EPA-660/2-73-017
September 1973
Environmental Protection Technology Series
Lime Disinfection of Sewage Bacteria
At Low Temperature
Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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been grouped into five series. These five broad
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was consciously planned to foster technology
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This report has been assigned to the ENVIRONMENTAL
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conducted to develop new or improved methods and
instrumentation for the identification and
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EPA-660/2-73-017
September 1973
LIME DISINFECTION OF SEWAGE BACTERIA
AT LOW TEMPERATURE
by
S.M, Morrison, K.L. Martin and D.E. Humble
Colorado State University
Fort Collins, Colorado 80521
Project 16100 PAK
Program Element 1BB044
Project Officer
Dr. Ronald C. Gordon
Arctic Environmental Research Laboratory
College, Alaska 99701
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.28
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ABSTRACT
Small isolated communities in cold climatic areas need a simple,
inexpensive, reliable sewage system which includes disinfection. This
laboratory study provides clarifying data on the action of lime as a
sewage disinfectant at low temperatures. Nutrient level reductions
were also studied.
Lime was added to raw and activated sludge treated sewage to attain pH
intervals between 10 and 12 at temperatures of 1°, 5°, 10° and 15°C.
Membrane filter procedures were used to follow decreases in total and
fecal coliform populations and total plate counts at each test pH and
temperature. In both sewages, it was observed that pH values above 11
were required to reduce coliform populations to levels below 100/ml
in less than 8-12 hours. To attain coliform population reductions to
I/ml or less, 24 hours were required at pH 11 but only 90 minutes at
pH 11.5. Coliforms and other organisms concentrated in the precipitated
solids during lime treatment; their numbers decreased as pH and/or
contact time increased. Temperature was a less significant factor in
the disinfection mechanisms than was pH.
An additional effect of lime treatment of sewage is the reduction of
organic and inorganic chemical loads in the effluent. The reductions
at 15°C for raw and 10°C for secondary treated, measured by BOD
and orthophosphate tests, reached maximum BOD removals of 77 and 94%,
respectively, at pH 11 in 24 hours for raw sewage and at pH 11.5 in
90 minutes for treated sewage. Likewise, maximum orthophosphate
removals, 93 and 97%, respectively, were obtained at pH 12.0 for 60
minutes with raw sewage and pH 12.0 for 60 minutes for treated
samples.
This report was submitted in fulfillment of Project 16100 PAK by
Colorado State University under the sponsorship of the Environmental
Protection Agency. Work was completed as of April, 1973.
ii
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CONTENTS
Page
Abstract ii
List of Figures iv
List of Tables vii
Acknowledgements ix
Sections
I Conclusions 1
II Recommendations 2
III Introduction 3
IV Materials and Methods 17
V Experimental Results 24
VI Discussion 76
VII References 85
iii
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FIGURES
No. Page
1 Effects of Lime and 3 N KOH on the pH of 2 liter
Sewage Samples at 5°C 25
2 Effects of Lime on the pH of 2 liter Secondary Treat-
ment Sewage Samples at 5°C 26
3 Effect of Adding Lime Slurry to Sewage, Followed by
3 N KOH, at 5°C 27
4 Reduction of Total Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 10.0, at 1 to 15°C .... 30
5 Reduction of Total Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 10.5, at 1 to 15°C .... 31
6 Reduction of Total Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 11.0, at 1 to 15°C .... 32
7 Reduction of Total Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 11.5, at 1 to 15°C .... 33
8 Reduction of Total Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 12.0, at 1 to 15°C .... 34
9 Reduction of Total Coliform Bacteria in Lime Treated
Secondary Effluent at Initial pH's of 10.0, 10.5 and
11.0, at 10°C 35
10 Reduction of Total Coliform Bacteria in Lime Treated
Secondary Effluent at Initial pH's of 10.0, 10.5 and
11.0, at 1°C 36
11 Reduction of Total Coliform Bacteria in Lime Treated
Secondary Effluent at Initial pH's of 11.5 and 12.0,
at 10°C 37
12 Reduction of Total Coliform Bacteria in Lime Treated
Secondary Effluent at Initial pH's of 11.5 and 12.0,
at 1°C 38
13 Reduction of Fecal Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 10.0, at 1 to 15°C . . . . 39
14 Reduction of Fecal Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 10.5, at 1 to 15°C .... 40
iv
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No. Page
15 Reduction of Fecal Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 11.0, at 1 to 15°C .... 41
16 Reduction of Fecal Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 11.5, at 1 to 15°C .... 42
17 Reduction of Fecal Coliform Bacteria in Lime Treated
Sewage at an Initial pH of 12.0, at 1 to 15°C .... 43
18 Reduction of Fecal Coliform Bacteria in Lime Treated
Secondary Effluent at Initial pH's of 10.0, 10.5 and
11.0 at 10eC 44
19 Reduction of Fecal Coliform Bacteria in Lime Treated
Secondary Effluent at Initial pH's of 10.0, 10.5 and
11.0, at 1°C 45
20 Reduction of Fecal Coliform Bacteria in Lime Treated
Secondary Effluent at Initial pH's of 11.5 and
12.0, at 10°C 46
21 Reduction of Fecal Coliform Bacteria in Lime Treated
Secondary Effluent at, Initial pH's of 11.5 and 12.0,
at 1°C 47
22 Survival of Total and Fecal Coliform Bacteria in
Sewage Controls at 1 to 15°C 48
23 Survival of Bacteria- in Secondary Effluent Controls
at 1 and 10°C 49
24 Survival of Total and Fecal Coliform Bacteria in
Sewage Control at 1 to 15°C 50
25 Survival of Bacteria in Secondary Effluent Controls
at 1 and 10°C 51
26 Reductions in BOD and Orthophosphate Concentrations
of Sewage at pH 10.0 through 11.0, at 1°C 64
27 Reductions in BOD and Orthophosphate Concentrations of
Sewage at pH 11.5 and 12.0, at 1°C 65
28 Reductions in BOD and Orthophosphate Concentrations of
Sewage at pH 10.0 through 11.0, at 5eC 66
29 Reductions in BOD and Orthophosphate Concentrations of
Sewage at pH 11.5 and 12.0, at 5°C 67
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No. Page
30 Reductions in BOD and Orthophosphate Concentrations of
Sewage at pH 10.0 through 11.0, Lime Treatment at
10°C 68
31 Reductions in BOD and Orthophosphate Concentrations of
Sewage at pH 11.5 and 12.0, Lime Treatment at 10°C . . 69
32 Reductions in BOD and Orthophosphate Concentrations of
Sewage at pH 10.0 through 11.0, Lime Treatment at
15°C 70
33 Reductions in BOD and Orthophosphate Concentrations of
Sewage of pH 11.5 and 12.0, Lime Treatment at
15°C 71
vi
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TABLES
No. Page
1 Back-titration of Neutral and High pH Sewages
(2 liters each) with 2 M Calcium Chloride at 5°C ... 28
2 Survival of Standard Plate Count Organisms (SPG) in
the Supernatant Phase of Lime Treated and Control
Sewages 52
3 Survival of Standard Plate Count Organisms (SPC) in the
Supernatant Phase of Lime Treated and Control
Sewage 53
4 Comparative Numbers of Total Coliform Bacteria Found
in Sewage Supernatant and Precipitated Solids During
Lime Treatment 54
5 Comparative Numbers of Fecal Coliform Bacteria Found in
Sewage Supernatant and Precipitated Solids During Lime
Treatment 55
6 Comparative Numbers of Standard Plate Count Bacteria
Found in Sewage Supernatant and Precipitated Solids
During Lime Treatment 56
7 Comparative Numbers of Total Coliform Bacteria Found in
Secondary Effluent Supernatant and Sludge During Lime
Treatment 57
8 Comparative Numbers of Fecal Coliform Bacteria Found in
Secondary Effluent Supernatant and Sludge During Lime
Treatment 58
9 Comparative Numbers of Standard Plate Count Bacteria
Found in Secondary Effluent Supernatant and Sludge
During Lime Treatment 59
10 Reductions of BOD and Orthophosphate Concentrations in
Lime Treated Sewage at 1, 5, 10 and 15°C 61
11 Reductions of BOD and Orthophosphate Concentration in
Lime Treated Secondary Effluent at 1 and 10°C ... 63
12 Observed pH Changes in Lime Treated Sewage Samples Over
the Contact Period 72
13 Observed pH Changes in Lime Treated Secondary Effluent
Over the Contact Period 72
vii
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No. Page
14 Observed Temperature Variations in Lime Treated Raw
Sewage Samples Over the Contact Period . 73
15 Observed Temperature Variations in Lime Treated
Secondary Effluent Over the Contact Period 73
16 Average Quantities (ml) of Lime Slurry (132 mg/CaO/ml)
Used to Produce Treatment pH Values in 2 liter Raw
Sewage Samples , ....... 74
17 Average Quantities (ml) of Lime Slurry (117 mg/CaO/ml)
Used to Produce Treatment pH Values in 2 liter
Secondary Effluent Samples «... 74
18 Ranges and Means of the Measured Values of the Various
Sewage Characteristics (5/3/71 to 12/2/71) 75
viii
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ACKNOWLEDGEMENTS
The authors wish to acknowledge the cooperation of the statf of the
Fort Collins sewage department and the technical assistance provided
in the laboratory by Gary C. Newton, C. Mack Sewell and Sue Burmeister
Martin. The financial assistance provided D. E. Humble through
EPA-OWP Manpower and Training Grants Branch traineeship grant
T900-266 (S.M.M. , Director) is acknowledged. The advice and guidance
provided by Mr. Cecil W. Chambers and Dr. Ronald C. Gordon, EPA research
microbiologists, has been appreciated.
ix
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SECTION I
CONCLUSIONS
Even in the presence of relatively high concentrations of organic
matter and under the adverse conditions of cold temperature sewage
can be disinfected to a safe level by lime treatment to pH 11.5 or
12.0.
A variety of generic types of bacteria can be destroyed during lime
treatment, as evidenced by the large reductions in raw sewage, settled
solids and treated sewage total and fecal coliform and total bacterial
concentrations.
The process of disinfection can be completed within a very short time
period (30 minutes or less), even at 1°C.
Effluents with greatly reduced concentrations of biologically oxi-
dizable organic materials and orthophosphate can be produced, also in
relatively short time periods (under 30 minutes).
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SECTION II
RECOMMENDATIONS
Additional investigations should be directed at the effects of dif-
fering concentrations of organic matter on the rate of disinfection
and the efficiency of organic matter and orthophosphate removals from
raw and settled sewages with lime. Rudolfs and Gehra (62) indicated
that primary settling may not be necessary, or desirable, for maximum
removal of organic material by chemical precipitation. Therefore,
there exists a need to determine the rate of disinfection in a system
where organic matter concentrations could be varied under controlled
conditions.
Further investigations could also be directed toward the determination
of the form or forms of organic material remaining in effluents from
lime treatment of sewage. Results of this study indicate that almost
all of the large and finely divided suspended organic matter are
removed by lime precipitation; however, a large portion of the bio-
logically degradable material is represented by colloidal and soluble
organics which lime treatment may not affect. Rudolfs and Gehm (63)
stated that the soluble fraction of the BOD was least affected by
chemical precipitation, which is probably the case with lime
precipitation.
The results obtained in this study represent laboratory batch scale
tests and probably do not provide adequate data for a flow-through
system. Therefore, laboratory bench scale studies should be carried
out with a flow-through system to determine disinfection rates and
efficiency. The laboratory tests should be scaled up to pilot size
in an operating domestic sewage collecting system. The efficiency
of disinfection under these conditions would provide the needed op-
erational design criteria.
Additional information is also needed on the affects of elevated pH on
the survival of pathogenic viruses, nematodes and other aquatic life
forms.
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SECTION III
INTRODUCTION
When nomadic people began to form communities, sewage disposal be-
came a problem and many such small isolated communities still exist
today throughout the United States and the world. Geographically,
many of these settlements are located in regions where severely cold
climatic conditions prevail through much of the year. In these
regions, the problems associated with sewage disposal have been in-
tensified as the result of decreased biological decomposition of
wastes at low temperatures. Where the communities have been unable
to support public sewage treatment facilities because of the high
costs involved in their construction and maintenance sewage disposal
has been the responsibility of the individual homeowner.
In dealing with the problem to date, disposal methods have included
the pit privy, septic and Imhoff tanks, lagooning systems, chemical
treatment^ abandonment on ice packs and, in some instances, direct
outfall into waterways and estuaries. All of these disposal methods
are unsafe from an epidemiological point of view because of the
preservation of pathogenic organisms at cold temperatures. Con-
current with the recognition of danger to health we have become in-
creasingly aware of environmental pollution and its association
with inadequate sewage disposal practices. Therefore, in order to
curtail the spread of disease and preserve our environment it is
necessary to adequately disinfect and purify, to an acceptable level,
all domestic sewages and associated wastes.
If the contamination from sewage can be contained by retention the
adverse effects to the environment will be minimal. However, when
natural biological decomposition is retarded, as is the case at
low temperature, it is possible for the contamination to become
dispersed over a large area with serious environmental degradation.
The natural processes of eutrophication may be increased, previously
used sources of domestic water may be rendered unfit for use,
epidemiologic hazards increase, the ecology of an entire region may
be severely upset and wildlife and recreational areas may be badly
damaged or destroyed.
Because the methods of sewage treatment and disinfection currently
employed by many small communities in cold regions are inefficient,
there exists a need for modified, new or improved systems. This
study is an endeavor to better understand the variables and relation-
ships in a modification of a well known system.
Lime (CaO) treatment of domestic wastes will be studied for its
bacterial disinfection capabilities along with attendant reductions
in nutrient levels. Lime has been chosen because of its past record
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of effectiveness in the clarification of domestic water supplies and
precipitation of sewage solids, as well as its low cost.
OBJECTIVES
(1) To determine the effects of high pH on raw and treated sewage
bacteria at low temperatures (1° to 15° C).
(2) To determine the degree of BOD removal from sewage at high pH
and low temperatures.
(3) To determine the effectiveness of lime as a precipitant of
orthophosphate (o-PO,) from sewage at low temperatures.
LITERATURE REVIEW
Considerable literature has been published on the bactericidal effects
of hydroxides, especially in the area of domestic water treatment
(33,35,59,73,80). Likewise, ample information has been reported
on the removal of suspended solids, BOD and phosphate compounds
from sewage using both conventional biological treatment systems
and physical-chemical methods (11,54,56,61,78). On the other hand,
little information can be found relating the disinfection of sewage
with the removal of suspended solids, BOD and phosphates, using r
alkalies in a single treatment procedure. Furthermore, most methods
of sewage treatment are adversely affected by low operational temp-
eratures (5,15,36,44) and insufficient information exists relating
the effects of low temperatures on the clarification and disinfection
of sewage with lime and other caustics.
The literature pertaining to this study will be reviewed under the
following headings: Adverse effects of high pH on bacteria;
Evaluation of the germicidal efficiency of hydroxides; Factors, other
than high pH, affecting the bactericidal efficiency of hydroxides;
Sewage disposal problems in the Arctic; Effects of low temperature on
conventional sewage treatment systems; Removal of suspended solids,
BOD and orthophosphate from sewage with lime.
