β Scribed by Khanal, Samir Kumar
No coin nor oath required. For personal study only.
Anaerobic microorganisms, especially methanogens, are highly susceptible to changes in environmental conditions. Many researchers evaluate the performance of an anaerobic system based on its methane production rate because methanogenesis is regarded as a rate-limiting step in anaerobic treatment of wastewater. Methanogens' high vulnerability and extremely low growth rate in an anaerobic treatment system require careful maintenance and monitoring of the environmental conditions. Some of these environmental conditions are temperatures, either mesophilic or thermophilic, nutrients and trace mineral concentration, pH (usually in the neutral range), toxicity, and optimum redox conditions. A thorough discussion of these factors follows.
Anaerobic processes, like most other biological systems, are strongly temperature dependent. In an anaerobic system, there exist three optimal temperature ranges for methanogenesis: psychrophilic, mesophilic, and thermophilic. Accordingly, the corresponding methanogens are classified as psychrophiles, mesophiles, and thermophiles. The anaerobic conversion rates generally increase with temperature up to 60 β’ C (Pohland 1992). Anaerobic conversion has its highest efficiency at 5-15 β’ C for psycrophiles, 35-40 β’ C for mesophiles, and about 55 β’ C for thermophiles, with decreased rates between these optima as shown in Fig. 3.1 (Lettinga et al. 2001;van Haandel and Lettinga 1994). Makie and Bryant (1981) suggested that low rates between these optima could be due to a lack of adaptation. Anaerobic processes, however, can still operate in a temperature range of 10-45 β’ C without major changes in the microbial ecosystem (Henze and HarremΓΆes 1983). As a rule of
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