QUHDE DGinFECTl OF TREfllED UJBSIE11ER
in BBFFLEO COHTBCT
Bl <1°C
U. S. ENVIRONMENTAL PROTECTION AGENCY
ARCTIC ENVIRONMENTAL RESEARCH LABORATORY
COLLEGE, ALASKA 99701
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CHLORINE DISINFECTION OF TREATED WASTEWATER
IN A BAFFLED CONTACT CHAMBER AT <1°C
Ronald C. Gordon
Charlotte V. Davenport
Barry H. Reid
Working Paper No. 21
U.S. ENVIRONMENTAL PROTECTION AGENCY
ARCTIC ENVIRONMENTAL RESEARCH LABORATORY
COLLEGE, ALASKA
Associate Laboratory of
National Environmental Research Laboratory
Corvallis, Oregon
Office of Research and Development
October 1973
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A Working Paper presents results of investigations which are, to some
extent, limited or incomplete. Therefore, conclusions or recommendations
expressed or implied, are tentative. Mention of commercial products or
services does not constitute endorsement.
-------
Abstract
This study was designed to examine the disinfection process at low
temperatures because effluent in the Arctic and Subarctic can be expected
to be in the 0 to 10°C range during a significant portion of each year.
Disinfection was considered effective if the effluent contained no more
than 1000 total and 200 fecal coliforms/100 ml. Total chlorine residual
was monitored with the orthotolidine and iodometric methods, and the memr
brane filter method was used for all bacteria enumeration.
During the first phase of the study, batch treatment was used to ex-
amine three secondary and one primary effluent. The results indicated
that effective disinfection was attained in samples from all sources at
<1°C when the actual contact time was 60 minutes and the final chlorine
residual was approximately 1 mg/1 (orthotolidine).
The second phase of the study was conducted in an 8-compartment,
over-under baffled, 60-liter contact chamber at <1°C and 10°C. Flow
rates providing 30, 60 and 120 minutes theoretical contact time were used.
Dye studies at each flow rate indicated that extensive short-circuiting
occurred, and that the 120 minute contact time flow rate was the only
one which provided 60 or more minutes residence time for the majority of
the effluent.
Regardless of the flow rate or chlorine residual maintained, the
fecal coliforms were essentially destroyed (<5/100 ml) at <1°C. However,
reduction of the total coliforms to <1000/100 ml did not occur when
the theoretical contact time was 30 minutes, even when the chlorine
residual was 3.3 mg/1 (orthotolidine). At 60 minutes theoretical con-
tact time, nearly 2 mg/1 chlorine residual (orthotolidine) were required
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11
before the total coliforms were sufficiently reduced. Only slightly
more than 0.5 mg/1 chlorine residual (orthotolidine) was required for
the total coliforms at the 120 minutes theoretical contact time flow
rate. The fecal streptococci numbers were generally reduced to a level
between those found for the total and fecal col iforms.
Theoretical contact times of 30 and 60 minutes were used at the 10°
operating temperature. The results suggested that raising the tempera-
ture from <1°C to 10°C caused little or no change in the effectiveness
of disinfection.
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m
TABLE OF CONTENTS
PAGE
INTRODUCTION ' 1
MATERIALS AND METHODS 5
EXPERIMENTAL RESULTS 11
DISCUSSION 41
CONCLUSIONS 52
REFERENCES 54
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IV
LIST OF FIGURES
NUMBER PAGE
1 Flow through system used in the disinfection studies. 6
2 Instantaneous and continuous dye injection in flow
through contact'chamber studies. (60 minutes
theoretical contact time) 13
3 Average number of bacteria surviving disinfection at
<1°C with corresponding total chlorine residual average
and range. [60 minutes theoretical contact time, 1 mg/1
chlorine residual (OT)] 16
4 Average number of bacteria surviving disinfection at
<1°C with corresponding total chlorine residual
average and range. [60 minutes theoretical contact
time, 2 mg/1 chlorine residual (OT)] 19
5 Instantaneous and continuous dye injection in flow
through contact chamber studies. (30 minutes
theoretical contact time) 21
6 Average number of bacteria surviving disinfection at
<1°C with corresponding total chlorine residual average
and range. [30 minute theoretical contact time, 2.5
mg/1 chlorine residual (OT)] 25
7 Instantaneous and continuous dye injection in flow
through contact chamber studies. (120 minutes
theoretical contact time) 27
8 Number of bacteria surviving disinfection at <1°C
with corresponding total chlorine residuals. [120
minutes theoretical contact time, 1 mg/1 chlorine
residual (OT)] 30
9 Number of bacteria surviving disinfection at <1°C
with corresponding total chlorine residuals. [120
minutes theoretical contact time, 1 mg/1 chlorine
residual (OT)] 31
10 Number of bacteria surviving disinfection at 10°C
with corresponding total chlorine residuals. [60
minutes theoretical contact time, 1 mg/1 chlorine
residual (OT)] 37
11 Number of bacteria surviving disinfection at 10°C
with corresponding total chlorine residual. [30
minutes theoretical contact time, 2 mg/1 chlorine
residual (OT)] 38
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LIST OF TABLES
NUMBER PAGE
Effluent Sample Parameters from Flow Through
Contact Chamber Studies at <1°C. [60 minutes
theoretical contact time, 1 mg/1 total chlorine
residual (OT)] 15
Effluent Sample Parameters from Flow Through
Contact Chamber Studies at <1°C. [60 minutes
theoretical contact time, 2 mg/1 total chlorine
residual (OT)] 18
Effluent Sample Parameters from Flow Through
Contact Chamber Studies at <1°C. [30 minutes
theoretical contact time, 2.5 mg/1 total
chlorine residual (OT)] 23
Effluent Sample Parameters from Flow Through
Contact Chamber Studies at <1°C. [120 minutes
theoretical contact time, 1 mg/1 total chlorine
residual (OT)] 29
Effluent Parameters of Samples Subjected to 60
Minutes Batch Disinfection at <1°C in Parallel with
the Flow Through System. 34
Effluent Parameters Common to Samples Examined at
10°C. 35
Effluent Parameters of the 10°C Flow Through System
and Parallel 60 Minute Batch Disinfection at 10°C
and <1°C. 40
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Introduction
The use of chlorine as a disinfectant in water and treated wastewater
has come under rather intensive study, beginning with the early work of
Heathman ejt. al. (17) and Rudolfs and Gehm (27) in 1936, and the current
"State of the Art" has been well documented in several recent publications
(2, 5, 26, 35). With the exception of the early study of sewage disinfec-
tion by Rudolfs and Gehm (27), nearly all the literature indicates that
the disinfecting ability of chlorine is severely hindered by low tempera-
tures (5, 6). However, most of these studies used pure culture-pure
water systems to establish the disinfecting characteristics of chlorine
without the inherent interferences found in treated wastewater (5). In
1967, Marais et. al_. (24) pointed out the need for reliable laboratory
studies to establish the disinfecting ability of chlorine in the presence
of the inherent interferences found in treated wastewater. Subsequently,
some effort has been made in this direction (8, 21, 22), but these studies
have not considered the effect of low temperature on the disinfection pro-
cess.
Over a large portion of the world, water temperatures in waste treat-
ment systems and in effluents from these systems may approach 0°C during
several months each year, and disinfection may be difficult to achieve in
these cold effluents. Throughout the cold months, the receiving waters
into which the effluents are discharged will also have temperatures near
0°C. These very low receiving water temperatures accentuate any problems
caused by ineffective chlorine disinfection because cold effluents may
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contain more enteric bacteria than warm effluents (9, 29), and fecal in-
dicator bacteria survive for longer periods in 0°C receiving water (15)
than in warmer receiving water (3). Preliminary evidence also indicates
that salmonellae have increased survival at 0°C (34). Therefore, an ef-
fective effluent disinfection process is of great importance in cold cli-
mates where low temperatures may make disinfection difficult to achieve.
However, the process has received little or no special consideration in
actual cold climate waste treatment practice.
Minimum effective treated wastewater disinfection, as used throughout
this presentation, is based on the disinfection criteria established by
the U. S. Environmental Protection Agency, Region X (11). These criteria
are: [1] that effluents from chlorine contact chambers shall average
less than 1000 total coliforms and 200 fecal coliforms/100 ml when the ef-
fluent is discharged into recreational waters and [2] that the total chlo-
rine residual shall not be less than 1 mg/1 after 60 minutes of contact
time when conclusive coliform data are not available.
In order to determine whether or not effective treated wastewater dis-
infection could be achieved at less than 1°C (<1°C), a two-phase study was
conducted at the Arctic Environmental Research Laboratory. During the
first phase, batch treatment with rapid initial chlorine mixing and con-
tinuous stirring was used to study effluents from four waste treatment sys-
tems at <1°C with controls run in parallel at 25°C (16). These effluents
were from a primary sedimentation system, a 15 day detention time aerated
lagoon and two extended aeration systems. The results indicated that both
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chlorine demand and the rate or extent of coliform reduction were de-
creased at <1°C where compared to the 25°C results. Effective disinfec-
tion was attained in effluents from all sources at <1°C within the 60
minutes contact time in the presence of no more than 1 mg/1 final total
chlorine residual (orthotolidine method). The ease with which effective
disinfection was attained varied significantly among the four effluents
at <1°C, but there was essentially no difference in the 25°C controls.