Adverse Effects of High pH on Bacteria
Bacterial inhibition from caustic conditions has long been known. As
early as 1878, Endemann (26) observed that "soda" was inhibitory to
bacteria. It was later that Houston (35) first proposed the appli-
cation of excess lime treatment to raw waters with the expressed
purpose of removing bacteria of the "colon-typhoid" group. According
to Houston, the first to apply the excess lime treatment in a water
supply to destroy "plankton" development and produce an epidemio-
logically safe water was Accra in 1917. Eddy (22), investigating the
same general problem, related the pH at which maximum precipitation
of aluminum hydroxide occurs in alum treated waters with the "possible"
control of growths in filter plants.
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About the same time Hoover and Scott (34), while examining lime,
softened water, discovered that bacterial tests were negative
92% of the time in 1 ml samples. Efforts to understand these findings
led to the theory that the bactericidal action resulted from the
presence of lime in the water. It was discovered that when enough
lime was added to remove the free and half-bound carbonic acid and
precipitate the magnesium, the bacteria of the "colon-typhoid" group
were killed in 48 hours. Furthermore, the sterilizing action was
found to persist indefinitely.
Additional data presented by Houston (35) indicated that lime treat-
ment of raw river water resulted in large reductions in turbidity,
color and hardness. In addition, no "Bacterium coli" could be found
in 100 ml samples when the causticity of the effluent water was at
least 5.0 mg/1. Edwards (23,24) reported that water with greatly
reduced bacterial loads could be produced from heavily contaminated
Ohio River water by application of the excess lime treatment. The
Escherichia coli index was reduced from 20-40,000 per 100 ml to 100
per 100 ml when 20-25 mg/1 causticity was applied to the primary
settling basins. During early investigations, Hoover (33) noted that
lime treatment of raw water supplies enhanced suspended solids
removal and that it was also possible to remove a higher percentage
of potentially pathogenic microorganisms when excess lime treatment
was used, 20 mg/1 yielded bacteriologically safe conditions in water
mains.
Not everyone agreed that caustic conditions were necessary to produce
water free of "colon" bacteria. Bahlman (4) found that effluents
practically free of "colon" bacteria could be produced with "sub-
caustic" doses of lime. Investigations led to the conclusions that
"coli" were actually killed by doses of lime which produced "caustic"
conditions and were not merely removed by entrainment in the pre-
cipitated solids. On the other hand, exposure to low alkaline
treatments was thought to result in physical removal (33).
By 1930, excess lime treatment of water supplies had been practiced for
a number of years. Van Arnum (77) reported that waters containing low
coliform concentrations had been produced for 11 years in Youngstown,
Ohio, using the excess lime method. Streeter (73) studied some of
the chemical effects of lime treatment on a raw water supply. He
found that increases in bactericidal efficiency paralleled increasing
degrees of causticity; furthermore, the application of the excess lime
treatment (relatively high pH values) was capable of producing ef-
fluents which compared favorably to those produced by raw water pre-
chlorination in combination with ordinary postchlorination. Streeter
(73) was unable to confirm the findings of Bahlman (4) who reported
bactericidal actions from "subcaustic" doses of lime.
Extensive studies on the survival of bacteria during the excess lime
treatment of water were performed by Wattie and Chambers (80). They
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concluded that the death rate of .E. coll was very slow over a 10 hour
contact period when exposed to a pH range of between 9.01-9.50 at 25°C.
Increasing the pH range to 9.51-10.00 reduced the lag period to six
hours and to three hours when the pH range was 10.01-10.50. In the
pH ranges of 10.51-11.00 and 11.01-11.50, there were sudden drops in
.E. coli numbers in the first two to three hours. Two strains of
Aerobacter aerogenes proved to be more resistant than the JE. coli
tested. Salmonella typhosa did not survive hydroxyl ion concentrations
in the range of pH 11.01-11.50 longer than two hours, while Shigella
dysenteriae was destroyed rapidly in all pH ranges studied; pH 11.01-
11.50 produced 100% kill in 75 minutes.
Further confirmation of the efficiency of high pH came from Riehl,
Hartung and Taylor (59) who demonstrated that during lime softening
of raw river water, a bacteriologically safe water could be produced
if the pH was kept above 11.4 for a minimum of three hours; however,
the water was too caustic for domestic use.
Recent investigations on lime treatment of water supplies (58) in-
dicated that addition of lime, sufficient to absorb the free and half-
bound carbonic acid and precipitate the magnesium, reduced the
"colon-typhoid" bacteria 99.67% in five hours. When an excess of
one grain and three grains per gallon were added the action was 99.93
and 100% effective, respectively, in five hours.
Investigations directed toward the effects of high pH upon bacterial
growth were not limited to those of the water treatment industry.
Cohen and Clark (17) studied the growth of E_. coli in media of high
pH and indicated that there was a marked increase in the lag phase
at a pH of about 8.9. Although the exact mechanism was unknown, it
was theorized that acid or alkaline media may affect specific ferment-
ative processes, specific rates of death and reproduction in quite
different ways.
Scott and McClure (68) reviewed the available literature which in-
dicated that bacteria of the "colon-typhoid" group were killed in
media of low hydrogen ion concentrations. The data suggested that
pH 9.5 was the lower limiting value in various media. They indicated
that the limiting pH in the excess lime treatment of domestic water
supplies was also 9.5. McCulloch (46) revealed that pH 10.00 was
very germicidal against 15. coli, S^. typhosa and Salmonella paratyphosa,
while a pH of 12.2 was required to produce the same action against
S taphylococcus aureus^.
Disinfectants have been commonly used in the agricultural industry
for many years. Several investigators have evaluated high pH for its
germicidal efficiency. Mudge and Lawler (50) concluded that sodium
hydroxide solutions yielding pH values greater than 12.3 were very
efficient bactericides.. Bacteria from unwashed milk bottles, at a
concentration of 8 x 10 /ml, were completely destroyed in less than
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four minutes, when the pH was adjusted with sodium hydroxide to 13.3-
13.4 at 48.8°C. Myers (53) reported that in the course of sanitizing
milk bottles, those washing powders that gave washing solutions of
high pH were decidedly more effective as germicides than those that
gave washing solutions of low pH. It was also shown that addition of
sodium hydroxide to solutions of neutral pH greatly increased germici-
dal efficiency. Schaffer and Tilley (65) stated that soap solutions
produced from neutral coconut oil and sodium hydroxide were much more
effective against bacteria than those soaps that did not contain
sodium hydroxide.
More recently, Le Compte (41) reported experimental results obtained
from the lime treatment of wastewater from a paper processing mill.
Addition of lime to effluent mill water resulted in the formation of
a magnesium hydroxide precipitate which removed a. large percentage of
the suspended fiber material. In addition, the water from the excess
lime treatment step was reported to have been "sterile" because of
the high pH, and control over odors was achieved.
In the process of washing and transporting sugar beets, large numbers
of bacteria have been reported to accumulate in the water. Schuyler
(67) found that bacteria (predominately Leuconostoc mesenteroides)
indigenious to sugar beet wastewater were not appreciably affected by
lime additions resulting in pH values less than 11.2 at 25°C, while
under the same set of conditions a laboratory strain of IS. eoli was
rapidly destroyed.
Early reports on the use of lime in the treatment of sewage indicated
that there were problems in evaluating the germicidal efficiency of
lime. Data presented by an anonymous author (3) on sewage treatment
with lime alone versus an electrolytic-lime treatment indicated that
substantially better removals of IE. coli were achieved with an electro-
lytic-lime system than with lime alone. Treatment pH values were not
reported; however, the lime dosage was 3720 pounds per million gallons,
electrolytic contact was 70 seconds, the total alkalinity of the
effluents was 350 mg/1 and the effluents were reported to be free of
_E. coli. A few years later, Lanphear (40) observed that there was no
real advantage to an electrolytic-lime treatment because all effluents
with total alkalinity values of 100 mg/1 or more were bacteriologically
stable without electrolytic treatment.
Results obtained from lime treatment of sewage were reported by Doyle
(20) who indicated that the survival of £>_. typhosa was directly depen-
dent upon the pH of sewage sludge filter cake. Furthermore, S_. typhosa
could not be cultured, even by enrichment procedures, when the pH of
the filter cake was maintained above 11.00 for 24 hours.
Several viruses have been reported to be very susceptible to excess
lime treatment. Thayer and Sproul (74) extensively researched the
inactivation of T-2 phage during a variety of lime softening procedures.
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T-2 phage was shown to be inactivated by lime additions resulting in
a pH of about 9.2, with only 0.1% remaining active at pH 10.8. In ad-
dition, they stated that "many animal viruses are at least as pH
sensitive as the T-2 bacteriophage" and that most viruses are unable
to tolerate pH values above 11.0 and retain their infective activity.
Van Vuuren et al. (78) found that by maintaining a concentration of
300 mg/1 of hydrated lime in humus tank effluents, a polio virus IDcn/
ml of zero could be produced when the contact time was 43 minutes.
The E^. coli concentration was observed to be reduced from 760/ml to
0/ml in the same contact period.
Evaluation of the Germicidal Efficiency of Hydroxides
The need to evaluate the germicidal efficiency of various hydroxides
prompted investigators to determine the components responsible
for their germicidal actions. Lamanna and Mallette (38) recognized
the value of alkalies, asserting that they are efficient and econ-
omical disinfectants, the efficiency being a function of hydroxyl
ion concentration. They stated that alkalies hydrolyze many proteins
and nucleic acids at room temperature and sufficiently high hydroxyl
ion concentrations will destroy organisms by direct reaction with
physiologically active cellular constitutents and structures. Pelczar
and Reid (57) concurred that the disinfectant action is dependent
upon the dissociation of the alkali and the resulting hydroxyl ion
concentration; however, they stated that lime has little, if any,
activity as a disinfectant. In addition to the bactericidal action
from the hydroxyl ion, many hydroxides have been reported to possess
added bactericidal activity due to their cation (38,57).
Belief that low hydrogen ion concentrations (high pH) were respon-
sible for the germicidal action of alkalies developed early in the
application of the excess lime treatment to water supplies. Scott
and McClure (68) reviewed the available literature, concluding that
low hydrogen ion concentrations were responsible for bacterial re-
ductions in lime treated water. McCulloch (46) also supported the
theory that the germicidal action of alkalies, sodium hydroxide in
particular, was primarily influenced by hydroxyl ion concentrations.
Levine et_ al. (41), however, stated that pH alone cannot be used as
an index of the germicidal properties of different alkaline compounds,
even though the germicidal efficiency of any particular alkali was
shown to be a direct function of the hydroxyl ion concentration.
For instance, the germicidal efficiencies of sodium carbonate, sodium
phosphate and sodium hydroxide, at the same pH and temperature, were
shown to be quite different. Likewise, Myers (52) concluded that the
effects of pH cannot be compared when two or more buffer systems are
used. Levine et al. (42) demonstrated that the presence of carbonate
in commercial washing compounds enhanced the germicidal efficiency of
sodium hydroxide in such compounds, although there was no appreciable
affect upon the pH.
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Additional investigations into the effects of salt additions to
alkalies led Levine et al. (43) to conclude that sodium chloride,
potassium chloride, sodium carbonate or sodium phosphate, when added
to sodium hydroxide solutions, increased the germicidal efficiency of
the hydroxide substantially. Myers (53) studied the interrelated
effects of pH, osmotic pressure and buffer index upon the death rate
of spores. He concluded that the death rate was accelerated by
holding any two factors constant and increasing the third. The
osmotic pressure had the least influence of the three factors studied.
Schuyler (67) noted a marked difference in the death rate of bacteria
found in sugar beet wash water at pH 11.2 and 11.4. He suggested
that two modes of destructive action may occur from high pH values
produced by lime addition. Up to some critical pH the determining
factor may be the hydroxyl ion concentration, while above this pH
value, the determining factor may be the large concentration of undis-
sociated calcium hydroxide resulting from the proportionately greater
quantities of lime needed to attain such high pH values. It has been
shown that almost twice as much hydrated lime (Ca(OH) ) is needed to
produce pH 11.4 as compared to pH 10.4. As a result of this, much of
the lime (hydrated) remains undissociated at high pH values in the form
of calcium hydroxide (59,67).
Factors, Other than High pH, Affecting the Bactericidal Efficiency
of Alkalies
Many factors, other than high pH, have been shown to affect the germi-
cidal efficiency of alkalies. The temperature at which bacteria are
exposed to high pH must be considered in evaluating the germicidal
efficiency of alkalies. Scott and McClure (68) recognized the in-
fluence of temperature on the efficiency of hydroxides and reported
that increasing the temperature of softened water from 8° to 27°C re-
sulted in a pH change from 10.32 to 9.89. It was therefore concluded
that in cold weather the caustic alkalinity would have to be higher
to produce a pH destructive to most bacteria.
Results obtained by Mudge and Lawler (50) also upheld the principle
that increased germicidal efficiency paralleled increasing temperature,
for a given alkali at a fixed pH value. Levine et ad. (42) indicated
that as treatment temperatures were increased, the discrepancy between
the germicidal efficiency of sodium hydroxide washing compounds with and
without carbonate also increased. Myers (52) also came to the con-
clusion that increased bactericidal powers paralleled higher temp-
eratures at a fixed pH value. Tilley and Schaffer (76) found that the
germicidal efficiency of solutions of sodium carbonate, trisodium
phosphate or mixtures of either of these with sodium hydroxide was en-
hanced by increased temperatures.
Watkins and Winslow (79) found that when sodium hydroxide was the dis-
infectant, the rate of bacterial death was temperature dependent
-------
between 22° and 50°C. Wattle and Chambers (80) and Chambers and Berg
(13) showed that the death rate of 13. coli decreased as temperatures
were lowered from 25° to 1°C at a fixed pH value. More recently,
Schuyler (67) found that Leuconostoc mesenteroides suspended in sugar
beet wash water was more resistant to high pH at 10°C than at 25°C.
Contrary to these findings, McCulloch (46) stated that the rate of
disinfection produced by sodium hydroxide appeared to be practically
independent of temperature changes between 2° and 25°C.
Subsequent work by McCulloch and Costigan (47) indicated that even
though the activity of sodium hydroxide showed but little variation
between 2° and 25°C, it was somewhat more active at 40°C. In complete
agreement with McCulloch1s findings, were those of Cohen (16), who
showed that there was practically no difference in the death rate of
12. coli at 0°, 10° and 20°C when exposed to dilute phosphate buffers.
Further temperature increases up to 30°C resulted in an increase in
the death rate of 15. coli.
Another factor which has been shown to affect the bactericidal
efficiency of alkalies is the quantity of organic matter present.
Lamanna and Mallette (38) stated that the protection provided by
"colloidal organic matter against chemical disinfection may be called
a protective colloid effect." Because organic matter is of biological
origin, there is interaction between the hydroxide and the organic
matter, which essentially reduces the effective concentration of the
hydroxide.
