EPA-670/2 75-012
April 1975
Environmental Protection Technology Series
LIME STABILIZED SLUDGE:
ITS STABILITY AND EFFECT ON
AGRICULTURAL LAND
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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EPA-670/2-75-012
April 1975
LIME STABILIZED SLUDGE: ITS STABILITY
AND EFFECT ON AGRICULTURAL LAND
By
Gary A. Counts and Alan J. Shuckrow
Pacific Northwest Laboratories
Battelle Memorial Institute
Richland, Washington 99352
Program Element 1BB043
Project Officer
J. E. Smith, Jr.
Advanced Waste Treatment Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
NATIONAL ENVIRONMENTAL RESEARCH CENTER
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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REVIEW NOTICE
The National Environmental Research Center/Cincinnati has
reviewed this report and approved its publication. Approval
does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency
nor does mention of trade names or commercial products consti-
tute endorsement or recommendation for use.
11
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FOREWORD
Man and his environment must be protected from the adverse
effects of pesticides, radiation, noise and other forms of
pollution, and unwise management of solid waste. Efforts
to protect the environment require a focus that recognizes
the interplay between the components of our physical
environment—air, water, and land. The National Environmental
Research Centers provide this multidisciplinary focus through
programs engaged in:
• studies on the effects of environmental contaminants
on man and the biosphere, and
• a search for ways to prevent contamination and to
recycle valuable resources.
The research reported here was performed for the Ultimate
Disposal Section of the Advanced Waste Treatment Research
Laboratory to optimize and demonstrate an alternative method
of sludge (concentrated pollutant stream) stabilization.
Since sludge handling and disposal represents a significant
part of the total wastewater treatment cost, a new stabiliza-
tion technique which promises elimination of obnoxious odors
and essentially all pathogenic bacteria at a high treatment
rate and reduced cost is very welcome.
A. W. Breidenbach, Ph.D.
Director
National Environmental
Research Center, Cincinnati
111
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ABSTRACT
An optimum system for the lime stabilization of municipal
sewage sludge was first developed and then evaluated. The
primary objectives of this work were: 1) to determine the
degree of stability induced in a sludge by lime addition
and 2) to determine the effects of spreading lime-stabilized
sludge on agricultural land. Lime doses and contact times
required to eliminate the pathogenic bacteria and odors
from a raw sludge were determined by laboratory studies, and
the information obtained was translated into design and opera-
tional parameters for a pilot scale, continuous flow process.
Physical, chemical, and biological characteristics of both
the raw and stabilized sludges were measured. Soil and crop
studies, both in a greenhouse and on controlled outdoor plots,
were performed to determine the effects of spreading lime-
stabilized sludge.
Effective lime stabilization of sludge was accomplished by
elevating the pH to 12.0 with lime addition and maintaining
this pH level for at least 30 minutes. Air sparging of the
lime sludge system provided better mixing than mechanical
methods and resulted in approximately a 50 percent reduction
in sludge NH3-N concentration. From 102 to 208 g of Ca(OH)2
was needed to stabilize 1.0 kg of sludge solids. The average
amount required was 150 g. Total O&M costs for lime stabili-
zation were estimated to be $10 per metric ton. Improved
sludge thickening capability was an additional benefit of
lime stabilization.
IV
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CONTENTS
Paqe
FOREWORD iii
ABSTRACT iv
FIGURES vi
TABLES Vii
ACKNOWLEDGMENTS .' . . . .. . x
SUMMARY AND CONCLUSIONS 1
LABORATORY STUDIES .....;.. 1
PILOT PLANT STUDIES . . . 2
GROWTH STUDIES 3
INTRODUCTION 4
RECOMMENDATIONS FOR FUTURE RESEARCH 6
GENERAL 6
EFFECT OF LIME STABILIZATION ON HIGHER ORGANISMS. , . 6
LONG TERM EFFECTS OF SPREADING LIME-TREATED
SLUDGE ON CROPLAND 6
PRIOR STUDIES ON LIME STABILIZATION •- -7
LABORATORY STUDIES • • • • H
GENERAL 11
LIME DOSE REQUIREMENTS. ........... 11
LIME-SLUDGE pH REACTION TIME DEPENDENCY ....... 14
EFFECT OF LIME TREATMENT ON PATHOGENS 17
EFFECT OF LIME TREATMENT ON SLUDGE ODOR ....... 22
EFFECT OF MIXING TECHNIQUE 24
USE OF CONDUCTIVITY MEASUREMENTS FOR
PROCESS CONTROL ........ ..... 25
PILOT PLANT STUDIES - 28
GENERAL ..... 28
LIME DOSE REQUIRED TO MAINTAIN pH >JL2.0 . . . . ... 29
BACTERIOLOGICAL RESULTS 32
COMPREHENSIVE CHEMICAL ANALYSIS 37
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EFFECT OF LIME TREATMENT ON SLUDGE FILTERABILITY
AND SETTLING CHARACTERISTICS 41
Filterability Studies 41
SETTLING CHARACTERISTICS OF LIME TREATED SLUDGE ... 46
SAND DRYING BED TESTS 51
GROWTH STUDIES 53
GENERAL 53
GREENHOUSE STUDIES 54
Results From First Greenhouse Study 55
Results From Second Greenhouse Study 61
GROWTH STUDIES ON OUTDOOR PLOTS 69
DESIGN AND COST CONSIDERATIONS 80
PROCESS DESIGN 80
PROCESS COSTS 80
PROCESS APPLICATIONS 85
REFERENCES 86
FIGURES
Figure
1 Lime Doses Required to Raise pH in Sludges
With Different Solids Concentrations ....... 12
2 Lime-Sludge pH Reaction Time Dependency
for Sludges With Different Solids
Concentrations .... .............. 1G
3 Comparison of Mechanical and Air
Sparge Mixing ................... 25
4 Relationship Between Conductivity and
pH in Lime-Stabilized Sludge ........... 26
5 Lime Stabilization Process Flowsheet ....... 28
6-14 Effect of Lime Treatment on Sludge
Filterability .................. 43-45
VI
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FIGURES (continued)
15-23 Effect of Lime Treatment on Sludge
Settling Characteristics 48-50
24 Comparison Between Raw and Lime-Treated
Sludge Drying Characteristics 52
25 Greenhouse Used in Growth Studies 53
26 Barley Growth During First Greenhouse Study. . . 56
27 Sludge Splasher Plate Showing Design
and Distribution Pattern 71
28 Application of Sludge to Outdoor Plots ..... 72
29 Sudan Grass Harvesting Operation 74
30-32 Sudan Grass After 1 Month Growth Period
on Outdoor Plots 77-79
33 Lime Stabilization Process Conceptual
Flowsheet 81
TABLES
Table
1 Lime Dose Required to Keep Sludge
pH >11.0 for at Least 14 Days
2 Variation of ATP During Storage of
Lime-Stabilized Sludge ........... • • 10
3 pH Response to Varying Lime Dose in Sludges
With Different Solids Concentrations ...... 1J
4 Lime-Sludge pH Reaction Time Dependency Data . • ^5
5 Effect of Lime on Fecal Coliform and Fecal
Streptococci at 2 Percent Sludge Solids
Concentration ..................
VII
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TABLES (continued)
6 Effect of Lime on Salmonella Species and
Pseudomonas Aeruginosa at 2 Percent
Sludge Solids Concentration ........... 19
7 Effect of Lime on Fecal Coliform and
Fecal Streptococci at 4.4 Percent
Sludge Solids Concentration ........... 20
8 Effect of Lime on Salmonella Species and
Pseudomonas Aeruginosa at 4 . 4 Percent
Sludge Solids Concentration ........... 21
9 Threshold Odor Numbers for Treated and
Untreated Sludges With Different Solids
Concentrations ................. 23
10 Results of Test Comparing Mechanical
Mixing and Air Mixing at 4 Percent Sludge
Solids Concentration .............. 24
11 Lime Dose and Corresponding pH and
Conductivity in Sludges With Different
Solids Concentration .............. 27
12 Summary of Pilot Plant Operating Data ...... 30
13 Fecal Coliform and Fecal Streptococci in
Untreated and Treated Sludge Samples ...... 33
14 Salmonella Species and Pseudomonas^
Aeruginosa in Untreated and Treated
Sludge Samples ................. 35
15 Physical and Chemical Characterization
of Sludges Processed During Pilot
Plant Optimization Studies ........... 38
16 Results of Sludge Filterability Studies ..... 42
17 Results of Studies of Sludge Settling
Characteristics ................. 4?
18 Physical Characteristics of Soils Before
and After Barley Growth in the First
Greenhouse Study ................ 58
Vlll
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TABLES (continued)
19 Macro- and Micronutrient Concentrations in
Sludge-Soil Mixtures Before and After Barley
CrovfLh in the First Greenhouse Study 59
20 Barley Weight Gains From the First
Greenhouse Study 62
21 Macro- and Micronutrients in Barley Tissue
From the First Greenhouse Study 63
22 Physical Characteristics of Soils Before
and After Barley Growth in the Second
Greenhouse Study 65
23 Available Macro- and Micronutrient
Concentrations in Sludge-Soil Mixtures
Before and After Barley Growth in the
Second Greenhouse Study 66
24 Barley Weight Gains From the Second
Greenhouse Study 68
25 Macro- and Micronutrients in Barley Tissue
From the Second Greenhouse Study 70
26 Physical Characteristics of Soils Before
and After Sudan Grass Cultivation in the
Outdoor Plot Studies 73
27 Macro- and Micronutrient Concentrations in
Outdoor Plots Before and After the
Outdoor Growth Study 75
28 Average Maximum Plant Heights and Tonnage
Yields of Sudan Grass Grown in Outdoor Plots . . 76
29 Macro- and Micronutrient Concentrations in
Sudan Grass Tissue From Outdoor Growth Study . . 79
30 O&M Costs for Lime Stabilization 84
IX
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ACKNOWLEDGMENTS
Dr. A. J. Shuckrow served as program manager for this study
with C. A. Counts acting as deputy program manager. Profes-
sional assistance was provided by J. F. Cline, M. P. Fujihara,
B. W. Mercer, and R. C. Routson. The excellent technical
assistance provided by J. A. Coates, C. C. Hill, M. J. Mason,
R. G. Parkhurst, G. S. Schneiderman, R. G. Swank, and
R. G. Upchurch is especially appreciated. The secretarial
and technical typing efforts of Pattie Freed, Jan Greenwell,
Nancy Painter, Dee Parks, Shirley Rose, Nancy Straalsund,
and Sheree Whitten are gratefully acknowledged.
Special thanks go to various members of the staff of the EPA
National Environmental Research Center/Cincinnati, Ohio.
Dr. James E. Smith, Jr., Dr. R. B. Dean, and B. A. Kenner
provided helpful guidance throughout the program.
x
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SUMMARY AND CONCLUSIONS
A procedure for the lime stabilization of sludge was developed
and operated successfully at pilot scale. Significant reduc-
tions in pathogenic bacteria and obnoxious odors resulted
from lime treatment. Growth studies, both in a greenhouse
and on outdoor plots, indicated that disposal of lime-stabi-
lized sludge on cropland had no detrimental effects. On the
basis of laboratory, pilot plant, and crop growth studies,
the following major conclusions were drawn.
LABORATORY STUDIES
• Lime dose required to raise the pH of a given sludge to
a specified level was significantly influenced by the
chemical characteristics of the sludge and by the tech-
nique used to mix the lime and sludge. The required
amount of lime to elevate the pH of mixed primary and
trickling filter sludge to 12.4 was found to vary from
4 to 10 gin/1 as the sludge's total solids varied from
1.0 to 4.4 percent.
• The chemical demand for lime exerted by the chemical
components of the sludge caused a pH decay over time,
although an oversupply of OH" ions by addition of
excess Ca(OH)2 can retard this decay.
• Significant reductions in indicator and pathogenic
bacteria were achieved by lime treatment of sludge to
pH >_ 12.0.
• Lime treatment had a deodorizing effect on sludge. The
threshold odor number (TON) in a sludge with a 2.0 per-
cent TS concentration was reduced by 88 percent at
pH >^ 11.2. Eighty-three percent TON reduction was
obtained in a sludge with a 4.4 percent TS concentration
at pH _> 11.6. This effect is not permanent, however,
and as the pH of the sludge drops due to absorption
of C02 from the air, an optimum growth environment will
again be present for microorganisms which create
obnoxious odors. The addition of surplus amounts of
lime to the sludge can retard pH decay.
• For sludge, air mixing was found to be superior to
mechanical mixing.
• Process control should be based on direct measurement
of system pH. This approach achieves positive control
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through optimization of lime dose at the level required
to maintain pH at a point where consistently high patho-
gen kills will be effected.
PILOT PLANT STUDIES
• The lime dose required to maintain the pH at or above
the desired level was affected by the natural varia-
bility of a sludge's chemical composition and by any
type of sludge treatment which altered the sludge's
chemical makeup. The lime dose was found to vary with
the sludge solids concentration, and this variation
can be approximately represented as: Dose (gm/1) =
4.2 gm/1 + 1.6 (TS) , where TS = fraction of total solids
in the sludge.
• Continuous processing of sludge to pH >^ 12.0 reduced
the pathogenic bacteria indicator organism populations
by >_ 99.0 percent.
• Lime treatment significantly increased the total alka-
linity of the sludge.
• The ammonia nitrogen concentration in sludge was reduced
by approximately 50 percent with lime treatment to high
pH levels and air sparging.
• The filterable phosphorus concentration decreased as a
result of lime treatment.
• The biochemical oxygen demand and total organic carbon
concentration in the sludge liquid phase increased as a
result of lime treatment.
• Threshold odor numbers in the supernatants from settled
lime treated sludges were from 83-97 percent lower than
those from settled raw sludges.
• Total solids in the supernatants from settled lime
treated sludges were consistently higher than those
from settled raw sludges.
• Lime treatment significantly improved the sludge's
sett1ing charac ter i s tic s.
• In sand drying bed studies, lime-treated sludge dewatered
at a more rapid rate and yielded a higher utlimate total
solids concentration than raw sludge.
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GROWTH STUDIES
• In a silt loam type soil, application of sludge appeared
to increase permeability with water; whereas, sludge
application to a sandy soil appeared to decrease perme-
ability.
• Application of lime-treated sludge did not significantly
increase soil pH. The pH level in the soil-sludge mixtures
was lower after plant growth than before.
• Application of lime-treated sludge to cropland did increase
the concentration of nutrients available to plants.
• Application of the proper amount of lime-treated sludge
appeared to improve soil productivity as indicated by
mass of plant material produced.
• Excessive concentration of nutrients by plants did not
appear to be a problem. The concentration of iron was
consistently higher in the soils which received sludge
applications.
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INTRODUCTION
Sludge treatment and ultimate disposal represent a major por-
tion of municipal wastewater treatment costs. Most efforts
have been directed toward reducing the quantity of sludge
requiring disposal and the sludge's potential for producing
nuisance conditions and public health hazards during and
after disposal. Processes such as aerobic digestion,
anaerobic digestion, and incineration have been used exten-
sively for sludge treatment. However, each of these processes
adds significantly to the cost of wastewater treatment, and
none totally eliminates residues which require disposal.
The practice of returning organic waste material to cropland
to restore nutrients and improve soil tillability has been
practiced for centuries in many parts of the world. A
revival of interest in developing this concept of waste
disposal for widespread use in the United States is presently
underway. The idea of returning nutrients and organic mate-
rial to the soil for reuse is especially appealing at this
time of increased public awareness of resource limitations.
Although spreading of sewage sludge on land may at first
appear to be a simple and uncomplicated method of disposal,
many factors must be considered in order to make the practice
operationally feasible. The amount of sludge and the fre-
quency of application are two important factors. If the only
objective of sludge spreading operations were disposal and
soil protection was considered unimportant, high application
rates would be acceptable within the limitations of preventing
water and air pollution, and nuisance conditions. However, if
the sludge is spread on cropland to add nutrients, water, and
organic matter, the operating options are more limited since
the productivity of the soil and the integrity of the crops
must be protected.
The use of sewage sludge on cropland is limited by several
factors which are of particular concern to environmentalists
and public health officials: the nitrogen content of the
sludge, the concentration of metals and other trace elements,
and the survival of pathogens. Treatment of sludge to reduce
its pathogen content and, therefore, its potential for intro-
ducing pathogens into cropland was a major concern of this
program.
Historically, lime has been used to treat nuisance conditions
resulting from open pit privies and the graves of deceased
domestic animals. The scope of this program followed from
the work of Farrell, et al.,1 at the Lebanon, Ohio, wastewater
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treatment plant. In that work, Parrel1 and his co-workers
were concerned with developing a treatment technique for
processing that portion of the plant's sludge production
which exceeded its digester design capacity. In the Lebanon
study, lime addition to the sludge was found to be effective
in both deodorization and disinfection. The current program
was designed as an investigation of the pertinent operating
parameters for lime stabilization of sludges and the subse-
quent effects of application of the lime-treated sludges
directly to cropped lands.
The two major objectives of this program were: 1) to deter-
mine the degree of stability caused in sludges by the addition
of large amounts of lime and resulting pH elevation, and 2) to
determine the effects of spreading lime stabilized sludges on
land used for crop production. Initial work to achieve the
first objective was accomplished through bench scale laboratory
studies designed to aid in selection of pilot plant equipment
and operational parameters. The majority of the work in this
part of the study, however, was conducted on the larger pilot
scale. Work on the second objective was accomplished in small
scale greenhouse studies and on larger outdoor plots which
received varying amounts of sludge. After sludge application,
the outdoor plots were cultivated and cropped using standard
agricultural techniques.
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RECOMMENDATIONS FOR FUTURE RESEARCH
GENERAL
Results from laboratory and pilot scale testing show that
addition of large amounts of lime to achieve high pH in sludge
results in excellent pathogen reductions. Greenhouse and out-
door growth studies indicate that large applications of lime-
stabilized sludge to cropland have no detrimental effects on
soil productivity. Areas where additional research would be
beneficial are discussed below.
EFFECT OF LIME STABILIZATION ON HIGHER ORGANISMS
Work should be initiated to determine the effect of lime
treatment on higher organisms such as Ascaris, nematodes,
and amoebic cysts. This type work might best be accomplished
by acclimating cultured organisms to a raw sludge environment
and then observing their response to lime treatment to pH
>.12.0. This approach would provide direct measurement of
the effects of lime treatment on these organisms.
LONG TERM EFFECTS OF SPREADING LIME-TREATED SLUDGE ON CROPLAND
The crop growth studies conducted in this program indicated
that the spreading of lime-treated sludges had no detrimental
effect on soil productivity. The sludge spreading and .crop
growth studies were conducted over a period of only one
growing season so prediction of long term effects from these
results should not be attempted. Therefore, research into
the long term effects of spreading lime-stabilized sludges
on soil should be undertaken.
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PRIOR STUDIES ON LIME STABILIZATION
The chemical reactions between lime and sewage sludge have
not been extensively studied and, consequently, are not well
understood. It can be said, however, that mild reactions
such as the splitting of complex molecules by hydrolysis,
saponification, and acid neutralization should occur.
More information is available on the effectiveness of lime in
reducing the microbiological hazards in water and wastewater.
Riehl, et al.,2 reviewed the work done in treating water with
excess lime to destroy bacteria and concluded that lime clearly
has bactericidal properties. They reported that Escherichia
coli and Salmonella typhosa were destroyed in the pH range of
11.0 to 11.5 when held at 15°C for 4 hours. Grabow, et al.,3
added lime and maintained the pH level of humus tank effluent
at 11.5 for 1 hour. This treatment destroyed all gram-negative
bacteria and reduced the plate count by more than 99 percent.
Surviving microorganisms were spore formers. In a study of
the removal of algal nutrients from wastewater with lime,
Buzzell and Sawyer1* observed that pH levels of 10.9 or
greater maintained for 1 hour produced 'fecal coliform reduc-
tions in excess of 99 percent. Black and Lewandowski5 added
175 mg/1 of lime to raw sewage and noted that the chemical
solids resulting were stable, readily thickened, and contained
no coliform bacteria after 4 weeks storage.
