EPA 660/2-74-074
July 1974
Environmental Protection Technology Series
Rum Distillery Slops Treatment
by Anaerobic Contact Process
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Office of Research and Development
U.S. Environmental Protection Agency
Washington, D.C. 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and
Monitoring, Environmental Protection Agency, have
been grouped into five series. These five broad
categories were established to facilitate further
development and application of environmental
technology. Elimination of traditional grouping
was consciously planned to foster technology
transfer and a maximum interface in related
fields. The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
H. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ENVIRONMENTAL
PROTECTION TECHNOLOGY series. This series
describes research performed to develop and
demonstrate instrumentation, equipment and
methodology to repair or prevent environmental
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.
EPA REVIEW NOTICE
This report has "been reviewed by the Office of Research and
Development, EPA, and approved for publication. Approval
does not signify that the contents necessarily reflect the
views and policies of the Environmental Protection Agency,
nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
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EPA-660/2-74-074
July 1974
RUM DISTILLERY SLOPS TREATMENT
BY ANAEROBIC CONTACT PROCESS
By
T. G. Shea, E. Ramos
J. Rodriguez, and G. H. Dorion
Project 800935
Program Element 1BB037
Roap/Task 21 BAG 13
Project Officer
H. George Keeler
Industrial Pollution Control Division
Room 3702F Waterside Mall
Washington, D. C. 20460
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D. C. 20460
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.75
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ABSTRACT
The rum distillery slops stream, i.e., the underflow produced
in the distillation of the fermented molasses mixture, typically
contains 70 to 100 gm/1 COD, 75 to 85 gm/1 dissolved solids, and 3 to
10 gm/1 suspended solids, and typically contributes two-thirds of the
wastewater flows and over 95 percent of the organic emissions, in the
wastewater streams emanating from rum distillery operations.
The general objectives of the present study were to develop an
anaerobic digestion process for the treatment of the slops stream at the
pilot scale, and to establish design criteria for the full-scale appli-
cation of the process. Both bench and pilot-scale experimental studies
were conducted with the anaerobic contact process flow sheet (incorporating
biomass recycle) to permit determination of the Monod kinetic constants
and the kinetic relationships describing the anaerobic treatment of the
slops. The process kinetics were used to examine the operating and
performance characteristics of a plant-scale application (predicted
effluent quality, mixed liquor volatile suspended solids concentrations,
methane production rates, etc.). A process flow sheet was established
and design criteria developed as the basis for estimating the cost of a
plant-scale installation. The process kinetic relationships and the
economic analysis were used to structure a cost-performance relationship
to examine tradeoffs between cost, performance, and selected design
variables.
The results of the above indicate the feasibility of the anaerobic
contact process for treatment of rum distillery slops as follows:
1. Capability to produce an effluent containing less than 30 gm/1 of
COD at solids retention times greater than 40 days, in the treat-
ment of a slops stream containing from 70 to 100 gm/1 of COD.
2. Range of total annual costs (including amortized, operating, and
maintenance costs) varying from $3.74 per cu m treated at a design
capacity of 190 cu m/day ($14.18 per 1,000 gallons at 50,000 gpd)
to $2.13 per cu m treated at a design capacity of 1,140 cu m/day
($8.07 per 1,000 gallons at 300,000 gpd).
n
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3. The recovery of methane as an energy byproduct of anaerobic contact
treatment of rum distillery slops can, at current energy costs,
reduce the above unit treatment costs from one-third at the 190
cu m/day (50,000 gpd) capacity to two-thirds at the 1,140 cu m/day
(300,000 gpd) capacity.
Additional treatment of the effluents of the anaerobic contact
process will be required to attain effluent quality levels currently
defined as BPTCTCA (best practicable control technology currently
available) by the Environmental Protection Agency.
This report was submitted in fulfillment of Project 800935 by
Bacardi Corporation under the partial sponsorship of the Environmental
Protection Agency. Work was completed as of December 1973.
• • *
m
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CONTENTS
Page
Abstract i i
List of Figures v
List of Tables vi
Acknowledgements vii
Sections
I Conclusions 1
II Recommendations 2
III Introduction 4
IV Development of Technical Program 10
V Experimental Apparatus and Procedures 27
VI Results 43
VII Design and Operational Analysis 70
VIII Economic Analysis 81
IX References 89
X List of Publications 92
XI Glossary 93
XII Appendix 95
IV
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FIGURES
No. Page
1 Schematic of General Treatment System 15
2 Determination of Kinetic Constants 21
3 Unified Operational Relationship for Anaerobic
Contact Process 23
4 Bench-Scale Anaerobic Contact Unit 28
5 Pilot Plant Process Schematic 30
6 Pilot Plant Clarifier/Thickener 31
7 Rum Pilot Plant Correlation Between Total
Suspended Solids and Optical Density 42
8 Slops Neutralization Relationship Between pH
and Lime Dose 47
9 Steady State Characteristics - Rum Distillery Slops
Treatment by Anaerobic Contact Process 53
10 Rum Distillery Slops Treatment by Anaerobic Con-D
tact Process-Determination of Values of Y and K
for Steady State Data 56
11 Rum Distillery Slops Treatment by Anaerobic Contact
Process-Determination of Values of k and K for
Steady State Data • 57
12 Unified Operational Relationship for Rum Distillery
Slops Treatment by Anaerobic Contact Process 60
13 Allowable Mixed Liquor Surface Loading Rate vs
MLTSS Concentration - Zone Settling 63
14 Relationship between Solids Removal Efficiency and
Solids Loading Rate (with and without Polymer) 66
15 Process Flow Sheet - Rum Distillery Slops Treatment
by Anaerobic Contact Process 77
16 Rum Distillery Slops Treatment by Anaerobic Contact
Process-Unit Treatment Costs °°
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TABLES
No. Page
1 Wastewater Generation in Rum Production 6
2 Monitoring/Analytical Schedule 34
3 Summary of Slops Characteristics 44
4 Ionic Composition of Slops (Units of mg/1) 45
5 Steady State Operations: Summary of Loading Rate,
Mixed Liquor, and Effluent Characteristics 51
-6 Steady State Operations: Summary of Operating and
Performance Characteristics 52
7 Values of Constants in Various Studies 58
8 Summary of Zone Settling Data 62
9 Summary of Results-Pilot Plant Clarification Tests 65
10 Design Criteria for Anaerobic Contact Process 78
11 Capital Costs (January, 1974) 82
12 Annual Operating and Maintenance Costs (January 1974) 84
13 Unadjusted Annual Costs for Rum Distillery Slops
Treatment by Anaerobic Contact Process 86
14 Nomenclature . 94
15 Summary of Parameters for Determination of km
and K - Steady State Data 99
VI
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ACKNOWLEDGMENTS
Of the many individuals in Bacardi Corporation who contributed to
the project effort, special acknowledgments are extended to: Mr.
William E. Paterson, Vice President and General Manager, for his
extensive support in all aspects of the project. Mr. Evelio Gonzalez
assisted in the design and set-up of the pilot plant, and Mrs. Nydia
Cancel and Mr. Jorge Bracero of Bacardi Corporation provided valuable
assistance in the laboratory operations. Dr. John F. Andrews of
Clemson University, Dr. A. D. Carr of the University of Capetown,
South Africa, and Dr. Paul Smith of the University of Florida, served
as Special Consultants to the project.
The firm of W. E. Gates and Associates, Inc. served as Project
Consultants, in the latter stages of the effort, and the contributions
of several of its staff members are acknowledged: Mr. John D. Stockton
and Mr. T. J. Smith, who designed and conducted the pilot plant solids
separation tests; Mr. J. E. Hensley, who assisted in data analysis and
presentation; and Mrs. Bitsy Smith, for editing and typing the report.
The contributions of Mr. Eric Jerome of Engineering-Science, Inc.,
with whom the senior author was associated during the early stages of
the project, are acknowledged.
The participation and support of Mr. H. George Keeler and Mr.
K. A. Dostal of EPA in all phases of the project effort are gratefully
acknowledged.
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SECTION I
CONCLUSIONS
The conclusions of the present investigation of rum distillery
slops treatment by the anaerobic contact process are as follows:
1. Rum distillery slops are amenable to treatment by the anaerobic
contact process; effluents containing less than 30 gm/1 of COD
are produced at solids retention times greater than 40 days in
the treatment of slops streams containing from 70 to 100 gm/1
of COD.
2. The Monod model describes the response of the anaerobic contact
process for the treatment of rum distillery slops even when
engineering-type parameters such as VSS (volatile suspended solids)
and COD (chemical oxygen demand) are used as measures of viable
biomass and limiting substrate, respectively, and is a useful
tool in engineering design and analysis of full-scale applications
3. The operational relationships between effluent quality and the
primary variables 9,. (hydraulic residence time) and C° (recycle
factor) provide a unifying basis for examining the design problem
and establishing operating requirements in the application of the
anaerobic contact process for treatment of rum distillery slops
4. The recovery of methane as an energy byproduct of rum distillery
slops treatment by the anaerobic treatment process can reduce
the unit treatment costs ($/unit volume treated) in a plant-scale
installation, at current energy costs, by at least one-third at a
design capacity of 190 cu m/day (50,000 gpd) and as much as two
thirds at a design capacity of 1,140 cu m/day (300,000 gpd).
5. Additional treatment of effluents from the anaerobic contact
process (for removal of COD, suspended solids, and color) will be
required in order to attain the effluent quality levels currently
defined as best practicable control technology currently available
by the Environmental Protection Agency.
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SECTION II
RECOMMENDATIONS
Based on the results of the present investigation as documented
herein, it is recommended that:
1. The anaerobic contact process, incorporating the recovery of
methane as an energy byproduct, be considered as a viable
alternative for the treatment of rum distillery slops
2. The development of criteria for a full-scale application of the
anaerobic contact process for rum distillery slops treatment be
based on (a) the transferable kinetic characterization of the
response of the anaerobic contact process, and (b) the framework
for development of design criteria to meet specific effluent
quality objectives, as presented herein
Specific design criteria are recommended herein (Section VII) for
the example design of an anaerobic contact process application to
achieve, as a treatment objective, an effluent quality of 30 gm/1 COD,
equivalent (for a raw slops COD concentration of 100 gm/1) to a soluble
COD removal efficiency of 70 percent. The recommended design criteria
for the key elements of the process train, as based on an evaluation of
experimental results presented in Section VI, are as follows:
1. OT/C°(sludge age) @ 40 days
2. QT (hydraulic residence time) @ 15 days, and C° (recycle factor)
@ 0.375
3. Solids loading rate to clarifier @ 100 kg/day/sq m (20.5 Ibs/day/
sq ft) on overflow basis
4. Lime addition (standby basis) @ 4 kg CaO per cu m/day of slops
flow (33.3 Ib @ CaO/1,000 gpd)
5. Phosphorus addition (to balance phosphorus requirements for anaero-
bic biological treatment) @ 0.3 kg P per cu m/day slops flow
(2.5 Ib P/1,000 gpd)
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6. Polymer addition (for conditioning of mixed liquor solids prior
to separation) @ 15 gm per cu m/day of slops flow (0.125 lb/
1,000 gpd)
In conjunction with process application at the full-scale, additional
research is recommended in the following areas:
1. Evaluation of alternative unit process technologies for solids
separation (e.g., centrifugation and flotation) and sludge
processing, such that cost-performance tradeoffs can be examined
in the selection of a separation system.
2. Evaluation of the nutritional value of byproduct sludges as a
feed extender.
3. Evaluation of the effectiveness of in-stream process control
measures, such as sulfide stripping from the recycled gas stream
to control mixed liquor sulfide concentrations, or C02 stripping
from the recycled gas stream to control mixed liquor pH.
4. Evaluation of alternative strategies for minimizing the time delay
in re-startup of an anaerobic contact treatment system at the end
of seasonal rum production shutdowns; alternative strategies that
merit evaluation include:
a. Minimizing the degree of reduction in raw slops supply by
staggering the shutdown of sectors of the rum production
facility
b. Holding in reserve a quantity of slops to be used to
re-start feeding in advance of the resumption of full produc-
tion
c. Using an alternative feed supply, such as raw municipal
primary sludge, during the shutdown/slowdown period
5. Evaluation of the efficacy of the anaerobic treatment of raw
municipal sludges jointly with rum distillery slops, allowing the
beneficial use of the nutrient release and alkalinity production
associated with the digestion of raw municipal sludges in the
treatment of the rum distillery slops.
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SECTION III
INTRODUCTION
STUDY OBJECTIVES
The following objectives were established for the study:
1. General objectives
a. to develop an anaerobic digestion process for the treatment
of the slops stream on a pilot scale
b. to establish design criteria for the full-scale application
of the process
2. Specific objectives
a. to refurbish, install, and operate an existing pilot plant
for the treatment of slops
b. to determine the process response characteristics and operating
boundaries for the anaerobic digestion process and the varia-
tions in process efficiency as a function of operating
parameters
c. to define at the bench scale an information base necessary
to design the above pilot scale experimentation
d. to verify the applicability of proposed kinetic relationships
for the anaerobic treatment of slops, and to establish values
of the kinetic constants for these relationships
e. to establish design criteria and to develop a preliminary
engineering design for the full-scale process
f. to estimate capital, operation, and maintenance costs for a
plant scale installation
BACKGROUND
The production of rum is accomplished by age-old processes that,
in their modern application, are similar in function throughout the
industry. The basic sequence of steps in rum production consist of:
the mixing of molasses, water, nutrients, and antifoamant; acidification
of the above mixture; propagation of the biomass used in the fermentation;
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the fermentation itself; and the distillation of the ferment. The
distilled spirits are transferred sequentially to holding tanks, to
oak barrel filling, to the aging warehouse, and (after a legally-defined
period of aging) to barrel emptying operations and thence to the bottling
line, in the typical operation. The above rum production and bottling
operations are often conducted on a seasonal basis, with shutdown
periods of one to two months each year for equipment maintenance and
replacement and other reasons.
The basic types of process waste streams generated in the produc-
tion of rum include:
1. The slops stream, i.e., the underflow produced in the distillation
of the fermented molasses mixture.
2. Barrel washings.
3. Cooling tower and boiler plant blowdown.
4. Regenerant water from water treatment facilities, analytical
laboratory wastewaters, and fermenter washdown.
Presented in Table 1 is a profile of (1) the total facility wastewater
generation per proof gallon produced from all of the above process
streams, and (2) an analysis of the percent contribution to the total
wastewater generation by each type of process stream. In review of
these data:
1. The slops discharge constitutes 66 percent of the waste flow,
over 98 percent of the BOD and COD emissions, over 90 percent of
the solids emissions, and essentially all of the nitrogen and
phosphorus emissions in rum production operations.
2. The second most important wastewater source on a flow volume basis
is the boiler and cooling water blowdown/fermenter washdown stream,
the flow component of which is derived primarily from the blowdown
streams, and the organic component of which is derived from the
fermenter washdowns.
It is apparent from the preceding that the slops stream constitutes the
major wastewater management problem in this industry.
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TABLE 1. WASTEWATER GENERATION IN RUM PRODUCTION
Waste
Parameter
or
Constituent
Vol ume
COD
BOD
Total Solids
Total Dissolved
Solids
Total Suspended
Solids
Total Kjehldahl
Nitrogen
Total Phosphate
Total
Facility Waste
Generation
per
Proof Gallon
55.6 1 (14.7 gal)
3.0 kg (6.6 Ib)
1.0 kg (2.3 Ib)
4.2 kg (9.2 Ib)
3.9 kg (8.6 Ib)
0.25 kg (0.56 Ib)
0.06 kg (0.14 Ib)
0.003 kg (0.007 Ib)
% Contribution by
Slops Barrel
Stream Washings
66% 5%
98% 1%
99%
9H
91%
97%
100%
100%
Type of Waste Stream
Boiler/Cooling Water Treatment
Water & Fermenter & Analytical Lab.
Washdown Wastewaters
26% 3%
1%
9%
9%
3%
—
—
Source: Bacardi Corporation
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The slops stream typically has the following characteristics
(a detailed characterization is presented in Section VI):
1. COD - 70 to 100 gm/1
2. BOD - 20 to 60 gm/1
3. Total suspended solids - 3 to 10 gm/1
4. Total dissolved solids - 75 to 85 gm/1
5. Total nitrogen - 0.8 to 1.5 gm/1
6. Total phosphorus - 60 to 100 mg/1
7. Sulfate - 3 to 5 gm/1
8. pH - 4.0 to 4.7
9. Color - 100,000 units
10. Temperature - 80 to 90°C
The principal factors associated with the magnitude and variation of
these characteristics are: the variable sugar and ash contents of the
molasses, which itself is a byproduct of sugar production; and the
amount of acidification (HgSOJ of the molasses-water mixture to
obtain an optimal pH level for the fermentation. The slop is rich
in nutrient materials having value as cattle feed extenders and soil
supplements. From a biological treatment perspective, the slops
stream typically contains a deficiency of nitrogen and phosphorus,
and most of the volatile suspended solids component of the slops
stream is derived from the yeast crop produced in the fermentation.
In recognition of the significance of the slops stream as a
wastewater management problem for the rum industry, the present study
was initiated to examine the efficacy of an anaerobic biological
treatment system as the initial processing step in the treatment of
slops. There are several basic reasons for selecting anaerobic biologi-
cal treatment for examination, the foremost of which are:
1. The organic content of the slops (70 to 100 gm/1 COD) is well in
excess of the point where the oxygen demand in an aerobic system
exceeds economically attainable rates of oxygen transfer.
2. The anaerobic fermentation process is characterized by low kinetic
reaction constants and biomass yields, the intramolecular breakdown
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of complex organic compounds, and the production of methane
gas as a byproduct.
