EPA-600/2-78-015
February 1978
Environmental Protection Technology Series
INVESTIGATIONS OF HEAT TREATMENT FOR
PAPER MILL SLUDGE CONDITIONING
Industrial Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and appfication of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. tnteragency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-015
February 1978
INVESTIGATIONS OF HEAT TREATMENT
FOR PAPER MILL SLUDGE CONDITIONING
by
Duane W. Marshall
Frank C. Fiery
National Council of the Paper Industry
for Air and Stream Improvement, Inc.
Central-Lake States Regional Center
Kalamazoo, Michigan 49008
Russell 0. Blosser
National Council of the Paper Industry
for Air and Stream Improvement, Inc.
New York, New York 10016
Grant ^o. R-803347-01
Project Officer
Victor J. Dallons
Industrial Pollution Control Division
Industrial'Environmental Research Laboratory
Corvallis, Oregon 97330
INDUSTRIAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Industrial Environ-
mental Research Laboratory, U.S. Environmental Protection Agency,
and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation
for use.
11
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FOREWORD
When energy and material resources are extracted, processed, converted,
and used, the related pollutional impacts on our environment and even on
our health often require that new and increasingly more efficient pollution
control methods be used. The Industrial Environmental Research Laboratory -
Cincinnati (IERL-C1) assists in developing and demonstrating new and im-
proved methodologies that will meet these needs both efficiently and econo-
mically.
Sludges produced by pulp and paper mills and biological treatment of
their waste streams need to be disposed of in a dewatered and environmentally
sound state. Sludge dewatering is made easier by conditioning. Discussed
herein is thermo-conditloning of pulp and paper mill sludges including pro-
cess, chemical, and biological sludges. This paper is useful to those eval-
uating sludge dewatering alternatives and the sludge conditioning methods
to be employed. For more information contact the Food and Wood Products
Branch of the Industrial Pollution Control Division.
David G. Stephan
Director
Industrial Environmental Research Laboratory
Cincinnati
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ABSTRACT
The capability of oxidative and nonoxidative heat treatment
processes for the conditioning of hydrous sludges originating in
pulp and paper industry manufacturing or wastewater treatment
operations was defined on the basis of laboratory scale investi-
gation. Sludges employed in the study included (a) alum water
treatment sludge, (b) groundwood fines, (c) alum-coagulated bio-
logical solids and (d) waste activated sludge. The benefit of
acid assisted oxidative conditioning of the latter was also
assessed. Results were related in terms of improved filtration
properties, the extent and significance of solids solubilizatioh
and the resulting impact on filtrate quality.
IV
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CONTENTS
Foreword iii
Abstract iv
Figures vi
Tables ix
Acknowledgments xi
1. Introduction 1
Characterization of Thermal Conditioning
Regimes , 1
Responses to Process Variables 4
Further Considerations 14
2. Conclusions 18
3. Recommendations 20
4. Experimental Procedures .... * 21
Analytical Methods 21
Equipment Description and Operation 24
Raw Sludge Characterization and Processing . . 29
5. Results 32
Waste Activated Sludges 32
Acid Assisted Oxidative Conditioning 42
Chemical Based Sludges 48
Groundwood Fines 57
5. General Discussion 64
Liquor Treatability 64
Cost Considerations 65
Operational Concerns 67
References 69
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FIGURES
Number Page
1 Impact of sludge oxidation upon filterability .... 3
2 Response of sludge filterability to nonoxidative
thermal conditioning 5
3 Response of sludge filterability to oxidative
thermal conditioning 5
4 Reactive solids 8
5 Impact of solids hydrolysis upon sludge
filterability 8
6 Increase in filtrate COD resulting from heat induced
sludge hydrolysis 10
7 Increase in filtrate BOD resulting from heat induced
solids hydrolysis 10
8 Effect upon filtrate nitrogen of heat induced solids
hydrolysis 12
9 Effect upon filtrate phosphorus of heat induced
solids hydrolysis 12
10 Effect on the specific resistance by varying the pH
in heat treatment 15
11 Comparison of laboratory scale Wetox and Zimpro
processes for wet oxidation of sewage sludge ... 15
12 Biological sludge filterability characteristics ... 22
13 Relationship of specific resistance to capillary
suction time 23
14 Sensitivity of filtration parameters to sludge
consistency for well-conditioned sludges 23
15 Autoclave utilized for thermal conditioning 25
VI
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FIGURES
(continued)
Number Page
16 Schematic diagram of thermal conditioning apparatus . 27
17 Filtration response as a function of conditioning
time 33
18 Sludge filterability response to thermal conditioning 38
19 Significance of solids hydrolysis to sludge filter-
ability 41
20 Effect of solids hydrolysis upon filtrate COD .... 43
21 Correlation of filtrate COD-BOD concentrations ... 43
22 Effect of incremental acid addition upon pH 45
23 Sludge filterability response to acid assisted oxida-
tive conditioning 47
24 Significance of solids solubilization to the filter-
ability of sludge exposed to acid assisted
oxidative conditioning 49
25 Effect of solids solubilization upon the COD of
sludge filtrates following acid assisted oxidative
conditioning 51
26 Relative COD-BOD concentrations in filtrates from
sludges after acid assisted oxidative conditioning 51
27 Impact of volatile solids solubilization upon the
dewatering properties of alum coagulated biological
solids after heat treatment 55
28 Relationship between filtrate COD and volatile solids
solubilization resulting from the thermal condi-
tioning of alum coagulated biological solids ... 58
29 Correlation of BOD/COD for filtrates resulting from
the thermal conditioning of alum coagulated bio-
logical solids 58
30 Impact of solids solubilization on the filterability
of thermally conditioned groundwood fines 61
vii
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FIGURES
(continued)
Number Page
31 Correlation of BOD/COD for filtrates from thermally
conditioned groundwood fines 63
32 Significance of plant capacity to costs 66
33 Significance of sludge consistency to plant costs . . 66
vin
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TABLES
Number Page
1 Raw Sludge Characteristics 30
2 Sludge Filterability Response to Oxidative Condition-
ing 34
3 Sludge Filterability Response to Nonoxidative Condi-
tioning 36
4 Filter Leaf Results with Thermally Conditioned
Biological Sludge 39
5 Comparison of Solids Hydrolysis and Filterability . . 40
6 Corresponding Changes in Sludge Volatile Solids and
Filtrate COD 44
7 Sludge Filterability after Acid Assisted Oxidative
Conditioning 46
8 Corresponding Changes in Sludge Volatile Solids and
Filtrate COD Associated with Acid Assisted
Oxidative Conditioning 50
9 Filtration Properties of Alum-Coagulated Biological
Solids after Thermal Conditioning (Oxidative) ... 52
10 Filtration Properties of Alum-Coagulated Biological
Solids after Thermal Conditioning (Nonoxidative) . . 53
11 Filter Leaf Results with Thermally Conditioned Alum
Coagulated Biological Solids 54
12 Corresponding Changes in Sludge Volatile Solids and
Filtrate COD for Chemically Coagulated Aerated
Basin Residues Exposed to Thermal Conditioning ... 56
13 Filtration Properties of a Thermally Conditioned Alum
Water Treatment Sludge 59
IX
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TABLES
(continued)
Number Page
14 Filtration Properties of Groundwood Fines Following
Thermal Conditioning 60
15 Corresponding Changes in Sludge Volatile Solids and
Filtrate COD for Groundwood Fines Exposed to
Thermal Conditioning 62
x
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ACKNOWLEDGMENTS
It is appropriate to first point out here the contributions
of Mr. Frank Fiery, formerly Research Chemist with the Central-
Lake States Center, who was responsible for assembling the equip-
ment used in this investigation, as well as supervision of the
data collection effort.
Furthermore, the efforts of the NCASI technician staff,
especially those of Mrs. Denise Allen Trainer, Mrs. Marcia
Hubbard Sprague, Mr. Thomas McAlpine, and Mr. Jeff Marks, in
addition to the secretarial assistance of Mrs. Elizabeth Kavelman
and Cathy Clark was most appreciated.
Appreciation should also be extended to the following coop-
erating NCASI member companies for their assistance in providing
the hydrous sludges addressed in this study:
1. International Paper Company
2. Kimberly Clark Corporation
3. Proctor and Gamble
4. Westvaco Corporation
Finally, the support of this study by the Research and
Development Office of the United States Environmental Protection
Agency, and the assistance provided by the Project Officer,
Mr. V. Dallons, is gratefully acknowledged.
XI
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SECTION 1
INTRODUCTION
The wider application of high rate biological treatment, as
well as the technology proposed to meet evolving effluent stan-
dards, will amplify existing sludge disposal problems and broaden
the range of sludges requiring disposal to those of physical-
chemical origin. Included among the latter would be residuals
resulting from wastewater filtration or chemical coagulation Of
biologically treated effluents and process waters. Moreover,
hydrous sludges associated with primary treatment from certain
manufacturing operations, groundwood sludges for example, will
continue to pose tenuous problems.
The magnitude of sludge disposal difficulties has and con-
tinues to warrant several levels of investigation. To illus-
trate, surface properties of hydrogels have been investigated in
previous NCASI research conducted by Zettlemoyer (1). In addi-
tion, the significance of the polysaccharadic nature of cellular
components to water retention was the subject of a two-year study
sponsored by the National Council at the Institute of Paper Chem-
istry (2). Such fundamental knowledge is prerequisite to devel-
opment of new approaches to sludge dewatering. For the present,
the capability of known technologies for the conditioning and/or
dewatering of exceds sludges must be understood and considered as
an integral part of any waste treatment system. It is within
this context that this investigation of thermal processes for the
conditioning of hydrous sludges was carried out.
CHARACTERIZATION OF THERMAL CONDITIONING REGIMES
Nonoxidative Conditioning
If a hydrogel is sufficiently heated, bound water will be
liberated from within the gel framework. High temperatures
induce this phenomenon identified as syneresis by sufficiently
increasing molecular movement to overcome electrostatic repul-
sion. The increased internal contact of the gel's structural
elements will result in a breakdown of the hydrogel structure.
Lumb (3) reports that the temperature to achieve the full effect
with sludges ranges from 290° to 369°F (143° to 187°G). The
response of sludge constituents to hydrolysis reactions at those
conditions has been detailed by Brooks (4) and would indicate
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that mechanism to be of great significance to hydrogel destruc-
tion by thermal means.
Harrison's work (5) conducted at the Virginia Polytechnic
Institute indicates that maximum filter loading rates could be
attained at temperatures ranging from 347° to 365°F (175° to
185°C) corresponding closely with the 349.7°F (176.5°C) optimum
reported by Jepson and Klein (6). Brooks (4) and Harrison (5)
concur that filtration is not appreciably improved Until the
temperature is in excess of 266°F (130°C).
Results of Follett's investigation (7) are compatible with
the previously cited studies. At conditioning temperatures ap-
proaching 266°F (130°C), filterability was actually inferior to
the nonconditioned control. However, conditioning at 365°F
(185°C) effected dramatic improvement.
W. K. Porteus is credited with the initial patent of a heat
.conditioning process incorporating the aforementioned principles
and operating conditions over 35 years ago. Commercially avail-
able systems are characterized by reactor detention times of 30
to 40 minutes at temperatures from 338° to 401°F (170° to 205°C),
and corresponding pressures of 150 to 300 psi.
Oxidative Conditioning
In conjunction with syneresis and hydrolysis effects, de-
struction of the hydrogel structure characteristic of secondary
sludges may be further accelerated by thermal oxidation. In
theory, any organic compound can be oxidized in aqueous solution,
if sufficient energy in the form of heat and/or pressure is pro-
vided to complete the reaction.
Figure 1, developed from data collected in previous NCASI
study, parallels the results reported by others (8) in illustrat-
ing the impact of progressive sludge oxidation upon specific
resistance. Of note is the significant reduction in resistance
with only 10 to 15 percent oxidation. This should not be inter-
preted, however, as establishing oxidation as the dominant
mechanism. Such a degree of oxidation is accomplished in commer-
cially available equipment at temperatures from 300° to 400°F
(150° to 204°C) with associated pressures from 150 to 300 psi,
and detention times from 30 to 45 minutes.
The primary effect of low degrees of oxidation is hydrolysis
of the large macro-molecules to constituent compounds. The hy-
drolyses which break up the water binding protein and lipid
macro-molecules have been cited as a mechanism for the dramatic
increase in filterability at low degrees of oxidation (9).
As oxidation increases, the products of hydrolysis are found
in lower concentration, indicating that wet air oxidation
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TOTAL COD DECREASE (%)
Figure 1. Impact of sludge oxidation upon filterability.
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proceeds through hydrolysis followed by oxidation of the smaller
molecules to carbon dioxide and water. At high degrees of oxi-
dation only the more stable of the hydrolysis and oxidation pro-
ducts such as acetic acid remain (4). In commercial equipment,
high levels of oxidation are affected at temperatures of 450° to
600°F (232° to 315°C), corresponding pressures of 500 to 3000 psi
and detention times of 30 to 45 minutes.
From a sludge conditioning perspective, lower degrees of
oxidation are, in most cases, economically advantageous in com-
parison to higher degrees of oxidation (5). Though perhaps
possessing only a somewhat lower specific resistance, highly
oxidized sludges have a much smaller volume of residual solids
remaining for ultimate disposal. However, ash handling may pose
a problem for high oxidation systems. Observations have been
made that the resulting finely divided ash is not amenable to
vacuum filtration (10).
