Effect of temperature increase from 55 to 65 degrees C on performance and microbial population dynamics of an anaerobic reactor treating cattle manure

The effect of a temperature increase from 55 to 65 degreesC on process perf ormance and microbial population dynamics were investigated in thermophilic , lab-scale, continuously stirred tank reactors. The reactors had a working volume of 3 l and were fed with cattle manure at an organic loading rate o f 3 g VS/l reactor volume/d. The hydraulic retention time in the reactors w as 15 days. A stable reactor performance was obtained for periods of three retention times both at 55 degreesC and 65 degreesC. At 65 degreesC methane yield stabilized at approximately 165 ml/g VS/d compared to 200 ml/g VS/d at 55 degreesC. Simultaneously, Ibe level of total volatile fatty acids, VF A, increased from being below 0.3g/l to 1.8-2.4g acetate/l. The specific me thanogenic activities (SMA) of biomass from the reactors were measured with acetate, propionate, butyrate, hydrogen, formate and glucose. At 65 degree sC, a decreased activity was found For glucosc-, acetate-, butyrate- and fo rmate-utilizers and no significant activity was measured with propionate. O nly the hydrogen-consuming methanogens showed an enhanced activity at 65 de greesC. Numbers of cultivable methanogens, estimated by the most probable n umber (MPN) method, were significantly lower on glucose, acetate and butyra te at the increased operational temperature, while the numbers of hydrogeno trophic methanogens remained unchanged. No viable propionate-degrading bact eria were enriched at 65 degreesC. Use of ribosomal oligonucleotide probes showed that an increase in temperature resulted in a decreased contribution of the rRNA of the domain bacteria from 74-79 to 57-62% of the universal p robe, while the rRNA of the domain archaea, increased from 18-23 to 34-36%. (C) 2001 Elsevier Science Ltd. All rights reserved.