3. Sludges produced in a properly functioning anaerobic fermenter are
generally more easily dewatered than are aerobic sludges, and a
lesser mass of waste solids is produced per unit volume of waste-
water treated in the anaerobic process than in the aerobic process.
The anaerobic biological treatment of rum distillery slops has
been examined by a number of researchers prior to the present investiga-
tion. The studies conducted thus far have been done on a case-by-case
basis, and while having demonstrated the amenability of slops to
anaerobic fermentation, prior effort hasn't led to the establishment
of a generally applicable kinetic model for predic ng the performance
of the anaerobic fermentation process as a function of the design vari-
ables. Additionally, the applicability of the anaerobic contact process
(incorporating the recycle of biomass from a solids separator back
into the anaerobic fermentation as a means of maintaining greater bio-
mass concentrations and greater sludge ages at reduced fermenter hydrau-
lic residence times) has not yet been examined for treatment of rum
distillery slops, although its applicability for treatment of other
concentrated organic streams is well documented.
STUDY ORGANIZATION
The study was initiated in May 1972 with the development of a
laboratory facility and pilot plant site at the Palo Seco, Puerto Rico
distillery of Bacardi Corporation. During the latter half of 1972:
1. Two bench-scale anaerobic contact process units were designed
and made operational
2. Pilot plant facilities and instrumentation were leased from the
University of Puerto Rico, and refurbished to incorporate a
separate clarifier/thickener for use (in an anaerobic contact
process configuration) in the present study
3. Work plans and preliminary reports for the investigations were
developed
4. Seed culturing techniques were established and seed cultures
were developed for use in the startup of each of the three units
8
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Biological treatability studies were initiated with the startup
of the two bench-scale systems in February 1973, and the pilot plant
in April 1973. The bench-scale units were operated over a nine-month
period under a wide range of hydraulic and organic loading rates, to
develop the information necessary to establish the process kinetics
(Monod kinetics) describing the anaerobic biological treatment of
slops in the anaerobic contact process. The pilot plant operations
were designed to develop the information necessary to verify the
process kinetic parameters at the pilot-scale, and to investigate the
settling characteristics of mixed liquor solids suspensions.
During the last month of pilot plant operations (December 1973),
the pilot plant was modified to permit evaluation of the settling
characteristics of the mixed liquor suspended solids under a wide
range of surface loading rates and sludge recycle rates, both with and
without polymer pre-conditioning of the mixed liquor solids suspension;
the results of this terminal activity in the study were used to develop
the design criteria for the gravity solids separation components of the
full-scale application.
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SECTION IV
DEVELOPMENT OF TECHNICAL PROGRAM
Consideration was given to several basic factors in the develop-
ment of the technical program: the historical experience in the
treatment of rum distillery slops by the anaerobic digestion process;
prior experience in the application of the anaerobic contact process
for industrial wastewater treatment; and the availability of a process
kinetic model for description of process performance under steady-state
conditions. The overriding interests in the process kinetic model were
to: (1) have a tool to guide the experimental design and decision-making
in the course of data acquisition; and (2) to provide a framework for
information transfer in the design of full-scale rum distillery slops
treatment systems incorporating the anaerobic contact process.
CURRENT STATUS OF TECHNOLOGY
Anaerobic Digestion of Rum Distillery Slops
Much of the experience on the treatment of spent molasses wastes by
the anaerobic digestion process has been summarized in an early (1959)
review by Pettet et a_l/ ' and in a later review by Hiatt et_ a_P . Two
factors reported by Pettet ejt al/ ' as interfering in the anaerobic
digestion of rum distillery slops are the high sulfate concentrations
in the slops stream, and the production of volatile acids in high con-
centrations during the anaerobic digestion. To circumvent the former
concern (sulfide inhibition as a result of sulfate reduction to sulfide)
and the general problem of high salinity concentrations in slops, much
of the research to date has been conducted using diluted spent molasses
(slops) waste feed streams. Stander^ ' was able to obtain a 66 percent
removal of organic carbon from a molasses slop diluted with an equal
volume of water at a hydraulic residence time of 3.75 days, an organic
loading of 8.8 kg volatile matter/day/cu m (0.55 Ib volatile matter/
day/cu ft), and at 33°C. In this study a repeated reinoculation
technique, equivalent to a form of solids recycle, was necessary to
sustain the fermentation. Hiatt et aP2', reported that a stable
fermentation was possible with a diluted slops stream (65 percent of
full strength) at a hydraulic residence time of 8.4 days, an organic
10
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loading of 7.7 kg total (unfiltered sample) COD/day/cu m (0.48 Ib total
COD/day/cu ft), and at a temperature of 35°C. A 71-percent removal of
total COD was obtained. These researchers also reported that a sustained
fermentation of full strength slops was obtained at a hydraulic resi-
dence time of 16 days, and at an organic loading rate of 5.9 kg total
COD/day/cu m (0.37 Ib total COD/day/cu ft), with a resultant COD
removal of 70 percent. After initial stabilization of the digesters,
the gas produced contained about 65 percent methane, and the methane
in the gas production represented about 69 percent of the COD removal.
These researchers suggested that gas scrubbing to remove hydrogen
sulfide and subsequent recirculation through the fermenter would be an
effective control action to relieve inhibition due to sulfide ion.
(2\
The observations of Hiatt et al_ that high volumetric loadings
are possible if the waste is diluted confirmed earlier work on the
(4)
anaerobic digestion of rum distillery slops by Radhakrishnan et alv '.
In laboratory studies conducted at 37°C, these investigators found
that the maximum possible loading with undiluted waste was 3 kg BOD/
day/cu m (0.18 Ib BOD/cu ft/day) at a hydraulic residence time of 11
days, whereas a maximum loading of 4.5 kg BOD/day/cu m (0.28 Ib BOD/
cu ft/day) was attained at a five-day hydraulic residence time with a
diluted waste (60 percent of full strength). BOD removals in these
studies averaged from 80 to 85 percent. The gas contained from 54 to
60 percent methane, and more than one percent hydrogen sulfide. In
evaluation of their results, the authors reported that volatile acids
levels in excess of 2,000 mg/1 (as acetic acid) did not impair the
fermentation, providing that a sufficiency of alkalinity was present
to maintain the pH of the system in excess of 7.0. Additionally, sulfide
concentrations as high as 240 mg/1 were not found to be inhibitory to
the digestion of undiluted wastes.
The preceding examples of prior experience with the anaerobic
digestion of spent molasses wastes are representative of the state-of-
the-art to date in that:
1. The efficacy of anaerobic digestion of this type of waste has been
established;
11
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2. Two types of toxic/inhibitory factors are commonly identified
in the applications: (a) high feed stream sulfate concentrations;
and (b) high volatile acid concentrations;
3. The high sulfate concentrations have been dealt with in several
investigations by reduction of the strength of the waste stream
to levels where its effect was deemed marginal
4. The high volatile acids concentrations anticipated in the digestion
process have been dealt with either by dilution of the raw waste
or by control of the rate of loading of undiluted wastes such
that the rate of alkalinity production was sufficient to balance
the rate of volatile acid generation.
Unfortunately, due to the inconsistent frameworks used in reporting
information derived in prior investigations, it is not possible to
characterize the anaerobic digestions achieved in prior studies and
to evaluate the effectiveness the operational controls used on a
rational kinetics basis, or even on a solids balance basis. Without
such information, it is impossible to interpret the significance of
empirical measures such as volumetric organic loading rate or hydrau-
lic residence time in terms of the viable biomass inventory associated
with the observed performance; nor is it possible, in the absence of
information on such parameters as mixed liquor solids concentrations
to ascertain, or even imply, the nature of the solids handling problems
to be dealt with in the design and operation of a full-scale application.
The absence of a rational basis to characterize the prior work
raises further questions with respect to evaluation of the operational
strategies used to control toxic substances in the fermentation of spent
molasses wastes. That is, there are two generic classes of toxic
substances, those which can serve as substrates after acclimation and
those which cannot serve as substrates. To compensate for toxicants
in the former class it is necessary to decrease the mass loading rate
of biodegradable matter per unit mass of viable organisms by one or more
of the following strategies * ':
1. Reduction of the mass loading rate of biodegradable matter, holding
the viable biomass constant;
12
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2. Increasing the viable biomass while holding the mass loading rate
of biodegradable matter constant
In the latter category of toxicants, and depending on the type of inhi-
bition (competitive or noncompetitive), the alternative strategies are:
1. Reduce the concentration of the toxicant to a level below which
its effect is marginal or neutralized by other chemical/biological
interactions
2. Neutralize the effect of the toxicant by the addition of chemical
agents
3. Reduce/eliminate the concentration of the toxicant in the waste
stream prior to anaerobic treatment (i.e., source control)
The volatile acids generated in the anaerobic fermentation are
indicative of a toxicant in the former category in that volatile acids
can serve as a substrate, but judicious operation is required. Un-
fortunately one cannot ascertain from the literature the ranges of
rational loading rates (e.g. Ib volatile matter per Ib solids per day)
in which the volatile acids concentration can be stabilized in the
application.
Several authors ^z>6»'' discuss the ionic content of spent molasses
wastes, the origin of which can be related to the "salt pickup" in the
production of molasses, the chemical conditioning of the molasses
mixture prior to fermentation, the "pickup" of metal components from
equipment in the distillation of the ferment, etc. While sulfides are
classifiable as a toxicant which cannot serve as a substrate in anaerobic
fermentation, there has been little examination in prior investigations
of the chemical interactions between the sulfide ion generated in the
reduction of sulfate in the anaerobic fermentation of spent molasses
wastes, and the heavy metal ion inventory found in these wastes.
Given the absence of a transferable information base for the design
and application of a full-scale anaerobic treatment system for rum
distillery slops, the overriding priority of the present study was
deemed to be the development of a rational kinetic basis for unifying
the understanding of the performance characteristics of anaerobic
fermentation systems in the application. Given the importance of
solids recycle in biological treatment systems, attention was directed
to the anaerobic contact process.
13
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Anaerobic Contact Process
The anaerobic contact process (Figure 1) basically consists of
two unit processes, an anaerobic fermenter and a solids separator
(either gravity or mechanical), with provisions for recycle of concen-
trated biomass from the separator to the fermenter and complete mixing
of the fermenter. Heating of the fermenter contents is provided in
those cases where higher throughput rates (resulting in hydraulic
residence time of hours rather than days) do not preclude its economic
feasibility, or when sufficient methane is produced in the fermentation
to satisfy heating requirements.
Fundamentally, the anaerobic contact process as originally des-
cribed and documented '8'9' differs from anaerobic sludge digestion
in that biomass recycle and relatively low substrate concentrations are
used. The literature contains reports on the use of the anaerobic
contact process for the treatment of cannery, packinghouse, brewery,
distillery, fatty-acid, wood fiber, and synthetic-milk wastewaters.
In evaluation of the literature, it was found that an anaerobic
process was originally classified (on the basis of applications experience)
to be of the contact type if it met the following criteria^ ': (1) an
influent concentration of 4,000 mg/1 BOD or less; (2) use of sludge
recycle; and (3) a liquid detention time of four days or less based on
influent flow. Thus, the application of the anaerobic contact process
for the treatment of rum distillery slops, in the present study, has
represented an initial effort toward establishing the feasibility of
the anaerobic contact process for treatment of high-strength wastes
containing BOD concentrations in excess of 4,000 mg/1.
The slaughterhouse application represents the most successful and
detailed study of the anaerobic contact process to date. The initial
stages of this study were reported by Fuller' . Subsequent work
was presented by Schroepfer et ar ', and Schroepfer and Ziemke'12' 13'.
The laboratory and pilot-plant work conducted by these investigators
resulted in the construction and operation of a full-scale facility^ '.
During the series of investigations it was determined that vacuum
degasification preceding gravity sedimentation was the most suitable
method for obtaining sufficient solids concentration to permit continuous
14
-------
FIGURE 1. SCHEMATIC OF GENERAL TREATMENT SYSTEM
Influent
Q, XN, X°
o o
J
_ Waste
N „&>
f\ %/ Y
Xu/> "D' n
" K K
^^
r^
Anaerobic
Reactor
Reactor Effluent ^
Q(l+r), Xj, X° ^
Solids
Separator
_ Recycle '
M in
»«n Y'' Y"
"4> A^, A^
Separator
Effluent
^
0 XN X°
y » A« » Ao
-------
solids recycle. Reactor hydraulic residence times as low as 2.3 hours
and loadings varying from 0.6 to 5.3 kg BOD/day/cu m were used success-
fully. The range of 9T/C° values reported for this application was
(g\ '
from 12 to 45 daysx '. BOD reductions ranged from 70 to 97 percent,
and raw wastewater BOD averaged approximately 1,400 mg/1.
The investigation of synthetic-milk waste treatment by the anaerobic
/Q\
contact process was reported by Gates et a]_ '. The investigation was
conducted at the laboratory-scale using an upflow anaerobic contact
unit (settler positioned over fermenter) in a vertical configuration.
The settler consisted of a baffle-type upflow separator which showed
good potential for accomplishing solids separation in the process.
Fermenter hydraulic residence times as low as six hours and loadings
varying from 0.8 to 5.4 kg BOD/day/cu m (0.05 to 0.34 Ib/day/cu ft)
were used successfully. BOD reductions varied from 30 percent at a
hydraulic residence time of six hours to levels in excess of 75 percent
at hydraulic residence times equal to or greater than 12 hours. 9T/C
tg\ '
values ranging from 10 to 28 days were reportedv. The influent BOD
concentration averaged 1,200 mg/1.
PROCESS KINETIC MODEL
(0}
The Monod model, as adapted by Gates ejt al_x ' to the anaerobic
contact process, was selected for use in the present study because of
its ability to describe the performance (effluent substrate concentration)
produced in the anaerobic contact process as a function of the hydraulic
residence time in the fermenter, biomass recycle, and kinetic constants
specific to the biodegradation of a given wastewater.
Basic Relationships
In the development of the growth kinetic model based on the work
(15)
of Monod* ' it is assumed that gross bacterial growth is always
exponential in character, that is:
where:
o
= time, and
X = organism concentration, mg/1
k = specific growth rate, time"
16
-------
The expression for net growth then becomes:
'
-------
When Equations 1, 2, 3, and 6 are applied to a continuous flow,
completely-mixed reactor at steady rate with solids recycle (as
exemplified in Figure 1), the equations required to describe the
characteristics of such a reactor can be derived from substrate and
solids balances around the anaerobic contact system. The resultant
equations are presented below, and the physical significance of the
symbology used is illustrated in the process flow sheet of Figure 1:
vO/v N - v N*
X,° = Y (Xo Xl ) (7)
KD9T + C°
H = K (KD9T
- (KD0T
k = KD + C°/0T (9)
C° = XW°/X1° (10)
where:
N
X, = effluent organism concentration, mg/1
XQ = influent substrate concentration, mg/1
X-, = effluent substrate concentration, mg/1
K = specific autodestruetion rate, time"
9,. = theoretical hydraulic detention time,
C° = recycle factor (unitless), and
= mass of organisms leaving system per unit time/total flow
leaving system per unit time, mg/1.
18
-------
In general, the value of XM° is the weighted average of the
concentration of organisms leaving the solids separator in the effluent
and in any sludge that would be wasted. The value of C° is zero when
•
all the organisms are recycled and one when no recycle is used.
The above equations assume that the controlling substrate is non-
settleable, thus, the substrate level in the system's effluent is the
same as that in the reactor. The equations can be modified to consider
a settleable substrate, as was observed to be the case in both the bench
and pilot systems used in the present investigation. The modified
equations as used herein were developed to account for the loss of
substrate and biomass from the anaerobic contact process in both sampling
and sludge wastage streams. The modified forms of Equations 7 and 10 are
as follows (no modifications were required to Equations 8 and 9):
KD9T + C°
and:
o
C° = QwXR + (Q~Qs~V X2 + ^s (12)
QX^o Q~
where:
XR = recycle stream substrate concentration, mg/1
XD° * recycle stream (and sludge wastage stream) organism concen-
K .
tration, mg/1
Q = sample flow rate (average), I/time (not shown in Figure 1),
Q = sludge wastage flow rate, I/time
W
C" = degree of concentration of substrate in the solids separator
r = fraction of influent recycled.
Determination of Kinetic Constants
For purposes of determining the kinetic constants, Y , K , k , and K
of the model, engineering-type parameters such as soluble (filterable)
19
-------
COD have been used to represent the rate-controlling (biodegradable)
substrate concentration (X, ) and volatile suspended solids (VSS) as
a parameter representing the viable biomass concentration (X,°) in
the above equations. The determination of the process kinetic constants
requires process evaluation (flow, solids and substrate balances) over
a range of variation of 9y/C° values (biomass retention times) of one-
half to one order of magnitude.
The kinetic constants are determined by using linear forms of
Equations 11 and 8 (Figure 2) to analyze the experimental points
obtained in the balances. From Equation 11:
X." - X^ [l-r (C«-ljj _ i x £ /»r\ (13)
QN
Y° Y° \C°
From Equation 8:
6T . 1 +
KD9T + C° km
A plot of Equation 13 is presented in Figure 2a, in which the intercept
is the inverse of the value of Y°, and the slope represents the ratio
K /Y°, for the best-fit line of the set of experimental data used.
Presented in Figure 2b is a plot of Equation 14; the intercept of the
best-fit line in this figure is the inverse of the value of km and the
slope is equal to K/km. In consideration of the best-fit lines used in
determining the kinetic constants, it is apparent that from five to
ten well-spaced experimental points are sufficient to define the process
with the Monod model in any application.
