svEPA
United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
EPA-600/2-78-029
March 1978
Research and Development
Full-scale Demonstration
of Nitrogen Removal
by Breakpoint Chlorination
Environmental Protection
Technology Series
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecotogical Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
-------
EPA-600/2-78-029
March 1978
FULL-SCALE DEMONSTRATION OF NITROGEN REMOVAL
BY BREAKPOINT CHLORINATION
by
Richard W. Stone
Sacramento Area Consultants
Sacramento, California 95814
for
Sacramento Regional County Sanitation District
Sacramento, California 95827
EPA Grant No. S-803343-01-0
Project Officers
James J. Westrick
Francis L. Evans III
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
-------
DISCLAIMER
This report has been reviewed by the Municipal Environmental
Research Laboratory, U.S. Environmental Protection Agency, and
approved for publication. 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.
-------
FOREWORD
The Environmental Protection Agency was created because of
increasing 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 testimony
to the deterioration of our natural environment. The complexity
of that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in
problem solution and it involves defining the problem, measuring
its impact, and searching for solutions. The Municipal Environ-
mental Research Laboratory develops new and improved technology
and systems for the prevention, treatment, and management of
wastewater and solid and hazardous waste pollutant discharges
from municipal and community sources, for the preservation and
treatment of 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 research; a most vital cpmmunications link between the
researcher and the user community.
This report summarizes the results of a demonstration
program which was carried out to establish design and operating
criteria for breakpoint chlorination nitrogen removal systems
for use in municipal wastewater treatment applications. The
development and demonstration of such processes provides addi-
tional tools for use by water pollution control agencies in
their efforts to maintain and enhance the quality of the
environment.
Francis T. Mayo, Director
Municipal Environmental Research Laboratory
Xll
-------
ABSTRACT
This work constitutes the first large-scale demonstration of
breakpoint chlorination for removal of ammonia nitrogen from
municipal wastewater. The report includes a discussion of
breakpoint chlorination process chemistry, an evaluation of
chemical consumption, and recommendations for process control.
Breakpoint chlorination can occur in wastewater effluents
following addition of sufficient chlorine for the oxidation of
ammonia nitrogen tor principally, nitrogen gas. Theoretically,
7.6 mg/1 of chlorine are required for the conversion of 1.0 mg/1
of ammonia nitrogen to nitrogen gas. In the breakpoint
chlorination process evaluation at Rancho Cordova, an average
dosage of 10 mg/1 chlorine was required for the conversion of
1.0 mg/1 ammonia nitrogen to nitrogen gas. The difference
between theoretical and actual chlorine dosages was found to be
largely due to chlorine consumption from the oxidation of
ammonia nitrogen to nitrate nitrogen, a competing side reaction
with a less desirable end product. Overall, about 96 percent of
the chlorine dosed to the Rancho Cordova system was accounted
for in reactions between chlorine and nitrogenous specias in
specific, identified chemical pathways, and free chlorine
residual remaining in solution following breakpoint.
Tests with mechanical mixing devices showed that mixing
intensity at the point of chemical addition had little effect on
chemical consumption and efffluent quality. The rate of the
breakpoint reaction was found to vary depending upon the system
pH, with fastest rates at a pH of 7.0. At pH 7.0, about 60 sec
to 90 sec elapsed between chemical addition and completion of
the chemical reactions. The Rancho Cordova evaluation showed
that the process requirement for alkalinity supplementation (pH
control) was almost 'exactly equal to that predicted from the
chemical stoichiometry. A compound loop control strategy was
recommended for dosage control of chlorine and alkalinity
supplement.
This report was submitted in fulfillment of Grant
No. S-803343-01-0 by Sacramento Area Consultants for the
Sacramento Regional County Sanitation District. The project
was carried out under the sponsorship of the U.S. Environmental
Protection Agency. This report covers work completed as of
June 30, 1977.
xv
-------
CONTENTS
Foreword ........ .... iii
Abstract iv
Figures vii
Tables viii
1. Introduction • • 1
2. Conclusions 2
3. Chemistry of the Breakpoint
Chlorination Process 5
Chemistry of ammonia in water 5
Chemistry of chlorine in water 6
Formation of chloramines 6
The breakpoint reaction 7
The breakpoint curve 8
Other reactions encountered in
breakpoint chlorination 9
pH and Alkalinity Considerations 10
4. Experimental Methods . 13
Breakpoint Chlorination Facilities 13
Control and Monitoring Equipment 17
Free chlorine residual analyzer. ... 17
Ammonia nitrogen analyzer 18
pH monitor . 18
Laboratory Testing Procedures 18
Ammonia nitrogen (NH3 -N) 19
Nitrate nitrogen (N0~ -N). . . . . . .19
Chlorine species 19
5. Results and Discussion 20
Process Influent Characteristics 20
Initial Mixing 20
Reaction Rates i . 22
Nitrogenous Residuals . . 27
Nitrogen trichloride ... 27
Nitrate 29
Organic nitrogen 30
Overall Chlorine Consumption 30
Alkalinity Supplementation 31
Chlorine Injector Water
Considerations .32
Breakpoint Model Predictions 34
6. Process Control 35
Process and Component Descriptions. . . . . 35
Ammonia analyzer .35
Flowmeter 36
v
-------
Contents (continued)
6. Process Control (continued)
Chlorinators 36
Free chlorine analyzer 38
pH analyzer 39
Sodium hydroxide feeder 39
Control Requirements 39
Control Systems . 40
Simple feedback control 40
Simple feedback plus flow paced
control . 44
Flow modified feedback control
plus flow paced control 46
Ammonia nitrogen mass flow paced
control 48
Recommended Control System 48
Alkalinity supplement feed
control 48
Chlorine feed control 49
Instrumentation Requirements 51
Control components . 51
Drift in zero and linearity 51
Feedback controller scaling 51
Signal redundancy 51
Calibration signals 51
Summary 52
References 53
Appendices
A. Rancho Cordova Breakpoint Chlorination
Demonstration Program - Data Summary 54
B. Rancho Cordova Breakpoint Chlorination
Demonstration Program - Breakpoint
Model Predictions 58
VI
-------
FIGURES
Number Pag,
3-1 Theoretical Breakpoint Curve 8
3-2 Conceptual Model for pH Change in Breakpoint
Chlorination 't ^2
i
4-1 Process Flow Schematic 14
4-2 Flow Splitter Box !.*!!!! 15
4-3 Automatic Chlorine Transfer Piping. ......... ie
4-4 Chlorine and NaOH Application Point ! ! 17
4-5 Sampling System ! ! ! 18
5-1 Process Influent Variations 21
5-2 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 6.5 23
5-3 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 7.0 23
5-4 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 7.0 24
5-5 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 7.3 24
5-6 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 7.5 25
5-7 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 7.7 25
5-8 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 8.0 26
5-9 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 8.5 26
5-10 Effect of Breakpoint Chlorination on Organic
Nitrogen. . . 30
5-11 Summary of Cl2:NH4 -N Observations [31
5-12 Breakpoint Chlorination Chlorine Consumption.' ! ! ' * 32
5-13 Lb NaOH/Lb C12 Added ! 33
6-1 Simplified Process Diagram. ... 36
6-2 Control Panel !!.*.*.*'' 37
6-3 Typical pH Characteristics ..!.!.!.! 41
6-4 Simple Feedback Control - Chlorine Feeders.' .*!.*!! 42
6-5 Control Response - Simplified Control Loop .'43
6-6 Simple Feedback Plus Flow Paced
Control - Chlorine Feeders 44
6-7 Simple Feedback Plus Flow Paced
Control - Alkalinity Supplement 45
vii
-------
Figures (continued)
Number
6-8 Effects of Flow Responsive Control
on Free Chlorine Residual . .
6-9 Flow Modified Feedback Plus Flow Paced
Control - Chlorine Feeders. .......
6-10 Recommended Control - Alkalinity Supplement
6-11 Recommended Control - Chlorine Feeders. . .
46
47
49
50
Number
3-1
3-2
3-3
5-1
5-2
5-3
TABLES
Common Reactions Encountered in Breakpoint
Chlorination.
Chlorine Requirement for Chemical Transformations
Commonly Encountered in Breakpoint Chlorination
Acidity and Alkalinity Considerations in
Breakpoint Chlorination ....
Secondary Effluent Quality, Rancho Cordova,
California ,
Reaction Rate Data Summary. ....
Formation of Nitrogen Trichloride and Nitrate .
6-1 Summary of Process Control Signals,
9
10
11
22
27
28
38
viix
-------
SECTION 1
INTRODUCTION
Chlorination can be used to remove ammonia nitrogen from
wastewater. It requires the addition of chlorine, and makes use
of the rapid, specific reactions between chlorine and ammonia in
dilute aqueous solution which can lead to the oxidation of
ammonia to nitrogen gas and other end products. The term
"breakpoint" has been applied to the process because a point of
minimum chlorine residual occurs at the chlorine dosage required
to complete the chemical reaction.
Testing of breakpoint chlorination for nitrogen removal
from sewage has, to date, largely been carried out in small
pilot-scale systems. Data on breakpoint chlorination from
pilot-scale systems have contributed greatly to our understand-
ing of process chemistry, but actual application data and design
criteria for full-scale breakpoint systems have not been readily
available to the design engineer and planner. The work dis-
cussed here was carried out to provide information and design
recommendations from a full-scale breakpoint chlorination system
in the specific areas of process control techniques and instru-
mentation, chemical consumption, and breakpoint reaction end
products. The system tested during this program was designed to
accept variations in flow rates and chemical composition which
are characteristic of effluent from nonnitrifying secondary
wastewater treatment plants.
The full-scale demonstration of breakpoint chlorination was
carried out at Rancho Cordova, California, between December,
1975 and March, 1976. Costs of the evaluation were borne
jointly by the U.S. Environmental Protection Agency, the
Sacramento Regional County Sanitation District and the State of
California.
-------
SECTION 2
CONCLUSIONS
A full-scale breakpoint chlorination facility was
constructed at the Rancho Cordova Sewage Treatment Plant in
Rancho Cordova, California. The system was operated 24 hours
per day, 5 days per week from December, 1975 until March,
1976. Process flow rates varied,from about 0.1 mgd to 1.2 mgd.
Influent ammonia nitrogen concentrations were ordinarily in the
range of 15 mg/1 to 25 mg/1.
Flexibility was incorporated into the breakpoint chlorina-
tion chlorine dosage and pH control systems to facilitate the
testing of several control strategies. Data from automatic on-
line analyzers and from laboratory analysis of samples collected
manually provided the basis for process chemistry investiga-
tions.
A number of specific observations and conclusions made as a
result of the Rancho Cordova breakpoint chlorination demonstra-
tion program are enumerated below:
1. The dosage of chlorine at Rancho Cordova required to
reach breakpoint and maintain a controllable free
residual in the process stream averaged 10 mg/1 for
each 1.0 mg/1 ammonia nitrogen present in the process
influent.
2. Approximately 70 percent of the breakpoint chlorine
dosage was consumed to produce nitrogen gas (N2) from
ammonia (NH4> at pH set points between pH 7 and 8.
The oxidation of ammonia to nitrate consumed 8 percent
to 19 percent of the total chlorine dosed to the
system. Overall, about 96 percent of the total
chlorine dosage was accounted for in reactions between
chlorine and nitrogenous species in specific chemical
pathways and free chlorine residual remaining in
solution following breakpoint.
3. Nitrate (N03) production in breakpoint chlorination
was not found to be pH sensitive, with about 1.0 mg/1
of nitrate (as N) produced from ammonia across a final
system pH range of pH 6.5 to 8.5. The production of
-------
nitrate from nitrite was wholly dependent upon
influent nitrite concentration.
4. Nitrogen trichloride production was observed to be
fairly insensitive to pH across a range of final
system pH values from pH 7 to 8. The median value for
nitrogen trichloride production was about 0.4 mg/1 (as
N) when breakpoint effluent was used as the source of
chlorine injector water. While the amount of chlorine
consumed in its formation was relatively small (4 per-
cent to 6 percent of total chlorine dosed), nitrogen
trichloride generation affects the minimum ammonia
concentration that can be achieved in breakpoint,
since it decays slowly in dilute solution and it is
converted to ammonia upon dechlorination with sulfite.
5. The concentration of organic nitrogen compounds was
not affected by breakpoint chlorination.
6. The rate of reaction for breakpoint chlorination was
found to vary depending upon the pH control point
(final system pH ), with fastest rates observed at a
pH set point of pH 7.0. The time to completion was
found to be between 60 sec and 90 sec at pH 7.0. The
reaction rate slowed considerably at a pH set point of
6.5, and also became progressively slower as pH was
increased from pH 7.3 to pH 8.5.
7. Variations in the amount of mechanical mixing
intensity in the zone of breakpoint chemical applica-
tion had no effect upon overall system chemical
consumption and effluent quality. Mechanical mixing,
to facilitate a rapid and thorough blending of process
chemicals and influent stream, was important in
damping oscillations in free chlorine concentration
for control purposes.
8. Sodium hydroxide (NaOH) was used throughout the
study as an alkalinity supplement. The amount re-
quired to neutralize all breakpoint acidity (1.53 Ib
NaOH/lb Cl2) was essentially identical to that
predicted from chemical stoichiometry.
9. In breakpoint chlorination systems which have gaseous
chlorine as the chlorine source, the volume and
chemical composition of the chlorine injector water
may be important factors in process performance and
control. At Rancho Cordova, when secondary effluent
(breakpoint process influent) was used as the injector
water source, more nitrogen trichloride formed in the
injector water than when breakpoint effluent with low
-------
ammonia content was used. Specific design recommenda-
tions for breakpoint chlorination chlorine injector
water systems are given in the text.
