Use of two-stage anaerobic treatment for distillery waste

Anaerobic digestion of distillery waste was studied in a mesophilic two-stage system consisting of an anaerobic filter (AF) and an upflow anaerobic sludge blanket (UASB) reactor. The experiments were conducted with hydraulic retention times (HRT) ranging from 10 to 19 days at loading rates of 2.5-5.1 kg COD/(m(3) day) in the first stage, and up to 20-39 days, corresponding to loading rates 0.6-2.5 kg COD/(m(3) day) in the second stage. The treatment efficiencies (COD removals) achieved were 54 and 93% in the first and second stage, respectively. The acidogenic reactor provided satisfactory conversion of initial COD to volatile fatty acids (VFAs), averaging 20.5%. As a result of self-regulation, pH in the methanogenic reactor was in the range of 7.2-7.8. The generation of biogas in the second stage was significantly higher (6 1/day) than that in the first stage (1 1/day). The bacterial growth rate of acetogenic/methanogenic populations, determined by microcalorimetry, was higher in the separated methanogenic stage (average mu(max)=0.433 1/h) as compared to the single-stage reactor (acidogenic stage, average mu(max)=0.159 1/h). To accelerate start-up of the process, increase gas generation and retard production of VFAs in the acidogenic stage small amounts of the algal preparation Biotreat 100 were used. (C) 2002 Elsevier Science Ltd. All rights reserved.