Operational Relationships
Equation 8 can be rewritten to formulate an operational relationship
N
between the effluent substrate concentration, X, , of the anaerobic
20
-------
FIGURE 2. DETERMINATION OF KINETIC CONSTANTS
0)
4->
at
+J
V)
.a
=j
V)
to
CO
X
o
X
X
o
Figure 2a. Autodestruction (K°) and Yield Yc
k°/Y°
Y°~mg/VSS/mg BOD
or ITT ""'—
Ku~ Days
mg VSS/mg
-1
COD
0T/C°, Days
to
>>
(0
o
°0
CD
a
Figure 2b. Saturation Constant (K) and Maximum
Specific Growth Rate (k }
~ Days'1
K~ mg COD/1 or
mg BOD/1
1/xA l/(mg Substrate/1)
21
-------
contact process, and the basic design parameters, QT (hydraulic residence
time) and C° (recycle factor), as follows:
9T K + X,N
_T _ 1
C° " (km-KD)X1N - KKD
A plot of Equation 15 is presented in Figure 3, from which it is
apparent that, for a given set of kinetic constants and a specified
effluent quality, the ratio 9,./C0 is specified. The relationship
defined by Equation 15 is a hyperbola which becomes asymptotic to an
ordinate value equal to K K/(km-K ) and to an abscissa value equal
to l/(km-KD). The value of KDK/(km-KD) represents the minimum substrate
concentration which can be realized in the effluent and is obtained
when C° is zero (i.e., 100 percent recycle of biomass) or 9T is infinity.
m T\
The value of l/(k -K ) is approached as the effluent substrate concen-
tration (X, ) approaches the influent concentration (X ), i.e., when
biomass washout occurs.
Several basic premises of the kinetic formulation for the anaerobic
contact process are embodied in this expression:
1. Effluent quality as predicted by Equation 15 is directly a function
of the viable biomass in the fermenter.
2. Effluent quality is not a function of influent quality; the only
way that the biological process can respond to changes in the
influent quality (or more appropriately, to changes in the mass
loading rate of biodegradable matter), is by an increase or decrease
•t-
in the inventory of viable biomass in the system.
3. For any given 9y, an increase in C° results in a decrease in
effluent quality; a decrease in the value of C° results in an
improvement in effluent quality.
The basic objective of the design of an anaerobic contact system
is to achieve the 9T/C° ratio as specified by the desired effluent
quality and the determined kinetic constants for the least cost. The
22
-------
FIGURE 3.,, UNIFIED OPERATIONAL RELATIONSHIP FOR ANAEROBIC CONTACT PROCESS
Equation:
Zone of Unstable Performance
Zone of Stable
Performance
Minimal X.N 0 QT/C°
0T/C°, Days
23
-------
costs associated with 9T are the tankage cost, the cost of mixing, and
• -^
the optional cost of heating. The costs associated with C are those
for the solids separator and the necessary pumps and piping, and the
power costs for operation of the separator and for pumping. Thus, a
consideration of the costs associated with the size of the fermenter
and separator, pumps and piping, mixing and power and other operational
costs can be used to define the least cost region for a design of an
anaerobic constant process to realize the specified 9j/C° value.
The problems of operation are somewhat more arduous than those of
design. The net result of design is almost inevitably the specifica-
tion of a fermenter of fixed size (which provides the desired QT based
on a design flow rate), a solids separator of fixed solids handling
capacity, and a capacity to vary the quantity of underflow from the
solids separator that is pumped back to the fermenter. Thus, in
effect, the only controllable operational variable is C°. The major
factors which affect C° are the effectiveness of the solids separator
in controlling the biomass concentration in the liquid effluent from
the separator, and the capacity to recycle biomass from the clarifier.
After the design of a solids separator has been established, its
effectiveness can be controlled only by the recycle rate and/or the
addition of primary coagulants or coagulant aids (i.e. polymers).
Three regions of operation can be defined with the operational
curve for the anaerobic contact process (Figure 3):
1. A zone of "stable" performance, in which a unit change in the 9T/C°
results in little change in the effluent quality.
2. A zone of transition or "unstable" performance, in which a unit
change in the 9j/C° value will generate significant change in the
effluent quality.
3. A critical zone, in which effluent quality deteriorates rapidly.
Because as previously discussed, C° is typically the only operational
variable available, the anaerobic contact process has its greatest
operational sensitivity in the "unstable" zone. Thus, when the desired
effluent quality is based on a pretreatment or effluent standard (the
24
-------
most likely case), the objective of the operation becomes primarily
that of ensuring that C° is equal or less than the design value at
all times. However, if the actual 9T is variable, that is, if the
actual flow rate deviates widely from the design flow value, then the
objective of operation is to vary C° such that at all times, the ratio
9T/C is equal to or greater than that necessary to provide the desired
effluent quality.
RATIONALE AND EXPERIMENTAL STRATEGY
The experimental program was organized to deal with the following
types of information needs:
1. Delineation of criteria for startup of a methanogenic fer-
mentation.
2. Delineation of the process performance characteristics of the
anaerobic contact process in this application within the context
of Monod kinetics.
3. Documentation of the performance characteristics of alternative
solids separation and handling unit processes.
4. Development, from the above, of design criteria for a full-scale
application.
5. Economic evaluation of the full-scale application on a cost-
performance basis.
In consideration of these needs, the following sequence of steps
were taken in the conduct of the experimental program:
1. A process kinetic model of the anaerobic contact model (described
herein) was selected as the basis for:
a. providing a unifying framework for integrating the use of
biomass recycle to overcome the low growth rates of the metha-
L
nogenic bacteria, such that the resultant process descriptions
are transferable from one case to the next.
b. experimental design, i.e., for the design of experimental
facilities, selection of operating conditions, and for the
continuous updating of experimental conditions being examined
as process response information was developed.
25
-------
2. Bench-scale anaerobic contact systems (incorporating 20-liter
anaerobic fermenters) were developed and operated over a range of
hydraulic loading rates sufficient to permit definition of the
kinetic constants of the Monod Model.
3. The kinetic constants were used to develop an operational relation-
ship for predicting pilot plant performance as a function of 9j
(hydraulic residence time) and C° (recycle factor), and the relation-
ship was used to select pilot plant operating conditions to be
examined.
4. The pilot-scale anaerobic contact system (incorporating a 1,890
liter anaerobic fermenter) was operated at the selected operating
conditions to provide a data base for confirming the kinetic
relationships.
5. Upon completion of the process kinetic characterization, the pilot-
plant system was modified to permit operation of the clarifier
over a wide range of solids loading rates, using the mixed liquor
suspended solids in the pilot plant as a recyclable feecf stream,
6. Laboratory studies were conducted prior to the pilot-scale settle-
ability testing to guide the selection of a coagulant aid and to
develop dosing criteria with the selected coagulant aid.
26
-------
SECTION V
EXPERIMENTAL APPARATUS AND PROCEDURES
The objectives of the experimental program were: (1) to
document the performance characteristics of the anaerobic contact
process in the treatment of rum distillery slops, and (2) to determine
the clarification capacity required for separation of mixed liquor
solids. To accomplish these objectives, two bench-scale anaerobic
contact units were designed, and the pilot plant of the University of
Puerto Rico was converted into an anaerobic contact unit. All three
units were set up at the laboratory facility and pilot plant site
provided by Bacardi Corporation at their Palo Seco, Puerto Rico distillery.
The bench-scale units were designed to permit the evaluation of anaerobic
biological process kinetics over a range of hydraulic residence times
varying from five to 200 days. The pilot plant was redesigned to
\
permit examination of anaerobic biological response over a necessarily
more limited range of hydraulic residence times (five to 50 days), and
to permit evaluation of the settling characteristics of mixed liquor
solids suspensions, both without and with the use of coagulant aids, as
a function of clarifier loading rate.
EXPERIMENTAL APPARATUS
Bench-Scale Units
A schematic flow diagram of the bench-scale anaerobic contact unit
is presented in Figure 4. The bench-scale systems (two were utilized)
each consisted of a 20-liter completely-mixed anaerobic fermenter,
temperature-controlled at 33 to 36°C, and a four-liter gas and solids
separator vessel. Each system was equipped for continuous flow feeding,
sludge recycle, and gas recycle. Feed was pumped continuously from a
refrigerated reservoir; flow traversed upward through the reactor into
the gas/solids separator, from which separated gas and sludge streams
could be pumped either back to the fermenter or to wastage/storage.
27
-------
FIGURE 4. BENCH-SCALE ANAEROBIC CONTACT UNIT
To
Liquid
Effluent
Reservoir
(Refrigerated)
Gas Separator-
Solids Separator
Vessel (4,0
Anaerobic
Fermenter
(20 j?)
NOTES: 1. Anaerobic Reactor
9 33-35° C
Gas
Recycle|
Pump
_t23 LLJ
Sludge
Recycle
Pump
Sludge
Wastage
2.
= Sample Port
From Influent
Stream Reservoir
(Refrigerated)
-------
Pilot Plant
A schematic diagram showing the components of the pilot plant is
presented in Figure 5. The pilot plant consisted of the following:
1. A 1,130-liter (300-gallon) insulated slops storage tank used to
hold feed slops batches.
2. A 1,890-liter (500-gallon) insulated anaerobic fermenter, equipped
with: an electric heat tape system, thermostatically controlled
to maintain the temperature of the mixed liquor in the fermenter
at 33 to 36 C; gas recycle at a rate of 0.15 standard cu m/min/cu m
of mixed liquor (20 SCFM/1,000 gallons); and liquid recycle at a
rate of 0.06 cu m/min/cu m of mixed liquor (60 gpm/1,000 gallons)
3. Hydrogen sulfide scrubbers (two), each consisting of cylindrical
tanks, 0.1 m diameter by 0.6 m in height (4-in diameter by 2-ft
height), filled with steel wool and designed for removal of
approximately 1/2 kg elemental sulfur per kg steel wool
4. A vacuum degasifier, consisting of a cylindrical tank 0.15 m
diameter by 0.6 m in height (6-in diameter by 2-ft height),
for degasification of the mixed liquor flow at a vacuum of 15 mm Hg.
5. A gravity clarifier/thickener (Figure 6), constructed from the
internal conical element of the pilot plant as furnished; the key
features of the clarifier/thickener were as follows:
a. the conical (clarifier) sector of the unit has a cross-sectional
area of one sq m (10.7 sq ft) at the liquid surface and 0.21
sq m (2.2 sq ft) at the bottom of the cone.
b. effluent is withdrawn from the clarifier in four effluent
funnels, presenting a total weir length of 2.57 m (8.4 ft).
c. the thickener sector of the unit is equipped with a thickener
screen that can be rotated at rates of 1/8 to 1/2 revolution/
minute.
d. sludge withdrawal is accomplished by means of a variable speed
pump capable of a maximum sludge withdrawal rate of 985
liters/day (260 gallons/day).
29
-------
FIGURE 5. PILOT PLANT PROCESS SCHEMATIC
To waste gas flareoff
GO
O
Slops
Feed
Batches
r
Anaerobic
Fermenter
Gravity
Clarifier
hickener
Note: (s)= Sampling Point
-------
FIGURE 6. PILOT PLANT CLARIFIER/THICKENER
l"D1a.Thickener
Drive Shaft —
Driven & 1/8 to~\
1/2 Rev/M1n. \
k.
Thrust Pulley, , Ml .
Block
T
12" to 14"
42'
1" Dia. "H"-
Manifold
1/4 HP
Motor
-Platform
Effluent
Funnels
4 Each of -8"
Dia. On
"K" Manifold
1" Dia. Piping
Existing Cone;
All Internal
Baffles Removed
Thickened
Sludge
Withdrawal-
And Recycle
To Digester
Pillow
Block
V'xV'Mesh Thickener
Screen (Tack to
Bar Supports)
-1/2" x 1/2" x 12" Bar
Supports for
Thickener Screen
-Install 4 Each,
1 1/2" xl 1/2" x 8"
Angles @
90° Around
Thickener Screen
31
-------
6. A 190-liter (50 gallon) mix-head tank and a stock polymer solution
feed tank; the mix-head tank was equipped with a constant-head
overflow (the overflow being recycled directly back to the anaerobic
fermenter); stock polymer solution was fed into the mix-head tank
and the contents of this tank could be mixed with a recycle pump
at a rate of one volume every five minutes.
The entire pilot plant was constructed of stainless steel, and
was equipped and instrumented to provide: (a) sludge recycle from the
gravity clarifier/thickener to the slops feed line to the fermenter;
and (b) complete mixing of the anaerobic fermenter utilizing recycled
gas and/or mixed liquor from the fermenter.
During the first phase of pilot plant operations (evaluation of
anaerobic biological process kinetics), raw slops were fed from the slops
storage tank at preselected continuous flow rates, and flows of mixed
liquor from the anaerobic fermenter were transferred directly to the
pilot plant (i.e., the flow path through the mix-head tank was not
used). During the final phase of pilot plant operations (evaluation of
mixed liquor settling characteristics), all mixed liquor flows were
directed to the mix-head tank, and from this point by gravity into the
clarifier-thickener.
Both the bench and pilot systems were designed with the sampling
ports necessary to permit characterization of liquid volumes within
each component of the system, liquid and material transfer rates into,
within, and from the components of systems, and gas production rates.
The approximate locations of the sampling ports are shown in the
schematics of Figures 4 and 5.
OPERATIONAL PROCEDURES
Process Kinetic Characterization
The biological process kinetic studies were conducted in three
phases of operation: seed culture development; startup and acclimation
of the bench and pilot scale units; and routine operations.
32
-------
Development of Seed Culture^ - Seed cultures for use in the startup of
the bench and pilot systems were propagated in anaerobic vessels equipped
with feed and sampling ports, and with bunsen-type gas release valves.
Selected as a source of methanogenic material was the bottom mud of a
brackish water inlet to San Juan Bay (Puerto Rico); this inlet has received
slops discharges from a small rum distillery and cooling water discharge
from an electrical power generation station for a number of years. Each
seed culture vessel was filled with deoxygenated tap water at 35°C; about 40
percent of which was displaced with a C02:N2 gas mixture; bottom mud was
added in an amount of about 25 percent of the volume of the vessel; and then
the vessel was "topped off" with undiluted slops that had been neutralized
to pH 7.0 with sodium bicarbonate.
The seed cultures were maintained by daily batch feeding of
gradually increased amounts of raw slops neutralized to pH 7.0 with
sodium bicarbonate. Daily observations were made on the pH of the seed
culture and the gas production and composition generated in each vessel.
The first trace of methane was typically observed within two to four
weeks after initiation of seed culturing and a minimum time of four
months was allowed before the seed cultures were transferred to the
fermenters.
Startup and Acclimation - The two bench-scale and the pilot-scale
anaerobic fermenters were "seeded" with the seed cultures using the
same procedure as outlined above, i.e., the fermenters were filled with
water, a portion of the water volume displaced with a C02:N2 gas mix-
ture, the seed culture added, and neutralized slops added, in the pro-
portions outlined above. After seeding, all three units were fed
neutralized (pH 7.2) undiluted slops at flow rates allowing hydraulic
residence times in excess of 30 days, to permit the buildup of MLVSS
(mixed liquor volatile suspended solids) concentrations to minimal
levels of 300 mg/1.
Throughout the four-month acclimation period; as well as in
subsequent periods of operation, each anaerobic contact unit was moni-
tored in accordance with the schedule presented in Table 2 and described
in detail below.
33
-------
TABLE 2. MONITORING/ANALYTICAL SCHEDULE
Measurement or
analysis
Flow rates (all)
COD
BOD
TSS/VSS
TKN
NH3-N
Total P
Volatile Acids
PH
Alkalinity
Gas Composition
Temperature
Sul fides
Sulfate
Influent,
stream
D
_3
_3
_3
_3
_3
_3
_3
_3
3
M
Fermenter,
contents
TW
TW
BM
BM
BM
D
D
D
D
W
Liquid 9
effluenr
D
TW
TW
SI udge
wastage
_4
5
Gas
reservoir
D
D
Notes:
Continuous flow influent stream to anaerobic fermenters.
separator-solids separator.
Done once per batch of refrigerated feed in bench system and once per
.batch of stored slops in pilot plant.
^Measure volume/record date and time for each withdrawal.
For each sludge withdrawal.
D = grab sample daily, W = grab sample weekly, BM = grab sample bimonthly;
TW = grab sample three times per week.
34
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An evaluation of the operating experience acquired during the four
month period of acclimation and buildup of a viable biomass inventory
in each unit led to the development of the following guidelines for
startup:
1. The maximal rate of slops feed should not exceed on kg soluble
COD/day/kg MLVSS if the buildup of volatile acids is to be avoided
2. The pH of the mixed liquor should be maintained in the range of
7.2 to 7.3 at all times.
3. Continuous gas and/or liquid recycle mixing of the fermenter
contents should be provided at all times.
Routine Operations - After completion of acclimation, it was possible
to sustain a methanogenic fermentation of undiluted and unneutralized
slops stream at a pH in excess of 7.0 during operations at hydraulic
residence time greater than of 20 days. Neutralization was required to
maintain a mixed liquor pH in excess of 7.0 at residence times below 20
days, indicative of a differential between the required and the internally-
generated buffering capacity; this differential was observed to increase
with decreasing hydraulic residence times at hydraulic residence times
less than 20 days (Section VI). During routine operations, neutraliza-
tion was accomplished, as needed, by the addition of sodium bicarbonate
directly into the bench and pilot-scale fermenters.
Monitoring and Analytical Program - A summary of the monitoring and
analytical schedule used in process kinetic evaluation of both the bench
and pilot systems is presented in Table 2. This schedule was designed
and utilized to permit the routine development of the following informa-
tion:
1. Substrate balances (mass transfer rate basis).
2. Solids balances (mass transfer rate basis).
3. Flow balances.'
4. Organic loading and removal rates.
5. Gas production rates and composition.
6. Fermentation control information (alkalinity, concentration, pH,
and volatile acids concentration).
