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71 DETERMINATION OF OPERATING CONDITIONS IN AN ANAEROBIC ACID-PHASE REACTOR TREATING DAIRY WASTEWATER B. Kasapgil, Lecturer Department of Environmental Engineering Istanbul University, Avcilar Istanbul, Turkey O. Ince, Lecturer Department of Environmental Engineering Istanbul Technical University 80626, Istanbul, Turkey G.K. Anderson, Senior Lecturer Department of Civil Engineering University of Newcastle upon Tyne NE1 7RU, U.K. INTRODUCTION Anaerobic digestion of organic material is a multistep process. Two groups of bacteria, namely acidogenic and methanogenic bacteria, are responsible for the acidification and for the methane formation, respectively. The growth requirements of the two groups of bacteria are rather different. In order to create optimum conditions for the process, it was first proposed to separate the process into two phases.1 Operating variables applicable for the selection and enrichment of microbial populations in phased digesters include digester loading, hydraulic retention time (HRT), pH, temperature, reactor design, and operating mode. By proper manipulation of these operating parameters it is possible to prevent any significant growth of methane bacteria and at the same time achieve the required level of acidification in the first reactor. Further enrichment of two cultures is possible by biomass recycle around each phase. In order to increase efficiency of a two-phase anaerobic digestion system it is particularly important to optimize conditions for acid-phase digester since hydrolysis and liquefaction are usually considered to be the rate-limiting fermentation step. As volatile fatty acids (VFAs) can be anticipated as the primary products of the first phase, pH control in the second phase may be necessary when the buffer capacity has been exceeded. A reported study2 on the influence of pH on the acidogenic phase was carried out, and a large increase in acetic acid at a pH greater than 6.8 (30°C) was observed. The concentration of butyric acid increased with decreasing pH. and reached a peak at a pH of about 6.5. Contrary to these results, more acetic acid production at pH 5.2 to 5.5 than at pH 6.7 to 7.0 (35°C) was observed.3 These results cannot be directly compared since the solids retention time was different in each case. The importance of pH in the acidogenesis of a particular waste was investigated4 and showed that acidogenesis of proteins at 30°C was higher at a pH range of 6.5 to 8.0. Similar indications of a high pH requirement for the hydrolysis and acidogenesis of proteins at mesophilic temperatures (30°C) were reported.5 An upflow reactor was operated using glucose as a substrate at HRT between 0.4 and 20 hours at 30"C.6 No methane was detected and the main acid produced was butyric, while the second most important was acetic, but at substantially lower concentrations. Under similar conditions, maximum acetic acid production was observed using sucrose as substrate (35°C) at HRT of 10 hours.3 In another study7 treating glucose at HRTs of 16 to 24 hours (35 °C), maximum acetic acid production was measured at the lowest HRT. However, when using biomass recycle, the amount of acetic acid concentration decreased while the amount of butyric acid increased. Al- 50th Purdue Industrial Waste Conference Proceedings, 1995. Ann Arbor Press. Inc.. Chelsea. Michigan 48118. Printed in U.S.A. 669
Object Description
Purdue Identification Number | ETRIWC199571 |
Title | Determination of operating conditions in an anaerobic acid-phase reactor treating dairy wastewater |
Author |
Kasapgil, B. Ince, O. Anderson, G. K. |
Date of Original | 1995 |
Conference Title | Proceedings of the 50th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://e-archives.lib.purdue.edu/u?/engext,45474 |
Extent of Original | p. 669-682 |
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 | 2009-11-24 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 669 |
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 | 71 DETERMINATION OF OPERATING CONDITIONS IN AN ANAEROBIC ACID-PHASE REACTOR TREATING DAIRY WASTEWATER B. Kasapgil, Lecturer Department of Environmental Engineering Istanbul University, Avcilar Istanbul, Turkey O. Ince, Lecturer Department of Environmental Engineering Istanbul Technical University 80626, Istanbul, Turkey G.K. Anderson, Senior Lecturer Department of Civil Engineering University of Newcastle upon Tyne NE1 7RU, U.K. INTRODUCTION Anaerobic digestion of organic material is a multistep process. Two groups of bacteria, namely acidogenic and methanogenic bacteria, are responsible for the acidification and for the methane formation, respectively. The growth requirements of the two groups of bacteria are rather different. In order to create optimum conditions for the process, it was first proposed to separate the process into two phases.1 Operating variables applicable for the selection and enrichment of microbial populations in phased digesters include digester loading, hydraulic retention time (HRT), pH, temperature, reactor design, and operating mode. By proper manipulation of these operating parameters it is possible to prevent any significant growth of methane bacteria and at the same time achieve the required level of acidification in the first reactor. Further enrichment of two cultures is possible by biomass recycle around each phase. In order to increase efficiency of a two-phase anaerobic digestion system it is particularly important to optimize conditions for acid-phase digester since hydrolysis and liquefaction are usually considered to be the rate-limiting fermentation step. As volatile fatty acids (VFAs) can be anticipated as the primary products of the first phase, pH control in the second phase may be necessary when the buffer capacity has been exceeded. A reported study2 on the influence of pH on the acidogenic phase was carried out, and a large increase in acetic acid at a pH greater than 6.8 (30°C) was observed. The concentration of butyric acid increased with decreasing pH. and reached a peak at a pH of about 6.5. Contrary to these results, more acetic acid production at pH 5.2 to 5.5 than at pH 6.7 to 7.0 (35°C) was observed.3 These results cannot be directly compared since the solids retention time was different in each case. The importance of pH in the acidogenesis of a particular waste was investigated4 and showed that acidogenesis of proteins at 30°C was higher at a pH range of 6.5 to 8.0. Similar indications of a high pH requirement for the hydrolysis and acidogenesis of proteins at mesophilic temperatures (30°C) were reported.5 An upflow reactor was operated using glucose as a substrate at HRT between 0.4 and 20 hours at 30"C.6 No methane was detected and the main acid produced was butyric, while the second most important was acetic, but at substantially lower concentrations. Under similar conditions, maximum acetic acid production was observed using sucrose as substrate (35°C) at HRT of 10 hours.3 In another study7 treating glucose at HRTs of 16 to 24 hours (35 °C), maximum acetic acid production was measured at the lowest HRT. However, when using biomass recycle, the amount of acetic acid concentration decreased while the amount of butyric acid increased. Al- 50th Purdue Industrial Waste Conference Proceedings, 1995. Ann Arbor Press. Inc.. Chelsea. Michigan 48118. Printed in U.S.A. 669 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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