Morrison and Martin6 studied lime disinfection of raw settled
domestic sewage and secondary sewage effluent at low tempera-
ture. These studies showed that rapid destruction of coliform
indicator bacteria occurred at pH 11.5 and 12.0, even at
temperatures as low as at 1°C. Lime treatment to pH 11.5
reduced the fecal coliform concentration in raw sewage from
about 1.25 x 106 to 7.00 x 104 counts/100 ml within a 90-minute
contact time. At pH 12.0, the reduction in fecal coliform con-
tent was even more dramatic, and the concentration of viable
organisms dropped from about 1.30 x 10° counts/100 ml before
lime addition to less than 50 after treatment. Contact time
was again 90 minutes. Total bacterial counts were reduced
at the elevated pH levels but in a less consistent manner
than the coliforms. This reflects the varying resistances
of diverse organism types. Treatment at pH values of >.11.0
failed to adequately disinfect effluents within a reasonable
time period at any of the treatment temperatures studied.
Indications are that some critical factor exists which
influences the rate of disinfection at a pH value above
11.0. Whether this factor is pH alone or a combination
of pH, osmotic pressure, and some threshold phenomenon,
however, was not determined.
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Information is also available on bactericidal effects of add-
ing lime to sludge. Experience at the Allentown, Pennsylvania,
wastewater treatment plant showed that all pathogenic enteric
bacteria and odors were eliminated in anaerobically digested
sludge which had been lime treated to pH 10.2-11.0, vacuum
filtered, and then stored.7 Evans8 noted that lime addition
to sludge caused the release of ammonia and destroyed Bacillus
coli.
Trubnick and Mueller9 presented data which showed the relation-
ship between pH and viable coliforms for dewatered raw sludge.
They concluded that coliform counts are low in most sludges
that are lime treated prior to dewatering, since these sludges
are usually dewatered in the pH range of 11.5 to 12.5.
Doyle10 observed variations in the intensity of obnoxious odors
produced during vacuum filter operations. He correlated reduc-
tions in odor intensity with increases in the amount of lime
used to condition the sludge prior to dewatering and concluded
that the elevated pH in lime conditioned sludges produced an
environment hostile to survival of microbial populations which
could cause nuisance conditions. Further investigations showed
that pH values greater than 12.0 held for contact times of
approximately 2 hours yielded complete destruction of Salmonella
typhosa. Doyle also noted that after lime addition, the pH
decays significantly from its initial value unless excess lime
is added to raise the initial pH above 12.0. Sontheimer11 also
observed the phenomenon of pH decay with time after elevation
to an initial level.
Farrell, et al.,1 conducted studies to determine the effects
of lime treatment on a sludge's filterability, odor reduction,
chemical characteristics, and pathogen reductions. The
results of these studies showed that the addition of lime to
alum and iron chemical-primary sludges increased vacuum filter
yields to reasonable rates. These workers also restated the
fact that lime addition does not significantly reduce the
amount of organic matter present in the sludge. The system
pH may decrease and regrowth of surviving bacteria as well
as that of bacteria inoculated into the sludge from the soil
may occur if conditions become favorable. The microbiological
portions of these investigations indicated that lime treat-
ment of sludge to a pH of 11.5 reduced bacterial (and probably
viral) hazards to a negligible value. Higher organisms such
as Ascaris (round worms) survived short term exposure at pH
11.5. These investigators stated that the hazards from higher
organisms in the lime-treated sludge are probably no greater
than from a well-digested sludge, and hazards from bacteria
and virus are probably far less.
8
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Work by Paulsrud and Eikum12 in Norway was designed to obtain
information which could be used in the operation of lime
stabilization processes. They found that the minimum amount
of lime required to raise the pH of a particular type sludge
to a specified level could not be used in plant operations,
since lime doses in excess of this amount were required to
prevent pH decay to levels where growth of microbial popula-
tions could occur. The lime additions required to keep pH
>11.0 for at least 14 days in various type sludges are
summarized in Table 1.
TABLE 1. Lime Dose Required to Keep Sludge
pH >11.0 for at Least 14 Days12
Ca(OH)2 Dose
Type of Sludge g/kg ss Ibs/ton ss
Primary sludge 100-150 200- 300
Septic tank sludge 100-300 200- 600
Biological sludge 300-500 600-1000
Al-sludge (secondary precipitation) 400-600 800-1200
Al-sludge (secondary precipitation
+ Primary sludge (ssA1:SSPrim=1:1) 250-400 500- 800
Fe-sludge (secondary precipitation) 350-600 700-1200
SS = suspended solids in the raw sludge
Temperature during the storage tests was maintained at 20°C.
Paulsrud and Eikum12 used adenosine triphosphate (ATP) levels
as a measure of microbial activity during storage of lime-
stabilized sludges. These workers determined the ATP content
of sludges prior to lime addition and at different time inter-
vals after lime additions were made. The results from this
study are summarized in Table 2. Microbial activity was
observed in the biological sludge even 4 days after lime
addition. However, this was not the case for primary sludge
where, at the highest dose used, no ATP was detected 30 minutes
after lime addition and no increase was observed during the
4-day storage period.
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TABLE 2. Variation of ATP During Storage
of Lime-Stabilized Sludge
Lime Added
Type of g Ca(OH) 2
Sludge
Primary
Sludge
Biological
Sludge
kg bb
28
56
140
280
44
88
220
440
ATP Before
Lime Additio
(yq/D
1430
1430
1430
1430
2500
2500
2500
2500
n ATP After Lime
1/2 hr
125
96
52
<1
718
850
648
533
6 hrs
66
25
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LABORATORY STUDIES
GENERAL
Bench scale laboratory studies were conducted to develop
basic information on the lime stabilization process itself
and to develop data for use in design and operation of a
pilot plant. These bench scale studies were concerned with:
1. lime requirements to achieve specified pH levels
within a range of pH 11.0 to 12.4,
2. pathogenic bacteria and obnoxious odor .reduction
as a function of pH and contact time between the
lime and the raw sludge,
3. time dependency of the lime/sludge reaction, and
4. comparison of paddle mixing with air diffusion
agitation.
Studies 1 and 2 provided information about the lime dose
required to attain a pH level which achieved consistently
high reductions in pathogen counts and obnoxious odor levels.
This information was useful in design and operation of the
pilot plant lime feed system. Studies 2 and 3 were designed
to determine the lime/sludge contact time required for good
pathogen/odor reductions and the resulting information was
used to design the pilot plant lime/sludge contact tank.
Study 4 was undertaken to determine the most effective mix-
ing technique for use in the pilot plant.
Other laboratory work conducted during this initial phase
included a feasibility study to assess the desirability and
accuracy of monitoring lime dose with conductivity rather
than pH.
Unless otherwise noted, all sludge used in the laboratory
studies was a mixture of primary sludge and trickling filter
humus and was taken from the digester feed line at the
Richland, Washington municipal sewage treatment plant.
LIME DOSE REQUIREMENTS
Laboratory studies were conducted at the beginning of the
program to determine the lime dose required to raise the pH
tb a specified level. The results of these studies were used
11
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in design and operation of the pilot plant facility, which
was employed to produce lime-stabilized sludges for use on
the plots used in outdoor growth studies.
The pH levels chosen for investigation were 11.0, 11.2,
11.4, 11.6, 11.8, 12.0, and 12.4. One liter raw domestic
sewage sludge samples with known total solids concentrations
were dosed with a 100 mg Ca(OH)2/ml lime slurry and mixed
with a paddle stirrer until the change in pH reached
equilibrium. Lime dose and the resulting pH were then
recorded. This procedure was repeated until the specified
pH level was reached. Sludges with different total solids
concentrations were treated to raise the pH to specified
levels in sludges with different solids contents.
The results from these studies are shown in Figure 1 and
Table 3. These results indicate that total solids concentra-
tion affects the lime dose required to raise the pH to
a specified level. As can be seen from Figure 1, the lime
requirements increased as total solids concentration increased,
This variation in lime requirements is probably caused by
13 r
12 -
11 -
10 -
9 •
8 -
7 -
o LO* SOLIDS
2,0* SOLIDS
a 3.0% SOLIDS
• 3.5% SOLIDS
A 4.4%SOLIDS
2000
4000 WOO
Ca(OH>2 DOSE Img/l)
8000
10,000
FIGURE 1,
Lime Doses Required to Raise pH in Sludges
With Different Solids Concentrations
12
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TABLE 3» pH Response to Varying Lime Dose in Sludges
With Different Solids Concentrations
Total Solids Concentration (percent by weight)
Ca(OH)2 Dose,
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
7500
8000
8500
9000
9500
10,000
1%
PH
6.3
8.0
9.75
11.1
11.7
12.0
12.25
12.35
12.4
gAg*
0.0
50.0
100.0
150.0
200.0
250.0
300.0
350.0
400.0
2%
PH
6.0
7.0
7.9
8.75
9.7
10.5
11.2
11.6
11.8
12.0
12.25
12.3
12.35
12.4
3%
gAg*
0.0
25.0
50.0
75.0
100.0
125.0
150.0
175.0
200.0
225.0
250.0
275.0
300.0
325.0
PH
6.1
6.35
6.75
7.35
8.1
9.0
9.8
10.75
11.4
11.75
12.0
12.2
12.3
12.35
12.4
gAg*
0.0
16.7
33.3
50.0
66.7
83.3
100.0
116.7
133.3
150.0
166.7
183.3
200.0
216.7
233.3
3.
PH
6.1
6.25
6.45
6.75
7.1
7.5
8.0
8.6
9.25
9.8
10.25
10.7
10.9
11.2
11.35
11.6
11.8
11.9
12.0
5%
g/kg*
0.0
14.3
28.6
42.9
57.1
71.4
85.7
100.0
114.3
128.6
142.8
157.1
171.4
185.7
200.0
214.3
223.6
242.9
257.1
4.
PH
6.1
6.25
6.6
6.8
7.2
7.65
8.10
8.35
8.65
8.9
9.15
9.3
9.4
9.7
10.1
10.5
10.85
11.15
11.5
12.15
12.4
4%
g/kg*
0.0
11.4
22.7
34". 1
45.5
56.8
68.2
79.5
90.9
102.3
113.6
125.0
136.4
147.7
159.1
170.5
18L.8
193.2
204.5
215.9
227.3
*Liroe dose expressed as grains Ca(OH)2 per kilogram of raw sludge total solids,
-------
a combination of factors including: 1) difficulty in estab-
lishing good mixing patterns in the thicker sludges and
2) chemical demand caused by reaction of the hydroxyl ions
with dissolved COn* bicarbonate alkalinity, and organic
materials (neutralizing organic acids, hydrolysis,
saponification). A low shear, paddle mixing technique
was used to prevent homogenization of the sludge. Dif-
ficulty in establishing good mixing patterns in the sample
container was encountered with the sludges which had higher
solids concentrations. This difficulty could possibly have
prevented intimate contact between the lime slurry and the
liquid phase component of the sludge. Thus, dissolution
of Ca(OH)2 introduced into the sludge would be hindered and
more lime would be required to elevate the pH of the system.
The lime demand would also increase as solids content
increased, since more organic matter would be introduced,
with a concomitant increase in the hydroxyl ion requirement
for neutralizing organic acids and reactions involving
hydrolysis and saponification.
Prom this discussion, it appears that the lime dose
required to raise the pH of a given sludge to a specified
level would be significantly influenced by the chemical
characteristics and the solids concentration of the sludge
and by the technique used to mix the lime and sludge.
LIME-SLUDGE pH REACTION TIME DEPENDENCY
Previous work on lime-sludge systems has shown that a
pH decay is experienced as the treated sludge ages.1'10'12
Decay from high pH levels to lower levels can change the
system environment from one hostile to microbial survival
to one suitable for organism existence and growth.
Therefore, laboratory studies were undertaken to define
the extent of pH decay experienced in sludges with different
total solids concentrations. Sludge samples with total
solids concentrations of 2.0 and 4.4 percent were collected
and divided into one liter batches which were then lime
treated to pH levels of 11.0, 11.2, 11.4, 11.6, 11.8, 12.0,
and 12.4. pH decay in each of these samples was monitored
over a 24 hour time period. Results from this study are
shown in Table 4 and Figure 2.
As can be seen from the results, pH decay was observed
in all samples as the lime-treated sludges aged. However,
the degree of decay significantly decreased when the
initial value of a sample was 12.0 or greater. This decay
is believed to be caused by the sludge chemical demand
exerted on the hydroxyl ions supplied in the lime slurry.
14
-------
TABLE 4. Lime-Sludge pH Reaction Time Dependency Data
Mixed Primary and Secondary ,Sludge
Elapsed
Time (Hrs)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
5.0
24.0
% Change
Between
Initial &
Final pH
Total
Solids
= 2%
Total Solids
pH Value
11.0
10.4
10.1
10.1
10.0
9.8
9.8
9.8
9.8
9.8
— "-— «.
9^
\ •
16.0
11.2
10.6
10.5
10.4
10.2
10.0
10.0
10.0
10.0
9.9
:-—•-. ~\
^9.2
i,9
22.0
11.4
11.1
10.8
10.6
10.5
10.5
10.4
10.3
10.3
10.2
•.. .->
9.6
\ti
16.0
11.6
11.4
11.3
11.1
10.9
10.9
10.9
10.8
10.8
10.8
C" ~" .-'
Va
•\ j_)
16.0
11.8
11.8
11.7
11.7
11.5
11.5
11.6
11.6
11.5
11.5
11.5
^
3.0
12.0
11.9
11.9
11.8
11.9
11.9
11.9
11.9
12.0
11.9
11.8
• ^
2.0
12.4
12.2
12.0
12.0
12.2
12.2
12.3
12.3
12.3
12.3
12.3
* '
1.0
11.0
10.7
11.0
10.2
10.1
10.1
10.2
10.0
9.9
9.8
i *. '
11.0
11.2
11.3
10.7
10.5
10.5
10.5
10.4
10.2
10.1
10.0
\r1
11.0
= 4.4%
pH Value
11.4
10.7
10.4
10.3
10.2
10.1
10.0
9.9
9.7
9.9
/ t
13.0
11.6
11.5
10.8
10.7
10.7
10.6
10.4
10.4
10.2
10.1
*
13.0
11.8
11.8
11.2
10.9
10.9
10.7
10.6
10.5
10.3
10.2
'"'
15.0
12.0
11.8
11.7
11.7
11.6
11.5
11.4
11.4
11.3
11.2
:- ~>
7.0
12.4
11.9
11.9
11.8
11.8
11.7
11.6
11.6
11.4
11.4
8.0
-------
x
a.
7
13
11
9
7
13
11
9
7
13
11
9
7
13
11
9
7
13
11
9
7
13
11
9
7
pH0-11.2
TS-2%
pH0=11.4
15=2%
pH0=11.6
TS=2%
pH0zll.8
TS:2%
TS = 2%
pH0-12.4
TS -2%
ELAPSED TIME (MRS)
SLUDGE TS = 2%
24
13
,11
9
7
13
lH
9
7
13
11
9
7
13
11
9
7
13
11
9
7
13
11
9
7
13
11
9
7
iH&= 11.0
TS=4.4%
pH0- 11.2
TSi4.4%
PH0- 11.4
TS.4.4%
»H0= 11.6
TS=4.4%
PH0= 11.8
TS-4.4%
pH0=12.0
TS • 4.4%
pH0= 12.4
TS=4.4%
24
ELAPSED TIME (MRS)
SLUDGETS-4.4%
FIGURE 2. Lime-Sludge pH Reaction Time Dependency for
Sludges With Different Solids Concentrations
16
-------
Many of the reactions which exert this demand probably proceed
slowly in this type of system (nonoptimal chemical reactor)
and thus pH decays slowly as hydroxyl ions enter into chemical
reactions. The degree of decay probably decreases as initial
pH increase because of the extremely large quantities of lime
required to elevate pH to 12.0 or greater. Large concentra-
tions of both hydroxyl ions and undissociated Ca(OH)2 are
supplied in the slurry. Therefore, at high pH, sufficient
OH~ species are present in the system to allow chemical
reactions to proceed without an attendant decrease in pH.
In summary pH decay depends upon both the quantity of lime
added and the total solids concentration of the sludge.
EFFECT OF LIME TREATMENT ON PATHOGENS
Public health protection must be carefully considered in any
attempt at sewage sludge disposal on agricultural land.
Protection of public health can best be achieved by elimina-
tion of the pathogens present in sludge. A major portion of
this program was concerned with definition of the effects of
high lime dose on the pathogen populations in sewage sludges.
Therefore, a laboratory study was conducted in which mixed
primary and secondary sludges with total solids concentrations
of 2.Q and 4.4 percent were lime treated to various pH levels
within the 11.0 to 12.4 range. Laboratory beakers containing
the lime-treated sludge were allowed to stand open to the
atmosphere at room temperature and samples for bacteriological
analysis were collected after lime-sludge contact times of
1 and 24 hours. The microorganisms chosen as indicators of
pathogen response to lime treatment were fecal coliform,
fecal streptococci, Salmonella species, and Pseudomonas
aeruginosa. Bacteriological methods used for determination
of Salmonella species and Pseudomonas aeruginosa were devel-
oped by Kenner, et al.13 The membrane filter technique and
plate count technique, both described in Standard Methods,***
were used to count fecal coliforms and fecal streptococci,
respectively.
Results of these studies are shown in Tables 5 through 8.
After 1 hour of contact time, pathogen reductions were
observed in the lime-treated sludges at all pH values within
the range under study. In general, the degree of reduction
increased as pH increased with consistently high pathogen
reductions occurring only after the pH reached 12.0. Fecal
streptococci appeared to resist inactivation by lime treatment
particularly well at the lower pH values in the study range.
However, at pH >.12.0 these organisms were also inactivated
after 1 hour of contact time.
17
-------
TABLE 5. Effect of Lime on Fepal Coliform and
Fecal Streptococci at 2 Percent
Sludge Solids Concentration
00
Initial
pH Value
6.0 (Raw Sludge)
6.0 (Raw Sludge)
11.0
11.0
11.0
11.0
11.2
11.2
11.2
11.2
11.4
11.4
11.4
11.4
11.6
11.6
11.6
11.6
11.8
11.8
11.8
11.8
12.0
12.0
12.0
12.0
12.4
12.4
12.4
12.4
Lime
Contact
Time
(hrs)
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
pH When
Sample
Taken
10.9
10.9
9.3
9.3
11.1
11.1
9.5
9.5
11.2
11.2
9.8
9.8
11.5
11.5
10.2
10.2
11.6
11.6
10.7
10.7
11.7
11.7
10.4
10.4
11.9
11.9
11.5
11.5
Fecal Coliform
per 100 ml
1.63x10?
