Population dynamics during startup of thermophilic anaerobic digesters: The mixing factor
KAUST DepartmentWater Desalination and Reuse Research Center (WDRC)
Biological and Environmental Sciences and Engineering (BESE) Division
Environmental Science and Engineering Program
Water Desalination & Reuse Research Cntr
Environmental Biotechnology Research Group
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AbstractTwo thermophilic digesters were inoculated with manure and started-up under mixed and stagnant conditions. The Archaea in the mixed digester (A) were dominated by hydrogenotrophic Methanobateriaceae (61%) with most of the methane being produced via syntrophic pathways. Methanosarcinales (35%) were the only acetoclastic methanogens present. Acetate dissipation seems to depend on balanced hydrogenotrophic-to-acetotrophic abundance, which in turn was statistically correlated to free ammonia levels. Relative abundance of bacterial community was associated with the loading rate. However, in the absence of mixing (digester B), the relationship between microbial composition and operating parameters was not discernible. This was attributed to the development of microenvironments where environmental conditions are significantly different from average measured parameters. The impact of microenvironments was accentuated by the use of a non-acclimated seed that lacks adequate propionate degraders. Failure to disperse the accumulated propionate, and other organics, created high concentration niches where competitive and inhibiting conditions developed and favored undesired genera, such as Halobacteria (65% in B). As a result, digester B experienced higher acid levels and lower allowable loading rate. Mixing was found necessary to dissipate potential inhibitors, and improve stability and loading capacity, particularly when a non-acclimated seed, often lacking balanced thermophilic microflora, is used. © 2013 Elsevier Ltd.
SponsorsThis work was supported by the National Council for Scientific Research, Lebanon and the Masri Institute of Energy and Natural Resources at the American University of Beirut. Special thanks are extended to the United States Agency for International Development for its support in acquiring the equipment used in the experimental program. Also, special thanks are extended to Mr. M. Alarawi and Dr. S. Ali at the Bioscience Core Laboratory at KAUST.
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