RESPONSES TO PROCESS VARIABLES
The overall response of sludges to thermal conditioning
must be understood in terms of the effects of variations in pro-
cess temperature, reaction time and operational regime upon the
extent of solids "destruction" and associated supernatant qual-
ity, as well as solids filterability. Observations documented
within the literature may be most appropriately related within
the framework of previous NCASI investigation (11) evaluating
such effects upon a waste activated sludge generated in the
treatment of wastewaters associated with bleached kraft/combined
NSSC manufacturing. That study was conceived:
1. To assess from a sludge conditioning perspective the
relative performance of oxidative and nonoxidative
processes over a broad temperature range.
2. To determine the magnitude of solids hydrolysis asso-
ciated with those processes and the resulting impact
upon organic strength, as well as nitrogen, and
phosphorous concentrations, contained in the heat
treatment liquors. Figures 2 through 9 are illus-
trative of results from that study.
Filtration Properties
Figures 2 and 3, respectively, illustrate the time-
temperature dependency of nonoxidative and oxidative conditioning
processes. The former figure demonstrates the benefit of greater
detention times at the specified reactor temperature. Compara-
tively, extending the retention time at a given temperature
proved to be of less benefit than conditioning at higher tempera-
tures. Similarly, Everett and Brooks (12) reported that a given
degree of conditioning was attainable in less time at greater
4
-------
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TOTAL REACTION TIME, MIN
Figure 2. Response of sludge filterability to
nonoxidative thermal conditioning.
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TOTAL REACTION TIME, MIN
Figure 3. Response of sludge filterability to
oxidative thermal conditioning.
-------
I O
temperatures. Within a temperature range of 350° to 400°F (177'
to 204°C) specific resistance was reduced to within 3 to 10 (10?)
sec^/gm, well into the range cited for successful filtration.
Values as low as 7.5 (106) were attainable at 500°F (260°C).
Little further benefit was seen at 600°F (315°C). However, the
practical benefit of conditioning at those elevated temperatures
would be dependent upon the relative economy of higher tempera-
ture reactors as opposed to expanded filter capacity. As shown
by Figure 3 dramatic improvement in sludge filterability by oxi-
dative conditioning was observed for even the lowest temperature
studied. While additional benefit to increasing the reaction
temperature to 315°F (157°C) is apparent, subsequent increase to
330°F (166°C) was of little further advantage. The conditioning
effects at 350°F (177°C) would appear to be less suitable were it
not for the fact that the resistance of the raw sludge used for
the 350°F (177°C) series was 60 percent greater than that of
those remaining sludges conditioned at temperatures less than
400°F (204°C).
The apparent departure for the results at 350°F (177°C)
illustrates the importance of original sludge composition. It is
reasonable to assert that original sludge characteristics other
than specific resistance are of undoubted significance to thermal
conditioning processes. As a consequence, extrapolation of
results for a given sludge to others will require caution. In
addition, the influence which the normal compositional variation
in sludges originating from a given source exerts upon predicta-
bility of process performance requires further study. Lacking
that predictability will require inherent process flexibility
most readily attainable by designing for operation over a span
of temperature conditions. At oxidative temperatures of 375°F
(191°C) and 400°F (204°C), sludge filterability worsened as
retention time was extended. Conditions associated with those
temperatures would appear to constitute a transition range in
which further alteration of the sludge structure is detrimental.
Experience reported by Everett (13) affirms the existence of a
minimum specific resistance, which varies for different sludge
types. He relates this phenomena to heat treatment effects upon
increased solubilization of sludge organic matter, citing that
having attained that minimum specific resistance, additional
solids solubilization will not further decrease specific resis-
tance; but, in fact, may increase it. Increasing temperatures to
450°F (232°C) did result in improvement in filtration properties
as reaction time was extended. However, results were not signi-
ficantly better than those observed at 350°F. It should be added
that original specific resistances for sludges conditioned at the
above three temperatures were of the same order of magnitude
[1000-1300(107) sec2/gm]. Considering the relative performance
of conditioning at those temperatures, it would appear that oxi-
dative conditioning beyond 350°F (177°C) is not of substantial
benefit to sludge filterability. In any event, within the tem-
perature range of 300° to 350°F (149° to 177°C), the same as
-------
quoted for low level wet oxidation, sludge specific resistance
was reduced to within (3 to 7) 107 sec2/gm.
Thus, nonoxidative and oxidative thermal conditioning pro-
cesses in temperature ranges of equipment currently available
were capable of reducing sludge specific resistance to similar
levels. At least from a sludge conditioning standpoint, the
processes would appear comparable. That is not to suggest that
the processes are or are not economically competitive, all
factors considered.
Solids Hydrolysis
A graphical comparison for each conditioning regime indi-
cated that the magnitude of solids hydrolyzed increased as a
function of time to some limiting value dependent upon the
reaction temperature. As shown by Figure 4, that limiting value
increased linearly with the reaction temperature. Furthermore,
at a given temperature up to 450°F (232°C), the quantity of
solids undergoing reaction by oxidative conditioning was approxi-
mately double that for the nonoxidative means. That relationship
assumes a reaction environment which is not oxygen limiting.
Where oxygen is limiting, solids available for reaction would
conceivably lie between the two curves. Sludge hydrolysis by
nonoxidative means is limited at temperatures up to 600°F (316°C)
to approximately"60 percent; whereas, hydrolysis by oxidative
conditioning would appear to be limited only by the volatile
content of the secondary sludge. The data would also illustrate
that solids hydrolysis exceeding 60 percent is of no further
benefit to sludge filterability.
Takamatsu (14), in his study of the thermal decomposition
kinetics of activated sludge, concluded that solids hydrolysis
could be approximated as a first order relationship, and, as
such, would be independent of initial sludge concentration. This
would corroborate previously reported data indicating that vola-
tile matter reduction is independent of sludge solids concentra-
tion (15). However, where the proportion of initial sludge sol-
ids available for reaction at a given temperature is greater, it
would follow that the required destruction of the hydrogel com-
ponents would be accelerated. Thus, because a greater fraction
of solids is available for reaction under oxidative conditions,
it is reasonable to expect that equivalent conditioning by oxi-
dative means, in contrast to nonoxidative, could be accomplished
at lower temperatures. Furthermore, the magnitude of solids
reacted could likely be regulated by extent of oxygen availabil-
ity.
The impact of solids hydrolysis upon filtration properties
is illustrated by Figure 5. The linear curves shown were devel-
oped for and are limited to results in which the magnitude of
sludge hydrolysis was 56 percent and less.
-------
80
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• NON OXIDATION
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300
400
500
600
TEMPERATURE *F
Figure 4. Reactive solids.
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SLUDGE SOLIDS HYDROLYZED (%)
Figure 5. Impact of solids hydrolysis upon sludge filterability,
8
-------
A similar relationship has been documented by Everett (13)
in his studies of the nonoxidative regime of conditioning. The
curves suggest that, conditioning by low level oxidative and non-
oxidative means to a specific resistance of 5 (107) sec2/gm,
would be accompanied by respective solids hydrolyses on the order
of 50 percent and 35 percent.
Supernatant Quality
Whatever the benefit of solids hydrolysis to filterability,
it is of additional consequence to the composition of sludge fil-
trates that require further processing prior to discharge to
receiving waters. Brooks (16) has concluded that the COD of heat
treatment liquors is proportional to the solids hydrolyzed. As
shown in Figure 6, a similar trend is indicated by the data
developed in this study where sludge solids hydrolysis does not
exceed 55 percent. A dramatic decline in liquor COD is apparent
at hydrolysis levels beyond 60 percent, a region limited to oxi-
dative conditioning. Results indicate that nonoxidative condi-
tioning of a 1 percent sludge within a temperature range of
350° to 400°F (177° to 204°C) would yield an increased filtrate
COD of approximately 4300 mg/liter. With oxidation at tempera-
tures of 300° to 350°F (149° to 177°C), filtrate COD for a simi-
lar sludge would be increased to 4800 mg/liter. High level
oxidation produced filtrate COD increases ranging from 2600 to
4000 mg/liter. For the entire range of nonoxidative condition-
ing, as well as oxidation reactions less intense than 450°F
(232°C) for 20 minutes, BOD constituted a relatively consistent
58 percent fraction of the measured COD.
Further, sludge oxidation under higher level conditions in-
creased that ratio to an average 74 percent. However, the ratio
was highly variable at sludge hydrolyses beyond 80 percent. At
those conditions, filtrate composition is no longer predominantly
a function of solids reactions, but rather filtrate oxidation. A
more direct comparison of measured BOD with solids hydrolysis is
presented in Figure 7. The pattern is comparable to the similar
relationship for COD with the notable exception that the decline
of filtrate BOD associated with high level oxidation is not so
dramatic.
Representative BOD concentrations observed for the low level
oxidation regime were approximately 3400 mg/liter, in comparison
with a 3000 mg/liter magnitude for nonoxidative conditioning in
the 350° to 400°F (177° to 204°C) range. High level oxidation
was intermediate. Thus, conditions for either process adequate
to reduce sludge specific resistance to a range of 3 to 10 (107)
sec2/gm would not yield heat treatment liquors with significantly
different BOD concentrations.
The cumulative effect of recycling thermal conditioning
liquors would impose an additional organic load of at least
-------
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4000
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® OXIDATION
• NON OXIDATION
40
60
80
100
SLUDGE SOLIDS HYDROLYZED (%)
Figure 6. Increase in filtrate COD resulting from
heat induced sludge hydrolysis.
- 4000
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2000
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• NON OXIDATION
20
40
60
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SLUDGE SOLIDS HYDROLYZED (%)
Figure 7. Increase in filtrate BOD resulting from
heat induced solids hydrolysis.
10
-------
20 percent upon the treatment system, assuming a sludge yield of
0.5 Ib solids/lb BOD. The subsequent costs for additional treat-
ment, as well as the associated additional sludge conditioning
capacity, must be considered in assessing costs of handling the
original sludge mass.
Results herein, and those of other investigators, imply that
concentrations of organics and other constituents in filtrates
associated with the thermal conditioning of a 1 percent consis-
tency sludge may be extrapolated to similar sludges of greater
consistency. Brooks (16), as well as Everett (15) , have demon-
strated that concentration of individual components in a heat
treatment liquor increased in proportion to the feed solids con-
centration. That result would also be corollary to the previ-
ously described first order kinetics.
The brown color characteristic of heat treatment liquors has
been attributed to high molecular weight compounds originating
from the high temperature combination of reducing sugars and
amino acids (4). Dark supernatant color persisted over the
entire spectrum of nonoxidative conditioning. However, with
oxidative conditioning at 400°F (204°C), supernatant color
evolved from dark brown to colorless as reaction time was in-
creased. Colorless supernatants were subsequently encountered
at more intense conditions.
Filtrate nitrogen concentrations, as shown in Figure 8,
increased dramatically with progressive solids hydrolysis. At
hydrolysis levels of 50 percent and greater, attainable by wet
oxidation, the concentration approached 270 mg/liter, approxi-
mately three-fourths of the available nitrogen. In the tempera-
ture range typical of nonoxidative conditioning processes,
filtrate nitrogen did not exceed 180 mg/liter. Thus, oxidation
would appear to return greater quantities of nitrogen.
In work since reported on, Everett (17) cites studies by
others indicating that nonoxidative conditioning of digested
sewage sludges released approximately 72 percent of the sludge
nitrogen. Considering the potential for differing degrees of
hydrolysis and the predigestion, such a result is not incom-
patible.
When exposed to conditions of heat treatment, bacterial
nucleic acids, which contain up to 50 percent of cellular phos-
phorous, may either polymerize into an amorphous mass or hydro-
lyze, releasing soluble phosphorous (9). For a given intensity
of conditioning, as manifested by sludge hydrolysis, filtrate
phosphorous concentrations associated with oxidative conditioning
consistently exceeded values observed for nonoxidation, as shown
by Figure 9. The oxidative environment or its chemical end
products apparently accelerates the solubilization of the phos-
phorous constituents in the sludge mass. Subsequent hydrolysis
11
-------
260
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OXIDATION
• NON OXIDATION
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20
40
60
80
100
SLUDGE SOLIDS HYDROLYZED (%)
Figure 8. Effect upon filtrate nitrogen of heat induced
solids hydrolysis
50
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10
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• NON OXIDATION
\ fl
20
40
60
80
100
SLUDGE SOLIDS HYDROLYZED (%)
Figure 9. Effect upon filtrate phosphorus of heat induced
solids hydrolisis
12
-------
to the orthophosphate form and reaction with such anions as cal-
cium would result in phosphate precipitation. An observation of
decreasing filtrate phosphorous concentrations was made in pilot
scale thermal conditioning of sludges generated in treatment of
lime neutralized wastewaters of sulfite mill origin (18). As
data in Figure 9 illustrates, the latter reaction appears to
dominate where conditioning intensity has resulted in respective
solids hydrolyses of 35 percent and 50 percent for the nonoxi-
dative and oxidative regimes.
