The effect of temperature on slaughterhouse wastewater treatment in anaerobic sequencing batch reactors

High strength slaughterhouse wastewater was treated in four 42 1 anaerobic sequencing batch reactors (ASBRs) operated at 30 degreesC, 25 degreesC and 20 degreesC. The wastewater contained between 30% and 53% of its chemical oxygen demand (COD) as suspended solids (SS). The ASBRs could easily support volumetric organic loading rates (OLRs) of 4.93, 2.94 and 2.75kg/m(3)/d (biomass OLRs of 0.44, 0.42 and 0.14 g/g volatile SS (VSS)/d) at 30 degreesC, 25 degreesC and 20 degreesC, respectively. At all operating temperatures, the total COD (TCOD) and soluble COD (SCOD) were reduced by over 92%, while average SS removal varied between 80% and 96%. Over the experimental period, 90.8%, 88.7% and 84.2% of the COD removed was transformed into methane at 30 degreesC, 25 degreesC and 20 degreesC, respectively. The decrease in the conversion of the COD removed into methane as operating temperature was lowered, may be partly explained by a lower degradation of influent SS as temperature was reduced. The reactors showed a high average methanogenic activity of 0.37, 0.34 and 0.12 g CH4-COD/gVSS/d (22.4, 12.7;and 11.8 l/d) at 30 degreesC, 25 degreesC and 20 degreesC, respectively. The average methane content in the biogas increased from 74.7% to 78.2% as temperature was lowered from 30 degreesC to 20 degreesC. Crown Copyright (C) 2000 Published by Elsevier Science Ltd. All rights reserved.