PILOT-SCALE STUDIES OF THE ANAEROBIC DIGESTION - cIRcle

165 Pages·2008·5.19 MB·English

PILOT-SCALE STUDIES OF THE ANAEROBIC DIGESTION OF COMBINED
WASTEWATER SLUDGES AND MITIGATION OF PHOSPHORUS RELEASE
by
DYANNE NIEDBALA
B.Sc. (Microbiology), The University of British Columbia, 1989
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF APPLIED SCIENCE
in
THE FACULTY OF GRADUATE STUDIES
(Department of Civil Engineering)
We accept this thesis as conforming
to the required standard
THE UNIVERSITY OF BRITISH COLUMBIA
April 1995
® Dyanne Niedbala, 1995
In presenting this thesis in partial fulfilment of the requirements for an advanced
degree at the University of British Columbia, I agree that the Library shall make it
freely available for reference and study. I further agree that permission for extensive
copying of this thesis for scholarly purposes may be granted by the head of my
department or by his or her representatives. It is understood that copying or
publication of this thesis for financial gain shall not be allowed without my written
permission.
Cj. 9^r\c^ i
Department of J I \ /Vd^LiW „
The University of British Columbia
Vancouver, Canada
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.
Date
DE-6 (2/88)
ABSTRACT
The City of Penticton has operated a biological nutrient removal (BNR) treatment
plant since 1991, in order to achieve lower phosphorus discharge limits into the Okanagan
Lakes. Excess waste activated sludge (WAS) from the BNR process accounts for about 80%
of total sludge wastage at the plant.
Pilot-scale anaerobic digestion studies were conducted on-site at the Penticton
wastewater treatment plant to investigate the influence of the codigestion of primary
fermented sludge (PFS) and phosphorus rich WAS on the solubilization of phosphorus and
on digester performance. Research was conducted in two phases: the first phase included
the initial start-up of the digester and a control run of the digester using only PFS as feed
at a 20 day HRT; the second phase used a combination of PFS/WAS (35/65 by volume) as
feed at an HRT of 20 and 10 days.
Anaerobic digestion of WAS resulted in a 70% release of the total phosphorus flow
into the digester and about an 80% release of phosphorus previously removed during the
BNR process. During the codigestion of PFS/WAS, HRT had no effect on the solubilization
of phosphorus within the anaerobic digester.
Addition of WAS to the anaerobic digester resulted in a significant reduction in
volatile mass destruction and unit gas production, as well as a deterioration in the quality of
the digester supernatant.
During the codigestion of PFS/WAS, the digester operational efficiency, in terms of
volatile mass destruction and unit gas production, decreased as HRT was reduced. However,
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HRT had no effect on the methane content of the anaerobic off-gas or the quality of the
digester supernatant.
Lab-scale studies demonstrated that chemical fixation of the digester effluent with
lime, ferric chloride, or alum could produce high phosphorus removal efficiencies. In terms
of overall effluent quality, ferric chloride, at a 2000 mg/L dosage, resulted in the highest
removal efficiencies for orthophosphorus, COD, and TSS.
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TABLE OF CONTENTS
ABSTRACT ii
TABLE OF CONTENTS iv
LIST OF TABLES vii
LIST OF FIGURES viii
ACKNOWLEDGEMENTS x
1. INTRODUCTION 1
1.1. Research Objectives 3
2. LITERATURE REVIEW 5
2.1. Anaerobic Sludge Digestion 5
2.2. Digestion System Description 6
2.3. Microbiology of Anaerobic Digestion 7
2.4. Operation and Control of Anaerobic Digestion 11
2.4.1. pH and Alkalinity 12
2.4.2. Digester Gas 15
2.4.3. Temperature 16
2.4.4. Anaerobic Environment 16
2.4.5. Detention Time and Digester Mixing 17
2.4.6. Nutrients and Trace Elements 18
2.4.7. Toxic Substances 19
2.4.8. Performance 22
2.5. Anaerobic Digestion of Phosphorus Rich Secondary Sludge . .. 22