Both oxidative and nonoxidative conditioning results in the
recycling of nitrogen compounds in excess of that required for
biological oxidation of the filtrate organic constituents/
assuming a required ratio of BOD to nitrogen of 20:1. Low level
oxidation yielded a 50 percent excess quantity of nitrogen,
whereas nonoxidative conditioning produced a 30 percent surplus
at temperatures associated with the 35 percent hydrolysis level.
Filtrates associated with low level oxidative conditioning con-
tained a quantity of phosphorous adequate to meet an assumed BOD
to phosphorous requirement of 100:1. However, nonoxidative con-
ditioning in the 350° to 400°F (177° to 204°C) range made avail-
able only half that quantity.
Summary
Malina (19) advances the major advantages of heat treatment
systems as the elimination of odor, elimination of the need for
chemical conditioning of sludges, and the production of a steri-
lized filter cake. Cited as major disadvantages are fuel re-
quirements necessary to sustain process temperatures, where
necessary, and the need for treatment of supernatant liquor.
Past investigation would suggest that solids hydrolysis
represents the principal mechanism for destruction of hydrogel
properties by both nonoxidative and low level oxidative thermal
conditioning. Both processes are capable of affecting equivalent
degrees of sludge conditioning, which, for a given sludge, is
dependent upon the magnitude of solids hydrolyzed.
The capacity of thermal conditioning processes to hydrolyze
sludge solids is predominantly a function of temperature, with
greater degrees of hydrolysis attainable in an oxidative environ-
ment. However, the capacity of temperatures within the range of
300° to 400°F (149° to 204°C) to decompose the hydrophilic sludge
constituents would appear to lend little justification from a
sludge conditioning perspective for further decomposition through
utilization of higher temperatures.
Heat treatment liquors associated with oxidative and non-
oxidative conditioning processes contain BOD concentrations of
significant and comparable magnitude. Liquors generated with the
processing of biological sludges of pulp mill origin contained
13
-------
nitrogen concentrations up to 50 percent greater than required
for their biological treatment. Low level oxidation contained
at best, phosphorous adequate only for biological assimilation
of the organic constituents contained therein. Liquors associ-
ated with nonoxidative conditioning or high level oxidation were
significantly deficient in phosphorous.
FURTHER CONSIDERATIONS
Incremental Benefits of Acid Hydrolysis
The conditioning of hydrous residues prior to dewatering has
been commonly approached by chemical means, with thermal pro-
cesses receiving only more recent widespread application, pre-
dominantly in the municipal treatment sector. However, it is
conceivable that the benefits of chemical energy could be ex-
tended by use in some optimum combination with thermal processes.
It would follow that a corresponding reduction in the necessary
intensity of thermal conditioning processes could be affected.
Accordingly, interest in acid hydrolysis in conjunction with
thermal conditioning processes has recently emerged.
Everett (20) reports that pH was found to have a marked
effect both on solubilization and specific resistance of sludges
exposed to nonoxidative conditioning. His results, showing
effects on the specific resistance of sludge by varying the pH
in heat treatment by sulfuric acid addition, are shown in
Figure 10- At 338°F (170°C) lowering the pH from 5.5 to 2.5
reduced the specific resistance by between two and three orders
of magnitude. At 356°F (180°C), a minimum specific resistance
was attained at a pH of 4.0. At a pH less than 4, specific
resistance increased, suggesting an "overcooking" phenomenon
only found previously at temperatures of 428°F (220°C) or more.
Everett attributed the benefit of acid addition to accelerated
sludge solubilization. However, Everett concedes that the oper-
ation of conventional, nonoxidative heat treatment equipment at
low pH would be difficult due to corrosion and other operational
problems.
Such a limitation would not apply to the same extent in
equipment conventionally applied to oxidative conditioning, due
to its inherent design for accommodating more corrosive environ-
ments. A similar benefit of acid addition to sludge oxidation
has been reported by Seto and Smith (21). As shown in Figure 11,
high level oxidation of sewage sludge is achieved at less intense
reactor temperatures with acid addition than without. Both the
rate and extent of sludge oxidation were reported to increase
with acid addition at an operating temperature of 450°F (232°C).
That is not to imply, however, any inherent benefit to the dewa-
terability of the residual solids at that temperatuere. More
importantly from a solids conditioning perspective, the question
remains as to the extent to which acceptable filtration
14
-------
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90
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(200°C)
0.0
0.5 1.0
REACTION TIME, HOURS
Figure 11. Comparison of laboratory scale Wetox
and Zimpro processes for wet oxidation of sewage
sludge [after Seto and Smith (19)].
15
-------
properties can be achieved with less intense reactor temperatures
than normally associated with low level oxidative conditioning.
Chemical Sludges
The literature is largely void of experience with the use of
thermal processes for the conditioning of chemical sludges.
Hudgens and Silveston (22) do describe results of studies with
high level wet oxidation for the destructive oxidation of mixed
chemical-biological sludges produced by chemical precipitation of
nutrients and other components in several conventional municipal
waste treatment plants. However, emphasis is given to the degree
of destruction of organic matter, and the fate of organic carbon
and phosphorous during progressive oxidation at temperatures of
450°F (232°C) or greater. Conditioning benefits at that and
lower levels require further assessment.
Conditioning of Cellulosic Residuals
From studies dealing with the relationship between the con-
stitution and dewatering properties of hydrous sludges, Attala
(2) infers that groundwood fines should be amenable to condition-
ing by conventional thermal conditioning means. In laboratory
studies, Khanh (23) is reported to have observed the complete
destruction of peat moss slurried in water during wet air oxida-
tion at temperatures between 450° to 550°F (232° to 288°C).
However, the conditioning of hydrous cellulosic fines at condi-
tions of lower intensity would seem less assured. Teletzke
et al. (9) cites that the cellulosic components of sewage sludges
are among the more resistant to degradation during wet oxidation,
a phenomenon which accounts for their beneficial presence in the
vacuum filtration of sewage sludges exposed to low level wet
oxidation. Thus, the capacity of low level thermal conditioning
processes to improve the filterability of groundwood fines would
seem in question.
Summary
The preponderance of investigative activity dealing with
the thermal conditioning of sludges has been concentrated upon
primary and secondary sludges resulting from conventional waste-
water treatment. Furthermore, those studies have typically been
oriented toward wastes of domestic origin. What little attention
that has been given to chemical sludges, or cellulosic residuals
for that matter, has been directed toward their thermal destruc-
tion in contrast to the potential conditioning benefits associ-
ated with less intense reactions.
Similarly, identification of the benefits of acid hydrolysis
in oxidative thermal processes has been limited to high level
destructive regimes. The documented benefit of acid hydrolysis
in reducing the intensity of nonoxidative conditioning necessary
16
-------
to maximize sludge filterability would seemingly warrant deter-
mination if such a result could be extended to low level oxida-
tive conditioning as well. Accordingly, it was the objective of
this study to assess such issues in the applicability of nondes-
tructive heat treatment techniques for the processing of waste
sludges anticipated from manufacturing and waste treatment oper-
ation associated with the pulp and paper industry. More speci-
fically, to:
1. Evaluate the capabilities of nondestructive heat
treatment for the conditioning of hydrous sludges
(a) from treatment of effluents from pulp and
paper manufacturing and (b) those from physical-
Chemical treatment of biologically treated efflu-
ents and process water treatment.
2. Determine the benefit of acid hydrolysis in re-
ducing the intensity of nondestructive oxidative
heat treatment for the conditioning of hydrous
sludges.
17
-------
SECTION 2
CONCLUSIONS
Hydrous groundwood fines and waste activated sludges associ-
ated with the treatment of wastewaters from pulp and paper manu-
facturing, inclusive of sludges resulting from chemical treatment
of biologically treated effluents, were all demonstrated to be
highly responsive to thermal conditioning. That was not the case
for alum based water treatment sludge. For waste activated
sludge, acid assisted oxidative conditioning offered only a very
slight, if any, advantage beyond that achieved with only a non-
oxygen limiting environment.
Improvement in sludge filterability is related to the solu-
bilization of sludge volatile constituents up to some optimum
solubilization level between 40 and 60 percent. Beyond that
degree of solubilization, a capability limited to oxidative con-
ditioning, solids dewaterability exhibited a classical reversion.
Oxidative conditioning in a nonoxygen limiting environment
poses no distinct conditioning advantage over nonoxidative pro-
cesses. In fact, in the case of alum coagulated biological sol-
ids, filter leaf tests confirmed results with conventional fil-
tration parameters showing that oxidative conditioning was less
effective than conditioning in the absence of oxygen. However,
the presence of oxygen accelerates the rate and extent of vola-
tile solids solubilization.
Regardless of the mode of conditioning or acid addition,
solubilization of activated sludge volatile constituents resulted
in an associated supernatant COD increase equivalent to approxi-
mately 50 percent of the mass of volatile solids hydrolyzed. The
corresponding ratio for the alum coagulated biological solids was
less, suggesting the possible importance of aeration system
sludge age to the character of the supernatant. The ratio of
filtrate BOD to COD for groundwood fines and waste activated
sludge including when acidified was 0.5 to 0.6—in comparison to
0.3 for the alum coagulated biological solids.
Heat treatment represents a viable means of conditioning the
most difficult of sludges. However, technical personnel at in-
stallations contemplating its use should be aware of (a) its im-
plications to significantly increased raw waste and color load
18
-------
and (b) such reported operational problems as corrosion, scale,
equipment maintenance and possible odor generation.
19
-------
SECTION 3
RECOMMENDATIONS
Existing evidence to suggest that the extent of thermal con-
ditioning is affected by sludge solids concentration suggests
the existence of an optimum consistency where combined thermal
and dewatering costs will be minimized. Definition of such a
limit will require further evaluation employing prototype equip-
ment for the dewatering of sludge thermally conditioned at
varying consistencies.
Though this study has identified the capabilities of thermal
processes for the conditioning of hydrous sludges, questions
remain regarding the relative extent to which those results can
be achieved with prototype equipment of existing proprietary
systems. Factors contributing to potential differences would
include the nature of reactor mixing, as well as heat and/or
oxygen transfer characteristics. Differences between available
alternative systems can be resolved only through comparative
pilot testing analagous to process performance studies proposed
by the Los Angeles/Orange Country Metropolitan area (46). The
conduct of such a program would also allow (a) assessment of day-
to-day variability in process performance, (b) detection of such
operational problems as scale, abrasion or plugging and (c) the
response of actual prototype dewatering equipment. Objective
cost comparisons would constitute an appropriate addition.
If thermal conditioning is to find application in the pulp
and paper industry, the penalty represented by the incremental
increase in raw waste and color load must be satisfactorily
dealt with. Its contribution to effluent character must either
be recognized in individual mill discharge permit limitations or
alternative measures must be found for the processing and ulti-
mate disposal of the waste liquors by means other than the waste-
water treatment system. For integrated mills, in-process dis-
posal options warrant a systematic, but cautious assessment.
20
-------
SECTION 4
EXPERIMENTAL PROCEDURES
ANALYTICAL METHODS
Filtration Properties
Capillary suction time (CST) as described by Baskerville
and Gale (24) was selected as a parameter by which sludge filtra-
tion properties were compared. In addition, where sludge volumes
permitted, sludge specific resistance, as proposed by Coakley and
Jones (25) was determined as an additional basis for comparison.
In doing so, a Whatman No. 2 filter media and a vacuum of 15
inches of mercury were utilized. Data analysis and computation
paralleled that proposed by Lutin (26).
A comparison of the two parameters for an unconditioned bio-
logical sludge over an array of solids consistencies is shown in
Figure 12. The comparison illustrates the linear dependence of
capillary suction time upon slurry consistency, whereas a differ-
ent order relationship is suggested for specific resistance.
However, specific resistance did not vary significantly over the
range of 1 to 2 percent solids consistency. Correlation of the
two dewatering indices is most conveniently made by comparing
capillary suction time with the product of specific resistance
and sludge solids concentration (24) , as graphically shown by
Figure 13. A near linear relationship is observed for capillary
suction times ranging from approximately 30 seconds to 125 sec-
onds. This corresponds to consistencies up to 2 percent.
It should, perhaps, be added here that such a dependence
upon slurry consistency was seen to deteriorate with highly con-
ditioned sludges, as illustrated in Figure 14, developed from
study data. It suggests that observations within the range of
consistencies encountered in this study were largely independent
of consistency. Everett (15) makes a similar observation for
thermally conditioned sludges at consistencies up to 8 percent.
In addition, specific resistance data previously collected by
the Council staff in the course of thermal conditioning pilot
studies conducted by others showed comparable values for sludges
evaluated at 1.4 and 7 percent solids consistency (18).
Nevertheless, in the determination of capillary suction time
(CST), consistencies were adjusted to the original consistency
21
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22
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Figure 14. Sensitivity of filtration parameters to
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23
-------
exposed to thermal conditioning where sample volumes permitted.
Reported values represent the average of three replicates.
Reported values for specific resistance are the result of a
single assessment conducted at conditioned sludge consistency.
Though specific resistance and capillary suction time are
useful means for comparing conditioning effects, they bear little
correlation with absolute dewatering performance on prototype
equipment. For instance, with vacuum filtration, unlike Buchner
funnel testing, forces of gravity and pressures of flow are
opposing. In addition, Buchner funnel results are not equally
dependent upon the cohesive or adhesive qualities of the filter
cake. As a consequence, for the two most prominent sludges
employed in this study, supplemental vacuum filter leaf testing
was conducted. Procedures are outlined in NCASI Technical Bulle-
tin 190 (27). In each case a 15-inch Hg vacuum was used.
