Microbial population dynamics during start-up and overload conditions of anaerobic digesters treating municipal solid waste and sewage sludge

Microbial population dynamics were investigated during start-up and during periods of overload conditions in anaerobic co-digesters treating municipal solid waste and sewage sludge. Changes in community structure were monitored using ribosomal RNA-based oligonucleotide probe hybridization to measure the abundance of syntrophic propionate-oxidizing bacteria (SPOB), saturated fatty acid-beta-oxidizing syntrophs (SFAS), and methanogens. These changes were linked to traditional performance parameters such as biogas production and volatile fatty acid (VFA) concentrations. Digesters with high levels of Archaea started up successfully. Methanosaeta concilii was the dominant aceticlastic methanogen in these systems. In contrast, digesters that experienced a difficult start-up period had lower levels of Archaea with proportionally more abundant Methanosarcina spp. Syntrophic propionate-oxidizing bacteria and saturated fatty acid-beta-oxidizing syntrophs were present at low levels in all digesters, and SPOB appeared to play a role in stabilizing propionate levels during start-up of one digester. Digesters with a history of poor performance tolerated a severe organic overload event better than digesters that had previously performed well. It is hypothesized that higher levels of SPOB and SFAS and their methanogenic partners in previously unstable digesters are responsible for this behavior.