35
-------
7. Nutrient balances (nitrogen and phosphorus).
The substrate, solids, and flow balances were developed on a
weekly basis for each of the three units, and the balance data was
reduced to develop a single set of experimental points per week, for
each unit, for the kinetic characterizations. The solids and flow
balances were used to characterize the performance of the solids
separators. The nutrient balances were used to ascertain the sufficiency
of influent nitrogen and phosphorus concentrations (in relation to the
influent BOD concentration). The organic loading and removal rate data,
and the gas production rate and composition data were used to develop
overall measures of performance of the anaerobic contact units. The
fermentation control information and the daily rate gas production rate
data were used as real-time measures of the status of the fermentation
and to establish the day-to-day operating changes required.
The data reduction process outlined above is illustrated by the
example calculations presented in Appendix A of Section XII. The
schedule of analyses presented in Table 2 was done using procedures
of "Standard Methods"' '. The BOD and COD analyses were made on
both unfiltered and filtered samples in the determination of total
BOD and COD and soluble BOD and COD respectively.
Determination of Clarification Capacity
The objective of this phase of effort was to develop a relationship
between clarifier performance and loading rate that could be used to
examine tradeoffs between the recycle factor (C°) attainable, and a
loading parameter from which (1) the size and (2) the cost of the
clarifier system could be established. The factors that were considered
in the design of the experimental procedures were:
1. The inherent limitations of the pilot plant facility on the
flexibility of operations.
2. The dependent (performance-related) and independent (loading-
related) parameters to be selected.
3. The anticipated "shape" of the response surface relating the
performance and loading parameters.
36
-------
4. The selection of a suitable coagulant aid to improve the settle-
ability of the mixed liquor solids, i.e., to improve the conversion
of soluble, colloidal, and non-sett!eable suspended solids forms
to a sett!eable form.
Evaluation of Experimental Variables - The pilot plant facility as
utilized in the process kinetic characterization imposed several
limitations on the clarification experiments, in that:
1. During the process kinetic characterizations, the maximum feed
rate used (in the order of 190 liters/day or 50 gpd) resulted in
maximal clarifier liquid loading rates of 0.204 cu m/day/sq m
(5 gpd/sq ft), about 50 fold less than the maximal liquid loading
rate capacity of 10.2 cu m/day/sq m (250 gpd/sq ft) desired for
the clarification experiments.
2. Only a limited mass of suspended solids (approximately 50 kg of
total suspended solids), at a constant concentration level of 12,000
to 14,000 mg/1 was available for use in the clarification experiments;
given the need to recycle (conserve) this inventory in the experi-
ments, important considerations in evaluating the results of this
effort were: (a) the recycle of coagulant aid with the recycled
solids; (b) the buildup of a residual coagulant aid dose in the
mixed liquor solids inventory; and (c) the potential adverse effects
of a buildup to a coagulant-aid overdose situation.
The following steps were taken to resolve these limitations:
1. The pilot plant was modified to permit the recycle of both settled
solids and clarified effluent back to the anaerobic fermenter -
a measure necessary to conserve the essentially fixed supply of
mixed liquor solids available.
2. Larger pumps were installed to permit the transfer of: (a) mixed
liquor into the mix-head tank, and thence by gravity into the
clarifier at a maximum surface loading rate of 10.2 cu m/day/sq m
(250 gpd/sq ft); and (b) settled solids in the sludge recycle stream
and clarified effluent back to the anaerobic fermenter.
The parameter selected as a measure of clarifier performance was
the efficiency of total suspended solids (TSS) removal; when this
37
-------
efficiency parameter is expressed as a decimal fraction, the value of
the recycle factor (C°) is equal to 1-(TSS removal efficiency). The
loading parameter selected was the solids loading rate (units of kg
TSS/day/sq m or Ibs/day/sq ft); this parameter can be related, through
a scale-up factor, with the solids-handling-capacity parameter determined
in laboratory zone settling assays. With TSS removal efficiency as
the performance parameter, and solids loading rate as the independent
parameter, the response surface relationship between these parameters
can be defined as one of efficiency decreasing at an increasing rate
with increasing loading rate, as documented in the literature^ .
The selection of a coagulant aid was done by a jar testing program
that was designed with the objective of screening a wide range of
high and low molecular weight polymers. Polymers as opposed to metal
ion coagulants or lime were selected for the screening tests because of
(1) the high fraction of dissolved and colloidal materials in the slops
stream (as discussed in Section VI), and (2) the desire to minimize the
i
dosing levels required and the associated waste sludge production.
Polymers typically have a helical structure comprised of carbon chains
with ionizing groups attached. These radicals ionize to effect a
straightening of the chain by electrical repulsion. Colloidal solids
can then interact with the straightened chain by electrical interaction
and adsorption. As the charges neutralize, the polymer starts to coil
again, and eventually forms a large enough floe to be susceptible to
removal.
A basic problem with most polymers is that an overdose leads
to an excess of charged sites being present in the aqueous solute, such
(18)
that they cannot be neutralizedv '. In this case, the straight chain
structure is maintained, the system can become highly stable, and there
is a diminished level of removal effected. Because of the potential
overdosing problem associated with the use of polymers, and the antici-
pated accumulation of recycled residual polymer in the anaerobic contact
process applicationj a primary criterion in the screening of candidate
polymers was the identification of a polymer providing a high degree of
conversion/separation over a wide range of polymer doses.
38
-------
The polymer selected on the basis of jar testing was Nalco 627,
a moderately cationic, high molecular weight polymer^19). With this
polymer, it was possible to attain in excess of 80 percent TSS removals
in the jar test beakers after 30 minutes of quiescent settling at
specific polymer doses varying from 1 to 5 mg per gm TSS. At a mixed
liquor TSS concentration of 10,000 mg/1, this specific dose range is
equivalent to polymer doses of;10 to 50 mg/1.
Operating Procedures - The evaluation of clarification capacity was
conducted as a two-step effort consisting of laboratory zone settling
assays followed by pilot plant experimentation.
The zone settling assays were conducted with the objective of
determining the solids handling capacity of the limiting layer as a
function of specific polymer dose and initial TSS concentration in the
suspensions. The zone settling assays were performed in one-liter
graduate cylinders, using three mixed liquor slurries having initial
TSS concentrations of approximately 6,000 mg/1, 12,000 mg/1, and 28,000
mg/1, respectively. Batches of slurries at each concentration were
prepared by the dilution or settling of mixed liquor solids obtained
from the pilot plant, and aliquots of each of the three slurries were
pretreated at specific polymer doses of about 1 mg/gm TSS and 5 mg/gm
TSS respectively. The observations made during each assay were inter-
face height and elapsed time, from which settling curves were plotted.
The settling curves were analyzed using the procedure described by
Eckenfelder^17', for the determination of limiting layer solids
handling capacity. The results of the zone settling assays are compared
with the pilot plant experimental results (Section VI) as a basis for
the selection of a design solids loading rate for the full-scale applica-
tion.
Two consecutive series of experimental runs were conducted with
the pilot plant to document the relationship between efficiency of TSS
removal and solids loading rate. In the first series, no polymer
addition was used, and runs were conducted at TSS loading rates of 48
kg/day/cu m (9.8 Ib/day/sq ft) and 89 kg/day/cu m (18.1 Ib/day/sq ft),
39
-------
equivalent to liquid loading rates of 2.64 cu m/day/sq m (65 gpd/sq ft)
and 7.97 cu m/day/sq m (195 gpd/sq ft) respectively. In the second
series, polymers were dosed throughout each of five runs conducted, at
a specific polymer dose varying from 1 to 3 mg/gm, paced to the mass rate
of transfer of mixed liquor TSS into the mix-head tank. The runs were
conducted at TSS loading rates varying from 63.5 kg/day/sq m (13 lb/day/
sq ft) to 125 kg/day/sq m (25.3 Ibs/day/sq ft), equivalent to liquid
loading rates varying from 4.87 cum/day/sq m (119 gpd/sq ft) to 8.48
cu m/day/sq m (297 gpd/sq ft). All of the above solids and liquid
loading rates are expressed on an overflow basis.
The runs in each series were conducted in sequence over time periods
varying from one to four hours per run. Observations were made at half-
hourly intervals during the runs for the determination of the mixed
liquor flow rate into the mix-head tank, clarified effluent flow rate,
and sludge recycle flow rate. Samples were taken of each of the above
streams at half-hourly intervals for determination of TSS concentra-
tions. Aliquots of the samples taken from the mixed liquor stream
entering the mix-head tank and from the clarifier effluent were
analyzed immediately by an on-line optical density method (discussed
below) for determination of estimated TSS concentrations in each of
these streams on a real-time basis. The estimated TSS concentration
in the mixer liquor stream was used to compute the mass rate of Tnixed
liquid solids transfer into mix-head tank, as a basis for pacing the
mass rate of polymer feed at the desired specific dose, and the esti-
mated TSS concentrations in the clarified effluent and mixed liquor
streams were used to calculate the TSS removal efficiency. All real
time parameters developed on the basis of TSS concentrations determined
with the on-line measurement technique were later recalculated using
actual TSS measurements (which were available within 24 hours of
sampling).
The on-line optical density method for estimation of TSS concen-
tration was based on a correlation curve between (1) percent transmittance
of a 1: 50 dilution of sample aliquot, as measured against a distilled
water blank at a wave length of 625 my on a Bausch and Lomb Spectronic
20 instrument, and (2) the TSS concentration of the undiluted sample
40
-------
as determined by "Standard Methods"^ '. The correlation curve used
in the pilot plant experimentation is presented in Figure 7, and was
developed by the determination of the optical density (according to the
above procedure) and the TSS concentration of over 100 samples of mixed
liquor and clarified effluent.
41
-------
FIGURE 7. CORRELATION BETWEEN TOTAL SUSPENDED SOLIDS AND OPTICAL DENSITY
20,000-
TO.OOO
7,000
4,000
-2,000
T
I
Notes
-1. TSS on whole sample
2. % T on 1:50 dilution
3. Distilled H20 blank
4. O.D. @ 625 mp
5. Bausch and Lomb Spectronic 20
o
e°
en
£
o
o
o
to
10
o
o
o
% Transmittance
o
20
30
40
50
60
42
-------
SECTION VI
RESULTS
CHARACTERISTICS OF SLOPS
Each of the slops batches used as a raw waste supply to the bench
and pilot units was characterized as to organic, solids and nutrient .
composition, and several of the batches were analyzed for ionic compo-
sition. This effort was done to provide data on the influent loadings
for the process performance analysis, and to permit a general character-
ization of this waste stream. From the data base developed, a summary of
the wastewater parameters characterizing the slops is present in Table 3,
and a summary of observations on the ionic composition of slops is
presented in Table 4.
In the evaluation of these analytical results, it was found that
the data sets on the soluble and total BOD and COD parameters (Table 3)
can be categorized into two data distributions, each associated with one
of the two distillation column modes in operation at the time the slops
batches were collected. A similar differentiation (on the basis of
distillation column operating mode) could not be developed with the data
for the other parameters. The operating mode associated with the lower
mean soluble and total COD and BOD concentrations was used about 75 percent
of the time during the study, and the second mode was used the remainder
of the time.
The mean soluble and total COD concentrations characteristic of
slops obtained during the predominant operating mode were 72,000 mg/1
and 74,800 mg/1, respectively (soluble COD: total COD ratio of 96 percent).
The mean soluble and total COD concentrations characteristic of slops
obtained during the other operating mode were 92,000 and 99,800 mg/1,
respectively (soluble COD: total COD ratio of 0.92). Thus in the samples
analyzed, both the soluble and total COD concentrations characterizing
the slops during the latter mode of operation were about 30 percent
greater, respectively, than those characterizing the slops in the pre-
dominant operating mode.
43
-------
TABLE 3. SUMMARY OF SLOPS CHARACTERISTICS
Parameter
Soluble COD (mg/1)
Total COD (mg/1)
Soluble BOD (mg/1)
Total BOD (mg/1)
Alkalinity (mg/1 & CaC03)e
Volatile Acids (mg/1 G> HAc)e
pHe
Solids (mg/l)e
Total
. total fixed
. total volatile
Total dissolved
. fixed dissolved
. volatile dissolved
Total suspended
. fixed suspended
. volatile suspended
Nitrogen (mg/1 @ N)e
. total Kjehldahl
. organic
Total Orthophosphate (mg/1
@P04)d
Mean
72,000a
92,000b
74,800a
99,800C
26,500^
47,400g
32,900°
54,900e
912
4,920
4.36
83,500
20,500
63,000
77,700
19,800
57,900
6,220
800
5,400
1,140
1,060
93
Range
67,100 - 75,700
81, 100 •• 106,300
71,500 - 78,900
83,800 -115,500
17,600 - 32,300
40,600 - 57,500
19,800 - 41,900
45,800 - 67,000
80'6 - 1 ,320
3,610 - 5,920
4.28- 4.45
70,200 - 95,800
19,400 - 22,200
50,700 - 73,600
77,400 - 85,600
17,900 - 21,500
45,600 - 64,000
2,540 - 10,280
40 - 1 ,720
2,500 - 9,620
790 - 1,450
770 - 1,280
59 - 98
samples
^Seven samples
dFour samples
eFive samples
44
-------
TABLE 4. IONIC COMPOSITION OF SLOPS
(Units of mg/1)
Constituent
Zn
Cd
Pb
Fe
Na
Cu
Co
Mn
Ca
Mg
Cr
K
Al
Cl
so4
Mean
9.89
0,18
1.10
81.0
372.
32.8
0.60
10.6
2,088.
824.
0.30
4,259.
0.38
2,110.
4,120.
Range
2.38 -
0.09 -
0.77 -
42.0 -
209. -
2.0 -
0.19 -
2.38 -
1,850. - 2
391. - 1
0.25 -
4,011. - 4
0.10 -
1,330. - 4
3,500. - 4
19.93
0.32
1.60
150.0
523.
124.
0.76
15.6
,476.
,728.
0.33
,845.
0.58
,400.
,800.
Observations
4
4
4
5
5
5
4
4
4
5
4
5
4
4
3
45
-------
The mean soluble and total BOD concentrations characteristic of
slops obtained during the predominant operating mode were 26,500 mg/1
and 32,900 mg/1 respectively (soluble BOD: total BOD ratio of 0.80).
During the second operating mode, the mean soluble and total BOD
concentrations were 47,400 and 54,900 mg/1, respectively (soluble
BOD: total BOD ratio of 0.86). Thus, both the soluble and total BOD
concentrations characterizing the slops during the second mode of
operation were about 20 percent greater than those in the first
operating mode. Additionally, the average soluble and total BOD:COD
ratios in slops generated during the first operating mode were about
0.35, whereas the same ratios for slops generated during the second
operating mode were about 0.58.
The mean alkalinity of the slops samples analyzed was 912 mg/1
CaCOo, the mean volatile acids concentration was 4,920 mg/1 as acetic
acid, and the mean pH was 4.36 (Table 3). A titration curve, relating pH and
lime dose required in the neutralization of a representative slops
sample, is presented in Figure 8. The titration curve exemplifies,
from an operational viewpoint, the interrelationship of the above
parameters. The trend in the titration curve of Figure 8 is indicative
of the existence of a buffering capacity in the slops at pH levels
greater than 7.2. For this reason, the mixed liquor pH was maintained
at or in excess of pH 7.2 throughout the experimental program by the
addition of sodium bicarbonate as discussed in Section V. The lime
dose required to neutralize the slops sample to pH 7.2 was 4,000 mg/1
as CaO. At a lime dose of 4,000 mg/1 as CaO, the calcium ion increment
added to the slops (2,400 mg/1) represents an increase of approximately
115 percent in the average calcium content of the slops (2,088 mg/1)
(Table 4).
The mean total solids concentration characteristic of the samples
analyzed was 83,500 mg/1, approximately 25 percent of which was present
as total fixed solids, and 75 percent of which was present as total
volatile solids. Based on the mean values of concentrations reported
for the dissolved and suspended solids parameters:
46
-------
FIGURE 8. SLOPS NEUTRALIZATION RELATIONSHIP BETWEEN pH AND LIME DOSE
Note: slops batch MP-7
2,000
4,000
mg/1 as CaO required
6,000
8,000
-------
1. Approximately 7.5 percent of the total solids were present as
total suspended solids (mean concentration, 6,220 mg/1) and 92.5
percent as total dissolved solids (77,700 mg/1).
2. Approximately 75 percent of the total dissolved solids were present
as volatile dissolved solids (mean concentration of 57,900 mg/1)
and the remaining 25 percent as fixed dissolved solids (mean con-
centration of 19,800 mg/1).
Thus, if it were assumed that the total volatile solids concentration
is an implicit measure of the organic content (both biodegradable and
refractory) of the slops stream, then approximately 85 percent of the
organic content of the slops was present in soluble form as volatile
dissolved solids (mean concentration, 57,900 mg/1) and the remaining 15
percent as volatile suspended solids, the latter consisting predominantly
of spent yeast cells. These observations indicate that the organic
content of the slops is predominantly of a soluble/colloidal nature
rather than of a solids form, and suggest that the slops stream is well-
suited for the anaerobic contact process application because of the
high ratio of the concentrations of organic matter: suspended solids in
the slops stream.
The mean total Kjehldahl nitrogen content characteristic of the
slops samples analyzed was 1,140 mg/1, and the mean total orthosphosphate
concentration was 93 mg/1 as phosphate, or 31 mg/1 as phosphorus. From
a biological treatability perspective, if it is assumed that the slops
can be characterized as having an average total BOD concentration of
50,000 mg/1, then the "average" slops is characterized by a BOD:N:P
ratio of 100:2.2:0.06. On comparison of this ratio with the rule-of-
thumb ratio of 100:5:1 for a nutrient-balanced waste stream, it is
apparent that there exists on the average a phosphorus deficiency of
94 percent and a nitrogen deficiency of 56 percent, in the stream.