2.6. Chemical Precipitation of Wastewaters 25
3. EXPERIMENTAL SET-UP . 29
3.1. Sludge Source 31
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3.2. System Start-Up 32
3.3. Digester Operation 32
3.4. Experimental Sequence 33
4. ANALYTICAL METHODS 35
4.1. Solids 35
4.2. Chemical Oxygen Demand 36
4.3. Volatile Fatty Acids 36
4.4. Alkalinity 37
4.5. pH 37
4.6. Temperature 38
4.7. Total Phosphorus 38
4.8. Orthophosphorus 38
4.9. Ammonia-N 39
4.10. Gas Production and Gas Composition 39
4.11. Oxidation-Reduction Potential 40
4.12. Chemical Treatment of Secondary Supernatant 40
5. RESULTS AND DISCUSSION 42
5.1. DIGESTER PERFORMANCE 42
5.1.1. Phosphorus 42
5.1.2. Solids 50
5.1.3. Arnmonia-N 55
5.1.4. Volatile Fatty Acids 55
5.1.5. Alkalinity 59
5.1.6. pH and Temperature 62
5.1.7. Gas Production and Gas Composition 64
5.1.8. Chemical Oxygen Demand 71
5.1.9. Oxidation-Reduction Potential 73
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5.2. CHEMICAL TREATMENT OF SECONDARY Supernatant . . 76
5.2.1. Experimental Run #1 - 20 Day HRT 76
5.2.2. Experimental Run #2 - 10 Day HRT 81
5.2.3. Assessment of Chemical Treatment Results 84
5.3. FULL-SCALE APPLICATION OF RESULTS 87
6. CONCLUSIONS AND RECOMMENDATIONS 92
6.1. CONCLUSIONS 92
6.2. RECOMMENDATIONS 94
7. REFERENCES 95
8. APPENDICES 98
Appendix A: Fermenter Data 99
Appendix B: RAS Data 106
Appendix C: Primary Digester Data 113
Appendix D: Secondary Supernatant Data 120
Appendix E: Secondary Solids Data 127
Appendix F: Gas Production Data 134
Appendix G: Gas Composition Analysis 141
Appendix H: Jar Test Data 143
Appendix I: Jar Test Average Percent Removals 151
Appendix J: Penticton WWTP Average Monthly Data 153
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LIST OF TABLES
Table 3.1 Composition of PFS and RAS 31
Table 3.2 Anaerobic Codigestion Experimental Sequence 34
Table 5.1 Average Effluent OP Concentration and Percent OP/TP . . .. 44
Table 5.2 Average Phosphorus Release 49
Table 5.3 Average Percent Reduction of Total Volatile Solids 52
Table 5.4 Average Inorganic Content of Secondary Solids 55
Table 5.5 Average VFA Concentration and Range of VFA
Concentrations for the Primary Digester and the
Secondary Supernatant 59
Table 5.6 Average Alkalinity and Range of Alkalinities for the
Primary Digester and the Secondary Supernatant 61
Table 5.7 Average Volume of Gas Produced 66
Table 5.8 Average Unit Gas Production 68
Table 5.9 Gas Composition Analysis 69
Table 5.10 Gas Composition Analysis Based on Methane and Carbon
Dioxide Only 70
Table 5.11 Run #1 - Average Percent Removals During Chemical
Treatment of Secondary Supernatant 80
Table 5.12 Run #2 - Average Percent Removals During Chemical
Treatment of Secondary Supernatant 84
Table 5.13 Penticton WWTP Average Yearly Data 88
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LIST OF FIGURES
Figure 2.1 Three Stages of Anaerobic Digestion 9
Figure 3.1 Pilot-Scale Anaerobic Digester 30
Figure 5.1 Orthophosphorus 43
Figure 5.2 Total Phosphorus Flow 45
Figure 5.3 Phosphorus Balance 47
Figure 5.4 Total Solids 51
Figure 5.5 Total Volatile Solids 53
Figure 5.6 Ammonia-N Values 56
Figure 5.7 Volatile Fatty Acids 58
Figure 5.8 Alkalinity .' '. 60
Figure 5.9 pH Profiles 63
Figure 5.10 Gas Production at 20°C 65
Figure 5.11 Unit Gas Production at 20°C 67
Figure 5.12 Chemical Oxygen Demand 72
Figure 5.13 Oxidation-Reduction Potential 74
Figure 5.14 Run #1 - 20 Day HRT
Supernatant Orthophosphorus Removal 78
Figure 5.15 Run #1 - 20 Day HRT
Supernatant COD Removal 78
Figure 5.16 Run #1 - 20 Day HRT
Supernatant TSS Removal 79
Figure 5.17 Run #1 - 20 Day HRT
Supernatant pH 79
Figure 5.18 Run #2 - 10 Day HRT
Supernatant Orthophosphorus Removal 82
Figure 5.19 Run #2-10 Day HRT
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Figure 5.20 Run #2 - 10 Day HRT
Supernatant TSS Removal 83
Figure 5.21 Run #2 - 10 Day HRT
Supernatant pH 83
Figure 5.22 Penticton Operational Data 89
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