10. The breakpoint chlorination control system recommended
here, while comprised of commercially available
components, can provide satisfactory nitrogen removal
with minimum chlorine consumption only if it is
tailored to the individual application. Specific
recommendations for breakpoint process chlorine dosage
control and pH control are made in the text.
-------
SECTION 3
CHEMISTRY OF THE BREAKPOINT CHLORINATION PROCESS
The use of chlorine as a disinfectant in water treatment
began in about 1800 in Europe. In about 1893, chlorine was
applied as a wastewater disinfectant in New York. In the early
1920's, Houston1 observed that high dosages of chlorine removed
tastes and odors from water. The use of high dosages of chlo-
rine in water treatment led some operators to observe the
increase, disappearance and subsequent reappearance of chlorine
residual as chlorine dosage was incrementally increased. These
observations gave rise to the term "breakpoint" chlorination.
Calvert^ recognized in 1940 that the breakpoint phenomena was
the result of the oxidation of ammonia nitrogen in solution.
This section presents the chemistry of chlorine and ammonia
in aqueous solution, and describes the breakpoint reactions
which can lead to oxidation of ammonia nitrogen to end products
composed principally of nitrogen gas. Compounds of chlorine and
of nitrogen may occur in a variety of species and proportions.
For this reason quantitative terms herein are, unless otherwise
noted, expressed in terms of the elemental forms, chlorine or
nitrogen.
CHEMISTRY OF AMMONIA IN WATER
The actual chemical form of ammonia in dilute aqueous solu-
tion depends largely upon pH and temperature. The relative
distribution of nondissociated ammonia and ammonium ion may
be defined according to the equation below:
t
NH3 + H+ K = 5 x 10-10 at 20 C (1)
where NH3 = nondissociated ammonia
NH4 = ammonium ion
H+ = hydrogen ion
K = dissociation constant
-------
According to the dissociation constant, the pH value at which
nondissociated ammonia and ammonium ion are present in equal
proportions (pK) is about pH 9.3 at 20 C. Above pH 9.3, non-
dissociated ammonia predominates. Below pH 9.3, ammonium ion
predominates.
CHEMISTRY OF CHLORINE IN WATER
When chlorine gas is dissolved in water, a hydrolysis
reaction occurs according to the following relationship:
C12 (GAS) + H2O *+—» HOC1 + H* + Cl~ (2)
followed by a dissociation reaction:
. HOC1 * » OC1" + H+ K = 3.3 x 10~8 at 20 C (3)
where HOC1 = hypochlorous acid
OC1" = hypochlorite ion
H"1" = hydrogen ion
K = dissociation constant
The pH value at which hypochlorous acid and hypochlorite
ion are present in equal proportions (pK) is about 7.5 at 20 C.
Above pH 7.5, hypochlorite ion predominates. Below pH 7.5,
hypochlorous acid predominates. The total concentration of both
hypochlorous acid and hypochlorite ion is commonly termed "free
available chlorine."
Formation of Chloramines
When chlorine and ammonia are present in dilute aqueous
solution, reactions can occur according to a number of chemical
pathways. Reactions between chlorine and ammonia which result
in the formation of chloramines are described below:
NH4 + HOC1 »* NH2C1 (monochloramine) + H20 + H+ (4)
NH2C1 + HOC1 9- NHC12 (dichloramine) + H20 (5)
and
NHC12 + HOC1 *• NC13 (nitrogen trichloride) + H20 (6)
The relative amounts of the chloramine species which exist in
solution depend upon certain process variables, including pH,
temperature, contact time and the initial chlorine to ammonia
-------
ratio (Cl2:NH4 -N). The total of the chloramine species pre-
sent in solution is termed "combined" chlorine residual.
The ammonia nitrogen concentration of a wastewater effluent
is typically in the range of 10 mg/1 to 40 mg/1, unless an
ammonia removal process such as biological nitrification has
been employed. When chlorine is added to such an effluent for
disinfection purposes (dosage of 2 mg/1 to 15 mg/1), the predom-
inant chlorine residual species in solution is ordinarily
monochloramine (NH2C1).
The Breakpoint Reaction
Breakpoint chlorination occurs when sufficient chlorine has
been added to a water or wastewater sample to cause the chemical
oxidation of the ammonia in solution to nitrogen gas and other
end products. Some disagreement still exists in the literature
concerning the actual chemical pathway(s) for breakpoint chlo-
rination, but the following set of reactions appear to be the
most reasonable:
2NH4 + 2HOC1 »- 2NH2C1 + 2H20 + 2H+ (4)
2NH2C1 + 2HOC1 +~ 2NHC12 + 2H20 (5)
NHC12 + H20 »- NOH + 2H+ + 2C1~ (7)
NHC12 + NOH »- N2 + HOC1 + H+ + Cl~ (8)
3HOC1 »- N2 + 3H2O + 5H+ + 3C1~ (9)
where NOH = catalytic intermediary compound.
Combined with equation (2), the overall reaction is:
(10)
Note that breakpoint occurs through the sequential formation of
monochloramine and dichloramine with the subsequent catalytic
decomposition of dichloramine to end products of nitrogen gas,
with a partial return of free residual (HOC1) to the solution.
These reactions confirm that 1.5 moles (gram molecular weights)
of chlorine are required to oxidize 1.0 mole of ammonia to
nitrogen gas.
Stoichiometrically, the breakpoint reaction requires a
weight ratio of chlorine to ammonia nitrogen (Cl2:NH4 -N) at
the breakpoint of 7.6:1, as shown below:
Molecular weight Cl2 = 70.9
Moles Cl2 required = 1.5
-------
Molecular weight NH4 = 14.0 (expressed as N)
Moles NH4 required = 1.0
Therefore, C12:NH4 -N = (1.5)(70.9):(1.0)(14.0) = 7.6:1.
The Breakpoint Curve
The breakpoint chlorination curve is a graphic representa-
tion of chemical relationships which exist as varying amounts of
chlorine are added to dilute solutions of ammonia nitrogen.
The theoretical breakpoint curve shown in Figure 3-1 has several
characteristic features. The characteristics of the breakpoint
curve shown in Zone 1 include principally the reaction between
chlorine and ammonium indicated in Equation 4. The hump of the
breakpoint curve occurs, theoretically, at a chlorine to ammonia
nitrogen weight ratio of 5:1 (molar ratio of 1:1). That ratio
corresponds to the point at which the reacting chlorine and
ammonia molecules are present in solution in equal numbers.
,
CHLORINE
APPLIED
AMMONIA-N CONG
MEASURED
CHLORINE
RESIDUAL
BREAKPOINT-
IRREDUCIBLE
MINIMUM CHLORIN
RESIDUAL
•:
*
I
WEIGHT RATIO
Figure 3-1 Theoretical Breakpoint Curve
-------
The chemical equilibria of Zone 2 favor the formation of
dichloramine and the oxidation of ammonium according to Equa-
tions 5, 7 and 8. These reactions proceed to, theoretically, a
chlorine to ammonia nitrogen weight ratio of 7.6:1. At the
breakpoint, the ammonium concentration is minimized.
To the right of breakpoint, Zone 3 chemical equilibria
require the buildup of free chlorine residual.
In practical applications of breakpoint chlorination,
reactions occur which result in the formation of nitrate,
nitrogen trichloride and other end products. These reactions
consume chlorine, cause the Cl2:NH4 -N ratio to exceed the
theoretical value of 7.6:1 and affect the shape of the break-
point curve. All of these observations are discussed in
detail in subsequent sections of this report.
Other Reactions Encountered in Breakpoint Chlorination
Breakpoint chlorination of wastewater effluent can result
in chemical reactions other than the direct oxidation of ammonia
to nitrogen gas. Reaction products and chlorine consumption for
such reactions are governed by factors such as the type and
degree of pretreatment, initial chlorine to ammonia nitrogen
ratio, pH and alkalinity. A summary of the common reactions
encountered in breakpoint chlorination is given in Table• 3-1.
Table 3-1. Common Reactions Encountered in Breakpoint Chlorination
Description
Reaction Stoichiometry
"Breakpoint Reaction"
Nitrogen trichloride
formation
Nitrate formation
(1) from ammonia
(2) from nitrite
Reaction with other
inorganics
Chloro-organic
reactions
2 NH + 3 HOC1-**N2 + 3 H2O + 5 H + 3 Cl
+ 3 HOC1 — NC13
* + 4HOC1 — NC>3 + H20 + 6 H+ + 4
NO
inorganics + HOC1—•* oxidized inorganics
organics + HOC1—"-oxidized organics
(9)
(ID
(12)
(14)
(15)
-------
The total amount of chlorine residual consumed (by weight)
for each of the common reactions encountered in breakpoint
chlorination has been summarized in Table 3-2. For example, a
total of 20.3 mg/1 of chlorine residual (as Cl2) is consumed in
the conversion of 1.0 mg/1 ammonia nitrogen to 1.0 mg/1 nitrate
(as N). A similar conversion from nitrite to nitrate requires
only 5.1 mg/1 chlorine.
Table 3-2. Chlorine Requirement for Chemical Transformations
Commonly Encountered in Breakpoint Chlorination
Initial
species
NH+-N
NH^-N
NHj-N
NO~-N
*
Other
inorganics
Organic s
Reaction
product
N2
NC13
NO^-N
NOg-N
Oxidized
inorganics
Oxidized
organ ics
Cl2:N molar
ratio required
1.5:1
3:1
4:1
1:1
Varies
Varies
C12:N weight
ratio required
7.6:1
15.2:1
20.3:1
5.1:1
Varies
Varies
In effluents from biological secondary treatment processes,
reduced inorganic compounds such as sulfides and ferrous iron
have become oxidized by the aerobic treatment. Hence, reactions
of inorganic compounds with chlorine are usually not quantita-
tively significant/ Partially oxidized and slowly degradable
organic matter is present, both in solution and in particulate
suspended matter, which does react, particularly with free
chlorine. Such matter includes nitrogen-containing protein-
aceous matter.
pH AND ALKALINITY CONSIDERATIONS
The nature and concentration of the breakpoint chlorination
end products, chlorine dosage required to reach breakpoint and
the rate of the breakpoint reaction are all affected by the
initial pH (following chemical addition) and the pH change which
10
-------
occurs as the breakpoint reaction proceeds. The initial pH in
the reaction zone and pH change through breakpoint depends upon
the pH and alkalinity of the process influent stream, ammonia
concentration and chlorine dosage, and the amount of alkalinity
supplementation.
Acidity is generated in breakpoint chlorination applica-
tions from both the hydrolysis and dissociation of chlorine gas
(when gaseous chlorine is used), and the oxidation of ammonia
nitrogen as shown in Table 3-3. Stoichiometrically, three moles
of hydrogen ions are liberated in the hydrolysis and dissocia-
tion of sufficient chlorine for the oxidation of one mole of
ammonia nitrogen, assuming the initial pH in the reaction zone
is alkaline. One mole of hydrogen ions is liberated in the
oxidation of ammonia to nitrogen gas.
Table 3-3. Acidity and Alkalinity Considerations in Breakpoint Chlorination
Acidity source
Hydrolysis and dissociation of chlorine
Oxidation of ammonia
Total
Alkalinity source
Lime
Sodium hydroxide
3 C12 + 3 H2U^ OCP +- 6H* + 3C1"
2 NH^ + 3 OCI~-^N2 + 3 H2O + 2H+ + 3 CI~
3 C10 + 2 NH"!J— »N0 + 8H+ + 6 CI~
4 CaO + 4HnO-^4Ca + 8 OH~
8 NaOH-^8 Na+ +8 OH~
(16)
(17)
(10)
(18)
(19)
When an alkalinity source is added to neutralize breakpoint
acidity, the acidity from chlorine hydrolysis and dissociation
is neutralized immediately. The acidity from the oxidation of
ammonia is released as the breakpoint reaction progresses. As a
result, the pH in the breakpoint reaction chamber decreases as
reaction time increases. At high initial ammonia concentrations
and low system alkalinity, the pH excursion in the breakpoint
reaction zone may be relatively large. Figure 3-2 shows a
conceptual model for the range of pH values which would be
encountered in breakpoint chlorination of 20 mg/1 ammonia
nitrogen in a secondary effluent with moderate pH buffer
capacity.
11
-------
11
10
9
8
6
ESTIMATED pH
IMMEDIATELY FOLLOWING .
ADDITION OF BREAKPOINT '
CHEMICALS
OXIDATION OF AMMONIA (1 H+)
PREDICTED PATH OF
pH CHANGE DURING
BREAKPOINT CH LOR I NATION
CHLORINE HYDROLYSIS (3 H+)
OH" ADDITION (4 OH")
TYPICAL pH
TITRATION CURVE
INITIAL CONDITIONS
pH - 7.4
ALKALINITY - 165 mg/l ( as CaCO3)
AMMONIA = 20 mg/l (as N)
6
4 2
OH~ ADDITION, meq/l
2 4
H+ ADDITION, meq/l
Figure 3-2 Conceptual Model for pH Change in Breakpoint Chlorination
12
-------
SECTION 4
EXPERIMENTAL METHODS
The breakpoint chlorination demonstration program described
here was carried out at the Rancho Cordova Wastewater Treatment
Plant. The Rancho Cordova Plant, located in the Sacramento,
California area, serves an area of 3,500 acres and a population
of nearly 25,000. The average daily flow of about 2.4 mgd is
composed primarily of domestic sewage. Secondary treatment is
provided through primary sedimentation and a Spiro-Vortex
activated sludge process. The secondary effluent is chlorinated
for disinfection and discharged to the American River.
