ANAEROBIC DIGESTION OF CLASSIFIED - Engineering

99 Pages·2003·3.28 MB·English

ANAEROBIC DIGESTION OF CLASSIFIED
NN NICIPAL SOLID WASTES
By
Michael K. Stenstrom
Associate Professor and
Principal Investigator
and
Adam S. Ng
Prasanta K. Bhunia
Seth D. Abramson
Graduate Research Assistants
A Final Report to Cal Recovery Systems, Inc.
and Southern California Edison Company
October 1981
ACKNOWLEDGMENTS
This work was supported by the Southern California
Edison Company . The first year it was funded directly by
Southern California Edison . During the second year it was
funded by Edison through Cal Recovery Systems of Richmond,
California .
The authors are appreciative of the help and sugges-
tions of Mr. Lory Larsen of Edison and Dr . Luis Diaz of
Cal Recovery Systems .
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ABSTRACT
Municipal Solid Waste is presently a serious problem in urban areas
such as Los Angeles. There is an increasing demand for more landfill
area, but political pressure and the mushrooming cost of real estate
makes acquisition of new landfill sites nearly impossible.
In response to the need for municipal solid waste disposal, a number
of alternative disposal systems have been proposed. Many are based on
classification of waste followed by some type of thermal processing . An
alternate method is to use anaerobic digestion of a portion of the organic
materials in the waste. Anaerobic digestion has the advantage of produc-
ing a medium BTU gas which can be used for electric power production or
can be upgraded to produce home heating fuel .
This report discusses the results of a two-year investigation to
determine the suitability of Los Angeles area municipal solid waste for
producing digester gas. An experimental study was conducted using four
50 gallon pilot-scale digesters . The digesters were operated at organic
loading rates ranging from 0.10 lb VS/ft3 day to 0.25 lb VS/ft3 day and
over hydraulic retention times ranging from 15 to 30 days . Feed solids
concentration ranged from 3 .1 to 10.1% VS. In all cases the municipal solid
waste was blended with raw, primary sludge obtained from the Hyperion
Treatment Plant in a ratio of 80% waste to 20% sludge, on a volatile solids
mass basis.
The results of the experimental investigation show that a medium BTU
gas (55-60% methane) can be produced at a rate of 6 .5 to 7.5 ft3 gas/lb VS
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applied. The highest gas productions were obtained at the lowest load-
ing rate. At higher loading rates reduced gas productions were observed,
and this reduction is attributed to the inability to adequately mix the
digesters .
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TABLE OF CONTENTS
ACKNOWLEDGEMENT i
ABSTRACT ii
TABLE OF CONTENTS iv
LIST OF TABLES vii
LIST OF FIGURES viii
INTRODUCTION 1
LITERATURE REVIEW 3
I . Background 3
II . The Anaerobic Digestion Process 5
III . Technical Evaluation 7
A. Sources, Quantity, and Characteristics of MSW 9
1 . Moisture Content 19
2. Particle Size 19
3. Particle Density 20
4. Chemical Composition 20
5. Mechanical Properties 21
B. Preprocessing Unit Operations for Resource Recovery 21
1 . Shredders 22
2. Screens 23
3. Air Classifiers 24
4. Magnetic Separators 24
C. Preprocessing Systems for Energy Recovery 25
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D. Pretreatment 26
E . MSW Digestion Performance Parameters 32
1 . Nutrient Requirements 32
2. Organic Loading Rate and Hydraulic Retention 33
Time
3. NSW Feed Slurry Concentration 35
4. Temperature 35
5. Mixing 36
6. Gas Quantity and Quality 38
7. Dewatering Characteristics and Residue Disposal 40
8. Reactor Design 42
IV. Economic Studies 43
V. Summary 48
EXPERIMENTAL PROCEDURES
51
I . Feedstock 51
II . Experimental Apparatus 53
III. Start-Up Procedure 53
IV. Feeding Procedures 55
V. Analytical Methods 55
A. pH, Alkalinity, Ammonia 55
B. Volatile Fatty Acids, Gas Composition 56
C. Solids Analysis 57
RESULTS AND DISCUSSION 58
I . Santa Monica Survey 58
II . Digestion Results 58
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III . Effects of Organic Loading Rate and Hydraulic 74
Retention Time in Digesters
CONCLUSIONS AND RECOMMENDATIONS 81
REFERENCES CITED 84
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LIST OF TABLES
1 . Typical Operational Criteria for the Anaerobic Digestion 8
Process- Mesophilic Range
2. Projection of Municipal Solid Waste Generation Rates 10
3 . Refuse Composition Data 11
4. Estimated Average Municipal Solid Waste Composition, 1970 15
5.
Quantities and Percentages of Municipal Refuse 16
6. Municipal Refuse Composition, Percent by Weight 17
7. Comparative RDF Characteristics 28
8. Methods for Treatment of Cellulose to Increase Digestibility 30
9. Alternate Reactor Designs 44
10. State of the Art Design Criteria for MSW Digestion 50
Survey Categories for Santa Monica Municipal Solid Waste 52
Results of the Santa Monica Municipal Solid Waste Survey 59
Gas Production per Unit Volatile Solids Summary 65
Digester Parameter Summary 66
Municipal Solid Waste to Methane Studies
82
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LIST OF FIGURES
1 . Anaerobic Digestion Preprocessing Systems 27
2. Flow Process Diagram of Anaerobic Digestion Used 45
for Dynatech Economic Analysis
3. Pilot Scale Digester 54
4. Gas Production for Digester Number 1 60
5. Gas Production for Digester Number 2 61
6. Gas Production for Digester Number 3 62
7. Gas Production for Digester Number 4 63
8. Digested Sludge pH as a Function of Time 67
9. Digested Sludge Alkalinity 68
10. Digested Sludge Ammonia Concentration 69
11 . Digested Sludge Total Volatile Acids Concentration 70
12. Digested Sludge Total Solids Concentration 71
13. Digested Sludge Volatile Solids Concentration 72
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LIST OF FIGURES (Continued)
14. Gas Production as a Function of Organic Loading Rate 76
15 . Volatile Solids Destruction as a Function of Organic 77
Loading Rate
16 . Total Volatile Solids as a Function of Organic 78
Loading Rate
17 . Gas Production as a Function of Hydraulic 80
Retention Time
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