Suspended Matter
Concentration of suspended matter contained in unconditioned
sludges was calculated as the difference between total and fil-
terable residue. Total residue was assessed by evaporating to
dryness a known sludge volume in a forced draft oven maintained
at 217°F (103°C). Filterable residue was determined by similarly
drying a filtrate sample obtained by filtering through a glass
fiber filter media sludge supernatant separated from the raw
sludge by centrifugation.
Suspended matter concentrations remaining in conditioned
sludges were evaluated by filtration of a known volume of sludge
through a Gooch crucible fitted with a glass fiber filter disc,
supplemented with Celite Filter Aid as outlined in NCASI Techni-
cal Bulletin 230 (28). In all cases, sludge volumes were mea-
sured by a cut-off pipette. Volatile matter was also assessed in
accordance with methods cited in Bulletin 230.
Organic Concentrations
Chemical oxygen demand (COD) of filtrates was determined in
accordance with Standard Methods (29). Biochemical oxygen demand
(BOD) of filtrates was evaluated by the direct dilution technique
outlined in NCASI Technical Bulletin No. 230.
EQUIPMENT DESCRIPTION AND OPERATION
Thermal conditioning of sludges was accomplished in a two-
liter magnedrive Autoclave, Model AFP-1005, manufactured by Auto-
clave Engineers, Inc. The basic autoclave unit is illustrated in
Figure 15.
Modifications to the basic autoclave unit to effect ease
and rapidity of sludge introduction and sample removal are
24
-------
ro
CT!
Figure 15. Autoclave utilized for thermal conditioning,
-------
illustrated in Figure 16. Valved openings into the autoclave
included a sludge inlet line extending to the bottom center of
the unit; a sampling line, open also from the bottom of the unit;
and a pressure relief valve located in the cover above the liquid
level. A non-valved protective rupture disc was also present in
the autoclave cover as a safety requirement. Pressure was moni-
tored via a 0-3000 psi Bourdon tube gage connected into the
autoclave cover. Temperature was monitored via a West Model
J30B1VS26 thermocouple introduced into a thermowell in the reac-
tor cover plate. Reactor temperature was subsequently displayed
on a thermocouple activated temperature indicator, West Model 1.
Reactor heating was provided by a 2.1 kilowatt jacket-type
electric heater regulated by a Barber Coleman Model 72C temper-
ature controller in conjunction with a Type K thermocouple.
Temperature excursions beyond preset levels were countered by
passing cooling water through the internal coil until temperature
was reduced.
A two-liter stainless steel Whitey pressure bomb preceded
the autoclave in the sample inlet line. A three-way valve at
the bottom of the bomb allowed the vessel to be evacuated or
permitted sludge to be forced into the autoclave. A three-way
valve at the top of the pressure vessel allowed sludge to be
drawn into the bomb after evacuation and subsequent pressuriza-
tion of the vessel via high pressure nitrogen or oxygen tanks.
Equipment operation consisted of five basic elements:
(1) autoclave preparation, (2) a preheating of sludge superna-
tant, (3) injection of the sludge sample, (4) withdrawal of
conditioned sludge samples at prescribed time intervals and (5) a
final washing of residual solids from the autoclave.
Autoclave Preparation
Prior to supernatant injection the pressure cylinder was
evacuated, filled with tap water, and repressurized with nitro-
gen. The autoclave was subsequently charged with the water and
further pressurized with nitrogen through the pressure cylinder.
After 2 to 5 minutes agitation, the autoclave was drained.
Supernatant Preheating
Having prepared and purged the autoclave, the pressure
cylinder was again evacuated, filled with 500 ml of sludge super-
natant and pressurized with nitrogen to 500 psi. The autoclave
was then charged with the supernatant and the residual nitrogen
bled off to achieve atmospheric pressure. The supernatant was
subsequently heated to a temperature approximately 90°F (32°C)
greater than the desired conditioning temperature.
26
-------
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High Pressure
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SLUDGE INLET AND
WASHING SECTION
SAMPLE LINE
WASHOUT CONTROL
Heat
Sample Out
SAMPLE COOLING
SECTION
Figure 16. Schematic diagram of thermal conditioning apparatus,
-------
Sludge Injection
During the preheating period, the pressure cylinder was
evacuated and filled with 1000 ml of sludge. The cylinder was
pressurized with either nitrogen or oxygen (dependent upon the
conditioning regime) to a pressure exceeding ultimate autoclave
pressure by 500 psi. Once having reached the desired preheating
temperature, the autoclave was charged with the sludge. After
an initial immediate temperature drop of 75° to 150°F (24° to
66°C) the desired conditioning temperature was established in
3 to 8 minutes and maintained there by periodic bursts of cold
water through the autoclave cooling coil. Unless otherwise in-
dicated, in subsequent discussion, reaction time is measured from
the point at which specified operating temperatures are attained.
Autoclave pressure was maintained at approximately 500 psi in
excess of the vapor pressure of water at the conditioning temper-
ature by either nitrogen or oxygen addition, dependent upon the
conditioning regime. In the case of oxidative conditioning, the
oxygen environment was restored at approximately five-minute
intervals.
Sample Withdrawal
At the conclusion of the conditioning period, the autoclave
sample valve was opened, allowing passage of a controlled volume
of the autoclave contents through the heat exchanger for subse-
quent collection and analysis. During the course of the study,
two approaches were taken in sample extraction, sequential and
complete.
In the sequential sampling mode, portions of the autoclave
contents were periodically removed at selected time intervals up
to one hour as the conditioning progressed. Prior to doing so,
the sample line was purged; and following the sample collection,
the heat exchanger portion of the sample line was flushed and
drained. Sequential sampling was utilized to determine relative
compositional characteristics of the autoclave contents with pro-
gressive conditioning. However, it was found to be inadequate
for assessing the concentration or mass of sludge/filtrate con-
stituents.
To do so for any given conditioning time, it was necessary
to completely remove the autoclave contents; that is, collect
the complete contents. This sampling mode was employed to deter-
mine solids and filtrate COD concentrations. In addition, the
availability of larger sample volumes permitted determination of
sludge specific resistance.
Autoclave Washing
At the conclusion of all sampling and removal of the auto-
clave contents, the autoclave was charged with 1800 ml of
28
-------
distilled water in a manner similar to autoclave preparation.
After 3 minutes agitation, the wash water was removed. In the
case of complete sampling, the wash water was collected and
analyzed for suspended and volatile solids concentrations.
RAW SLUDGE CHARACTERIZATION AND PROCESSING
Composition and filtration characteristics of the sludges
employed in this investigation are shown in Table 1.
Biological Sludge
The biological sludge was generated in an activated sludge
plant treating wastewaters originating from an integrated
bleached kraft mill with combined NSSC production. Characteris-
tics of the system include (a) a 25.4 mgd [6.7(10^) liters per
minute] wastewater feed, (b) a sludge recycle ratio of 24 per-
cent, (c) an average mixed liquor suspended solids of 2000
rag/liter and (d) a detention time of 2.4 hours.
Most commonly during the course of the study, this sludge
was added to the autoclave at a nominal 3 percent consistency.
During that phase of study dealing with acid assisted hydrolysis,
the biological sludge was acidified to a pH of 4.5 ± 0.1 by
addition of IN sulfuric acid. The pH was selected based upon
results previously reported by Everett (20) , as well as acid
requirements in a range commonly cited for a proprietary thermal
process employing acidification.
Alum Coagulated Biological Solids
This chemical sludge was generated by the alum coagulation
of biologically treated effluent from an integrated bleached
kraft mill. The 21.4 million gallon I81.0(106) liters] daily
flow from the mill is aerated in a basin of 2.8 days detention
time. Residual solids are separated in a secondary clarifier
following addition of 250 mg/liter alum supplemented with poly-
mer. Of the nonorganic fraction in the sludge, 50 percent is
assessed to be alum. Autoclave addition consistency was approx-
imately 3 percent.
Alum Water Treatment Sludge
The alum water treatment sludge utilized had been previously
thickened from 0.6 percent solids to 4 percent consistency in a
flotation thickener following a 6 Ib/ton (3 mg/gm) polymer addi-
tion. Feed consistency to the autoclave was approximately 2.5
percent.
29
-------
TABLE 1. RAW SLUDGE CHARACTERISTICS
FiIterability
Sludge description
Volatile
content,
Capillary
Capillary suction Specific Specific re-
suction time test resistance, sistance test
time, sec consistency, % 10^ sec2/gm consistency, %
CJ
o
Waste activated
sludge
72
Alum coagulated
biological residue 63
Alum water treatment
sludge 33
Screened groundwood
fines 51
189.0
49.1
58.0
25.5
3.3
3.0
2.5
1.5
178
52
3.3
1.3
-------
Groundwood Sludge
Primary sludge was obtained from a newsprint mill in which
groundwood constituted 61 percent of total mill production.
Fines were segregated by removing sludge components retained on
a 60-mesh screen, based upon Attala's observation (2) that par-
ticles finer than 60 mesh pose the most difficult dewatering
problems. The thickened fines were charged to the autoclave at
1.4 percent consistency.
After collection and thickening of the sludges at the re-
spective mills, 5 mg/liter formaldehyde was added prior to ship-
ment via surface transportation to the NCASI Central-Lake States
Center. In addition, a 5-gallon sample, unpreserved, was shipped
by air and subsequently utilized for developing sludge BOD/COD
relationships.
31
-------
SECTION 5
RESULTS
It should, perhaps, be indicated here at the outset that the
conduct of this study was not intended to duplicate process con-
ditions associated with existing or proposed proprietary pro-
cesses for the thermal conditioning of sludges or other waste
residuals. Furthermore, performance of equipment utilized in the
investigation does not necessarily simulate, from the standpoint
of process kinetics, operating characteristics of prototype
reactors finding application in commercial systems. Rather, it
is intended herein to develop wider public understanding of the
potential responses of a variety of pulp and paper industry
sludges to conditioning by thermal means. y
WASTE ACTIVATED SLUDGES
Filtration Properties
Possibly the most striking observation made in this segment
of the study and which the equipment configuration used in the
previously cited NCASI investigation did not permit was the
rapidity of the conditioning reaction. Figure 17, which illus-
trates the filtration properties of sludge progressively sampled
over an 8-minute interval between the time the sludge was
injected into the reactor and its attaining the desired condi-
tioning temperature, would suggest that acceptable conditioning
is virtually complete in a matter of several minutes. The con-
gruence of the oxidative and nonoxidative profiles is also note-
worthy .
Data pertinent to improvement in filtration properties as a
consequence of oxidative and nonoxidative conditioning is shown
respectively in Tables 2 and 3 and graphically summarized as
Figure 18. In the figure, the range of observations for all
detention times at the indicated temperature is shown about a
curve drawn through points specific to a 20-minute reaction
period. Examination of the data indicates no practically signi-
ficant difference between the two conditioning regimes. Both
were capable of achieving capillary suction times (CST) of 10 to
15 seconds, most commonly within a temperature range of 360° to
400°F (182° to 204°C). As might be anticipated from the demon-
strated rapidity of the reaction, the detention time was of con-
sequence principally at temperatures less than 350°F (177°C);
32
-------
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injection
4 6
TIME, MINUTES
10
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• Oxidative
Note: Time is measured
from the point of
sludge injection.
8
10
TIME, MINUTES
Figure 17. Filtration response as a function of conditioning
time.
33
-------
TABLE 2. SLUDGE FILTERABILITY RESPONSE TO OXIDATIVE CONDITIONING
Capillary suction time,
Temperature
300°F (150°C)
315°F (157°C)
330°F (166°C)
345°F (174°C)
350°F (177°C)
Time ,
min
0
5
10
15
20
25
30
40
50
60
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10
15
20
25
30
0
5
10
15
20
25
30
0
5
10
15
20
25
30
40
50
60
0
10
20
40
Number of
observations
4
2
4
2
5
1
1
3
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
1
—
—
--
--
2
2
2
3
sec
range
20.1-38.0
18.2-23.2
18.0-21.4
16.4-18.3
15.9-19.6
—
—
16.6-18.6
—
—
—
—
—
—
--
—
—
—
—
—
—
—
—
—
16.6-20.8
16.0-18.7
15.0-18.8
13.3-17.4
—
—
—
—
—
16.8-17.8
16.4-20.1
16.0-18.7
15.5-20.0
average
25.9
20.7
19.7
17.4
17.8
16-8
15.9
17.6
13.9
13.0
29.8
15.8
17.4
16.2
16.5
16.7
16.2
26.0
18.6
17.3
18.4
16,4
17.5
16.7
23.8
18.7
17.4
16.9
15.4
13.3 ,
17.4
16.6
15.5
15.5
17.3
18.3
17.4
17.4
Note: Time is measured from the point at which the specified
operating temperature is attained.