BREAKPOINT CHLORINATION FACILITIES
v
Breakpoint chlorination facilities were constructed at
Rancho Cordova as indicated in the process schematic of Figure
4-1. A flow splitter box was constructed downstream of the
secondary clarifier so that a predetermined fraction of the
plant effluent could be passed through the breakpoint system.
V-notch weirs in the splitter box were designed to pass 30
percent of the plant flow to the breakpoint system (Figure 4-2).
That percentage was observed to be constant across the full
range of plant flow rates. A capacitance probe, visible in
Figure 4-2, was installed to sense liquid level upstream of the
weir and electronic components were provided to perform flow
computations.
Two existing chlorinators were used in the breakpoint study
to control and meter the flow of chlorine to the breakpoint
process. The chlorinators were 2,000 pound per day capacity
Wallace and Tiernan variable V-notch devices. One was equipped
with a 2,000 pound per day orifice and rotameter, the other had
a 1,000 pound per day orifice and rotameter. Each had variable
vacuum and automatic V-notch positioner controls. Chlorine gas
was fed directly from ton cylinders, arranged in a dual manifold
configuration with four cylinders per manifold. The automatic
transfer system pictured in Figure 4-3 assured an uninterrupted
flow of chlorine gas upon depletion of the cylinders on one
manifold.
Sodium hydroxide was utilized throughout the study as an
alkalinity supplement. It was purchased at 50 percent strength
13
-------
and stored in a tank of approximately 8,000 gal. capacity. NaOH
freezing problems encountered during cold weather were solved by
insulation of the storage tank and heating of exposed caustic
feed piping. A Wallace and Tiernan variable speed chemial feed
pump, equipped' with an SCR drive, was used to provide the
required dosages of sodium hydroxide to the breakpoint system.
-SAMPLE TAPS (TYPICAL)
PH
CONTROL
SIGNAL
BREAKPOINT
CHLORINATION
BY-PASS 27"»
NaOH
BULK
STORAGE
CI2 '
DOSAGE
CONTROL
SIGNAL
NaOH
FEED
PUMP
IN-LINE
MIXER
(VARIABLE
SPEED)
NaOH SYSTEM
FLOW SPLITTER
BOX
INJECTOR
WATER
CI2 BULK
STORAGE
SECONDARY
CLARIFIER
CI2GAS
Cl 2 SYSTEM
Figure t-1 Process Flow Schematic
The 50 percent sodium hydroxide stream was added to the
chlorine injector water immediately upstream of the chlorine
application point, as shown in Figure 4-4. The chemicals were
introduced into the process flow through a 4-inch diameter PVC
injector pipe which extended across the 27-inch diameter in-
fluent pipe from the crown to the invert. Three-eighths inch
diameter orifices were spaced along the injector pipe to allow a
uniform application of the 100 gpm chlorine-sodium hydroxide
chemical solution to the process influent stream. The orifices
provided a head-loss of about 10 feet which assured near-equal
distribution of the chemical solution across the influent pipe
cross-section and provided an increment of initial mixing
energy.
14
-------
It!
Figure 4-2 Flow Splitter Box
15
-------
Figure 4-3 Automatic Chlorine Transfer Piping
A 3 hp variable speed mixing device (Figure 4-4) was
installed in the process stream immediately downstream of the
chemical application point. Two mixer propellers installed on
the mixer shaft were capable of delivering mixing intensity, as
measured by the mean velocity gradient (G), of up to 1,500 to
2,000 sec"* in the chemical addition zone.
Eight sample taps (extending to the center of the break-
point process pipeline) and two sampling pumps allowed selective
withdrawal of samples from the process pipe. The exact contact
period could be determined for each of the samples collected by
means of the sampling system. A photo of the sampling system is
given in Figure 4—5.
16
-------
Figure 4-4 Chlorine and NaOH Application Point
A sulfur dioxide (SC>2) dechlorination system was in-
stalled to provide emergency dechlorination for the Rancho
Cordova plant effluent when measured effluent chlorine residuals
exceeded tolerable levels. Breakpoint process control was
maintained throughout the study so that emergency dechlorination
was required on very few occasions.
CONTROL AND MONITORING EQUIPMENT
Several important primary elements in the overall process
control and monitoring system are discussed below. Design
considerations which can contribute to the successful operation
of each of the elements in the control system are given in
Section 6, Process Control.
Free Chlorine Residual Analyzer
The free chlorine residual analyzer used throughout the
breakpoint program was a Fischer and Porter "Anachlor" unit. A
small chemical feed pump provided a continuous feed of pH buffer
17
-------
and bromide to the measuring cell. The flow of sample from the
constant head tank to the measuring cell was controlled by a
needle valve. Free chlorine residual was determined ampero-
metrically from the amount of bromide converted to bromine under
acidic conditions in the measuring cell.
Figure 1-5 Sampling System
Ammonia Nitrogen Analyzer
The concentration of ammonia nitrogen in the process
influent was analyzed continuously using an automatic analyzer,
Technicon Type I. An alkaline phenate colorimetric procedure
was used.
pH Monitor
A continuous analysis of breakpoint effluent pH was main-
tained using a Leeds and Northrup system.
LABORATORY TESTING PROCEDURES
Chemical and physical analyses were performed according
to Standard Methods for the Examination of Water and Wastewater3
14th edition, except as noted below for specific analyses.
18
-------
Ammonia Nitrogen (NH3 -N)
The ammonia nitrogen determinations performed on-site were
made using a commercial ammonia nitrogen probe (Orion Research,
Inc., Model 95-10) combined with a pH-specific ion meter (Leeds
and Northrup Model 7417). The probe was calibrated daily using
ammonium chloride standard solutions.
Samples collected and preserved for subsequent testing of
ammonia nitrogen at a commercial laboratory were analyzed, using
distillation and titration procedures for ammonia levels greater
than 1 mg/1, and by distillation and nesslerization at ammonia
concentrations below 1 mg/1.
Nitrate Nitrogen (NC>3 -N)
Nitrate analyses were performed according to brucine
procedures, except for chlorine injector water samples which
interfered with the brucine analysis. Injector water samples
were analyzed using cadmium reduction techniques.
Chlorine Species
Both free and combined chlorine residual species were
analyzed routinely throughout the breakpoint study using a
Wallace and Tiernan Amperometric Titrater. lodometric tech-
niques were used to measure the high chlorine residuals found in
samples of the chlorine injector water.
19
-------
SECTION 5
RESULTS AND DISCUSSION
Breakpoint chlorination testing was carried out at Rancho
Cordova, California, during a three-month period, from mid-
December, 1975 through March 15, 1976. Test data were collected
to provide insights into process chemistry and control. The
system was operated continuously, 24 hours per day, 5 days per
week. Technicians were present at all times to collect opera-
ting data and adjust the system as needed. Specific results of
the breakpoint chlorination testing program are presented and
discussed below and presented in Appendix A. Additional data
from continuous recording devices, too bulky for inclusion in
this report, are retained on file by the engineers.
PROCESS INFLUENT CHARACTERISTICS
The breakpoint chlorination system at Rancho Cordova func-
tioned on-line, with full effluent flow and chemical quality
variations. Diurnal variations in flow caused breakpoint
process flow rates to vary from about 0.1 mgd to 1.2 mgd.
Ammonia nitrogen concentrations were also observed to vary on a
diurnal basis over a range of about 15 rog/1 to 25 mg/1. Ammonia
mass flow, the product of process flow and ammonia concentra-
tion, was found to vary on a typical day according to the plot
of Figure 5-1. As therein indicated, the ratio of ammonia mass
rate maximum to minimum was typically about 8 to 1.
Rancho Cordova Wastewater Treatment Plant effluent is a
high quality secondary effluent, as evidenced by the data
summarized in Table 5-1. The concentrations of nitrogen species
and the average alkalinity of 165 mg/1 are typical of non-
nitrified secondary effluent.
INITIAL MIXING
A series of tests were conducted in which the mechanical
mixing intensity at the point of chemical application was varied
and effects upon process performance were monitored. None of
the observations showed any effect upon chemical consumption
or effluent quality as the mechanical mixing intensity was
increased from zero (mixer turned off) to the maximum (G - 1500
20
-------
to 2000 sec 1) level attainable. With the mechanical mixer
off, the free residual analyzer sensed somewhat greater varia-
tions in free chlorine residual as compared to that with the
mixer on full speed; however, the mid-point in the oscillation
was the same in both cases. While the increased amplitude of
the free chlorine residual excursions did not affect chemical
consumption or effluent quality, process control functions were
made more complicated and, for this reason, mechanical mixing
was employed throughout the study.
2.0
1.5
5 1.0
o
0.5
3l
2C
-i 200
150
£
U
"•
J
2
:
S
•
100 eg
:
-I 0
M
0400
0800
1200
TIME
1600
2000
,-:
Figure 5-1 Process Influent Variations
From the Rancho Cordova data, the total dosage of chlorine
necessary to reach breakpoint is not measurably affected by the
intensity of initial mixing. However, process control consid-
erations dictate that segregation of the reactants be minimized.
For design purposes, sufficient hydraulic or mechanical energy
should be provided to facilitate rapid and thorough blending of
the chlorine solution, pH adjustment chemical and process
influent. Rapid mix design criteria from water treatment
practice should serve as a design guideline.
21
-------
Table 5-1. Secondary Effluent Quality, Rancho Cordova, California
Parameter
BOD
COD
PH
Alkalinity (as CaCOJ
NH| (as N)
NOg (as N)
NOg (as N)
Total organic nitrogen (as N)
Soluble organic nitrogen (as N)
Turbidity
Average value
8 mg/1
32 mg/1
7.2
165 mg/1
20.6 mg/1
0 . 6 mg/1
0 . 8 mg/1
2 . 4 mg/1
1.2 mg/1
4 JTU
Range
6-10 mg/1
11-45 mg/1
7.0-7.4
150-175 mg/1
15-25 mg/1
0.01-1.4 mg/1
0.07-1.4 mg/1
1-5 mg/1
1-2 mg/1
2-10 JTU
REACTION RATES
The time required for the breakpoint reactions to reduce to
a minimum the ammonia nitrogen in solution depends upon the
initial concentration of ammonia, chlorine dosage, pH, alkalin-
ity and temperature. The consistent chemical quality of the
Rancho Cordova effluent did not permit testing of all process
variables across a wide range of conditions. Test data were
collected which clearly documented the effect of pH set point
(final system pH) upon the rate of reaction.
Figures 5-2 through 5-9 present breakpoint chlorination
reaction rate data collected at Rancho Cordova for final pH
values between pH 6.5 and pH 8.5. For each test, the control
system was set to provide a free residual chlorine concentration
in the process effluent of 12 mg/1. This was done to ensure
sufficient chlorine residual in the combined breakpoint and
nonbreakpoint stream to facilitate adequate disinfection of
the plant effluent. Influent ammonia nitrogen concentrations
exceeded 15 mg/1 except in two test periods (pH set point 7.3
and 7.7) when the breakpoint effluent used as injector water
diluted the influent ammonia concentration at low flows to
concentrations of about 9 mg/1 to 15 mg/1. The implications of
the chlorine injector water source are discussed in a subsequent
section of this report.
The reaction rate data are summarized in Table 5-2. The
rate of the breakpoint reaction was observed to be fastest at a
pH set point (final pH) of 7.0. The reaction rate slowed con-
siderably at pH set point 6.5, with gradual reductions in rate
observed across a range of pH set points from pH 7.3 to 8.5.
22
-------
0
LU
DC
CO
z
z
o
QC
LU
Q.
100
50
20
10
10
INITIAL CONDITIONS
CI2-.NH3-N - 10.4-12.2 TO 1
NH3-N = 18.2 TO 20.3 mg/l
TEMP = ABOUT 15° C
pH = 7.4
ALKALINITY = 165 mg/l AS CaCOj
NaOH = 104 TO 122 mg/l
* *
* *
NOTE
FREE RESIDUAL SET POINT - 12 mg/l
BREAKPOINT EFFLUENT AS INJECTOR WATER
20 30 40 50 60 70 80 100
TIME, SECONDS
200
300
100
Figure 5-2 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 6.5
1
LU
-------
100
C3 50
111
tc.
co
I
Z
u
ec
ui
Q.
20
10
10
INITIAL CONDITIONS
CI2:NH3-N = 9.BO-11.2TO1
NH3-N = 14.0 TO 19.0 mq/l
TEMP = ABOUT 15° C
pH = 7.4
ALKALINITY- 165 mg/l AS Ca COj
NaOH = 147 TO 198 mg/l
NOTE
FREE RESIDUAL SET POINT = 12 mg/1
SECONDARY EFFLUENT AS INJECTOR WATER
** **
20 30 40 50 60 70 80 100
TIME, SECONDS
200 300
Figure 5-4 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 7.0
Z
z
<
LJJ
-------
o
z
z
tr
z
co
I
Z
H
UJ
O
cc
100
50
20
10
10
FREE RESIDUAL SET POINT = 12 mo/I
SECONDARY EFFLUENT AS INJECTOR WATER
INITIAL CONDITIONS
NH3-N
TEMP
pH
ALKALINITY
NaOH
= 9.55-11.1 TO 1
• 16 TO 18 mg/l
= ABOUT 15° C
- 7.4
- 165 mg/l AS CaCOj
- 163 TO 201 mg/l
20 30 40 50 60 70 80 100
TIME, SECONDS
200 300
Figure 5-6 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 7.5
100
z
z
<
UJ
CC
f)
I
Z
H
LU
O
tc
UJ
0.