The primary sedimentation system produced a more uniform effluent which
was consistently easier to disinfect than the secondary effluents. How-
ever, it did require a slightly greater initial chlorine dose to provide
a final 1 mg/1 chlorine residual.
When disinfection is conducted using a batch system, theoretical
and actual contact time are the same. This is analogous to plug flow in
a flow through system. It has been pointed out in several recent publica-
tions (7, 8, 20, 21, 23, 28, 30, 35) that plug flow provides the most
nearly ideal situation for disinfection because all liquid entering the
contact chamber is retained in tne chamber for the theoretical contact
time. In actual practice, short-circuiting in the contact chamber pre-
cludes the attainment of residence time approaching theoretical contact
time. Thus, theoretical contact time has little meaning, rendering in-
correct the assumption that batch disinfection results can be extrapolated
to flow through contact chambers (7).
As was previously discussed, the first phase of this study showed
that effective disinfection could be attained with batch treatment at <1°C
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with no more than 60 minutes contact time in the presence of 1 mg/1 or
less final total chlorine residual (orthotolidine method). Since higher
bacterial quality can be expected in the effluent after batch disinfec-
tion than in flow through contact chambers, a second phase of this study
was conducted at <1°C using a well baffled flow through chlorine contact
chamber. The objective of this study was to determine if minimum effec-
tive disinfection could be achieved in a contact chamber built according
to the design guidelines established by the U. S. Environmental Protec-
tion Agency, Region X (11). Briefly, these design guidelines state that:
[1] the chlorine contact chamber must be sized to provide 60 minutes con-
tact time at design flow with 20 minutes contact time at peak hourly flow
or maximum pumping rate, which ever is greater; [2] the contact chamber
must be designed to minimize short-circuiting; and [3] chlorine must be
thoroughly mixed with the treated wastewater to achieve maximum disinfec-
tion efficiency.
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Materials and Methods
Effluent Source and Sampling
The primary sedimentation system effluent examined during the first
phase of this study (16) was from the 2.5 million gallon/day Fairbanks,
Alaska city plant. This effluent was selected for further study because
it had uniform physical and chemical characteristics, and because it was
relatively easy to disinfect in batch treatment. The day prior to each
experiment of the second phase, approximately 150 gallons of effluent
were collected in 15 gallon polyethylene barrels and transported immedi-
ately to the laboratory.
Effluent Preparation After Arrival in the Laboratory
The barrels of effluent were placed in a controlled temperature room
where the ambient air temperature was maintained at or slightly below the
experiment temperature. The effluent temperature was determined, then
cooled to 0.3-0.5°C, or adjusted to 10°C, in three 50 gallon batches using
the 55 gallon barrel and cooling apparatus shown in Figure 1. These
batches were stirred continuously until the next day.
Flow Through and Batch System Description
Figure 1 is a schematic diagram of the flow through system showing
the pattern of effluent and chlorine feed, and movement of the liquid
through the contact chamber. The various flow rates were obtained using
Holter model ER 161 variable speed pumps equipped with different size tub-
ing. All liquid, was moved in Tygon or latex rubber tubing. It was neces-
sary to continuously stir the effluent in the feed barrel and the constant
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REFRIGERATED
WATER BATH;
VTH^
3 LITER CONSTANT
LEVEL CHAMBER
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55 GAL. FEED BARREL
CHLORINE
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BAFFLES
CHLORINE CONTACT CHAMBER
TO
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Figure 1. Flow through system used in the disinfection studies.
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level chamber to maintain solids in suspension.
The contact chamber was an eight compartment over-under baffled unit,
having a 60 liter capacity. Effluent passed the under baffles through a
0.8 cm slot the full width of the chamber, and passed the over baffles at
a depth of 0.8 cm. The first seven compartments were the same size, 38.1
cm wide by 16.2 cm deep by 10.2 cm long. The last compartment was 21.3
cm long.
Flow rates through the contact chamber were 0.5, 1.0 and 2.0 liters
per minute providing theoretical contact times of 120, 60 and 30 minutes,
respectively. The pump speed was adjusted so that it took 60 ± 1 second
to fill an appropriate size class A volumetric flask with liquid as it
was discharged from the chamber. The flow rate was monitored frequently
throughout each run and adjustments in pump speed were made as necessary
to maintain the desired flow rate.
Chlorine stock solution was pumped from the reservoir into the con-
stant level chamber, a modified 100 ml polypropylene graduated cylinder
with the top closed to minimize volatilization of chlorine. The flow
rate was adjusted so that there was a continuous overflow to waste from
the constant level chamber rather than returning the overflow to the
stock solution reservoir. The constant level chamber was mounted above
the contact chamber so that the hydrostatic head would easily permit
gravity flow of chlorine through a rotameter used to control and monitor
the volume of chlorine being injected into the effluent feed line.
The batch system run in parallel with the flow through system was
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8
set up as described previously (16). A 60 minute contact time was used
regardless of the flow rate used in the contact chamber.
All studies were conducted in a controlled temperature room with the
temperature adjusted to maintain the effluent at <1°C or 10°C in the con-
tact chamber.
Glassware and Glass Distilled Mater Preparation
x
All glassware used during this study was made chlorine demand free
(1) and glass distilled water was prepared as described previously (16).
Both the glassware and the glass distilled water were allowed to equili-
brate at the temperature to be used for the particular disinfection ex-
periment.
Chi orination Methodology
A chlorine stock solution volume sufficient for all needs was prepared
by dilution of household bleach (Purex brand) with glass distilled water
immediately prior to each experiment. The stock solution was made up to
500, 1000 or 2000 mg/1 chlorine depending on the effluent flow rate through
the contact chamber and the chlorine residual desired. Varying the chlo-
rine concentration permitted the stock solution flow rate to be maintained
at no more than 13 ml/minute, minimizing any dilution effect in the efflu-
ent.
Immediately prior to the start of each disinfection experiment, the
initial chlorine demand and the 60 minutes contact time chlorine demand
were determined in the effluent, as previously described (16).
Total chlorine residual was determined by both the orthotolidine (OT)
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and iodometric methods as described in Standard Methods (1). At the start
of each experiment, chlorine residual determinations were made with both
methods in the unchlorinated effluent. The OT method was then used to
monitor the residual at predetermined time intervals until a fairly con-
stant concentration was reached. Both methods were then employed through-
out the remainder of each experiment.
Bacteria Enumeration
Total coliforms, fecal coliforms and fecal streptococci were enumer-
ated with the membrane filter method (13). The media were M-Coliform
Broth (BBL), M-FC Broth (BBL) and KF-Streptococcal Agar (BBL and Difco),
respectively. Each time the M-FC Broth was prepared, the pH was measured
and adjusted to 7.4 if necessary.
Effluent samples for bacteria enumberation were collected in sterile,
220 ml, polypropylene containers (Falcon Plastics) which contained 0.5 ml
of 10 percent sodium thiosulfate solution.
The potential problems and their possible effect on coliform enumer-
ation with the membrane filter method in chlorinated effluents were dis-
cussed previously (16).
Physical and Chemical Parameter Measurement
Chemical oxygen demand (COD), total solids (TS), total suspended
solids (TSS), volatile suspended solids (VSS), total dissolved solids
(TDS), volatile dissolved solids (VDS) and total volatile solids (TVS)
were determined by the methods described in Standard Methods (1). Am-
monia nitrogen (NH3-N) and total nitrogen (kjeldahl) were determined ac-
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10
cording to Techinicon AutoAnalyzer Methodology (31, 32). Nitrite (N02-N)
and nitrate (N03-N) were determined according to U. S. Environmental Pro-
tection Agency methods (10). A Leeds & Northrup pH meter (model 7401),
equipped with a Leeds & Northrup automatic temperature compensator and a
Beckman Combination Probe (GP Glass), was used for pH determinations.
Dye Studies in the Chlorine Contact Chamber
For these experiments, tap water cooled to <1°C was pumped into the
contact chamber at rates of 0.5, 1.0 or 2.0 liters/minute. The Rhodamine
B dye was injected in the same manner and location as the chlorine in the
disinfection studies (Figure 1). Dye concentration was measured using a
G. K. Turner Associates model 111 Fluormeter equipped with a flow through
door, and recorded on a Beckman model 1005 recorder.
To determine residence time of particles entering the chamber, a vol-
ume of dye was rapidly injected and its passage through the system fol-
lowed. To establish operating time required for constant concentration,
dye was injected continuously for several hours. The volume or rate of
dye injection and the instrument sensitivity were adjusted so that maxi-
mum readings of 60-90 percent of full scale were obtained on the recorder.
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n
Experimental Results
The results presented here were derived from 16 flow through contact
chamber experiments. Of these, 14 were conducted at <1°C and two at 10°C
using four total chlorine residual:theoretical contact time relationships.
As a parallel control with each flow througn experiment, effluent was
treated in batch using 60 minutes contact time with a 1 mg/1 final total
chlorine residual.
The study was conducted from November 15, 1972 to April 15, 1973,
during which time the city waste treatment system operating temperature
was 8-10°C. Because a large sample volume was collected for each experi-
ment, it was necessary to transport the effluent in an open truck. As a
result, the effluent temperature was generally lowered by the ambient air
temperature during the trip. Effluent temperature measured immediately
after arrival in the laboratory ranged from 0.6°C to 9.2°C. Temperature
variations were random throughout the time the study was conducted and
there did not appear to be any correlation with the disinfecting charac-
teristics of a particular sample. The only apparent effect resulting
from this temperature variation was the length of time required to cool
the effluent to 0.3-0.5°C.