(continued)
34
-------
TABLE 2 (continued)
Capillary suction time,
Temperature
360°F (182°C)
•
380°F (193°C)
400°F (204°C)
e
425°F (218°C)
450°F (232°C)
Time ,
min
0
5
10
15
20
25
30
40
50
60
0
5
10
15
20
25
30
0
5
10
15
20
25
30
40
0
5
10
15
20
25
30
0
10
20
40
Number of
* * \A4 L LX^ ^^ Jm \J J^
observations
2
2
2
2
2
1
2
1
1
1
2
2
3
2
3
2
3
3
1
3
1
3
1
1
2
1
1
1
1
1
1
1
2
2
2
2
sec
range
18.6-19.7
14.7-16.4
13.7-13.8
12.6-15.8
12.1-14.3
—
10.8-16.9
—
—
—
11.7-17.0
10.4-16.1
10.0-16.2
9.1-12.1
10.4-15.0
0.6-15.0
9.2-18.0
12.8-21.0
—
13.9-19.4
—
13.5-19.1
—
—
15.5-30.0
—
--
—
—
—
—
—
15.3-18.9
16.6-23.1
15.4-24.0
13.4-18.4
average
19.2
15.6
13.8
14.2
13.2
15.3
13.9
11.1
10.6
11.0
14.4
13.3
14.2
10.6
13.1
12.3
12.5
16.3
14.7
16.2
14.1
15.5
16.7
17.1
22.8
13.2
13.2
10.9
13.2
13.6
13.2
13.2
17.1
19.9
19.7
15.9
Note: Time is measured from the point at which the specified
operating temperature is attained.
35
-------
TABLE 3. SLUDGE FILTERABILITY RESPONSE TO
NONOXIDATIVE CONDITIONING
Capillary suction time,
Temperature
300°F (150°C)
315°F (157°C)
345°F (174°C)
350°F (177°C)
360°F (182°C)
Time ,
min
0
5
10
15
20
25
30
40
50
60
0
5
10
15
20
25
30
0
5
10
15
20
25
30
40
50
60
0
10
20
40
0
5
10
15
20
25
30
40
50
60
Number of
observations
4
2
4
2
5
1
2
4
1
1
1
1
1
1
1
1
1
2
2
2
2
2
1
1
1
1
1
2
2
3
3
2
2
2
2
2
1
2
1
1
1
sec
range
22.7-31.5
21.3-24.3
17.5-20.5
15.7-20.8
16.5-20.9
—
14.0-19.9
15.9-18.9
--
—
—
—
—
—
—
—
—
22.2-24.2
19.1-20.7
17.1-17.2
17.2-17.5
16.9-17.7
—
—
—
—
—
15.3-19.3
17.1-17.4
18.6-20.9
14.3-16.7
16.7-17.4
16.0-17.9
14.1-19.1
13.8-15.4
13.8-17.6
—
13.7-15.0
—
—
—
average
33.8
22.8
19.2
18.3
18.5
14.9
17.0
17.2
14.7
18.7
19.6
19.2
20.5
18.7
19.2
16.3
15.8
23.2
19.9
17.2
17.4
17.3
15.3
16.8
17.4
14.6
13.9
17.3
17.3
18.2
15.3
17.0
17.0
16.6
14.6
15.7
15.6
14.4
15.5
12.6
13.5
(continued)
36
-------
TABLE 3 (continued)
Capillary suction time,
Temperature
380°F (193°C)
400°F (204°C)
425°F (218°C)
450°F (232°C)
Time ,
^ *Jl*&llV^ f
min
0
5
10
15
20
25
30
0
5
10
15
20
25
30
40
50
60
0
5
10
15
20
25
30
0
5
10
15
20
25
30
40
Number of
J»lt \JlJ i • f*J ^^ ^^ VX ^^
observations
2
2
3
2
3
2
2
3
2
3
—
4
1
2
3
1
1
1
1
I
1
1
1
1
3
1
3
1
3
1
1
2
sec
range
12.5-24.5
12.5-18.6
12.0-17.3
11.6-18.4
10.8-16.4
11.5-17.5
10.7-16.7
18.3-19.3
16.1-24.1
16.3-19.2
—
12.2-19.1
—
13.0-14.1
10.3-14.2
—
—
--
—
—
—
—
—
—
13.6-20.1
—
12.1-15.9
—
12.1-15.5
—
—
11.8-12.0
average
18.5
15.6
14.2
15.0
13.0
14.5
13.7
18.8
20.1
17.3
—
15.5
13.4
13.6
12.8
13.0
14.7
20.0
15.3
15.8
15.6
14.9
12.3
14.0
17.0
16.4
14.2
16.0
13.5
15.1
16.6
11.9
37
-------
u>
00
30
(0
O
LJJ
w
UJ
Z 20
O
O
£
cc
5 10
Q.
O
0
III!
- ,
-r
,
^
|
i i
T Range of observations
associated with all
1 retention time
-,- • Observation at 20 min
T- retention time
_ T
,">...
I **s.,l
1 I ,r~-I—
-
Oxidative
i i i i
T
s' ' \_
> J'"'
-"\
-
Conditioning
i i
ii i i i i
I Range of observations
associated with all
retention time
• Observation at 20 min
retention time
T T T ~
>^**^ T
*J !^ T
"~ J1 o
| 1 f |
-
Nor>-Oxidative Conditioning -
i i i i i i
300
350
400
450
300
TEMPERATURE, °F
350 400
TEMPERATURE, °F
450
Figure 18. Sludge filterability response to thermal conditioning.
-------
even there, little further improvement, if any, was experienced
beyond 5 minutes. That is not to infer, however, that compar-
able mixing, mass transfer, or associated kinetics can be ex-
pected in large scale prototype reactors. With oxidative condi-
tioning, a nominal reversion is suggested by the CST data.
Results of supplemental filter leaf testing conducted at
respective form and dry times of 2 and 4 minutes, at a vacuum of
15 inches of mercury are shown in Table 4. In comparing the
respective loading rates associated with the two conditioning
regimes, the relative sludge consistencies at which the tests
were conducted should be noted. In extrapolating a curve cor-
relating nonoxidative loading rates with consistency to a 2.4
percent solids level and assuming a consistency exponent of 1.0,
a filter loading rate comparable to that indicated for the sludge
conditioned oxidatively is suggested. Doing so cannot be con-
sidered conclusive, however. While the sludges were conditioned
at differing temperatures, CST data would dispute a lower oper-
ating temperature dewaterability advantage for the oxidative
regime.
TABLE 4. FILTER LEAF RESULTS WITH
THERMALLY CONDITIONED BIOLOGICAL SLUDGE
Nature of
conditioning
Nonoxidative Oxidative
400°F/204°C 350°F/177°C
Unconditioned for 40 min for 30 min
Specific resistance
sec2/gm 160 (107)
Sludge consistency, % 3.9
Cake solids, % 16.3
Solids recovery, % 9.0
Filter loading rate
Ib/ft2/hr 0.4
7.9 (107)
3.9 7.0
24.3 23.4
99.0 99.0
6.0
10.7
16.1 (107)
2.4
30.4
94.0
2.4
Effects of Solids Solubilization
Data tabulated in Table 5 and graphically arrayed in Figure
19 illustrates the importance of the magnitude of volatile solids
hydrolysis in achieving optimal conditioning. Lowest values of
CST, as well as specific resistance occurred within the range of
40 to 60 percent solids hydrolysis. The curves would indicate
that the lowest specific resistance achievable with oxidative
39
-------
TABLE 5. COMPARISON OF SOLIDS HYDROLYSIS AND FILTERABILITY
Temperature
300°F (150°C)
03
M/
£ 350°F (177°C)
«
•H
O
400°F (204°C)
450°F (232°C)
300°F (150°C)
0)
•$ 350°F (177°C)
T3
•H
O
fl
O
a 400°F (204°C)
450°F (232°C)
Time,
min
0
10
20
20
40
0
10
20
40
40
0
10
20
20
40
0
10
20
20
40
0
0
10
20
20
40
40
0
10
20
20
40
40
0
10
20
20
40
0
10
10
20
40
% Volatile
solids
hydrolyzed
11
27
33
43
49
34
56
65
67
67
66
74
67
66
77
72
88
85
86
92
17
14
25
18
21
30
29
16
30
22
17
28
43
35
41
49
37
49
44
45
44
47
53
CST,
sec
20.1
18.0
18.2
18.3
18.6
16.8
20.1
18.7
16.7
20.0
21.1
19.4
19.1
20.6
30.1
18.9
23.1
23.5
24.0
18.4
22.7
40.5
18.2
20.9
17.7
15.9
16.9
15.3
17.1
18.6
20.9
14.3
16.7
18.3
16.3
15.6
15.6
13.8
17.2
14.5
16.3
13.0
11.8
Specific
resistance
sec^/qm
34.1
15.4
11.4
—
18.5
11.3
8.9
8.2
—
9.3
9.9
29.2
23.5
--
29.4
25.3
37.4
--
43.7
26.4
50.0
—
15.6
—
15.3
12.8
—
11.3
7.9
5.1
5.0
7.7
5.9
4.3
— —
2.5
17.0
3.4
3.7
3.5
3.3
40
-------
CO
o
UJ
CO
lif
Q
CO
Q.
O
30
25
20
15
10
5
0
60.0
^o 40.0
2 30.0
O
°6 20.0
UJ
CO
III
Z 10.0
fe 8.0
I 6.0
g 4.0
O 30
UJ °'u
Q.
CO
2.0
0
o Non-Oxidative
• Oxidative
i i
o Non-Oxidative
• Oxidative
1.0
Figure 19.
20 40 60 80
VOLATILE SOLIDS HYDROLYZED, %
Significance of solids hydrolysis to
sludge filterability.
100
41
-------
conditioning occurs at a solubilization level of 50 percent. An
equivalent degree of conditioning was accomplished with hydroly-
sis of 30 percent of the volatile solids during nonoxidative con-
ditioning. The data would further suggest that such degrees of
hydrolysis are attainable at comparable temperature levels.
However, oxidative conditioning, where oxygen is not limiting,
would yield fewer solids requiring ultimate disposal.
It should, perhaps, also be noted here that comparison of
the CST and specific resistance curves would indicate the latter
to be the more sensitive parameter for detecting differences
among well-conditioned sludges.
Supernatant Quality
Highest values of filtrate COD observed in the study were
on the order of 11 to 13000 mg/liter and generally associated
with oxidative conditioning at 350°F (177°C) for extended deten-
tion times (40 minutes). At extreme levels of nonoxidative
conditioning, values in excess of 10000 mg/liter were encountered
as well. The incremental increase in filtrate COD as a conse-
quence of volatile solids hydrolysis is shown in Figure 20,
developed from data presented in Table 6. The trend of the data
indicates that approximately 50 percent of the mass of volatile
solids hydrolyzed is reflected as filtrate COD. The relationship
seems common to both conditioning regimes with the exception that
a decrease appears to be associated with oxidative conditioning
at temperatures of 400° to 450°F (204° to 232°C). A filtrate BOD
to COD ratio of 0.5 was consistent over the entire range of con-
ditions, as illustrated in Figure 21.
ACID ASSISTED OXIDATED CONDITIONING
Acid requirements to reduce sludge to 4.5 were in excess of
0.3 gm/liter of sludge solids, or, as shown in Figure 22, greater
than the 3 gm/liter threshold indicated by Seto and Smith (21).
As expected, acid addition was accompanied by the evolution of
hydrogen sulfide and foaming, a phenomenon which complicated the
quantitative transfer of solids.
Filtration Properties
CST data shown in Table 7 shows no significant advantage
to acid pre-hydrolysis over that associated with conventional
oxidative conditioning insofar as its capacity to improve
sludge dewaterability. This is, perhaps, better illustrated
in Figure 23 in which the range of capillary suction times (CST)
corresponding with various reaction temperatures are superimposed
on the similar relationship (designated by the shaded area)
developed in the previous section for activated sludge without
acid addition.
42
-------
15
CO
o
LU
CO
LU
CC
o
o
8
LU
CC
10
o Non -Oxidative
• Oxidative
0 5 10 15 20
VOLATILE SUSPENDED SOLIDS DECREASE, QMS
Figure 20. Effect of solids hydrolysis upon filtrate COD.
4500
3500
I
M 2500
1500
o Non-Oxidative
• Oxidative
2,000
4,000 6,000 8,000
FILTRATE COD, MG/L
10,000
Figure 21. Correlation of filtrate COD-BOD concentrations.
43
-------
TABLE 6. CORRESPONDING CHANGES IN SLUDGE VOLATILE
SOLIDS AND FILTRATE COD
Temperature
300°F (150°C)
CD
> 350°F (177°C)
•H
4J
US
-H
O
400°F (204°C)
450°F (232°C)
300°F (150°C)
CD
•H 350°F (177°C)
rd
•H
M
O
C
O
52 400°F (204°C)
450°F (232°C)
Time,
min
0
10
20
20
40
0
10
20
40
40
0
10
20
20
40
0
10
20
20
40
0
0
10
20
20
20
40
0
10
20
20
40
40
0
10
20
20
40
0
10
10
20
40
Sludge volatile
suspended solids
decrease, gm
2.6
6.4
7.7
6.8
11.4
7.9
13.1
15.0
15.6
15.0
15.6
17.3
15.6
15.2
17.9
18.1
21.7
21.2
19.4
21.4
4.0
2.9
6.3
4.1
4.7
7.0
6.9
5.2
6.9
4.9
3.9
9.5
6.5
8.2
9.5
11.5
8.3
11.3
11.6
10.5
9.5
11-0
—
Filtrate COD
increase, gm
1.0
3.5
3.8
6.2
5.8
2.9
5.5
7.9
10.9
11.7
6.5
8.8
8.2
8.7
8.1
10.6
8.6
8.6
7.7
6.7
1.3
2.7
1.6
0.7
1.9
3.3
1.7
2.9
4.5
2.8
3.8
4.8
3.9
2.5
4.3
4.3
3.7
9.0
3.1
5.2
6.2
7.9
—
44
-------
I
Q.