INITIAL CONDITIONS
CI2:NH3-N = 10.8 TO 12.6 TO 1
NH3-N = 8.6 TO 15.0 ma/I
TEMP = ABOUT 15° C
pH = 7.4
ALKALINITY = 165 mg/l AS CaCO3
NaOH = 112 TO 152 mg/l
FREE RESIDUAL CHLORINE SET POINT' 12 mg/l „.
BREAKPOINT EFFLUENT AS INJECTOR WATER
40 50 60 70 80 100
TIME, SECONDS
200 300
Figure 5-7 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 7.7
25
-------
100
O 50
z
z
ui
oc
m
I
UJ
U
OC
UJ
0.
20
10
5
10
INITIAL CONDITIONS
9.5 TO 11. 2TO1
18.STO21 ms/l
ABOUT 15° C
7.4
ALKALINITY - 166 mgll AS CaCO3
NaOH - 212TO244mg/l
C12:NH3-N
NH3-N
TEMP
pH
FREE RESIDUAL SET POINT-12 ma/I *
SECONDARY EFFLUENT AS INJECTOR WATER
* *
20 30 40 50 60 70 80 100
TIME. SECONDS
200
300
Figure 5-8 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 8.0
UJ
oc
CO
I
UJ
U
OC
100
50
20
10
5
10
INITIAL CONDITIONS
- 11.1-12.3 TO 1
* 16.8 TO 17.5 mg/1
TEMP - ABOUT 15° C
pH •= 74
ALKALINITY - 165 mg/1 AS CaCOj
- 166 TO 180 n<9/l
NOTE #
FREE RESIDUAL SET POINT - 12 mgll
BREAKPOINT EFFLUENT AS INJECTOR WATER
20 30 40 50 60 70 80 100
TIME, SECONDS
200
300
Figure 5-9 Ammonia Removal with Breakpoint Chlorination
in a Pipe Reactor - pH Set Point 8.5
26
-------
Table 5-2. Reaction Rate Data Summary
pH set
point
6.5
7.0
-7.0
7.3
7.5
7.7
8.0
8.5
Injector
water source
BP
SE
SE
BP
SE
BP
SE
BP
Influent
NH+-N cone.
18.2-20.3 mg/1
19.5-22.5 mg/1
14-19 mg/1
9.5-15.5 mg/1
16-18 mg/1
8.6-15 mg/1
18.5-21 mg/1
16.8-17.5 mg/1
Estimated time to
completion of
breakpoint reaction
> 200 sec
60 sec
90 sec
130 sec
150 sec
180 sec
200 sec
> 200 sec
1
BP = breakpoint effluent
SE = secondary effluent
NITROGENOUS RESIDUALS
Nitrogenous residuals formed in breakpoint chlorinatj.on
include both nitrogen trichloride (NC13) and nitrate (N03).
Nitrogen trichloride may be formed according to Equation 6,
although Saunier, et al.4 noted that reaction kinetics suggested
that formation occurred through a more complex chemical pathway.
Nitrate is formed in breakpoint chlorination through the oxida-
tion of nitrite (NO2) according to Equation 13, or by oxidation
of ammonia as shown in Equation 12 (see Table 3-1). Formation
of nitrogen trichloride or nitrate is undesirable, since large
quantities of chlorine may be consumed, nitrogenous residuals
persist in solution which reduce the nitrogen removal capability
of the process, and obnoxious odors can result.
Nitrogen Trichloride
The residual ammonia concentration achieved following
breakpoint chlorination was shown by Saunier, et al.^ to be a
function of nitrogen trichloride formation, since NC13 is con-
verted to ammonia upon dechlorination with sulfite. Nitrogen
trichloride is formed in breakpoint chlorination and, since it
has a relatively slow decay rate, the amount formed serves to
limit the degree of ammonia removal which can be attained in
breakpoint chlorination.
27
-------
The amount of "apparent" ammonia nitrogen remaining in
solution (see Table 5-3) following breakpoint chlorination was
assumed in this study to be a measure of the amount of nitrogen
trichloride in solution. Nitrogen trichloride formation did
not appear to be sensitive to the pH set point (final pH), with
values generally observed to be in the range of 0.3 mg/1 to 0.7
mg/1. This is contrary to the observations of Pressley, et
al.5 and Wei6 who noted a strong pH dependency for nitrogen
trichloride production. In a recent study by Sa.unier4 some
pH dependency was noted, but not to the degree reported by
Pressley, et al., and Wei.
Table 5-3. Formation of Nitrogen Trichloride and Nitrate
pH set point
6.5
7.0
7.0
7.3
7.5
7.7
8.0
8.5
Injector
water source
BP
SE
SE
BP
SE
BP
SE
BP
NClg formed.
mg/1 as N
Mean
_
0.43
0.65
0.34
0.57
0.52
0.73
_b
Standard
deviation
_
0.15
0.14
0.12
0.13
0.27
0.22
_b
~" C
NO, formed ,
mg/1 as N
Mean
0.95
-
1.14
0.93
1.18
1.19
0.78
1.25d
Standard
deviation
0.18
-
0.17
0.27
0.14
0.31
0.19
-
BP = breakpoint effluent.
SE = secondary effluent.
Reaction had not progressed to completion in samples collected.
°This category includes NO. formed from NH . , does not include NO, formed from NO .
One data point.
A careful analysis of the nitrogen trichloride data showed
that the chlorine injector water source influenced the amount
produced in the Rancho Cordova breakpoint system. A detailed
discussion of the effect of injector water on that formation is
given in a subsequent section of this report.
One possible explanation for the apparent discrepancy in
observations on nitrogen trichloride production is that the
choice of sampling and analysis procedures may be important in
the results obtained. Nitrogen trichloride is known to be
soluble to a very limited degree in water. Its characteris-
tically pungent odor was noticeable at times in the sample
building at Rancho Cordova. However, any which escaped from the
breakpoint process in a gaseous form was not accounted for in
any of the analytical measurements. Loss in gaseous form could
28
-------
have occurred inside the breakpoint contact pipe. Nitrogen
gas from the breakpont reaction may have stripped nitrogen
trichloride from solution as it precipitated from solution and
migrated, as bubbles, toward the top of the pipe. The milky
appearance of samples pumped from the breakpoint system attested
to the presence of gas bubbles in the breakpoint stream. Also,
NCI3 could have escaped from solution as the samples were being
taken at the sample tap. In any case, it is possible that
gaseous losses of NC13 in the Rancho Cordova system contributed
to the apparent discrepancy in observations on NC13 formation vs
system pH.
Another potential source of disagreement in NC13 observa-
tions is that different analytical techniques give different
degrees of accuracy and precision. The DPD-FAS method was
observed by Pressley, et al.5 to have poor reproducibility,
whereas the spectrophotometric method employed in the Blue
Plains work was of questionable accuracy due to the carbon
tetrachloride extraction and potential for interferences.
The amount of chlorine residual consumed in the oxidation
of NH4 to NC13 was found to be about 4 to 6 percent of the
total chlorine dose across a pH range of pH 7 to 8. A complete
data summary of the chlorine consumption of the chemical
reactions encountered in breakpoint chlorination is given in
Appendix A.
From the NC13 data and other qualitative observations made
at Rancho Cordova, it appears that breakpoint systems may be
designed without any provision for off-gas collection and
treatment (for NC13 odors) if proper attention is given to the
design of chlorine dosage and pH control systems. A complete
discussion of factors to consider in the design of breakpoint
process control is given in Section 6.
Nitrate
Data on NC>3 formation in the Rancho Cordova breakpoint
system are summarized in Table 5-3. It should be noted, how-
ever, that the data of Table 5-3 show the concentration of NC>3
formed from NH|, and do not include that formed from NC>2. High-
ly variable N02 concentrations in the breakpoint influent stream
tended to obscure the rather consistent pattern of NC>3 forma-
tion which was observed to occur through the chemical pathway
from NH4. A more complete presentation of NC>3 data is in
Appendix A.
Nitrate formation was not observed to be pH dependent in
this study. This is consistent with the experimental observa-
tions and breakpoint mathematical model predictions of Saunier4,
but it does not agree with the findings of Pressley, et al.5
29
-------
e^ amount of chlorine consumed in the formation of N03
from NH4 was significant, varying from about 8 percent to 19
percent of the total chlorine dosage. As such, it represented
the second largest chlorine consumption of the chemical reac-
tions identified during the study.
Organic Nitrogen
Analysis of data collected to determine the effect of
breakpoint chlorination on organic nitrogen compounds showed
little change in organic nitrogen concentrations through the
process. A statistical summary of total organic nitrogen data
is given in Figure 5-10.
4.5
4.0
3
1
Ul
I
z
o
cc
o
3.0
2.5
2.0
1.5
1.0
OJ5 \-
MEDIAN = 22 mg/l
BREAKPOINT
EFFLUENT
BREAKPOINT
INFLUENT
_L
_L
0.01
10 30 SO 70 90
PROBABILITY OF LOWER VALUE, %
99
99.99
Figure 5-10 Effect of Breakpoint Chlorination on Organic Nitrogen
OVERALL CHLORINE CONSUMPTION
The total chlorine dosage necessary to maintain breakpoint
chlorination at Rancho Cordova averaged 10.0 mg/l chlorine for
each 1.0 mg/l of influent ammonia nitrogen (Cl2:NH4 -N = 10:1).
30
-------
The statistical distribution of Cl2:NH4 -N values observed
at Rancho Cordova is presented in Figure 5-11. This value may
be compared to that predicted by the stoichiometry of the break-
point reaction (Equation 9), which predicts only 7.6 mg/l
chlorine consumed for each 1.0 mg/1 ammonia. The difference in
chlorine consumption between the theoretical and actual value
may be attributed largely to other chemical reactions (Equations
11-1^2) which occur between chlorine and ammonia to form nitrate
(NO3-) and nitrogen trichloride (NC13), as well as the free
chlorine residual remaining in solution. A presentation of
Rancho Cordova data showing the proportionate chlorine demand
for each of the breakpoint reactions is given in Figure 5-12.
12.0
11.0
10.0
CO
X
Z
9.0
8.0
pH SET POINT BETWEEN pH 7 AND 8
INITIAL NH3 -N 8 mg/l TO 22.5 mg/l
DATA POINTS ADJUSTED TO FREE CHLORINE
RESIDUAL OF 8 mg/l
MEDIAN = 10.0
_L
_L
0.01
10 30 50 70 90
PROBABILITY OF LOWER VALUE, %
99
99.99
Figure 5-11 Summary of CL: NH^-N Observations
ALKALINITY SUPPLEMENTATION
An analysis of the quantity of sodium hydroxide fed to the
breakpoint system for purposes of pH control showed that an
average of 1.53 l.b NaOH were added for each 1.0 Ib chlorine to
maintain the breakpoint system pH between pH 7.0 and 7.5. The
31
-------
statistical distribution on the NaOH dosage data is presented in
Figure 5-13. The value of 1.53 Ib NaOH/lb Cl2 compares favorably
with the 1.50 Ib NaOH/lb C\2 requirement predicted from stoi-
chiometry (Equation 19). It should be noted that if lime (CaO)
were used for pH control, chemical stoichiometry (Equation 18)
predicts a requirement of 1.05 Ib CaO/lb
pH SET POINT = 7-8
INITIAL NH3 = 8-225
(EQUATION 9)
66-73%
(EQUATION 11)
8-19%
NH3 -~ NCI3
(EQUATION 10)
46%
UNIDENTIFIED
0-8%
^ NO3
(EQUATION 12)
0-2%
FREE RESIDUAL REMAINING
5-10%
Figure 5-12 Breakpoint Chlorination Chlorine Consumption
CHLORINE INJECTOR WATER CONSIDERATIONS
When chlorine'gas is used as the chlorine source in break-
point chlorination, the volume and source (chemical composition)
of the injector water may become important in process operation.
Ordinary chlorine injector design criteria restricts the chlo-
rine concentration in the injector water to 3,500 mg/1 or less
under maximum feed conditions. As a result, the high chlorine
application rates in breakpoint chlorination can cause the
injector water flow to be a significant fraction of the total
process stream at low breakpoint process flow rates. If break-
point process influent is used as injector water, reactions
between chlorine and ammonia which occur in the injector water
can consume chlorine in undesirable side reactions. If break-
point process effluent is used as injector water, the reacting
32
-------
constituents are diluted and reaction rates reduced, though the
reduction would not be noticeable in most cases.
1.80 -
CM
U
£
TO MAINTAIN pH BETWEEN 7.0 and 7.50
0.01
10 30 50 70 90
PROBABILITY OF LOWER VALUE, %
99.99
Figure 5-13
Lb NaOH/Lb CI2 Added
An analysis of Rancho Cordova data collected at pH set points
between 7.0 and 8.0 showed that approximately 0.2 mg/1 more
NC13 was present in the process stream when secondary effluent
(breakpoint influent) was used as injector water than when
breakpoint effluent was used for chlorine injection. Contact
time in the injector system was about 20 sec.
Samples of injector water were collected just prior to and
following NaOH additions. Some of the samples were vigorously
agitated during collection in an effort to drive off any NC13
which had "formed, so that the amount of NC13 formed in the
chlorine injector water could be estimated. The sampling
techniques and analysis of injector water samples confirmed
that NC13 was formed in significant amounts in the secondary
effluent used as injector water. Nitrate concentrations in the
injector water were not appreciably increased.
33
-------
Based upon the Rancho Cordova testing, chlorine injector
water in breakpoint chlorination applications should be designed
according to the following criteria:
• If possible, locate the chlorine injector at the
chemical application point and use process influent as
injector water.
• If the injector must be remote from the actual appli-
cation point, use process effluent as injector water.