Early investigations of lime softened water (34) indicated that the
bactericidal effectiveness of lime decreased in the presence of
large concentrations of organic matter. McCulloch and Costigan (47)
substantiated this fact when they showed that much more alkali was
required to produce germicidal conditions when organisms were sus-
pended in heavy suspensions of fecal matter and in broths as well.
More recent investigations (20,58,78) also indicated that organic
matter provides protection for bacteria against the bactericidal
action of alkalies.
In contrast to evidence supporting the protective effects of organic
matter, Tilley and Schaffer (76) found that the presence of chicken
feces, skim milk or defibrinated horse blood had little effect upon
the germicidal efficiency of sodium carbonate, trisodium phosphate*
or a mixture of either of these with sodium hydroxide.
In addition to the effects of temperature and organic matter, several
other factors play an important role in determining the efficiency of
alkalies. Bacterial load has been shown to influence the bactericidal
efficiency of alkalies. Lang (39) found that dead cells in a medium
apparently provided some type of protective effect for surviving
organisms. Winslow and Falk (81) studied this effect and surmised
10
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that the protection was due to the liberation of acidic materials
from dead cells, which created a zone of lower alkalinity around viable
cells.
Shaughnessy and Falk (69) reported that when viable cells were exposed
to excessive concentrations of calcium, they underwent lysis liber-
ating buffer-like substances into the medium. Subsequent investi-
gations by Shaughnessy and Winslow (70) indicated that E_. coli changed
the pH of the surrounding medium by excretion of acid-like substances.
Watkins and Winslow (79) found that large populations of bacteria were
able to survive high pH values more efficiently than small populations.
They theorized that bacteria excrete base neutralizing acids into the
medium, creating a microenvironment of reduced alkalinity in the
area immediately surrounding each cell. Apparently large populations
were able to do so more efficiently.
The age of bacterial cultures has also been shown to affect the
bactericidal efficiency of disinfectants (38,75). Recently, Grabow,
Grabow and Burger (29) reported that physiologically active cells from
humus tank effluents were much more susceptible to high pH than those
cells that were in the stationary phase of growth. Watkins and Winslow
(79) recognized the importance of culture age in determining the death
rate of vegetative cells. They found that vegetative cells followed a
logarithmic death curve when exposed to alkalinity and heat, while
spores were found to die at an accelerated rate as time of exposure
increased. Myers (53) also showed that the death rate of spores in-
creased as the length of exposure to high pH increased.
Varying genera and species of bacteria respond to high pH differently.
Cohen (16) reported that E. coli was more resistant to high pH than
S_. typhosa in distilled and tap water. Wattie and Chambers (80)
performed extensive tests on the survival of various genera of bacteria
exposed to high pH. They found that A. aero genes was somewhat more
resistant to high pH than 12. coli, both of which were more resistant
than either S^. typhosa or S_. dysenteriae. The work of Doyle (20) on
lime treatment of sewage sludge filter cake confirmed the findings of
Wattie and Chambers; E_. coli survives longer at high pH than
S^. typhosa.
Relatively concentrated solutions of sodium and potassium hydroxide
have been used in the isolation of acid-fast Mycobacterium tuberculosis
bacilli (9,57); testimony to the extreme resistance of the acid-fast
organisms to extremely high pH. Recently, Grabow, Grabow and Burger
(29) reported a marked difference in the bactericidal action of lime
against Gram negative, Gram positive and acid-fast bacteria. Gram
negative organisms were found to be more susceptible to high pH than
either the Gram positive or acid-fast organisms. The acid-fast
organisms proved to be practically unaffected by the high pH. Main-
taining a pH of 11.5 for 60 minutes resulted in complete destruction
of all Gram negative bacteria, the primary survivors being bacterial
spores.
11
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The fact that the organisms of the coliform group (E^. coll, A.
aerogenes» etc.) are more resistant to high pH than the "colon-typhoid"
group (Salmonella, Shigella, etc.) is important. By setting standards
which predicate that sewage effluents must be very low in coliform popu-
lations, it may be possible to determine, within certain confidence
limits, the relative safety of those effluents as far as the "colon-
typhoid" organisms are concerned. Kehr and Butterfield (37) emphasized
the value of the coliform test as an indicator of the possible presence
of pathogenic bacteria, even when the coliform populations were very
small. Doyle (20), on the other hand, stated that the presence or
absence of IS. CQJ.J in high pH systems should not be used as an indicator
of the presence or absence of SL typhosa. Instead, determination and
subsequent application of high pH values which are destructive to J^.
typhosa should be used.
Sewage Disposal Problems^ in the Arctic
According to Boyd and Boyd (8) , "one of the most difficult problems
of the North, especially in inland regions, is sewage disposal." A
review of the early methods of sewage disposal along coastal regions
of the Arctic (7) revealed that one of the most primitive and econ-
omical methods practiced was deposition of sewage in 55 gallon oil
drums, transporting them to and abandoning them on the coastal ice.
The development of such devices as "electric toilets" and fuel oil
sewage-carrier systems were reported to show promise; however,
operational problems made them somewhat undependable. Lagoons were
said to be promising if "starter" cultures could be developed which
would be enzymatically active at low temperatures.
Dickens (19) indicated that the primary method of sewage disposal in
permafrost areas of northern Canada was the "pail" system, where the
raw sewage was disposed on the open tundra or in local water courses.
The use of insulated and heated septic tanks in arctic regions was
reported to be somewhat successful; however, the effluents presented
problems because of pathogenic organisms. The widespread use of
water-carried sewage systems in arctic regions has been limited due
to the excessive expense involved in preventing freeze-up (19).
Furthermore, low temperatures in arctic regions were reported to
greatly impair most methods of sewage treatment. Thus the use of
leaching pits, septic tank disposal fields and the pit privy are
relatively impractical in arctic regions.
The feasibility of sewage disposal within the icecap of Greenland was
studied by Ostrum, West and Shafer (55). Careful examination of ice
cores from the area surrounding the sewage sump indicated that the
contaminated ice volume was about twice the volume of the waste-water
discharged. Others (15) theorized that the use of such sewage sumps
would preclude the future use of the area and could possibly undermine
the camp in subsequent years. A report on waste disposal by Navy
camps in polar regions (15) revealed that about half of these camps
12
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did not treat their sewage at all before discharge. Of those that did,
the most common treatments used included extended aeration, septic
tanks and stabilization ponds.
Several investigators have emphasized the need to adequately disinfect
all sewages before discharge into the environment (15,19). Pathogenic
bacteria have been shown to remain viable for extended periods when
exposed to extremely cold temperatures. The magnitude of the
potential health problems that exist when untreated sewage is deposited
on the frozen tundra was pointed out by Gordon and Babbott (27).
They showed that shigellae and salmonellae survived frozen con-
ditions in seeded stools left on the open trundra for 17 and 45
days, respectively. The evidence indicated that these bacteria are
very resistant to the cold and other natural features of the arctic
environment. Gastroenteritis was reported to be relatively common
in the Arctic. Disease was generally thought to be associated with
the lack of adequte water treatment and sewage disposal, along with
unclean conditions from the lack of wash water. To further emphasize
the durability of intestinal organims in arctic environments, a report
by Carey (12) revealed that intestinal bacteria had survived for
about 50 years in frozen stools left by the members of the Scott and
Shackelton Antarctic expeditions of 1915-16. A recent study on a
subarctic river by Gordon (28) indicated the extended survival of
index organisms.
The need to adequately disinfect all domestic sewage in polar regions
is obvious; however, the methods are not! Clark, Alter and Blake (15)
reviewed the possible methods, most of which were reported to be
unsuitable for use in arctic environments. A system of electro-
chemical disinfection was reported to hold promise; however, location
near salt water was a prerequisite. McKinney (48) reported that the
rate of chemical reactions is temperature dependent, chlorination
being no exception. The activity of chlorine was shown to be
extremely low at 0°C. As temperatures increased, the reaction rate
increased rapidly resulting in about twice the rate of kill for each
10°C rise in temperature. Butterfield (10) indicated that low temp-
eratures reduced the disinfection efficiency of free chlorine and
monochloramine. Dickens (19) reported that temperatures below 10°C
caused difficulties with gaseous chlorination because of the formation
of chlorine hydrate crystals. Other proposed treatment procedures
(20) required the use of expensive fuels or elaborate equipment
making them impractical for use in small arctic communities.
Effects of Low Temperature on Conventional Sewage Treatment Systems
Ludzack, jit al. (44) indicated that the temperature of activated sludge
operations affected BOD and COD removals. Operation at 5°C resulted
in 10% lower removals than those obtained at 30°C. Likewise, lower
temperatures adversely affected flocculation characteristics. Keefer
(36) reviewed the literature pertinent to the temperature and efficiency
13
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of activated sludge systems and reported that very low temperatures
may decrease the efficiency of the system.
Trickling filters are probably more adversely affected by cold temp-
eratures than activated sludge systems. Benzie (5) stated that
"trickling filters operate more effectively in warm rather than cold
climates." Furthermore, severely cold Michigan winters were reported
to have resulted in the formation of thick layers of ice on rotating
distributors and filter bed media. Some filters were so severely
iced that they had to be removed from service, reducing the efficiency
of the plant to the status of a primary treatment system. Clark,
Alter and Blake (15) concluded that if conventional sewage treatment
systems are to be used in arctic regions, they will have to be housed
in heated, well insulated buildings to insure maximum operating
conditions and avoid freeze-up.
Removal of Suspended Solids, BOD and Qrthophosphate from Sewage with
Lime
Stauffer (72) reported that the first patent for a chemical process of
sewage purification was issued to Deboissieu in 1762. Lime was the
chemical most commonly used, probably because of its effectiveness and
low cost.
The lime softening process for water supplies was developed in 1841
by Dr. Clark of Edinburg, Scotland (14) and is now referred to as the
Porter-Clark process (58). The formation of calcium carbonate and
magnesium hydroxide precipitates, in conjunction with high pH, results
in the flocculation of suspended solids with improved settling. Be-
cause the same general chemical reactions take place in wastewater,
the early use of the lime softening process as an aid in the removal
of suspended solids probably led to the use of lime as an aid in
coagulation of sewage solids. Early reports on sewage treatment in
America indicate that lime was used extensively in this capacity (71).
Rudolfs and Gehm (60) found that there are two pH zones where optimum
removal of suspended solids occurs; pH 2-3 on the acid side and pH
10-11 on the alkaline side. These pH zones were not fixed, but varied
with such factors as dissolved oxygen concentration, quantity and type
of trade wastes and the quantity of iron coagulants needed for maximum
coagulation. Investigations into the relationship between turbidity,
suspended solids and BOD (61) led to the general conclusion that de-
creasing turbidity paralleled increasing removals of suspended solids
and BOD. The effects of raw sewage presettling on the efficiency of
suspended solids removal during subsequent lime treatment was also
studied (62). There was little difference in suspended solids removal
using lime in conjunction with and without presettling. The coagulation
of unsettled sewage was, in some instances, superior to that of pre-
settled sewage.
Van Vuuren, et al. (77), using a combined system of lime softening and
14
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microbubble aeration, found that the COD of settled sewage could be
reduced from 600 mg/1 to less than 100 mg/1. The system, when used
in conjunction with recarbonation, resulted in a reduction of total
dissolved solids, a valuable deterrent to the salinity problem.
Buzzell and Sawyer (11) noted that lime treatment of domestic sewages
resulted in 50-70% BOD removals and that the supernatant liquids were
generally "clear and sparkling". Attempts to further reduce BOD
values by activated sludge treatment were unsuccessful due to the low
BOD values in those effluents. Recently, Mulbarger, Grossman and
Dean (51) found that lime treatment of secondary effluents produced
an average removal in suspended solids and total organic carbon of
97 and 51%, respectively.
In the last two decades considerable attention has been directed
toward undesirable algal growths in many lakes and ponds. The general
opinion has been that these algal blooms were the result of excessive
nutrient concentrations, including orthophosphate, in water courses
receiving sewage effluents (1,56,66).
Sawyer (64) stated that the ultimate goal in phosphate removal was
the maintenance of less than 0.01 mg/1 of inorganic phosphates in
waters receiving sewage effluents. More recent investigations by
Dryden and Stern (21) indicate that orthophosphate levels of 0.5 mg/1
or less will not support the growth of algae.
Many systems of phosphate removal have been reported in the literature
(54,66). The general consensus of opinion has been that a system of
chemical precipitation followed by biological treatment (66) or
straight lime precipitation (1,54) would be most desirable from the
standpoint of both economics and efficiency. Owen (56) reported that
soluble phosphates could be removed from sewage plant effluents by
lime addition; pH 10.0 usually being sufficient to precipitate most
of the soluble phosphates. Lime addition of 545 mg/1 of sewage
resulted in a pH of 10.5, total -phosphates were lowered 77% when
settled for one hour. Results obtained by Schmid and McKinney (66)
indicated that total phosphates could be lowered as much as 80% by
lime treatment. Albertson and Sherwood (1) discovered that ortho-
phosphate was more difficult to remove, using lime treatment, than
either the organic phosphates or the complex polyphosphates. Lime
addition in a successful tertiary treatment system to reduce phosphate
levels as well as residuals was reported by Gulp (18).
The exact chemical reactions in the precipitation of phosphate
compounds with calcium hydroxide (hydrated lime) are not known. How-
ever, it has been shown that orthophosphate combines with calcium
and magnesium at pH values above 10.5. The compounds formed closely
approximate the hydroxyapatites of calcium [Ca^PO^^K- Ca(OR)~
and magnesium [Mg3(P04)2 - Mg(OH)2J, which are only slightly
soluble at pH > 10 (45).
Buzzell and Sawyer (11) also recognized the importance of limiting
15
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the phosphate concentrations in the control of excessive algal blooms.
Results obtained from their investigations of phosphate removal from
sewage with lime indicated that a maximum phosphate removal of 97%
was obtained at a pH of about 11.0, while maximum precipitation of
suspended solids occurred at pH 10.5. Proportionately greater
concentrations of lime were required to attain pH values greater
than 11.0 which resulted in calcium carbonate turbidity and little
additional orthophosphate removal. In a comprehensive report on
nutrient removal from wastewater, Eliassen and Tchobanoglous (25)
stated that orthophosphate concentrations could be reduced to the
level of 0.5 mg/1 using lime coagulation-sedimentation and that
chemical recovery was possible by calcination of the sludge.
Effluents from lime treatment systems are relatively caustic (59) and
recarbonation of the high pH effluents has been practiced in the
past. Lecompte (41) reported using scrubbed boiler flue gas, while
Van Vuuren, et al. (78) used a source of gaseous carbon dioxide;
however, they too recommended the use of flue gases. Mulbarger,
Grossman and Dean (51) indicated that the carbon dioxide liberated
from the calcination of the sewage sludge could be used in the re-
carbonation of effluents from the lime treatment system. Other
methods of recarbonation include the use of alum and carbonic acid
generated from coke, nitric cake solutions and sodium bicarbonate,
were described by Houston (35) ; however, the use of gaseous carbon
dioxide was superior to the other methods.
