Composition of the microbial population in a membrane anaerobic reactor system during start-up

Changes in the numbers and the composition of the microbial population in a pilot-scale membrane anaerobic reactor system were studied during 14 weeks operation. The membrane reactor was inoculated with the sludge taken from a digester of a municipal wastewater treatment plant. An initial epifluorescent microscopic examination of the seed sludge revealed that the most dominant group was Methanococcus followed by Methanosarcina, short rods, medium rods, filaments and long rods. Changes in the composition of the dominant methanogenic species were observed throughout the operation. Methanococcus species were found to be the most dominant group at the end of the study followed by medium rods, short rods, Methanosarcina, long rods and filamentous species. The numbers of both methanogens and non-methanogens were found 50% and 20% increased in the reactor after 14 weeks operation while the numbers of viable methanogens sharply increased, i.e. 20 times, resulting in a 50 times increase in the metabolic activity of the fluorescent methanogens. Within the fluorescent methanogenic population, Methanosarcina, Methanococcus, Methanobacterium and Methanobrevibacteria species have been tentatively identified. Acclimatization of the digester sludge was completed after 40 days operation after which the COD removal efficiency of the system was found to be over 98% showing that a satisfactory microbial population had been established in the digester.