• In large installations, it may be preferable to feed
liquid chlorine (rather than gaseous), mixed with the
alkalinity supplement chemical and sufficient process
effluent to yield a maximum chlorine residual in the
feed stream of 8,000 mg/1.
BREAKPOINT MODEL PREDICTIONS
As a supplementary part of this study, the breakpoint
chlorination computer model developed at the University of
California by Saunier and Selleck^ was used to predict process
performance under a variety of conditions, including many which
could not have been tested under actual field conditions at
Rancho Cordova. Those predictions are given in Appendix B of
this report.
Figures B-l through B-8 represent breakpoint model predic-
tions under the exact conditions of the field-scale measurements
presented in Figures 5-2 through 5-9. As such, the curves can
be compared directly to determine the correlation between the
model and field measurements. In most cases, the correlation
was excellent.
Figures B-9 through B-14 show the effect of alkalinity
supplement addition (in this case, NaOH) on final pH, percent
ammonia remaining in solution and reaction time as a function of
C1-2LNH3~ and_C>p. C-j is the total inorganic carbon (sum of C02,
HCC>3 and CO-j) in the system, expressed in moles per liter.
The alkalinity supplement addition ("NaOH added") in each case
refers to the NaOH added to solution beyond that required for
neutralization of the acidity from hydrolysis and dissociation
of the chlorine dosage (Equation 16, Table 3-3).
34
-------
SECTION 6
PROCESS CONTROL
A breakpoint chlorination control system should be reliable
and should facilitate the efficient use of chemicals and man-
power. Chlorine overdosages can be quite expensive, with
additional costs for chlorine and alkalinity supplement as well
as dechlorinating agent. Chlorine and alkalinity costs alone
can reach $800 per year for an overdosage of 1 mg/1 in a 1 mgd
application. Chlorine underdosages can result in significant
reductions in ammonia removal efficiency and high combined
chlorine residuals in the process effluent.
The nature of the breakpoint chlorination process is such
that manual control is difficult, requiring the undivided
attention of an operator. One aspect of this study was the
evaluation of various process control systems and associated
instrumentation.
PROCESS AND COMPONENT DESCRIPTIONS
The breakpoint chlorination process flow diagram is
presented on Figure 6-1 and shows only those signals involved in
control. The pilot plant control panel is shown on Figure 6-2.
Principal signals generated and displayed are listed in Table
6-1.
The final control elements include the chlorinators and
sodium hydroxide feeder, and the measured variables include
ammonia, free chlorine residual, and pH analyzers and flow-
meters .
Ammonia Analyzer
This device was a continuous on-line analyzer which
utilized metered reagents in the colorimetric determination of
ammonia. The calibrated accuracy was ±0.2 mg/1. Occasional
drift was observed to be as high as 2 mg/1 over a 12-hr period.
"Noise" amplitudes as high as 3 mg/1, principally due to sample
turbidity or occasional air bubbles, were observed. Disturbance
durations ranged from seconds to several minutes. A sample
filter was not used. Total dead time for the analyzer was about
17 min, consisting primarily of analysis time. (Dead time, in
35
-------
process control, is the period of time after a force is applied
during which no response is observed; it is the lag time between
action and response.)
DATA
ONLY
JM-Smgd
2-12 pH
i
0-30 m»/l
AMMONIA-
NITROGEN
ANALYZER
PROBE
UNTREATED STREAM
0 = 0.25-1.25 ingd
NH^CONC. 16-26 mgfl
2000 LB/DAY
CHLOR1NATOR
4500 LB/DAY
SODIUM HYDROXIDE
FEEDER
4 INJECTOR WATER FROM TREATED STREAM
Figure 6-1 Simplified Process Diagram
Flowmeter
The flowmeter consisted of a level-measuring capacitance
probe and appropriate circuits to convert level measurement to a
linear flow signal. Calibrated accuracy was ±1 percent which
was maintained for periods from one to several days. Zero and
span drifts up to 0.2 mgd were observed. These were usually
corrected by cleaning the probe of grease accumulations. The
response of the flowmeter was essentially instantaneous.
Hydraulic noise oscillations with amplitudes from 7 to 10
percent at periods from about 5 to 10 sec were transmitted.
This noise was eliminated by appropriate electrical damping
circuits.
Chlorinators
Chlorine was added to the process by vacuum injection into
liquid stream prior to the mixing chamber. Chlorine gas flow
36
-------
was controlled by a linear variable orifice positioner in
response to signals from the automatic controls. A constant
but adjustable differential pressure was maintained across the
linear variable orifice. All observations were based on flow as
displayed on the gas flow rotameter. Repeatability was about
±1 percent. Maximum deviation from linearity over the range
from 15 to 90 percent output was about 1-1/2 percent. Response
dead band was about 1 percent. Full-scale output change re-
quired less than 1 minute.
Figure 6-2 Control Panel
Electric linear flow transmitters were provided which
operated with a maximum deviation from linearity of about 4 per-
cent when used from 25 to 100 percent full-scale.
The chlorinators were also provided with dosage (ratio
control) and vacuum controls. These controls were immobilized
after calibration because of the non-linearity they induced in
the response of the variable orifice control.
37
-------
Free Chlorine Analyzer
This analyzer was a continuous amperometric titration unit,
providing an electric signal proportional to free chlorine
residual. The analyzer maintained an accuracy better than
±1 mg/1 over a period of several months and was free of spu-
rious noise. The dead time for this analysis consisted of a
plant flow variant of 12 to 60 sec with an additional 2 minute
fixed time for transit from the sampling point through the
analyzer.
Table 6-1. Summary of Process Control Signals
Signal
Free chlorine residual concentration
Total chlorine residual concentration
Sodium hydroxide feed rate
Plant flow (influent)
PH
Gas flow, chlorinator No. 1
Gas flow, chlorinator No. 2
NHj-N concentration
NH^-N flow rate
Total chlorine gas flow rate
Total CL.2 gas flow rate/NHt-N flow rate
Units
mg/1
mg/1
Ibs/day
mgd
2 to 12
Ibs/day
Ibs/day
mg/1
Ibs/day
Ibs/day
(none)
Notes
(M)
(M)
(M)(I)(T)
(M)(T)
(M)
(M)
(M)
(M)
(C)(T)
(C)(T)
(C)
All of the above signals were recorded
(T) Integrated - totalized
(C) Computed
(M) Measured by transducer
(I) Inferred from speed measure
The useful range of the analyzer is limited at the low end
to values about 3 to 4 mg/1 because of interference from com-
bined residuals below breakpoint. This in turn limits the
minimum reliable process control set point to values of about 7
to 9 mg/1 of free chlorine. These erroneous readings appeared
to be consistent and repeatable and were equal to the sum of the
free chlorine plus about 1/10 of the combined chlorine.
It is important that system design provide sufficient dead
time at maximum plant flow rate to allow the reaction to go to
completion before entering the analyzer; however, it is also
important that this dead time be minimized because control
38
-------
difficulties increase with dead time. Therefore, the chlorine
residual analyzer was located at a distance downstream of the
mixing chamber such that the travel time between the chamber and
analyzer equaled the maximum reaction time.
pH Analyzer
The pH analyzer consisted of a glass measuring electrode, a
reference electrode, and a thermistor temperature sensor mounted
on a. flow-through electrode holder. A signal preamplifier was
externally mounted on the electrode holder to provide a contin-
uous high-level temperature-compensated pH signal.
The analyzer was accurate to 0.1 pH units over a period of
several months and was free of spurious noise. The accuracy of
the pH signals was unaffected by the chlorine dosage either
above or below breakpoint concentrations.
The dead time on the analysis consisted of a plant flow
variant of 12 to 60 sec with an additional 20 sec fixed time for
transit from the sampling point through the analyzer electrode
holder. System design considerations for pH analyzer dead time
are the same as those for the Free Chlorine Analyzer.
Sodium Hydroxide Feeder
The sodium hydroxide feed system consisted of a metering
pump which fed a 50 percent solution from a liquid storage tank.
The metering pump was a positive displacement unit with manual
pump stroke control, and powered by a variable-speed d-c motor.
Feed control was achieved by automatic motor speed variation in
response to signals from the automatic control system. The
local motor speed controller was a closed-loop system that
compared motor speed as measured by a tachometer with the
incoming automatic speed order.
Initial calibrated accuracy from 5 to 100 percent of output
was ±1 percent. Some instability was observed for outputs
below 5 to 6 percent. An output zero drift of about ±10 percent
was observed after about 6 weeks of operation at which time the
equipment was recalibrated and no further drift was observed.
System response was on the order of 2 sec for 5 to 100 per-
cent without overshoot.
CONTROL REQUIREMENTS
The principal parameters for breakpoint chlorination
control are free chlorine residual for chlorine dosage control
and pH alkalinity supplement dosage control. The degree of
resolution and repeatability of chemical feed rates is one of
39
-------
the major factors which determines how efficiently the break-
point process can be controlled.
At Rancho Cordova, the chlorine feed requirement varied
from 160 Ib/day to 2,300 Ib/day. Control of free chlorine
residual to ±3 mg/1 required a control tolerance of about
±3 percent at minimum chlorine feed rates, and ±1 percent at
maximum feed rates. The resolution of the chlorinators was
about 1 percent, or about 10 Ib/day on the small unit and
20 Ib/day on the large one. At a minimum flow of 0.25 mgd,
a feed-rate error of 10 Ib/day would lead to free chlorine
variations of about 4 mg/1. At maximum flows of 1.25 mgd, a
feed-rate error of 10 Ib/day gives an error of about 1 mg/1.
Previous discussion of the chemistry indicates that about
1.5 pounds of sodium hydroxide is required per pound of chlo-
rine. This ratio is approximate and valid only if the untreated
stream pH is near the desired reaction end point (i.e., all
breakpoint acidity neutralized). The slope of the alkalinity
curve at the control point determines the difficulty in obtain-
ing proper control. A family of alkalinity curves is shown on
Figure 6-3. pH control would be more difficult for wastewater
with low alkalinity. The abscissas of these curves in relation
to the pH control point could be interpreted as error of con-
centration or error of sodium hydroxide feed rate. At Rancho
Cordova the minimum feed rate was about 250 Ib/day, with maximum
feed rates reaching about 3,450 Ib/day.
If the pH/feed-rate curve is very nonlinear, a special non-
linear element should be inserted into the measurement loop to
hold constant gain at all feed rates.
CONTROL SYSTEMS
Four systems were evaluated for their effect on breakpoint
chlorination control: simple feedback control, simple feedback
plus flow paced control, flow modified feedback plus flow
paced control, NH4 -N mass flow paced control.
Simple Feedback Control
Figures 6-4 and 6-5 show a simple feedback control system.
This control system functions solely in response to deviations
of free chlorine residual from the selected set point. Figure
6-5 shows a typical response (output) curve to an error signal.
If the controller generates an output in response to a process
error signal that will overcorrect to the extent that the new
error is equal to or greater than the original eror and the new
error is of opposite sign, then the output will violently
oscillate. In terms of feed rate, if the analysis showed a
deficiency of 10 Ib/day and this provided a positive change in
output of 20 Ib/day or greater, then the system would oscillate.
40
-------
MODERATE ALKALINITY
FEED RATE OF ALKALINITY SUPPLEMENT
Figure 6-3 Typical pH Characteristics
Referring again to Figure 6-5, the output is continually
changing as long as error is sensed by the controller. Since
the output will continue to change until the results of the
initial change are analyzed and returned to the controller, this
effect must also be evaluated.
A conservative initial system design will provide for
approximately half the feed rate correction to be made with the
proportional band setting immediately (-100% x % ERROR, refer to
% PB
Figure 6-4) with the remaining correction to be made over a
period of time equal to twice the system dead time. Thus, an
error signal indicating a deficiency of 10 Ib/day feed rate
would provide an increase in output of 5 Ib/day immediately
with the remaining 5 Ib/day to be incremented over a period
time equal to twice the dead time.
of
A plant flow rate of 0.25 mgd with a free chlorine residual
error of 1.0 mg/1 requires a correction of 2.08 Ib/day in chlo-
rine feed rate. The same error at a plant flow rate of 1.25 mgd
41
-------
0-20%
= 0-20 mo/1
FREE
CHLORINE
SIGNAL
MANUAL SET
FEEDBACK
CONTROLLER
PROPORTIONAL
+
INTEGRAL
0-100% ADJUSTABLE
SET 10% (10 mft/l)
0-100% % 0-3000 LB/DAY
ORDER TO
CHLORINATOR
1
ORDER TO
CHLORINATOR
2
% CONTROLLER OUTPUT = C% - 100% x
ERROR
PB
%PBxT
% ERROR
•dt ]
X ERROR = SET %- SIGNAL %
% PB = % PROPORTIONING BAND ADJUSTMENT (ADJUSTABLE 0-200%)
T = RESET TIME ADJUSTMENT. MINUTES (ADJUSTABLE 0-20 MIN)
t = REAL TIME, MINUTES
C% = ADJUSTED VALUE AT t = O
Figure 6-1 Simple Feedback Control - Chlorine Feeders
42
-------
requires a correction of 10.41 Ib/day in chlorine feed rate.
Using simple feedback control, the control system response, as
limited by stability criteria, is set for the maximum response
at minimum flow. With a desired correction of 2.08 lb/day/mg/1
free chlorine error at minimum flow, the correction should
be 1.04 lb/day/mg/1 error (immediate) plus 0.17 lb/day/min/mg/1
error.