1.90xl07
l.OOxlO4
0.00
2.00xl04
2.25x10*
0.00
S.OOxlO3
0.00
0.00
0.00
S.OOxlO3
l.OOxlO4
5.25xl04
2.00xl04
l.OOxlO4
2.50xl04
S.OOxlO4
0.00
0.00
0.00
l.OOxlO4
2.00xl04
2.50xl04
9.60xl05
4.50X104
0.00
0.00
,0.00
0.00
Fraction of
Original
Remaining
5.6xlO~4
0.00
1.13x10-3
1.27xlO~3
0.00
2.83xlO-4
0.00
0.00
0.00
2.83xlO-4
5.67xlO-4
2.9?xlO-3
1.13x10-3
5.67xlO~4
1.41xlO-3
2.83x10-3
0.00
0.00
0.00
5.67X10'4
1.13x10-3
1.41x10-3
0.05
2.55xlO"3
0.00
0.00
0.00
0.00
Fecal Streptococci
per 100 ml
6.3x10*
6.7xl06
3.30x105
3.75xl05
3.77x106
1.25X107
5.85x106
1.60xl06
1.77xl07
3.75xl06
3.15x105
1.20xl05
9.20x10^
9.20xl05
1.40xl05
3-OOxlO4
3.60xl07
4.00xl06
2.00xl05
1.70xl05
4.00xl06
4.00x106
2500
2600
3.30xl06
3. 00x106
2000
2700
3.35xl06
1.90x106
Fraction of
Original
Remaining
0.05
0.06
0.58
1.92
0.90
0.25
2.72
0.58
0.05
0.02
0.14
0.14
0.02
4.16x10-3
5.54
0.61
0.03
0.03
0.61
0.61
3.84xlO-5
4.00xlO"5
0.51
0.46
3.07x10-5
4.15x10-5
0.52
0.29
-------
TABLE 6. Effect of Lime on Salmonella Species and
Initial
pH Value
6.0 (Raw Sludge)
6.6 (Raw Sludge)
11.0
11.0
11.0
11.0
11.2
11.2
11.2
11.2
11.4
11.4
11.4
11.4
11.6
11.6
11.6
11.6
11.8
11.8
11.8
11.8
12.0
12.0
12.0
12.0
12.4
12.4
12.4
12.4
Pseudomonas Aeruginosa at 2 Percent
Sludge Solids Concentration
Line
Contact
Time
(hrs)
re)
re)
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
pH When
Sample
Taken
10.9
10.9
9.3
9.3
11.1
11.1
9.5
9.5
11.2
11.2
9.8
9.8
11.5
11.5
10.2
10.2
11.6
11.6
10.7
10.7
11.7
11.7
10.4
10.4
11.9
11.9
11.5
11.5
Saroonella
Species
per 100 ml
270
460
130
76
110
45
45
40
110,
68
0
20
45
20
0
0
45
110
45
45
20
20
45
45
340
130
45
20
45
0
Fraction
of Original
Remaining
0.36
0.21
0.30
0.12
0.12
0.11
0.30
0.19
0.00
0.05
0.12
0.05
0.00
0.00
0.12
0.30
0.12
0.12
0.05
0.05
0.12
0.12
0-.93
0.36
0.12
0.05
0.12
0.00
Pseudomonas
Aeruoinosa
per 100 ml
520
310
74
36
0
0
18
18
0
0
0
0
0
0
18
20
0
0
20
20
20
0
0
0
0
0
0
0
20
0
Fraction
of Original
Remaining
0.18
0.09
0.00
0.00
0.04
0.04
0.00
0.00
0.00
0.00
0.00
0.00
0.04
0.05
0.00
0.00
0.05
0.05
0.05
0.0
0.00
0.00
0.00
0.00
0.00
0.00
0.05
0.00
-------
TABLE 7. Effect of Lime on Fecal Coliform and
Fecal Streptococci at 4.4 Percent
Sludge Solids Concentration
Initial
pH Value
6.8 (Raw Sludge)
6.8 (Raw Sludge)
11.0
11.0
11.0
11.0
11.2
11.2
11.2
11.2
11.4
11.4
11.4
11.4
11.6
11.6
11.6
11.6
11.8
11.8
11.8
11.8
12.0
12.0
12.0
12.0
12.4
12.4
12.4
12.4
Lime
Contact
Time
(hrs)
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
pH When
Sample
Taken
10.3
10.3
8.6
8.6
10.6
10.6
8.7
8.7
10.7
1C. 7
9.2
9.2
11.1
11.1
9.5
9.5
11.5
11.5
9.9
9.9
11.8
11.8
10.6
10.6
12.1
12.1
11.4
11.4
Fecal Coliform
per 100 ml
1.60xl07
2.03xl07
3.65xl04
4.35xl04
2.87xl04
3.25xl04
3.72xl04
2.70xl04
1.70xl04
1.37xl04
1.63xl04
2.10xl04
3,20xl04
4.95xl04
5.15xl04
5.03X104
2.55xl04
3.80X104
6.65xl04
3.48xl04
5.34X104
5.77xl04
3.70xl04
2.25xl04
l.lSxlO4
2.20xl04
2.70xl04
5.35xl04
7.13xl04
7.78X104
Fraction of
Original
Remaining
2.01x10-3
2.40xlO-3
1.58xlO~3
1.79x10-3
2.05x10-3
1.49x10-3
9.37x10-*
7.55xlO"4
8.90xlO~4
1.16x10-3
1.76x10-3
2.09xlO-3
2.84xlO"3
2.77x10-3
1.40x10-3
2.09x10-3
3.66x10-3
1.92xlO~J
2.94x10-3
3.18x10-3
2.04x10-3
1.24x10-3
6.34x10-3
1.21xlO"3
1.49x10-3
2.95x10-3
3.93xlO"3
4.28x10-3
Fecal Streptococci
oer 100 ml
4.13xl07
4.67xl07
5.37xl07
6.50xl07
7.33xl07
7.50xl07
8.50x10?,
8.50x10
7.70xl07
7.50xl07
6.43xl07
6.57xl07
8.47xl07
8.57xl07
4.47xlOs
4.53xl06
8.30xl07
8.33xl07
8.33xl06
8.50xl06
8.27x10°
8.70x106
3.27xl05
3.37xl05
3.09xl06
2.50xl06
7.20xl05
7.87xl05
2.61xl06
2.55x106
Fraction of
Original
Remaining
1.22
1.47
1.66
1.70
1.93
1.93
1.75
1.70
1.46
1.49
1.93
1.95
0.10
0.10
1.89
1.89
0.19
0.19
0.19
0.20
7.43x10-3
7.66x10-3
0.07
0.06
0.02
0.02
0.06
0.06
-------
TABLE 8. Effect of Lime on Salmonella Species and
Pseudomonas Aeruginosa at 4.4 Percent
Sludge Solids Concentration
Initial
pH Value
6.8 (Raw Sludge)
6.8 (Raw Sludge)
11.0
11.0
11.0
11.0
11.2
11.2
11.2
11.2
11.4
11.4
11.4
11.4
11.6
11.6
11.6
11.6
11.8
11.8
11.8
11.8
12.0
12.0
12.0
12.0
12.4
12.4
12.4
12.4
Lime
Contact
Time
(hrs)
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
1
1
24
24
pH When
Sample
Taken
10.3
10.3
8.6
8.6
10.6
10.6
8.7
8.7
10.7
10.7
9.2
9.2
11.1
11.1
9.5
9.5
11.5
11.5
9.9
9.9
11.8
11.8
10.6
10.6
12.1
12.1
11.4
11.4
Samonella
Species
per 100 ml
10,800
5600
1080
220
340
340
340
340
440
260
22
320
560
260
44
93
220
52
260
98
220
34
4
9
28
28
16
14
40
66
Fraction
of Original
Remaining
0.13
0.03
0.04
0.04
0.04
0.04
0.05
0.03
2.68x10-3
0.04
0.07
0.03
5.37xlO~3
0.01
0.03
6.34xlO~3
0.03
0.01
0.03
4.14xlO~3
4.88xlO~*
l.lOxlO"3
3.41x10-3
3.41x10-3
1.90x10-3
1.66xlO~3
4.88xlO-3
8.05x10-3
Pseudomonas
Aeruqinosa
per 100 ml,
2800
8600
144
128
7000
1400
28
28
9
9
100
94
1840
62
14
16
8
4
4
4
9
9
0
0
0
8
0
0
26
26
Fraction
of Original
Remaining
0.03
0.02
1.23
0.25
4.91x10-3
4.91xlO"3
1.58xlO-|
1.58xlO"3
0.02
0.02
0.32
0.01
2.39x10-3
2.74x10-3
1.40xlO"3
7.02xlO~4
7.02x10'*
7.02x10-*
1.58xlO~3
1.58xlO~3
0.00
0.00
0.00 ,
1.40xlO~J
0.00
0.00
4.56x10-3
3.86x10-3
-------
An increase in pathogen counts was usually observed in the
samples taken after 24 hours of contact time. It should
also be noted that the pH of the lime-sludge system usually
decreased during this time period. Work done by Paulsrud
and Eikum12 on lime stabilization of sewage sludges in Norway
showed that pH could be maintained at high levels by over-
dosing the system with CafOH)^. This procedure provides
surplus lime to the system so that the chemical demand for
hydroxyl ions does not cause a significant decrease in pH.
For sludge which is to be spread on agricultural land, the
addition of excess quantities of lime in some cases might
harm crop production.
EFFECT OF LIME TREATMENT ON SLUDGE ODOR
An important factor in any stabilization process is its
ability to significantly reduce the obnoxious odor-producing
potential of the sludge. Odors usually result from anaerobic
decomposition of the sludge's organic content. Conventional
methods of reducing the odor-producing potential in sludge
are based on controlled biochemical degradation of the sludge
organic matter (aerobic and anaerobic digestion) or total
destruction of the organic matter (incineration). The lime
stabilization process achieves reductions in odor-producing
potential by creating a high pH, hostile environment in the
sludge, thus eliminating or suppressing the growth of micro-
organisms that produce nuisance conditions.
Tests to quantitatively measure odor are subject to inaccu-
racies, since test panels of supposedly unbiased, randomly
selected people are usually required. However, since no
standard tests were available, the threshold odor number
test described in Standard Methods1 ** was used in this study
to measure odor in raw and lime-treated sludges. Threshold
odor number is defined as the greatest dilution of the sample
with odor-free water which yields the least perceptible odor.
The tests were conducted on mixtures of primary and secondary
sludge which had been lime-treated to pH levels of 11.0, 11.2,
11.4, 11.6, 11.8, 12.0, and 12.4. The threshold odor numbers
of the treated samples were compared to those of sludge
samples which had received no treatment. Sludge samples
with total solids concentrations of 2.0 and 4.4 percent were
used. Samples were tested after 1 and 24 hour contact times.
The results from this study are shown in Table 9. In both
cases, the threshold odor number of the raw sludges was found
to be 8000 while that of the treated samples usually ranged
22
-------
TABLE 9. Threshold Odor Numbers for Treated and
Untreated Sludges With Different Solids
Concentrations
Sludge Type
and pH Level
Total Solids=2.0%
6.8 (Untreated)
11.0
11.2
11.4
11.6
11.8
12.0
12.4
Total Solids=4.4%
6.8 (Untreated)
11.0
11.2
11.4
11.6
11.8
12.0
12.4
Threshold Odor Numbers
1 Hr Contact % Reduction 24 Hr Contact % Reduction
8000
1000
1000
1000
1000
1000
1000
1000
BOOO
1330
1330
1330
1330
800
800
1330
88
88
88
88
88
88
88
83
83
83
83
90
90
83
8000
8000
1000
1000
1000
1000
1000
1000
8000
4000
1330
4000
1330
800
1330
1330
0
88
88
88
88
88
88
50
83
50
83
90
83
83
from 800 to 1330. This data indicates that lime treatment
does have a deodorizing effect. Qualitative observations
in the laboratory substantiate this finding. The intense
putrid odors liberated from the raw sludge samples at the
commencement of each test changed to relatively innocuous
humus-like odors after lime treatment. This deodorizing
effect is not permanent, however. Surplus amounts of lime
added to the sludge can retard pH decay and reoccurrence
of nuisance conditions.. Further/ once the lime stabilized
sludge is incorporated into the soil, odors are no longer
a problem.
23
-------
EFFECT OF MIXING TECHNIQUE
A study to determine the best method of mixing the lime-
sludge systems was initiated early in the program. Mechani-
cal mixing by paddles and air sparge mixing were chosen as
the two mixing techniques for testing. The mechanical mix-
ing device was simply a flat-bladed paddle driven by a
laboratory gang stirrer. The air mixing device was a length
of plastic tubing formed to fit around the bottom of a mixing
vessel. The wall of the tubing was punctured at intervals
to provide, air release ports. Mixing effectiveness was
determined by observing pH change with elapsed mixing time
after 1 liter sludge batches had been subjected to step
additions of 5 g and 10 g of Ca(OH)2. The equilibrium pH
value and the time required to reach that value were observed
and recorded.
Results from the comparison study of mechanical and air
mixing are shown in Table 10 and Figure 3. In both tests
TABLE 10,
Ca(OH)2
Concentration
(g/D
10
Results of Test Comparing Mechanical
Mixing and Air Mixing at 4 Percent
Sludge Solids Concentration
Mixing
Time
0
10 sec
20 sec
30 sec
1 min
2 min
3 min
5 min
6 min
11 min
0
10 sec
20 sec
30 sec
40 sec
1 min
1.5 min
2 min
3 min
Mechanically
Mixed
5.8
7.6
9.0
9.2
9.4
9.6
9.7
9.5
5.8
9.1
9.5
10.0
10.2
11.2
12.3
12.3
Air
Mixed
5.8
7.0
7.3
8.2
9.7
10.8
10.6
10.6
10.5
5.8
9.7
11.4
12.0
12.1
12.3
12.4
12.4
24
-------
LIMEDOSE=5gil
A MECHANI CALLY MIXED
0,AIR MIXED
*
3456
MIXING TIME (MINUTES)
11
II ME DOSE-10 g/l
MECHANICALLY MI XED
o AIR MIXtC
1 2
MIXING TIME (MINUTES)
FIGURE 3. Comparison of Mechanical and Air Sparge Mixing
equilibrium levels were reached within two minutes after
Ca(OH)2 addition. Also, in both cases the equilibrium
pH values were higher in the air sparged system. This
phenomenon may be the result of C02 liberation from the
sludge during aeration. CC>2 liberation would reduce the
hydroxyl ion sink in the system, thus allowing the existence
of more free OH" ions and consequently, a higher ultimate
pH. Qualitative observations made during the test indicated
that mixing action in the air sparged system was much
better than in the mechanically mixed system. Observations
during other tests where the mechanical paddle stirrers
were used revealed the paddles to be subject to blade
fouling by fibrous material in the sludge. This blade
fouling greatly reduced mixing action. No similar fouling
problem was encountered in the air sparged mixing system.
Based on the results of this study, the decision was made
to use air sparge mixing in the pilot plant.
USE OF CONDUCTIVITY MEASUREMENTS FOR PROCESS CONTROL
A short study was conducted to determine the feasibility
of using conductivity as an alternative to direct pH
measurement for process control purposes. In this study
primary-secondary sludge mixtures with varying total solids
concentrations were dosed with lime slurry and mixed
until system pH reached equilibrium. Lime dose and corres-
ponding pH and conductivity of the system were continuously
monitored. Measurement was made with a specific conductance
cell and conductivity calculated as described in Standard
Methods. ltt
25
-------
The relationships between sludge conductivity and pH for
sludges with different solids concentrations are shown in
Figure 4 and Table 11. At pH levels below 11.5, conductivity
is not highly sensitive to changes in pH. However, at values
greater than pH 12.0, it appears that conductivity could be
used as an approximate indicator of pH in a lime-sludge system.
In the process under study, the most dramatic reductions in
pathogens occurred at pH values of 12.0 and greater. If a
certain value of conductivity were chosen as the set point in
a control system, the corresponding pH in the system could be
any value within a range influenced by sludge solids concentra-
tion, ionic species present in the sludge at any point in time,
and chemical demand. Sludge solids concentration could be
maintained at a relatively constant value by use of properly
operated sludge thickening processes; however, the ionic
species present and the components which exert lime demand
may be subject to temporal variations. Therefore, it is
recommended that process control be based on direct measure-
ment of pH. This approach allows optimization of lime dose at
the level required to maintain pH at a point where consistently
high pathogen kills are obtained.
7000
MOO
5000
4000
0 3000
2000
1000
A LM SOLI OS
• aw sou DS
o 3.0* SOLIDS
a 3.5% SOLI OS
A 4.WSOLIDS
8 9 10 11 12 13
P«
FIGURE 4. Relationship Between Conductivity and pH in Lime'
Stabilized Sludge
26
-------
TABLE 11.
Lime Dose and Corresponding pH and Conductivity in
Sludges With Different Solids Concentrations
Solids Concentration (% by Wt.).
CafOHJo Dose
(mg/1)
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
5500
6000
6500
7000
7500
8000
8500
9000
9500
10,000
EH
6.3
8.0
9.75
11.1
11.7
12.0
12.25
12.35
12.4
1%
Conduct.
(pH/cm)
870
800
750
1110
1610
2600
3500
3700
4300
EH
6.0
7.0
7.9
8.75
9.7
10.5
11.2
11.6
11.8
12.0
12.25
12.3
12.35
12.4
!i
Conduct.
(pM/cm)
1150
1210
1250
1190
1110
1210
1320
2200
2780
3400
4400
4600
4750
5300
£H
6.1
6.35
6.75
7.35
8.1
9.0
9.8
10.75
11.4
11.75
12.0
12.2
12.3
12.35
12.4
3%
Conduct.
(yM/cm)
1570
1700
1810
1780
1500
1450
1820
1950
4750
5400
6010
6700
3.5%
PH
*•
6.1
6.25
6.45
6.75
7.1
7.5
8.0
8.6
9.25
9.8
10.25
10.7
10.9
11.2
11.35
11.6
11.8
11.9
12.0
Conduct
(liM/cm)
1700
1800
1900
1970
2020
2100
2180
2100
1960
1650
1700
1750
1800
2000
2110
2500
2900
3170
3200
4.4%
EH
6.1
6.25
6.6
6.8
7.2
7.65
8.10
8.35
8.65
8.9
9.15
9.3
9.4
9.7
10.1
10.5
10.85
11.15
11.5
12.15
12.4
Conduct.
(MM/cm)
1700
1710
1810
1870
1900
1900
1800
1760
1700
1600
1580
1530
1480
1420
1390
1580
1790
2050
2450
4000
5800
*pM/cm = micromhos/centimeter
-------
PILOT PLANT STUDIES
GENERAL
After development of pilot plant design and operational
parameters, construction of the pilot facility commenced.
A schematic diagram of the process is shown in Figure 5.
The process flowsheet is quite simple, since it basically
consists of a sludge-lime mixing vessel and contact tank to
provide the desired contact time. Process control was main-
tained by periodically monitoring pH of the discharge from
the sludge-lime contactor. Since initial laboratory studies
showed that air diffusion mixing was more effective than
paddle mixing, an air diffuser was employed in the sludge-
lime mixing vessel.
Ca(OH)?
SLURRY
FEED PUMP
SLUDGE/
Ca(OH)?
MIXING
VESSEL
RAW
SLUDGE
STABILIZED
SLUDGE
TO ULTIMATE
DISPOSAL OR
DEWATERING
FIGURE 5. Lime Stabilization Process Flowsheet
28
-------
Sludge flows ranging from 3 to 5 gpm were treated during pilot
plant operations. Lime dose required to achieve the desired
sludge pH was monitored routinely and recorded. This allowed
optimization of lime feed to minimize process operating costs.
For the most part, influent to the reactor consisted of a
mixture of primary and secondary sludge from the Richland,
Washington municipal trickling filter plant. This mixture
of sludges was pumped directly from the line which feeds the
Richland plant's anaerobic digesters. Additional work was
carried out with raw primary sludge and trickling filter
secondary sludge, separately, and on mixed sludge iprethickened
with gravity settling.
The pilot operation was monitored routinely with a comprehen-
sive analytical program. Measurements made and information
recorded included type and flow rate of sludge, total solids
concentration, nitrogen forms (NH3, NOq~, organic), pH and
alkalinity, phosphorus forms (total ana filterable), and
bacterial content including fecal coliforms, fecal strepto-
cocci, Salmonella species and Pseudomonas aeruginosa.
Occasional filterability and settling tests were also per-
formed on both the limed and unlimed sludges. TOC, BOD,
odor, and total solids content of the supernatants from these
tests also were determined.
The bacterial content of the lime-treated sludges was deter-
mined from samples taken 60 minutes and 24 hours after treat-
ment. Fecal coliform, fecal streptococci, Salmonella species,
and Pseudomonas aeruginosa were determined as previously
described.Sludge physical and chemical characterizations
were also conducted using sludge samples composited daily
during pilot plant runs. Analytical techniques prescribed
in Standard Methodsl ** were used.
Most of the sludge produced during pilot plant operations
was applied to the outdoor growth study plots; however,
several batches were used in sand-drying beds which were con-
structed adjacent to the pilot plant. The sludge blankets on
the bed surfaces were periodically monitored for solids con-
tent as a function of drying time.
LIME DOSE REQUIRED TO MAINTAIN pH >.12.0
In order to optimize chemical feed during pilot plant opera-
tions, the lime dose applied to the raw sludge was varied
and system pH response was observed. The system was allowed
to come to equilibrium after each dose change and pH was
recorded. The results from this study are shown in Table 12.
