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67 TWO-PHASE ANAEROBIC DIGESTION OF COFFEE WASTEWATER F.R. McDougall, Research Associate G.K. Anderson, Senior Lecturer L.M. Evison, Senior Lecturer Department of Civil Engineering University of Newcastle upon Tyne United Kingdom INTRODUCTION The extraction process used in the production of instant coffee results in the generation of large amounts of high strength recalcitrant liquid waste. Coffee wastewater is usually discharged to the sewerage system, and therefore must conform to consent conditions imposed by regulating agencies. Even with the utilization of mechanical techniques such as skimming and pressing, large volumes of high strength wastewaters are still produced. The suitability of anaerobic digestion as a treatment process for coffee wastewater has been recognized and the SERC anaerobic digestion facility, a pilot-scale plant consisting of four different anaerobic digester systems has been set up at an instant coffee processing factory near London. The facility is comprised of a 13m3 balance tank supplying the four reactors: an Upflow Anaerobic Filter, a UASB, a Contact Process (all nominally 5m3) and an Expanded Bed Reactor (0.5m3). The purpose of this current research project was to investigate the optimization of the pre-acidification of coffee wastewater in a two-phase system. This study was part of a coordinated 5-university investigation entitled "The anaerobic treatment of wastes containing recalcitrant and inhibitory compounds."3"5 Pohland & Ghosh' proposed the physical separation of the two kinetically dissimilar groups of bacteria, the acidogens and methanogens, found in anaerobic digestion. In principle this separation allows optimization of both the hydrolysis-acidification and the acetogenisis-methanogenisis phases, theoretically ensuring maximum efficiency of the overall system. The pre-acidification phase should enable many of the complex organic (recalcitrant) chemicals present in the coffee wastewater to be converted to short chain volatile fatty acids (VFAs) and other simple compounds. This in turn buffers the slow growing methanogens from possible toxins or inhibitors and ensures a uniform feed stock for the methanogens. The specific objectives of this phase of the study were to optimize the pH and temperature requirements of acidogenic bacteria being fed wastewater from the production of instant coffee. MATERIALS AND METHODS Feed Material It was decided to use a synthetic wastewater based upon observations of the actual waste produced at the factory. There were two reasons for this: first, the distance from the factory to the University laboratory, and second, to allow a uniform feedstock to be used throughout the 3-year project at all five participating universities. The synthetic coffee wastewater was largely based upon instant coffee powder. A COD of 10,000 mg/L was selected as being similar to the average strength of the wastewater from the factory. The addition of 10.0 g of instant coffee powder to 1 liter of dechlorinated tap water resulted in a synthetic wastewater with the characteristics shown in Table I. This synthetic wastewater was low in available nitrogen, which should be present in the ratio COD:N:P of 400:5:1 in anaerobic systems. To supplement this, 0.22 g/liter of urea was added. Trace elements were supplied by the addition of 0.1 mL/liter Nutromex Plus (Omex Environmental Ltd). The latter is a proprietary nutrient mixture available for biological treatment systems. Failure to provide these trace elements was found to result in a rapid decrease in the VFAs produced in the preacidification tank, a decrease in overall gas production and methane yield and an increase in VFAs present in the final effluent. This general system breakdown, due to trace element deficiency is being 677
Object Description
Purdue Identification Number | ETRIWC199367 |
Title | Two-phase anaerobic digestion of coffee wastewater |
Author |
McDougall, F. R. Anderson, G. K. Evison, L. M. |
Date of Original | 1993 |
Conference Title | Proceedings of the 48th Industrial Waste Conference |
Conference Front Matter (copy and paste) | http://earchives.lib.purdue.edu/u?/engext,21159 |
Extent of Original | p. 677-684 |
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 | 2009-11-10 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Resolution | 300 ppi |
Color Depth | 8 bit |
Description
Title | page 677 |
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 |
Capture Device | Fujitsu fi-5650C |
Capture Details | ScandAll 21 |
Transcript | 67 TWO-PHASE ANAEROBIC DIGESTION OF COFFEE WASTEWATER F.R. McDougall, Research Associate G.K. Anderson, Senior Lecturer L.M. Evison, Senior Lecturer Department of Civil Engineering University of Newcastle upon Tyne United Kingdom INTRODUCTION The extraction process used in the production of instant coffee results in the generation of large amounts of high strength recalcitrant liquid waste. Coffee wastewater is usually discharged to the sewerage system, and therefore must conform to consent conditions imposed by regulating agencies. Even with the utilization of mechanical techniques such as skimming and pressing, large volumes of high strength wastewaters are still produced. The suitability of anaerobic digestion as a treatment process for coffee wastewater has been recognized and the SERC anaerobic digestion facility, a pilot-scale plant consisting of four different anaerobic digester systems has been set up at an instant coffee processing factory near London. The facility is comprised of a 13m3 balance tank supplying the four reactors: an Upflow Anaerobic Filter, a UASB, a Contact Process (all nominally 5m3) and an Expanded Bed Reactor (0.5m3). The purpose of this current research project was to investigate the optimization of the pre-acidification of coffee wastewater in a two-phase system. This study was part of a coordinated 5-university investigation entitled "The anaerobic treatment of wastes containing recalcitrant and inhibitory compounds."3"5 Pohland & Ghosh' proposed the physical separation of the two kinetically dissimilar groups of bacteria, the acidogens and methanogens, found in anaerobic digestion. In principle this separation allows optimization of both the hydrolysis-acidification and the acetogenisis-methanogenisis phases, theoretically ensuring maximum efficiency of the overall system. The pre-acidification phase should enable many of the complex organic (recalcitrant) chemicals present in the coffee wastewater to be converted to short chain volatile fatty acids (VFAs) and other simple compounds. This in turn buffers the slow growing methanogens from possible toxins or inhibitors and ensures a uniform feed stock for the methanogens. The specific objectives of this phase of the study were to optimize the pH and temperature requirements of acidogenic bacteria being fed wastewater from the production of instant coffee. MATERIALS AND METHODS Feed Material It was decided to use a synthetic wastewater based upon observations of the actual waste produced at the factory. There were two reasons for this: first, the distance from the factory to the University laboratory, and second, to allow a uniform feedstock to be used throughout the 3-year project at all five participating universities. The synthetic coffee wastewater was largely based upon instant coffee powder. A COD of 10,000 mg/L was selected as being similar to the average strength of the wastewater from the factory. The addition of 10.0 g of instant coffee powder to 1 liter of dechlorinated tap water resulted in a synthetic wastewater with the characteristics shown in Table I. This synthetic wastewater was low in available nitrogen, which should be present in the ratio COD:N:P of 400:5:1 in anaerobic systems. To supplement this, 0.22 g/liter of urea was added. Trace elements were supplied by the addition of 0.1 mL/liter Nutromex Plus (Omex Environmental Ltd). The latter is a proprietary nutrient mixture available for biological treatment systems. Failure to provide these trace elements was found to result in a rapid decrease in the VFAs produced in the preacidification tank, a decrease in overall gas production and methane yield and an increase in VFAs present in the final effluent. This general system breakdown, due to trace element deficiency is being 677 |
Resolution | 300 ppi |
Color Depth | 8 bit |
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