ERROR SIGNAL
FEEDBACK
CONTROLLER,
PROPORTIONAL
+
INTEGRAL *
OUTPUT -A
* \ ^
PROCESS
tc.
o
O
INTEGRAL TIME
•« T
'1 j
100
IMMEDIATE RESPONSE
TO ERROR
TIMED RESPONSE
RESET FUNCTION, / * % ERROR • dt
T
r
REAL TIME, t
Figure 6-5 Control Response - Simplified Control Loop
At Rancho Cordova, plant flow varied from a minimum to
maximum in a period of; about five hours. These plant flow
variations at median NH4 -N concentrations required a chlorine
feed rate variation from about 375 to 1,850 Ib/day. The rate of
change of chlorine feed rate was:
= 5 lb/dav/min
This value is conservative since, under some conditions, a
10 Ib/day/min rate of change was required. Simple feedback con-
trol set for stability at minimum flow with an error of 3 mg/1
43
-------
could only provide about 3 x 0.17 lb/day/min/mg/1 error or about
0.51 Ib/day/min. Therefore, simple feedback control could not
keep up with required dosage variations and a compound control
system was required.
Simple Feedback Plus Flow Paced Control
This compound system incorporated a flow paced control loop
in addition to the free chlorine residual feedback loop. The
control system is shown on Figures 6-6 and 6-7. This system
FREE
CHLORINE
SIGNAL t
PLANT FLOW SIGNAL
FEEDBACK
CONTROLLER.
PROPORTIONAL
+
INTEGRAL »
0-100%
MANUAL
RATIO
ADJUST*
REFER TO FIGURE 6-4 FOR
CONTROLLER OUTPUT DEFINITION
REFER TO FIGURE 6-4 FOR VALUES
MULTIPLICATION FACTOR
ADJUSTABLE 0.00 TO 1.0
PRODUCT OF RATIO ADJUST
FACTOR TIMES INPUT SIGNAL
0-100% £^ 0-1.5 mgd
MANUAL
RATIO
ADJUST
t- \-
SUMMATION
0-100% =0-3000 LB/DAY
ORDER TO
CHLORINATOR
1
ORDER TO
CHLORINATOR
2
Figure 6-6 Simple Feedback Plus Flow Paced Control - Chlorine Feeders
44
-------
was satisfactory for sodium hydroxide feed maintaining the
treated stream within ±0.3 pH units of the set point.
1.PH
SIGNAL
0-100%
^ 2-12.pH
MANUAL SET
7.2 pH. (52%)
i
FEEDBACK
CONTROLLER,
PROPORTIONAL
+
INTEGRAL *
• REFER TO FIGURE 6-4
FOR CONTROLLER OUTPUT
DEFINITION
A MULTIPLICATION FACTOR
ADJUSTABLE 0.00 TO 1.0
AA PRODUCT OF RATIO ADJUST
FACTOR TIMES INPUT SIGNAL
PLANT FLOW SIGNAL
0-100%= 0-1.5mgd
0-100%
MANUAL
RATIO
ADJUST A
MANUAL
RATIO
ADJUST A
AA
L
SUMMATION
T
0-100% ^ 0-3000 LB/DAY
ORDER TO
FEEDER OF
ALKALINITY SUPPLEMENT
Figure 6-7 Simple Feedback Plus Flow Paced Control - Alkalinity Supplement
Figure 6-8 shows the effect of a Manual Ratio Adjust
block in the plant flow signal line prior to the summation
Optimum adjustment for direct plant flow paced signal
provide somewhat less dosage than is required for br+eak-
at minimum NH| -N ion concentrations and C12/NH4 -N
For a flow change of 1.0 mgd in 150 min, the chlorine
feed rate would change at about 6 Ib/day/min. At median chlo-
rine dosages, a rate of change of chlorine feed of about 10 lb/
day/min would be required. The feedback controller would, then,
be required to supply the difference, or 4 Ib/day/min in this
example. The control error would be 4.0/0.17 or about 24 mg/1.
block.
should
point
ratios.
45
-------
In these tests, free chlorine excursions, using this chlo-
rination control system at plant flows above 0.5 mgd, were large
and erratic and operation was generally unsatisfactory.
z
-------
required increment of chlorinator capacity that was not obtain-
able through the flow modified feedback control portion. The
flow modified feedback control was limited by scaling of the
free chlorine signal and the proportional band adjustment of the
controller.
FREE
CHLORINE
SIGNAL +
-0-20% as
0-20ma/l
FEEDBACK
CONTROLLER,
PROPORTIONAL
+
INTEGRAL *
PLANT FLOW SIGNAL
PLANT FLOW SIGNAL
0-100% =
0-1.5 mgd
-0-100%
REFER TO FIGURE 6-4 FOR
CONTROLLER OUTPUT DEFINITION
REFER TO FIGURE 6-4 FOR VALUES
MULTIPLICATION FACTOR
ADJUSTABLE 0.00-1.0
PRODUCT OF RATIO ADJUST
FACTOR TIMES INPUT SIGNAL
MULTIPLIER
OUTPUT = A x B x 0.67
"B"
-0-67%
NOTE: DUE TO MULTIPLIER SCALING
FACTOR, MAXIMUM FEED RATE WAS
LIMITED TO 2000 LB/DAY (3000 x 0.67)
0-67% +
WHERE 0-100%
S 0-3000 LB/DAY (NOTE)
ORDER TO
CHLORINATOR
1
ORDER TO
CHLORINATOR
2
Figure 6-9 Flow Modified Feedback Plus Flow Paced Control - Chlorine Feeders
Within the limits of signal output capacity, chlorinator
control on flow modified feedback control only (with no contri-
bution of direct plant flow signal) provided satisfactory
control with free chlorine excursions of 5 to 6 mg/1 from
control point. These excursions were random and not partic-
ularly related to plant flow variations. Addition of direct
plant flow control signal up to about one-half of the total
control signal appeared to have little effect on the 5 to 6 rag/1
excursions from the control set point.
47
-------
Experience at Raneho Cordova showed that required chlorine
dosages varied from about 12fl rag/1 to 250 mg/1 as a function of
NH4 concentration and the NH4 -N/C12 ratio. For chlorine dosage
variation of this magnitude over a 10-hour period, the rate of
change of chlorine dosage was (250-120)/(10 x 60) = 0.217 mg/1/
min. The flow modified feedback controller can increment 0.68
Ib/day chlorine feed/min/mgd plant flow/mg/1 of free chlorine
error, or can correct for .0817 mg/1 per minimum concentration
change for a free chlorine residual error input signal of 1.0
mg/1. Control offset from set point would then be:
Ammonia Nitrogen Mass Flow Paced Control
In this control mode, NH4 -N concentration Was measured and
continuously multiplied by plant flow to provide an NH4 -N mass
flow rate (Ib/day). This flow rate was used as a direct feed
forward signal in lieu of plant flow in several control schemes
for chlorine and sodium hydroxide feed. NH4 -N concentration,
as a raw signal, was not suitable for control due to the pres-
ence of noise. This signal was conditioned by resistance-
capacitance filtering which added a 5-min time constant to the
17-min analysis dead time.
After conditioning, the signal was used for control. No
improvement in control was noted. Control overshoots were
occasionally noted that appeared to be coincidental with changes
in the rate of change of NH4 -N concentration. These over-
shoots were the probable result of the analysis dead time and
signal conditioning time which introduced out-of -phase signals
into the control system.
RECOMMENDED CONTROL SYSTEM
Based on the proceeding discussion of process control
systems, a control scheme was selected for both alkalinity
supplement feed and chlorine feed.
Alkalinity Supplement Feed Control
Sodium hydroxide feed control at Raneho Cordova was satis-
factory with the control system shown on Figure 6-7. However, a
flow modified feedback control with plant flow paced control as
shown on Figure 6-10 is recommended. This control configuration
will provide better pH control in breakpoint applications with
low influent alkalinity. The direct plant flow paced portion of
the total control signal should be less than the ratio of break-
point chlorine dosages for minimum to maximum process require-
ments.
48
-------
PLANT FLOW
FEEDBACK
CONTROLLER
PROPORTIONAL
+
INTEGRAL *
0-100%
-0-100%
REFER TO FIGURE 6-4 FOR
CONTROLLER OUTPUT
DEFINITION
MULTIPLICATION FACTOR
ADJUSTABLE 0.00-1.0
PRODUCT OF RATIO ADJUST
FACTOR TIMES INPUT SIGNAL
PLANT FLOW
"A"
"B" "C"
MULTIPLIER OUTPUT = A x B x C
- 0-100% x C
0-100%
SUMMATION
NOTE: THEORETICALLY THIS
CONTRIBUTION SHOULD BE
REDUCED TO ZERO,
BUT THIS WAS NOT VERIFIED
IN ACTUAL OPERATION
0-100%x
ORDER TO
FEEDER OF ALKALINITY
SUPPLEMENT
Figure 6-10 Recommended Control - Alkalinity Supplement
Chlorine Feed Control
The recommended system for control of chlorine feed equip-
ment is shown on Figure 6-11. Two chlorinators are used, one
large and one small. For this configuration , the large
chlorinator is controlled solely by plant now rate and the
small chlorinator is controlled by a flow modified feedback
controller.
The recommended control scheme of Figure 6-11 showed
average excursions from the free residual control point of about
±3 mg/1 free chlorine. The excursions were somewhat larger at
low plant flows and low NH4 -N concentrations than they were
at higher flows and concentrations.
The chlorinator feed rate resolution is suggested as an
important element in the superior performance of the recommended
49
-------
chlorine control mode. The difference may occur because the
large chlorinator in the recommended scheme is not called upon
to make both positive and negative adjustments in any short
period of time since it is totally flow responsive. The flow
signal, as previously notedr was conditioned to remove noise.
This would tend to minimize any errors due to lack of resolution
of the large chlorinator feed rate, because over any period of
time changes in feed rate would tend to be unidirectional and
infrequent.
I
FREE
CHLORINE
SIGNAL
4—0-30
PLANT
FLOW
SIGNAL
I 0-30
0-30% a
0-30 mgfl
REFER TO FIGURE 6-4 FOR
CONTROLLER OUTPUT DEFINITION
MULTIPLICATION FACTOR
ADJUSTABLE 0.00-1.0
PRODUCT OF RATIO ADJUST FACTOR
TIMES INPUT SIGNAL
FEEDBACK
CONTROLLER,
PROPORTIONAL
+
INTEGRAL •
0-100%
PLANT
FLOW
SIGNAL
0-100%
"B"
MULTIPLIER
OUTPUT = A x B x C
"C"
(0-100%) xC-
ORDER TO
LARGE
CHLORINATOR (S)
ORDER TO
SMALL
CHLORlNATORtS)
Figure 6-11 Recommended Control - Chlorine Feeders
To obtain optimum response from the chlorinators, the
control vacuum should be reduced until full linear travel of the
variable orifice produces only the minimum quantity required to
meet the current maximum process requirements. The small chlo-
rinators should be carefully sized to provide 125 to 150 percent
of the amount of chlorine feed needed between anticipated
50
-------
maximum and minimum breakpoint chlorine dosages. The large
chlorinators should be sized to provide breakpoint concentra-
tions of chlorine for maximum plant flows and minimum NH4 -N
concentrations and Cl2:NH4 -N ratios.
INSTRUMENTATION REQUIREMENTS
Control Components
Since process control is critical, requiring a chlorine
feed rate resolution of 1 percent or better, control components
which have dead bands should be avoided.
Drift In Zero and Linearity
Since breakpoint process control depends partly on feed
forward flow signals, zero or linearity errors have to be com-
pensated for through the feedback controller. Zero drift
in control components causes system gain changes which can
result in severe control problems at low plant flow rates.
Components should be selected which are as linear and drift-free
as possible and should be readily adjustable to eliminate zero
and linearity errors.
Feedback Controller Scaling
Control loop and component characteristics should be care-
fully analyzed to allow the initial calculated proportional band
for the controller to be about 40 percent at the point where
oscillations will first commence. If this requirement cannot be
met by appropriate scaling of free chlorine residual or pH
signal alone, then an additional attenuator (or amplifier) must
be added directly in the feedback controller output to the
multiplier and the multiplier (or divider) appropriately re-
scaled. Full signal range must be retained in the multiplier
output.
Signal Redundancy
If the process is required to run on a continuous basis,
redundant automatic plant flow, free chlorine residual and pH
input signals will be required to maintain operation while these
transmitters are routinely cleaned, serviced and adjusted.
Calibration Signals
To initially align the control system and to periodically
check its proper operation after startup, calibration input
signals will be simultaneously required for free chlorine
residual, plant flow and pH. It is recommended that these
calibration signals be permanently built into the control system
51
-------
with appropriate readouts, stepless 0 to 100 percent adjustments
and "operate-calibrate" selector switches. Plant flow calibra-
tion inputs should have separate "operate-calibrate" switches
for each input into each chlorinator control and alkalinity
supplement feed control system.
SUMMARY
The control system can provide satisfactory control only if
it is properly tailored to the application. Oversizing of feed
capacity will proportionately reduce the control tolerances.
Prior to finalizing system design, data should be collected on
plant flow covering maximum and minimum values and maximum rates
of change. Data should also be available on NH4 -N concentra-
tion maximums, minimums and maximum rates of change. Alkalinity
data should also be collected to determine the system's response
to addition of alkalinity supplement.
52
-------
REFERENCES
1. Houston, Sir A. C. 19th and 20th Annual Reports of the Metro-
politan Water Board, London, England (1925 and 1926).
2. Calvert, C. K. "Treatment with Copper Sulfate, Chlorine,and
Ammonia," JAWWA, 3_2 (17) : 1155-64, 1940.
3. Standard Methods for the Examination of Water and Wastewater,
13th Ed., Amer. Public Health Assoc., New York, 1971.