29
-------
TABLE 12. Summary of Pilot Plant Operating Data
U)
o
No. of Process
Control '
Checks Hade
1
2
3
4
5
6
7
8
9
10
Averages
No. of Process
Control
Checks Made
1
2
3
4
5
6
7
8
9
10
Averages
July 24
Dose
a/t er/lrcr*
2.4
3.8
4.2
4.8
4.6
4.9
4.2
a/I
4.9
4.9
4.9
4.9
5.0
5.0
4.9
5.0
4.9
5.3
5.0
61.5
97.4
107.7
123.1
117.9
125.6
105.5
August 6
Dose
_ *if*~'i
140.0
140.0
140.0
140.0
142.9
142.9
140.0
142.9
140.0
151.4
142.0
PH
12.0
12.1
12.2
12.3
12.3
12.3
12.2
pH
12.3
12.4
12.3
12.2
12.4
12.*
12.3
12.3
12.2
12.3
12.3
July 25
Ca(OH)2
Dose
4.9 144.1
4.9 144.1
4.9 144.1
4.9 144.1
4.8 141.2
4.8 141.2
4.5 132.4
4.6 135.3
4.4 129.4
4.7 139.5
August 7
Ca(OH)2
Dose
4.4 200.0
4.4 200.0
4.6 209.1
4.6 209.1
4.8 218.2
4.8 218.2
4.4 200.0
4.6 207.8
PH
12.4
12.3
12.3
12.3
12.3
12.4
12.4
12.3
12.1
12.3
pH
12.2
12.2
12.3
12.4
12.4
12.4
12.4
12.3
July 26
Ca (OH) 2
Dose
4.2 120.0
4.3 -122.9
4.4 125.7
4.8 137.1
5.2 148.6
5.2 148.6
5.4 154.3
5.7 162.9
6.4 182.9
5.1 144.8
August 8
-Ca(OH)2
Dose
q/1 q/kq*
4.4 125.7
4.4 125.7
4.7 134.3
4.8 137.1
5.0 142.9
5.0 142.9
5.0 142.9
4.8 135.9
pH
12.0
12.1
12.2
12.2
12.3
12.3
12.3
12.2
12.2
12.2
July "31
Ca (OH) 2
Dose
q/* g/kg*
4.8 123.1
5.1 130.8
5.4 138.5
5.8 148.7
5.6 143.6
5.4 138.5
5.4 138.5
5.3 135.9
5.4 137.2
pB
12.2
12.3
12.3
12.3
12.4
12.4
12.4
12.4
12.3
August 13
PH
12.3
12.3
12.3
12.3
12.3
12.3
12.3
12.3
Ca (OH) j
Dose
g/t g/kg*
6.3 218.8
6.1 174.3
5.8 165.7
5.7 162.9
5.5 157.1
5.5 157.1
5.3 15.1.4
5.2 148.6
5.6 160.0
5.8 165.7
5.7 166.2
PH
12.4
12.4
12.4
12.4
12.3
12.3
12.3
12.3
12.3
12.4
12.4
August 1
Ca(OH)2
Bose
g/* g/lcg*
4.6 135.3
4.8 141.2
4.7 138.2
4.7 138.2
4.7 138.2
4.7 138.2
August 14
Ca(OH)2
Dose
g/t g/kg*
4.7 95.9
4.8 97.9
4.5 91.8
5.0 102.0
5.0 102.0
5.4 110.2
5.3 108.2
5.2 106.1
5.2 106.1
S.O 102.2
12.3
12.3
12.3
12.3
12.3
12.3
PH
12.1
12.3
12.3
12.3
12.3
12.4
12.4
12.4
12.4
12.3
•Grams Ca(OH), per kilogram total solids in the raw sludge.
••To obtain CatOH)2 doae in Ibs/ton dry sludge solids multiply dosage in gm/kg by 2.
-------
Average system pH for the series of daily runs ranged from
12.2 through 12.4, and at no time during the runs did pH
fall below the desirad 12.0 level. The average lime dose
ranged from 4.2 to 5.7 g Ca(OH)2 per liter of sludge, and
the average overall pilot plant studies was 4.9 g/1. The
daily average lime dose expressed as grams Ca(OH)2 per'kilo-
gram of raw sludge total solids ranged from 102.2 through
207.8, and the for the average was 141.9. These lime doses
are considered the minimum required to maintain pH at or
above the desired level (pH >.12.0) during sludge processing.
However, since excess lime was not added to the system,
slight pH decay with time would be expected to occur.
Paulsrud and Eikum12 determined that the lime dose required
to maintain sludge pH greater than 11.0 for 14 days varied
considerably with the type sludge being treated and prior
chemical treatment.
Regression analysis of pilot plant operating data resulted
in the following equation which related the required lime
dose and the sludge total solids concentration:
lime dose = 4.2 + 1.6 (TS)
where: lime dose is expressed as grams Ca(OH),?
per liter of sludge
TS = total solids fraction in the sludge
This equation suggests that the greatest portion of the lime
requirement is associated with the liquid phase and only a.
small fraction of the lime demand is dependent upon the
solids concentration. It should be recognized, however,
that the above equation describes only the initial lime
demand and does not take pH decay with time into account.
Data used to derive the relationship were obtained during
pilot plant operation when lime dose was adjusted to maintain
a pH range between 12.2 and 12.4 and lime-sludge contact time
was 30 minutes. Lime dose is defined as the amount of lime
required to satisfy the chemical demand present in the sludge
and to provide the hydroxyl ion concentration necessary to
raise the pH to the desired level. The total sludge chemical
demand is a combination of the demand present in the liquid
phase and that present in the solid phase. The demand present
in the sludge liquid phase is largely governed by the reaction
of the lime with dissolved C02 and biocarbonate ion. This
demand is probably satisfied with relatively short lime-sludge
31
-------
contact time. The solids demand is characterized by jnuch
slower reactions of. hydroxyl ions with organic materials in
the sludge (neutralizing organic acids, hydrolysis, and
saponification) so that this demand may be exerted over long
periods of time (hours or days). This long term demand
exerted by the sludge solids causes the pH decay discussed
earlier and may account in part for the greater lime doses
required to reach pH 12.4 in the laboratory jar tests than
in the pilot plant study. In the jar tests, system pH was
allowed to equilibrate after each incremental lime dose, so
that several hours were usually required to reach pH 12.4.
During this time period, hydroxyl ions were satisfying liquid
and solids demand as well as elevating pH. In the pilot plant
study, the sludge received slug doses of lime to elevate and
maintain pH >.12.0 after a 30-minute sludge-lime contact time.
Therefore, in the laboratory tests, more time was available
for reaction with organic material in the sludge solids and
thus more lime was required than in the pilot plant study.
In conclusion, the lime dose required to achieve pH >12.0 is
significantly affected by the chemical demand exerted by the
chemical components in the sludge liquid and solid phases,
and the long term chemical demand is a function of the sludge
total solid concentration.
The results derived in this study also indicate that the lime
dose required to maintain the pH at or above the desired level
will be affected by the natural variability of sludge chemi-
cal composition and by any type of sludge treatment which
alters the sludge chemical makeup. Therefore, in practice,
lime dose requirements would have to be determined for each
specific sludge to be treated.
BACTERIOLOGICAL RESULTS
As part of the comprehensive testing work conducted during
the pilot plant phase of the program, studies were made of
the reductions in pathogenic organisms achieved by lime
treatment in the pilot process. Once again the organisms
measured were fecal coliforms, fecal streptococci,. Salmonella
species, and Pseudomonas aeruginosa. The results from these ~
studies are shown in Tables 13 and 14.
These results show that significant pathogen reductions can
be achieved in sludges which have been continuously lime
treated to pH >.12.0. Reductions of fecal coliforms and
fecal streptococci were consistently greater than 99 percent.
Salmonella species and Pseudomonas aeruginosa appear to be
almost totally inactivated by lime stabilization.
32
-------
TABLE; 13. Fecal Coliform and Fecal Streptococci in Untreated
and Treated Sludge Samples (pilot runs were made
mixed primary sludge and humus unless otherwise r
Line
Contact
Initial Time
pH Value (hrs)
June 25, 1973
Untreated sludge
6.0 0.0
6.0 0.0
Treated sludge
12.3 0.5
12.3 0.5
July 9, 1973
Untreated sludge
6.1 0.0
6.1 0.0
Treated sludge
12.2 0.5
12.2 0.5
July 16, 1973
Untreated sludge
6.1 0.0
6.1 0.0
Treated sludge
12.3 0.5
12.3 0.5
July 23, 1973
Untreated sludge
6.0 0.0
6.0 0.0
Treated sludge
12.0 0.5
12.0 0.5
July 25, 1973
Untreated sludge
6.2 0.0
6.2 0.0
Treated sludge
12.2 0.5
12.2 O.S
July 26, 1973
Untreated sludge
6.1 0.0
6.1 0.0
Treated sludge
12.1 0.5
12.1 0.5
July 31, 1973 (1)
Untreated sludge
5.9 0.0
5.9 0.0
Treated sludge
12.0 0.5
12.0 O.S
pH When
Sample
Taken
e.o
6.0
12.3
12.3
£.1
6.1
12.2
12.2
6.1
6.1
12.3
12.3
6.0
6.0
11.8
11.8
6.2
6.2
12.2
12.2
6.1
6.1
12.1
12.1
5.9
5.9
11.7
11.7
Fecal
Coliform
per 100 ml
2.00 x loZ
2.37 x 107
<1000
<1000
5.10 X loZ,
4.50 x 10 '
<1000
<1000
1.56 x 10H.
2.28 x 10'
<1000
<1000
4.8 x 10'
5.2 x 10'
<1000
<1000
4.95 x 10*
3.70 x 10'
500
<1000
1.08 x 10?
1.12 x 10;
2.50 x loj
1.00 x 10*
5.20 x idl
5.45 x 10'
1.00 x lol
2.50 x 10'
Fraction Fecal
of Original Streptococci
Remaining per 100 ml
7.23 x 10$
7.53 x 10
<4.56 x 10~? 100
<4.56 x 10 300
5.83 x 10.Z
7.40 x 10
<2.09 x 10~| 100
<2.09 ic 10 100
1.72 x loZ
1.65 x 10'
<5.22 x 10~* 200
<5.22 x 10~3 170
9.23 x 10«
8.76 x 10°
<2.00 x 10"-! 1330
<2.00 x 10"3 1160
5.00 x ia|!
5.50 x 10°
1.16 x 10"5 100
9.25 x 10~3 0
7.96 x ID?
8.53 x 10
1.87 x 10~J 0
4.69 x 10~* 0
1.89 x 10^
1.88 x 10
1.87 x 10"1 200
4.69 x 10"* 0
Fraction
Of Original
Remaining
1.35 x 10~f
4.06 x 10~3
1.51 x 10"|
1.51.x 10"°
1.18 x 10~f
1.01 x 10"*
1.47 x lO^J
1.29 x 10 *
1.90 x 10*5
0.0
0.0
0.0
1.06 x 10"5
0.0
(1) Primary sludge
33
-------
TABLE 13 (continued)
Lime
Contact
Initial Time
pH Value (hrs)
August 1, 1973 (2)
Untreated sludge
6.4 0.0
6.4 0.0
Treated sludge
12,3 0.5
12.3 0.5
August 6. 1973 (1)
Untreated sludge
6.2 0.0
6.2 0.0
Treated sludge
12.4 0.5
12.4 0.5
August 7, 1973 <2)
Untreated sludge
6.2 0.0
6.2 0.0
Treated sludge
12.3 0.5
12.3 0.5
August 8, 1973 (2)
Untreated sludge
6.1 0.0
6.1 0.0
Treated sludge
17.3 0.5
12.3 0.5
August 13, 1973 (1)
Untreated sludge
5.9 0.0
5.9 0.0
Treated sludge
12.2 0.5
12.2 O.S
August 14, 1973
Untreated sludge
6.2 0.0
6.2 0.0
Treated sludge
12.2 0.5
12.2 0.5
pH When
Sample
Taken
6.4
6.4
12.3
12.3
6.2
6.2
12.4
12.4
6.2
6.2
12.3
12.3
6.1
6.1
12.3
12.3
5.9
5.9
12.2
12.2
6.2
6.2
12.2
12.2
Fecal Fraction
Coliform of Original
per 100 ml Remaining
6.5 x loZ.
5.60 x 10'
1.85 x 10J 3.05 x 10"*
1.80 x 10 2.97 x ,10"*
5.80 x Ifl!
2.95 x 10°
<1000 2.29. x 10~f
<1000 2.29 x 10
4.25 x 10
-------
TABLE 14. Salmonella Species and
Pseudomonas Aerucrinosa in
Untreated and Treated Sludge Samples (pilot runs
were made on mixed primary sludge and humus
unless otherwise noted)
Salmonella Paeudomonas
pH When Species Fraction Aeruginosa Fraction
Initial Lime Contact Sample MPN per of Original MPN per of Original
OH Value Tine (hrs) Taken 100 ml Remaining 100 ml Remaininq
June 25, 1973
Untreated sludge
6.0
6.0
Treated sludge
12.3
12.3
July 9, 1973
Untreated sludge
6.1
6.1
Treated sludge
12.2
12.2
July 16, 1973
Untreated aludge
6.1
6.1
Treated sludge
12.3
12.3
July 23, 1973
Untreated sludge
6.0
6.0
Treated sludge
12.0
12.0
July 25, 1973
Untreated sludge
6.2
6.2
Treated sludge
12.2
12.2
July 26, 1973
Untreated sludge
6.1
6.1
Treated sludge
12.1
12.1
July 31, 1973 (1)
Untreated sludge
5.9
5.9
Treated sludge
12.0
12.0
0.0
0.0
0.5
O.S
0.0
0.0
0.5
O.S
0.0
0.0
0.5
0.5
0.0
0.0
0.5
0.5
0.0
0.0
0.5
0.5
0.0
0.0
O.S
0.5
0.0
0.0
0.5
0.5
6.0
6.0
12.3
12.3
6.1
6.1
12.2
12.2
6.1
6.1
12.3
12.3
6.0
6.0
11.8
11.8
6.2
6.2
12.2
12.2
6.1
6.1
12.1
12.1
5.9
5.9
11.7
11.7
4,400
6,200
0
0
28,000
28,000
9
8
9,200
9,200
0
0
2,200
2,200
0
0
5,200
5,400
0
0
4,200
5,400
0
0
6,800
7,800
0
0
28,000
15,800
0.0 0 0.0
0.0 0 0.0
320,000
320,000
3.20 x 10"J 4 1.25 x 10~f
2.85 x 10 8 2.50 x 10
9,800
14,000
0.0 0 0.0
0.0 0 0.0
22,000
14,000
0.0 0 0.0
0.0 0 0.0
34,000
22,000
0.0 0 0.0
0.0 0 0.0
70,000
48,000
0.0 0 0.0
0.0 0 0.0
Y
020,000
020,000
0.0 0 0.0
0.0 0 0.0
(1) Primary sludge
35
-------
TABLE 14 (continued)
Initfial Lime Contact
pH Value Time (hrs)
August 1, 1973 (2)
i
Untreated sludge
6.4
6.4
Treated sludge
12.3
12.3
August 6, 1973 (1)
Untreated sludge
6.2
6.2
Treated sludge
12.4
12.4
August 7, 1973 (2)
Untreated sludge
6.2
6.2
Treated sludge
12.3
12.3
August 8, 1973 (2)
Untreated sludge
6.1
6.1
Treated sludge
12.3
12.3
August 13, 1973 (1)
Untreated sludge
5.9
5.9
Treated sludge
12.2
12.2
August 14, 1973
Untreated sludge
6.2
6.2
Treated sludge
12.2
12.2
0.0
0.0
0.5
0.5
0.0
0.0
0.5
0.5
0.0
0.0
0.5
0.5
0.0
0.0
0.5
0.5
0.0
0.0
0.5
0.5
0.0
0.0
0.5
0.5
pH When
Sample
Taken
6.4
6.4
12,3
12.3
£.2
6.2
12.4
12.4
6.2
6.2
12.3
12.3
6.1
6.1
5.9
5.9
12.2
12.2
6.2
6.2
12.2
12.2
Salmonella
Species
MPN per
100 ml
4,800
5,400
0
0
3,4(W)
4,400
0
0
12,800
8,600
0
0
2,600
7,000
0
0
4,400
4,800
0
0
io,aoo
7,000
0
0
Pseudomonaa
Fraction Aeruginosa
of Original MPH per
Remaining 100 ml
320,000
320,000
0.0 0
0.0 0
10,800
7,000
0.0 0
0.0 0
3,400
14,000
0.0 0
0.0 0
22,000
15,800
0.0 0
0.0 0
44,000
103,000
0.0 0
0.0 0
56,000
56,000
0.0 0
0.0 0
Fraction
of Original
Remaining
0.0
0.0
0.0
0.0
0.0
0.0
0 .0
0.0
0.0
0.0
0.0
0.0
(1) Primary sludge
(2) Humus
36
-------
Viable organisms of these types were observed only once after
lime treatment in the pilot process (July 9 pilot plant run).
The only unusual occurrence was found in the pilot plant runs
made on July 26, July 31, and August 1. Lime treated sludges
on these days were found to contain fecal coliform counts
approximately ten times greater than had been encountered in
other sludges which had received similar treatment. A review
of pilot plant operating records for these days revealed
nothing which would explain this decrease in killing effi-
ciency. Sludge flow rates were constant at 5 gpm and pH
levels were maintained above 12.0 during the entirety of the
runs. Thus, pilot process conditions were identical to those
which produced the lower residual pathogen counts. It should
be noted that even though the treated sludge pathogen counts
on those days were ten times higher than normal, reduction
still exceeded 99 percent.
COMPREHENSIVE CHEMICAL ANALYSIS
Results from comprehensive physical and chemical characteri-
zation of raw and lime stabilized sludges from pilot process
optimization operations are shown in Table 15. Analyses con-
ducted on whole sludge samples included pH, total solids,
total alkalinity, ammonia nitrogen, organic nitrogen, nitrate
nitrogen, total phosphorus, total filterable phosphorus,
filterability, and settling characteristics. Supernatants
from settling tests were analyzed for TOC, BOD, odor, and
total solids. Primary sludge, secondary sludge (trickling
filter humus), a mixture of primary and secondary sludges
(generally referred to as mixed sludge), and a gravity
thickened mixed sludge were processed during this phase
of the study. The total solids concentrations of the raw
and unthickened sludges ranged from 2.2 to 3.9 percent by
weight. The average solids concentration of these sludges
was 3.4 percent. The total solids concentrations in the same
sludges after lime treatment was always lower than before
treatment, with the solids concentration range and average
being 2.1-3.6 percent and 3.1 percent, respectively. Since
about 50 ml of 100 g/1 lime slurry was added to each liter
of sludge, an average increase of 8 percent in total solids
would occur if no volatile substances were formed. The loss
of solids, therefore, indicates the formation of a signifi-
cant amount of volatile substances which are evaporated during
the drying step of the total solids determination. The forma-
tion of water by the reaction of lime with bicarbonate alka-
linity would account for a small loss from the sum of solids
initially present and the lime added. However, this repre-
sents only 1 percent of the total. The decomposition of
pectin, a minor constituent of settleable organics in sewage,
by reaction with lime forms methanol, which would also
volatilize and cause a small loss in solids.
37
-------
TABLE 15.
PhysicaJ. and Chemical Characterization
of Sludges Processed During Pilot
Plant Optimization Studies
Parameter and Sludge Treatment
Whole Sludge
PH
Raw Sludge
Treated Sludge
Total Solids (wt%)
Raw Sludge
Treated Sludge
Total Alkalinity
(mg/1 as CaCo3>
Raw Sludge
Treated Sludge
Ammonia Nitrogen (mg N/l)
Raw Sludge
Treated Sludge
Organic Nitrogen (mg N/l)
Raw Sludge
Treated Sludge
Nitrate Nitrogen (mg N/l)
Raw Sludge
Treated Sludge
Total Phosphate (mg P/l)
Raw Sludge
Treated Sludge
Filterable Phosphate (mg P/l)
Raw Sludge
Treated Sludge
Supernatant
TOC (mg/1)
Raw Sludge
Treated Sludge
BOD (mg/1)
Raw Sludge
Treated Sludge
Threshold Odor Number
Raw Sludge
Treated Sludge
Total Solids (wt%)
Raw Sludge
Treated Sludge
7/24/73
Mixed
Sludge1
6.0
11.8
3.9
3.6
1060
5080
206
90
1258
1274
23
29
441
339
92
33
1200
2600
1280
2450
400
67
0.2
0.7
7/25/73
Mixed
Sludge
6.2
12.2
3.4
3.1
1260
5920
148
90
1135
1176
19
31
369
340
72
22
1125
2150
1020
1980
400
67
0.2
0.7
7/26/73
Mixed
Sludge
6.1
12.1
3.5
3.1
1320
6280
222
82
1299
847
5
32
595
333
75
27
1200
2000
1110
1875
2000
67
0.3
0.6
7/31/73
Primary
Sludge
5.9
11.7
3.9
3.5
810
6120
238
90
880
1085
2
23
323
215
118
42
1075
2250
1120
2357
2666
200
0.1
0.6
8/1/73
Trick.