The effluents of the three experimental units were monitored routinely
for nitrogen and phosphorus content to ensure that these nutrients were
not limiting in the fermentations (Section V). It was found necessary to
add phosphorus, but not nitrogen, to each of the slops batches throughout
the process kinetic studies. Phosphorus was added in the form of a
phosphate salt to satisfy a BOD:P ratio of 100:1.
48
-------
The ionic composition of the slops is characterized by the analytical
results summarized in Table 4. The ionic composition varied widely from
sample to sample. The variation was attributable to factors such as
changes in: (a) the composition of the feedstock molasses used in rum
production, (b) the extent of chemical pretreatment of the molasses
mixture prior to fermentation, and (c) the distillation operation. The
mean iron concentration reported is 81 rng/1; this concentration comprises
nearly two-thirds of the sum of mean concentrations of all heavy metal
constituents in the slops analyzed. The mean sulfate concentration
reported is 4,120 mg/1 (equivalent to 1,373 mg/1 as sulfide-sulfur).
The ratio of mean heavy metal to mean sulfide sulfur concentration
(approximately 9 percent) suggests the probability of precipitation of
heavy metal sulfide compounds in the fermentation, the significance of
which as a factor in controlling sulfide inhibition could not be
evaluated in the scope of the present study. The mean potassium and
calcium contents of the slops (4,260 mg/1 and 2,100 mg/1 respectively)
are similar in magnitude to values reported by Bhaskaran* ' in the
characterization of spent molasses washes from molasses distilleries
in India.
PROCESS KINETICS
Data Base
The data base for the kinetic characterization was comprised of
the weekly substrate, solids, and flow balances for the two bench-scale
units and the pilot plant^20'. The three biological systems were
operated a total of 110 weeks, including acclimation operation over 16
week periods with each system. Exclusive of observations made during
the startup phases in each of the three units, a total of 62 weekly
sets of experimental data were available for use in the kinetic charac-
terization. This data set was screened to eliminate data points not
deemed representative of steady state operation. The criteria defined
for steady state operation were as follows: less than 15 percent
variation in flow rate; 10 percent variation in mixed liquor/effluent
soluble COD concentration, 20 percent variation in mixed liquor/effluent
49
-------
VSS concentration, and 20 percent variation in 9T/C° (sludge age),
based on a comparison of a three-week running average of each measure
with a given weekly value during the three-week period. A total of 14
sets of experimental data representative of steady-state were identified
using these criteria, seven from operation of the two bench units, and
seven from the pilot plant operations.
The characteristics of the fermentations in these units at each
steady state point are summarized in Tables 5 and 6, and illustrated
by the data presented in Figure 9. The values of 9T/C° (sludge age)
at which steady state was obtained varied from 35 to 220 days, and the
values of Qj (hydraulic residence time) varied from 19 to 221 days.
The soluble COD loading rate, expressed in rational units of mass/
time-mass of MLVSS, varied from a minimum of about 0.26 kg/day/kg
MLVSS (0.26 lb/day/1b MLVSS) at a 9T/C° of 220 days, to a maximum of
0.74 kg/day/kg MLVSS at a 9T/C° of 35 days. The soluble BOD loading
rates corresponding to the above were 0.059 kg/day/kg MLVSS at 9j/C
of 220 days, and 0.45 kg/day/kg MLVSS at 9T/C° of 35 days. Thus, the
maximum soluble COD loading rate observed under steady state conditions
(0.74 kg/day/kg MLVSS) was approximately 25 percent less than the
maximal loading rate of one kg/day/kg MLVSS recommended for startup
(Section V).
On a volumetric basis, the soluble COD loading parameter varied
from a minimum of about 0.4 kg/day/cu m (0.024 Ib/day/cu ft) at Oy/C°
of 220 days, to a maximum of 3.6 kg/day/cu m (0.23 Ib/day/cu ft) at
9j/C° of 53 days, as shown in Figure 9. The volumetric soluble BOD
loading rates varied from 0.086 to 1.19 kg/day/cu m(0.005 to 0.074
Ib/day/cu ft), increasing with decreasing 9-.-/C0 values in a pattern
similar to that for the soluble COD pattern.
The alkalinity of the mixed liquors varied from 8,500 to 11,000
mg/1 as CaCO-, and the pH levels varied from 7.11 to 7.32. The ranges
of values of each of these parameters reflected the effect of buffer
addition as necessary to maintain the pH of the mixed liquors at about
7.2 (Section V). The volatile acids concentrations in the fermentations
50
-------
TABLE 5. STEADY-STATE OPERATIONS: SUMMARY OF LOADING RATE, MIXED LIQUOR, AND EFFLUENT CHARACTERISTICS
Syst.
B/S 1
B/S 2
PP
Wk.
25
26
29
30
31
32
33
21
22
24
25
26
33
34
9T
(days)
35.1
35.4
221
149
147
143
145
25.2
20.6
19.0
20.3
19.3
31.0
36.9
Loading Rates
Kg Sol COt
Day-Cu ni
1.69
1.95
0.38
0.56
0.57
0.58
0.58
2.67
2.90
3.57
3.33
3.44
3.36
3.01
Kg Sol BOD
Day- Cum
1.03
1.19
0.086
0.127
0.129
0.132
0.131
0.701
0.760
0.935
0.872
0.901
0.991
0.888
Kg Sol COD
)ay-KgMLV5S
0.729
0.738
0.261
0.380
0.390
0.399
0.395
0.622
0.557
0.700
0.582
0.686
0.560
0.497
Kg Sol BOD
Day-KgMLVSS
0.443
0.449
0.059
0.086
0.088
0.089
0.089
0.163
0.146
0.183
0.152
0.159
0.165
0.147
Mixed Liquor Characteristics
Sol. .COD
(X,") mg/1
21 ,230
21*250
17,790
16,460
16,790
15,110
14,500
18,950
22,770
21,570
23,810
24,420
26,260
29,450
VS§
(X?)
mg/1
2,320
2,647
1,458
1,475
1,462
1,480
1,469
1,293
5,200
5,100
5,720
5,020
6., 000
6,067
MLTSS
mg/1
3,287
3,867
2,120
2,400
2,200
2,713
2,518
6,587
7,360
6,990
7,853
7,333
8,600
9,027
PH1
7.21
7.2d
7.32
7.31
7.23
7.24
7.27
7.15
7.12
7.16
7.16
7.11
7.20
7.19
Alkalinity
(mg/1 CaCO-,
9,170
9,410
9,280
9,180
9,080
8,880
8,570
8,710
8,780
8,900
8,860
9,070
11,010
10,820
Vol. Acid
(mg/1 HAc
94
87
59
60 '
57
75
54
92
143
436
549
618
220
154
Effluent
Soft COD
(XS) mg/1
20,070
19,390
__
20,910
16,030
16,300
—
16,530
21 ,780
20,430
23,430
22,900
28,040
28,270
Note:
controlled by buffer addition
-------
TABLE 6. STEADY STATE OPERATIONS: SUMMARY OF OPERATING AND PERFORMANCE CHARACTERISTICS
en
ro
System
B/S 1
B/S 2
PP
Week
25
26
29
30
31
32
33
21
22
24
25
26
33
34
eT
(days)
35.1
35.4
221
149
147
143
145
25.2
20.6
19.0
20.3
19.3
31.0
36.9
Gas Production Parameters
Recyc .
Factor
(C°)
0.604
0.523
1.004
0.992
1.000
1.012
1.002
0.410
0.372
0.359
0.525
0.598
0.417
0.492
'Dally gas
Production
(I/day)
14.7
16.7
16.6
18.0
17.5
18.6
19.8
2,053.
2,045
2,386
2,379
2,181
2,055
1,860
%
CH4
53.7
54.6
54.4
58.7
59.9
58.5
58.8
58.3
56.9
54.8
59.4
59.5
58.0
58.1
1 CH4 per
gm VSS-day
0.160
0.106
0.291
0.336
0.337
0.345
0.372
- 0.147
- 0.120
0.131
0.131
0.136
0.105
0.094
1 CH* per gm
Sol COD removd
0.317
0.316
0.333
0.289
0.290
0.282
0.303
0.329
0.324
0.285
0.333
0.313
0.249
0.265
Sol. COD Removal
Influent
Hxed
.iquor(%)
69.3 ~
69:3
78.8
80.4
79.9
82.0
82.7
71.7
66.0
67.8
64.5
63.6
74.7
71.6
Influent
Separator
Effluent (%)
71.0
72.0
__
75.0
80.9
80.5
—
75.3
67.5
69.5
65.1
65.9
73.0
72.7
9T
~C*~
(days)
58.1
67.7
220.
150.
147.
142.
144.
51.5
63.0
53.0
38.7
34.6
74.3
75.0
-------
FIGURE 9. STEADY-STATE CHARACTERISTICS-RUM DISTILLERY SLOPS TREATMENT
BY ANAEROBIC CONTACT PROCESS
O
fO U
•!->
ro i—
o cn
> E
600 A.
- V
LlflO
A
A
A00
Plant
OB/S #1
80
i— O
-Q E
3
-------
varied from less than 100 mg/1 (as acetic acid) at 9T/C° values in
excess of 100 days, to maximal values of 600 mg/1 at 9.J./C0 values of
35 days. The volatile acid concentration tended to increase with
decreasing 9y/C° values, as shown by the data in Figure 9.
The MLVSS concentrations (Table 5) varied from a minimal level of
about 1,500 mg/1 at 9T/C° of 220 days to maximal levels of 6,000 mg/1
at 9T/C° of 35 to 40 days. The volatile fraction of the MLTSS, i.e.,
ratio of MLVSS:MLTSS concentrations for the steady state points varied
between 0.55 and 0.73; for all 14 data points the average volatile
fraction was 0.67.
The soluble COD removal efficiency (influent -** mixed liquor basis)
increased with increasing 9T/C° from a minimal value of about 65 percent
at a 9T/C° of 35 days to a maximal level of about 80 percent at 9T/C°
values in excess of 150 days. From a comparison of soluble COD removal
efficiencies computed on (1) an influent-*- mixed liquor basis and
(2) an influent-*-separator effluent basis (Table 5), it is evident that
the additional soluble COD removal obtained in the separator sector is
insignificant relative to removals obtained in the anaerobic fermenters.
The methane (CH.) content of the gas produced in the fermentations
varied from 53 to 60 percent, and averaged 57.4 percent for the 14
steady state points. The methane production varied from 0.28 to 0.33
liters of CH. per gm of soluble COD removed (4.5 to 5.3 cu ft/lb
soluble COD removed), and averaged 0.302 liter/gm soluble COD removed
(4.8 cu ft/lb soluble COD removed) for all observations. That is, an
average of 86.3 percent of the soluble COD (or about 82 percent of the
total COD) removed from the feed stream was recovered in the form of
methane during the steady state observations.
Determination of Process Kinetics
For purposes of determining the kinetic constants, it was assumed
that the VSS parameter represented viable biomass concentration (X,°),
and the soluble COD parameter represented the rate-controlling substrate
N
concentration (X, ).
54
-------
Equations 13 and 14 were used to analyze the steady-state data for
determination of the kinetic constants. Presented in Figure 10 is a
plot of Equation 13, in which the intercept is the inverse of the value
of Y°, and the slope represents the ratio KD/Y°. The steady-state data
are presented in Figure 11 for determination of the values of K and km
using Equation 14. The intercept of the straight line fit in Figure 11
is the inverse of the value of km, and the slope is equal to K/km.
The values of the kinetic constants obtained from this analysis
are as follows (the calculations required are presented in Appendix A
of Section XII):
Y° = 0.225 mg VSS/mg soluble COD
KD = 0.0667 days"1
K =12,270 mg/1 soluble COD
km = 0.129 days"1
In order to provide some basis of comparison for the values of the
kinetic constants, a summary of the kinetic constants determined in
this and prior studies is presented in Table 7. Included are data for
a packinghouse waste' '% synthetic milk waste' ', and the results
(2i\
reported by Andrews and PearsonA .
The value of km for the slops and synthetic milk wastes are similar
in magnitude (0.13 days). Given the 10°C difference in temperature
used in these two studies, it was anticipated based on observations by
Schroepfer and Ziemke^11'12^ that the anaerobic stabilization rate for
the slops would have been about double that for the synthetic milk waste.
(21)
However, since the temperatures used by Andrews and Pearson v ',
Schroepfer et al, Schroepfer and Ziemke^12^, and in this study were
nearly equal, it would appear that km is influenced by substrate composi
tion as well as temperature.
The KD value obtained for slops treatment by the anaerobic contact
process is nearly equivalent to that reported for' the synthetic milk
waste^. The Y° value obtained for rum slops is greater than that
reported by Andrews'21' for the methane organism dominated system and
less than that reported by Gates et ar9' for the synthetic milk waste.
The variation of Y° values appears to be attributable both to
55
-------
FIGURE 10. RUM DISTILLERY SLOPS TREATMENT BY ANAEROBIC CONTACT PROCESS-
DETERMINATION OF VALUES OF Y° AND Ku FOR STEADY-STATE DATA
a
8
a>
JD
3
"o
CO
en
co
CO
i
o
X
l-p
X
80
70
60
50
40
30
20
10
0
Notes: APilot plant
OB/S #1
DB/S #2
A
50
KD/Y°
mg VSS __
SglbTuFTTcOD
K° = 0.0667 days'1
100
150
200
250
, days
56
-------
cr>
TO
16
>>
to
-a
CD
12
en
10
Notes
APilot plant
OB/S II
QB/S #2
a a
O 70
m c
70 O
3 «-H
t-t CO
O m
Z 73
O
-n co
-co
3> -o
r~ co
m —I
CO 73
m
CO
, m _ ,__ , -1
k =0.129 days
K = 12,270 mg/1 soluble COD
30 §
t/7 DO
— i 1-1
m o
3>
O O
-< o
3456
) x 105, (mg/1 soluble COD)"1
8
CO
-------
TABLE 7. VALUES OF THE KINETIC CONSTANTS (km, KD, K, and Y°) IN VARIOUS STUDIES
Ul
00
Source
Packinghouse waste
(11,12)
Anaerobic digester
(21)
Ac id- formers
Methane formers
Synthetic Milk
Waste (9)
Rum Slops (this
study)
Constants
k^days"1)
0.24
1.33
1.33*
0.14
0.129
KD(days"1)
0.17
0.87
0.02
0.07
0.0667
K(mg COD/1)
5.5
•*> urn
24.3
12,270
vofmg VSS\
r Uq COD/
0.76
0.54
0.14
0.37
0.225
Temp (°C)
35
38
38
20-25
33-36
*At least some of the methane formers exhibited this value
-------
temperature and to different relative combinations of organisms existing
in the different systems. The K value for the rum slops is several
hundredfold greater than the value reported for the other wastes. That K
did change with temperature and/or substrate composition is apparent.
However, too little is known about the effect of transport-controlled
mechanisms to support any definite conclusions about the impact of the
environment on K.
Operational Relationship
Equation 15 and the values of the constants for rum slops treatment
by the anaerobic contact process were used to formulate the operational
relationship defining process performance as a function of QT and C°, as
presented in Figure 12. The measure of process performance is the
N
soluble COD concentration of the process effluent, X, . The operational
relationship is a hyperbola which becomes asymptotic to an ordinate value
equal to KDK/(km-KD) and to an abscissa value equal to l/(km-KD). The
equation describing the operational relationship is as follows:
12'270 + *N
C° 0.0623 X.,N - 818
(16)
The value of the ordinate asymptote represents the minimum effluent
substrate concentration which can be obtained when C° is equal to zero
(i.e., 100 percent biomass recycle) or when QT is infinity. The value
of the abscissa asymptote is approached as the effluent substrate
Kl ' N
concentration X, approaches the influent concentration (XQ ), i.e.,
when biomass washout occurs. In the case of rum distillery slops, these
asymptotic values are X^ = 11,430 mg/1 and 9T/C° = 14.7 days, respectively.
Three regions of operation can be defined with the operational curve
(Figure 12): No
1. A zone of stable operation (small ratio of AX] : A0T/C ), existing
at 0j/C° values greater than 75 days.
2. A zone of transition (in which X^ varies significantly with changes
in 0T/C°), existing at 9T/C° values between 40 and 75 days.
59
-------
FIGURE 12. UNIFIED OPERATIONAL RELATIONSHIP FOR RUM DISTILLERY SLOPS
TREATMENT BY ANAEROBIC CONTACT PROCESS
3€
o>
u
o
o
o
o
o
OJ
.Q
o
CO
I
UJ
2(
15
10
9T _ 12,270 + XTN
C° 0.0623 XiN - 818
A
A
'O O
Notes:
Apilot plant
OB/S #1
-QB/S #2
50
C
** 11,430 mg/1 8 0T/C
100 150
9T/C°, days
200
250
60
-------
3. A zone of instability (occurring at 9T/C°) values less than 40 days),
in which the effluent quality rapidly deteriorates.
Within the zone of stable operation, effluent soluble COD concentra-
tions of less than 20,000 mg/1 were obtained. This effluent concentration
is equivalent (for a slops feed stream concentration of 80,000 mg/1 soluble
COD), to a soluble COD removal efficiency of 75 percent.
CLARIFICATION CAPACITY
Both laboratory zone settling tests and pilot clarification tests
were conducted according to procedures described in Section V, to permit
the development of the desired relationship between clarifier performance
and loading.
