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A MEMBRANE TECHNIQUE FOR BIOMASS RETENTION IN ANAEROBIC WASTE TREATMENT PROCESSES C. B. Saw, Senior Research Associate G. K. Anderson, Senior Lecturer A. James, Reader Department of Civil Engineering University of Newcastle Upon Tyne Newcastle Upon Tyne United Kingdom NE1 7RU M. S. Le, Head Biotechnology Group Domnink Hunter Filters Limited Birtley, Durham Co. United Kingdom DH3 2SF INTRODUCTION In the current energy and pollution situation, the cost of waste treatment is becoming more acute every year. Anaerobic digestion is economically and ecologically a significant step forward in industrial effluent treatment. The anaerobic method of treating high strength industrial wastes offers a number of significant advantages with few serious or insuperable drawbacks compared to other treatment methods. A wide variety of anaerobic treatment processes has been evolved to meet the various needs of industrial effluent treatment and to attempt to overcome any inherent disadvantages of the anaerobic process [I]. One of the major difficulties in anaerobic digestion has always been to retain a sufficient quantity of active biomass in the reactor. In anaerobic systems, the microorganisms reproduce less rapidly than in aerobic systems and a longer minimum SRT (solids retention time) is required to accomodate the slower net growth rate. Numerically, the reciprocal of the solids retention time is the net growth rate of the system. For the system to function satisfactorily, the reciprocal of the design SRT of the process must be in excess of the minimum time it takes for the microorganisms to reproduce in the process. Below this minimum SRT, the microbial cells will be washed out of the system at a faster rate than they can multiply and the system fails. The loading rates attainable in an anaerobic waste treatment process are primarily dictated by the biomass retention in the reactor. Loss of biomass will affect the digester performance in terms of gas yield and will also result in a poor quality effluent due to the high solids content. For a completely mixed digester, the slow growth rate of the methane producing bacteria necessitates maintenance of reactor solids retention times generally of 12-15 days. This would lead to reactors of very large volume and hence unsuitable for industrial wastes. The capital cost of an anaerobic digestion process is most sensitive to the size of the digester. These limitations can be overcome by retaining the biomass within the digester for periods longer than the waste undergoing digestion thereby increasing the density of the bacterial populations in the reactor. In the contact process, a settlement tank is used to concentrate and recycle the biomass to the digester. However, settling is not an efficient process at high MLSS (above 10000 mg/1), and hence it limits the range of loading rates which can be used. This paper presents the development of a new concept of operating completely mixed digesters using crossflow filtration units for biomass retention. 805
Object Description
Purdue Identification Number | ETRIWC198579 |
Title | Membrane technique for biomass retention in anaerobic waste treatment processes |
Author |
Saw, C. B. Anderson, G. K. James, A. Le, M. S. |
Date of Original | 1985 |
Conference Title | Proceedings of the 40th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,36131 |
Extent of Original | p. 805-812 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital object copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Date Digitized | 2009-07-15 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 805 |
Collection Title | Engineering Technical Reports Collection, Purdue University |
Repository | Purdue University Libraries |
Rights Statement | Digital copyright Purdue University. All rights reserved. |
Language | eng |
Type (DCMI) | text |
Format | JP2 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | A MEMBRANE TECHNIQUE FOR BIOMASS RETENTION IN ANAEROBIC WASTE TREATMENT PROCESSES C. B. Saw, Senior Research Associate G. K. Anderson, Senior Lecturer A. James, Reader Department of Civil Engineering University of Newcastle Upon Tyne Newcastle Upon Tyne United Kingdom NE1 7RU M. S. Le, Head Biotechnology Group Domnink Hunter Filters Limited Birtley, Durham Co. United Kingdom DH3 2SF INTRODUCTION In the current energy and pollution situation, the cost of waste treatment is becoming more acute every year. Anaerobic digestion is economically and ecologically a significant step forward in industrial effluent treatment. The anaerobic method of treating high strength industrial wastes offers a number of significant advantages with few serious or insuperable drawbacks compared to other treatment methods. A wide variety of anaerobic treatment processes has been evolved to meet the various needs of industrial effluent treatment and to attempt to overcome any inherent disadvantages of the anaerobic process [I]. One of the major difficulties in anaerobic digestion has always been to retain a sufficient quantity of active biomass in the reactor. In anaerobic systems, the microorganisms reproduce less rapidly than in aerobic systems and a longer minimum SRT (solids retention time) is required to accomodate the slower net growth rate. Numerically, the reciprocal of the solids retention time is the net growth rate of the system. For the system to function satisfactorily, the reciprocal of the design SRT of the process must be in excess of the minimum time it takes for the microorganisms to reproduce in the process. Below this minimum SRT, the microbial cells will be washed out of the system at a faster rate than they can multiply and the system fails. The loading rates attainable in an anaerobic waste treatment process are primarily dictated by the biomass retention in the reactor. Loss of biomass will affect the digester performance in terms of gas yield and will also result in a poor quality effluent due to the high solids content. For a completely mixed digester, the slow growth rate of the methane producing bacteria necessitates maintenance of reactor solids retention times generally of 12-15 days. This would lead to reactors of very large volume and hence unsuitable for industrial wastes. The capital cost of an anaerobic digestion process is most sensitive to the size of the digester. These limitations can be overcome by retaining the biomass within the digester for periods longer than the waste undergoing digestion thereby increasing the density of the bacterial populations in the reactor. In the contact process, a settlement tank is used to concentrate and recycle the biomass to the digester. However, settling is not an efficient process at high MLSS (above 10000 mg/1), and hence it limits the range of loading rates which can be used. This paper presents the development of a new concept of operating completely mixed digesters using crossflow filtration units for biomass retention. 805 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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