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Microbial communities were analyzed in six full-scale anaerobic digesters and a lab-scale digester using the random cloning method. The purposes were to confirm the applicability, reproducibility, and error range of this method; to discuss the difference in the dominant microbes determined by this method in different operational conditions of temperature (mesophilic and thermophilic) and substrate (garbage, sewage sludge, and livestock waste); and to determine key microbes in each digester. Each sample was analyzed in triplicate. In one of the samples, 373 clones were analyzed to study the composition of microbial community in the digester. Time course analysis was conducted from the start-up period for approximately one year in one of the digesters. Similar microbial diversity was obtained corresponding to the type of substrate change (sewage sludge to garbage). Operational taxonomic units (OTUs) closely related to Coprothermobacter sp. and unidentified bacterium clones TUG14 and TUG22 disappeared during the first 40 d, while OTUs closely related to Bacillus sp. and Clostridium sp. increased later. Microbial diversity in digesters is strongly affected by the operational conditions, and similar microbial diversity can be obtained in triplicate analysis and under similar operational conditions. The present study verified the applicability of this method to discuss the overall difference in microbial communities. [Copyright &y& Elsevier]

Abstract: Two feeding strategies for start-up of continuously stirred tank reactors (CSTR) treating source-sorted organic fraction of household municipal solid waste (SS-OFMSW) at 55°C were evaluated. Two reactors were started up separately with a limited amount of initial inoculum (i.e. 10% of the final volume of 3.5l) and operated in a fed batch mode until the reactors were filled (30 days). A reference reactor was filled up with 3.5l of inoculum and fed at a constant rate (11.4g volatile solids (VS)/d). Loading at progressively increasing rate (from 1.7 to 15gVS/d), as calculated based on an activated biomass concept, showed superior process performance compared to a fixed feed rate (5.7gVS/d). Methane yield of 0.32m3/kg VS was produced during the start-up in reactor filled at progressively increasing rate and was comparable to the reference reactor. On the contrary, significant inhibition due to volatile fatty acid (VFA) build-up, mainly due to butyrate, was noticed in the reactor filled at constant rate. Thus, low initial and progressive increasing inoculum loading rate could be used as a strategy for a successful start-up of CSTR treating SS-OFMSW as it allowed a gradual acclimation of the biomass. Lab-scale results were further reaffirmed from the start-up of a full-scale plant (7000m3 total capacity) which was supplied with inoculum corresponding to approx. 16% of final volume and operated in a fed batch mode until the reactors were filled (58 days). Stable biogas production with low VFA (<3g/L; based on titration method) were noticed during the start-up period when fed at progressively increasing rate. Thus, a controlled and reliable start-up procedure was found essential, which could allow rapid process stabilization and time to focus on other technical aspects of plant operation. In addition, the influence of substrate to inoculum amount (1.5–30% TS) and temperature (5–65°C) on anaerobic degradation and methane production of SS-OFMSW was investigated in batch assays as a protocol for start-up procedure. [Copyright &y& Elsevier]