Zone Settling Tests
The results of the six zone settling assays, conducted using three
initial MLTSS concentrations and two polymer doses per initial MLTSS
concentration, are presented in Table 8. The actual MLTSS concentrations
at which the tests were conducted were approximately 6,500 mg/1, 12,000
mg/1, and 28,000 mg/1, the lower and upper values being representative of
the anticipated range of MLTSS concentrations to be carried in a full
scale application. The data on solids loading rate in the limiting layer
(Table 8) were calculated using the zone settling curves (plots of inter-
face height vs settling time) for each test, and an assumed underflow
concentration of 50,000 mg/1 (TSS). The allowable liquid loading rate
was then calculated from the initial MLTSS concentration and solids
handling rate data for each test. The allowable liquid loading rate and
initial MLTSS data have been plotted in Figure 13 to determine, for the
laboratory data, a relationship between maximum rate of clarification as
related to the settling velocity of the limiting layer, and initial MLTSS
concentration.
A trend can be defined between allowable liquid loading rate and
initial MLTSS concentration at the lower range of polymer doses (0.63
to 1.44 mg/gm MLTSS), as exemplified by the best-fit curve in Figure 13.
The allowable liquid loading rate decreased from 26 cu m/day/sq m (635 gpd/
sq ft) at an MLTSS concentration of 7,000 mg/1 to 11.5 cu m/day/sq m (260
gpd/sq ft) at 30,000 mg/1.
61
-------
TABLE 8. SUMMARY OF ZONE SETTLING DATA
ro
Test i
1
2
3
4
5
6
Initial
MLTSS
(mq/1 )
6,770
6,295
12,850
11,635
30,527
26,594
Poly-
mer dose-i
(mq/qm)
1.44
7.25
1.06
5.26
0.63
3.15
Solids Loading
in Limit. Layer2
(kq/day-sq m)
178
112
293
381
317
1,001
Allowable
Liquid
Loading Rate
(cu m/day/sq m)
26.4
17.9
22.8
32.8
10.5
37.7
Superna-,
tant TSS"3
(mq/1 )
1,450
3,130
1,200
1,700
2,230
2,930
% TSS
Removal
78.5
50.2
90.7
85.4
92.7
89.0
Notes: ^alco 627
"Assumed underflow TSS concentration - 50,000 mg/1
Sampled after 30 minutes of settling
-------
FIGURE 13. ALLOWABLE MIXED LIQUOR SURFACE LOADING RATE VS MLTSS
CONCENTRATION - ZONE SETTLING
36
°3.15
Best fit curve @ specific
polymer dose of 0.5 to
1.5 mg/gm
Notes:
1. Specific polymer dose, mg NALCO 627/
gin MLTSS, as noted
2. Assumed underflow at 5% TSS
8 12 16 20
Initial TSS concentration, gm/1
63
-------
Insufficient points were available to define similar trends for
liquid loading rates associated with the high polymer doses. However,
it is apparent from the data presented in Figure 13 that at polymer doses
greater than 1.5 mg/gm MLTSS, the allowable liquid loading rate at any
given MLTSS concentration (in comparison with the trend obtained at
polymer doses in the range of 0.63 to 1-44 mg/gm):
1. Increased with increasing polymer dose to a maximal level at a
polymer dose of 3 mg/gm, and;
2. From this maximal level then decreased with polymer doses greater
than 3 mg/gm to a minimal level at a polymer dose of 7.25 mg/gm.
This optimal dose effect was anticipated in view of prior experience with
polymer applications as discussed in Section V.
The decrease in polymer effectiveness with increased polymer dose is
also evidenced by the TSS removal efficiency data presented in Table 8.
That is, the percent removal of initial MLTSS, as determined by sampling
the supernatants after 30 minutes of settling, decreased from 85 percent
at a polymer dose of 5.26 mg/gm to 50 percent at a dose of 7.25 mg/gm.
Thus, the results of the zone settling assays confirmed the conclusions
from the jar testing that the polymer selected (Nalco 627) would be
effective at doses from 1 to 5 mg/gm MLTSS.
Pilot Plant Clarification Tests
The pilot plant clarification tests were conducted in two series of
runs. The first series was done without polymer addition, and the second
series with polymer addition, using the procedures described in Section V.
A summary of the results obtained in each series/run is presented in
Table 9, and the relationships between solids removal efficiency and
solids loading rate derived from these results are presented in Figure 14.
The information presented in Table 9 includes: run duration; average
cumulative polymer dose; liquid and solids loading rates; and average
MLTSS removal efficiency over the duration of the run. The average
cumulative polymer dose reported in Table 9 for each Series II run is
equal to the cumulative mass of polymer added per mass of MLTSS in the
entire pilot plant system, during each run. The actual rate of polymer
64'
-------
TABLE 9. SUMMARY OF RESULTS-PILOT PLANT CLARIFICATION TESTS
Series
run
1-1
1-2
II-l
2
3
4
5
Duration
(hours)
1.0
4.0
2.0
3.0
1.5
4.0
1.5
Average
Cumulative
Polymer
Dose
—
—
0.29
0.80
1.20
1.85
5.91
Liq. Load. Rates
(cu m/da/sq m) u
Overflow
basis
2.63
7.96
8.45
7.65
5.08
5.03
4.86
Total"
basis
5.48
10.8
11.3
10.5
7.94
7.88
7.71
Sol Load Rate
(kgMLTSS/da/sq m)u
Overflow
basis
48.0
88.5
124.
102.
73.5
69.6
63.7
Total"
basis
100.0
120.3
165.
140.
115.
109.
101.
Influent
MLTSS
(rag/1 )
10,833
11,144
14,660
13,330
14,500
13,880
13,150
Average
MLTSS
Removal
Efficiency
(%)
21.8
8.8
45.3
49.8
36.7
50.1
68.6
in
Notes: Cumulative mass of polymer (Nalco 627) added per mass of MLTSS in pilot plant
Based on overflow as clarified effluent plus sludge recycle flow
-------
FIGURE 14. RELATIONSHIP BETWEEN SOLIDS REMOVAL EFFICIENCY AND SOLIDS LOADING RATE (WITH AND WITHOUT POLYMER)
10CL
60l
> 40
o
cc
(/)
CO
20
0
Notes:
1. Average polymer dose, mg/gm, as noted
2. Polymer: Nalco 627
o 5.91
1.85
©
1.20
•©.
Series I-
(No Polymer)
•CL29
20
40 60 80 100 120
Solids loading rate (overflow basis), Kg/day/sq m
140
-------
dosing into the mixed liquor stream during the Series II runs was set
at from 1 to 3 mg/gm of MLTSS transferred into the mix-head tank. The
"overflow" liquid and solids loading rate data reported in Table 9 were
calculated on the basis of the clarified effluent flow rate, and the
"total" liquid and solids loading rate data were calculated using the
sum of the clarified effluent and sludge recycle flow rates. The influent
MLTSS concentrations averaged about 11,000 mg/1 during the Series I runs
and 14,000 mg/1 during the Series II runs. The solids loading rates for
each run were computed using the corresponding liquid loading rates and
influent MLTSS concentrations as reported in Table 9.
The effectiveness of the polymer addition in improving the settle-
ability characteristics of the mixed liquor solids is evident from the
relationships presented in Figure 14 for the Series I and II data. In
the Series I relationship, the TSS removal efficiency decreased from 22
percent at a solids loading rate (overflow basis) of 48 kg/day/sq m
(9.8 Ibs/day/sq ft) to a level of eight percent at a solids loading rate
of 88.5 kg/day/sq m (18 Ibs/day/sq ft); i.e., without polymer addition,
the mixed liquor solids were effectively unsettleable at these solids loading
rates. With polymer addition in the Series II runs, the TSS removal varied
from an average of 52 percent at a solids loading rate of about 70 kg/day/
sq m (14.3 Ib/day/sq ft) to 45 percent at 120 kg/day/sq m (24.6 Ib/day/sq
ft). The solids loading rates of 70 and 120 kg/day/sq m were equivalent
to liquid loading rates (overflow basis) of 5 cu m/day/sq m (123 gpd/sq ft)
and 8.4 cu m/day/sq m (205 gpd/sq ft) respectively. Additionally, at the
solids loading rate of 70 kg/day/sq m, the TSS removal efficiency tended
to increase with increasing cumulative polymer dose in the pilot plant
system, varying from 37 percent at a cumulative dose of 1.2 mg/gm to
nearly 70 percent at a cumulative dose of 5.9 mg/gm.
Based on the preceding observations, it is evident that polymer
addition is a requisite for any full-scale application, and that the
"residual" effect of the polymer recycled in the system (as measured in
the present study by the average cumulative dose), was beneficial, within
the range of average cumulative doses at which the tests were made, to
the settleability of the mixed liquor solids.
67
-------
A major equipment limitation in the pilot plant, which could not
be resolved in the course of the pilot plant testing, was the clogging
of several of the funnel weirs in the clarifier (Figure 6). Because of
the clogging, only 0.32 m (1.05 ft) of the design weir length of 2.57 m
was usable, and the operative weir loading factor was equal to 3.13 cu
m/day/meter of weir length per cu m/day/sq m of liquid loading rate
(250 gpd/ft per cu m/day/sq m). Thus, during the Series II runs, the
weir loading rates varied from approximately 15 cu m/day/m (1,210 gpd/ft)
to 26.4 cu m/day/m (2,120 gpd/ft). While these weir loading rates are
low in comparison with rates used in design of primary sedimentation tanks
(greater than 50,000 gpd/ft), the malfunction of the pilot plant weirs
disrupted the flow distribution pattern at the surface of the clarifier.
Because of the short circuiting of the surface flow pattern in the
clarifier, it is anticipated that TSS removal efficiencies on a full-scale
application can be increased at least 20 percent by the careful design of
the flow pattern in the clarification units, and the use of weir loading rates
of less than 12.4 cu m/day/m (1,000 gpd/ft).
A comparison can be made between the zone settling results and
the pilot plant clarification tests by using the curve of Figure 13, to
determine the allowable solids loading rate as the product of the allowable
liquid loading rate and the initial TSS concentration. The allowable solids
loading rate in the initial TSS concentration range of 10,000 to 14,000 mg/1,
as determined from the zone settling results, is 239 to 302 kg/day/cu m
(49 to 62 Ibs/day/sq ft). Allowing a scale-up factor of 3 to 4 to
conservatively account for scale-up differences (hydrodynamics) between
the laboratory apparatus and the pilot plant, then a comparability of
clarification efficiency at the pilot scale would be expected at a pilot
plant solids loading rate (overflow basis) of 80 to 100 kg/day/cu m
(16.4 to 20.5 Ibs/day/sq ft). Because of the stability of pilot plant
performance observed over this range of pilot plant solids loading rates
(Figure 14), and the above cited weir loading rates in the pilot plant
clarifier, the comparability of the zone settling results and the pilot
plant results was reasonable. On this basis, it was concluded that, with
a properly designed full-scale clarification unit, a clarification efficiency
68
-------
of 70 percent can be attained at a solids loading rate of 100 kg/day/sq m
(20.5 Ibs/day/sq ft) and a weir loading rate of 12.4 cu m/day/m (1,000 gpd/
ft) or less, with polymer doses in the range of 1 to 5 mg/gm MLTSS in the
clarifier influent stream.
69
-------
SECTION VII
DESIGN AND OPERATIONAL ANALYSIS
The results of the bench and pilot studies provide the process
documentation and experience for examining the design, operational, and
economic aspects of the full-scale application of the anaerobic contact
process for slops treatment. An analysis of the design, and operational
requirements for the application is presented in this section, and an
economic analysis of the required system is presented in Section VIII.
The three elements of the design and operational analysis presented
herein are:
1. The selection and specification of a steady-state operating
region for the application;
2. The specification of operating requirements;
3. The specification of a process flow sheet and design criteria
for the physical system.
STEADY-STATE OPERATING REGION
The specification of a steady-state operating region for a full-scale
installation requires: (!) the selection of a desired effluent quality;
(2) determination of the 9T/C° value for this influent quality from the
relationship of Figure 12; (3) selection of a value of C° and the associated
solids loading rate from the clarifier efficiency and loading relationships
of Figure 14; and (4) calculation of the design 9,. value for the values of
GT/C° specified and C° selected. The specification can then be completed
using the above, the process kinetic constants and various conversion
factors presented in Section VI, and material balance expressions presented
in Section IV.
The selected treatment objective, i.e., the desired effluent quality
in a full-scale application, will vary with factors such as effluent
standards, additional treatment required, existing facilities available,
etc. The treatment objective selected for exemplifying process specifica-
tion subsequently is a design effluent soluble COD concentration of 29 gm/1,
for which a QT/C° value of 40 days is specified (Figure 12). This design
"point" was selected because it represents the lower limit of the zone
70
-------
of transition in the operational relationship and because of the
demonstrated stability of the anaerobic contact process at 0T/C° values
in excess of 35 days. A C° value of 0.375 (equivalent to a TSS removal
efficiency of 62.5 percent), and a solids loading rate of 100 kg/day/sq m
(approximately 20.5 Ibs/day/sq ft) were selected as design values based
on recommendations presented in Section VI. For the selected values of
9T/C° @ 40 days and C° (j> 0.375, the required hydraulic residence time,
9T, is 15 days.
In the subsequent computations to complete the specification of the
steady-state operations, the following relationships and parameter values
were used (from data presented in Section VI):
1. Ratio of effluent soluble COD: total COD concentration = 0.95
2. Volatile fraction of MLTSS =0.67
3. Methane production factor = 0.30 liter CH^ per gm soluble COD removed
4. Average methane content of gas stream = 60 percent
5. Design influent COD concentration = 100 gm/1
The steady-state MLVSS concentration was computed using Equation 7,
the values of the constant Y° and K determined for the process, and the
design values of 9j and C° as follows:
Yo 1,225 (100.000-29,000)
Al " [(0.129) (15B+ 0.375
- 6,915'mg/l (MLVSS)
For an assumed MLTSS volatile fraction of 0.67, the MLTSS concentration
corresponding to the above MLVSS concentration is equal to 10,320 mg/1.
The rational organic loading rate for the design point and the
above MLVSS concentration is:
(100,000)
= (6,915)05)
= 0.964 kg soluble COD/day/kg MLVSS,
and the corresponding volumetric loading rate is equal to 6.67 kg/day/cu m
(0.416 Ib/day/cu ft).
71
-------
The methane gas production was computed as the product of the volu-
metric substrate reduction (gm soluble COD removed per liter of slops
treated), and the methane production factor of 0.30 liter CH4 per gm
soluble COD removed, as follows:
Methane gas production:
= 0.30 (100-29)
= 21.3 liter CH4 per liter slops treated
The above production is equivalent to a methane production rate of 21.3
cu m CH4/day per cu m/day of slops treated (2,850 cu ft CH4/day per 1,000
gpd of slops treated). For an average methane content of 60 percent in
the gas stream, the daily gas production rate is equal to 35.5 cu m per
cu m/day of slops treated (4,750 cu ft/day per 1,000 gpd of slops
treated).
The waste MLVSS production rate is equal to the difference between
the rates of synthesis and autodestruction per unit volume of slops
treated and is computed as follows:
Waste MLVSS production rate:
= Y° FxJJ - J*\ - KD9TX° (17)
= 0.225(100,000-29,000) - 0.129(15)(6,915)
=2,595 mg MLVSS per liter slops treated.
For an assumed MLTSS volatile fraction of 0.67, then,
Waste MLTSS production rate
= 3,870 mg MLTSS per liter slops treated.
The above is equivalent to a waste MLTSS production rate of 3.87 kg/day
per cu m/day of slops flow treated.
The clarifier design requirements can be specified using the design
C° value, the associated solids loading rate, and the steady state MLTSS
concentration. For a C° value of 0.375, the design MLTSS removal efficiency
is 62.5 percent; at a design MLTSS concentration of 10,320 mg/1, the
estimated TSS concentration in the clarified effluent is 3,870 mg/1. For
72
-------
a design solids loading rate of 100 kg/day sq m, and the above MLTSS
concentration of 10,320 mg/1, the corresponding liquid loading rate
(overflow basis) is:
= 100 x IP3
10,320
= 9.69 cu m/day/sq m (238 gpd/sq ft)
OPERATING REQUIREMENTS
Three phases of operation need to be considered in the treatment of
rum distillery slops by the anaerobic contact process: (1) startup;
(2) routine operations; and (3) restartup after a seasonal shutdown of
distillation operation. The factors of concern in each phase of operation
are the operating requirements and the associated control and environmental
variables available to the operator. Because the attainment and/or sustenance
of steady-state conditions is a goal common to each phase of operation, the
operating requirements can be developed in consideration of the preceding
analyses of the steady state operating region.
Two basic premises inherent in the process kinetic theory, as found
applicable in the present study for the characterization of rum distillery
slops treatment by the anaerobic contact process, are that:
1. The effluent quality of the process is directly a function of the
viable biomass in the system.
2. The only way that the biological process can respond to changes in
influent quality, or more appropriately, to changes in the mass
loading rate of biodegradable matter, is by an expansion or contraction
of the viable biomass inventory in the system.
Corrollary to the preceding, the only way that process control can be
effected is by control of the viable biomass inventory in the system.
From the perspective of operating requirements, the single transferrable
parameter specifying the viable biomass inventory in the system is 9T/C .
In the present design example, the primary operating requirement is the
maintenance of a 9T/C° value of 40 days at all times, if the design effluent
quality is to be maintained.
From the analysis of the steady-state operating region presented above,
the MLVSS concentration specified by a 9T/C° value of 40 days is equal to
73
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6,900 mg/1. At the design hydraulic residence time, the required MLVSS
inventory for an MLVSS concentration of 6,900 mg/1 is equal to 103.7 kg
MLVSS per cu m/day of slops treated (864 Ibs MLVSS per 1,000 gpd of slops
treated), and the attainment of this level of biomass inventory during
startup, and its maintenance during routine operation and restartup, is
the second operating requirement for the selected design condition.