Pilt.
Humus
6.5
12.3
3.4
3.0
646
6260
148
131
436
806
11
27
157
118
49
16
600
1500
536
1352
4000
200
0.1
0.5
'Mixture of Primary Sludge and Trickling Filter Humus
38
-------
TABLE 15 (continued)
Parameter and Sludge Treatment
Whole Sludge
pH
Raw Sludge
Treated Sludge
Total Solids (wt%)
Raw Sludge
Treated Sludge
Total Alkalinity
(mg/1 as
Raw Sludge
Treated Sludge
Ammonia Nitrogen (mg N/l)
Raw Sludge
Treated Sludge
Organic Nitrogen (mg N/l)
Raw Sludge
Treated Sludge
Nitrate Nitrogen (mg N/l)
Raw Sludge
Treated Sludge
Total Phosphate (rag P/l)
Raw Sludge
Treated Sludge
Filterable Phosphate (mg P/l)
Raw Sludge
Treated Sludge
Supernatant
TOC (mg/1)
Raw Sludge
Treated Sludge
BOD (mg/1)
Raw Sludge
Treated Sludge
Threshold Odor Number
Raw Sludge
Treated Sludge
Total Solids (wt%)
Raw Sludge
Treated Sludge
8/6/73
Primary
Sludge
6.2
12.4
3.5
3.2
1220
6800
173
75
1225
1151
2
20
369
372
69
26
775
1800
4000
400
0.1
0.5
8/7/73
Trick.
Pilt.
Humus
6.2
12.3
2.2
2.1
1500
5640
263
115
1003
929
5
20
291
242
104
16
850
1775
1455
2130
8000
400
0.1
0.5
8/8/73
Trick.
Filt.
Humus
6.1
12.3
3.5
3.1
1308
6820
411
197
2097
1250
5
18
467
346
134
20
1300
2375
900
2460
4000
400
0.1
0.5
8/13/73
Primary
Sludge
5.9
12.2
3.5
3.0
1394
7840
222
107
1094
1201
5
32
333
320
88
29
1150
2200
8000
800
0.1
0.6
8/14/73
Thick .
Mixed
Sludge
6.2
12.2
4.9
4.5
1632
7260
180
90
1464
1250
7
32
392
310
85
26
1000
2000
8000
800
0.2
0.6
39
-------
The principal.causes for the loss in total solids in the sludge
following lime treatment are unknown but are believed to be
largely related to reactions of nitrogenous organic matter
with lime. Hydrolysis of proteins and destruction of amino
acids are known to occur by reaction with strong bases. The
formation of volatile substances such as ammonia/ water, and
low molecular weight amines or other volatile organics are
strong possibilities.
Total alkalinity in the, raw sludges varied from 646 to 1632 mg/1
as CaC03. ' The initial pH of all these sludges was well below
8.3 (the phenolphthalein end point) so that all the alkalinity
was present either in the bicarbonate form or as titratable
organic matter (e.g., proteins). Total alkalinity in the
lime treated sludges ranged from 5080-7840 mg/1 as CaCC>3.
Ammonia nitrogen concentrations in the treated sludges were
always lower than those in the raw sludges. This was caused
by a shift in equilibrium conditions caused by the radical
increase in system pH. In the raw sludges, which ranged from
pH 5.9-6.5, ammonia was present as ammonium ion (NH^), but
after lime treatment, which elevated conditions to pH 11.7-
12.3, ammonia existed as the dissolved gas NH3. The air
sparging technique used to mix sludge and lime slurry in the
pilot process removed some of this gaseous NH^ from the sys-
tem, thus reducing the ammonia nitrogen concentration in the
sludge. The nitrate nitrogen concentration increased during
sludge processing. This increase is not understandable and
there is no plausible explanation for it.
The organic nitrogen concentration in both the raw and lime
treated sludges varied considerably, making it impossible to
determine effects of lime treatment on this parameter. One
would expect to observe a decrease in organic nitrogen after
lime treatment, since high pH conditions should result in
partial destruction of nitrogenous organic material in the
sludge. This type ofi decrease was observed in five of the
nine sludges analyzed, but significant .organic nitrogen
concentration increases were found in the remaining samples.
Possible explanations for these results are sampling and
analytical variations.
The results in Table 15 show that an average decrease of
4 percent in total phosphate resulted from lime treatment.
Ideally, total phosphate concentration in the whole sludge
would not be greatly affected by lime treatment, since the
hydroxyapatite precipitate resulting from lime treatment should
be redissolved during sample preparation prior to analysis.
These decreases were probably caused by either unequal distri-
bution of hydroxyapatite precipitate throughout the sludge
when sample aliquots were drawn or the dilution effect of
40
-------
adding lime slurry. The dilution effect of adding lime slurry
would account for about a 5 percent decrease in total phosphate.
As might be expected, filterable phosphorus concentration
decreased as a result of lime treatment. The mechanism which
causes this phosphate concentration decrease is the chemical
reaction between Ca(OH)2 and dissolved orthophosphate. This
reaction results in a hydroxyapatite precipitate which removes
phosphate from solution. Residual phosphorus in the supernatant
liquid after lime treatment is believed to be largely organic
in nature.
Biochemical oxygen demand (BOD) and total organic carbon (TOG)
concentrations in supernatants from settling tests increased
as a result of lime treatment. Reactions which would cause
dissolution of organic material include, but are not limited
to:
• saponification of fats and oils which releases soluble
glycerine;
• hydrolysis of proteins which release soluble amino acids;
• dissolution of proteins; and/or
• destruction of pectins wfiich form methanol.
Threshold odor numbers in the supernatants from lime treated
sludges were significantly lower than those from raw sludges.
This indicates that lime treatment does have a beneficial
deodorizing effect.
Total solids in the supernatants from lime treated sludges
were consistently higher than those from raw sludges as a
result of the soluble lime and dissolved organics present.
EFFECT OF LIME TREATMENT ON SLUDGE FILTERABILITY AND SETTLING
CHARACTERISTICS"—
Filterability Studies^
Studies to determine the effect of lime treatment on sludge
filterability were conducted on sludges processed in the pilot
plant. Raw and lime treated sludge samples of a known volume
and total solids concentration were dewatered in a Buchner
funnel and the volume of accumulated filtrate recorded as a
function of filter time. Total solids content of the filtrate
was then determined and used in mass balance calculations to
determine the total solids concentration of the sludge remain-
ing in the Buchner funnel at various times. The results from
these studies are shown in Table 16 and Figures 6-14.
41
-------
TABLE 16. Results of Sludge Filterability Studies
Total Solids Concentration (percent
July 24
Filter
Time
(Hin.)
0
1
2
3
4
5
10
15
20
30
45
60
90
120
Mixed
Sludge
Raw
3.9
4.1
4.2
4.4
4.5
4.6
5.2
5.8
6.4
7.9
10.3
12.9
15.6
19.7
Treat.
3.6
3.7
3,8
3.9
4,0
4,1
4.5
4.9
5.3
6.2
7.9
9.6
13.0
16.4
July 25
Mixed
Sludge
Raw
3.4
3.6
3.8
4.0
4.1
4.3
4.8
5.5
6.2
8.2
11.8
16.2
23.9
25.9
Treat.
3.1
3.2
3.5
3.6
3.7
3.9
4.4
5.0
5.5
6.4
8.2
10. 5
14.4
15.7
July 26
Mixed
Sludge
Raw
3.5
3.6
3.7
3.9
4.0
4.0
4.6
5.2
5.7
7.3
10.5
13.4
17.6
19.7
Treat.
3.1
3.3
3.5
3.6
3.B
3.9
4.6
5.4
6.4
9.5
16.2
20.6
2E.6
25.6
July 31
Primary
Sludge
Raw
3.9
4.1
4,3
4.5
4.7
4.9
5.5
6.2
7.1
8.8
12.0
15.3
21.2
24.6
Treat.
3.5
3.7
3.8
4.0
4.1
4.1
4.7
5.2
5.9
7.5
10.8
15.5
22.1
25.9
August 1
Humus
Ratf
3.4
4.9
5.7
6.7
7.4
8.2
15.8
26.5
31.5
38.9
41.3
41.3
41.3
41.3
Treat,
3.0
4.2
4.9
5.7
6.2
6.7
12.1
17.2
19.0
20. 5
20.5
20. 5
20.5
20.5
by wt.]
August 6
Primary
Sludge
Raw
3.5
3.7
3.8
4.0
4.1
4.2
5.0
5.8
6.7
9.5
14.3
19.0
21.4
24.4
Treat.
3.2
3.4
3.5
3.6
3.7
3.8
4.4
5.0
6.1
7.5
10.0
13.4
21.3
26.2
August 7
Humus
Raw
2.2
2.5
2.6
2.7
2.9
3.0
3.5
4.3
5.2
7.6
12.5
16.3
19.2
20.1
Treat .
2.1
2.4
2.6
2.7
2,8
2.9
3.7
4.5
5.8
15.0
17.3
17.3
17.3
August 13
Primary
Sludge
Raw
3.5
3.7
3.9
4.0
4.1
4.2
4.8
5.3
5.9
7.3
9.5
11.6
16.3
18.0
Treat.
3.0
3.3
3.4
3.5
3.6
3.7
4.2
4.5
4.9
5.8
7.3
8.9
12.0
14.7
August 14
Thickened
Sludge
Raw
4.9
5.0
5.2
5.3
5.5
5.6
6.3
6.9
7.7
9.2
12.6
16.4
22.3
26.3
Treat.
4.5
4.8
5.0
5.2
5.4
5.6
6.3
7.1
7.9
10.0
14.8
20.1
28.5
29.5
-------
20
MIXED PRIMARY AND SECONDARY SLUDGE
PI U)T PLANT RUN! JULY 24. W7J
e RAW SLUDGE
* LIME TREATED SLUDGE
I I I I I I I I I I 1
FIGURE 6
7/24/73
0 20
60 SO 100 120
TIME. MINUTES
FIGURE 7
7/25/73
10
MIXED PRIMARY AND SECONDARY SLUDGE
PI LOT PLANT RUN: JULY 25. »73
e RAW SLUDGE
A LIME TREATED SLUDGE
I I I I I I I I I
25 -
£
uf
MIXED PRIMARY AND SECONDARY SLUDGE
PILOT PLANT RUN: JULY 24. 1773
e RAW SLUDGE
« LIME TREATED SLUDGE
20 40 60 SO
TIME, MINUTES
IOC 120
FIGURE 8
7/26/73
10 -
5 -
0 I • I • I . I . I . I . I . I . I . I . I . I .
0102030405060 70 80 90 100 110 120
HME, MINUTES
Effect of Lime Treatment on Sludge Filterability
43
-------
FRIAURr SLUOCE
PIIOT PIANI BUN; JUIV H 1773
• HAW SUIDtt '
A UNTREATED SLUDGE
tl«, WNUIB
FIGURE 10
8/1/73
X -
FIGURE 9
7/31/73
TRICKLING FILTER HUMUS
PILOT PLANT RUN: August L.
o RAW SLUDGE
A LIME TREATED SLUDGE
J 1 1 L.J 1 ' '
PRIMARY SLUDGE
PI LOT PLANT RUN: AUGUST 6. 1973
e RAW SLUDGE
LIME TREATED SUJDGE
Ol 1 I I I L_l I I I
0 20 40 60 JO 100 120
40 60 SO
TIME, MINUTES
100
120
FIGURE 11
8/6/73
Effect of Lime Treatment on Sludge Filterability
44
-------
20 -
PRIMARY SLUDGE
PI LOT PLANT RUN: AUGUST 7. 1973
a RAW SLUDGE
UME TREATED SLUDGE
40 40 80
TIME. MINUTES
120
FIGURE 13
8/13/73
FIGURE 12
8/7/73
20
u
PRIMARY SUJOGE
PILOT PLANT RUN: AUGUST C. 1973
o RAW SLUDGE
A LIME TREATED SU1DCE
_L_J L_l 1 I I I
20 40 60 SO
TIME. MINUTES
J L_L
100
120
I
UMTttATOSUIKC
J I
I I I
m
tl«. MINUT8
FIGURE 14
8/14/73
Effect of Lime Treatment on Sludge Filterability
45
-------
Improved filterability should have been evident from an increased
rate of total solids concentration buildup in the funnel and an
increased ultimate total solids concentration at the end of the
filtering time. The results do not indicate any trends which
would lead to generalizations about the effect of lime treatment
on sludge filterability. The rate of total solids buildup (or
filtrate removal) appears to be about the same for both raw and
treated sludges during the first 10 to 15 minutes of each test.
After about 20 minutes of filtering time, the rates of solids
buildup in the funnels usually changed. In some instances,
the lime treated sludges exhibited enhanced filterability, and
in others,' the raw sludges dewatered more easily. The highest
ultimate total solids concentration was usually achieved by the
sludge which exhibited the highest rate of solids buildup dur-
ing the latter stages of the filtration period.
SETTLING CHARACTERISTICS OF LIME-TREATED SLUDGE
Studies to determine the effect of lime treatment on sludge
settling characteristics were conducted.on sludge processed in
the pilot process. One liter samples of raw and lime treated
sludges were placed in 1 liter graduated cylinders and allowed
to settle for a specified length of time. The sludge volume at
the sludge-supernatant interface was read and recorded periodi-
cally. _The sludge samples were also gently stirred periodically
to eliminate the effect of bridging among sludge particles.
The results of these tests are shown in Table 17 and Figures
15-23. y
In all but one instance, sludge settling characteristics were
enhanced by lime treatment. This phenomena is probably caused
by the formation of floe which settles better than the dis-
persed particles in the raw sludge. The supernatants recovered
from these tests were clear and had total solids concentrations
ranging from 0.1 to 0.3 percent and 0.5 to 0.7 percent in the
raw sludge and treated sludge supernatants, respectively. The
higher total solids concentrations in the treated sludge super-
natants are caused by the high concentrations of dissolved
Ca(OH)2 introduced in the lime slurry and by an increase in
the concentration of dissolved organics as a result of lime
treatment.
These results indicate that lime treatment of sludges prior to
thickening operations would enhance the effectiveness of the
thickener. Removal of a portion of the sludge liquid phase
would reduce the overall volume of the sludge to be further
treated or removed from the treatment plant. If the thickened,
lime treated sludges were to be applied to agricultural land,
removal of a portion of the liquid phase would reduce the
volume of sludge to be transported to the disposal site. The
high pH conditions created by lime treatment would also prevent
46
-------
TABLE 17. Results of Studies of Sludge
Settling Characteristics
Settling
Time (min)
0
15
30
60
90
120
180
240
300
360
Settling
Time (min)
0
15
30
60
90
120
180
240
300
Volume
July 24
Mixed
Sludge
Raw Treat .
1000 1000
998 995
997 992
996 988
996 981
996 975
995 965
Volume at
August 6
Mixed
Sludge
Raw Treat.
1000 1000
1000 990
995 985
990 975
985 965
980 953
978 940
970 910
970 890
at Sludge/Supernatant Interface, (mis)
July 25
Mixed
Sludge
Raw Treat .
1000 1000
997 990
990 982
988 974
982 960
975 945
963 920
950 900
940 870
930 842
July 26
Mixed
Sludge
Raw Treat.
1000 1000
985
2 965
g ° 940
SB 910
H rt
S £ 880
Oi M-
a 845
815
760
July 31
Mixed
Sludge
Raw Treat.
1000 1000
1000 990
1000 985
995 967
995 945
993 930
990 895
990 860
990 835
August 1
Mixed
Sludge
Raw | Treat.
1000 1000
860 985
700 965
555 925
480 880
440 835
390 750
380 680
380 610
Sludge/Supernatant Interface (mis)
August 7
Mixed
Sludge
Raw Treat.
1000 1000
995 990
990 970
980 945
970 915
965 885
945 830
925 770
900 715
August 13
Mixed
Sludge
Raw Treat .
1000 1000
1000 990
997 985
995 985
995 975
993 970
990 955
990
990 905
August 14
Mixed
Sludge
Raw Treat.
1000 1000
995 988
995 985
990 975
985 965
980 955
970 920
960 890
955 865
47
-------
JULYH. m
MIXED Ml MM YtttCONMRY SU8MX
INITIAL SLUDGE SOUOS CQNC.-3.H
• HAW SLUDGE
4 UME TREATED SLUDGE
FIGURE 15
7/24/73
to to an
stmiNG nut, MINUTES
FIGURE 16
7/25/73
JULY 25. 1973
Ml XCD Pill MMV'SECONaAftY SLUOCC
INITIAL SUIOtt SOLIDS CONC.. 14*
o MW SUIOCE
»U«TMAltDSUJOia
BO BO OT 240
JtnUNCtl«,MIUJTB
NO
3
3 w
TO
no
JUIY24, M7}
MIXED PRIMMVIStCONOARY SUIOd
INITIAL SLUDGE SOUK CONC., 15*
o MW SUIWE
FIGURE 17
7/26/73
eo HO 200
SCTTUNC TIM. MINUTES
2M
Effect of Lime Treatment on
Sludge Settling Characteristics
48
-------
JULY 11 Iff]
INITIAL SUIt«CONC..!.n
• IAD SWOOt
A UMCTKAItOSUIOGt
J I
I I I I
120
HO
FIGURE 18
7/31/73
AUODSI1. »n
SICOWMYSU10CC
INITIAL IUJCCE SOIIOS CONC.. J.ft
• MWSLUOCt
» LIW£ TREAHO SLUDOt
FIGURE 19
8/1/73
M BO 1M SO
JEHUKC TIME. MlNUTU
m
„ «
§ NO
3 M
sf -
g MO
HO
HO
MO
BO
- AUGUST t, NT)
INITIALSUlOa SOLIDS CO.NC..1W
• Mwsuioa
-------
AUGUST;, wn
SECONDARr SLUDGE
INITIAL SLUDGE SOLI OS CONC. -Z.?»
o RAW SLUDGE
* LIME TREATED SLUDGE
FIGURE 21
8/7/73
120 160 200
SETTLING TIME, MINUTES
280
FIGURE 22
8/13/73
AUGUST 13. 1973
PRIMARY SLUDGE
INITIAL SLUDGE SOLIDS CONC..15*
o RAW SLUDGE
& LIME TREATED SLUDGE
120 160 200
SETTLING TIME. MINUTES
- AUGUST 14. W73
THICKENEDJVIIXEO SLUDGE
INITIAL SLUfrGE SOLIDS CONC. .4.9*
e RAW SLUDGE
A LIME TREATED SLUDGE
J 1 1 1 I I I. 1
J 1 'I''
40 tO 120 UO 200
SETTLING TIME, MINUTES
240
280
FIGURE 23
8/14/73
Effect of Lime Treatment on
Sludge Settling Characteristics
50
-------
odor production in thickeners so longer residence times could
be used. Longer residence times would also improve the effec-
tiveness of the thickener.
SAND DRYING BED TESTS
Results from the comparative study of drying characteristics
of raw and lime treated sludges are shown in Figure 24.
Meteorological conditions existing during the test are also
presented. The test was conducted in two adjacent sand drying
beds, each having a surface area of approximately 1.5 m2
(16 ft^). The sludges were dried concurrently so both were
exposed to the same climatic conditions. Ten centimeters
(4 inches) of sludge were initially applied to each bed. The
sludge blanket was sampled every working day and tested for
total solids. The test was suspended when the drying rate
decreased significantly. Two observations can be made from
this test. First, the ultimate total solids concentration
in the lime treated sludge was higher than in the raw sludge.
Upon termination of the test, the lime treated sludge total
solids concentration was 47 percent; whereas, the final total
solids concentration in the raw sludge was 41 percent. This
represents a 15 percent greater concentration of solids in
the lime^treated sludge than in the raw sludge. The second
observation is that 16 days were required for the raw sludge
to reach a total solids concentration of 41 percent, but only
10 days were necessary for the lime stabilized sludge to
reach that same solids concentration. This represents a
38 percent reduction in the time required to achieve an optimal,
ultimate total solids concentration. This point is of consider-
able importance when considering seasonal time constraints
placed on sand drying bed use in some regions. Decreasing the
sludge turn-over time from application to removal from drying
beds would increase the total volume of sludge which could be
dried during the time period when bed use was possible.
Increasing the total volume of sludge passing through this
drying process would reduce the volume of sludge storage
required to carry treatment plant operations through severe
winter months.