The range of values obtained for effluent parameters was generally
random throughout the entire study. However, some variation could be ex-
pected during the five month period that samples were taken. The chlo-
rine concentration added initially varied with the chlorine demand of
each sample and the desired residual in the contact chamber during each
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12
series of experiments.
Dye Studies at 60 Minutes Theoretical Contact Time
Figure 2 shows typical results of instantaneous and continuous dye
injection at the 60 minute theoretical contact time flow rate. After in-
stantaneous injection, dye was first detected in the effluent from the
contact chamber in 14 minutes. Other results showed first dye appearance
in 12 to 15 minutes at the same flow rate. The dye concentration then
increased rapidly and the peak was reached 42 minutes after injection.
The curve produced by dye passage was not symmetrical, and it required
50 to 51 minutes for 50 percent of the dye to pass. Thirty-three percent
of the dye was still in the chamber after 60 minutes residence time,
which was theoretical contact time at this flow rate. Recently,
Kothandaraman et^ a_K (21) discussed chlorine contact chamber performance
and pointed out that plug flow was represented by a Morril index of 1.0.
The Morril index for this chamber at the 60 minute theoretical contact
time flow rate was 2.8 which indicated that plug flow was not even ap-
proached.
When the dye was injected continuously, elapsed time for first dye
appearance was approximately the same as the instantaneous injection.
However, the concentration increased at a much slower rate and reached
maximum concentration after approximately 160 minutes elapsed time. The
dye concentration then continued at a nearly constant level for the re-
mainder of the time the chamber was operated.
Disinfection Studies a_t <1°C Using (50 Minutes Theoretical Contact Time
1 mg/1 Total Chlorine Residual (OT)
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lOOr
INSTANTANEOUS DYE INJECTION
CONTINUOUS DYE INJECTION
20
40
60
80
100
120 140 160 I6C
ELAPSED TIME, minutes
"20O~
220
240
260
280
300
Figure 2. Instantaneous and continuous dye injection in flow through contact chamber studies.
60 minutes theoretical contact time.
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14
The five replicate experiments in the 60 minute theoretical contact
timerl mg/1 total chlorine residual (OT) series at <1°C were conducted
over a 39 day period. The arithmetic mean, and maximum and minimum para-
meter values are shown in Table 1. This value range is comparable for
most values obtained throughout the study.
Preliminary determinations indicated that total chlorine residual
in the contact chamber effluent reached its maximum concentration in
about the same elapsed time as observed for the dye. Therefore, moni-
toring of the effluent for chlorine residual and viable bacteria began
after the system had operated for 120 minutes. As shown in Figure 3,
the average total chlorine residual (OT) became stable at 0.9-1.0 mg/1
after 150 minutes elapsed time, with a range of 0.57-1.5 mg/1 for the
five experiments in this series. The average iodometric residual reached
a concentration of 4.2 mg/1 in 120 minutes and continued to increase un-
til it reached 4.5 mg/1 at 270 minutes. The minimum and maximum concen-
trations determined by the iodometric method during the series were 3.4
and 5.0 mg/1, respectively, and the average was 3.4-3.6 mg/1 higher than
obtained with the OT method.
The average number of total coliforms, fecal coliforms and fecal
streptococci surviving disinfection in the presence of these total chlorine
residuals are also shown in Figure 3. The initial total coliform count in
the unchlorinated effluent ranged from 2.2-3.6 x 10/100 ml. When the to-
tal chlorine residual in the contact chamber effluent reached its maximum
average concentration, the lowest average total coliform count was 3.4 x
10 /100 ml. The lowest total coliform count recorded for any sample dur-
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15
Parameter
Initial temperature, °C
Final temperature, °C
Initial pH
Final pH
Chlorine added as HOC1 , mg/1
TS, mg/1
TVS, mg/1
TSS, mg/1
VSS, mg/1
VDS, mg/1
TDS, mg/1
NH3-N, mg/1
N02-N, mg/1
N03-N, mg/1
Kjeldahl-N, mg/1
COD, mg/1
Arithmetic
mean
0.6
0.5
7.2
7.3
5.6
444
256
65
49
183
363
16.8
0.020
0.052
24.6
235
Maximum
value
0.7
0.8
7.4
7.4
6.9
490
380
81
59
280
400
20
0.04
0.07
30
289
Minimum
value
0.4
0.2
7.1
7.2
4.6
400
200
54
40
120
320
14
<0.01
0.04
20
183
Number
of
samples
5
5
5
5
5
5
5
5
5
4a
4a
5
43
5
5
5
a Results not available for some samples.
Table 1. Effluent Sample Parameters from Flow Through Contact Chamber
Studies at <1°C.
60 Minutes Theoretical Contact Time, 1 mg/1
Total Chlorine Residual (OT).
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16
10
10'
E ;
O lO
10
a:
UJ
H
< in3
OD 10
at
ii1 ,~2L
10
O TOTAL COLIFORMS
A FECAL COLIFORMS
D FECAL STREPTOCOCCI
. 6
1 =
V)
uj 4
IT
UJ 3
5
O I
O IODOMETRIC RESIDUAL
D ORTHOTOLIDINE RESIDUAL
3O 60 90 120 150 180 210 240 270 3OO
ELAPSED TIME, minutes
33O 36O 39O 42O
Figure 3. Average number of bacteria surviving disinfection at <1°C
with corresponding total chlorine residual average and range.
60 minutes theoretical contact time, 1 mg/1
chlorine residual (OT).
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17
o
ing the series was 1.8 x 10/100 ml. From an initial count of 6.8 x
10^-7.0 x 105/100 ml in the unchlorinated effluent, the fecal coliforms
were rapidly reduced to <100/100 ml. They continued to decrease in all
samples during this series until, after 240 minutes elapsed time, all
samples contained <5/100 ml (shown as 5/100 ml in Figure 3). The aver-
age fecal streptococci number was reduced to <1000/100 ml from initial
5
counts of 2.1-6.1 x 10 /100 ml. The lowest average number was 110/100 ml
with 30/100 ml as the lowest count in any sample.
Disinfection Studies a_t <1°C Using 6J3 Minutes Theoretical Contact Time
2 mg/1 Total Chlorine Residual (OT)
In the 60 minute theoretical contact time:2 mg/1 total chlorine re-
sidual (OT) series at <1°C, four replicate experiments were conducted dur-
ing a 23 day period. The arithmetic mean, maximum and minimum parameter
values for the effluent samples examined in this series are presented in
Table 2.
The total chlorine residual, total coliform, fecal coliform and fe-
cal streptococci results for this series of experiments are shown in Fig-
ure 4. Monitoring of the effluent was begun after the system had operated
for 120 minutes. The average total chlorine residual, as measured by the
OT method, continued to increase from 1.4 mg/1 at 120 minutes to 2.3 mg/1
at 420 minutes elapsed time. The minimum and maximum concentrations were
1.1 mg/1 at 120 minutes and 2.5 mg/1 at 420 minutes, respectively. The
residual, as measured by the iodometric method, did not show the continu-
ous increase found with the OT method but became stable at 5.6-5.8 mg/1
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18
Parameter
Initial temperature, °C
Final temperature, °C
Initial pH
Final pH
Chlorine added as HOC1 , mg/1
TS, mg/1
TVS, mg/1
TSS, mg/1
VSS, mg/1
VDS, mg/1
TDS, mg/1
NH3-N, mg/1
N02-N, mg/1
N03-N, mg/1
Kjeldahl-N, mg/1
COD, mg/1
Arithmetic •
mean
0.4
0.5
7.2
7.3
6.8
470
285
70
49
188
363
19.0
0.022
0.072
23.8
263
Maximum
value
0.6
0.6
7.3
7.4
7.7
540
340
no
78
220
400
22
0.04
0.08
25
332
Minimum
value
0.3
0.4
7.0
7.1
6.3
440
240
52
35
160
330
14
0.01
0.07
23
215
Number
of
samples
4
4
4
• 4
4
4
4
4
4
4
4
4
4
4
4
4
Table 2. Effluent Sample Parameters from Flow Through Contact Chamber
Studies at <1°C.
60 Minutes Theoretical Contact Time, 2 mg/1
Total Chlorine Residual (OT).
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19
io8
io7
OlO6
O>
o
o
o
§I04
CD
U
O
IO1
IOC
7
O TOTAL COLIFORMS
A FECAL COLIFORMS
D FECAL STREPTOCOCCI
o>
E
o
V)
O IODOMETRIC RESIDUAL
D ORTHOTOLIDINE RESIDUAL
I
30 60 90 120 150 180 210 240 270
ELAPSED TIME, minutes
300 330 360 390 420
Figure 4. Average number of bacteria surviving disinfection at <1°C
with corresponding total chlorine residual average and range.
60 minutes theoretical contact time, 2 mg/1
chlorine residual (OT).
-------
20
after 240 minutes elasped time. During the time when the average residual
was stable, the minimum and maximum residuals recorded were 5.2 mg/1 and
6.2 mg/1, respectively.