16
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SECTION IV
MATERIALS AND METHODS
ANALYSIS OF LIME AND LIME SLURRY PREPARATION
Commercial grade lime was obtained locally and analyzed for per-
centages of calcium oxide (CaO), magnesium oxide (MgO), iron and
aluminum oxides (Fe20-j and A^O^), silicon oxide (Si02) and loss on
ignition by the Ideal Cement Co., Fort Collins, Colorado.
Analyses I Raw Sewage II Secondary
Studies Treatment Studies
Mo-rj
ngu
Al n
CM O
Tr*t- «
iota
i
70 on'v'
— — — — — /J./CUA
Oli 97
OOQ
O/i n 7
jZ » DU /^
Q Q Q 0 7
Loss on ignition represents the percent CaC03, therefore the lime used
in this study was strongly carbonated as the result of contact with
atmospheric carbon dioxide.
The slaked lime slurry contained: I., 180 mg of lime per milliliter,
with an available calcium oxide content of 132 mg per milliliter;
II., 180 mg lime/ml and 117 mgCaO/ml. -As contact with atmospheric
carbon dioxide progressed, the appearance of solid calcium carbonate
became apparent and the unused portion was discarded after one month.
To prepare the lime for use, it was slaked (mixed) with boiled, deion-
ized water to produce a viscous slurry which could be pipetted, but
concentrated enough to produce high pH values with minimal sample
dilution. A slurry composition of five parts deionized water plus one
part powdered quicklime (v/w) was found to be best suited for this
study (each milliliter of slurry contained approximately 0.2 g of
lime). Approximately 600 g of lime slurry were prepared and stored
tightly sealed in a one liter polypropylene container until needed.
The unused portion was discarded at the end of one month.
PREPARATION OF SEWAGE SAMPLES FOR TITRATION AND HIGH pH STUDIES
Throughout this study, sewage samples were collected at approximately
9:00 A.M. in an attempt to increase sample uniformity and minimize
variations brought about by changes in flow rate, sewage composition,
etc. Sampling was postponed for a 24 hour period after rain or snow.
17
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All raw samples used in this study were collected from the Fort
Collins trickling filter sewage plant #1 as the sewage left the grit
removal chamber. Treated sewage samples were collected at the #2
treatment plant, an activated sludge unit, and taken from the secondary
settling tank. Polypropylene containers (20 1), chlorine sanitized
and then thiosulfate neutralized (2) were used for sample collection.
Delivery to the laboratory required less than 15 minutes.
Ambient air and sewage temperatures were measured at the sample site
with a Weston dial thermometer (± 0.5°C). In addition to the 20 liter
sample, two 300 ml biochemical oxygen demand (BOD) bottles were care-
fully and completely filled with raw sewage and securely stoppered for
rough estimation of the dissolved oxygen concentration upon delivery
to the laboratory.
Immediately upon arrival at the laboratory, the 20 liter sewage sample
was thoroughly mixed by shaking the container for one minute. The
sewage was then decanted into five sterile 3 liter Erlenmyer flasks,
capped with aluminum foil and placed in a -20°C freezer for settling
of suspended solids and cooling.
For lime treatment at 1° and 5°C, the sewage was settled and cooled for
one hour, after which the supernatant was aseptically siphoned into
sterile 3.8 liter containers for additional cooling to the desired
treatment temperature. The treatment containers were then removed from
the cooling unit and placed in a temperature controlled environmental
room, preset to either 1° or 5°C for treatment. For lime treatment at
10° and 15°C, the sewage was settled at -20°C until the desired treat-
ment temperature was attained. The containers were then removed from
the cooling unit and placed in an environmental room, preset to 10° or
15°C, to complete one hour of settling. After settling, the super-
natant was siphoned into sterile 3.8 liter containers for treatment.
Before lime treatment, the contents from all containers were thoroughly
intermixed to obtain sample uniformity. The final volume in each
container was adjusted to two liters, the excess from each container
being decanted back into the 20 liter polypropylene container for
sterilization before discard. Each treatment container was covered
with aluminum foil and transferred to a six-place magnetic stirring
apparatus (Lab-Line Instruments, Inc.), located in the environmental
room for subsequent treatment at the selected temperature.
TITRATION OF SEWAGE WITH LIME, POTASSIUM HYDROXIDE AND CALCIUM CHLORIDE
Titration of raw, settled sewage with lime was performed at temperatures
of 5°, 10° and 15°C. Samples were continuously mixed during titration
on a magnetic stirrer. All samples of sewage were mixed in this man-
ner at a fixed speed. Prior to titration, the temperature and pH of
the sample were determined using a Tele-Thermometer model 43TZ (Yellow
Springs Instrument Co., Inc.) and an Accumet 220 pH meter (Fisher
Scientific Co.), respectively.
18
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During titration, prepared lime slurry was added to the sewage samples
in increments large enough to produce a pH change of between 0.1 and
0.8 pH units. Successive lime additions and pH measurements were
continued until a pH value of approximately 12.3 was attained. Dup-
licate sewage samples were titrated with lime slurry in this manner,
at each temperature, and the results averaged.
Using potassium hydroxide (commercial grade - 85% maximum KOH) , dup-
licate two liter sewage samples were titrated at 5°C and the results
averaged into one titration curve.
A single titration curve was determined for a two liter sewage sample
at 5°C, using a combination of lime to about pH 10.0, followed by
the addition of 3 N potassium hydroxide to a pH of 12.3. Again, the
procedure was the same as that used during the titration of sewage
with lime slurry.
The pH of two, two liter sewage samples was adjusted to approximately
12.3, one with lime slurry and one with 3 N KOH, as described. Each
sample was then back-titrated using a 2 M calcium chloride solution
added in 10 ml aliquots and the resulting pH was measured. The effects
of calcium chloride on high pH values as produced from lime and potas-
sium hydroxide additions were determined at 5°C. The effects of a 2 M
calcium chloride solution on the pH of an untreated sewage sample
(pH 7.4) at 5°C were also determined, in the same manner.
LIME DISINFECTION OF SEWAGE BACTERIA AT COLD TEMPERATURES
Two liter sewage samples were prepared as described above. To deter-
mine the disinfection rate at the various pH values, two treatment
procedures were followed because widely varying contact periods were
necessary at initial treatment pH values of 10.0, 10.5 and 11.0 as
compared to contact periods at initial pH values of 11.5 and 12.0.
Therefore, they will be described separately.
Disinfection at pH 10.0, 10.5 and 11.0
Four, two liter samples, pH 10.0, 10.5, 11.0 and control, respectively,
were thoroughly mixed for five minutes after which a 10 ml aliquot
was withdrawn from each container for zero time bacterial enumeration.
All samples were withdrawn with a sterile pipette and placed in sterile,
labeled 25 x 150 mm screw-cap test tubes.
The temperature and pH of each treatment container was measured and
the ambient air temperature in the controlled environmental room was
continuously recorded with a Hydro-Thermograph model 594 (Freiz
Instrument Div.).
Starting at time zero, with continued mixing, lime was added to the
containers, adjusting the sewage pH to the desired treatment value.
The control container recieved no lime. All containers were allowed to
19
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mix for a total period of five minutes, after which each was allowed
to quiescently settle. At time intervals of 2, 4, 6, 8, 10, 12, 18,
24, 36 and 48 hours, samples of 10-30 ml were aseptically withdrawn
from each high pH container for bacterial enumeration. A sample of
the control sewage was likex^ise removed at 48 hours. The temperature
and pH of the contents in each container were measured each time a
sample was withdrawn. All samples were withdrawn from the containers
as close to the center and five centimeters below the sewage surface
as possible. Three sewage samples collected on different days were
exposed to these high pH values at 1°, 5°, 10° and 15°C, and the
results obtained at each pH and temperature were averaged. All
quantities of lime used to produce high oil values were recorded.
Disinfection at pH 11.5 and _12_._0
Two liter samples were thoroughly mixed for five minutes, after which
a 10 ml aliquot was withdrawn from each for zero time bacterial
enumeration. The temperature and pH were measured before lime
additions were made. Starting at time zero, with continued mixing,
lime slurry was added to the containers adjusting the pH to the
desired treatment values of 11.5 and 12.0. As before, the control
received no lime. After a total iaixing period of five minutes, the
contents of each container were allowed to quiescently settle. Over
a 90 minute contact period, 50 ml aliqucts were aseptically with-
drawn from each container at 10 minute intervals for bacterial
enumeration. The control was sampled after 90 minutes of contact.
As before, the temperature and pH were measured each time a sample
was removed. Three sewage samples collected on different days were
exposed to these high pH values at 1°, 5°, 10° and 15°C, and the
results obtained at each pH and temperature were averaged.
PREPARATION OF PRECIPITATED SOLIDS FOR BACTERIAL ENUMERATION
The examination of precipitated sludge produced in all five high pH
treatments was performed identically, except for the ranges of
dilutions needed for bacterial enumeration.
At the termination of 48 hours of exposure to pH values of 10.0,
10.5 and 11.0, a 10 ml alJquot of the precipitated material from each
container was aseptically removed, using a wide bore pipette, and
placed in a separate sterile microblender with 90 ml of sterile
phosphate buffered (0.02 !i) dilution water. Likewise, at the end of
90 minutes contact with pH values of 11.5 and 12,0, a 10 ml aliquot
of the precipitated material from each container v/as prepared. Each
sample of precipitated material was immediately blended at high speed
for 30 seconds and allowed to quiescently settle for five minutes.
Serial 10-fold dilutions were then prepared from the supernatants of
each to cover trie expected range of bacterial concentrations found
in the solids. In some cases, it was necessary to membrane filter
5 ml, 10 ml or even larger quantities of the supernatant, without pre-
paring dilutions, in order to obtain countable plates.
20
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ENUMERATION OF TOTAL COLIFORM, FECAL COLTFORM AND TOTAL PLATE COUNT
BACTERIA
Difco media, used exclusively throughout this study, were freshly
prepared, as needed, according to the manufacturer's specification.
Total coliform bacteria were grown on m-Endo Broth M F, fecal coliform
bacteria on m-F C Broth (plus rosolic acid) and the total plate counts
were enumerated on m-Plate Count Broth. All media were stored at
refrigerator temperature.
Enumeration of total and fecal coliforms were performed on the various
samples immediately after being removed from the treatment container
by the membrane filter method described in Sta_nd_ard_Me_thpds_ (2). Total
plate counts, also called standard plate counts, were enumerated by a
Millipore procedure adopted by this laboratory (67).
Bacterial counts in this study are reported in numbers per milliliter
rather than the usually used numbers per 100 ml because of the high
bacterial loading of the waste material studied.
All samples, other than precipitated sludge, were first thoroughly
mixed for 30 seconds in sterile tubes with a vortex mixer. Immediately
after mixing, serial 10-fold dilutions were prepared from each,
anticipating the range of bacterial concentrations. Each dilution
was then membrane filtered and washed three times with approximately
35 ml of sterile phosphate buffered (0.02 M) dilution water.
White-grid 0.45 ji Millipore membrane filters were used for enumeration
of total and fecal coliform bacteria, while black-grid membranes
were used for total plate counts. Incubations were according to
Standard Methods (2) as follows-: fecal coliforms, 44.5 ± 0.2°C for
24 hours with the plates enclosed in Whirl-Pac plastic bags submerged
in a water bath; total coliforms, 35 ± 0.5°C for 24 hours; total
plate counts, 20°C for 48 hours. Colony counting was under a 10-
power stereoscope.
REDUCTIONS IN NUTRIENT LEVELS OF SEWAGE WITH LIME
Raw and secondary treatment sewage was collected and prepared as de-
scribed previously, except that sterile conditions were not maintained.
The biochemical oxygen demand (BOD) of a 100 ml aliqout of raw sewage
which had been homogenized in a microblender for 15 seconds was deter-
mined in duplicate using the azide modification (2). Likewise, the
BOD of an aliquot of the supernatant from the same sewage settled
for one hour was determined in duplicate. The orthophosphate con-
centration in fresh and settled samples was determined by the
vanadomolybdate colorimetric technique, as described in Standard
Methods (2). "~
21
-------
Sewage samples settled as described earlier were thoroughly mixed
on a six-place magnetic stirring apparatus. The pH of the sewage in
f±ve of the containers was then adjusted with lime to values of 10.0,
10.5, 11.0, 11.5 and 12.0, respectively, and another container was
the control. All samples were continuously mixed for five minutes
during lime addition with pH monitoring. Then the sewage in each
container was allowed to quiescently settle.
Residual BOD and orthophosphate concentrations were determined in
the supernatants of the lime treated sewages at the end of contact
periods at the various temperatures, as outlined in the protocol.
Residual BOD and orthophosphate concentrations in lime treated sewages
were determined on samples of sewage acquired on three separate days
at temperatures of 1°, 5°, 10° and 15°C as previously described, and
the results obtained at each pH and temperature were averaged.
Protocol for BOD and Orthophosphate
Protocol
Temp.
<*c>
1
5
10
15
Characteristic
measured
BOD
o-P04
BOD
0-P04
BOD
o-P04
BOD
o-PO,
4
Treatment
10.0, 10.5, 11.0
and control
48 hours
24 hours
48 hours
24 hours
48 hours
48 hours
24 hours
24 hours
pH values
11.5, 12.0
and control
90 minutes
90 minutes
60 minutes
60 minutes
60 minutes
60 minutes
60 minutes
60 minutes
MEASUREMENTS OF PHYSICAL AND CHEMICAL SEWAGE CHARACTERISTICS
Measurements of the physical and chemical characteristics of many of
the sewage samples were performed.
Tests
Settleable Solids - from a well mixed container of raw sewage, one
liter was decanted into an Imhoff cone and allowed to stand upright
for one hour. Settleable solids were determined and recorded as
milliliters per liter of raw sewage
22
-------
Suspended Solids - 100 ml of settled sewage (one hour) were filtered
through asbestos in Gooch crucibles, evaporated to dryness and re-
ported as tag/100 ml (2)
Conductivity - measured directly at 20°C on a sewage sample with a
conductivity meter model RA-2A (Industrial Instruments, Inc.)
Turbidity - determined with a Klett Colorimeter (Summerson
Photoelectric Colorimeter model 800-3) , with a Blue #42 filter
Orthophosphate - determined using both the aminonaphtholsulfonic
acid and the vanadomolybdate colorimetric techniques (2)
Calcium Hardness - determined in accordance with the procedure
described in the Hach Chemical Company's Methods Manual, 7th Edition
(31)
Total Alkalinity - measured by Hach sulfuric acid titration (31)
pJH - Accumet 220 pH meter (Fisher Scientific Co.) at 20°C
Temperature - measured directly using a Weston dial thermometer
Dissolved Oxygen Concentration - determined in accordance with the
modified azide technique as described in Standard Methods (2)
Biochemical Oxygen Demand - by the azide modification of Standard
Methods (2).