51
-------
UJ
Q_
Ul
ro
50
40
30
20
10
METEOROLOGICAL CONDITIONS
PUR ING TEST
TEMPERATURE (Of)
0
A LIME TREATED SLUDGE
O RAW SLUDGE
1
I
I
7 8 9 10 11
TIME, DAYS
12 13 14 15 16
HIGH... 101 98 89 80 77 85 93 93 86 82
LOW
62 61 55 48 52 52 56 54 49 56
77 80 83 84
46 48 51 56
49
90 76
57 54
RELATIVE HUMIDITY <%} ...... 23 16 31 32 28 20 25 25 29 31 39 45 35 33 38 38
WIND SPEED (MPH) .......... 8.2 10.8 11.09.6 6.6 6.8 6.4 a5 6.4 9.7 8.1 3.8 6.5 12.57.0 9.2
40
FIGURE 24. Comparison Between Raw and Lime-Treated Sludge Drying Characteristics
-------
GROWTH STUDIES
GENERAL
The phase of the program dealing with the effects of spreading
lime stabilized sludges on land used for crop production
involved both greenhouse studies and a larger scale outdoor
plot study.
A small greenhouse, pictured in Figure 25, was constructed
adjacent to the treatment plant for the conduct of growth
studies. These greenhouse studies were designed to study the
response of plants grown in various sludge-soil mixtures. The
first of two greenhouse studies yielded information which was
used in design of the outdoor plot study. This outdoor plot
study was conducted during the summer of 1973 at the Washington
State University Irrigated Agriculture Research and Extension
Center in Prosser, Washington.
FIGURE 25. Greenhouse Used in Growth Studies
53
-------
GREENHOUSE STUDIES
Two greenhouse studies were conducted to determine the effects
of spreading lime treated sludge on soil to be used for crop
production. In the first greenhouse study, the soil used was
Ritzville silt loam while a Rupert sand was used in the second
greenhouse study. Anaerobically digested sludge and lime-
treated sludges (primary, humus, and mixed primary-humus) were
applied to soils at five application rates ranging from 11 to
220 metric tons/hectare (5 to 100 tons dry solids/acre),
In the first greenhouse study, the sludges were dried prior to
mixing with the soil. It was observed that the sludge contained
a large amount of fibrous material which combined with the
undissolved lime and formed a hard, crusty material after dry-
ing. This material had to be mechanically ground to form a
product which could be mixed with the soil to produce a rela-
tively homogeneous mixture. One disadvantage of dry application
of the sludge was the loss of nutrient transport in the sludge
liquid phase which normally percolates through the soil after
sludge application. This problem was solved by the sludge
application technique used in preparation for the second green-
house study.
For the second greenhouse study, digested and lime stabilized
sludges in liquid form were applied at the designated rates on
small outdoor plots. The sludges were dewatered by the mechan-
isms of draining and evaporation and the sludge solids were
left on the surface of the plots. After the sludge dried, the
solids were spaded into the underlying soil to an approximate
plow depth of 20 cm (8 inches). These sludge-soil mixtures
were transferred to the pots and barley was grown as in the
first greenhouse study. This sludge application technique
very closely simulated conditions encountered in large scale
sludge spreading operations.
In both greenhouse studies, four replicates were used to mini-
mize the effects of random variations. The sludge-soil mix-
tures were placed in clay flower pots (18 cm top diameter,
11 cm bottom diameter, 17 cm height) and readied for use.
Control pots were prepared for use in comparing plant growth
characteristics and soil response to sludge application. The
control set contained only soil with no sludge additions and
received optimum additions of chemical fertilizer during the
actual plant growth phase of the studies. The fertilizer
requirements for the Ritzville silt loam used in the first
greenhouse study were 100 Ibs nitrogen/acre, 40 Ibs P205/acre,
and 2 Ibs boron/acre. For the Rupert sand used in the second
greenhouse study, the fertilizer requirements were 60 Ibs
nitrogen/acre, 150 Ibs P2O5/acre, 100 Ibs potash/acre, 40 Ibs
sulfur/acre, 5 Ibs zinc/acre, and 1 Ib boron/acre. Barley
54
-------
(Hordeum vulgare) was sown in the pots and the growing plants
maintained through a full growth cycle as indicated by the
formation of grain heads.
After the full growth cycle of approximately 2.5 to 3 months,
the plant material and sludge-soil mixtures were subjected
to analyses. The plant tissue was weighed to determine the
mass yield and then chemically analyzed for micro- and macro-
nutrient content. The sludge-^soil mixtures were analyzed
both before and after plant growth for available micro- and
macronutrient content, pH, permeability with water, hydraulic
conductivity, and field capacity (a measure of the soil's
ability to retain moisture). Available nutrient concentrations
in the sludge-soil mixtures were determined by a commercial
soil testing laboratory using techniques certified by the
Washington State University Agricultural Extension Service.
The techniques used for determining pH, permeability with
water, hydraulic conductivity, and field capacity are described
in Methods of Soil Analysis. 5
Results From First Greenhouse Study
Figure 26 compares the barley growth for various sludges and
application rates midway through the growth cycle during the
first greenhouse study.
The results from analyses of physical characteristics of the
sludge-soil mixtures used in the first greenhouse study are
shown in Table 18. The only.general trend that can be seen
from the intrinsic permeability with water data is that
permeability appears to increase after the soil has been used
as a growth medium. This increase in permeability appeared
in all the sludge-soil mixtures except in those with primary
sludge. The mixtures of primary sludge and soil all showed
a decrease in permeability after the barley growth cycle.
The results also vindicated that, in general, soil permeability
is improved by the addition of sludge, but no general trend
which would correlate permeability with sludge type and applica-
tion rate seemed to exist.
In almost every case, the pH values of the sludge-soil mixtures
were lowered during the growth study. This phenomenon is
probably caused by CC>2 production during biological breakdown
of organic matter and nitrification in the soil. Acid buildup
in the soil results in a lower pH.
Field capacity of the mixtures decreased slightly during the
growth studies. Results from analyses of sludge-soil mixtures
for available macro- and micronutrients before and after the
plant growth are shown in Table 19. No general trends were
55
-------
FIGURE 26. Barley Growth During First Greenhouse Study
56
-------
FIGURE 26 (continued)
57
-------
TABLE 18.
Physical Characteristics of Soils Before and After
Barley Growth in the First Greenhouse Study
oo
Intrinsic Permeability
Hydraulic
Sludge/Soil Type and
Sludge Application Rate
(tons dry solids/acre)
Control
100% Ritzville Silt
Loam (RSL)
Mixed Primary and
Secondary and RSL
5
30
55
80
100
Digested Sludge and RSL
5
30
55
80
100
Primary Sludge and RSL
5
30
55
80
100
Secondary Sludge and
RSL
5
30
55
80
100
with Water - K'
t .-,_ ? \ •*
Pre-Gro
1 (I
9.01x10 "
8.31x10-10
1.03x10-9
2.78x10-9
9.20x10-9
2.04xlO-8
1.01x10-9
9.23x10-9
6.37x10-1°
5.29x10-1°
6.67x10-1°
8.27x10-10
5.62xlO-9
1.16x10-8
1.34x10-8
1.48xlO-8
7.64xlO-10
3.10x10-1°
2.46x10-1°
1.94x10-1°
2.26x10-10
Post-Gro
1.03xlO~9
9.05x10-10
4.89x10-9
6.99x10-9
1.51x10-8
1.65x10-8
7.61x10-10
1.81x10-9
8.26x10-9
5.30x10-9
3.15x10-9
2.05x10-10
8.05x10-1°
9.44x10-9
4.10x10-9
1.26xlO"9
1.50x10-9
2.95x10-9
5.80x10-1°
1.03x10-1°
1.06x10-9
Conductivity - K m
(cm/ sec)
Pre-Gro
l.OlxlO"4
9.29x10-5
1.15x10-4
3.11x10-4
1.02x10-3
2.28x10-3
1.13x10-4
1.03x10-4
7.12x10-5
5.92x10-5
7.48x10-5
9.27x10-5
6.29x10-4
1.30x10-3
1.50x10-3
1.66xlO-3
8.56x10-5
3.47x10-5
3.03x10-5
2.16x10-5
2.54x10-5
Post-Gro
1.16x10"*
1.01x10-4
5.47x10-4
7.92x10-4
1.69x10-3
1.135x10-3
8.52x10-5
2.03x10-4
9.^5x10-4
5. 'J Oxl 0-4
3.52x10-4
2.29x10-5
9.02x10-5
1.05x10-3
4.58x10-4
1.42x10-4
1.69x10-4
3.03x10-4
6.50x10-5
1.15x10-4
1.18x10-4
Pre-Gro
1.00
0.92
1.14
3.07
10.01
22.6
1.11
1.03
0.70
0.59
0.74
0.91
6.23
12.87
14.65
16.44
0.85
0.35
0.30
0.20
0.25
'«c
Post-Gro
1.15
1.00
5.42
7.74
16.73
18.32
0.84
2.01
9.16
5.84
3.48
0.23
0.89
10.40
4.53
1.41
1.67
3.00
0.64
1.14
1.17
pH of
Mixture1'
Pre-Gro
7.90
8.00
8.15
8.20
8.35
8.30
7.80
7.60
7.10
6.90
6.90
8.25
8.35
8.40
8.65
8.50
8.10
8.40
8.60
8.75
8.80
Post-Gro
6.40
7.85
7.42
7.70
7. 02
7.18
7.80
7.55
7.02
7. 10
7.10
7. 51
7.69
7.88
7.27
7.45
8.05
8.30
8.00
8.40
8.58
Field Capacity
of Mixture^
(% of soil dry wt.)
Pre-Gro Post-Gro
31
29
29
31
43
42
28
27
29
30
30
22
24
28
38
39
20
21
26
29
31
25
27
30
30
34
34
26
22
27
29
29
27
25
20
25
26
29
28
29
30
31
1. Ratio of the hydraulic conductivity of the sludge/soil mixture (K,,,) to that of the
control (Kc) before the growth cycle.
2. Soil pH measured in water.
3. 1/3 bar percentage.
-------
TABLE 19.
Macro- and Micronutrient Concentrations in Sludge-Soil
Mixtures Before and After Barley Growth in the
First Greenhouse Study
Sludge/Soil Type and
Sludge Application Rate
(tons dry solids/acre)
Control
100% Ritzville Silt
Loam (RSL)
Phosphorus (ppm)
rc-Gro Post-C
250 170
Potassium (ppm)
rc-Gro Post-
260 110
Sulfur (ppm)
Magnesium (ppra)
Calcium (ppm)
Nitrate-N (ppm)
Prc-Gro Post-Gro Prc-Gro Post-Gro Prc-Gro Post-Gro Pre-Gro Post-Gro Pre-Gro Post-Gro
Prc-Gro Post-Gro
444
384
6000
1640
Mixed Primary and
Secondary Sludge and RSL
5
30
55
SO
100
I
(Jl
vo
I
Digested Sludge and RSL
5
30
ss
so
loo
0.23
0.23
2.0
1.1
0.4S
16.0
77.0
12.0
63.2
18.5
130
175
230
245
245
25
90
130
240
270
200
190
300
280
380
190
190
130
230
240
104
112
120
132
146
16
39
63
104
llfl
300
300
320
348
364
324
324
348
336
360
2240
3520
3580
3860
4000
2440
4240
5000
4680
4740
0.45
0.23
1.35
0.68
0.23
6.0
S.9
10.8
e.e
16.3
440
535
14
62
120
29
110
115
ISO
165
340
380
220
200
190
iao
180
170
140
ISO
60
64
66
74
88
29
62
92
112
130
300
324
336
432
468
300
252
264
264
240
2040
2600
3140
4300
4400
2740
3080
37SO
3820
4000
Primary Sludge and RSL
5
30
SS
60
100
1.6
l.t
0.68
1.1
0.45
0.23
8.6
29.0
17.2
27.1
20
33
290
130
370
44
80
140
200
230
200
240
420
260
320
200
170
180
170
180
ia
24
24
62
62
6
6
48
36
44
324
324
336
384
420
240
240
327
264
276
1B20
2800
280C
4060
4160
2960
3280
5000
4240
4360
Hunus and RSL
5
30
55
80
100
0.45
0.68
2.5
0.68
0.90
5.2
213.0
171.0
4.7
2.0
475
655
750
41
135
50
300
528
825
770
500
700
800
240
280
200
200
510
640
BOO
34
54
56
14
68
14
43
85
130
138
360
372
396
396
408
312
312
324
360
444
2760
3040
4740
5000
6080
2600
4780
5760
- 4500
5760
-------
46
92
104
115
138
35
46
46
115
115
210
220
230
70
145
28
90
130
285
320
J02
95
140
!»0
no
85
100
120
80
135
1.0
1.1
0.4
0.3
0.2
0.7
1.0
1.5
1.2
0.5
6.5
4.6
2.8
3.5
2.0
5.5
13.0
15.5
4.5
5.5
155,0
185.0
65. a
9.5
50.0
5.7
50.0
65.0
120.0
12.0
TABLE 19 (continued)
Sludge/Soil Type and
Sludge Application Rate Sodium (ppm) Iron (ppm) j.anganese (ppm) Boron (ppn) Copper (ppm) Zinc fppra)
(tons dry solids/acre) Pre-Gro Poat-Gro Pre-Gro Poet-Cro Jijr.'-Gro Post-Gro Pre-Gro Post-Gro Pre-Gro Post-Gro Pre-Gro Post-Gro
Control 81 23 70 85 45 JO 1.0 0.6 13.0 4.5 55.0 1.7
100% Ritsville Silt
Loam (RSI.)
Kixed Primary and
Secondary Sludge and RSL
5
30
5S
eo
100
I Digested Sludge and RSL
S 5 35
I 30 69
55 92
eo lei
100 173
Primary Sludge and RSL
5
30
ss
80
100
Humus and RSL
5
30
55
80
100
35
92
92
92
104
312
305
52
85
190
28
60
180
205
210
92
9i
4S
73
«5
60
100
163
138
105
0.5
0.7
0.4
0.8
1.1
0.7
0.8
1.1
1.4
1.5
6.0
9.3
4.0
8.0
9.0
9.0
8.0
10.5
8.5
8.5
60.0
80.0
10.0
60.0
120.0
21.0
26.0
181.0
150.0
185.0
46
35
127
69
138
69
69
69
104
115
40
60
114
130
350
50
52
110
78
78
27
£0
85
120
110
110
100
140
90
90
0.4
0.5
0.3
0.5
0.6
0.6
0.7
1.2
1.1
0.9
4.5
3.6
1.5
6.3
3.6
2.5
3.6
14.5
8.0
8.0
1.0
3.5
37.0
16.0
50.0
4.0
10.0
65.0
26.5
40.0
46
46
115
253
253
175
195
310
64
110
100
75
100
290
490
97
8!.
110
61
138
135
95
75
80
75
0.3
0.2
0.6
0.5
0.5
0.5
0.8
1.1
0.9
1.7
3.0
5.0
4.5
4.5
1.6
5.5
10.0
14.0
6.5
11.0
73
85
105
5.0
4.3
12.0
45.0
70.0
110.0
140.0
-------
developed from this data since in many instances the available
nutrient concentrations after plant growth exceeded that
present in the mixture before germination of the barley.
However, the results do show that no significant buildup of
any macro- or micronutrient occurred. Variations in the soil
data were unavoidable because sludge-soil mixtures are hetero-
geneous and it is difficult to get a sample that is representa-
tive of the whole pot.
The barley weight gains from the first greenhouse study are
shown in Table 20. The maximum weight gains occurred in the
sludge-soil mixtures containing lime-treated primary sludge
and the mixture of primary sludge and trickling filter sludge.
Weight gains from barley grown in these two mediums slightly
exceeded that in the control which was 100 percent soil with
optimum chemical fertilizer additions. The control pots with
digested sludge applications equivalent to 220 metric tons/hec-
tare (100 tons/acre) also produced a weight yield that exceeded
that of controls which received only chemical fertilizer.
Results from analyses of macro- and micronutrient content of
the barley are shown in Table 21. None of the nutrients
appear to be significantly concentrated in the plant tissue
except iron whose concentration was consistently higher in
the plants grown in soils which received sludge treatment
than in the control pots which received no sludge.
Results From Second Greenhouse Study
The results from analyses of the physical characteristics of
the sludge-soil mixtures used in the second greenhouse study
are shown in Table 22. in this study the soil used was classi-
fied as a Rupert sand which is very porous. Addition of sludge
to the soil appears to have reduced the soil's permeability
with water. This would be expected in a sandy soil since the
sludge organic matter acts to retain moisture; whereas, in a
silty or clay soil, the organic matter would tend to open the
pore structure and cause an increase in permeability. Again,
no well defined trend developed which would correlate perme-
ability with the amount of sludge applied. In general, perme-
ability appears to be reduced after plant growth. This could
possibly be caused by biodegradation of the coarse organic
components in the sludge to finer humus-like material which
would fill pore spaces between larger sand particles.
The pH values in the sludge-soil mixtures were usually lower
after plant growth than before. This same phenomenon was
observed in the first greenhouse study and is believed to
be caused by CO2 buildups resulting from biological activity
in the soil.
61
-------
TABLE 20.
Barley Weight Gains From the
First Greenhouse Study
ot
Sludge/Soil Type and
Sludge Application Rate
(tons dry solids/acre)
Control
100% Ritzville Silt
Loam (RSI)
Mixed Primary Sludge
and Kumus and RSL
5
30
55
BO
100
Digested Sludge and RSL
5
30
55
80
100
Primary Sludge and RSL
5
30
55
80
100
Humus and RSL
5
30
55
8C
100
Total
Number
Plants
12
.16
15
12
15
13
16
15
15
16
16
15
16
12
16
17
16
15
4
0
0
Total Weight of
All Plant Tissue Produced
_ (grams)
422.4
120.8
276.2
347.3
426.5
476.6
108.3
198.6
257.1
392.0
431,2
83.3
151.2
232.4
486.7
617.9
181.1
403.9
21.7
0.0
0.0
Average Weight of
Tissue in Each Plant
(grams/plant)
35.2
7,6
17,3
23.2
28.4
36,7
6.8
13.2
17.1
24.5
26.9
5.6
9.5
19.4
30.4
36.4
11.3
26.9
5.4
0.0
0.0
Yield Ratio*
(grams/gram)
1.00
0.21
0.49
0.66
0.81
1.04
0.19
0.38
0.49
0.70
0.76
0.16
0.27
0.55
0.86
1.03
0.32
0.76
0.15
0.00
0.00
*Calculated as grams plant tissue from the sludge/soil mixtures per gram plant tissue from the
control pots.
-------
TABLE 21.
Macro- and Micronutrients in Barley Tissue From the
First Greenhouse Study (All Sludges Lime Treated
Except the Digested Sludge)
Sludge/Soil Type and
Sludge Application Rate
(tons dry solids/acre)
Control
100% Rltzville Silt
Loam (RSL)
Mixed Primary and
Secondary Sludge and RSL
5
30
55
80
100
Digested Sludge and RSL
5
30
55
80
100
Primary Sludge and RSL
5
30
55
80
100
Humus and RSL
5
30
55
80
100
Total N
1.82
0.99
1.30
2.07
1.89
1.62
0.85
1.18
1.07
1.24
1.60
0.19
0.24
1.87
0.28
0.25
1.57
1.13
1.46
Phosphorus
0.34
0.36
0.50
0.68
0.70
0.57
0.32
0.39
0.45
0.51
0.50
0.32
0.50
0.83
0.66
0.66
0.40
0.41
0.55
Potassium
0.40
Magnesium Calcium Sodium Iron Manganese
(%) (%) (*) (ppm) (ppm)
0.16
0.25
0.32
0.12
740
115
1.35
1.53
1.05
1.17
0.93
1.17
1.37
1.17
1.25
1.25
1.05
1.42
1.00
1.90
1.45
1.50
0.97
1.00
0.18
0.28
0.33
0.40
0.40
0.16
0.20
0.23
0.27
0.31
0.19
0.24
0.33
0.20
0.25
0.40
0.26
0.22
0.32
0.25
0.35
0.32
0.27
0.27
0.30
0.32
0.32
0.22
0.25
0.32
0.25
0.27
0.32
0.30
0.32
0.45
1.07
3.94
1.40
1.34
0.47
0.70
1.27
1.35
1.34
0.80
0.87
2.15
1.00
1.22
1.00
1.25
1.70
NO PLANTS
NO PLANTS
0.10
0.17
0.21
0.37
0.37
0.12
0.14
0.17
0.21
0.32
0.08
0.10
0.32
0.29
0.17
0.21
0.22
0.20
2,000
6,000
6,010
3,500
4,000
2,400
2,000
6,240
6,240
3,800
5,040
3,800
10,560
3,000
4,240
4,560
4,800
10,400
77
165
225
110
119
77
183
207
190
175
140
110
218
70
107
145
240
274
Boron Copper
(ppm) (ppm)
12
15
10
10
17
25
3
8
9
12
17
7
11
14
10
9
13
8
5
11
23
80
19
70
15
25
34
28
31
28
22
35
25
15
21
19
38
Zinc
(ppm)
330
27
86
260
70
120
40
80
120
140
114
54
176
210
80
86
40
64
120
-------
TABLE 22. Physical Characteristics of Soils
Before and After Barley Growth in
the Second Greenhouse Study
en
Sludge/Soil Type and
Sludge Application Rate
(tons dry solids/acre)
Control
lOOt Rupert Sand (RS)
Mixed Primary
Humus and RS
S
30
55
80
100
Digested Sludge and RS
5
30
55
80
100
Primary Sludge and RS
5
30
55
BO
100
Humus and RS
5
30
55
80
100
Intrinsic Permeability
with Water - K'
(cm2) w
Pre-Gro
3.91xlO~8
3.36x10"*
1.91x10"!
