Anaerobic codigestion of municipal solid waste and biosolids under variousmixing conditions - II: Microbial population dynamics

Microbial population dynamics were evaluated in anaerobic codigesters treat ing municipal solid waste and sewage sludge. Ribosomal RNA based oligonucle otide probes were used to characterize changes in population abundance of s yntrophic volatile fatty acid degrading bacteria and methanogens. Changes i n community structure were linked to traditional performance parameters dur ing the recovery of previously unstable codigesters induced by a reduction in mixing levels. Methanosarcina spp. were the most abundant aceticlastic m ethanogens in unstable codigesters with high acetate concentrations, while Methanosaeta concilii was dominant in stable systems with low levels of ace tate. Growth of Syntrophobacter wolinii was enhanced during stabilization o f a codigester with a well-developed population of Methanobacteriaceae, pos sibly because the presence of adequate numbers of these hydrogenotrophic me thanogens encouraged the syntrophic oxidation of propionate, Mesophilic sat urated fatty acid beta-oxidizing syntrophs were most abundant in previously unstable codigesters. One minimally mixed reactor became unstable after sw itching to continuously mixed conditions. After the switch, total archaeal abundance decreased sharply, though Methanobacteriaceae and Methanosarcina spp. levels increased as the fermentation became unbalanced. Based on the r esults presented here, mixing appears to inhibit the syntrophic oxidation o f volatile fatty acids, possibly by disrupting the spatial juxtaposition of syntrophic bacteria and their methanogenic partners. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.