23
-------
SECTION V
RESULTS
Investigations into the use of lime as a low temperature chemical
sewage treatment process were performed in phases in order to obtain
a better understanding of the potential of such a system: Titration
of Sewage with Lime, Potassium Hydroxide, and Calcium Chloride; Lime
Disinfection of Sewage Bacteria; Reductions in the Biochemical
Oxygen Demand (BOD) and Orthophosphate Concentrations of Sewage with
Lime; Measurements of Temperature, pH and Quantities of Lime Added to
Sewage; Measurements of the Physical and Chemical Characteristics of
Raw Sewage Samples.
TITRATION OF SEWAGE WITH LIME, POTASSIUM HYDROXIDE, AND CALCIUM
CHLORIDE
The data in Fig. 1 shows the general relationship between the quantity
of lime slurry added to a two liter settled raw sewage sample and
the resulting pH values at 5°C. Similar results were obtained at
10° and 15°C; however, more lime was required to produce pH values
above 11.0 at 10° and 15*C than was required to produce equivalent
pH values at 1° or 5°C. Figure 2 shows comparable pH increases when
lime slurry was added to secondary treated sewage at 5°C.
Investigations into the use of potassium hydroxide to raise the pH
of a two liter settled raw sewage sample are also shown in Fig. 1.
The titration curve produced with potassium hydroxide was very
similar to that produced with lime slurry, except at pH values above
9.3, where proportionately greater quantities of potassium hydroxide
were required, compared to lime, to produce an equivalent pH
change.
Investigations into the use of lime in conjunction with potassium
hydroxide to reduce the quantity of lime needed in raw sewage to
produce pH values above 10.0 are shown in Fig. 3. The titration
curve was very similar to that produced when titrating with either
lime or potassium hydroxide individually.
The pH of a two liter settled raw sewage sample was adjusted to 12.12
with lime at 5°C. Using a 2 M CaCl2 solution, this sewage was then
back-titrated to detect any pH repression. Addition of 50 ml of
CaCl2 solution resulted in a pH repression of 0.67 units; 50 ml to
an equivalent two liter sewage sample adjusted to pH 12.00 at 5°C
with 3 N KOH resulted in a pH repression of only 0.14 units. Further-
more, an additional 50 ml of 2 M CaCl2 did not affect the pH of this
sewage significantly; 50 ml in a two liter settled sewage sample at
pH 7.58 (untreated raw sewage) resulted in a pH repression of 0.28
units (Table 1).
24
-------
U1
pH
O lime slurry (5:1 v/w)
D 3 N KO H
23456 789 10
Titrant added (ml)
12 14
FIG. I. Effect* of lime and 3N KOH on the pH of 2 liter sewage tamples at 5* C.
-------
OS
O Lime slurry (5*1, v/w)
fc
ID
FIG. 2.
Lime added (ml)
Effects of lime on the pH of 2 liter secondary treatment
sewage samples at 5°C.
•k-
-------
12
II
10
I I I I
D lime slurry (5>
A 3 N KOH
0 I 2 ' 0
Lime added (ml)
I 2 3 4
3 N KOH added (ml)
FIG. 3. Effect of adding lime slurry to «ewaget followed by 3 N KOH, at 5° C.
-------
Table 1. Back-titration of neutral and high pH sewages (2 liters each)
with 2 M calcium chloride at 5°C.
Calcium
chloride
added
(ml)
0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
100.0
Lime
treated
sewage
12.12
11.91
11.82
11.63
11.57
11.53
11.50
11.50
11.45
pH values 9/8/71
KOH
treated Control
sewage sewage
12.00 7.58
7.52
7.53
7.49
7.48
7.47
7.46
7.45
7.44
7.43
11.96 7.42
11.92
11.87
11.85
11.82 7.30
28
-------
LIME DISINFECTION OF SEWAGE BACTERIA
The effects of temperature and an Initial pli of 10.0 on the survival
of total coliform bacteria in raw sewage are shown in Fig. 4. Success-
ive increases in the pH by one-half unit and the resulting reductions
in the total coliform concentrations are shown in Figures 4 through 8.
Comparison of the results in these figures shows the parallel between
increasing pH values and accelerated rates of total coliform mortality
and a sharp breakpoint in the rate of coliform death at a pll of about"
11.5. Figures 9 through 12 show the reduction of total coliforms in
lime-treated secondary effluent at 1° and 10°C.
The effects of treatment temperatures and pH values on the survival
of fecal coliform bacteria are shown in Figures 13 through 21. Al-
though the initial concentrations of fecal coliform bacteria were
generally one log unit lower than total coliform concentrations, the
mortality rates of both groups were very similar. This is clearly
shown by comparing the data for total coliform death with the corre-
sponding data for fecal coliform death at the same pH and temperature.
In order to determine if any coliform death resulted from factors
other than high pH, sewage controls were prepared and treated in
the same manner as the high pH sewages except that no lime was added.
Figures 22-23 show the survival of total and fecal coliform bacteria
in controls held at low temperatures for 90 minutes. Likewise, sur-
vival of total and fecal coliform bacteria and standard plate count
organisms in sewage controls at low temperatures for 48 hours are
shown in Figs. 24-25. It is of interest to note that the data in
Fig. 24 also shows that both total and fecal coliform bacteria were
capable of growth in sewage controls at 15°C, but not at or below
10°C.
In order to obtain a better understanding of the effects of high pH
on the survival of bacteria, total plate counts were performed
initially and at the end of each high pH treatment. Tables 2 and 3
show the results obtained from such high pH treatments at the various
temperatures, and from untreated sewage controls.
The possibility that large concentrations of organic matter affords
protection to bacteria from the toxic effects of high pH was also
investigated. Comparative counts of total and fecal coliform and
standard" plate counts in the supernatant and precipitated solids were
performed at the end of each high pH treatment in order to determine
this. The data is presented in Tables 4 thrcmgh 9.
REDUCTIONS IN THE BIOCHEMICAL OXYGEN DEMAND (BOD) AND QRTHOPHOSPHATE
CONCENTRATIONS OF SEWAGE USING LIME
Along with the destructive action of high pH against bacteria,
sewage solids and orthophosphate were simultaneously removed during
29
-------
5-
i i i I
8 10 12
Time (hr)
18
24 ' 48
FIG. 4. Reduction of total coliform bacteria in lime treated
sewage at an initial pH of 10.0, at I to 15° C.
30
-------
0 2
FIG. 5.
8
12 18
Time (hr)
24
1—//—J
&7/ Zi
48
Reduction of total col If can bacteria in lime treated
Mwage at an initial pH of 10.5, at I to 15° C.
31
-------
0 2
FIG. 6.
O |° C
D 5°C
A 10° C
OI5° C
8 10
12 18
Time (hr)
24
48
Reduction of total coliform bacteria in lime treated
sewage at an initial pH of II.0, at I to 15* C.
32
-------
O
u
i
o
'>
0>
o
40 50 60
Time (min)
80 90
FIG. 7. Reduction of total coliform bacteria in lime treated
sewage at an initial pH of 11.5, at I to 15° C.
33
-------
E
¥>
E
o
o
0
S
ore
D 5° C
A 10° c
Ol5° C
O IO 20
Time (min)
FIG.8. Reduction of total coliform bacteria in lime treated
sewage at an initial pH of 12.0, at I to 15° C.
34
-------
n 10.0
A !0.5pH
O M-OpH
-2
D
24
48
024 6 8 10 12 18
Time ihr)
FIG. 9. Reduction of total collform bacteria In lime treated
•econdary effluent at initial pH's of 10.0, 10.5
and 11.0, at 10° C.
35
-------
I
o
V
20
-I
n 10.0
A 10.5 pH
O M.O pH
0 2 46 8 10 I
2
Time (hr)
a
48
RG. 10. Reduction of total conform bacteria in lime treated
•econdary effluent at initial pH'e of 10.0, 10.5
and 11.0, at PC.
36
-------
O 11.5 pH
D 12.0 pH
-2
40 50 60
Time (min)
70 80 90
FIG.
Reduction of total cdiform bacteria in lime treated
secondary affluent at initial pH't of 11.5 and
12.0, at 10° C.
37
-------
E
o
o
u
o
o
JD
>
O»
o
O 11.5 pH
D 12.0 pH
-2
IO 20 30
40 50 60
Time (min)
70 80 90
FIG. 12. Reduction of totol coliform bocterio in lime treated
secondary effluent at initial pH's of 11.5 and
12.0. at I*C.
38
-------
0 2
8
10 12 18
Time (hr)
O
D
24
FIG. 13. Reduction of fecal coliform bacteria in lime treated
sewage at an initial pH of 10.0, at I to 15* C.
39
-------
O 1° C
D 5° C
A10° C
Ol5e C
(hr)
FIG. 14. Reduction of fecal coliform bacteria in lime treated
sewage at an initial pH of 10.5, at I to 15° C.
40
-------
o i° c
D 5e C
A 10° C
OI5° C
Time (hr)
FIG, 15. Reduction of fecal col if or m bacteria in lime treated
sewage at an initial pH of 11.0, at I to 15° C.
41
-------
s
o
o
0
20 30
70 80 90
FIG. 16.
40 50 60
time (min)
Reduction of fecal colifomv bacteria in lime treated
sewage at an initial pH of 11.5, at I to 15° C.
42
-------
I
O
U
O
U
a
>
5
O 1° C
D 5° C
A 10° c
O 15° C
10 20 30
70 80 90
40 50 60
Time (min)
FIG. 17. Reduction of fecal conform bacteria in lime treated
sewage at an initial pH of 12.0, at I to 15 ° C.
43
-------
D 10.0 pH
A lO.SpH
O M.OpH
D
0 2
10 12 18
Time (hr)
FIG. 18. Reduction of fecal colifomn bacteria In lime treated
secondary effluent at initial pHs of 10.0, 10.5
and 11.0, at 10* C.
44
-------
n 10.0
-2
0 2 4 6 8 10 12 18
Time (hr)
48
FIG. 19. Reduction of focal coliform bacteria In lime
treated secondary effluent at initial phi's of
10.0, 10.5 and t 1.0, at I°C.
-------
-2
11.5 pH
12.0 pH
10 20 30
40 50 .60
Time (min)
70 80 90
FIG. 20. Reduction of fecal coliform bacteria in lime
treated eecondary effluent at initial pH's
of 11.5 and 12.0, at IO* C.
46
-------
-2
O H.5 pH
D 12.0 pH
10 20
30 40 50 60
Time (min)
90
FIG. 21. Reduction of ftcal colifbrm bacteria In lime
trtattd Mcondary •fflutnt at Initial pH*t
of 11.5 and 12.0, at |» c.
47
-------
b
O
O
O
O
o>
O
10 20 30
40 50 60
Time (min)
I
70 80 90
FIG. 22. Survival off total and fecal conform bacteria in
sewage controls at I to 15° C.
O total cotiforms at 1° C
O total conforms at 5°C
A total conforms at 10* C
O total conforms at 15* C
fecal colt forms at 1° C
fecal conforms at 5° C
fecal conforms ot 10* C
fecal conforms ot 15* C
48
-------
E 5
JO
o
o
f3
-D
60 80 90
Time (min)
FIG. 23. Survival of bacteria in secondary effluent
controls at I and 10 ° C.
D total coliforms at I°C
A fecal conforms at I ° C
O SPC at I* C
total conforms at 10*C
fecal coliforms at 10* C
SPC at 10° C
49
-------
o
o
I 3
o
0
(2 24
Time (hr)
36
48
FIG. 24. Survival of total and fecal collform bacttria in
Mwag* control* at I to 15° C.
O total collformt at I* C
D total conforms at 5° C
A total conform* at 10* C
O Mai collform* at 15* C
• focal collform* at I* C
B f*cal collform* at 5* C
A f*eal conform* at 10* C
• f*cal coltform* at 15* C
50
-------
o
v_
o
JO
0
O
o»
o
I
0
FIG. 25.
12
24
Time
(hr)
36
48
Survival of bacteria in secondary effluent
controls at I and 10° C.
D total
A fecal
O SPC
conforms at 1°C
coliforms at 1° C
at I°C
total coliforms at 10° C
fecal coliforms at 10° C
SPC at 10s C
51
-------
Table 2. Survival of standard plate count organisms (SPG) in the supernatant phase of lime treated
and control sewages.
Ul
to
Treatment
temperature
(C)
1
5
10
15
1
10
Sewage
Type
R
R
R
R
SE
SE
Initial
count /ml
5.0
6.0
6.0
1.1
3.4
3.8
X
X
X
X
X
X
105
10s
10s
106
105
105
48 hour
pH 10.0
9,300
10,000
17,000
3.4 x 106
1,000
4.6 x 10*
count/ml in treatments and controls
pH
8,
2,
5,
2.3
1.5
10.5
300
900
000
x 106
380
x 101*
pH 11.0
2,200
1,300
900
1.2 x 106
110
340
control
4.
4.
1.
1.
1.
3.
1 x
1 x
7 x
7 x
8 x
6 x
105
105
106
107
105
105
R - raw sewage
SE - secondary effluent
-------
Ln
CO
Table 3. Survival of standard plate count organisms (SPC) in the supernatant phase of lime
treated and control sewage.
Treatment
temperature
(C)
1
.5
10
15
1
10
Sewage
type
R
R
R
R
SE
SE
Initial
count /ml
7.0 x 10s
5.6 x 105
5.8 x 105
8.8 x 105
5.4 x 10s
3.7 x 105
90 minute
pH 11.5
15,000
5,400
2,400
1,800
5,100
3,000
count/ml in treatments
pH 12.0
1,400
620
200
200
82
370
and controls
control
6.0 x 105
4.8 x 105
5.6 x 105
1.0 x 106
5.3 x 105
3.7 x 10s
R - raw sewage
SE - secondary effluent
-------
Table 4. Comparative numbers of total coliform bacteria found in sewage supernatant and precipitated solids during lime treatment.
Treatment Initial
temperature count/ml
7.6 x
1 C
7.3x
7.9 x
5°C
6.0 x
8.1 x
10°C
8.6x
7.7x
15t
8.7x
4
10
4
10
4
10
4
10
4
10
4
10
4
10
4
10
Exposure
interval
48
90
48
90
48
90
48
90
hrs.
min.
hrs.
min.
hrs.
min.
hrs.
min.
Final counts/ml in high pH
Phase pH 10.0
4
S 5. 7 x 10
3
L 4.0x10
S
L
S
L
S
L
4
S 2.8x10
2
L 2.5x10
S
L
5
S 1. 1 x 10
3
L 4. 3 x 10
S
L
PH
1.1
2.8
8.5
2.3
5.2
3.5
5.0
1.1
10. 5 pH
3
x 10 1.2
1
x 10 4.0
2a
x 10 1.0
x 102 8.0
2
x 10 2.5
1
x 10 1.0
2
x 10 2. 7
x 10 1.0
11.0
2
x 10
0
xlO
2
x 10
x 10
1
x 10
o
x 10
1
x 10
0
x 10
treatments
pH 11.5
6.
S.
6.
2.
3.
5.