3.67x10""
2.33xlO~"
4.82xlO~8
2.45x10"!
1.51x10"?
1.57x10"°
1.91x10"°
3.97x10""
2.05x10"!
2.46x10"?
2.77x10"°
4.30x10"?
2.68x10""
2.60x10"!!
2.32x10 2
5.09x10"?
4.42x10"°
2.22x10"°
Poat-Gro
1.44xlO"8
9.91x10"®
1.70x10""
l.B4xlO"l
1.73x10"?
2.85x10""
1.31xlO"8
2.58x10""
3.50xlO~"
2.53xlO~"
3.88x10""
6.86xlO~*
1.06x10"?
2.58x10"?
3.14x10"?
3.26x10""
1.22x10"*
2.02x10"?
5.38x10"?
4.35x10"?
4.26KlO~B
Hydraulic 1
Conductivity - K m /
(cm/sec) Kn
Pre-Gro
4 • 61x10
3 . 96x10 »
i 2 . 25x10
4.34x10";
2.75x10"?,
5.69xlO~J
2.90xlO~3
1'. 78x10^3
2i25xlO~3
4.69xlO~J
2.42x10"?.
2.90x10 ;
3.27x10"?.
5.07x10"^
3.16xlO~3
3.07x10"?,
2.74x10"?,
6.01x10"?.
5.22xlO~3
Z.62xlO~3
Post-Gro
1.74clO"3
1.17x10"?
2.00<10~3
2.17clO~;
2.04<10",
3.36clO~J
1.54 tiO~l
3.04 tlO^3
2*.99:10"3
4.5a:10"J
8.09::10"*
3.04::10"3
3.70::10,
3.B5::10~3
3^39::10"2
6.36x10^
5!o4:!lO"3
Pre-Gro
1.00
0.86
0.49
0.94
0.60
1.23
0.63
0.39
0.40
0.49
1.01
0.53
0.63
0.71
1.10
0.69
0.66
0.59
1.30
1.13
0.56
Poa t-Cro
0.38
0.25
0.43
0.47
0.44
0.72
0.33
0.66
0.89
0.64
0.99
0.18
0.27
0.66
0.80
0.84
0.31
0,74
1.38
1.11
1.09
1. Ratio of the hydraulic conductivity ot the Bludge-soil mixture (Kg,) to that of tha
control (KC) before the growth cycle.
2. Soil pH measured in water.
3. 1/1 bar percentage.
Field Capacity of
Mixture3 (% of
aoil dry wt.)
Pre-Gro Poat-Gro Pre-Gro Post-Gro
PK of
Mixture2
7.6
7.8
8.1
8.S
10.6
10.2
7.0
6.5
6.7
6.8
6.8
7.8
7.6
7.9
8.1
10.0
7.9
8.5
B.O
8.1
8.3
6.1
8.2
8.3
8.0
8.0
8.0
5.5
7.7
13.2
13.2
16.1
20.2
4.6
7.6
e.i
8.1
8.1
8.2
7.3
6.8
6.6
6.3
6.7
7.6
7.6
7.6
7.7
7.7
9.1
9.4
13.9
15.9
11.4
8.6
13.3
15.2
15.6
16.1
7.6
8.4
10.7
14.9
15.0
7.1
8.8
10.2
9.6
5.3
6,8
8.2
12.4
11.1
9.2
4.2
5.4
4.2
6.4
5.5
3.5
5.6
4.4
4.4
6.4
-------
The field capacities of the sludge-soil mixtures were lower
in the samples taken after plant growth than in those taken
before the barley was planted. The results obtained from
analyses of sludge-soil mixtures for available macro- and
micronutrients before and after the plant growth are shown
in Table 23. In general, the results show increases in
available nutrient concentrations in the sludge-soil mixtures
as sludge application rates increased. A decrease in avail-
able nutrient concentrations apparently occurs during plant
growth. This decrease is probably caused by nutrient uptake
in the growing plants. Sludge application to the soil at
rates as low as 11 metric tons dry solids per hectare (5 tons
dry solids per acre) significantly increased the concentrations
of available calcium and iron in the mixtures. The increase
in calcium concentration was expected because of the lime
added to the sludges. The increase in available iron was also
observed in the results from the first greenhouse study. Appli-
cation of moderate to high amounts of sludge caused significant
increases in the concentrations of available phosphorus, sodium,
manganese, and zinc.
Results from the study of barley weight gains in the second
greenhouse study are shown in Table 24. The total weights
of plant materials produced in this study were not as high
as in the first greenhouse study but the growth patterns were
more definite. The reduced overall yields probably resulted
from using Rupert sand as the soil upon which sludges were
applied. This type soil is not as good for crop production
as is the Ritzville silt loam used in the first greenhouse
study. The control pots which received only chemical fertilizer
yielded plants which averaged""bnly 4.7 grams each. However,
the addition of sludge to the soils significantly affected
the yield. The sludge-soil mixtures made from mixed primary
sludge and humus, primary sludge alone, and humus alone,
applied at the lowest rate of 11 metric tons dry solids per
hectare (5 tons dry solids per acre) all yielded less plant
material than the control pots which received only chemical
fertilizer. The mixture made from Rupert sand and digested
sludge applied at 11 metric tons dry solids per hectare
(5 tons dry solids per acre) produced plants whose average
weight exceeded that of the control by almost 2.5 times.
The mixtures made from mixed sludge and digested sludge
applied to Rupert sand all produced increasing plant material
yields as the sludge application rates increased from 66 through
176 metric tons dry solids per hectare (30 through 80 tons dry
solids per acre). Plant yield decreased for each of these
sludge-soil types when the application rate reached 220 metric
tons dry solids per hectare (100 tons dry solids per acre).
The mixtures made from primary sludge and humus applied to
65
-------
TABLE 23.
Available Macro- and Micronutrient Concentrations in Sludge-Soil
Mixtures Before and After Barley Growth in the Second Greenhouse Study
Sludge/Soil Type and
Sludge Application Rate
(tons dry solidi/aere)
Control
lOOt Rupert Sand (US)
Kitrate-M (pprn)
Pre-Gro Post-Gro
37
Phosphorus (ppn)
Pre-Gro Po«t-Gro
100
Potaislunv (ppml Sulfur (pptiQ __ Haqnoaiura
-------
TABLE 23 (continued)
Slidg«*Appiic«tion*Rft« Soditai (ppm) Iron (ppm) Manganese (ppra) Boron (PPIH) Copper (ppm) Zinc (ppra)
(ten's dry «olid«/acro) Pra-Cro Po»t-Cro Pre-Cro Po«t-0ro Pro-Cro Poet-Cro Pre-Gro Poat-Cro Pro-Rro Poat-Cro Pro-Cro Poat-Cro
Control
lOOt Rupert Sand (RS) 75 33 68 73 37 26 0.5 0.5 9514
Mixed Primary and
Secondary Sludge and RS
5 SO 44 197 42 95 102 0.4 0.6 8 6 2 7
30 87 55 210' 106 70 63 0.6 0.7 10 7 27 21
55 110 67 217 117 180 140 0.6 1.0 9 12 26 26
80 112 112 245 103 85 70 0.5 0.8 11 10 50 37
100 142 105 177 208 137 133 0.5 0.5 12 9 68 26
Digested Sludge and RS
"° 5 27 23 288 56 84 52 0.8 0.6 7 10 8 15
30 80 95 310 60 90 86 1.1 0.7 11 12 46 38
55 90 85 211 187 76 102 1.4 1.1 10 6 68 88
80 145 77 214 210 66 140 1.7 1.3 9 8 33 125
100 160 93 186 200 83 92 1.3 1.5 13 12 172 105
Primary lludg* and RS
S 52 67 S3 47 40 105 0.8 0.4 11 6 3 7
JO 30 63 70 97 «S 88 0.9 1.0 9 11 30 27
JS 140 aS 91 100 93 115 0.9 0.5 12 7 26 20
80 76 112 112 60 130 105 0.8 0.9 10 9 70 30
100 126 107 312 94 100 95 0.5 0.6 14 12 48 40
Humus and RS
5 28 43 108 85 8$ 110 0.4 0.5 9 8 2 5
30 33 40 88 96 97 62 0.7 1.2 12 7 10 10
55 122 113 96 105 83 105 0.9 0.6 11 12 22 18
80 207 86 300 80 70 72 1.0 0.8 10 12 40 36
100 237 120 420 106 100 55 1.1 0.9 12 9 37 34
-------
TABLE 24,
Barley Weight Gains From the
Second Greenhouse Study
a\
oo
Sludge/Soil Type and
Sludge Application Rate
(tons dry solids/acre)
Control
100% Rupert Sand (RS)
Mixed Primary Sludge
and Humus and RS
5
30
55
80
100
Digested Sludge and RS
5
30
55
80
100
Primary Sludge and RS
5
30
55
80
100
Humus and RS
5
3C
55
80
100
Total Total Weight of
Number All Plant Tissue Produced
Plants (grams)
16 74.8
16 67.0
16 158.6
15 200.1
IS 252.6
16 206.5
14 162.1
15 211.6
17 253.2
16 309.4
15 219.2
16 36.1
14 122,8
16 144.5
17 122.2
17 176.4
15 41.2
16 122.2
16 175.6
14 238.6
16 297.2
Average Weight of
Tissue in Each Plant
(grams/plant)
4.7
4.2
9.9
13.3
16.8
12.9
11.6
14.1
14.9
19.4
14.6
2.3
8.8
9.0
7.2
10.4
2.8
7.6
11.0
17.0
18.6
Yield Ratio*
(grams/gram)
1.00
0.89
2.12
2.83
3.57
2.74
2.47
3.00
3.17
4.13
3.11
0.49
1.87
1.91
1.53
2.21
0.60
1.62
2.34
3.62
3.96
'Calculated as grains plant tissue from the sludge/soil mixtures per gram plant tissue from the
control pots.
-------
Rupert sand produced increasing plant yields as sludge applica-
tion rates increased through 220 metric tons per hectare (100
tons per acre).
These results indicate that sludge addition to poor soils would
increase productivity and, therefore, would be beneficial. The
addition of large amounts of lime to the sludges did not appear
to produce any detrimental effects.
Results from analysis of macro- and micronutrient content of
the barley grown in this study are shown in Table 25. The
total nitrogen and phosphorus levels in the plants grown in
the test" pots which contained sludge-soil mixtures were consis-
tently lower than in the plants grown in the control which con-
tained only soil. These results cannot be interpreted as
indicating a nitrogen or phosphorus deficiency in the soils
which received sludge treatment since plant production in these
pots generally exceeded that in the control pots. The calcium
concentration in plant tissues from pots which received sludge
applications was higher than in the plant tissue from the con-
trol pots. Zinc concentration was considerably higher in the
tissue of plants grown in pots which received digested sludge
than in any of the other plant tissues tested.
GROWTH STUDIES ON OUTDOOR PLOTS
In order to further evaluate the short term effects of spread-
ing lime treated sludge on cropland, larger scale crop growth
studies were conducted on outdoor plots. The site chosen for
this study was located at the Washington State University
Irrigated Agriculture Experiment and Extension Center in
Prosser, Washington. The soil at the site was classified as
Warden silt loam. The site had not been used for any agricul-
tural experiments during the preceding year. Five 0.04 hectare
(0.1 acre) plots were used: one control plot received no sludge
(only application of 200 Ibs nitrogen/acre, 5 Ibs zinc/acre,
and 1 Ib boron/acre); two plots received applications of
anaerobically digested sludges at rates equivalent to 22 and
88 metric tons dry solids per hectare (10 and 40 tons per acre);
and two plots received lime-treated mixed primary sludge and
humus at the same application rates used for the digested
sludge. Buffer zones were provided between plots to assure
individual plot integrity during sludge spreading operations,
plant growth, and harvesting operations. The sludge was trans-
ported to the site by a contracted septic tank service.
Even distribution of the sludge on the plots was accomplished
by use of a splashe* plate attached to the tank truck discharge
port as shown in Figure 27. Figure 28 shows this spreading
operation.
69
-------
TABLE 25 . Macro- and Micronutrients in Barley Tissue from the Second Greenhouse
Study (all sludges lime treated except the digested sludge)
Sludge/Soil Typo and
Sludge Application Rate Total N Phosphorus
(t-gr.s tiry solids/acre) (%) (%)
Control
IGOt Rupert Sand {RS)
4.1
1.14
Potassium Sulfur Magnesium Calcium Sodium Iron
(i) «) («) (t) (%)
3.10
0.32
0.98
0.75
0.58
Manganese Boron Copper Zinc
(ppm) fppm) (pom) (ppm)
478
31
11
31
Kixed Primary and
Secondary Sludge and RS
5 1.2 0.45
30 1.3 0.62
55 1.6 0.51
80 1.5 0.46
100 1.9 0.52
Digested Sludge and RS
5 1.9 0.42
30 2.6 0.56
55 3.2 0.52
80 3.9 0.59
100 3.2 0.51
Primary Sludge and RS
5 1.4 0.44
30 2.1 0.39
55 2.1 0.39
80 2.0 0.55
100 2.7 0.42
Humus and RS
5 1.2 0.50
30 2.6 0.45
55 2.5 0.70
80 3.0 0.54
100 3.2 0.42
3.48
4.32
3.60
3.23
3.41
4.40
3.40
2.82
2.55
2.38
4. CO
3.75
3.41
3.87
3.05
4.00
3.60
3.55
3.23
3.00
0.32
0.49
0.38
0.34
0.43
0.40
0.40
0.41
0.36
0.39
0.35
0.39
0.48
0.50
0.49
0.31
0.36
0.40
0.40
0.40
0.37
0.44
0.45
0.45
0.44
0.37
0.45
0.45
0.41
0.38
0.41
0.41
0.37
0.37
0.38
0.38
0.37
0.40
0.43
0.43
1.12
1.23
1.20
1.45
1.25
0.92
1.50
1.68
1.68
1.50
1.15
1.20
1.37
1.12
1.25
0.87
1.20
1.55
1.55
1.75
0.21
0.26
0.38
0.63
0.58
0.59
0.75
0.95
1.20
1.00
0.38
0.70
0.85
0.70
1.00
0.38
0.75
0.85
0.95
1.00
450
700
800
433
445
800
820
550
950
550
1250
428
475
415
500
€50
950
550
600
700
60
102
215
221
187
55
44
60
53
65
44
97
145
138
135
14
16
16
24
21
23
34
55
50
45
16
19
14
13
15
20
27
31
25
21
11
16
14
11
12
14
19
21
23
21
13
13
11
14
14
9
15
15
16
16
92
450
500
550
500
70
77
84
110
90
57
62
84
95
79
-------
:
FIGURE 27.
Sludqe Splasher Plate Showing Design
and Distribution Pattern
71
-------
FIGURE 28. Application of Sludge to Outdoor Plots
After sludge application, the plots were allowed to dry and
then were prepared for planting. Samples for analyses of soil
physical and chemical characteristics were taken at this time.
Sudan grass, an annual pasture grass adapted to Eastern
Washington State, was used as an indicator plant. Maintenance
of the plots during plant growth mainly involved periodic appli-
cation of irrigation water and was carried out by the staff of
the WSU Experiment Center. In early autumn when danger from
frost damage was imminent, the grass was harvested as shown
in Figure 29. The yield from each plot was recorded and plant
matter and soil samples were collected for analyses. These
samples were subjected to the same tests as conducted on the
plant tissue and soil samples from the greenhouse studies.
The results from analyses of physical characteristics of soils
before and after Sudan grass cultivation are shown in Table 26.
Intrinsic permeability with water slightly improved in the
soils from all plots during the growth study. The greatest
improvements occurred in the plots which received sludge appli-
cations of 88 metric tons dry solids per hectare.
72
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TABLE 26. Physical Characteristics of Soils Before and After
Sudan Grass Cultivation in the Outdoor Plot Studies
Intrinsic Permeability Hydraulic
Sludge/Soil Type and with Water - K'w Conductivity - K
Sludge Application Bate (cm*) (cm/sec)
(tons dry solids/acre) Pre-Gro Post-Gro
1
pH Of
Mixture*
Control
100% Warden Silt
Loam (WSL)
Digested
and WSL
10
Lime Treated 10
and WSL
Digested
and WSL
40
Lime Treated 40
7.25xlO~9 7.98xlO~9
8.70xlO~9 9.43xlO~9
1.81xlO~8 1.96xlO~8
4.57xlO~8 5.22xlO~8
5.95xlO~8 6.60xlO~8
Field Capacity
of Mixture5
(% of soil dry wt.)
Pre-Gro Post-Gro Pre-Gro Post-Gro Pre-Gro Post-Gro Pre-Gro Post-Gro
8.56xlO~4 9.42xlO~4 1.0
1.1
6.7
6.5
1.02xlO~3 1. llxlO"3
2.14X10"3 2.31xlO~3
5.39xlO~3 6.16x10 3
7.02xlO~3 7.79xlO~3
22
23
1.2
2.5
6.3
8.2
1.3
2.7
7.2
9.1
6.6
7.3
6.6
8.0
6.3
6.8
6.7
6.8
25
28
23
32
24
30
26
34
1. Control plot received recommended chemical fertilizer application instead of sludge.
2. Lime treated sludge was a mixture of primary sludge and trickling filter humus.
3. Ratio of the hydraulic conductivity of the sludge/soil mixture (K,,,) to that of the
control (KC) before the growth cycle.
4. Soil pH measured in water.
5. 1/3 bar percentage.
-------
FIGURE 29. Sudan Grass Harvesting Operation
A slight decrease in soil- pH was observed in the samples
collected after the Sudan grass was harvested.
Field capacity varied slightly between the beginning and the
end of the growth study. No general trend could be established
and the variations in most cases were not significant.
The results from analysis of macro- and micronutrients in the
outdoor plots before and after plant growth are shown in
Table 27. Increases in the nutrient concentrations resulted
from the application of sludges at the rate of 88 metric tons
dry solids per hectare.
The average maximum plant heights and green tonnage yields of
the Sudan grass grown in this study are summarized in Table 28.