The third operating requirement is the provision of temperature,
pH, phosphorus, and mixing at levels specified below on the basis of
operating experience (Section VI):
1. Temperature to be maintained at 35 ± 2°C
2. pH to be maintained at 7.2; the estimated lime dose required is
4,000 mg/1 as CaO.
3. Phosphorus to be added to satisfy biological treatability require-
ments (the estimated dose required in 30 mg/1 as P)
4. Complete and continuous mixing to be provided; the capacity of
gas mixing provided in the pilot plant system (0.15 cu m/min/cu m
of mixed liquor, or 20 SCFM/1,000 gallons) was sufficient to
accomplish this.
Startup
The procedure recommended for startup on the basis of experimental
operating experience is as follows:
1. Fill anaerobic fermenter with water; heat to operating temperature
and maintain
2. Add seed sludge
3. Pretreat raw slops by neutralization to pH 7.2 and by phosphorus
addition
4. Feed the pretreated raw slops at an initial rate not to exceed
one kg soluble COD/kg MLVSS per day until the required biomass
inventory (of approximately 100 kg MLVSS per cu m/day of total slops
flow to be treated) is attained
5. Initiate polymer feed into the mixed liquor stream to the clarifier
to maximize capture of MLVSS; waste no MLVSS during startup
The entire system should be monitored daily for gas production,
alkalinity, pH, volatile acids, and temperature. Liquid, solids and
74
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nutrient balances should be performed at least weekly. The 9T/C° value
should be calculated on a weekly basis to ensure that it equals or
exceeds 40 days. The initial rate of feed of pretreated slops, as noted
above should be adjusted upward or downward as the startup progresses,
in consideration of system performance as tracked by the monitoring program.
The process of seed development took about four months, and the
acclimation of the seeded units an additional four months in the
present study. However, with the above guidelines for startup, developed
from experience accrued in the course of this arduous effort, it is
suggested that the entire process can be completed in half this period with
the use of municipal digested primary sludge to supplement a slops-based
seed sludge. Full-scale operational experience will be necessary before
"standard practice" can be defined.
Routine Operation
Routine operation is defined as the maintenance of steady-state
conditions within the framework of the above operating requirements.
Routine chemical additions will be required as follows:
1. Lime, for pH control at a level of 7.2
2. Phosphorus, to ensure that phosphorus is not rate limiting
3. Polymer addition, to convert non-sett!eable solids to a settleable
form
The entire system should be monitored as outlined above to establish the
basis for:
1. Managing the solids inventory at a level commensurate with the
mass organic loading rate
2. Controlling the dosage rates of the chemicals at the minimum
necessary levels
3. Defining other necessary operating adjustments
Restartup
Restartup is defined herein as the time delay required to re-attain
design load (steady-state) conditions after a period of interruption of
slops flow due to seasonal production slowdowns or shutdowns. The factors
associated with restartup are: (1) the duration of the shutdown or slow-
down period; (2) the degree of reduction in slops flows during this period;
75
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and (3) the time required to re-attain design loading after full
production resumes.
The following options are available for dealing with the problem
of minimizing the time delay.
1. Minimize the degree of reduction in feed supply by staggering the
shutdown of sectors of production operation
2. Hold in reserve a quantity of feed to be used to restart the
feeding of the system in advance of the resumption of full produc-
tion i
3. Use an alternative feed supply, such as raw municipal primary sludge,
during the shutdown/slowdown period
Each of the above factors and options are situation-specific and will
have to be examined on a case by case base to establish the economic
tradeoffs.
The operating requirements presented above for startup and routine
operation are equally applicable for restartup. These are:
1. The maintenance of the inventory of viable biomass in the system
at the level specified by the selected design point (in the present
case, approximately 104 kg MLVSS per cu m/day of total slops flow)
2. The control of the slops feed rate during restartup at a level not
exceeding one kg/soluble COD/day/kg MLVSS
3. pH control at 7.2, and phosphorus addition
4. Temperature control at 35 +_ 2°C
5. Complete and continuous mixing, reinitiated upon the resumption
of slops feed.
PROCESS FLOW SHEET AND DESIGN CRITERIA
The process flow sheet and design criteria for full-scale rum
distillery slops treatment by the anaerobic contact process were developed
in consideration of the preceding evaluations and the base of operating
experience accured over the two-year period of investigation. The
process flow sheet is presented in Figure 15, and the recommended design
criteria are summarized in Table 10 and discussed below:
Unit Processes/Operations
The function of the slops storage tank is to provide equalizing
of hour-to-hour flow variation, and to permit the cooling of the slops
76
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Slops
To FUreoff
or Sale
Polymar
Storage and Feed
Sulf*de
Strippe
Phosphorus
Storage & I
Feed
Digester
(One or More)
Slops
Storage
acuum
Degasification
-Becyclfi
Waste
Sludge
Storage
Tank
I N<^X j
Clarifier \ Liquid
Effluent
Lime Storage/^ ^
and Feed ( )
To Sludge Haulaway
FIGURE 15. PROCESS FLOW SHEET - RUM DISTILLERY SLOPS
TREATMENT BY ANAEROBIC CONTACT PROCESS
-------
TABLE 10. DESIGN CRITERIA FOR ANAEROBIC CONTACT PROCESS
Process Element
Recommended Design Criteria
(Units as Noted)
Slops storage tank
Digesters
1. Capacity
2. Gas Mixing
3. Heating
Clarifiers
1. Liquid loading rate
(overflow basis)
2. Weir loading rate
3. Recycle ratio
Thickeners
1. Dry solids loading rate
Waste sludge storage tank
Gas handling system
Sulfide stripper
Chemical feed systems
1. Lime
2. Phosphorus
3. Polymer
1 cu m per
cu m/day slops flow
15 cu m per cu m/
day slops flow
0.15 cu m/min per
cu m digester cap.
35 + 2°C
9.69 cu m/day/sq m
12.4 cu m/day/m
2:1
122 kg/day/sq m
0.52 cu m per cu
m/day slops flow
36 cu m of gas per
cu m/day slops flow
0.43 kg S per cu m/
day slops flow
4 kg CaO per cu m/
day of slops flow
0.3 kg P per cu m/
day slops flow
15 gm per cu m/day
slops flow
1,000 gal per 1,000
gpd slops flow
2,000 cu ft per
1,000 gpd slops flow
20 SCFM/1,000 gal
digester volume
95 + 3°F
238 gpd/sq ft
1,000 gpd/ft
2:1
25 Ibs/day/sq ft
70 cu ft per 1,000
gpd slops flow
4,750 cu ft of gas
per 1,000 gpd slops flow
3.6 Ib S per 1,000
gpd slops flow
33.3 Ibs'CaO per 1,000
gpd slops flow
2.5 Ibs P per 1,000
gpd slops flow
0.125 Ib per 1,000 gpd
slops flow
78
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stream emanating from the distillation columns to a temperature of 32
to 38°C. The excess sensible heat in this tank can be used to maintain
the digester temperatures at 35 + 2°C, as an option to using a portion
of the methane gas production for this purpose. A minimum storage
capacity of one cu m per cu m/day of slops flow (1,000 gal per 1,000 gpd
slops flow) is suggested, exclusive of situation-specific storage require-
ments for restartup should the latter be required.
The digester capacity required at the selected hydraulic residence
time of 15 days is 15 cu m per cu m/day of flow (2,000 cu ft per 1,000
gpd), and a minimum of two digesters should be provided for operational
flexibility. The digesters should be heated to 35 + 2°C. A gas mixing
capacity of 0.15 cu m/min/cu m of digester volume (20 SCFM/1,000 gal)
is suggested as a criterion for full-scale design based on the satis-
factory pilot plant experience at this level.
The clarifiers should be sized to provide for a solids loading
rate of 100 kg/day/sq m (20.5 Ibs/day/sq ft) which, at an MLTSS concen-
tration of 10,320 mg/1, is equivalent to a liquid loading rate (overflow
basis) of 9.69 cu m/day/sq m (238 gpd/sq ft). A recycle ratio of at
least 2:1 (ratio of slops feed flow: sludge recycle flow) is recommended
(14)
based on the experience of Steffen and Bedkerv ' in a slaughterhouse
waste/anaerobic contact process application. For a recycle ratio of 2:1,
the TSS concentration in the recycle stream is equal to 13,550 mg/1, and
the design liquid loading rate (total basis) is equal to 29 cu m/day/sq m
(713 gpd/sq ft). A design weir loading rate not to exceed 12.4 cu m/day/m
(1,000 gpd/sq ft) is recommended on the basis of pilot plant experience.
In the specification of criteria for the thickener, it was assumed
that: (1) the settled solids can be thickened at a loading rate of 122 kg/
day/cu m (25 Ibs dry solids/day/sq ft; and (2) the thickened sludge will
have a dry solids concentration of 10 percent. These values were
selected on the basis of design parameters typically associated with
the thickening of primary sludges in municipal wastewater treatment plants.
The functions intended for the waste sludge storage are to: (1) pro-
vide waste sludge storage for a reserve sludge quantity equal to one-
third of the biomass inventory in the digesters, to be available for
transfer to the digesters as needed; and (2) to provide interim sludge
79
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storage prior to haulaway. The MLVSS biomass inventory required (103.7
kg MLVSS per cu m/day of slops heated), at a volatile fraction of 0.67,
is equivalent to an MLTSS inventory of 155 kg MLTSS per cu m/day. For
the storage of one-third of this inventory in the waste sludge storage
tank, at an average concentration of 10 percent solids, the storage
capacity required is equal to 0.52 cu m per cu m/day of slops treated
(70 cu ft/1,000 gpd). At a waste MLTSS production rate 3.87 kg/day per
cu m/day, the waste sludge storage capacity provided is sufficient to
store 13 days of waste sludge production.
The gas handling system should be sized to handle 36 cu m of gas
production per cu m/day of slops treated. Assuming that the gas
stream contains 0.8 percent hydrogen sulfide by volume, then the sulfide
stripper should be sized to handle 0.43 kg elemental sulfur per cu m/
day of slops flow (3.6 Ib per 1,000 gpd of slops flow).
Chemical feed systems are required for the addition of lime, phos-
phorus and polymer. Based on observations presented in Section VI, it is
suggested that these systems be sized as follows:
1. Lime - feed at 4 kg as CaO per cu m/day of slops flow (33.3 Ibs/
1,000 gpd)
2. Phosphorus - feed at 0.3 kg as P per cu m/day of slops flow
(2.5 Ibs as P/1,000 gpd)
3. Polymer - feed at 15 gm polymer per cu m/day of slops flow
(0.125 Ib polymer per 1,000 gpd)
Layout
The layout as exemplified by the process flow sheet of Figure 15
incorporates the following material/liquid transfer capabilities:
1. From either digester to another or the same digester,
2. From the waste sludge storage tank to the digesters or to sludge
haulaway,
3. From the digesters to the clarifier,
4. From the clarifier to the thickener, the waste sludge storage
tank, and/or directly to the digesters.
The above transfer capabilities are required to support the types of
material/liquid transfers required in the startup, routine operation,
and restartup phases as discussed earlier in this section.
80
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SECTION VIII
ECONOMIC ANALYSIS
The economic analysis presented in this section was developed
using the following approach:
1. The design criteria of Table 10 and the process flow sheet of
Figure 15 were used to develop estimates of capital and operating/
maintenance costs at two design flow rates, 190 and 1,140 cu m/
day (50,000 and 300,000 gpd);
2. The above cost estimates were developed using available unit
process cost curves, updated to January 1974;
3. The heating requirements for the digesters at each design flow
were estimated in consideration of ambient conditions in Puerto
Rico, wherein most of the North American rum distilling capacity
is located;
4. The value of the energy available as methane byproduct was assumed
to be equal to the cost of purchasing an equivalent amount of
energy in the form of fuel oil; and,
5. The cost estimates at each design flow rate were converted to unit
treatment costs ($/volume treated) from which a cost capacity
relationship was then constructed.
CAPITAL COSTS
The estimated capital costs for anaerobic contact treatment systems
at design capacities of 190 cu m/day (50,000 gpd) and 1,140 cu m/day
(300,000 gpd) are presented in Table 11. These cost estimates were
(22)
developed from cost data presented by Eilers and Smithv ' and Patterson
et alj23), updated to January 1974 cost levels, and by vendor contact.
Overhead (engineering and administration) and contingency costs were
estimated at 38 percent of the construction cost.
The estimated total construction costs were $1,683,000 for a 190
cu m/day facility, and $5,596,000 for a 1,140 cu m/day facility. The
corresponding unit total construction costs are: $8,860 per cu m/day of
capacity ($33,660/1,000 gpd) at the design flow rate of 190 cu m/day;
81
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TABLE 11. CAPITAL COSTS (JANUARY 1974)
Item
Slops storage tank
Mechanical mixers -
slops storage tank
Control & solids handling
building2
Lime storage, slaking, and
feeding system
Phosphorus storage, dissolu-
tion and feeding system
Polymer storage and feeding
system
Sulfide stripper
Gas storage/handling
3
Anaerobic digesters
Vac. degasifi cation
Gravity separator
Gravity thickener
Waste sludge storage
Pumps
General work
site work, yard piping,
general elec. & HVAC
Construction Cost
Overhead; contingency
Total construction cost
Capacity @ 190 cu m/
day (50,000 qpd)
32,000
12,000
175,000
21 ,000
3,000
1,500
70,000
90,000
400,000
50,000
65,000
38,000
8,600
12,500
240,000
1,219,100
463,200
1,683,200
Capacity @ 1,140 cu m/
day (300,000 gpd)
112,300
42,000
634,000
78,000
10,000
5,000
200,000
270,000
1,400,000
170,000
125,000
80,000
28,000
46,000
855,000
4,055,300
1,541,000
5,596,300
Concrete in place @ $275/cu yd
2
Includes areas for control room, lime storage, slaking, feeding,
sulfide stripper and gas handling equipment, phosphorus storage,
dissolution and feeding equipment, polymer storage, dissolution and
feed equipment, pumps, etc.
3
Concrete @ 275/cu yd; covers; heat exchanger.
82
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and $4,910 per cu m/day ($18,650/1,000 gpd) at the design flow rate
of 1,140 cu m/day.
OPERATING AND MAINTENANCE COSTS
The estimated annual 0/M (operating and maintenance) costs for
anaerobic contact systems at design capacities of 190 cu m/day and
1,140 cu m/day are presented in Table 12. Labor costs were estimated
at a rate of $5.40 per man hour, including overhead. The chemical
costs were estimated as follows: lime at $17.50/ton; phosphorus at
$50/ton; and polymer at $l/lb. Sludge haulaway costs were estimated
at a unit cost of $0.30/ton dry solids/mile of haul, assuming a 25 mile
haul. Electricity costs were estimated by assuming a pumping require-
ment of 0.004 HP per 1,000 gpd of slops flow^22^, and an annual cost
of $330/yr/HP, the latter based on pump efficiencies of 60 percent and
electricity costs of $0.03/KWH.
Fuel costs for digester heating are not included in Table 12 on the
assumption that a portion of the methane production would be allocated
for this purpose. An evaluation of the allocation required, and of the
net methane production after the allocation is made, is presented below.
Exclusive of fuel cost for heating, the estimated annual 0/M costs
are $39,500 at the design capacity of 190 cu m/day (50,000 gpd), and
$150,400 at the design capacity of 1,140 cu m/day (300,000 gpd).
ECONOMIC VALUE OF METHANE PRODUCTION
The factors considered in determining the economic value of the
methane production were:
1. The gross methane production,
2. The allocation required, from the gross methane production, to
heat digesters;
3. The net methane production, i.e. the excess available after
deduction of the digester heating requirement from the gross methane
production.
The first step in the evaluation was the estimation of digester
heating requirements at each scale. The requirements were estimated
using the procedure of Babbitt and Baumann^ ' and the following
83
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TABLE 12. ANNUAL OPERATING AND MAINTENANCE COSTS (JANUARY 1974)
Item
Labor
Materials and supplies
(except chemicals)
Chemicals
Electricity
Other utilities
Sludge haulaway
Total 0/M Costa
Capacity @
190 cu m/day
(50,000 gpd)
16,200
8,000
6,000
6,800
500
2,000
39,500
Capacity @
1,140 cu m/day
(300,000 gpd)
54,000
20,000
35,400
27,000
2,000
12,000
150,400
Note: excludes heating cost.
assumptions (assuming location of the facilities in Puerto Rico):
1. Average ambient temperature: 21°C (70°F)
2. Digester feed stream and sludge recycle stream temperatures:
27°C (80°F)
On this basis, the estimated BTU requirements for digester heating were:
g
2.45 x 10 BTU/year at the design capacity of 190 cu m/day; and 13.8 x
Q
10 BTU/year at the design capacity of 1,140 cu m/day. Given that a
barrel of fuel oil has a BTU equivalent of approximately 6,000,000 BTU,
the preceding BTU requirements for digester heating are equivalent to
fuel oil consumption rates of: 408 bbl/yr at a design capacity of 190
cu m/day; and 2,300 bbl/yr at a design capacity of 1,140 cu m/day.