6.
1.
3
Ox 10
2
4x10
2
5x 10
. 1
6x 10
3
4x 10
1
8 x 10
2
Ox 10
1
Ox 10
pH 12.0
o
3.0 x 10
0
2. Ox 10
Oa
8. Ox 10
0
l.Ox 10
0
4. Ox 10
0
l.Ox 10
o
2. Ox 10
0
l.Ox 10
Only one value included in the average
L - supernatant liquid phase
S - semisolid material precipitated from sewage with lime
-------
Table 5, Comparative numbers of fecal coliform bacteria found in sewage supernatant and precipitated solids during lime treatment.
Treatment Initial
temperature count/ml
4
2.5x 10
1°C
4
2.5 x 10
4
2.6x 10
5°C
Ul
en
4
2.2 x 10
10°C
4
3.0 x 10
3
4.2 x 10
15t
3
8. Ox 10
Exposure
interval
48 hrs.
90 min.
48 hrs.
90 min.
48 hrs.
90 min.
48 hrs.
90 m in.
Final counts/ ml in high pH treatments
Phase pHlO.O
4
S 5. 3 x 10
2
L 5.4 x 10
S
L
S
2
L 3.6x10
S
L
3
S ' 1.4x10
2
L 1.5x10
S
L
3
S 7. 5 x 10
o
L 3.0x10
S
L
PH
6.0
4.5
6.0
8.0
4.5
4.0
1.0
1.0
10.5 pHll.O pHll.5
3 2
x 10 1.5x10
2 0
x 10 1.0x10
3
1.9x 10
1
3.8 x 10
Oa
x 10
0 0
x 10 1.0x10
2
1.4x 10
1
x 10 0
0 0
x 10 1.0x10
1
6. 5 x 10
0
8. Ox 10
0 0
x 10 5.0 x 10
0 0
x 10 1.0x10
2
2. 8 x 10
0
4.0x10
pH 12.0
o
l.Ox 10
o
2. Ox 10
0
l.Ox 10
0
0
l.Ox 10
0
0
l.Ox 10
Only one value included in the average
L - supernatant liquid phase
S - semisolid material precipitated from sewage with lime
-------
Table 6. Comparative numbers of standard plate count bacteria found in sewage supernatant and precipitated solids during lime treatment.
Treatment Initial
temperature count/ m 1
5. Ox 105
1°C
7.0 x 105
5
6.0 x 10
St
5.6x.lO
5
6.0 x 10
lot
5.8 x 10S
6
1. 1 x 10
. _o
15 C
8.8 x 10
Exposure
interval
48 hrs.
90min.
48 hrs.
90min.
48 hrs.
90m in.
48 hrs.
90 min.
Phase pHlO.O
S 3. 1 x lO6*
L 9. 3 x 103
S
L
S
L 1.0x10
S
L
6
S 9. 7 x 10
L 1.7x10
S
L
8
S 6.6 x 10
6
L 3.4x10
S
L
Final counts/ml in high pH treatments
pHlO.5 pHll.O pHll.5
3a 4a
1.9x10 3.0x10
3 3
8.3x10 2.2x10
1.7x 10
4
l.Sx 10
2.9 xlO3 1.3xl03
6a
4.0 x 10
3
5. 4 x 10
5 5
8.8x10 2.8x10
5.0x10 9.0x10
3. 1 x 10
3
2.4x 10
8 7
2.2x10 2.0x10
6 6
2.3x10 1.2x10
6
1.1 x 10
3
1.8 x 10
pH 12.0
1.4x 105
3
1.4x 10
4. 5 x 10 *
2
6.2 x 10
1. 1 x 105
2
2.0 x 10
8. 3 x 104
2
2. Ox 10
Only one value included in the average
L - supernatant liquid phase
S - semisolid material precipitated from sewage with lime
-------
Table 7. Comparative numbers of total coliform bacteria found in secondary effluent supernatant
and sludge during lime treatment.
Temp. Initial Exposure Phase Final counts/ml in high pH treatments
count/ml time pH 10.0 pH 10.5 pH 11.0 pH 11.5 pH 12.0
1°C 9.3 x 10* 48 hr S 3.8 x 101* 1.5 x 103 6.6 x 101
L 9.1 x 101 1.1 x 101 2.0 x KT1
6.1 x lo" 90 min S 9.0 x 101 1.1 x 101
L 4.4 x 101 4.0 x 10-1
10°C 1.7 x 105 48 hr S 3.6 x 102 4.2 x 102 1.1 x 101
L 1.6 x 101 4.6 x 10 4.9 x HT1
Ul
4.4 x 10** 90 min S 9.9 x 10° 4.9 x 10°
L 7.5 x 10 0 x 10°
S - semisolid material precipitated from sewage with lime
L - supernatant liquid phase
-------
Un
00
Table 8. Comparative numbers of fecal coliform bacteria found in secondary effluent supernatant and
sludge during lime treatment.
Temp. Initial Exposure Phase
count /ml time
1°C 4.1 x 103 48 hr S
L
8.8 x 103 90 min S
L
10°C 1.6 x 103 48 hr S
L
1.2 x 103 90 min S
L
Final counts/ml in high pH treatments
pH 10.0 pH 10.5 pH 11.0 pH 11.5 pH 12.0
7.1 x 102 9.7 x 101 3.3 x 10"1
6.2 x 10° 5.5 x lO"1 0 x 10°
4.3 x 10° 5.0 x Kf1
1.7 x 10"1 3.3 x 10-1
3.3 x 101 1.8 x 101 1.2 x 10°
1.9 x 10° 2.0 x 10-1 2.3 x Kf2
2.4 x 101 3.6 x 10°
1.2 x 10° 2.0 x Hr2
S - semisolid material precipitated from sewage with lime
L - supernatant liquid phase
-------
Ul
Table 9. Comparative numbers of standard plate count bacteria found in secondary effluent
supernatant and sludge during lime treatment.
Temp. Initial Exposure Phase
count /ml time
1°C 3.8 x 105 48 hr S
L
5.4 x 10s 90 min S
L
10°C 3.8 x 10s 48 hr S
L
3.7 x 10s 90 min S
L,
Final counts/ml in high pH treatments
pH 10.0 pH 10.5 pH 11.0 pH 11.5 pH 12.0
1.1 x 106 2.6 x 10s 7,1 x 10*
1.0 x 103 3.8 x 102 1.0 x 102
4.3 x 10s 2.6 x 103
5.1 x 103 8.2 x 101
1.1 x 107 3.2 x 10$ 7.2 x 105
4.8 x 10" 1.0 x 10* 2.7 x 102
3.4 x 106 2.5 x 105
2.9 x 103 3.7 x 102
S - semisolid material precipitated from sewage with lime
L - supernatant liquid phase
-------
lime treatment of settled sewage. Table 10 shows the percentage of
the BOD and orthophosphate concentrations removed during lime treat-
ment of settled sewage, primary settling of raw sewage for one hour
and that removed by extended settling of raw sewage in controls, all
at low temperatures. Table 11 shows the percent removals in secondary
effluent at 1° and 10°C. The relative magnitudes of the BOD and ortho-
phosphate concentrations in raw, settled and lime treated sewages are
shown in Figures 26 through 33.
MEASUREMENTS OF TEMPERATURE, pH AND QUANTITIES OF LIME ADDED TO
SEWAGE
Using lime slurry, the pH of all sewage samples, except controls, was
adjusted as close as possible to the desired treatment value. After
the initial pH adjustment, the samples were allowed to stand quiescently
for either a short period (90 minutes) or for an extended contact of
48 hours. The pH did not remain at the initial value but slowly
declined to a slightly lower value. The initial and final pH values
of the treatment containers, at the various temperatures, are shown
in Tables 12 and 13.
The treatment temperatures were carefully controlled and generally
varied only about ~t 0.5°C. The initial and final treatment temp-
eratures are shown in Tables 14 and 15.
The solubility of lime increases as the temperature decreases. This
fact, along with observations on the relative amounts of lime needed
to produce high pH values are shown in Tables 16 and 17.
MEASUREMENTS OF THE PHYSICAL AND CHEMICAL CHARACTERISTICS OF RAJ'/
SEWAGE SAMPLES
Sewage samples were subjected to extensive physical and chemical
tests. The characteristics measured, their ranges and means, and
the units of measurement used in each case are presented in Table 18.
60
-------
Table 10. Reductions of BOD and orthophosphate concentrations in
lime treated sewage at 1° 5?, 10° and 15PC.
Treatment
PH
10.0
10.5
11.0
11.5
Contact
time
(hours)
24
48
24
48
48
24
24
48
24
48
48
24
24
48
24
48
48
24
1.5
1.0
1.0
1.0
Treatment
temperature
(C)
1
1
5
5
10
15
1
1
5
5
10
15
1
1
5
5
10
15
1
5
10
15
Percent
BOD
removal
55.2
72.5
58.0
56.4
59.3
75.3
59.3
74.0
68.6
72.5
57.8
77.6
68.6
72.2
53.2
58.9
Percent
o-P04
removal
47.9
71.4
61.9
62.4
62.5
69.2
71.6
78.5
69.5
78.3
81.0
80.4
81.9
67.2
73.8
88.0
61
-------
Table 10. (Continued)
Treatment
pH
12.0
Settled
unadjusted
Control
unadjusted
Contact
time
(hours)
1.5
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
24
48
1.5
24
48
1.0
48
1.0
24
1.0
Treatment
temperature
(C)
1
5
10
15
1
5
5
10
10
15
1
1
1
5
5
5
10
10
15
15
Percent
BOD
removal
71.2
66.3
52.5
58.9
40.6
14.9
31.1
30.0
17.1
31.1
31.3
47.0
27.3
22.2
30.5
48.6
39.5
26.0
Percent
o-P04
removal
82.6
79-4
93.3
91.0
-16.2
-15.5
25.1
2.2
-34.6
47.7
-26.3
-14.0
62
-------
Table 11. Reductions of BOD and orthophosphate concentrations in lime
treated secondary effluent at l°and 10°C.
Treatment Contact
pH time
10.0 1 hr
24 hr
48 hr
1 hr
24 hr
48 hr
10.5 1 hr
24 hr
48 hr
1 hr
24 hr
48 hr
11.0 1 hr
24 hr
48 hr
1 hr
24 hr
48 hr
11.5 60 min
90 min
60 min
90 min
12.0 60 min
90 min
60 min
90 min
Treatment
temperature
(C)
1
1
1
10
10
10
1
1
1
10
10
10
1
1
1
10
10
10
1
1
10
10
1
1
10
10
Percent
BOD
removal
83
85
77
86
75
71
76
85
76
88
79
71
77
85
78
87
77
75
90
88
91
94
93
94
90
91
Percent
o-POij
removal
77
93
83
87
90
79
85
90
89
88
92
90
91
91
90
91
93
94
89
93
95
95
97
97
97
96
63
-------
12
10-
0 8
I 6
2
0
I
Row
(initial)
I
Settled
( 1 hr)
pH IO.O pH
S
300
200
100
0.5 pHII.O Control
FIG. 26. Reductions in BOD and orthophosphate concentrations
of sewage at pH IO.O through ll.O, at I°C.
Initial o-POu concentration*
Concentration of o-PO. after 48 hours contact
4
Initial BOO
BOD after 24 hours contact
64
-------
12
10
^ 8
6
0*
I «
2
O
•
-
-
i
I
•?:.'
'/i
*•%
•*.-
:••
V.
Raw Settled pH 1.5
(Initial) (1 hr)
pH
:$
Hf:
• • •
-
ra
i
1
ft
w
¥
%
concentrations
4
Concentration of o-PO. after 90 min contact
4
Initial BOD
v.| BOD after 90 min contact
65
-------
C 8
*s
I 6
2*«
1
o
2.
0
-
1
•^M
I
••i^H
.
^•KB
$
!•••
.« •
• ••
••••
. •;
el
•ft
•MM
• •*
•••
• *•
«'.N
;*•
'*:
t«;
K3
1
••^n
.* t
**•
••.i
^
.*.v
•« .
.'••
-:.v
tt.:
'$>
• ••
••t*
••.*.
:%s
•:.*•
•>.-.
•••«
ZOO
*x
o»
,00 f
O
O
00
0
Row Settled pH IO.O pHIO.5
(initial) (I hr)
pHILO Control
FIG. 28. Reductions in BOO and orthophosphate concentrations
of savage at pH IO.O through 11.0, at 5* C.
Initial o-PO concentrations
4
Concentration of o-PO. after 48 heurs contact
4
Initial BOD
BOD after 24 hours contact
-------
10
C 8
I 6
6* 4
o.
i
o
t
0
^»
i»
m
M
^^^^m
Row Settled
(initial) (Ihr)
1
W
PH
rtd
11.5 pH
•MIH
1
*.•••
V.'.
-
m
%
i
1
y\
9>
$
*.-H
•• * *
&
-
200
•s.
100 ~*
o
O
CO
0
12.0 Control
FIG. 29. Reductions in BOD and orthophosphate concentration*
of sewage at pH 11.5 and I2.O, at 5* C.
Initial o-PGL concentrations
4
Concentration of o-PO after 60 min contact
4
Initial BOD
i.-.«i BOD after 60 min contact
i-«»i
67
-------
10
8
o
0.
I
o
» *
2
0
i
-
••••'
••»•
Row Settled pH IO.O
(initial) (Ihr)
*.
200
100
Q
O
CD
pH 10.5 pH 11.0 Control
FIG. 30. Reductions in BOD and orthophosphate concentrations of
sewage at pH 10.0 through II.0, lime treatment at 10* C.
Initial o-P04 concentration*
Concentration of o-P04 after 48 hour* contact
Initial BOD
BOD after 48 hours contact
68
-------
10
8
01 6
0* 4
0.
1
o
2
O
-
I
I
•MM
nrr
I
* **•
**j>*
•MM
:/.;
vr-
**»
0
1
?
Y
»
TJ
ii:
• *
-
200
100 i
o
0
m
0
Raw Settled
(initial) (Ihr)
pHII.5 pH 12.0 Control
FIG. 31. Reductions in BOD and orthophosphate concentrations of
sewage at pH 11.5 and 12.0, lime treatment at 10'C.
Initial
concentration
Concentration of o-PO. after 60 min contact
4
Initial BOO
BOD after 60 min contact
-------
12
10
C 8
o»
E 6
f «
i
0
2
0
•
m
m
L \
\
•I^BH
\
\
•MM1
0
-------
10
.-. 8
I 6
0* 4
0.
t
o 2
O
-
I
WHM
I
MHHB
•mmrnm
• •*•*
$
Raw Settled pH 1.5
(initial) (1 hr)
ffl
pH
^^BHH
» • '
8
§
&
S
y
^
y
y
y
>o
~
* »
."'•*
-
200
100 -
0
o
0)
0
12.0 Control
FIG. 33. Reductions in BOD and orthophotphate concentrations of
sewage of pH LI.5 and 12.0, lime treatment at I5°C.