4. Saunier, B. M. and R. E. Selleck. Kinetics of Breakpoint
Chlorination and of Disinfection. Sanitary Engineering
Research Laboratory Report, University of California,
Berkeley, April, 1976.
5. Pressley, T. A., D. F. Bishop, and S. G. Roan. "Ammonia-
Nitrogen Removal by Breakpoint Chlorination," Environ. Sci.
and Techn., 6(7):622-28, July, 1972.
6. Wei, I. W. Chlorine-Ammonia Breakpoint Reactions; Kinetics
and Mechanisms.Ph.D. Thesis, Harvard Univ., Cambridge,
Mass., May, 1972.
53
-------
APPENDICES
APPENDIX A
RANCHO CORDOVA BREAKPOINT CHLORINATION
DEMONSTRATION PROGRAM
DATA SUMMARY
54
-------
U1
U1
Time
C12
feed,
Ib/day
I. pH set point
1450
1510
1530
1545
2030
2100
2075
1900
Flow,
mgd
C12
dose,
mg/l
Inijial
mg/l
(C,2/NH;-N)
Free
residual
remaining ,
mg/l
6.5 Breakpoint effluent used as Injector water, March 10,
1 .204
1.204
1.171
1.108
202
209
212
206
X =207
SD= 4
20.25
20.25
19,31
IB. 27
X =19.5
SD= 0.9
10.0
10.3
11.0
11,3
X =10.6
SD= 0.6
9.5
9.5
15
17
X =13
SD= 4
Final
NH^-N,
mg/l
976
1 .4*
1 .8*
2.3*
1.4*
II. pH set point 7.0 Secondary effluent used as Injector water, February 20,1976
0020
0105
0202
0301
0403
0703
0755
0907
1003
1104
1200
1625
1300
920
670
560
625
1060
1670
1780
1820
1830
0.944
0.774
0.544
0.404
0.324
0.374
0.684
1 .104
1 .174
1 .174
1 .044
206
201
203
199
207
200
186
181
182
186
210
X =1')6
?D= 11
22
22
22.5
22
21 .5
20.1
19.5
19.5
19.5
20.8
23
X =21.1
SD= 1 .3
9.4
9.1
9.0
9.0
9.6
9.9
9.5
9.3
9.3
8.9
9.1
X =9.3
SD=0.3
16
15
16.5
8
12
9
10
11 .5
9
6
r>
X =11
SD= 4
III . pH set point 7.0 Secondary effluent used as injector water , March 3-4 ,
1953
2051
2150
2252
0002
0055
0158
0251
0351
0451
0552
0651
oaoo
1890
1920
1830
1770
1370
1085
780
550
445
375
375
490
800
.124
.074
.174
.174
.094
0.684
0.524
0.354
0.304
0.284
0.284
0.354
0.624
202
214
187
131
150
190
178
186
176
158
158
166
154
X =177
SD= 19
19
19
19
18
17
17
17
16.5
16
16
16
15
14
X =16.9
SD= 1 .6
10.6
11 .3
9.8
10.0
8.8
11 .2
10.5
11 .3
11 .0
9.9
9.9
11.1
11.0
X =10.5
SD= 0.8
12.5
14
15
15
10
11 .5
13
16
18.5
20
12
10
1 2
X =14
SD= 3
0.58
0.34
0.38
0.29
0.38
0.53
0.29
0.47
0.28
0.75
X =0.43
SD=0.15
1976
0.68
0.75
0.82
0.80
0.52
0.54
i).M)
0.73
0.76
0.50
0.43
0_.J5
5T =0.65
SD=0.14
Initial
NOj-N,
mg/l
0.27
0.21
0.15
0.07
0.38
0.20
0.11
0.09
0.08
0.08
0.07
0.07
0.06
0 .08
0.10
0.10
0.27
Initial
NO^-N,
mg/l
0.20
0.17
0.15
0.08
Final
mg/l
1.2
1.4
1.2
1 .3
0 . 08
0.05
0.03
0.03
0.03
0.05
0 . 06
0.05
0.03
0.04
0.04
0.04
0.10
1.5
1 .3
1 .3
1 .2
-
.1
.2
.4
.3
.2
.2
.2
2.0
NO§
prod . In
Bpolnt,
mg/l
0.73
1 .02
0.90
1 .15
X =0.95
SD=0.18
Chlorine consumed by reaction
NHj~N2
mg/l
143
140
129
128
X =135
SD= 8
1.04 139
1.05 ' 139
1.1'.
1 .08
-
0.98
.07
.29
.21
.09
.06
.06
1 .63
X =1.14
SD=0.17
138
131
-
125
125
122
116
116
118
111
101
X =123
SD= 12
NHj— • NO3
mg/l
15
21
18
23
K =19
SD= 4
21
21
24
22
_
20
22
26
25
22
22
22
33
X =23
SD=23
NO2 — -NO3
mg/l
1
1
1
0
X =1
SD=1
2
1
1
0
0
0
0
0
0
0
1
1
1
X =1
SD=1
NH+— -NC13
mg/l
21
27
35
21
X =26
SD= 7
9
5
6
4
8
4
4
10
11
12
12
_
3
8
8
11
12
3
7
1 1
' X" = 10
SD= 2
Unidentified
loss,
mg/l
12
10
14
17
X =13
SD= 3
17
2=i
(-3)
1
_
25
10
14
5
(-12)
(-3)
15
(-4)
"X" ~8
SD=12
Table A-1. Rancho Cordova Breakpoint Chlorination-Data Summary
-------
U1
Time
IV. pH
0405
0450
0552
0652
0750
0858
1002
1102
1200
V. PH
2100
2153
2255
0001
0051
0157
0250
0351
0451
0552
0651
0800
0905
1000
VI. pH
0310
0342
0443
0555
0648
0800
0900
1000
1100
1200
1300
1400
feel
Ib/d»y
set polnl
300
300
290
340
1185
1375
1340
1610
1950
set point
2020
1815
1690
1460
1190
800
570
505
470
430
530
1050
1430
1270
Flow,
mgd
7.3 Br
0.314
0.314
0.304
0.362
0.934
1.174
1.104
1 .174
1 .304
C12
dose,
mg/l
Initial
NHj-N.
mg/t
(cn.XHHj-M,
Tree
residual
remaining ,
mg/l
eakpoint effluent used as inlector water, March 10,
115
115
114
113
152
140
I4f,
164
175
Y -137
SI.1- 24
9.5
9.8
9.5
10.0
14.0
14.0
13.9
15.5
18 2
X -12.7
SD« 3 . 1
7.5 Secondary effluent used
1 .114
1 .104
1 .104
0.934
0.774
0.524
0.374
0.324
0.304
0.284
0.364
0.734
1 .014
0.994
217
197
184
187
1B4
183
183
187
185
182
175
172
169
153
X -183
SD" 14
18
17.7
17
17
17
17
17
17
17
17
16
16
16
1 6
X -16.8
SD- 0.6
12.1
11.7
12.0
11 .3
10.9
10.0
10.5
10. h
,j 6
X '11.0
SI1'- 0.9
20
15
10
f,
15
It,
12.5
11
10
X M3
•.Hi" 4
as Injector water, March 2-3
12.1
11.1
10.8
11.0
10. B
10.8
10.8
11.0
10.9
10.7
10.9
10.7
10.6
9 6
X -10.8
SD» 0.5
15
17
14
14
12.5
12.5
12.5
15
14
20
12.5
15
14.5
12.5
X =14
SD- 2
rinal
NHj-N.
mg/l
976
0.39
0.29
0.33
0.15
0.48
0 . VI
0.20
0.37
_
X -.0.34
31. 0.12
, 1976
0.75
0.75
0.76
0 . 72
0.65
0.5S
0.39
0.49
0.44
0.50
0.46
0.52
0.53
0.45
X= 0.57
SD=0 . 1 3
set point 7.7 Breakpoint effluent used as Injector water, Marchll, 1976
300
250
230
200
250
940
1230
1290
1580
1620
1570
1800
0.374
0.324
0.304
0.304
0.374
0.824
1.104
1.164
1 .304
1.234
1.019
1.044
96
93
91
79
80
137
134
133
145
157
185
207
X -128
SD= 42
9.8
8.9
9.4
7.9
9.2
11.8
12.2
11.8
12.9
15.0
16.3
17.7
X -11.8
SD" 3.2
9.8
10.4
10.8
10.0
8.7
11 .6
11 .0
11 .3
11.2
10.5
11.3
11.7
X -10,7
SD- 0.9
7
7
12
12
9
16
13.5
12.5
10
10
11.5
1 3
X =11
SD- 3
0.70
0.70
0.17
0.64
0.16
0.57
0.62
0.43
0.31
0.88
0.86
0 14
X -0.52
SD-0.27
Initial
NCj-N,
nrsg/l
0.23
0,28
0.34
0.41
0.48
0.67
i). n
!I.B4
0.83
0 . 01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.02
0.02
0.07
0.07
0.06
0.03
0.01
0.01
0.01
0.10
0.27
0.15
0.03
0.03
Initial
NO,-!;,
mg/l
0.27
0.26
0.26
0.31
n.37
0 . 59
'i.79
1 .05
1 .30
0 . 09
0.07
0.06
0.06
0.05
0.05
0.05
0.06
0.07
0.06
0.06
0.07
0.08
0.08
0.05
0.06
0.06
0.06
0.06
0.06
0.06
0.13
0.19
0.20
0.21
0.20
Final
mg /t
1.1
1 .5
1 .0
.*>
2.1
2.5
2.4
2.4
_
1 .4
1 .4
1 .2
.2
1 .1
0.92
1 .1
1.2
1 .2
1.3
1 .3
1.3
1.5
1 .3
1.1
1.2
1.2
1.2
1.1
1.1
.1
.6
.7
.4
,6
.1
NO5
prod , In
B'polnt ,
mg/l
0.60
0.96
1.00
0.88
1.25
1.24
0.96
O.'il
_
f? -0.93
Sl:-0.27
1.31
1 .33
1 .14
1.15
1 .05
0.87
1.06
1.14
1.15
1.24
1.24
1.23
1 .40
1 .70
X =1.18
SD=0.14
0.98
1.07
1 .08
1 .11
1 .04
1.04
1 .04
1.37
1.24
2.05
1.36
0.87
X =1.19
SD-0.31
Chlorine consumed by reoctlon
mg/l •
69
72
70
75
103
103
104
115
_
;•: = 89
SD- 19
131
129
124
124
124
125 •
126
126
126
126
118
118
118
118
X" =124
SD* 4
69
62
63
55
69
85
88
86
96
107
117
134
X - 86
SD= 24
KHj -NO,
mg/l
12
19
20
IB
25
25
19
10
_
X -19
,'iD- 5
27
2T
23
23
21
18
22
23
23
25
25
25
28
34
X =25
SD* 4
20
22
22
23
21
21
21
28
25
42
28
18
X =24
SD= 6
NO! "-NOj
mg/l
1
1
2
2
2
3
4
4
4
X =3
sn=i
0
0
0
0
0
0
0
0
0
0
0
0
0
0
X =0
SD=-
0
0
0
0
0
0
0
1
1
1
0
0
X =0
SD=1
"HJ -*NO13
mg/l
f,
A
'T
2
7
8
3
6
X -!.
:;n=2
11
11
12
11
10
R
6
7
7
8
7
B
8
7
X =9
SD=2
11
11
3
10
2
9
9
7
5
13
13
2
X =8
SD=4
Unidentified
loss ,
mg/l
7
4
7
10
IJ
(-15)
3
18
-
5T - -1
SI)" 9
33
13
11
15
16
19
16
16
15
3
12
6
0
(-19)
X =11
SD=12
(-11)'
(-9)
(-9)
(-21)
(-21)
6
2
(-2)
8
(-16)
15
40
X =(-1)
SD=17
Table A-1. (Continued)
-------
U1
-J
Time
VII . pH
1655
1753
1013
1855
2055
2155
2255
2354
0052
0148
0249
0348
0450
VIII. PH
170S
1730
1750
1815
Cl,
•feed,
Ib/day
flow,
mtjd
set point H.O
1435
11.00
1550
1750
2080
2010
1950
1370
1135
855
625
515
490
O.R24
0.924
0.924
1 .000
1 .234
1 .174
1 .104
0.884
0.714
0.524
0.3114
0.324
0.284
set point 3.5
1450
1430
1445
1410
0.906
0.876
0.933
0.933
C12
dose .
mg/l
Initial
NliJ-N,
mq/l
(C12/NHJ.N)
Free
residual
remain ing ,
mg/l
Final
NH^-N,
mg/l
Secondary effluent used as injector water, March 4-5, 1976
209
208
201
210
202
205
206
186
191
196
195
191
207
X =201
SD= 8
21
20.8
21
20.5
21
19.8
20
' 19.5
19
19
19
18.7
18.5
St =19.8
sn= i .0
9.9
10.0
9.6
10.2
9.6
10.4
10.3
9.5
10.0
10,3
10.3
10,2
1U.2
X =10.1
SD= 0.4
7
11
12.5
11.5
11.5
14
16
9
13
12. 5
10
7
12
?; =11
SD= 3
0.52
0.54
0.83
t .02
0.97
0.93
0.88
-
0.58
O.Sb
-
0.43
_
X" =0.73
SD=0.22
Breakpoint effluent used as Injector water, March 10, 1976
192
196
186
181
X =189
sn= 7
17.7
17.2
16.9
16.9
X =17.2
SD= 0 . 4
10.8
11 .4
11.0
1^7
X =17.2
SD= 0.4
14
14
19.5
15
X =16
sn* 3
0.52
1 .1*
1 .3*
1.3*
Initial
NOj-N,
mg/1
0.01
0.01
0.01
0.01
0.01
0.05
0.01
-
0.01
0.01
0.01
0.01
0.01
0.07
0.13
0.04
0.03
Initial
NO'-N,
mg/1
0.05
0.05
0.05
0.05
0.05
0.05
0.04
-
0.01
0.04
0.05
0.04
0.05
0.08
-0.09
0.08
0.07
Final
NOj-N,
mg/1
1 .0
1 .0
1.2
1 .0
0.78
0.68
0.58
-
0.64
0.70
-
0.75
0.82
1 .4
1 .2
0.94
0.78
N03
prod . in
B'polnt,
mg/1
0.94
0.94
1.15
0.95
0.73
0.58
0.54
-
0.64
0.66
-
0.70
0.77
X = 0.78
sr= 0.19
1.25
0.98*
0.82*
0.68*
Chlorine consumed by reaction
NHj— N2
mg/1
156
154
153
148
152
144
145
-
140
MO
-
139
_
X =147
SD= 6
131
-
-
-
NH^-»NC>3
mg/1
19
19
23
19
15
12
11
-
13
13
-
14
16
X =1 6
SD= 4
25
-
-
-
NO~— -NOg
mg/l
0
0
0
0
0
0
0
-
0
0
0
0
0
X =0
SD=-
1
-
-
_
NH+— NC13
mg/l
8
8
13
16
15
14
13
-
9
9
-
7
-
X =11
SD= 3
8
8
-
_
Unidentified
loss,
mg/l
19
16
(-1)
15
8
21
21
-
16
21
-
24
~
X =16
SD= 7
13
-
-
_
Table A-1. (Continued)
-------
APPENDICES
APPENDIX B
RANCHO CORDOVA BREAKPOINT CHLORINATION
DEMONSTRATION PROGRAM
BREAKPOINT MODEL PREDICTIONS
58
-------
100
z
<
CO
X
z
O
tc.