The fuel oil equivalent of the gross annual methane production
was estimated using the following:
1. The gross methane production factor of 21.3 cu m CH, per cu m slops
treated (2,850 cu ft per 1,000 gallons treated) as presented in
Section VI
84
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2. An energy equivalent of 1,000 BTU/cu ft of methane, or 5.90 bbl
of fuel oil/1,000 cu m of methane (0.167 bbl of fuel oil/1,000
cu ft of methane)
3. An assumed annual production schedule of 300 days
For these conditions, the fuel oil equivalent of the gross annual
methane production is 37.7 bbl/year per cu m/day of capacity (143 bbl/
year per 1,000 gpd); i.e., is equal to 7,160 bbl/year at a design
capacity of 190 cu m/day (50,000 gpd), and 42,900 bbl/year at design
capacity of 1,140 cu m/day (300,000 gpd).
The allocation of gross methane production required for digester
heating purposes can be evaluated by comparing the ratio of fuel oil
equivalent consumption for digester heating with the above fuel oil
equivalent production rates, at each design scale. This ratio is equal
to 408/7,160 (5.7 percent) at 190 cu m/day capacity, and 2,300/42,900
(5.4 percent) at 1,140 cu m/day capacity. Thus, at either scale, less
than six percent of the gross methane production must be allocated for
digester heating in the Puerto Rico environment, and the net methane
production is equal to at least 94 percent of the gross methane production.
At 94 percent, the fuel oil equivalent of the net methane is equal to 35.4
bbl/year per 1,000 gpd). On a dollar basis, this fuel equivalent is worth
$0.119 per cu m of slops treated (0.45/1,000 gallons treated) for each $/bbl
of fuel oil cost on the open market.
TREATMENT COSTS
Annual treatment costs ($/cu m or $/l,000 gal of slops treated)
were estimated on an unadjusted basis (assuming a fuel oil value of
$0/bbl) and on an adjusted basis assuming fuel oil values up to $28/
bbl. A summary of the unadjusted annual costs at each design flow rate
is presented in Table 13. The amortization costs were developed assuming
an interest rate of eight percent, a 15-year life for 40 percent of the
capital investment, and a 25-year life for 60 percent of the capital
investment.
The unadjusted total annual cost of the full-scale applications is
$212,800 at the design capacity of 190 cu m/day (50,000 gpd), and $726,500
at 1,140 cu m/day (300,000 gpd). For a 300-day production schedule, the
85
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TABLE 13. UNADJUSTED ANNUAL COSTS FOR RUM DISTILLERY SLOPS TREATMENT BY
ANAEROBIC CONTACT PROCESS
Item
Capital costs
Annual costs ($/yr)
. Amortization2
. 0/M costs3
. Total annual cost^
Unit treatment costs**
. Per cu m treated
. Per 1,000 gallons treated
Capacity @
190 cu m/day
(50,000 gpd)
$1,683,200
173,269
39,500
212,769
3.74
14.18
Capacity @
1,140 cu m/day
(300,000 gpd)
$5,596,300
576,083
150,400
726,483
2.13
8.07
]From Table 11
2Amortization at 8% interest rate; 15 year life for 40% of capital
investment and 25 year life for 60% of capital investment
3From Table 12
^Exclusive of methane credit
5Based on 300 day production schedule
86
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unadjusted total annual costs are equivalent to unit treatment costs
of: $3.74/cu m treated ($14.18/1,000 gallons treated) at the design
capacity of 190 cu m/day; and $2.13/cu m treated ($8.07/1,000 gallons
treated) at the design capacity of 1,140 cu m/day.
The unadjusted unit treatment cost data of Table 13 were used to
construct the cost vs capacity curve of Figure 16 at the fuel oil value
of $0/bbl. The adjusted unit treatment cost curves of Figure 16,
at fuel oil prices of $4 to 28/bbl in $4/bbl increments, were developed
by deducting $1.80/1,000 gallons treated for each $4 increment, from
the unadjusted costs.
The significance of design capacity and fuel oil price on the
unit cost of rum distillery slops treatment by the anaerobic contact
process are clearly evident from the cost curves of Figure 16. The
unit treatment cost (in units of $/l,000 gallons treated) is $.80
less in a 100,000 gpd facility than in a 50,000 gpd facility and an
additional $3.30 less in a 300,000 gpd facility than in a 100,000 gpd
facility, for any given fuel oil price. If it is assumed (conservatively)
that fuel oil prices will soon average $12/bbl, then the incorporation
of methane byproduct recovery in a plant-scale installation can reduce
unit treatment costs from 35 percent (in a 50,000 gpd facility) to 65
percent (in a 300,000 gpd facility), as compared with unit treatment
costs for installations without recovery.
87
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FIGURE 16.
16P"
UNIT TREATMENT COSTS FOR RUM DISTILLERY SLOPS TREATMENT
BY ANAEROBIC CONTACT PROCESS
14
12
TJ
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SECTION IX
REFERENCES
CITED REFERENCES
1. Pettet, A. E. , T. G. Tomlinson, and J. Hemens. The Treatment of
Strong Organic Wastes by Anaerobic Digestion. Journal Institution
of Public Health Engineers. 170, July, 1959.
2. Hiatt, W. C., A. D. Carr, and J. F. Andrews. Anaerobic Digestion
of Rum Distillery Wastes. Presented at 28th Industrial Waste
Conference. Purdue University. May 1973.
3. Stander, G. J. and R. Snyders. Effluents from Fermentation
Industries. V. Journal Institute of Sewage Purification.
Part IV, 447, 1950.
4. Radhakrishman, I., S. B. De, and B. Nath. Evaluation of the
Loading Parameters for Anaerobic Digestion of Cane Molasses
Distillery Waste. Journal Water Pollution Control Federation.
41:R431, 1969,
5. Gates, W. E., Private Communication, July 1972.
6. Bhaskaran, T. R. Utilization of Materials Derived from Treatment
of Wastes from Molasses Distilleries." Advances in Water Pollution
Research, Volume 2. London, Pergamon Press, 1965.
7. Jackson, C. J. Journal Institute of Sewage Purification, Part III:
206, 1956.
8. McCarty, P. L. Discussion. Journal Sanitary Eng. Div, Proc.
American Society of Civil Engineers. 89: SA6, 65, December 1963.
V
9. Gates, W. E., J. H. Smith, S. Lin, and C. H. Ris. A Rational Model
for the Anaerobic Contact Process. Journal Water Pollution Control
Federation. 39:1951-70, December 1967.
10. Fuller, W. J. Anaerobic Digestion of Packing Plant Wastes.
Sewage and Industrial Wastes. 25:576, May 1953.
11. Schroepfer, G. J. et al. The Anaerobic Contact Process as Applied
to Packinghouse Wastes. Sewage and Industrial Wastes. 27:4, 460,
April, 1955.
12. Schroepfer, G. J., and N. R. Ziemke. Development of the Anaerobic
Contact Process. I. Pilot Plant Investigations and Economics.
Sewage and Industrial Wastes. ,31:2,164, February, 1959.
89
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13. Schroepfer, G. J. and N. R. Ziemke. Development of the Anaerobic
Contact Process. II. Ancillary Investigations and Special
Experiments. Sewage and Industrial Wastes. 31:6,697, June, 1959.
14. Steffen, A. J., and M. Bedker. Operation of Full-Scale Anaerobic
Contact Treatment Plant for Meat Packing Wastes. Proceedings of
16th Industrial Waste Conference. Purdue University, 1961. Ext.
Ser 109, 423.
15. Monod, J. The Growth of Bacterial Cultures. Annual Rev. Micro-
biol. 3:371, 1949.
16. Standard Methods for the Examination of Water and Wastewater
(13th Edition). 1971.
17. Eckenfelder, W. W., Jr. Industrial Water Pollution Control. New
York, McGraw-Hill. 1966.
18. Shea, T. G. Use of Polymers as a Primary Coagulant. Presented
in: Polyelectrolytes - Aids to Better Water Quality, American
Water Works Association Symposium. June 4, 1972.
19. Product Bulletin PC-627. Nalco Chemical Company. May, 1973.
20. Data Base for Biological Treatability Studies (Project 800935),
compiled for Industrial Pollution Control Division, U. S. Environ-
mental Protection Agency, by Bacardi Corporation, February, 1974.
21. Andrews, J. F. and E. A. Pearson. Kinetics and Characteristics
of Volatile Acid Production in Anaerobic Fermentation Processes.
Presented at 55th National Meeting American Institute of Chemical
Engineers. Houston, Texas. 1965.
22. Eilers, R. G., and R. Smith. Wastewater Treatment Plant Cost
Estimating Program. U. S. Environmental Protection Agency,
Cincinnati, Ohio. April, 1971.
23. W. L. Patterson, and R. F. Barker. Estimating Costs and Manpower
Requirements for Conventional Wastewater Treatment Facilities.
Environmental Protection Agency Project #17090 DAN, October 1971.
24. Babbitt, H. E., and E. R. Bauman. Sewage and Sewage Treatment.
New York, John Wiley and Sons, Eighth Edition, 1958.
pp. 598-9.
UNCITED REFERENCES
1. Jackson, C. J. The Treatment of Distillery and Antibiotics Wastes,
in Waste Treatment (Ed. P.C.G. Isaac). Pergamon Press, 1960.
p. 226.
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2. Jackson, C. J. Fermentation Waste Disposal in Great Britain.
Proceedings of 21st Industrial Waste Conference. Purdue
University, 1966. pp. 19-32.
3. Stander, 6. J. Treatment of Wine Distillery Wastes by Anaerobic
Digestion. Proceedings of 22nd Industrial Waste Conference.
Purdue University, 1967. pp. 892^907.
4. Smith R. E. and T. R. Forgey. Studies on the Biological Stabili-
zation of Thin Stillage. I and II. Canadian Journal of Microbiology,
11:561-571 and 791-795, 1965.
5. Sonoda, Y..and H. Ono. Effects of Digested Sludge in Mesophilic
Methane Fermentation. Jour. Ferment. Techno!. (Japan). 43:6,
896-403, 1965.
6. Sonoda Y., H. Ono, and T. Suzuki. Anaerobic Digestion of Yeast
Waste. Jour. Ferment. Techno!. (Japan). 44:12, 910-914, 1966.
91
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SECTION X
LIST OF PUBLICATIONS
The following publication is pending:
1. Shea, T. 6., and G. H. Dorion, "Investigation of Rum Distillery
Slops Treatment by Anaerobic Contact Process," presented at
Fifth National Symposium on Food Processing Wastes, April 17-19,
1974.
92
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SECTION XI
GLOSSARY
A listing of the nomenclature used in this report is presented in
Table 14. In addition to this nomenclature, the following abbreviations
have been used:
1. BOD - five day, 20°C, biochemical oxygen demand.
2. B/S - bench-scale
3. CH^ - methane
4. COD - chemical oxygen demand
5. MLTSS-mixed liquor total suspended solids
6. MLVSS-mixed liquor volatile suspended solids
7. P/P - pilot plant
8. TSS - total suspended solids
9. VSS - volatile suspended solids
93
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TABLE 14. NOMENCLATURE
K = a constant equivalent to the substrate concentration when k = km/2
KD = specific autodestruction rate, time"
k = specific growth rate, time''
Y° = mass of organisms produced/mass of substrate removed, mg/mg
X° = concentration of organisms, mg/1
X§, X°, X°> » influent; reactor effluent, and separator effluent
organism concentrations, mg/1, respectively
X° = mass of organisms leaving system per unit time/total flow leaving
system per unit time, mg/1
XR° = recycle stream (and sludge wastage stream) organism concentration, mg/1
C° = recycle factor = XJJ/X^
X^ = concentration of controlling substrate, mg/1
XQ, xj, X? = influent, reactor effluent, and separator effluent substrate
concentrations, mg/1, respectively
XR = recycle stream substrate concentration, mg/1
C" = degree of concentration of slibstrate in the solids separator
(-XRN/X1 >
9 = time
9j = theoretical hydraulic detention time, time
Q = influent flow rate, I/day
Qs = sample flow rate, I/day (average)
Qw = sludge wastage flow rate, I/day
r = fraction of influent recycled
94
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SECTION XII
APPENDIX
Page
A. Data Processing Procedures 96
95:
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APPENDIX A
DATA PROCESSING PROCEDURES
The two steps required in the processing of the information base
developed for each biological system, as derived from the monitoring
effort described in Table 2, were as follows:
1. The flow-weighted averaging of all daily parameter values obtained
on a weekly base, in the determination of average weekly flow
rates, and average weekly VSS (volatile suspended solids) and
soluble COD concentrations entering, within, and leaving the
anaerobic fermenter and the solids separator of each system.
2. The development, with the weekly averaged data base, of flow,
substrate (soluble COD), and solids balances in the format necessary
for development of the parameters from which the plots of Figures
2a and 2b could be developed.
The discussion below deals with the mechanics of the second step, i.e.,
the development of the required parameters.
The development of the paramters was done as follows:
1. The weekly averaged data base for each system was manipulated to
develop the values of the parameters, §§-tf [l-r(C"-l)]l /c°x°
and 9j/C°, necessary for determining the values of the kinetic
constants and K and Y° by the graphical procedure of Figure 2a.
2. The steady-state criteria described in Section VI were then applied
to the weekly averaged data base, and the values of the above two
parameters, to identify the weeks of operation with each system
deemed representative of steady-state.
3. The resultant values of the above parameters as associated with
steady-state operation were then plotted for the determination of
the values of Y and K (as presented in Figure ID of Section VI).
4. The value of K as established in the preceding step was then used
in the computation, for the steady-state data, of the values of
the parameters, 9y/(K QT + C°) and 1/X.J, necessary for determining
the values of the kinetic constants km and K by the graphical
procedure of Figure 2b.
96
-------
5. The values of the above parameters were then plotted for the
determination of the values of km and K, as is presented in
Figure 11 of Section VI.
The computational procedures used in determination of the weekly
values of the parameters, [x|J - xij1 [l-r(C"-l)]l /C°X° and 9T/C°
involves the computation first of the value of C° using Equation 12, and
then of the values of the parameters using the calculated value of C°.
This procedure is exemplified below, using weekly averaged data for the
22nd week of pilot plant operations.
(1) Weekly averaged data base
Q =82.1 liters/day (slops feed rate)
Q = 0 (no sludge wastage)
w
r = 6.08
9T = 20.6 days
X° = 5,200 mg/1 (VSS)
X° = 1,700 mg/1 (VSS)
XN = 67,050 mg/1 (soluble COD)
x!? = 22,770 mg/1 (soluble COD)
xS = 21,190 mg/1 (soluble COD)
K
(2) Determination of C° using Equation 12:
^o 0 + (82.1 - 0 - 0)0.700) . 0
C = - (82.0(5,200) 82.1
= 0.327
(3) Determination of [xJJ - xf [l-r(C"-l)]] /C°X°:
97
-------
f 21, 190 \1
- 67,050 - 22,770 L1-6.08\ 22.770 - IJJ
(0.327) (5, 200)
= 20.38 mg soluble COD/mg VSS
(4) Determination of 9-../C0:
= 20.6
0.377
= 63.0 days
A summary of the data used in the computation of the parameters
0_/(KD9, + C°) and l/X? is presented in Table 15. The weekly values
n-i
of the former parameters were determined using K = 0.0667 days
(from Figure 10). The parameter values reported in Table 15 were
used to develop the plot of Figure 11 for the determination of the kinetic
constants km and K.
98
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TABLE 15. SUMMARY OF PARAMETERS FOR DETERMINATION OF km AND K - STEADY
STATE DATA
System
P.P.
1
2
Week
21
22
24
25
26
33
34
25
26
29
30
31
32
33
9T
(days)
25.2
20.6
19.0
20.3
19.3
31.0
36.9
35.1
35.4
221
149
147
143
145
C°
0.411
0.327
0.359
0.525
0.558
0.417
0.492
0.604
0.523
1.004
0.992
1.000
1.012
1.002
X?
(mg/1)
18,950
22,770
21 ,569
23,813
24,422
26,257
29,452
21.230
21.250
17,785
16,456
16,790
15,109
14,504
9T
KD0T+C°
(days)
12.05
12.10
11.69
10.80
10.46
12.48
12.50
11.92
12.28
14.03
13.63
13.61
13.55
13.59
*T
X 105 ,
(mg/1)"1
5.28
4.39
4.64
4.20
4.09
3.81
3.40
4.71
4.71
5.63
6.07
5.96
6.62
6.89
Note: KD = 0.0667 days"1 (from Section VI)
99
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1. Report No,
W
4, Title
Rum Distillery Slops Treatment By
Anaerobic Contact Process
7. Authorfs)
Shea, T. G., E. Ramos, J. Rodriguez, and G. H. Dorion
9, Organization
Bacardi Corporation, San Juan, Puerto Rico
5. Report Date
8. •-F'srtorming Organization
Report No.
800935
? Type -f Report, and
Period Covered
Agency
Environmental Protection Agency report number, EPA-660/2-7l*-07U, July 197U
1C,
Abstract
An investigation was made of the feasibility of rum distillery slops treatment
by the anaerobic contact process. Both bench and pilot-scale experimental studies
were conducted to permit determination of the Monod kinetic constants for the
anaerobic treatment of neutralized, phosphorus-amended rum slops. The settling
characteristics of mixed liquor suspended solids from the anaerobic contact unit
were determined using a moderately cationic, high molecular weight polymer as a
coagulant aid. The experimental results, developed with the bench and pilot units,
were used to define a process flow sheet, detailed design criteria, and an economic
analysis for full-scale applications of rum distillery slops treatment, at design
capacities varying from 190 cu m/day (50,000 gal/day) to 1,140 cu m/day (300,000
gal/day).
Ua. Descriptors
industrial wastes, *Anaerobic digestion, *Energy conversion,
Fermentation, Methane
17b. Identifiers
*Rum slops, Monod kinetics, anaerobic treatment
llic, COWRR Field & Group
05D
18. Availability
». '.Security 'Class
(Page)
«. ffo'.-of
Pages
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 2O24O
T. G. Shea
. E. Gates and Associates, Inc.
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