FILTRATE SULFUR 1C ACID ADDITION, G/L
0.1 0.2 0.3 0.4
6.0
5.5
5.0
4.5
Filtrate
Sludge
0 1.0 2.0 3.0
SLUDGE SULFURIC ACID ADDITION, G/L
Figure 22. Effect of incremental acid addition upon pH,
45
-------
TABLE 7. SLUDGE FILTERABILITY AFTER ACID ASSISTED
OXIDATIVE CONDITIONING
Temperature
300°F (150°C)
350°F (177°C)
400°F (204°C)
450°F (232°C)
Time,
min
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
Capillary suction
time*, sec
observations
20.1
20.6
14.5
19.6
17.0
15.6
17.7
24.7
16.0
18.3
17.2
13.3
14.7
10.7
18.0
11.5
14.8
16.0
13.2
13.9
10.6
28.9
12.4
15.8
21.0
16.0
15.0
17.3
17.9
11.8
15.4
average
20.4
—
17.1
--
17.0
16.7
—
20.4
--
17.8
—
14.0
—
14.4
—
13.2
—
14.6
—
13.9
—
19.8
14.1
--
18.5
--
--
16.7
—
13.6
— —
Specific resistance,
107 sec2/gm
observations
42.6
21.0
4.2
14.5
7.6
4.4
9.5
43.8
4.9
8.6
—
2.7
4.8
6.2
15.2
5.6
4.8
12.0
6.4
11.5
3.5
19.0
6.6
5.8
8.8
—
1.9
—
14.3
4.4
10.9
average
31.8
—
9.4
—
7.6
7.0
—
24.4
--
8.6
—
3.8
—
10.7
—
5.2
—
9.2
—
11.5
11.2
—
6.2
—
8.8
—
8.1
—
— —
7.7
—
* Original sludge capillary suction time was 189 sec at 3.3 per-
cent consistency.
46
-------
£*
~J
Range of observations
associated with all
retention time
Observation at 20 mm
retention time
TEMPERATURE
Range of observations
associated with all
retention time
Figure 23.
—
TEMPERATURE, °F
-------
The rapidity with which conventional oxidative conditioning
was observed to occur masked any ability of acid to accelerate
the process. That is not to suggest that in prototype reactors
an acid benefit would not be realized; only that such a distinc-
tion could not be made, given the kinetics associated with equip-
ment utilized in this study and the sludge consistencies em-
ployed.
Solids Hydrolysis Effects
The relationship of solids filtration properties to volatile
solids hydrolyzed is shown in Figure 24 and was developed from
data shown in Tables 7 and 8 for acid assisted oxidative condi-
tioning. Comparison with the similar relationship for nonacid
conditioning, Figure 19, indicates somewhat better dewaterability
with the acid assist as hydrolysis progresses. However, optimum
filtration continues to fall in the 40 to 60 percent hydrolysis
range. Futhermore, acid addition dampened the reversion poten-
tial at extreme levels of hydrolysis. Thus, smaller residuals
can be handled without so great a sacrifice in their dewatering
properties.
Filtrate Quality
The incremental increase in filtrate COD as a consequence
of solid hydrolysis is approximately the same as that for non-
acid conditioning, as shown in Figure 25, compiled from data in
Table 8. However, there was some evidence to suggest a decrease
in the ratio with conditioning for extended times (40 minutes)
at temperatures exceeding 350°F (177°C). The ratio of BOD to COD
was observed to be 0.6, as taken from Figure 26.
CHEMICAL BASED SLUDGES
Other than its chemical content, the most distinguishing
quality between the alum coagulated biological solids and the
conventional waste activated sludge was the extraordinarily long
sludge age of the former resulting from high degrees of sludge
recycle.
Filtration Properties
A comparison of filtration properties associated with the
oxidative and nonoxidative conditioning of the alum coagulated
biological solids, tabulated in Tables 9 and 10 respectively,
indicates the latter conditioning regime to be the better. The
average of CST observations at individual times for oxidative
temperatures of 350°F (177°C) and less was never below 20
seconds, though that did occur at the initial 400°F (204°C) and
450°F (232°C) conditions. Reversion was evident at more inten-
sive conditions. However, with nonoxidative conditioning CST's
of less than 20 seconds were attainable at all temperatures,
48
-------
CO
o
LU
o
Q.
C$
30
25
20
15
10
5
0
1 1 n 1 1 r
^^ •
60.0
*o 40.0
^ 30.0
O
20.0
LU
CO
LU
Z 10.0
fe 8.0
LU 6.0
DC
s <.o
a 3.0
Q_
CO
2.0
1.0
'
1
1
1
20 40 60
VOLATILE SOLIDS HYDROLYZED, %
100
Figure 24. Significance of solids solubilization to the
filterability of sludge exposed to acid assisted oxidative
conditioning.
49
-------
TABLE 8. CORRESPONDING CHANGES IN SLUDGE VOLATILE SOLIDS AND
FILTRATE COD ASSOCIATED WITH ACID ASSISTED OXIDATIVE CONDITIONING
Sludge volatile
Temperature
300°F (150°C)
350°F (177°C)
400°F (204°C)
450°F (232°C)
Time,
rain
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
suspended
decrease
observations
3.9
4.0
7.9
5.3
8.1
14.0
7.4
7.9
9.3
12.1
13.6
12.9
14.2
17.1
20.0
19.7
16.5
16.0
18.7
20.3
18.8
15.7
16.3
19.6
15.5
18.6
18.8
14.2
15.1
21.2
12.8
19.0
solids
, gm
average
3.9
—
6.6
—
8.1
10.7
—
8.6
—
12.9
—
13.6
—
18.6
—
18.1
—
16.0
18.7
19.6
—
16.0
—
17.9
—
—
16.0
—
—
17.7
—
— —
Filtrate
COD
increase,
gm
observations
0.5
—
5.3
3.1
5.5
5.9
4.6
2.1
—
6.9
7.1
9.6
8.2
7.7
3.8
4.3
3.6
4.6
8.0
3.9
8.0
6.3
2.7
9.2
7.0
11.4
8.8
4.4
4.7
9.0
4.4
7.7
average
0.5
—
4.2
—
5.5
5.3
—
2.1
—
7.0
--
8.9
—
5.8
—
4.0
—
4.6
8.0
6.0
—
4.5
—
9.2
—
—
6.0
mm _
7.0
__
—
50
-------
15
CO
2
(3
iu
CO
<
UJ
CC
10
Q
8
UJ
05 10 15 20
VOLITILE SUSPENDED SOLIDS DECREASE, QMS
Figure 25. Effect of solids solubilization upon the
COD of sludge filtrates following acid assisted
oxidative conditioning.
7500
a
5 5500
Q
O
m
I
s| 3500
1500
4000
6,000 8,000 10,000
FILTRATE COD, MG/L
12,000
Figure 26. Relative COD-BOD concentrations in filtrates
from sludges after acid assisted oxidative conditioning.
51
-------
TABLE 9. FILTRATION PROPERTIES OF ALUM-COAGULATED
BIOLOGICAL SOLIDS AFTER THERMAL CONDITIONING
(Oxidative)
Temperature
300°F (150°C)
350°F (177°C)
400°F (204°C)
450°F (232°C)
Time,
min
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
Capillary suction Specific resistance,
time, sec 10' sec^/gm
observations
22.2
21.2
29.3
17.9
25.1
17.4
25.0
21.3
25.2
15.5
25.8
19.4
32.1
15.4
30.0
16.8
20.7
16.2
32.6
18.8
39.6
21.4
38.0
16.5
22.1
19.3
15.4
44.0
15.9
24.1
20.1
33.3
21.8
average
21.7
—
23.6
—
21.3
—
23.2
—
20.4
—
22.6
—
23.8
— •
23.4
—
18.5
_/_
25.7
—
30.5
—
27.3
—
18.9
—
—
30.0
—
22.1
—
27.6
— —
observations
25.5
—
25.6
—
—
25.8
2.8
25.7
23.3
—
35.5
—
39.6
--
55.6
—
12.6
—
43.8
—
60.1
—
61.0
—
14.9
31.1
— —
94.5
—
21.6
__
80.1
—
52
-------
TABLE 10. FILTRATION PROPERTIES OF ALUM-COAGULATED
BIOLOGICAL SOLIDS AFTER THERMAL CONDITIONING
(Nonoxidative)
Temperature
300°F (150°C)
350°F (177°C)
400°F (204°C)
450°F (232°C)
Time,
min
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
Capillary suction Specific resistance,
time, sec 107 sec2/gm
observations
27.2
23.6
79.6
20.6
32.2
20.4
29.3
32.7
19.0
16.9
14.2
18.4
25.0
16.8
23.0
18.3
19.8
15.4
16.0
20.3
22.0
17.4
16.1
15.1
15-1
13.4
15.7
14.8
—
15.6
16.5
14.9
16.0
17.5
15.6
--
14.1
16.3
16.1
average
37. '8
—
—
—
27.3
—
--
25.9
—
16.5
—
—
20.9
—
20.7
—
17.6
—
18.6
—
19.7
—
15.6
—
14.3
—
15.3
—
16.1
--
15.5
—
16.6
—
15.5
—
—
—
observations
„
74.4
140.0
—
50.6
—
60.0
40.4
—
8.3
11.7
—
30.4
—
14.9
—
14.3
—
5.7
—
15.3
--
6.9
—
6.3
—
6.7
--
3.0
6.4
—
4.9
—
6.7
—
3.6
—
4.4
— —
53
-------
with the necessary reaction time becoming progressively shorter
as temperature increased. A similar scenario could be made for
specific resistance results.
Results of vacuum filter leaf testing, shown in Table 11,
confirm the advantage of nonoxidative conditioning. At compar-
able conditions of consistency and form time, respectively 4 to
5 percent and 2 minutes, the loading rate was 5 Ib/ft2/hr
(24 Kg/m2/hr) for the nonoxidative sludge. The oxidized sludge
exhibited a 3 Ib/ft2/hr (15 Kg/m2/hr) loading rate.
TABLE 11. FILTER LEAF RESULTS WITH THERMALLY CONDITIONED
ALUM COAGULATED BIOLOGICAL SOLIDS
Nature of
conditioning
Unconditioned
Nonoxidative
400°F/204°C
for 40 min
Oxidative
350°F/177°C
for 30 min
Specific resistance*,
sec2/gm
Capillary suction
time , sec
Sludge consistency, %
Form time, min
Dry time, min
Cake solids, %
Solids recovery, %
Filter loading rate,
Ib/ft2/hr
160 (107) 7.9
65 27.5
3.2 4-5
2 2
4 4
17 18
82 90
1.8 5
(107)
38
7-8
2 1
4 2
18 17
96 92
9 13
16.1 (107)
33
4-5
1 2
2 4
20 21
84 86
4 3
* Sludge utilized herein differed from that previously described
and possessed better dewatering properties in both the condi-
tioned and unconditioned states.
Solids Hydrolysis Effects
Figure 27, compiled from data contained in Tables 9, 10 and
12, displays the relative effects of volatile solids hydrolysis
upon resulting filtration properties. It indicates, for oxida-
tive conditioning, that filtration properties do not improve
beyond initial hydrolysis levels and degenerate where hydrolysis
54
-------
30
25
20
15
10
5
0
60.0
^o 40.0
2 30.0
O
*0 20.0
LU
CO
CO
o
UJ
CO
z
o
§
to
cc
5
o
CO
Hi
DC
O
O
LU
CL
CO
10.0
8.0
6.0
4.0
3.0
2.0
1.0
i
o - Non Oxidative
• - Oxidative
o Non Oxidative
• Oxidative
20 40 60
VOLATILE SOLIDS HYDROLYZED, %
80
100
Figure 27. Impact of volatile solids solubilization upon the
dewatering properties of alum coagulated biological solids after
heat treatment.
55
-------
TABLE 12. .CORRESPONDING CHANGES IN SLUDGE VOLATILE SOLIDS AND FILTRATE COD FOR
CHEMICALLY COAGULATED AERATED BASIN RESIDUES EXPOSED TO THERMAL CONDITIONING
ui
Oxi dative
Temperature
300°F (150°C)
350°F (177°C)
400°F (204°C)
450°F (232°C)
volatile solids
Time, hydrolyzed, filtrate COD,
rain % rag/liter
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
10
26
29
38
20
29
62
71
41
75
85
85
89
89
85
5205
4935
5920
5960
5863
5081
6316
6820
6660
7137
6448
4990
6101
6068
4408
Nonoxidative
volatile solids
hydrolyzed ,
%
9
17
9
19
16
21
26
22
28
32 '
27
28
29
31
42
41
filtrate COD,
mg/liter
4333
3924
4695
4072
5049
4681
5127
5953
4941
5228
5335
4825
5294
5552
5296
4765
-------
levels exceed 40 percent. However, nonoxidative filtration pro-
perties exhibit progressive improvement up to the 40 percent
hydrolysis limit.