50
20
10
5
2
1
INITIAL CONDITIONS
10
Figure B-l.
pH
20 30 40 50 60 70 80 100
TIME, SECONDS
200
8 pH
Ammonia Removal with Breakpoint Chlorination in a
Pipe Reactor-Model Prediction-pH Set Point =6.5
300
100
O 50
ui
oc
n
I
Z
I-
UJ
O
cc
20
10
INITIAL CONDITIONS
CI2:NH3-N = 9.30 TO 1
NH3-N
TEMP
pH
ALKALINITY -
NaOH
21.05mg/l
15° C
7.4
165 mg/l
120 mg/l
pH
8 pH
10
Figure B-2.
20 30 40 50 60 70 80 100
TIME, SECONDS
200
Ammonia Removal with Breakpoint Chlorination in a
Pipe Reactor-Model Prediction-pH Set Point = 7.0
300
59
-------
100
INITIAL CONDITIONS
O
z
<
UJ
cc
z
i
m
UJ
U
CC
UJ
a.
50
20
10
CI2:NH3-N
NH3-N
TEMP
pH
ALKALINITY
NaOH
10.5 TO 1
16.9 mg/l
15° C
7.4
165 m«/l
92 mg/l
8 pH
10
20
30 40 50 60 70 80 100
200
300
Figure B-3.
TIME, SECONDS
Ammonia Removal with Breakpoint Chlorination in a
Pipe Reactor-Model Prediction-pH Set Point =7.0
o
z
z
<
tu
CC
m
X
z
UJ
U
flC
100
50
20
10
INITIAL CONDITIONS
NHj-N
pH
O2:NH3-N
NH3-N
TEMP
pH
ALKALINITY
NaOH
12.25 TO 1
12.02 mg/l
15° C
7.4
165 mg/l AS CaCO3
70 mg/l
8 pH
10
20
30 40 50 60 70 80 100
200
300
Figure B-4.
TIME. SECONDS
Ammonia Removal with Breakpoint Chlorination in a
Pipe Reactor-Model Prediction-pH Set Point =7.3
60
-------
100
z
z
<
LU
OC
CO
X
o
ec
UJ
0.
O
Z
z
<
5
m
X
z
I-
UJ
O
OC
111
a.
INITIAL CONDITIONS
CI2:NH3-N = 10.8 TO 1
3-
= 16.7mg/l
TEMP = 15.0°C
pH = 7.4
ALKALINITY = 165mg/l
NaOH
8 pH
40 50 60 70 80 100
TIME, SECONDS
200
300
Figure B-5. Ammonia Removal with Breakpoint Chlorination in a
Pipe Reactor-Model Prediction-pH Set Point - 7.5
100
CI2:NH3-N = 11.7 TO 1
NH3-N = 11.83mg/l
TEMP = 15° C
pH = 7.4
ALKALINITY = 165 mg/l AS CaCO3
NaOH = 94 mg/l
8 pH
20 30 40 50 60 70 80 100
TIME, SECONDS
200 300
Figure B-6. Ammonia Removal with Breakpoint Chlorination in a
Pipe Reactor-Model Prediction-pH Set Point = 7.7
61
-------
100
o
Z
<
tu
oc
CO
X
H
UJ
o
oc
Ui
Q.
50 60 7080 100
TIME, SECONDS
8 pH
200 300
Figure B-7.
Ammonia Removal with Breakpoint Chlorination in a
Pipe Reactor-Model Prediction-pH Set Point = 8.0
100
u
z
2
<
iu
K
n
X
Z
H
UJ
2
UI
o.
a2:NH3-N ~ 11.7 T01
- 17.2 mg/l
TEMP - 15° C
pH - 7.4
ALKALINITY- 165 mg/l
MiOH - 148 mo/I
8 pH
30
40 50 60 70 80 100
TIME, SECONDS
200
300
Figure B-8. Ammonia Removal with Breakpoint Chlorination in a
Pipe Reactor-Model Prediction-pH Set Point =8.5
62
-------
7.5
Q.
o
I
CC
I-
1
UJ
K
CD
7.0
6.5
INITIAL CONDITIONS
= 20 mg/l
= 15° C
NH3-N
= 7.20
TEMP
PH
ALKALINITY = 175 mg/l AS CaCO3
CT = 0.0036 MOLES/LITER
CI2:NH3-N = 10:1
CI2:NH3-N=11:1
1
-SYSTEM CLOSED TO ATMOSPHERE-
BEYOND THAT REQUIRED FOR
NEUTRALIZATION OF ACIDITY
FROM HYDROLYSIS AND
DISSOCIATION OF CHLORINE
(EQ. 16, TABLE 3-3).
6.0
25
50 75 100
NaOH ADDED1, mg/l
125
150
Figure B-9. Breakpoint Reaction Final pH vs NaOH Added,
CI2:NH3-N Variable
63
-------
8
I
oc
H-
1
OQ
CT = 0.006 MOLES/LITER
CT - 0.005 MOLES/LITER
CT = 0.004 MOLES/LITER
Cj = 0.003 MOLES/LITER
CT = 0.002 MOLES/LITER
INITIAL CONDITIONS
BEYOND THAT REQUIRED FOR
NEUTRALIZATION OF ACIDITY
FROM HYDROLYSIS AND
DISSOCIATION OF CHLORINE
(EO. 16, TABLE 3-3).
I I
CI2:NH3-N
NH3:N
TEMP
PH
ALKALINITY
= 9:1
= 20mg/l
= 15° C
= 7.20
= 175 mg/l AS CaCO3
-SYSTEM CLOSED TO ATMOSPHERE-
25
50
75
100
125
150
NaOH ADDED1, mfl/l
Figure B-10. Breakpoint Reaction Final pH vs NaOH Added, CT Variable
64
-------
20
10
<
III
ec
u
oc
CI2:NH3-N
1
0.5
BEYOND THAT REQUIRED FOR
NEUTRALIZATION OF ACIDITY
FROM HYDROLYSIS AND
DISSOCIATION OF CHLORINE
(EQ. 16, TABLE 3-3).
INITIAL CONDITIONS
NH3-N
TEMP =15° =
pH
ALKALINITY =
20 mo/I
15°C
7.20
175 rag/I ASCaCO3
0.0036 MOLES/LITER
-SYSTEM CLOSED TO ATMOSPHERE-
25
50
75 100
NaOH ADDED1, ma/I
125
150
Figure B-11 Ammonia Remaining (NC13 Formed) vs NaOH
Added, C12:NH3-N Variable
175
65
-------
i 3
ui
K
I
Ul
o
K
CT = 0.002 MOLES/LITER
1 BEYOND THAT REQUIRED FOR
NEUTRALIZATION OF ACIDITY
FROM HYDROLYSIS AND
DISSOCIATION OF CHLORINE
(EQ. 16. TABLE 3-3).
CT = 0.003-0.006 MOLES/LITER
INITIAL CONDITIONS
NH3-N
TEMP
pH
ALKALINITY
= 9:1
= 20mg/T
= 15° C
- 7.20
= 175 mg/l AS CaCO3
-SYSTEM CLOSED TO ATMOSPHERE-
25
50
125
150
75 100
NaOH ADDED1, mg/l
Figure B-12. Ammonia Remaining (NCI3 Formed) vs NaOH Added, CT Variable
66
-------
350
300
250
o
ai
u
200
150
100
50
INITIAL CONDITIONS
20 mg/l
15° C
7.20
175 mg/l AS CaC03
0.0036 MOLES/LITER
NH3-N
TEMP
pH
ALKALINITY
1 BEYOND THAT REQUIRED FOR
NEUTRALIZATION OF ACIDITY
FROM HYDROLYSIS AND
DISSOCIATION OF CHLORINE
(EQ. 16, TABLE 3-3).
-SYSTEM CLOSED TO ATMOSPHERE-
25
50 75 100
NaOH ADDED1, mg/l
125
150
Figure B-13. Time to Reach Minimum Ammonia Concentration vs NaOH
Added, CI2:NH3-N Variable
67
-------
400
350
300
250
M
ui 200
150
100
50
1
BEYOND THAT
REQUIRED FOR
NEUTRALIZATION
OF ACIDITY FROM
HYDROLYSIS AND
DISSOCIATION OF
CHLORINE
(EO. 16. TABLE 3-3)
INITIAL CONDITIONS
= 9:1
= 20 mg/l
= 15° C
= 7.20
= 175 mg/l AS CaCO3
CI2:NH3-N
NH3-N
TEMP
pH
ALKALINITY
CT = 0.002 MOLES/LITER
CT = 0.003 MOLES/LITER
CT = 0.004 MOLES/LITER
0.005 MOLES/LITER
Cj = 0.006 MOLES/LITER
-SYSTEM CLOSED TO ATMOSPHERE-
i I 1
25
50 75 100
NaOH ADDED1, mg/l
125
150
Figure B-14. Time to Reach Minimum Ammonia Concentration vs NaOH
Added, C. Variable
68
-------
CO
UJ
CO
ill
Z
DC
Q
z
til
o
o
U
_cg
U
<
E
LINES REPRESENT CONCENTRATIONS
PREDICTED BY COMPUTER MODEL
20
40 60 80 100
200
400 600 8001000 2000 3000
TIME, SECONDS
Figure B-15 Predicted Breakpoint Chlorination Kinetics in a Plug Flow Reactor,
pH = 6.80, NH3-N = 2.5 mg/l. Temp = 15 C, CI2/N = 9.0
ui
O
£
CO
UJ
z
£
3 «
X U
0 CO
z
O
o
U
LINES REPRESENT CONCENTRATIONS
PREDICTED BY COMPUTER MODEL
20
40 60 80 100
200
400 600 8001000 2000 3000
Figure B-16.
TIME, SECONDS
Predicted Breakpoint Chlorination Kinetics in a Plug Flow
Reactor, pH = 7.50, NH3-N = 2.5 mg/l. Temp = 15 C, CI2/N = 9.0
69
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-78-029
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
FULL-SCALE DEMONSTRATION OF NITROGEN REMOVAL
BY BREAKPOINT CHLORINATION
5. REPORT DATE
March 1978 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
Richard W. Stone
Sacramento Area Consultants
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Sacramento Regional County Sanitation District
4660 Ecology Lane
Sacramento, California 95827
10. PROGRAM ELEMENT NO.
1BC611
11. CONTRACT/GRANT NO.
S803343-01
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory--Cin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES
Project Officer: James J. Westrick (513) 684-7652
16. ABSTRACT
A large-scale breakpoint chlorination system was constructed and operated at Rancho
Cordova, CA. Reliable operation was demonstrated and a number of observations
regarding process chemistry and engineering were made, including (1) the chlorine
to ammonia-N ratio required to reach breakpoint and to maintain a controllable free
residual was 10:1; (2) nitrate production was not pH sensitive in the range 6.5 to
8.5; (3) the rate of reaction of ammonia oxidation varied with final pH, with
fastest rates observed at pH 7.0. Slower rates were observed at lower and higher
pH; (4) mixing intensity had no effect upon chemical requirements or effluent
quality, but was important for smooth process control; (5) the amount of sodium
hydroxide used for neutralization was identical to that predicted from stoichio-
metry; (6) the control system used here provided excellent control of the process
chemistry.
1 <
1
IV. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Chlorination
Ammonia
Oxidation
Waste treatment
Process control
Reaction time
18. DISTRIBUTION STATEMENT
Release Unlimited
b. IDENTIFIERS/OPEN ENDED TERMS
Demonstration
Rancho Cordova
19. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This page)
Unclassified
c. COS ATI Field/Group
13B
21. NO. OF PAGES
78
22. PRICE
EPA Form 2220-T (9-73)
70
8OI«tMBt-a60-880/58
------- |