The total coliforms in the unchlorinated effluent ranged from 1.6 to
7 4
7.4 x 10/100 ml, and were reduced to an average of 2.2 x 10/100 ml of
effluent from the contact chamber after 120 minutes of elapsed time. The
total coliforms continued to decrease until the average number surviving
disinfection was 830/100 ml after 210 minutes with the range of 420/100 ml
3
to 1.5 x 10/100 ml. The count/100 ml remained >1000 in one of the four
3
experiments during this series and ranged between 1.1 and 1.7 x 10
throughout that experiment. In spite of the high numbers in one experi-
ment, the average count remained <1000/100 ml after 210 minutes with a
low of 120/100 ml. The lowest total coliform number recorded during this
series was 23/100 ml.
The initial fecal coliform numbers were 5.2-7.3 x 10 /100 ml, and
were reduced to <200/100 ml by the time the first sample was taken at 120
minutes elapsed time. After a somewhat unstable period, the count was re-
duced to <5/100 ml at 240 minutes in all experiments and remained at this
very low level. Fecal streptococci, initially 3.4-6.0 x 10 , were reduced
to an average of <100/100 ml of contact chamber effluent after 210 minutes
elapsed time and remained fairly stable.
Dye Studies ajt 3_0_ Minutes Theoretical Contact Time
Typical results for instantaneous and continuous dye injection at the
30 minutes theoretical contact time flow rate are shown in Figure 5. In
-------
21
z
o
I- 2
% ? i
? 3
UJ Z
" UJ
CO O
u co
< o
I- ID
00 O
? O
O
-CM
O
O
ul
o 1
o
LU
UJ
o
CVJ
oo ooo ooooo
OCDI^tOio^rOcW —
S1INH 30N30S3dOn"ld 3AllV13d
Figure 5. Instantaneous and continuous dye injection in flow through
contact chamber studies.
30 minutes theoretical contact time.
-------
22
all instantaneous injection trials, four minutes were required for the dye
to be detected in effluent from the contact chamber. The dye concentration
increased rapidly and reached its peak 28 minutes after injection. At this
flow rate, 58 percent of the dye remained in the chamber for the 30 minutes
theoretical contact time, and it required 32 to 33 minutes for 50 percent
of the dye to leave the contact chamber. Only four percent of the dye had
60 minutes or more residence time. The Morril index was found to be 2.9
indicating a considerable divergence from plug flow.
Although time of initial dye detection in the continuous injection
studies was nearly the same as for the instantaneous injection, the con-
centration increased at a slower rate. Maximum concentration was reached
after about 65 minutes and remained essentially stable as long as dye was
being injected.
Disinfection Studies a_t <1°C Using 30 Minutes Theoretical Contact Time
2.5 mg/1 Total Chlorine Residual (OT)
The three replicate experiments for the 30 minute theoretical contact
time:2.5 mg/1 total chlorine residual (OT) series were conducted over a 34
day period. During this time, several of the effluent parameter values
shown in Table 3 deviated from the typical range for the entire study per-
iod. The ammonia and Kjeldahl nitrogen concentrations were all higher than
those found during any other series. Several other parameters had consist-
ently, high values even though maximums for the entire study were not neces-
sarily obtained during this series. These parameters were: initial and
final effluent temperature in the contact chamber, total solids, volatile
-------
23
Parameter
Initial temperature, °C
Final temperature, °C
Initial pH
Final pH
Chlorine added as HOC1 , mg/1
TS, mg/1
TVS, mg/1
TSS, mg/1
VSS, mg/1
VDS, mg/1
IDS, mg/1
NH3-N, mg/1
N02-N, mg/1
N03-N, mg/1
Kjeldahl-N, mg/1
COD, mg/1
Arithmetic
mean
0.6
0.9
7.2
7.4
8.5
497
233
89
73
137
403
29.0
0.033
0.053
32.0
306
Maximum
value
0.9
1.0
7.5
7.6
11.3
500
250
no
88
160
420
32
0.04
0.08
34
320
Minimum
value
0.2
0.9
7.1
7.2
6.7
490
220
71
55
120
390
27
0.03
0.03
31
283
Number
of
samples
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
3
Table 3. Effluent Sample Parameters from Flow Through Contact Chamber
Studies at <1°C.
30 Minute Theoretical Contact Time, 2.5 mg/1
Total Chlorine Residual (OT).
-------
24
suspended solids, total dissolved solids, nitrite nitrogen and COD.
Following initial chlorine injection, the contact chamber was oper-
ated for 60 minutes before starting chlorine residual and bacteriological
monitoring. The results are presented in Figure 6. At 60 minutes elapsed
time, the average total chlorine residual (OT) reached 1.6 mg/1. The con-
centration continued to increase, reaching a 1.9 mg/1 plateau after 90
minutes. Between 120 and 135 minutes, a second concentration increase be-
gan and reached 2.5 mg/1 when the sample was taken at 150 minutes elapsed
time. The average total chlorine residual then remained quite stable at
2.5-2.6 mg/1. Between 150 and 210 minutes elapsed time, the minimum and
maximum values determined by the OT method were 1.8 and 3.3 mg/1, respec-
tively. The average chlorine residual by the iodometric method ranged be-
tween 5.3 and 5.7 mg/1 starting with the measurements at 150 minutes. Dur-
ing the same time period, the minimum concentration was 4.6 mg/1 and the
maximum was 7.2 mg/1.
The total coliforms in the unchlorinated effluent ranged between 1.2
7 4
and 2.3 x 10/100 ml. Those surviving disinfection averaged <1 x 10 /100 ml
after 90 minutes elapsed time with the lowest average number being 2.7 x
3
10/100 ml. During one experiment in this series, numbers <1000/100 ml
were recorded at two time intervals with the lower being 630/100 ml. From
initial numbers of 3.8-8.9 x 10 /100 ml, the average fecal coliform count
was reduced to 23/100 ml after 90 minutes elapsed time. The average then
remained very low, except for the 120 minute samples which contained an
average count of 160/100 ml (450/100 ml maximum). The initial fecal strep-
-------
25
10°
io
10
o
o>
o
EI05
o
o
IKJ*
oc
tlJ
HI
3'°*
10'
10°
TOTAL COLIFORMS
FECAL COLIFORMS
FECAL STREPTOCOCCI (TOO NUMEROUS TO COUNT)
V) 4
Ul
(E
LJ 3
_l
<
O
D
IODOMETRIC RESIDUAL
ORTHOTOLIDINE RESIDUAL
30
60
90 120
ELAPSED TIME, minutes
150
ISO
Figure 6. Average number of bacteria surviving disinfection at <1°C
with corresponding total chlorine residual average and range.
30 minute theoretical contact time, 2.5 mg/1
chlorine residual (OT).
-------
26
c
tococci count was 5.1-9.5 x 10 /TOO ml in this series of experiments, and
their removal by disinfection presented somewhat of an anomaly. During
the first experiment 110-210/100 ml remained in effluent from the contact
chamber after 90 minutes elapsed time. The count was >500/100 ml through-
out the second experiment and was recorded as Too Numerous To Count (TNTC).
Effluent volumes for filtration were adjusted during the third experiment
3
to accommodate the higher number. However, >2.3 x 10 streptococci were
present and were again recorded as TNTC. Since no average number could
be established, fecal streptococci results are not shown in Figure 6.
Dye Studies ajt 120 Minutes Theoretical Contact Time
Typical results of instantaneous and continuous dye injection at the
120 minute theoretical contact time flow rate are shown in Figure 7. Dye
was first detected in effluent from the chamber 28 minutes after instan-
taneous dye injection (28 to 30 minutes for all results). The concentra-
tion increase was essentially continuous, but did not produce a smooth
curve at this flow rate. The first point of interest on this curve is
that the area remaining under the curve after 60 minutes elapsed time in-
dicated that 73 percent of the dye was still in the contact chamber. The
peak was reached in 65 minutes, and 81 to 82 minutes were required for 50
percent of the dye to be discharged in the effluent. Only 24 percent of
the dye had a residence time equal to or greater than the 120 minutes theo-
retical contact time. The dye concentration curve was extrapolated to zero
at 225 minutes to permit an approximate Morril index determination. This
index was 3.4 indicating a rather extreme departure from plug flow.
-------
100
OT 90
1 80
Ul
" 70
tJ
O 6O
V) bu
UJ
g 50
13
u! 40
Ul
20
10
0
INSTANTANEOUS DYE INJECTION
CONTINUOUS DYE INJECTION
80 ~ 100 T20 J40 160 180 200 220 240~ 260~
' ELAPSED TIME, minutes
20 40
280
Figure 7. Instantaneous and continuous dye injection in flow through contact chamber studies.
120 minutes theoretical contact time.
ro
-------
28
The curve produced by continuous dye injection was erratic throughout
most of the 280 minutes the contact chamber was operated. There appeared
to be an unstable concentration plateau which started at about 105 minutes
and continued until 165 minutes had elapsed. The dye concentration then
increased and approached a fairly stable plateau between 230 and 280 min-
utes elapsed time.
Disinfection Studies at <1°C Using 120 Minutes Theoretical Contact
Time 1 mg/1 Total Chlorine Residual (OT)
The two experiments in this series were conducted during an 18 day
period. The parameter values for both experiments are shown in Table 4.
These are comparable to other values obtained throughout the study.
Bacteriological and total chlorine residual results for both exper-
iments are presented in Figures 8 and 9. Monitoring of the total chlo-
rine residual by both methods was started after 60 minute.s elapsed time.