Filtrate Quality
As shown in Figure 28, filtrate COD resulting from solids
solubilization ranged from approximately 4000 to 7000 mg/liter,
significantly below that associated with conventional activated
sludge conditioned at a comparable consistency. At all but the
most intensive condition, oxidative filtrate COD exceeded that
associated with the nonoxidative regime, as shown in Table 10.
COD yield, based upon the mass of volatile solids hydrolyzed,
was estimated to be approximately half that associated with con-
ventional activated sludge. Moreover, the ratio of filtrate BOD
to COD was approximately 0.3, as shown in Figure 29. These
differences are possibly attributable to an altered nature of
the biological solids resulting from their extended aeration.
To the extent that the results of the alum water treatment
sludge is indicative, the effect of heat treatment on the alum
coagulated biological solids cannot be attributed to its effect
upon the alum component. As shown in Table 13, thermal condi-
tioning had very little effect on water treatment sludge fil-
terability. Seldom were capillary suction times less than 35
seconds. Associated measurement of specific resistance indicated
values ranging between 100 and 200(10') sec^/gm.
GROUNDWOOD FINES
Results tabulated in Table 14 indicate groundwood fines to
be amenable to thermal conditioning. On the basis of capillary
suction time, there would seem to be little practical difference
between the oxidative and nonoxidative modes. However, specific
resistance values exhibit a nominal oxidative reversion at ex-
treme temperature conditions, whereas filterability is seen to
progressively improve with increasing temperatures during non-
oxidative conditioning.
Filterability was not seen to be highly sensitive to the
magnitude of volatile solids hydrolyzed, as shown by Figure 30.
However, with oxidative conditioning, a slight reversion at
solids hydrolysis levels exceeding 40 percent was suggested by
the specific resistance data.
As shown in Table 15, filtrate COD ranged between 3000 and
5000 mg/liter, with no clear distinction between conditioning
regime. Data comparing the COD yield with the extent of solids
hydrolysis was too widely scattered to suggest any trend. How-
ever, filtrate BOD represented approximately half the filtrate
COD, as shown in Figure 31.
57
-------
o
5
CO
9
Q
8
<
e
o •
. -
• Oxidative
o - Non-Oxidative
10 30 50 70
VOLATILE SOLIDS HYDROLYZED, %
Figure 28. Relationship between filtrate COD and volatile
solids solubilization resulting from the thermal conditioning
of alum coagulated biological solids.
1500
a
§
LLJ
"- 1000
500
• Oxidative
o Non-Oxidative
s •
o^
" y '
iii
750 1500
FILTRATE COD, MG/L
2250
3000
Figure 29. Correlation of BOD/COD for filtrates resulting from
the thermal conditioning of alum coagulated biological solids.
58
-------
TABLE 13. FILTRATION PROPERTIES OF A THERMALLY CONDITIONED
ALUM WATER TREATMENT SLUDGE
Reaction Capillary suction time, sec
temperature Reaction time, 0-30 min
0 5 10 15 20 25 30
300°F (150°C)
315°F (157°C)
g> 330°F (166°C) 37.5 35.2 37.5 38.1 36.0 36.5 37.5
•H
£ 345°F (174°C) 48.5 ~ 38.6 39.2 49.8 39.1 42.0
T!
'x 360°F (182°C) 34.7 32.1 30.5 35.6 35.0 35.1 33.7
o
400°F (204°C) 41.3 — — 37.2 36.3 34.5 32.9
425°F (218°C)
300°F (150°C) 40.9 39.7 42.7 38.6 45.1 47.7 38.3
315°F (157°C) 33.3 27.8 30.6 31.4 29.0 26.5 34.1
> 330°F (166°C) 40.1 39.9 34.9 44.1 45.4 57.7 50.0
•H
•P
£ 345°F (174°C) 45.8 49.8 46.3 49.7 ~ 37.1 42.0
•H
§ 360°F (182°C) 36.4 — 34.5 36.0 — 38.5 34.9
§
2 400°F (204°C)
425°F (218°C) 36.4 — 34.5 36.0 — 38.5 34.9
Note: Original sludge capillary suction time was 58.0 sec at
2.5 percent solids consistency.
59
-------
TABLE 14. FILTRATION PROPERTIES OF GROUNDWOOD FINES
FOLLOWING THERMAL CONDITIONING
Oxi dative
Nonoxidative
Temperature
300°F (150°C)
350°F (177°C)
400°F (204°C)
450°F (232°C)
300°F (150°C)
350°F (177°C)
400°F (204°C)
450°F (232°C)
Time,
rain
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
Capillary
suction
time , sec
11.8
10.2
7.2
11.0
9.6
13.7
13.8
9.7
10.0
9.4
12.7
11.2
9.2
11.5
12.4
10.4
8.9
9.8
12.5
8.1
9.6
10.6
8.2
9.3
8.6
8.4
7.0
7.5
8.5
9.2
7.0
8.0
Specific
resistance,
10? sec2/gm
11.5
6.7
7.0
8.0
6.6
8.1
8.1
17.1
6.6
22.7
7.2
15.2
12.0
13.8
10.5
11.3
16.0
7.3
6.1
6.7
6.2
5.0
4.3
3.6
5.3
4.3
3.8
1.7
3.7
3.2
3.3
3.4
Note: Original sludge capillary suction time was 25.5
sec at 1.5 percent consistency.
60
-------
8
UJ
CO
UJ*
5
Z
O
3
§
E
O
<«•.
2
O
^^
UJ*
o
z
£
CO
111
cc
o
u.
o
UJ
Q.
CO
15
10
5
0
60.0
40-0
30.0
20.0
10.0
8.0
6.0
4.0
3.0
2.0
1.0
1 ' i i i i i i i
-
• «
0 • ,
• • a-.--"
«• •» •""* *"TP
0 0 •"^"" . "*
0 o^1^ a^^°°* *
Qfr
_ _
• Oxidative
o Non oxidative
i i i i i i i i i
iii i i i i i i
•
-
-
0
* £
• ^ + s
**•
""" ••__, r"""
o^vo^ •*• •
^^^
\. 0 o
0 ^"""^^___^ °
o o o
• Ox idative
—
^ o Non oxidative
i i ii i i i i i
20 40 60 80
VOLATILE SOLIDS HYDROLYZED, %
100
Figure 30. Impact of solids solubilization on the
filterability of thermally conditioned groundwood fines.
61
-------
TABLE 15. CORRESPONDING CHANGES IN SLUDGE VOLATILE SOLIDS AND FILTRATE COD FOR
GROUNDWOOD FINES EXPOSED TO THERMAL CONDITIONING
to
Oxidative
Nonoxidative
volatile solids volatile solids
Temperature
300°F (150°C)
350°F (177°C)
400°F (204°C)
450°F (232°C)
Time ,
mm
0
10
20
40
0
10
20
40
0
10
20
40
0
10
20
40
hydro ly zed,
%
16
29
44
30
21
28
49
54
35
67
64
70
45
69
82
filtrate COD,
rag/liter
4730
4590
3610
3780
4520
5120
3250
5720
5630
3350
2990
3150
3000
5860
4940
hydrolyzed,
%
2
11
6
22
15
38
14
15
34
41
37
32
22
43
36
31
filtrate COD,
mg/liter
4070
4810
4590
4620
4670
4300
4240
3950
4630
3990
4620
3810
4830
4060
4410
3360
-------
3000,
2000
1000
1 r
1000
3000 5000
FILTRATE COD, MG/L
7000
Figure 31. Correlation of BOD/COD for filtrates from
thermally conditioned groundwood fines.
63
-------
SECTION 6
GENERAL DISCUSSION
Though not specifically within the scope of this study, the
potential for application of thermal conditioning processes to
pulp and paper industry sludge sources warrants at least passing
attention to experience reported elsewhere dealing with (a) li-
quor treatability, (b) factors impacting on cost and (c) full
scale plant operational concerns.
LIQUOR TREATABILITY
Given the significant incremental addition to raw waste
load which heat treatment liquors constitute, their relative
treatability is an issue of considerable concern. While some
controversy would seem to exist within the literature dealing
with liquor treatability, Everett (30) concludes that there
appears to be no reason why heat treatment liquors should not
recirculate with incoming wastewaters through the treatment
system. This is common practice with heat treatment systems in
the United States. Difficulties with doing so, in some cases,
have been attributed to installation of systems at older plants
(31). This underscores the importance of anticipating the in-
cremental load in plant design. Erikson and Knopp (32) do con-
clude that direct recirculation of the undiluted liquors to the
treatment plant will result in a 10 percent increase in effluent
BOD. However, they estimate that elimination of an effluent BOD
increase would require separate biological treatment prior to
recirculation.
Pilot treatability studies for the separate processing of
oxidative heat treatment liquors were carried out by the City of
Kalamazoo. However, the approach was not considered further for
plant scale application due to (a) potential odors, (b) foaming
problems and (c) the necessity for extensive liquor dilution as
a consequence of its high strength and temperature (33). Rather,
given the compatibility of the liquors for treatment along with
the incoming wastewaters, it was considered preferable to pro-
vide additional treatment capacity for the overall plant as
opposed to installation of a segregated system. In at least
two U.S. installations, however, provisions have been made to
overcome the above cited difficulties in segregated treatment
where doing so has been considered advantageous in permitting
64
-------
single stage nitrification (34). Long term operating experience
is not yet available.
COST CONSIDERATIONS
In the development of economic comparisons for various
sludge processing options leading up to incineration available
to a 1000 TPD bleach kraft mill, Evans (35) concludes that lowest
overall investment involved (a) segregation of the mill primary
and secondary sludges, (b) dewatering the former by relatively
conventional means and (c) processing the biological sludge by
means of heat treatment and subsequent ce'ntrifugation.
Considering the highly capital intensive nature of thermal
processes, economic comparisons may be easily skewed dependent
upon the selection of an amortization period and interest rate.
Economic assessments offered in the literature _136)(37) (38) (40)
(40) frequently feature periods of 15 years or longer as did
Evans (35). His assessment is illustrative, however, in suggest-
ing the potential existence of a situation in which the dewater-
ing of primary and secondary sludges is most economically done
independently. Miner et al. (41) cites other instances where
sludge segregation is desirable. It is under those circumstances
where heat treatment of the hydrous fraction alone is most appro-
priately considered, along with other technologies or condition-
ing options, such as described elsewhere (41), capable of han-
dling such solids.
Relative unit capital and operating costs furnished by a
firm marketing a heat treatment process are shown in Figures 32
and 33 as a function of plant capacity and feed sludge consis-
tency, respectively. These indicate the greatest applicability
at large installations, as well as the importance of optimizing
feed sludge consistency. However, Everett (15) in extrapolating
specific resistance data has suggested that an optimum heat
treatment feed sludge consistency exists beyond which condition-
ing and associated filter yield at a given temperature is ad-
versely affected. Thus, it is conceivable that such process
performance limitations pose an upper limit to achieving heat
treatment economy alone in the interest of minimizing overall
conditioning and dewatering costs.
Kalinske (42) cites English experience where recycling of
heat treatment liquors represented an overall 30 percent increase
in raw waste load to the plant arid goes on to conclude that
total costs of such sludge processing systems can be correctly
evaluated only if the resulting costs of handling the incremental
waste load are considered. One equipment supplier urges the
design of solids handling capacities 10 percent greater than that
anticipated in the absence of heat treatment. In doing so, Doyle
and Gruenwald (43) estimate an incremental cost of nearly $10.00
per ton of original sludge solids, based upon a recycled liquor
65
-------
UJ
111
DC
10
15
20
CAPACITY, TON/DAY
Figure 32. Significance of plant capacity to costs.
I
LU
UJ
DC
\
• —•
25
01 2 345
SLUDGE CONSISTENCY, %
Figure 33. Significance of sludge consistency to plant costs,
66
-------
BOD load of 21 percent of that entering the Colorado Springs
plant and suspended solids contributions of 30 percent of the
incoming load.
OPERATIONAL CONCERNS
Municipal Experience
In one compilation of case histories of sludge treatment by
high temperature and pressure (31) it was indicated that several
U.S. installations had ceased operating heat treatment systems
due to (a) effluent quality problems and high process costs
associated with a much higher degree of sludge solubilization
than anticipated and (b) high costs of maintenance.
Recently cited studies in England (42) have shown that any-
where from 35 to 60 percent of sludge suspended solids are
solubilized by heat treatment, with higher values associated
with activated sludges. This range is consistent with results
reported herein.
Additional English experience reports operating problems
with scaling of heat exchanger surfaces. Kalinske (42) also
cites continual formation of hard calcium sulfate on heat ex-
changers as a potentially serious problem as well as corrosion
in the presence of high chloride concentrations.
Yet another troublesome problem which has emerged with
oxidative systems, as well as nonoxidative, has been odor in the
plant vicinity. Corrective measures taken include vapor inciner-
ation, water scrubbing, and carbon adsorption. Diffusion within
mixed liquor aeration tanks poses an additional option.
The recitation of such a list of potential operational
problems is not meant to imply that heat treatment systems are
unworkable or are not worthy of consideration in residual manage-
ment strategies. Their widespread application in municipal
sludge management systems provides ample evidence that such
problems can be endured where active measures are anticipated or
taken to control or minimize them.
