Kinetics of fatty acid degradation by psychrophilically grown anaerobic granular sludge

The kinetic parameters of anaerobic granular sludge, grown at 10-12 degrees C in an expanded granular sludge bed (EGSB) reactor and fed with volatile fatty acid (VFA) mixtures, were determined in batch assays. The homoacetoge nic, hydrogenotrophic and acetoclastic specific activities of the sludge at 10 degrees C, measured after 306 days exposure to psychrophilic conditions were 1.744, and 0.296 and 0.331 g COD g(-1) volatile suspended solids (VSS ) day(-1), respectively. At 30 degrees C these values were 18.024, 2.732 an d 2.204 g COD g(-1) VSS day(-1), respectively. The temperature characterist ics of the granular sludge and the homoacetogenic enrichment culture from c ultivated sludge showed that the temperature optima were still in the mesop hilic range (30-40 degrees C) even after long term (306 days) operation at low temperature (10-12 degrees C). In the overall conversion rate for aceta te and propionate, evidence for the temperature compensation effect was fou nd. In contrast, no temperature compensation effect was present for butyrat e degradation. The results of EGSB batch reactor experiments revealed appar ent K-m of the acetate and propionate degraders in the ranges of 39-58 mg C OD l(-1) and 7-14 mg COD l(-1), respectively. For butyrate degraders, highe r K-m values were found, i.e., 142-243 mg COD l(-1). The observed low K-m v alues could be attributed to prevailing mixing conditions in the EGSB react or system. (C) 1999 Elsevier Science Ltd. All rights reserved.