Little or no residual (OT) appeared in the contact chamber effluent prior
to 120 minutes, but then a continuous increase was observed, reaching a
maximum concentration of about 0.8 mg/1. There was approximately 60 min-
utes difference between the two experiments in the time required to reach
both the 0.5 mg/1 residual level and the maximum residual level measured
by the OT method. When the first chlorine residual samples were taken at
60 minutes, the iodometric method indicated the presence of 0.76 and 1.0
mg/1 chlorine, and continued to show an increase to stable concentrations
of 2.7 and 2.9 mg/1. These concentrations were both recorded initially
at the 330 minute elapsed time sampling.
-------
29
Parameter
Initial temperature, °C
Final temperature, °C
Initial pH
Final pH
Chlorine added as HOC1 , mg/1
TS, mg/1
TVS, mg/1
TSS, mg/1
VSS, mg/1
VDS, mg/1
IDS, mg/1
NH3-N, mg/1
N02-N, mg/1
N03-N, mg/1
Kjeldahl-N, mg/1
COD, mg/1
Experiment #1
0.8
0.8
7.0
7.0
5.2
410
—
59
49
300
340
21
0.01
0.03
24
241
Experiment #2
0.6
—
7.2
7.3
4.5
410
250
57
36
140
320
16
0.01
0.03
20
202
Table 4. Effluent Sample Parameters from Flow Through Contact Chamber
at <1°C.
120 Minutes Theoretical Contact Time, 1 mg/1
Total Chlorine Residual (OT).
-------
30
io7
o>
o
§i«f
a:
ui
o
10'
TOTAL COLIFORMS
FECAL COLIFORMS
FECAL STREPTOCOCCI
TOO NUMEROUS TO COUNT
E
- 3
O
V)
LU2
oc.
UJ
3 '
X
o
I
O IODOMETRIC RESIDUAL
D ORTHOTOLIDINE RESIDUAL
150 180 210 240 270
ELAPSED TIME, minutes
3OO 330 360 390 420
Figure 8. Number of bacteria surviving disinfection at <1°C with
corresponding total chlorine residuals.
120 minutes theoretical contact time, 1 mg/1
residual (OT).
-------
31
I07
10"
o
A
D
O
O
CT
Ul
io2
10'
TOTAL COLIFORMS
FECAL COLIFORMS
FECAL STREPTOCOCCI
TOO NUMEROUS TO COUNT
_ I0
o> _
E 3
§2
UJ
I '
o
O IODOMETRIC RESIDUAL
O ORTHOTOLIDINE RESIDUAL
30 60 90
120 I5p 180 210 240 270 300 330 - 360
ELAPSED TIME, minutes
Figure 9. Number of bacteria surviving disinfection at <1°C with
corresponding total chlorine residuals.
120 minutes theoretical contact time,
1 mg/1 chlorine residual (OT).
-------
32
The total coliform numbers were 5.5 and 9.2 x 10 in the unchlorinated
effluent, and were reduced to <1 x 10/100 ml at the 210 minutes elapsed
time. The elapsed time for total coliform reduction to <1000/100 ml was
about 300 minutes in Figure 8 (980/100 ml) and 240 minutes in Figure 9
(850/100 ml) which were the times required for the chlorine residual to
reach 0.5 mg/1 (OT). Although the elapsed times differed by 60 minutes,
the rates of decrease were similar with final counts of 45/100 ml (Figure
8) and 25/100 ml (Figure 9).
5
The initial fecal coliform counts of 2.7 and 3.7 x 10 were reduced
to <200/100 ml in no more than 210 minutes elapsed time. There was consid-
erable dissimilarity in the rates of decrease after 210 minutes, but the
numbers were reduced to <5/100 ml during the last 60 minutes the system
was operated. The fecal streptococci initial counts were 4.7 and 6.6 x
10 /100 ml. The number of these bacteria surviving disinfection in the
two experiments followed nearly the same rate of decrease with 280/100 ml
(Figure 8) and 220/100 ml (Figure 9) remaining viable at 210 minutes elap-
sed time. When the last samples were taken, the effluent still contained
140/100 ml (Figure 8) and 100/100 ml (Figure 9).
Batch Treatment Disinfection a_t <1°C 60_ Minutes Using Contact Time,
]_ mg/1 Total Chlorine Residual (OT)
A batch treatment control was run in parallel with each of the 14 dis-
infection experiments conducted in the flow through system at <1°C. The
solids, nitrogen and the COD concentrations (Tables 1, 2, 3, 4) apply to
the effluent used for batch treatment. Other parameters for batch treat-
-------
33
ment at <1°C are presented in Table 5. It was not possible to maintain a
uniform temperature throughout the controlled temperature room because
the air flow patterns created warm and cold spots. Although the room tem-
perature was adjusted to maintain <1°C in the contact chamber, some parts
of the room deviated more than 1°C from this setting. The temperature
variation affected the small effluent volume used for batch treatment, re-
sulting in batch temperatures which exceeded 1°C during five of the exper-
iments. This is reflected in.the average and maximum temperatures shown
in Table 5. During two of the experiments, it was not possible to obtain
final counts for total coliforms, fecal coliforms or fecal streptococci
and the total coliforms were TNTC in a third experiment. This biased the
final average and maximum bacteria counts in Table 5 to some extent, but
the numbers reported still indicate what was generally found.
Disinfection Studies at 1Q°C
An attempt was made to obtain comparative disinfection results with
the flow through system at 10°C. However, the transition from winter to
spring in the Fairbanks area began approximately one month earlier than
expected in 1973 and flow through the city waste treatment system increased.
The increased flow may have caused dilution of the wastewater in the' sys-
tem as shown by the parameter values in Table 6. Most of these concentra-
tions were either lower than the minimum values recorded or in the low.end
of the value range found during the <1°C studies, suggesting that direct
comparison with the <1°C results would be unsatisfactory. Nevertheless,
two experiments were conducted to acquire some information on what might
-------
Table 5. Effluent Parameters of Samples Subjected to 60 Minutes Batch Disinfection at <1°C in
Parallel with the Flow Through System.
Parameter
Initial temperature, °C
Final temperature, °C
Initial pH
Final pH
Chlorine added as HOC1 , mg/1
Final chlorine residual:
iodometric method, mg/1
orthotolidine method, mg/1
Initial total coliform count/100 ml
Final total coliform count/100 ml
Initial fecal coliform count/100 ml
Final fecal coliform count/100 ml
Initial fecal streptococci
count/100 ml
Final fecal streptococci
count/ 100 ml
Average
0.9
1.0
7.2
7.2
5.4
3.9
0.98
2.7xl07
132
4.8xl05
20
5.2xl05
67
Maximum
1.9
2.4
7.5
7.5
7.8
4.9
1.5
7.4xl07
• 470
8.9xl05
220
9.5xl05
230
Minimum
0.4
0.4
7.0
7.0
4.2
3.0
0.46
5.5xl06
30
6.8X101*
<5b
2.1xl05
5a
Number
of
samples
14
14
14
14
14
13C
14
14
llc
14
12C
14
12C
j* Average of less than 20 colonies per filter when triplicate filters were examined.
No coliform colonies on any filter when triplicate filters were examined.
c Results not available for some samples.
CO
-------
35
Parameter
TS, rng/1
TVS, mg/1
TSS, mg/1
VSS, mg/1
VDS, mg/1
IDS, mg/1
NH3-N, mg/1
N02-N, mg/1
N03-N, mg/1
Kjeldahl-N, mg/1
COD, mg/1
Experiment #1
400
210
78
40
150
300
13
0.01
0.04
17
170
Experiment #2
370
210
56
34
'120
330
12
0.01'
0.03
15
150
Table 6. Effluent Parameters Common to Samples Examined at 10°C.
-------
36
be expected when the effluent temperature in the contact chamber was
raised from <1°C to 10°C.
One experiment was conducted with 60 minutes theoretical contact
time and 1 mg/1 total chlorine residual (OT) in the contact chamber and
the second with 30 minutes theoretical contact time and 2 mg/1 total chlo-
rine residual (OT). In parallel with each experiment,.batch treatment
was conducted at both <1°C and 10°C using 60 minutes contact time and
1 mg/1 total chlorine residual (OT). Figure 10 shows the results of the
60 minutes theoretical contact time experiment. The total chlorine re-
sidual (OT) reached the maximum concentration plateau of 0.76-0.85 mg/1
after 180 minutes elapsed time, and 120 minutes was required to reach
the 2.2-2.5 mg/1 plateau measured by the iodometric method. The total
coliforms were reduced from an initial count of 3.0 x 10 /TOO to a low of
1000/100 ml after 180 minutes elapsed time. The count then increased to
2.0-2.5 x 103/100 ml where it remained. Starting with 4.0 x 105 fecal
coliforms/100 ml, disinfection reduced the count to 5/100 ml at the 180
minute elapsed time sampling and the number did not increase after this
5
time. The initial fecal streptococci count of 3.9 x 10 /100 ml was re-
duced to 95/100 ml after 180 minutes, and remained near this number.