Industry Related Experience
Pilot experience with the nonoxidative conditioning of
waste activated sludge resulting from waste treatment at a sul-
fite mill has been detailed by Moss et al. (42). Results
reported therein indicated suspended solids decreases ranging
from 28 to 35 percent dependent upon reaction temperature, which
was varied from 340° to 390°F (171° to 199°C), and detention
time. The incremental increase in supernatant BOD constituted
approximately 38 percent of the mass of solids solubilized.
Limited additional analysis (18) showed a corresponding ratio
67
-------
of approximately 7 percent for total kjeldahl nitrogen. The
associated supernatant color increase was observed to range
from 8600 to 11000 platinum cobalt units (PCU), again dependent
upon reaction conditions. Moreover, the uncondensed vent gas
from the unit contained 10000 odor units per ft3, indicating the
possible need for external odor control equipment. Condensates
from the vent gases were seen to contribute an additional BOD of
1300 mg/liter. Perhaps of greatest consequence, however, was a
scale/plugging problem resulting from precipitation of calcium
salts on the vertical reactor standpipe, sludge-steam mixing
nozzles, and the hot side of the heat exchanger.
The authors (44) concluded that cake discharge would pose a
problem with vacuum filtration, though cake consistencies up
to 22 percent were reported. A similar observation was made in
leaf test evaluations conducted concurrently by NCASI staff (18).
Within the range of acceptable .loading rates and solids losses
less than 10 percent, cake thicknesses did not exceed 0.2 inches
(5 mm). Moreover, fines retained within the filter media were
difficult to remove, further suggesting that cake removal might
be difficult. Additional dewatering effort cited by Moss et al.
(44) indicated that heat conditioned sludge could be dewatered
to 19 percent at a rate of 100 gpm (379 1pm) while achieving
88 percent revovery when fed to a Sharpies P5400. In contrast,
non-heat conditioned secondary sludge is centrifuged to an 11 to
15 percent consistency at comparable recovery only after polymer
conditioning costs reported at $60.00 per ton of production
($66.00 per metric ton) (45).
To date there are no large scale applications of oxidative
conditioning within the paper industry. However, one mill
employing high level wet oxidation for liquor recovery intends
to dispose of its waste activated sludge within that system.
68
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REFERENCES
1. Zettlemoyer, A. C., F. J. Micale, and L. R. Dole. Surface
Properties of Hydrogels Resulting from Treatment of Pulp and
Papermill Effluents, Part II. Technical Bulletin No. 225.
National Council of the Paper Industry for Air and Stream
Improvement, Inc., New York, New York, December, 1968.
2. Atalla, Dr. R. H. The Relation Between the Constitution and
Dewatering Properties of Hydrous Sludges. Technical Bulle-
tin No. 260. National Council of the Paper Industry for Air
and Stream Improvement, Inc., New York, New York, October,
1972.
3. Lumb, C. Heat Treatment as an Aid to Sludge Dewatering -
Ten Years Full Scale Operation. Journal, Institute of
Sewage Purification, 5:13, 1957.
4. Brooks, R. Heat Treatment of Activated Sludge. Water
Pollution Control, 67:5, 1968. pp. 592-601.
5. Harrison, J. , and H. R. Bungay. Heat Syneresis of Sewage
Sludges, Part I. Water and Sewage Works, 1968. p. 268.
6. Jepson, C., and L. Klein. Heat Treatment of Sewage Sludge.
Journal, Institute of Sewage Purification, Part I, 1951.
7. Follett, R. H. Effects of Heat on Dewaterability of Bio-
logical Sludges. Technical Bulletin No. 207. National
Council of the Paper Industry for Air and Stream Improve-
ment, Inc., New York, New York, July, 1967.
8. Teletzke, G. H. Low Pressure Wet Air Oxidation of Sewage
Sludge. In: Proceedings of 20th Purdue Industrial Waste
Conference, May, 1965. p. 40.
9. Teletzke, G. H. et al. Components of Sludge and Its Wet-Air
Oxidation Products. Journal Water Pollution Control Federa-
tion, 39:994-1005, 1967.
10. Blosser, R. 0. Unpublished NCASI Internal Memorandum.
Subject: Review of the Zimmerman Process Based Upon Inter-
views and Inspection of the Facilities at the Metropolitan
Sanitary District of Greater Chicago, December, 1964.
69
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11. Marshall, D. W., and W. J. Gillespie. Comparative Study of
Thermal Techniques for Secondary Sludge Conditioning. In:
Proceedings of the 29th Purdue Industrial Waste Conference,
May, 1974. p. 589.
12. Everett, J. G., and R. Brooks. Dewatering of Sewage Sludge
by Heat Treatment. Water Pollution Control, 70:4, 1971.
p. 458.
13. Everett, J. G. Dewatering of Wastewater Sludge by Heat
Treatment. Journal Water Pollution Control Federation,
44:1, January, 1972. p. 93.
14. Takamatsu, T. et al. Model Identification of Wet-Air
Oxidation Process Thermal Decomposition. Water Research,
4:33-39, Pergamon Press, Great Britain, 1970.
15. Everett, J. G., and Nagel. Effect of Concentration of
Sewage Sludge Solids and Ash in Heat Treatment. Effluent
and Water Treatment Journal, 11:10, 1971. p. 542.
16. Brooks, R. Heat Treatment of Sewage Sludges. Water
Pollution Control, 69:2, 1970. pp. 221-231.
17. Everett, J. G. The Effect of Heat Treatment on the Solu-
bilization of Heavy Metals, Solids, and Organic Matter from
Digested Sludge. Water Pollution Control, 73:207-209, 1974.
18. Marshall, D. W. Unpublished NCASI data collected during
mill-conducted pilot scale trials of thermal conditioning
by the Porteus Process, December, 1970.
19. Malina. Sludge Filtration and Sludge Conditioning. Water
Quality Improvement by Physical and Chemical Processes.
Gloynal and Eckenfelder, eds., University of Texas Press,
Austin, Texas, 1970.
20. Everett, J. G. The Effect of pH on the Heat Treatment of
Sewage Sludges. Water Research, 8:889-906, Pergamon Press,
1974.
21. Seto, P., and D. K. Smith. Evaluation of the Barber Coleman
Wetox Process for Sewage Sludge Disposal. Ontario Research
Foundation report submitted to the Technical Committee,
Canada/Ontario Agreement on Great Lakes Water Quality,
July 31, 1974.
22. Hudgins, R. R., and P. L. Silveston. Wet Oxidation of
Chemical Sludges. Project No. 72-5-5, Research Program for
the Abatement of Municipal Pollution Under Provisions of the
Canada/Ontario Agreement on Great Lakes Water Quality,
March, 1973.
70
-------
23. Khanh, P. V. Wet Air Oxidation of Mercury Contaminated
Peat Moss. In: Proceedings of Peat Moss in Canada Sympo-
sium, University of Sherbrooke, Sherbrooke, Quebec, 1972.
24. Baskerville, R. C., and R. S. Gale. A Simple Automatic
Instrument for Determining the Filterability of Sewage
Sludges. Journal of the Institute of Water Pollution
Control, No- 2, 1968.
25. Coakley, P., and B. R. Jones. Vacuum Filtration: Interpre-
tation of Results by the Concept of Specific Resistance.
Sewage and Industrial Wastes, 28:8, August, 1956. p. 964.
26. Luten, P., J. Nebiker, and D. Adrian. Experimental Refine-
ments in the Determination of Specific Resistance and
Coefficient of Compressibility. In: First Annual North
Eastern Regional Anti-Pollution Conference, University of
Rhode Island, Kingston, Rhode Island, July, 1968.
27. Manual of Practice of Sludge Handling in the Pulp and Paper
Industry. Technical Bulletin No. 190. National Council of
the Paper Industry for Air and Stream Improvement, Inc.,
New York, New York, June, 1966.
28. A Guide to the Determination of Biochemical Oxygen Demand,
Dissolved Oxygen, Suspended and Settleable Solids, and
Turbidity of Pulp and Paper Mill Effluents. Technical
Bulletin No. 230. National Council of the Paper Industry
for Air and Stream Improvement, Inc., New York, New York,
December, 1969.
29. Standard Methods for the Examination of Water and Waste-
water, 13th ed., American Public Health Association, New
York, New York, 1971.
30. Everett, J. G. Recent Developments in Heat Treatment.
Water Pollution Control, 72:428-435, 1973.
31. Process Design Manual for Sludge Treatment and Disposal.
U. S. Environmental Protection Agency, Technology Transfer,
October, 1974.
32. Erikson and Knoop. Biological Treatment of Thermally Condi-
tioned Sludge Liquor Advances in Water Pollution Research.
S. Jenkins, ed., Pergamon Press, New York, 1972.
33. Personal Communication. Sampayo, F. J., Jones and Henry
Engineers, Ltd., Toledo, Ohio, January 6, 1977.
34. Personal Communication. Bush, Paul, Malcolm Pirnie, Engi-
neers, West Chester, New York, January 6, 1977.
71
-------
35. Evans, R. R. Terminal Waste Treatment and Sludge Disposal
Methods. Paper Trade Journal, August 3, 1970.
36. Nicholson, R. W., D. G. Pedo, and J. Martinek. Wet Air
Oxidation of Sewage Sludge. The American City, April, 1966.
37. McKinley, Johnson B. Wet Air Oxidation Process. Water
Works and Wastes Engineering, September, 1965.
38. Blatter, Paul X. Wet Air Oxidation at Levittown. Water
and Sewage Works, February, 1970.
39. Metcalf, Cobern C. Unusual Collection/Treatment System
Benefits Kalamazoo. Water and Wastes Engineering, February,
1971.
40. Sherwood, R., and J. Phillips. Heat Treatment Process
Improves Economics of Sludge Handling and Disposal. Water
and Wastes Engineering, November, 1970. pp. 42-44.
41. Miner, R. A., and D. W. Marshall. A Pilot Plant Study of
Mechanical Dewatering Devices Operated on Waste Activated
Sludge. Technical Bulletin No. 288. National Council of
York, New York, November 1976-
42. Kalinske, A. A. Municipal Wastewater Treatment Plant Sludge
and Liquid Sidestreams. EPA 430/9-76-007, U. S. Environ-
mental Protection Agency, Washington, D. C., June, 1976.
43. Doyle, J. D., and D. D. Gruenwald. Colorado Springs Acti-
vated Sludge Plant Provides Treatment for Heat Treatment
Recycle Liquor. In: 47th Annual Conference of the Water
Pollution Control Federation, October 8, 1974.
44. Moss, O. H., A. E. Haberer, and C. A. Barton. Heat Treat-
ment for Dewatering Waste Activated Sludge in Pulp Mill
Waste Treatment. In: Proceedings of the 26th Purdue
Industrial Waste Conference, Lafayette, Indiana, May 6,
1971.
45. Hullar, G. C., A. T. Dombroski, and C. A. Barton. Waste
Fiber and Activated Sludge Handling in a Pulp and Paper
Mill. In : Proceedings of the 8th Tappi Environmental
Conference, 1971.
46. LA/OMA Project Releases Phase I Report, Outlines $3.4
Million Work Plan. Sludge, 1:9, December, 1976. p. 69.
72
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1, REPORT NO.
EPA-600/2-78-015
3. RECIPIENT'S ACCESSIOI*NO.
4. TITLE AND SUBTITLE
Investigations of Heat Treatment for Paper Mill
Sludge Conditioning
5. REPORT DATE
February 1978 issuing date
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Duane W. Marshall, Frank C. Fiery
Russell 0. Blosser*
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
National Council of the Paper Industry for Air &
Stream Improvement, Inc.
Western Michigan University(Cntrl.-Lake Sts. Reg.
Kalamazoo, Michigan 49008
10. PROGRAM ELEMENT NO.
1BB037
Cntr
11. CONTRACT/GRANT NO.
) R-803347-01
12. SPONSORING AGENCY NAME AND ADDRESS
Industrial Environmental Research Laboratory—Gin. ,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final 6/15/74 - 5/28/76
14. SPONSORING AGENCY CODE
EPA/600/12
15. SUPPLEMENTARY NOTES
*Russell 0. Blosser is with the National Council of the Paper Industry for Air and
Stream Improvement, Inc., New York, New York 10016
16. ABSTRACT
The capability of oxidative and nonoxidative heat treatment processes for the
conditioning of hydrous sludges originating in pulp and paper industry manufacturing
or wastewater treatment operations was defined on the basis of laboratory scale
investigation. Sludges employed in the study included (a) alum water treatment
sludge, (b) groundwood fines, (c) alum-coagulated biological solids and (d)
waste activated sludge. The benefit of acid assisted oxidative conditioning
of the latter was also assessed. Results were related in terms of improved
filtration properties, the extent and significance of solids solubilization
and the resulting impact on filtrate quality.
7.
KEY WORDS AND DOCUMENT ANAi-YSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/GlOUp
Sludge disposal, Pulp mills, Paper mills,
Dewatering
Heat treatment,
Oxidative heat treatment,
Alum water treatment
sludge,
Groundwood fines,
Waste activated sludge
50 B
8. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (ThisReport}
UNCLASSIFIED
21. NO. OF PAGES
85
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
73
U.S. GOVERNMENT PRINTING OFFICE 1978-757- 1W6697 Region No. 5-11
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