monthly'
(e) Is the SOj feed control system reliable? Yes [ ] No [ 1
Please explain
(f) Will the SO2 feed control system handle drastic changes m chlorine residual due to plant
upset or equipment malfunction? Yes [ ) No [1
Please explain
(g) Who calibrates the chlorine residual analyzer' Operator [ ] Chemist [ ] Others
(specify)
By what method? Amperometric Titration ( ] Starch Iodide [ ]
Colonmetric OT [ ] Or DPD ( ] Forward Titration [ ] Back Titration [ ]
(h) Do you have analyzer charts of residual chlorine before and after dechlormation available for
inspection? Yes I ] No [ 1
(i) Is there any unusual biological growth after dechlormation or slime buildup in outfall pipe'
Yes [ ] No ( ]
(|) Is your plant open for a visit' Yes [ ] No [ 1
IV. Water Quality Data: Weekly [ I Monthly I 1 Yearly ( 1
91
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APPENDIX. DECHLORINATION FIELD SURVEY QUESTIONNAIRE (CONT.)
Parameter
Total C1 2 Res., (mg/1)
Total Coliform (MPN/100 ml)
pH
Dissolved Oxygen (mg/1)
Alkalinity (mg/1)
TDS(mg/1)
End of Chlorine
Contact Tank
After SO2
Addition
After Aeration
and pH adjustment
V. Additional Comments:
Please return to: MR. John 0. Parkhurst
Chief Engineer and General Manager
County Sanitation Districts of Los Angeles County
Pomona Research Facility
295 Humane Way
Pomona California 91766
Attention: Mr. Henry B. Ghan
Project Engineer
92
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