The 30 minute theoretical contact time results are presented in Fig-
t,
ure 11. The total chlorine residual (OT) reached the plateau in no more
than 60 minutes and remained in the 1.5-1.7 mg/1 range. During the same
time period, the iodometric total chlorine residual was on a 3.1-3.4 mg/1
plateau. The total coliforms started with an initial count of 1.7 x
-------
I08
37
10'
10*
o
O
I03
o
m
I0<
10'
O TOTAL COLIFORMS
A FECAL COLIFORMS
D FECAL STREPTOCOCCI
_ 10*-
O
CO
tlJ
2
(T
O
_J
I
O
O IODOMETRIC RESIDUAL
D ORTHOTOLIDINE RESIDUAL
60
90 120 I5O 180 210
ELAPSED TIME, minutes
240 270 300 330
Figure 10.
Number of bacteria surviving disinfection at 10°C with
corresponding total chlorine residuals.
60 minutes theoretical contact time,
1 mg/1 chlorine residual (OT).
-------
38
TOTAL COLIFORMS (TOO NUMEROUS TO COUNT)
FECAL COLIFORMS
FECAL STREPTOCOCCI
O IODOMETRIC RESIDUAL
D ORTHOTOLIDINE RESIDUAL
90 120 150
ELAPSED TIME, minutes
180
>to-
Figure 11.
Number of bacteria surviving disinfection at 10°C with
corresponding total chlorine residual.
30 minutes theoretical contact time,
2 mg/1 chlorine residual (OT).
-------
39
107/100 ml and were reduced to 3.1 x 10/100 ml after 60 minutes elapsed
3
time. The count then remained >8.3 x 10/100 ml which was reported as
TNTC and does not appear in Figure 11. The initial fecal coliform count
of 3.4 x 10 /100 ml was reduced to 15/100 ml after 90 minutes, and re-
mained in the 5-10/100 ml range after that time. The initial count of
3.2 x 10 fecal streptococci/100 ml was reduced to 210/100 ml at the 90
minute sampling and remained between 130 and 200 for the rest of the time
the contact chamber was operated.
The parameter values for the batch controls at 10°.C and <1°C, along
with the temperature and pH values for the contact chamber, are shown in
Table 7. When the effluent was brought to the laboratory, a small por-
tion was cooled immediately to <1°C and the rest was adjusted to 10°C.
As soon as the effluent was brought to temperature, samples were taken
for an immediate total coliform, fecal coliform and fecal streptococci
count (experiment #2 only). The results indicated that changing the ef-
fluent temperature did not alter the numbers of bacteria present. The
effluent was then held overnight at those temperatures. When the ini-
tial counts were made at the start of each experiment on the second day,
there was a four to six fold difference in the total coliform numbers at
the two temperatures. However, this does not provide an adequate explan-
ation for the poor total and fecal coliform results at 10°C in experiment
#1. .
-------
Table 7. Effluent Parameters of the 10°C Flow Through System and Parallel 60 Minute Batch
Disinfection at 10°C and <1°C.
Parameter
Initial temperature, °C
Final temperature, °C
Initial pH
Final pH
Chlorine added as HOC1 , mg/1
Final chlorine residual:
iodometric method, mg/1
orthotolidine method, mg/1
Initial total coliform count/100 ml
Final total coliform count/100 ml
Initial fecal coliform count/100 ml
Final fecal coliform count/100 ml
Initial fecal streptococci count/100 ml
Final fecal streptococci count/100 ml
Experiment #1
Flow
through
system3
10.0
10.0
7.1
7.1
5.0
S.OxlO7
4.0x105
3.9xl05
Batch
10°C
10.3
10.5
7.1
7.2
5.0
2.7
1.1
3.0xl07
c
4.0xl05
TNTCf
3.9xl05
260
-------
41
Discussion
The hydraulic performance of chlorine contact chambers having various
configurations has been the subject of considerable study and discussion
during the past few years (7, 21, 23, 28, 30, 33, 35). The two major con-
siderations pointed out in these reports are: that the chlorine should be
thoroughly and rapidly mixed with the wastewater before entering the con-
tact chamber, and that the contact chamber design should be such that the
hydraulic performance approaches plug-flow. Even attaining plug-flow
would not be adequate unless the actual residence time of the thoroughly
mixed wastewater and chlorine in the contact chamber is long enough for
the enteric bacteria to be reduced to an acceptable number.
In current disinfection practice, non-plug-flow (short-circuiting)
characterizes contact chamber hydraulic performance. The extent of short-
circuiting is a measure of the degree to which the chlorine and waste-
water have less than theoretical residence time before leaving the chamber.
The degree of short-circuiting may be such that the effluent is inade-
quately disinfected unless excessive chlorine has been added before en-
tering the chamber. These problems will continue to exist as long as
wastewater disinfection receives minimal design and operational attention.
The configuration of the contact chamber used in this study, and
the method of adding chlorine before entering the contact chamber, pro-
vided a system which is comparable to any system that might be designed
in accordance with the previously mentioned guidelines (11). Short-
circuiting was a serious problem even though the contact chamber was well
-------
42
baffled. When the dye studies at the three flow rates were compared (Fig-
ures 2, 5, 7), the amount of dye having a residence time at least equal to
the theoretical contact time decreased with decreasing flow rate. That is,
short-circuiting appears to be magnified at lower flows. However, the
amount of dye having at least 60 minutes residence time increased with de-
creasing flow rate. Plug-flow was not approached at any of the flow rates,
and only the 120 minutes theoretical contact time provided residence time
approximating that obtained with 60 minutes batch treatment. In other
words, a reactor volume twice the design volume would probably provide more
adequate exposure time.
The disinfection guidelines (11) recommended a 1 mg/1 total chlorine
residual after 60 minutes contact time, but did not specify a method for
chlorine residual determination. Since the OT method is still widely
used for monitoring chlorine residual, it was selected for use during
the first phase of the study (16). Minimum effective disinfection (less
than 1000 total and 200 fecal coliforms/100 ml of effluent) could be re-
liably achieved at <1°C in the presence of 1 mg/1 total chlorine residual
(OT) after 60 minutes contact time, but the reliability decreased as re-
sidual concentrations decreased below 1 mg/1.
It has been well established that there can be a considerable dif-
ference between the total chlorine residual concentrations measured in
treated wastewater by the OT and iodometric methods (1, 25). The dif-
ference in concentrations measured by the two methods is usually in the
2 to 5 mg/1 range and may be even greater (1), the iodometric method in-
-------
43
cheating the higher residual. Some of the residual measured with the
iodometric method, and not measured with the OT method, is probably in
a tightly bound form which is ineffective in the disinfection process
(25). However, there is evidence that disinfection can proceed even
when no chlorine residual can be demonstrated with the OT method (7, 25).
All of the results presented here show that the total chlorine resi-
dual measured by the iodometric method is significantly greater than that
measured by the OT method. If the recommended 1 mg/1 total chlorine re-
sidual (11) is measured with the iodometric method, it is obvious that
an actual contact time considerably longer than 60 minutes would be re-
quired to achieve effective disinfection at <1°C and probably at 10°C;
assuming effective disinfection could be attained at all with such low
residual.
Since there is no apparent correlation between the total chlorine
residual measurements with the two methods, both the OT and iodometric
methods were used during this study. The OT method was used as the basis
for establishing the desired residual, and the iodometric method was used
for comparative purposes. The results (Figures 3, 4, 6, 8, 9, 10, 11)
showed that operating temperatures of <1°C apparently did not alter the
previously observed differences between the two methods.
Some of the chemical and physical effluent quality parameters (Tables
1, 2, 3, 4, 6), as well as effluent residence time in the contact chamber,
appeared to affect the chlorine demand. The chlorine concentration to
satisfy this demand, and to maintain a particular residual, seemed to be
-------
44
closely related to the ammonia nitrogen concentration and more casually
related to solids components. After the chlorine demand was satisfied,
the effluent quality parameters apparently were not a significant factor
in the disinfection process as <1°C with effluent from this source. Simi-
lar observations have been made under other operating conditions (7).
Under some operating conditions, the disinfection process has been
shown to be dependent on the contact time and total chlorine residual as
measured by the amperometric method (7, 35). Since the amperometric and
iodometric methods give essentially the same results (1, 25), disinfection
at <1°C would be expected to be more closely related to the total chlorine
residual as measured by the iodometric method than by the OT method. How-
ever, this relationship was somewhat less obvious than expected at both
operating temperatures (<1°C and 10°C). Regardless of the flow rate
through the contact chamber, a chlorine residual measureable by the OT
method was necessary before significant bactericidal action was apparent
(Figures 3, 4, 6, 8, 9, 10, 11). The extent of the reduction was thus de-
pendent upon both total chlorine residual concentration (OT), and resi-
dence time.
Reduction of total coliforms to an acceptable number (<1000/100 ml)
proved difficult to accomplish in the flow through system at <1°C. In
fact, this level of disinfection was not attained at the 60 minutes theo-
retical exposure time until the total chlorine residual (OT) approached
2 mg/1 (Figures 3 and 4). With the 30 minutes theoretical residence, a
total chlorine residual (OT) of 3.3 mg/1 was not effective (Figure 6).
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45
Extending the theoretical reaction time to 120 minutes permitted effective
disinfection to be achieved with only a 0.5-0.6 mg/1 total chlorine resid-
ual (OT) as shown in Figures 8 and 9. When the residual was increased to
approximately 0.8 mg/1, the total coliforms were held at <100/100 ml of
effluent. This suggested that the contact time is at least as important
for total coliform reduction as the maintenance of a particular chlorine
residual. Probably the most significant point was that the 120 minutes
theoretical contact time was the only one which provided 60 or more min-
utes residence time for more than 50 percent of the effluent.
