The efficiency of fermentation of biowaste (yield of biogas, etc) depends on a number of process parameters (kind of substrate, loading rate, hydraulic retention time, etc) of which the hydrolysis rate of organic material has the precedence. Pretreatment of material can be applied for increasing it, resulting in converting the substrate more accessible to anaerobic microorganisms. Generation of volatile fatty acids (VFAs) was studied during anaerobic digestion of thermally pre-treated (+70C to +95C) sludge. By experimental results the global optimum for mixture content and pre-treatment temperature (on the basis of gas production, total amount of acids and ratio of propionate and acetate) was the mixture inoculum: pre-treated sludge: raw sludge in the ratio of 1:1:8 and pre-treatment temperature +70C.

It was found that even partial thermal pre-treatment (10% of raw sludge) increased the production of biogas up to 20%. Considering products of metabolism during anaerobic digestion the acetoclastic metanogenesis dominated. Culture independent technique - denaturing gradient gel electrophoresis (DGGE) was used in order to determine the impact of different pretreatment methods on the microbial community structure. Most of the bacteria identified were representatives of the phyla Chloroflexi and Bacteroidetes; all the identified archae were shown to represent the genus Methanosarcina - anaerobic methanogens,the main biogas producers occurring in landfills, WWtPs, in sea sediments and mammal guts. These archaea are able to produce methane by all three known methanogenic pathways - the hydrogenothrophic, acetoclastic and methylotrophic pathway.


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