Effect of influent strength changes on the performance of a down-flow anaerobic fixed bed reactor treating piggery waste

A study of the anaerobic digestion of piggery waste was carried out in a laboratory-scale down-flow fixed bed mesophilic (26-30 degreesC) reactor working at different influent strengths, and hydraulic retention times (HRTs) from 5.0 to 1.25 days. Changes in the influent substrate concentration did not cause process failure. The system was capable of overcoming the variation of influent strength at a fixed value of HRT. The reactor also operated as an equalisation tank reducing the variation of effluent strength, making it more favourable for aerobic post-treatment. The system operated better as the HRT of the reactor and the buffering capacity of the wastewater increased. The system also operated at different influent substrate concentrations and HRTs to maintain the organic volumetric loading rate (B-v) constant at values in the range of 1.5-1.9 and 3.0-3.4 kg COD/m(3) day. The system operated best at the lowest B-v applied although the COD removal efficiency was near to 60% for the highest B-v studied. The results obtained showed the feasibility of using the anaerobic fixed bed reactor at variable conditions of influent strength and flow-rate for piggery wastes treatment through anaerobic digestion. (C) 2002 Elsevier Science B.V. All rights reserved.