No problems were encountered in reducing the fecal coliform numbers
to <200/100 ml of effluent (minimum effective disinfection) at <1°C.
Average numbers of <5/100 ml were eventually achieved at all flow rates
(Figures 3, 4, 6, 8, 9). However, minimum effective disinfection was not
attained at the 30 minutes theoretical contact time until the chlorine
residual (OT) was in excess of 1.6 mg/1 (Figure 6). When the theoretical
contact time was 120 minutes, approximately 0.3 mg/1 total chlorine re-
sidual (OT) was required for minimum effective disinfection (Figures 8
and 9). Again, as with the total coliforms, this suggested that resi-
dence time in the contact chamber is as important as total chlorine re-
sidual.
The reason for enumerating fecal streptococci in water pollution
control has generally been to aid in more accurately defining the source
of warm-blooded animal pollution (14). Even though the intestinal tract
of man and other warm-blooded animals is a normal habitat of these bac-
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46
teria (1), no guidelines have been established for the number of fecal
streptococci permitted in effluent from disinfection contact chambers.
The fecal streptococci have a different cell structure than the coliforms
and related bacteria, consequently treated wastewater disinfection with
chlorine would not necessarily affect these groups in the same manner.
During this series of experiments at <1°C, some possible differences were
noted. When the theoretical contact time was 60 minutes, increasing the
chlorine residual from 1 mg/1 (Figure 3) to 2 mg/1 (Figure 4) affected
the fecal streptococci in a manner very similar to that observed with the
total coliforms. When the theoretical contact time was reduced to 30 min-
utes, chlorine appeared to be less effective against the fecal strepto-
cocci than against either coliform group (Figure 6). At the 120 minutes
theoretical contact time flow rate (Figures 8 and 9), the reduction in
fecal streptococci numbers was very similar to that found with 1 mg/1 and
60 minutes contact time. This was in contrast to the rather sharply re-
duced numbers of total coliforms at 120 minutes contact time. Thus, it
appeared that the contact time was the controlling factor in fecal strep-
tococci reduction until a certain minimum was reached (approximately 60
minutes) with additional contact time having little apparent effect.
After this minimum time was reached, the chlorine residual concentration
(OT) became the factor controlling fecal streptococci numbers in the con-
tact chamber effluent.
It has been demonstrated during this series of experiments (Table 5),
and during the first phase of the study (16), that effective disinfection
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47
of treated wastewater could be achieved with a high degree of reliability
at <1°G if the actual contact time was 60 minutes (batch treatment) and
the total chlorine residual was 1 mg/1 (OT). These results also indi-
cated that batch treatment provided an effluent bacterial quality far su-
perior to that obtained in the short-circuit plagued contact chamber, un-
less the flow rate through the chamber provided 60 or more minutes of ac-
tual residence time for a large portion (>50 percent) of the effluent
(Figures 8 and 9). This points out that batch treatment laboratory re-
sults cannot necessarily be extrapolated to operating contact chambers,
an observation supported by studies conducted under other conditions (7).
Experiments conducted in the contact chamber at 10°C were too limited
in number for the results to give more than an indication of what might
occur if the temperature was raised from <1°C to 10°C. The contact cham-
ber results (Figures 10 and 11) did suggest that any improvement in ef-
fluent bacterial quality would be minimal. This suggestion was also sup-
ported by the parallel batch treatment results at 10°C and <1°C (Table 7).
Probably the most interesting observations from the limited 10°C studies
were the apparent changes in numbers of bacteria present at 10°C and <1°C
during the 24 hours the effluent was held at the two temperatures before
the disinfection studies were started. The total coliform numbers in-
creased several fold at 10°C, while they remained the same or decreased
at <1°C. The fecal coliform numbers showed no change at 10°C and either
no change or a decrease at <1°C. The fecal streptococci either did not
change or showed a slight increase in numbers at both temperatures.
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48
These results suggested that at least some portion of the total coliform
population was sufficiently cold adapted that significant reproduction
could occur at temperatures near their minimum for growth. Similar low
temperature reproduction has been observed previously in a mountain stream
(18).
During both the batch (16) and contact chamber studies at <1°C, fecal
coliforms were usually absent from the chlorinated effluent samples after
a shorter contact time in the presence of a lower chlorine residual than
was required to reduce the total coliform numbers to their minimim accep-
table level. This suggests that fecal coliforms are more susceptible to
chlorine disinfection at <1°C than are the total coliforms. Other work
has indicated that this also occurs at warmer temperatures (7). The po-
tentially detrimental effects on surface water quality in arctic and sub-
arctic regions resulting from this difference in susceptibility to chlorine
disinfection, and the current trend to de-emphasize or not use total col-
iform bacteria in determining recreational water quality, have been dis-
cussed previously (16). It has already been suggested that total coliforms
should be retained and used in conjunction with fecal coliforms for deter-
mining water quality (7, 16). This is particularly important in the Arctic
and Subarctic because there is little chance that any coliform bacteria
come from other than sewered sources during the winter months.
It has been shown (16) that chlorine varied significantly in its abil-
ity to disinfect effluent from different sources at <1°C, and it has been
reported that similar variations can be found with time in effluent from
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49
the same source (7, 19). This points out the fallacy of arbitrary chlo-
rine residual and contact time criteria, since the only real measure of
adequate disinfection is the number of enteric bacteria being discharged
into a receiving water. It has been suggested that the chlorine resid-
ual rcontact time relationship must be determined for the effluent from
each source if effective disinfection is to be attained (5, 19). In addi-
tion, the relationship must be determined at all operating temperatures
encountered in the disinfection system, particularly the lowest tempera-
ture.
The toxicity of residual chlorine to the biota in receiving waters
has been a subject of increasing interest during the past few years. A
comprehensive literature review has recently been prepared (4) pointing
out that the residual chlorine can be toxic at very low concentrations,
and several interim criteria were suggested for permissible concentrations
of total residual chlorine in receiving waters. One particular criterion
is probably of more interest than the others in relation to this study:
"In areas receiving wastes treated continuously with chlorine, total re-
sidual chlorine should not exceed 0.01 mg/1 for the protection of more
resistant organisms only, or exceed 0.002 mg/1 for the protection of most
aquatic organisms." No mention was made of the method used to determine
the chlorine residual, but it was pointed out that the total chlorine re-
sidual measured with the amperometric method was most closely related to
biological activity. Thus, the 0.002 mg/1 residual was probably measured
either by the amperometric or iodometric method. It has also been demon-
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50
strated that toxic effects persist for several days (12).
Temperature was not included as a factor in any of the proposed
toxicity criteria. The indigenous aquatic organism sensitivity to the
total chlorine residual is essentially unknown at low temperatures. It
is likely, however, that chlorine toxicity in receiving waters with tem-
peratures approaching 0°C is as great or greater than at warmer temper-
atures. If this toxicity is superimposed on the low dissolved oxygen
concentrations found in many arctic and subarctic rivers during the win-
ter months, there may be extremely serious consequences (6).
Considering that the total chlorine residual necessary for effec-
tive disinfection at <1°C (Figures 4, 8, 9) was between 2.7 and 6.2 mg/1
when measured by the iodometric method, it is apparent that a very large
dilution would be needed to reduce the chlorine residual to 0.002 mg/1
or less. Since most arctic and subarctic rivers have very low discharge
during the winter months, the least dilution would be available when the
highest total chlorine residual would probably be required for effective
disinfection. If effective disinfection is to be achieved using chlorine,
and toxicity in receiving waters minimized, dechlorination of the efflu-
ent before discharge must be considered in waste treatment plants opera-
ting in cold climates. Dechlorination methodology has been discussed re-
cently (35), and it has been demonstrated that dechlorinated effluents
are no more toxic to aquatic organisms than are the unchlorinated efflu-
ents (12).
This discussion has pointed out the lengths to which one must go if
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51
effective chlorine disinfection of treated wastewater is to be attained
at <1°C and at 10°C. The current practice of giving minimal attention
to the disinfection process not only fails to provide an effective bar-
rier to the spread of enteric disease, but also ignores the toxic ef-
fect of chlorine on the indigenous aquatic organisms in the receiving
water. To reduce this to a universal language: current practice is
simply pouring money down a rat hole, with the public footing the bill
and not realizing how little they are getting for their money. Since
the use of chlorine as a disinfectant will no doubt persist for some
time, technology must be improved so that effective disinfection is
achieved under all but possibly the most extreme conditions. This means
that disinfection must be given the role of a unit process having equal
importance with other unit processes in the treatment system. However,
under no conditions can disinfection be considered a substitute for ade-
quate treatment of the waste.
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52
Conclusions
1. Effective treated wastewater disinfection can be achieved at <1°C in
the presence of a 1 mg/1 or less total chlorine residual, if the effluent
receives sufficient contact time and the total chlorine residual is meas-
ured by the orthotolidine method.
2. The contact time is at least as important as a particular total chlo-
rine residual for attaining effective disinfection at low temperatures.
Since the chlorine residual:contact time relationship for effective coli-
form reduction varies with effluent source and temperature, this relation-
ship should be determined for each source and set of operating conditions.
3. The use of total coliforms, in conjunction with fecal coliforms, is
necessary for ascertaining the effectiveness of treated wastewater disin-
fection and the quality of receiving waters, at temperatures approaching
0°C.