Initial o-PO, concentration
4
Concentration of o- PO after 60 min contact
Initial BOD
BOD after 60 min contact
71
-------
Table 12. Observed pH changes in lime treated sewage samples over the contact period.
Treatment
temperature
(C)
1°
5°
10°
15°
Table 13.
pH values
Initial Final
10.0
10.0
10.0
10.0
Observed pH
9
9
9
9
.6
.6
.8
.5
changes
48 hour
contact
time
Initial Final
10.5
10.5
10.5
10.5
in lime
10.
9.
10.
9.
treated
2
9
0
9
Initial
11.0
11.0
11.0
11.0
secondary
Final
10.8
10.1
10.5
10.1
effluent
90 minute
Initial Final
11.5 11.3
11.5 11.4
11.5 11.4
11.5 11.4
contact
time
Initial Final
12.0
12.0
12.0
12.0
11.9
12.0
11.9
11.9
over the contact period.
Treatment
temperature
(C)
1°
10°
pH values
Initial
10.0
10.0
Final
9
9
.6
.8
48 hour
contact
time
Initial Final
10.5
10.5
10.
9.
0
9
Initial
11.0
11.0
Final
10.5
10.4
90 minute
Initial Final
11.5 11.2
11.5 11.4
contact
time
Initial Final
12.0
12.0
11.8
11.9
-------
Table 14. Observed temperature variations in lime treated raw sewage
samples over the contact period.
Treatment
temperature
(C)
1°
5°
10°
15°
Table 15.
Treatment
temperature
(C)
1°
10P
Measured temperatures (C)
48 hour
Initial
1.1
4.7
9.6
15.3
contact time
Final
1.1
4.9
9.7
15.0
Observed temperature variations in
effluent over the contact period.
90 minute
Initial
1.2
5.2
9.9
15.0
lime treated
contact time
Final
1.2
5.3
9.9
14.8
secondary
Measured temperatures (C)
48 hour
Initial
1.0
9.8
contact time
Final
1.2
10.1
90 minute
Initial
1.3
10.1
contact time
Final
0.9
9.7
73
-------
Table 16. Average quantities (ml) of lime slurry (132 mg CaO/ml) used
to produce treatment pH values in 2 liter raw sewage samples.
Treatment
temperature
(C) 10.0
1° 1.7
5° 1.8
10° 1.9
15° 2.0
Table 17. Average quantities (ml)
to produce treatment pH
samples .
Treatment pH
10.5 11.0 11.5 12.
2.4 2.9 4.0 5.
2.4 2.8 3.9 6.
2.8 3.4 4.2 5.
2.8 3.1 4.2 6.
of lime slurry (117 mg CaO/ml) used
values in 2 liter secondary effluent
0
1
6
2
3
Treatment
temperature
(C) 10.0
1° 3.3
10° 4.8
Treatment pH
10.5 11.0 11.5 12.
4.3 5.3 7.3 11.
6.7 8.3 10.0 17.
0
3
0
74
-------
Table 18. Ranges and means of the measured values of the various
sewage characteristics (5/3/71 to 12/2/71).
Characteristic
measured
Air temperature
Sample temperature
PH (20°C)
Turbidity^1*
Total alkalinity
Settleable solids
Suspended solids
Dissolved solids
*
Orthophosphate
Dissolved oxygen
Raw BOD*3)
Calcium hardness
Standard plate count
Total coliforms
Fecal coliforms
Low
-2.0
13.9
6.80
0.044
200
2.7
7. 1
450
5.5
0
90
103
3.9 x
1. 5 x
2.8 x
jt
As determined by the
(Do n mett
reading
Range
High
25.0
19-0
7.80
1.950
417
35.0
60.0
1440
12.38
1.85
268
180
105 1.5 x 106
104 1.2 x 105
103 3.4 x 104
vanadomolybdate
x 2
Mean
16.6
15.9
7.27
0.219
242
6.35
25. 1
756
7.92
0.83
168
128
9.0 x 105
7.0 x 104
1 . 7 x 1 04
colorimetric
Units
C.
C.
O.D.
mg/1
ml/1
mg/1
mg/1
mg/1
mg/1
mg/1
mg/1
per ml
per ml
per ml
technique.
1000
(2)
As determined by conductivity measurements.
Standard 5-Day, 20°C test.
75
-------
SECTION VI
DISCUSSION OF RESULTS
This study of lime disinfection of sewage at low temperature was pre-
dicated upon the needs of small communities located in regions with
cold climates. Low rates of biological waste decomposition at low
temperature as well as economic factors prompted this study of the use
of elevated pH to accomplish the destruction of potentially pathogenic
bacteria. Investigations were also directed toward the effects of low
temperature and elevated pH values on the flocculation-coagulation
of suspended sewage solids and dissolved orthophosphate.
EVALUATION OF ALKALIES FOR THE PRODUCTION OF ELEVATED pH
Investigations into the quantities of lime slurry (five parts water:
one part lime) required to produce elevated pH values in settled
sewage at 5°C (Figs. 1, 2) revealed that as pH increased, propor-
tionately greater quantities of slurry were necessary to produce
equivalent pH changes. This relationship held true to a pH of about
12.4, above which no further increases in pH were possible using
lime. Furthermore, pH values above 12.0 often resulted in severe
calcium carbonate turbidity so that the maximum practical experi-
mental pH was about 12.0.
Similar results were obtained at temperatures of 10° and 15°C. How-
ever, because the solubility of lime (CaO) decreases as temperature
increases (32), even greater amounts of lime were required to produce
equivalent pH changes at the higher temperatures.
The phenomenon of requiring proportionately greater quantities of
base to produce equivalent pH increases is not unique to lime. The
use of 3 N potassium hydroxide produced a titration curve (Fig. 1)
similar to the one with lime. The need for proportionately greater
quantities of KOH became apparent at about pH 9.5, while not until
about pH 11.0 when using lime. This could be attributed to the dibasic
nature of calcium hydroxide. These titration values are important
because they indicate that on a weight to weight basis it requires
less calcium hydroxide than potassium hydroxide to produce an equi-
valent pH change. The economics of operation, therefore, favors the
use of lime over potassium hydroxide (or other monobasic alkalies)
as a sewage disinfectant and coagulant. Potassium hydroxide was
tested instead of sodium hydroxide because potassium compounds are
bound and utilized in the soil more readily than sodium compounds and
thereby do not contribute as significantly to salinity problems.
The possibility of using a combined system of calcium hydroxide and
potassium hydroxide to produce pH values above 10.0 was investigated
(Fig. 3). Although such a system functions, the practicality is
questionable because of the apparent interference of KOH with the
76
-------
dissociation of calcium hydroxide. The apparent interference is
probably a manifestation of the common ion effect (6) where a base
which is strongly ionized in aqueous solutions, such as potassium
hydroxide, represses the dissociation of a weakly ionized alkali, such
as calcium hydroxide, when present in the same solution. As a result,
large concentrations of undissociated calcium hydroxide remain at
elevated pH values, the KOH being the major contributor of hydroxyl
ions.
To further test the hypothesis of a common ion effect, another strongly
ionizing compound (calcium chloride) containing an ion common to
calcium hydroxide was added to sewage with elevated pH produced with
calcium hydroxide and also with potassium hydroxide. The common ion
repression effect on pH was much greater with the CaCl,, - Ca(OH)9
system as compared to KOH - Ca(OH)_ (Table 1).
BACTERICIDAL EFFECTS OF ELEVATED pH VALUES AND LOW TEMPERATURES ON
TOTAL COLIFORM BACTERIA
Disinfection of raw sewage at pH 10.0 has little value as indicated
by results from bench scale studies (Fig. 4). Total coliform bacteria
in supernatant liquids and precipitated solids were very resistant
to this pH at cold temperature.
Similar to pH 10.0, pH 10/5 also lacks sufficient germicidal qualities
to be used as a sewage disinfectant at cold temperature (Fig. 5).
Even though total coliform bacteria died rapidly at this pH during
the first two to four hours, death was subsequently much slower.
Total coliforms were more susceptible to the toxic effects of pH 10.5
in the supernatant phase than in the sludge or precipitated solids
phase (Table A). Either the pH of the solids was below 10.5 or the
organic material present in them provided some protective colloidal
effect (38).
Unlike pH 10.0 and 10.5, pH 11.0 exhibited (Fig. 6) sufficient bacteri-
cidal power to warrant further investigations as to its use as a cold
temperature sewage disinfectant. Results do indicate, however, that
extended contact time is necessary to achieve satisfactory results
which lowers the applicability of this pH at low temperatures. Again,
a protective colloidal effect was apparent because total coliforms
survived significantly better in the solids than in the liquid super-
natant phase (Table 4).
Total coliform bacteria succumbed rapidly to the toxic effects of pH
11.5 (Fig. 7). Furthermore, little decline in the coliform death rate
throughout the contact period (90 minutes) was observed, as was the
case at the lower pH values. Destruction of total coliform bacteria
at pH 11.5 appears to be about 10 to 15 times more rapid than the death
rate produced at pH 11.0. It also appears that some critical pH
77
-------
exists (between 11.0 and 11.5) at which the lethal power of the
hydroxyl ion increases greatly. Whether this increase in germicidal
efficiency is due to increased hydroxyl ion concentration alone or
the added lethal effect of undissociated calcium hydroxide, as pro-
posed by Schuyler (67) during his studies, cannot be determined from
this study.
Total coliform bacteria survived slightly better in the precipi-
tated solids than in the supernatant (Table 4). However, greatly
improved coliform death rates were produced at pH 11.5 in the sludge,
over those produced at pH 11.0, indicating that the pH of those solids
was in the critical range of 11.0 to 11.5.
Death of total coliform bacteria at pH 12.0 was rapid (Fig. 8) vand
exponential in character. Many effluent samples from sewages treated
to pH 12.0 for 90 minutes yielded coliform counts of zero to one per
milliliter. The epidemiological safety of water has been based upon
the presence of absence of coliform indicator bacteria; therefore,
effluents with these low concentrations of coliforms are potentially
safe for reuse. Coliform death in the solid and liquid phases was
approximately equivalent (Table 4). Therefore, the sludge from lime
treatment of sewage should have the same epidemiological safety as
the effluents.
As a general rule, bactericidal efficiency of high pH increased as
the treatment temperature was elevated from 1° to 15°C (Figs. 4-8).
This effect on bactericidal efficiency was more apparent at the higher
pH values (11.0 to 12.0) than at the lower pH values (10.0 and 10.5).
At the lower temperatures, bacterial growth was extremely retarded,
possibly due to decreased enzymatic activity and lower diffusion rates
of oxygen and essential nutrients through membranes. With retarded
enzymatic activities, the effects of elevated pH inactivation may
not be as apparent at low temperatures as they are at higher temp-
eratures .
Lime treatment of secondary effluent at 1° and 10°C showed the same
degree of destruction of total coliforms as in the raw sewage
samples (Figs. 9-12; Table 6).
BACTERICIDAL EFFECTS OF ELEVATED pH VALUES AND LOW TEMPERATURES ON
FECAL COLIFORM BACTERIA
Fecal coliform bacteria were not appreciably affected by exposure to
pH 10.0 at low temperature (Figs. 13, 18, 19). Similar to total
coliforms, a population of fecal coliforms exhibited some initial
death at the onset of treatment but continued exposure produced little
significant death. The survival of fecal coliforms at pH 10.0 was
much more efficient in the solids than in the supernatant liquid,
again lending support to a protective colloidal effect (Tables 5, 8).
It can only be concluded that pH 10.0 does not provide adequate
78
-------
hydroxyl ion concentration to cause the destruction of indicator
coliform bacteria.
Initial fecal coliform death at pH 10.5 was greater than that produced
at pH 10.0; however^ final concentrations (at 24 hours) were too large
to indicate that pH 10.5 has any potential as a sewage disinfectant
(Figs. 14, 18, 19).
Fecal coliforms were killed almost as well in sludge as in sewage
supernatants, while total coliforms survived much better in the
solids. This indicates that fecal coliforms may be more susceptible
to elevated pH than total coliforms (Tables 5, 8).
The toxic effects of pH 11.0 toward fecal coliforms was considerably
greater than pH 10.5 (Figs. 15, 18, 19). However, even though effluents
with low concentrations of fecal coliforms were produced at pH 11.0,
contact periods were too long to be of practical value.
Fecal coliforms died very rapidly when exposed to pH 11.5 (Figs. 16,
20, 21). This pH produced death rates which approached a logarithmic
function, indicating that it has a great potential as a sewage dis-
infectant. Fecal coliform concentrations were, somewhat higher after
90 minutes in the precipitated solids (Tables 5, 8) than the super-
natant liquid phase, again indicating that a protective effect exists.
Destruction of fecal coliform bacteria at pH 12.0 (Figs. 17, 20, 21)
was very rapid, and exponential in rate. Sewage effluents containing
less than one organism per milliliter were produced in 70 minutes or
less, attesting to the bactericidal efficiency of this pH. Furthermore,
sludges and supernatants were generally disinfected equally well at
this pH (Tables 5, 8). It can be concluded that pH 12.0 is a very
efficient sewage disinfectant at low temperature.
At each test pH level, fecal coliform bacteria generally died more
rapidly as the treatment temperature was elevated from 1° to 15°C.
The reasons for this are probably identical to those proposed for
total coliforms.
BACTERICIDAL EFFECTS OF ELEVATED pH VALUES AND LOW TEMPERATURES ON
TOTAL PLATE COUNTS
Total (standard) plate counts, determined initially and at the termi-
nation of elevated pH treatments, reduced bacterial concentrations
greatly during treatment at pH 10.0 and 10.5 within 24 hours. However,
significant numbers of organisms survived, adding further evidence
that pH levels under 10.5 do not provide adequate bactericidal
activity (Table 2).
Far greater numbers of bacteria were found to survive treatment at
these pH treatments in precipitated solids than in the supernatant
79
-------
phase (Table 6, 9).
Viable organisms on standard plate counts were reduced even further
by treatment at pH 11.0 (Table 2). The reductions, however, do not
indicate a sizeable increase in bactericidal efficiency of pH 11.0
over the lower pH treatments. As with the lower pH values, there
was significantly greater survival of organisms in the solids than
in the supernatants (Table 6, 9).
Contact periods at pH 11.5 and 12.0 were 90 minutes instead of the
48 hours used at the lower pH values because bacterial death was
greatly accelerated at these higher pH values. Rapid destruction
of standard plate count organisms was achieved by exposure to pH
11.5 (90 minutes or less) (Table 3). The same degree of disinfection
at the lower pH values required between 12 and 48 hours. This
evidence again supports the observation that some critical pH exists
between 11.0 and 11.5 for bacterial death. Similarly, pH 12.0 gave
rapid destruction of large numbers of sewage organisms at all temp-
eratures; however, there were still considerable surviving organisms.
In the sludges, bacterial death did occur but not as efficiently as
in the supernatant (Tables 6, 9).