74
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TABLE 27. Macro- and Micronutrient Concentrations in Outdoor
Plots Before and After the Outdoor
Sludge Type and
Application Rate
(tons dry solids/acre)
Control*
Digested 10
Lirae Treated8 10
Digested 40
Line Treated0 40
•J
m
Sludge Type and
Application Rate
(tons dry solids/acre)
Control*
Digested 10
Lime Treated8 10
Digested 40
Lime Treated8 40
Nitrate-N (ppm)
Pre-Gro
2
25
84
63
87
Sodium
Pre-Gro
66
66
88
110
110
Post-Gro
12
19
6
7
15
(ppra)
Post-Gro
33
40
33
40
40
Phosphorus (ppm)
Pre-Gro Post-Gro
26 29
33
43
56
104
Iron
Pre-Gro
21
28
32
44
45
32
26
132
180
(ppm)
Post-Gro
40
52
54
73
70
Potassium
(ppm)
Pre-Gro Post-Gro
340
3SO
280
460
460
Manganese
300
220
180
270
300
(PPM)
Pre-Gro Post-Gro
9
13
14
27
23
16
49
82
93
110
Sulfur
Pre-Gro
5
15
22
58
54
Boron
Pre-Gro
0.3
0.4
0.4
0.6
0.5
Growth Study
(ppm)
Post-Gro
6
10
7
16
17
(ppn)
Post-Gro
0.5
0.5
0.4
0.7
0.7
Magnesium (ppm)
Pre-Gro
216
216
228
252
216
Copper
Pre-Gro
10.0
1.5
1.7
2.9
1.5
Poat-Gro
166
180
180
192
180
(ppro)
Post-Gro
1.1
2.5
2.6
8.8
6.0
Calcium (ppm)
Pre-Gro Post-Gro
1320 960
1280 960
1600 1140
1600 1240
2160 1560
Zinc (ppm)
Pre-Gro Post-Gro
18.5 4.2
11.5 16.5
12.0 14.8
30.0 68.0
15.0 SO.O
Control plot received optimum chemical fertilizer application instoad of sludge.
U
Line treated sludge was a mixture of primary and secondary sludge.
-------
TABLE 28.
Average Maximuin Plant Heights and
Tonnage Yields of Sudan Grass Grown
in Outdoor Plots
Test Plot
Control (no sludge)
Digested Sludge
22 metric tons dry solids/hectare
88 metric tons dry solids/hectare
Lime Stabilized Sludge
22 metric tons dry solids/hectcre
88 metric tons dry solids/hectcre
117
132
89
132
AVERAGE
HEIGHT
in
26
46
52
35
52
YIELD
m. tons/ tons/
hectare acre
11.77
20.35
24.20
17.16
25.96
5.35
9.25
11.00
7.80
11.80
The Sudan grass growth on the plots which received sludge
applications was more luxuriant than on the control plot which
received only an optimum application of chemical fertilizer.
Figures 30, 31, and 32 show the test plots 1 month into the
growth cycle. On the plots which received 22 metric tons dry
solids per hectare, the grass reached average heights of 117 cm
(46 inches) with digested sludge applied and 89 cm (35 inches)
with lime-stabilized sludge applied. The grass which received
lime-treated sludge had a yellowish tinge while the grass in
the digested sludge plot had a healthy dark green appearance.
In each of the plots which received 88 metric tons dry solids
per hectare of digested and lime-stabilized sludge, the grass
grew to a height of 132 cm (52 inches). The plants in both
of these plots appeared dark green and healthy.
Results from macro- and micronutrient content analyses of
Sudan grass are shown in Table 29. These results indicate
that the amount of nutrients concentrated in the plant tissue
was independent of the amount or type of sludge applied to the
land in which the plants were grown. Also, there were no indi-
cations of buildup of significant amounts of nutrients in the
plant material with the exception of calcium and iron which
did show concentration increases over those in the chemically
fertilized control plot.
76
-------
Control Plot - Chemical Fertilizer Only
• • *
Plot #2 Digested Sludge Applied at 22 Metric Tons/Hectare
FIGURE 30. Sudan Grass After 1 Month Growth
Period on Outdoor Plots
77
-------
Lime-Stabilized Sludge Applied at 22 Metric Tons/Hectare
Digested Sludge Applied at 88 Metric Tons/Hectare
FIGURE 31. Sudan Grass After 1 Month Growth
Period on Outdoor Plots
78
-------
Lime Stabilized Sludge Applied at 88 Metric Tons/Hectare
FIGURE 32. Sudan Grass After 1 Month Growth
Period on Outdoor Plots
TABLE 29. Macro- and Micronutrient Concentrations in
Sudan Grass Tissue From Outdoor Growth Study
Sludge Type & Nitrate P K Mg
Application Rate Nitrogen Phosphorus Potassium Sulphur Magnesium
Control
Digested
Lime Treated2
Digested
Lime Treated2
Control1
Digested
Lime Treated
Digested
Lime Treated
800 .5
10 100 .47
10 0 .52
40 600 .48
40 500 .42
Ca Na Fe
Calcium Sodium Iron
% % ppm
.52 .06 370
.77 .09 530
.80 .22 1800
1.00 .10 640
.95 .09 1850
3.05
3.20
2.85
2.75
2.37
Mn
Manganese
ppm
48
34
55
40
38
.24 .40
.19 .41
.14 .42
.15 .44
.16 .42
B Cu Zn
Boron Copper Zinc
ppm ppm ppm
7.0 10.5 66
7.0 11.0 80
9.5 8.5 50
8.0 12.0 50
7.5 6.5 34
1. Control plot received recommended chemical fertilizer application
instead of sludge.
2. Lime-treated sludge was a mixture of primary and secondary
sludge.
79
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DESIGN AND COST CONSIDERATIONS
PROCESS DESIGN
Based upon this work, it appears that the two most important
process variables which must be considered are pH and contact
time. Results indicate that the lime dose to the raw sludge
should be sufficiently high to initially attain pH>12.0.
Moreover, the lime dose should be high enough to prevent
significant pH decay during storage. In the laboratory and
pilot plant work conducted in this program, short term (1 hour)
lime-sludge contact at pH>12.0 provided excellent reductions
in viable pathogenic bacteria, but upon storage pH was subject
to decay. Therefore, in practice, excess lime should be added
to maintain the desired pH level during storage.
The lime dose required to achieve and maintain high pH levels
will vary considerably among different types of sludges, and
even for the sludge produced at a specific treatment plant,
the required dose will probably be subject to temporal varia-
tions. The quantity of lime required to achieve the desired
condition in any particular sludge can be determined easily
in the laboratory. Sludge samples of a known volume can be
titrated with a lime slurry until the desired pH level is
achieved. Sludge samples dosed with the minimum lime addition
required to reach the desired pH and others dosed with increas-
ing multiples of this amount could then be stored and pH decay
observed over a period of time. By using this procedure a good
indication of the lime dose required to attain and maintain the
desired conditions could be obtained. A full scale process can
be designed with automatic process control equipment.
A possible process flow scheme is shown in Figure 33, The
process flow is basically the same as that used in the pilot
plant operated for this study. The main variations are pro-
visions for automatic process control and the capability for
adding excess lime in the sludge-lime contactor.
Process operation consists of introducing sludge into a mixing
vessel where lime slurry is added. The pH level of the sludge
in this vessel is continuously monitored and lime slurry
addition automatically altered when the pH deviates from the
setpoint. Sludge whose pH had been, elevated to the desired
level is continuously passed from the mixing vessel to a
sludge-lime contactor. This contactor is also mixed and the
excess lime required to prevent pH decay is added at this
point. The quantity of excess lime is a specified multiple
of the dose being added in the sludge-lime mixing vessel.
This lime feed system provides positive process control since
80
-------
CatOH)2
SLURRY
.STORAGE
NO. 1
CaiOH)2
SLURR?
FEED
PUMP
NO. 2
Ca(OH)2
SUJRRY
FEED
PUMP
RAW SLUDGE
SLUDGE/
Ca(OH>2
MIXING
VESSEL
pH MONITOR
AND RECORDER
STABILIZED SLUDGE
TO THICKENER,
STORAGE. OR
IMMEDIATE DISPOSAL
FIGURE 33, Lime Stabilization Process Conceptual Flowsheet
lime additions in the mixing vessel vary in accordance with
temporal variations in sludge chemical demand. The addition
of excess lime to maintain desired conditions is directly
tied to the lime dose added in the mixing vessel.
Since an air agitation type mixing system was successfully
used in pilot plant operations both in this study and in
Farrell's work,1 this type of mixing is recommended for
further applications of the process. Air agitation provides
adequate mixing without the blade or paddle fouling problems
commonly encountered in mechanical sludge mixers. Also, air
agitation avoids development of high shear forces which could
tend to homogenize the sludge and cause dewatering problems.
No efforts were made to optimize the air mixing technique
in this program. Optimization of mixing may be an important
part of future process development work.
Lime addition is best accomplished by slurry feed. Dry
hydrated lime (Ca(OH)2) is preferred over quicklime (CaO) for
many reasons. Hydrated lime has superior storage characteristics
to those of quicklime. With dry storage, hydrated lime may be
kept for a period of up to 1 year without serious deterioration
of chemical activity. Quicklime, however, has a gueat affinity
for either carbon dioxide or water, and under improper con-
ditions of storage and handling, quicklime will air slake.
This phenomenon is caused by absorption of moisture and carbon
dioxide from the atmosphere and results in physical swelling,
decrepitation, and a marked loss of chemical activity. Because
81
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of gradual absorption of moisture from the atmosphere, 60 to
90 days is the usual limit for storage of quicklime in bags.
In small treatment plants where operating manpower is limited,
hydrated lime is the preferred form because of its ease of
handling. Since its solubility in water is so low, lime is
never fed in solution form. Instead a suspension of lime in
water is made, and the lime is fed to the waste in slurry form.
The obvious advantages of slurry feed are (1) easy transport
to the point of application, (2) better dispersion of the lime
in the waste when mixed, and (3) prewetting of the lime in the
feeder where agitation assures that all the particles are
wet thus preventing settling out in the reaction tank. Pro-
portioning feed pumps of the diaphragm or piston type are
capable of high accuracy and can be adapted to feed slurries.
Proportioning pumps are also easily adapted for use with inte-
grated instrumented control which is desirable since it provides
optimum process performance and efficiency of chemical usage.
Another disadvantage of using quicklime is that it must be
slaked (hydrated) before it is fed to the waste. Slaking
is generally accomplished in special mechanical equipment
operating at temperatures of from 180 to 210°F. The slaking
operation may take 30 minutes or slightly more to reach comple-
tion. This extra operation will introduce additional capital
and operating expenses into the overall treatment process.
Hydrated lime may be added directly to the water in the lime
slurry mixing tanks and no special processing steps are required
when using hydrated lime.
PROCESS COSTS
Cost estimates for a lime stabilization process must be based
on laboratory and pilot plant information. Lime costs may be
easily and accurately estimated from chemical dose data from
laboratory and pilot plant work. The chemical cost estimates
made in this section were based on a hydrated lime cost of
$22 per metric ton ($20 per short ton). Operating and
maintenance (O&M) costs were estimated from a similar process
at South Lake Tahoe which uses lime slurry feed.16 A break-
down of those O&M costs is shown below:
COSTS ($/Metric
Ton Sludge Solids)
Electricity $0.76
Operating labor 4.32
Maintenance labor 1.22
Repair materials 0.44
Other operating costs
not included above
Total estimated O&M costs
82
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The $0.26 included under "other operating costs..." was added
to account for sludge pumping and mixing costs which would have
been excluded otherwise. For a 37,850 m3/day (10 MGD) sewage
treatment plant which produces a total sludge flow of approxi-
mately 255 m3/day (67,000 gallons per day), the total capital
cost of a lime stabilization process would probably be less
than $8000. This cost includes tankage, piping, chemical
feed system, and automatic control instrumentation. This
cost is too small to be financed by a bond issue and would
probably be paid directly from an account set to finance such
low cost improvements of municipal facilities. Since capital
costs are considered insignificant, the major cost of the lime
stabilization process would be O&M costs which, as stated
above, would amount to approximately $7.00 per metric ton of
sludge solids treated.
From his work in Ohio, Farrell, et al.l estimated that lime
addition to an alum-primary sludge cost an average of $4.95
per metric ton sludge solids. By adding the O&M costs
developed previously to this chemical cost, a total O&M cost
estimate of $11.95 per metric ton sludge solids was obtained
Farrell, et al.1 also found that iron primary sludges had an
average lime cost of $2.50 per metric ton sludge solids.
Therefore, total O&M in this case would be about $9.50 per
metric ton sludge solids. The amount of lime applied to the
sludges in this study was, in general, the minimum dose
required to raise pH to 11.5. Excess lime to maintain pH
above a specified level was not added.
O&M cost estimates based on the work done by Paulsrud and
Eikum12 were also developed for.comparison purposes. The
dose required and the estimated costs for lime stabilization
of various types of sludges are summarized in Table 30. The
recommended lime doses are those required to maintain pH^ll.O
in sludges stored for 14 days at 20°C. The total estimated
O&M costs using these recommended lime doses range from $9
to $19 per metric ton sludge solids. These results indicate
that treatment costs will be mainly dependent on chemical
requirements which will vary with the type of sludge being
treated and the chemical pretreatment history of the sludge.
Process costs developed from the results of this program agree
with those developed from the results of the other investi-
gators. Chemical cost estimates were based on an average
lime dose of 150 g CafOHJj/kg sludge total solids required
to achieve pH^12.0 and maintain that level for 1 hour. Lime
costs in this case were found to be $3 per metric ton sludge
solids, so that estimated total O&M costs would be $10 per
metric ton sludge solids.
83
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00
*»•
Type of Sludge
Primary sludge
Septic tank sludge
Biological sludge
Al-sludge
(Secondary precipitation)
Al-sludge
(Secondary precipitation
+ Prim, sludge
-------
PROCESS APPLICATIONS
There are several situations where application of the lime
stabilization process could be advantageous. Small treatment
plants which do not produce large quantities of sludge and have
access to land for disposal by spreading could certainly use a
simple, reliable, and inexpensive sludge treatment process.
Another possible strategy, as suggested by Paulsrud and Eikum,12
is for small treatment plants to use lime stabilization as a
prepatory step for sludge storage. The stored, lime-treated
sludge would be periodically hauled away to larger facilities
for further treatment and/or disposal.
For plants which utilize digestion and do not have excess
digester capacity, lime treatment may provide a satisfactory
means of stabilizing sludge prior to ultimate disposal. Sludge
flows in excess of digester capacity could be bypassed to a
separate lime treatment facility. Another option would be to
use existing digesters to thicken lime-treated sludge prior to
dewatering or disposal.
Lime stabilization could also be used as a stop-gap technique
when digesters or other sludge treatment processes temporarily
are not working. in this context, lime stabilization would
be used as an emergency back-up process. A temporary lime
treatment process could be set up using the basic flow scheme
presented in Figure 6. in a temporary process, sludge pH
could be manually monitored on a periodic basis and the lime
dose adjusted as required. Alternatively, if sludge were
being hauled away regularly by tank truck, lime could be
injected into the sludge as it was pumped into the truck.
This technique was tried during the course of this program
and was found to work quite well. The septic tank truck used
to haul and spread lime-treated sludge on the outdoor plots
used a vacuum system for sludge loading. A vacuum was taken
on the truck tank and sludge was pulled into the tank. The
technique used to^inject lime slurry into raw sludge as it
was being loaded into the tank was quite simple. A suction
line with a 1/2 inch ball valve for slurry metering was
attached to an existing threaded opening in the tank sludge
loading port. Then, when suction was applied, both sludge
and lime slurry were pulled into the tank. Mixing occurred
at the point of slurry injection and during transport to the
outdoor plots. Composite samples were taken during sludge
spreading operations and were found to be at a pH of 12.2.
This technique of lime addition could easily be applied for
lime stabilization during emergency operations.
85
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REFERENCES
1. J. B. Farrell, J. E. Smith, Jr., S. W. Hathaway, R. B. Dean,
"Lime Stabilization of Primary Sludges," Journal Water
Pollution Control Federation, 46, 1, 113-122, January 1974.
2. M. L. Riehl, H. H. Weiser, B. T. Rheins, "Effect of Lime-
treated Water on Survival of Bacteria," Journal American
Water Works Association, 44, 5, 466-470, May 1952.
3. W. 0. K. Grabow, N. A. Grabow, J. S. Burger, "The Bacteri-
cidal Effect of Lime Flocculation Flotation as a Primary
Unit Process in a Multiple System for the Advanced Purifi-
cation of Sewage Works Effluent," Water Research, 3, 12,
943-953, December 1969. ~
4. J. c. Buzzell, Jr., C. N. Sawyer, "Removal of Algal Nutrients
From Raw Wastewater With Lime," Journal Water Pollution
Control Federation, 39, 10 (Part 2), R 16, October 1967.
5. S. A. Black, W. Lewandowski, "Phosphorus Removal by Lime
Addition to a Conventional Activated Sludge Plant," West
Ontario Water Resources Commission, Div. Res. Pub. No. 36,
1969.
6. S. M. Morrison, K. L. Martin, "Lime Disinfection of Sewage
Bacteria at Low Temperature," paper presented at the
International Symposium on Research and Treatment of
Wastewaters in Cold Climates, University of Saskatchewan,
Saskatchewan, Canada, August 1973.
7. "How Safe is Sludge?" Compost Science, 10-12, March-April
1970.
8. S. C. Evans, "Sludge Treatment at Luton," Journal Institute
of Sewage Purification, Part 5, 381-390, 1961.
9. E. H. Trubnick, P. K. Mueller, "Sludge Dewatering Practice,"
Sewage and Industrial Wastes, 30, 11, 1364-1368, November
1958.~~ —
10. C. B. Doyle, "Effectiveness of High pH for Destruction of
Pathogens in Raw Filter Cake," Journal WPCF, 39, 8, 1403,
October 1967.
11. H. Sontheimer, "Effects of Sludge Conditioning with Lime
on Dewatering," Proceedings of Third International
Conference on Water Pollution Research, Munich, 1966.
Published as "Advances in Water Pollution Research," 2,
165-194, WPCF, Washington, DC, 1967.
86
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12. Unpublished data, B. Paulsrud and A. S. Eikum, Norwegian
Institute for Water Research, P.O. Box 333, Oslo, Norway,
April 1974.
13. B. A. Kenner, G. K. Dotson, J. E. Smith, Jr., "Simultaneous
Quantitation of Salmonella Species and Pseudomonas
aeruginosa," EPA, National Environmental Research Center,
Cincinnato, OH, September 1971.
14. Standard Methods for the Examination of Water and Wastewater,
13th Edition, published by the American Public Health Associa-
tion, American Water Works Association, and the Water Pollu-
tion Control Federation, Washington, DC, 1971.
15. Methods of Soil Analysis, edited by C. A. Black, D. D. Evans,
J. L. White, L. E. Ensminger, F. E. Clark, American Society
of Agronomy, Madison, WI, 1965.
16. R. L. Gulp, G. L. Gulp, Advanced Wastewater Treatment,
Van Nostrand Reinhold Company, New York, 1971.
87
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-670/2-75-012
2.
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
LIME STABILIZED SLUDGE: ITS STABILITY AND
EFFECT ON AGRICULTURAL LAND
5. REPORT DATE
April 1975; Issuing Date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Gary A. Counts and Alan J. Shuckrow
9. PERFORMING ORG -VNIZATION NAME AND ADDRESS^
Battelle Memorial Institute
Pacific Northwest Laboratories
P.O. Box 999
Richland, Washington 99352
10. PROGRAM ELEMENT NO. '
1BB043;ROAP-21ASD;Task-16
11. CONTRACT/GfiXKTCNO.
68-03-0203
12. SPONSORING AGENCY NAME AND ADDRESS
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
16. SUPPLEMENTARY NOTES
16. ABSTRACT
w«,,1 the lime stabilization of municipal sewage sludge
was first developed and then evaluated. The primary objectives of this
hTT"6^-^ t0 ^efmine the de*ree of stability induced In a sludge
by lime addition and (2) to determine the effects of spreading lime-
stabilized sludge on agricultural land. Lime doses and contact times
required to eliminate the pathogenic bacteria and odors from a raw
sludge were determined by laboratory studies, and the information
obtained was translated into design and operational parameters for a
pilot scale, continuous flow process. Physical, chemical, and biologi-
cal characteristics of both the raw and stabilized sludges were measured
Soil and crop studies, both in a greenhouse and on condoled Sutt"r
plots, were performed to determine the effects of spreading lime-
Z E"ective lime stabilization of sludgers Lcom-
^__^« v.w ooaw.L.L.Lz.e x.u «:g or siuage solids. The average amount
estimated to be $10 per metric ton. 10n were
17- KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Calcium hydroxides
Sludge disposal
Disinfection
Odors
Odor control
b.lDENTIFIERS/OPEN ENDED TERMS
Sludge treatment
Sludge stabilization
Lime treatment
Liquid phase lime demands
Solid phase lime demands
Agricultural land
Crop response
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report}
UNCLASSIFIED
20. SECURITY CLASS (This page)
UNCLASSIFIED
c. COSATI Field/Group
13B
21. NO. OF- PAGES
98
22. PRICE
88
# U. S. GOVERNMENT PRINTING OFFICE:! 1975-657-592/5353 Region No. 5-11
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