4. The health effects resulting from inadequately disinfected effluents
being released into the receiving water make it imperative that the ex-
tent of enteric pathogenic bacteria survival, as compared to that of col-
iform bacteria, be determined in receiving waters approaching 0°C.
5. The source and significance of "non-fecal" coliforms (those not giv-
ing a positive elevated temperature test) found in waste treatment sys-
tems during the winter should be determined. Particular emphasis should
be given to the portion of the population which appears to have a signi-
ficant increase in numbers at 10°C.
6. Operating temperatures of <1°C had little or no effect on the 2-5 mg/1
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53
difference between the orthotolldine and iodometric methods of determin-
ing total chlorine residual. However, one method for total chlorine re-
sidual determination should be specified in order to eliminate possible
confusion.
7. Treated wastewater disinfection must be considered a unit process
which is given equal consideration with all other processes in the waste
treatment system. This means that the "State of the Art" should be con-
solidated so that design criteria employing the best technology can be
developed for rapid mixing of effluent and chlorine ahead of the contact
chamber and for contact chamber design which actually minimizes short-
circuiting and allows for maximum rather than average flow.
8. Total chlorine residual toxicity to the indigenous aquatic organisms
in the receiving water should be established for receiving water temper-
atures approaching 0°C. Emphasis should be given to determining the
possible synergistic effects on the organisms, of the chlorine toxicity
and low dissolved oxygen concentrations frequently found in arctic and
subarctic rivers during periods of ice cover.
9. Evaluation of disinfectants, other than chlorine, for possible ap-
plication in effluents at low temperatures, should be accelerated.
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54
References
1. American Public Health Association. Standard Methods for the Exami-
nation of Water and Wastewater. 13th Edition. New York, American
Public Health Association, 1971. 874 p.
2. American Society of Civil Engineers. Proceedings of the National
Specialty Conference on Disinfection. New York, American Society
of Civil Engineers, 1970. 705 p.
3. Ballentine, R. K. and F. W. Kittrell. Observation of Fecal Coliforms
in Several Recent Stream Pollution Studies. In: Proceedings of the
Symposium on Fecal Coliform Bacteria in Water and Wastewater. Bureau
of Sanitary Engineering. California State Department of Public
Health, 1968. p. 80-126.
4. Brungs, W. A. Effects of Residual Chlorine on Aquatic Life:Litera-
ture Review. Journal Water Pollution Control Federation. In Press.
5. Chambers, C. W. Chlorination for Control of Bacteria and Viruses in
Treatment Plant Effluents. Journal Water Pollution Control Federa-
tion. 43:228-241, February 1971.
6. Chambers, C. W. and G. Berg. Disinfection and Temperature Influ-
ences. In: International Symposium on Water Pollution Control in
Cold Climates, Murphy, R. S. and D. Nyquist (eds.). Environmental
Protection Agency, Fairbanks, Alaska. Publication No. 16100 EXH
11/71. November 1971 p. 312-328.
7. Collins, H. F. and R. E. Selleck. Process Kinetics of Wastewater
Chlorination. Sanitary Engineering Research Laboratory. Berkeley,
Ca. SERL Report No. 72-5. University of California, College of
Engineering, School of Public Health. November 1972. 91 p.
8. Collins, H. F., R. E. Selleck and G. C. White. Problems in Obtaining
Adequate Sewage Disinfection. In: Proceedings of the National Spec-
ialty Conference on Disinfection. New York, American Society of Civil
Engineers, 1970. p. 137-161.
9. Coutts, H. J. and C. Christiansen. Extended Aeration in Cold Regions.
Environmental Protection Agency, Fairbanks, Ak. In Preparation.
1973.
10. Environmental Protection Agency. Methods for Chemical Analysis of
Water and Wastes 1971. Environmental Protection Agency, Cincinnati,
Oh. Publication No. 16020 07/71. 312 p.
-------
55
11. Environmental Protection Agency, Region X. Disinfection Criteria
and Design Guidelines. Environmental Protection Agency, Seattle,
Wa. December 1970. 6 p.
12. Esvelt, L. A., W. J. Kaufman and R. E. Selleck. Toxicity Removal
From Municipal Wastewaters. In: A Study of Toxicity and Biostimu-
lation in San Francisco Bay-Delta Waters, Volume IV. Sanitary Engi-
neering Research Laboratory. Berkeley, Ca. SERL Report No. 71-7.
University of California, College of Engineering, School of Public
Health. October 1971. 224 p.
13. Federal Water Pollution Control Administration. Current Practices
in Water Microbiology. Federal Water Pollution Control Administra-
tion, Cincinnati, Oh. February 1970.
14. Geldreich, E. E. Sanitary Significance of Fecal Coliforms in the
Environment. Federal Water Pollution Control Administration,
Cincinnati, Oh. Publication No. WP-20-3. November 1966. 122 p.
15. Gordon, R. C. Winter Survival of Fecal Indicator Bacteria in a
Subarctic Alaskan River. Environmental Protection Agency, Fairbanks,
Ak. Publication No. EPA-R2-72-013. August 1972. 41 p.
16. Gordon, R. C. and C. V. Davenport. Batch Disinfection of Treated
Wastewater With Chlorine at less than 1°C. Environmental Protection
Agency, Fairbanks, Ak. Publication No. EPA-660/2-005. August 1973.
17. Heathman, L. S., B. S. Pierce and P. Kabler. Resistance of Various
Strains of £. typhi and Coli Aerogenes to Chlorine and Chloramine.
Public Health Reports. 51_: 1367-1387, October 1936.
18. Hendricks, C. W. and S. M. Morrison. Multiplication and Growth of
Selected Enteric Bacteria in Clear Mountain Stream Water. Water Re-
search (Oxford). 1:567-576, August/September 1967.
19. Heukelekian, H. and S. D. Faust. Compatibility of Wastewater Disin-
fection by Chlorination. Journal Water Pollution Control Federation.
33.: 932-942, September 1961.
20. Kothandaraman, V. and R. L. Evans. Hydraulic Model Studies of Chlo-
rine Contact Tanks. Journal Water Pollution Control Federation.
44:625-633, April 1972.
21. Kothandaraman, V., H. L. Southerland and R. L. Evans. Performance
Characteristics of Chlorine Contact Tanks. Journal Water Pollution
Control Federation. 45_:611-619, April 1973.
-------
56
22. Kott, Y. Chlorination Dynamics in Wastewater Effluents. In: Pro-
ceedings of the National Specialty Conference on Disinfection. New
York, American Society of Civil Engineers, 1970. p. 585-608.
23. Louie, D. S. and M. S. Fohrman. Hydraulic Model Studies of Chlorine
Mixing and Contact Chambers. Journal Water Pollution Control Feder-
ation. 4J):174-184, February 1968.
24. Marias, A. F., E. M. Nupen, G. J. Stander and J. R. H. Hoffman. A
Comparison of the Inactivation of Escherichia coli I and Polio Virus
in Polluted and Unpolluted Waters by Chlorination. In: International
Conference on Water for Peace. 1967. p. 670-689.
25. Marks, H. C. Residual Chlorine Analysis in Water and Waste Water.
In: Water and Water Pollution Handbook, Volume 3, Ciaccio, L. L.
(ed.). New York, Marcel Dekker, Inc., 1972. p. 1213-1247.
26. Morris, J. C. Chlorination and Disinfection - State of the Art.
Journal Water Pollution Control Federation. 63_:769-774, December 1971
27. Rudolfs, W. and H. W. Gehm. Sewage Chlorination Studies. Bulletin.
New Jersey Agricultural Experiment Station. 601. March 1936. 72 p.
28. Sawyer, C. M. and P. H. King. The Hydraulic Performance of Chlorine
Contact Tanks. In: Proceedings of the 24th Industrial Waste Con-
ference, part two, Lafayette, Purdue University. 1969. p. 1151-1168.
29. Slanetz, L. W., C. H. Bartley, T. G. Metcalf and R. Nesman. Survi-
val of Enteric Bacteria and Viruses in Municipal Sewage Lagoons. In:
2nd International Symposium for Waste Treatment Lagoons, McKinney,
R. E. (ed.). Meseraull Printing, Inc., 1970. p. 132-141.
30. Stephenson, R. L. and J. R. Lauderbaugh. Baffling Chlorine Contact
Tanks. Water & Sewage Works. V[8.:R100-103, 1971.
31. Technicon Corp. Ammonia in Water and Waste Water. Industrial Method
IND-18-69W, Technicon AutoAnalyzer Methodology. Technicon Corp.,
Tarrytown, N. Y., 1969.
32. Technicon Corp. Total Nitrogen (Kjeldahl). Industrial Method 30-69A,
Technicon AutoAnalyzer Methodlogy. Technicon Corp., Tarrytown, N. Y.,
1969.
33. Thomas, A. A. and W. H. Brown. Closed-Loop Chlorination for Waste-
waters. Journal Water Pollution Control Federation. 40:684-688,
April 1968.
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57
34. Van Donsel, D., R. C. Gordon and C. V. Davenport. Unpublished Data.
Environmental Protection Agency, Fairbanks, Ak. 1973.
35. White, G. C. Handbook of Chlorination. New York, Van Nostrand
Rheinhold Co., 1972. 744 p.
* U. S. GOVERNMENT PRINTING OFFICE: 1973-798-165
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