Total plate count organisms appeared to survive pH 10.0 more efficiently
as the temperature increased (Tables 2, 3, 6, 9). This result does
not follow that for total and fecal coliforms. However, the plate
counts represent many species of bacteria more resistant to high pH
than coliforms. It is possible that increasing the temperature
provided suitable conditions for the growth of some segment of these
organisms in spite of the elevated pH. Elevating the temperature from
1° to 10°C at pH 10.5 did not appear to significantly affect the death
of bacteria; however, at 15°C there was an increase in total bacterial
concentrations over that found in the settled untreated sewage. There-
fore, pH 10.5 has little lasting effect on total bacterial populations
when the temperature is high enough to allow growth to occur.
Increasing the temperature from 1° to 10°C at pH 11.0 caused gradual
reductions in total bacterial survival efficiency. At 15°C, however,
growth of the initial population occurred, indicating the pH had de-
creased during the contact period (Tables 11, 12). The final measured
pH at 48 hours was 10.1; further evidence that pH values below 11
have little value for sewage disinfection.
Survival efficiency of bacteria decreased at pH 11.5 and 12.0 as the
temperature was elevated from 1° to 15°C (Tables 3, 6, 9). Both
phases of sewage showed this type of temperature relationship. This
evidence therefore further supports the observations that pH 11.5 and
12.0 possess effective germicidal powers.
SEWAGE CONTROLS
80
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Untreated sewage controls were sampled at the beginning and end of
each treatment series to detect bacterial death produced by factors
other than pH modifications. There were slight decreases in total
and fecal coliform concentrations in these controls; however, they
do not appear to be related to treatment temperature because the
magnitude of the reductions was approximately equal at all temper-
atures (Figures 22-25). Fecal coliform bacteria appear to be slightly
more susceptible than total coliforms to storage at cold temperatures.
It can be concluded that no significant coliform death resulted from
the cold temperatures employed during this study.
OTHER FACTORS POSSIBLY INFLUENCING DISINFECTION WITH LIME
Effects of factors such as varying concentrations of organic matter,
variations in the size and age of bacterial populations, inorganic
constituents associated with osmotic pressure and ionic strength
and their relationship to bacterial survival, possible pH activation
of toxic agents present in sewage, and excretion of neutralizing
material by bacteria are difficult to evaluate from the results of
this study. This study does not provide information on the effects
of elevated pH on the death of viruses.
Sewage contains bacteria in all stages of growth and development.
Consequently, when using sewage, it is impossible to selectively
compare the relative susceptibility of bacteria of one physiological
age with those of another. It is possible that the initial rapid
decreases in total and fecal coliform concentrations represented the
death of more susceptible organisms such as those in the logarithmic
stage of growth. It is also possible that these reductions also
represent the death of more susceptible members of the total and
fecal coliform populations. Similarly, stress factors of many types
previously experienced by the organisms would condition their response
to pH change.
Decreases in treatment pH values during extended contact may be the
result of absorption of atmospheric and respiratory carbon dioxide
along with the excretion of base neutralizing substances.
Coliform bacteria were observed to be resistant to pH values in the
range of 10 to 11. It is possible that this resistance is a natural
phenomenon because the normal habitat of these bacteria, the
intestinal tract, has a moderately alkaline pH of 9.0 to 10.0 or
possibly higher (30).
EFFECTS OF LIME TREATMENT ON THE CONCENTRATIONS OF BIODEGRADABLE
ORGANIC MATTER AND ORTHOPHOSPHATE IN DOMESTIC SEWAGE
Lime treatment of settled, raw and secondary treatment sewage resulted
in the removal, by precipitation, of biodegradable organic matter
and dissolved orthophosphate. Primary settling of raw domestic
81
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sewage generally resulted in 15 to 30 percent reductions in the 5-
day 20°C BOD (Table 10, Figs. 26-33). Removal of large volumes of
settleable solids were usually accompanied by relatively large
reductions in the BOD, while minimal BOD reductions usually accompanied
smaller volumes of settleable solids. Primary settling of raw domestic
sewage did not produce any detectable lowering of the orthophosphate
concentration, probably because of its solubility (56).
It was noted during this laboratory study that visible coagulation of
sewage solids began to occur at a pH of 9.6, regardless of the treat-
ment temperature. Subsequent precipitation of the coagulated sewage
material appeared to be complete in 15 to 30 minutes.
When the supernatant liquid from primary and secondary settled sewage
was subjected to elevated pH treatments, significant BOD and ortho-
phosphate reductions were observed. Increasing the pH generally re-
sulted in greater removals of organic matter and orthophosphate;
however, increasing the temperature did not necessarily yield the
same result. Relatively short contact periods (60 to 90 minutes) at
the higher pH values (11.5 and 12.0) produced reductions in the BOD
and orthosphosphate concentrations which were equal to or better than
those produced by long contact periods (24 to 48 hours) at the lower
pH values (10.0 to 11.0).
In order to more accurately evalute the effects of temperature, contact
time and pH on the efficiency of organic matter removal from sewage
with lime, more extensive studies directed specifically at this problem
would have to be performed.
Lime treated sewage supernatants contained far less biologically
oxidizable organic material than either raw or secondary settled
sewages. The minimum BOD reduction produced by the combined system
of settling and lime treatment of raw sewage was 52%, while the maxi-
mum was 77%; with secondary effluent the removals were 71 and 94%,
respectively (Tables 10, 11). Although settling did not produce any
reduction in raw sewage orthophosphate concentrations, subsequent
lime treatment did. Removal of orthosphosphate appeared to be slightly
improved as temperatures increased. Maximum orthosphosphate removal
was 95% at pH 12.0 in 60 minutes at 15°C for raw sewage (Table 10).
In secondary effluent studies the maximum removal was seen at pH 12.0
in 60 minutes at 1°C (97%). The slight temperature effect seen with
raw sewage was not observed with the secondary effluent samples
(Table 11), indicating that orthosphosphate reduction is not temp-
erature dependent.
It is interesting to note that sewage controls with an unmodified pH
showed increases in orthophosphate concentrations over raw and settled
sewage concentrations. This increase was probably due to death and
lysis of a portion of the biological population, liberating orthophos-
phate into the medium. There is also the possibility that these in-
82
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creases in orthophosphate concentrations were due to sudden shifts in
environmental conditions such as the sudden rapid cooling to which
the sewage samples were subjected to attain treatment temperatures.
Mirrett (49) noted that it has been shown that bacteria release a
portion of their "luxury" phosphate when the dissolved oxygen concen-
tration is suddenly reduced. A similar mechanism may have occurred
when sewage temperatures were rapidly lowered causing stress conditions
with the release of "luxury" phosphate.
This study of cold temperature lime treatment of raw domestic sewage
produced effluents containing concentrations of biologically oxidizable
materials as low as 46.3 mg/1, and orthophosphate concentrations as
low as 0.87 mg/1. When compared with raw sewages containing approxi-
mately 200 mg/1 of biologically oxidizable material and 10 mg/1 of
orthophosphate, it can be seen that this system of sewage treatment
could be a valuable tool for the reduction of water nutrients.
Measurements of many chemical and physical sewage characteristics were
made on samples obtained throughout this study. Mean values and ranges
are shown in Table 17. Of the characteristics measured, sewage temp-
erature, pH and bacterial concentrations exhibited the least variation
over the eight month sampling period. It was fortunate that bacterial
concentrations remained fairly uniform because .this allowed more re-
liable comparisons of the rates of coliform disinfection from different
samples. The effects of the wide variation of some of the sewage
characteristics on the disinfection of sewage bacteria cannot be evalu-
ated.
SUMMARY
In this study of lime disinfection of settled domestic sewages at
low temperature, it was shown that rapid destruction of coliform
indicator bacteria occurred at pH 11.5 and 12.0, even at 1°C. Total
and fecal coliform concentrations in sewage effluents and precipitated
solids were reduced to about 10/ml (1000/100 ml) with a 90 minute con-
tact period. Treatment at pH values at or below 11.0 failed to ad-
equately disinfect effluents within a reasonable time period at any of
the treatment temperatures studied.
Results showed that the rate of coliform disinfection at pH 11.5
and 12.0 was greatly increased over that produced at the lower pH
values studied. Indications are that some critical factor exists
which influences the rate of disinfection at these higher pH values.
Whether this factor is pH alone, or a combination of pH, osmotic
pressure and some threshold phenomenon, however, cannot be determined
from these studies.
These laboratory studies indicate that a system of lime disinfection
may be applicable to small sewage treatment system in regions of
the world, such as Alaska, where severely cold climatic conditions
prevail throughout much of the year.
83
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In conjunction with disinfection, high pH systems also produce
large reductions in the concentration of biologically oxidizable
organic materials from settled sewage. A combined system of pri-
mary settling and lime treatment, at pH 12.0, produced a 71% re-
duction in the BOD in 90 minutes at 1°C; with secondary effluent
the comparable removal was 94%.
A valuable advantage to the treatment of sewage with lime over con-
ventional systems now in use is the large reductions in orthophosphate
concentrations obtained with lime, even at very low temperatures (1°
to 15°C).
84
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SECTION VII
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28. Gordon, R. C. Winter Survival of Fecal Indicator Bacteria in a
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29. Grabow, W. 0. K., N. A. Grabow, and J. S. Burger. The Bacterici-
dal Effect of Lime Flocculation/floatation as a Primary Unit Process
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30. Grollman, S. The Human Body. Its structure and physiology, 2nd
ed. London, The Macmillan Co., 1969. 543 p.
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33. Hoover, C. P. Water Softening as an Adjunct to Water Purification.
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34. Hoover, C. P., and R. D. Scott. Lime Sterilization of Water.
Eng. Rec. £8:257-259, 1913.
35. Houston, A. C. Purification of Water Supplies. Eng. and Con-
tracting. £2:821-823, 1924.
36. Keefer, C. E. Temperature and Efficiency of the Activated
Sludge Process. J. Water Pollut. Contr. Fed. 34:1186-1196, 1962.
37. Kehr, R. W., and C. T. Butterfield. Notes on the Relation
Between Coliforms and Enteric Pathogens. Pub. Health Rep. 58:586-607,
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methodik von desinfektionsversuchen.] Z. Hyg. Infektionskr. 96:92-
117, 1922. Cited in: Watkins, J. H., and C. E. A. Winslow. Factors
Determining the Rate of Mortality of Bacteria Exposed to Alkalinity
and Heat. J. Bacteriol. 24:243-265, 1932.
40. Lanphear, R. S. Lime Treatment of Sewage Compared with Direct
Oxidation. Eng. News Rec. jJ9:276-278, 1922.
41. Lecompte, A. R. Water Reclamation by Excess Lime Treatment of
Effluent. Tappi. 49_:121A-124A, 1966.
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42. Levine, M., E. E. Peterson, and J. H. Buchanan. Germicidal
Efficiency of Sodium Hydroxide and Sodium Hydroxide-carbonate Mixtures
at the same H-ion Concentration. Ind. Eng. Chem. 20_:63-65, 1928.
43. Levine, M., J. H. Toulouse, and J. H. Buchanan. Effect of
Addition of Salts on the Germicidal Efficiency of Sodium Hydroxide.
Ind. Eng. Chem. ^0:179-180, 1928.
44. Ludzack, F. J., R. B. Schaffer, and M. B. Ettinger. Temperature
and Feed as Variables in Activated Sludge Performance. J. Water Pollut.
Contr. Fed. _33:141-156, 1961.
45. Malina, J. F., and S. Tiyaporn. Effects of Synthetic Detergents
on Lime-soda Ash Treatment. J. Amer. Water Works Ass. 56^727-737,
1964.
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J. Bacteriol. 25:469-493, 1933.
47. McCulloch, E. C., and S. Costigan. A Comparison of the Efficiency
of Phenol, Liquor Cresolis, Formaldehyde, Sodium Hypochlorite, and
Sodium Hydroxide against Eberthella typhi at Various Temperatures.
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McGraw-Hill Book Company, Inc., 1962. 293 p.
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50. Mudge, C. S., and B. M. Lawler. Effects of Alkali Solutions on
Bacteria Found in Unwashed Milk Bottles. Ind. Eng. Chem. 20:378-380,
1928.
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cation, Recovery and Reuse for Wastewater Treatment. U.S. Dept.
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52. Myers, R. P. The Effect of Hydrogen Ion Concentration on the
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55. Ostrum, T. R., C. R. West, and J. J. Shafer. Investigation of
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. GOVERNMENT PRINTING OFFICS: 1973 540-312/1Z7 i-3
90
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
, J. Report N.Q.
w
4. Title
LIME DISINFECTION OF SEWAGE BACTERIA AT LOW TEMPERATURE
5. Report Date
' 0
' 8.
7. Author(s)
Morrison, S. M., Martin, K. L., and Humble, D. E.
9, Organization
Colorado State University
Department of Microbiology
Fort Collins, Colorado 80521
Report Iff.
10. Project Wo.
16100 PAK
fJ. Contract/CiTtxt
tj. Type vf Report aod
Pefiad Covered
Sp^aaoimr Organr
IS. Supplementary Notes
Environmental Protection Agency report
number. EPA-660/2-73-017, September 1973.
is. Abstract Small isolated communities in cold climatic areas need a simple, inexpensive,
reliable sewage system which Includes disinfection. This laboratory study provides
clarifying data on the action of lime as a sewage disinfectant at low temperatures.
Nutrient level reductions were also studied.
Lime was added to raw and activated sludge treated sewage to attain pH intervals
between 10 and 12 at temperatures of 1, 5, 10 and 15 C. Membrane filter procedures were
used to follow decreases in total and fecal coliform populations and total plate counts
at each test pH and temperature. In both sewages, it was observed that pH values above '
11 were required to reduce coliform populations to levels below 100/ml in less than 8-12
hours. To attain coliform population reductions to I/ml or less, 24 hours were required
at pH 11 but only 90 minutes at pH 11.5. Coliforms and other organisms concentrated in
the precipitated solids during lime treatment; their numbers decreased as pH and/or con-
tact time increased. Temperature was a less significant factor in the disinfection
mechanisms than was pH.
An additional effect of lime treatment of sewage is the reduction of organic and in-
organic chemical loads in the effluent. The reductions at 15 C for raw and 10 C for sec-
Dndary treated, measured by BOD and orthophosphate tests, reached maximum BOD removals of
77 and 94%, respectively, at pH 11 in 24 hours for raw and at pH 11.5 in 90 minutes for
treated sewage. Likewise, maximum orthophosphate removals, 93 and 97%, respectively,
were obtained at pH 12.0 for 60 minutes with raw and treated samples.
17a. Descriptors
*Lime, *Sewage treatment, *pH, *Low temperature, *Sewage bacteria, *Disinfection,
Calcium hydroxide, Alkali, Municipal wastes, Coliforms, Biochemical oxygen demand,
Orthophosphate, Coagulation, Alaska, High altitude, Bioindicators
17b. Identifiers
Excess lime treatment, bacterial control
17c. COWRR Field & Group 9 Q5D
IS. A variability
9.' Se<
(Page)
.
;. •" gages
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
Abstractor S. M. Morrison
institution Colorado State University
WRSIC 102 (REV, JUMP 197))
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