normally lower than the requisite level. The heating of digesters is also pretty important in this regard. The pH of the slurry has to be close to 7. This is pretty much possible provided that cow dung is employed in the form of a substrate. If favourable conditions may be provided then as much as sixty liters of biogas may be produce for one kilogram of cow dung. The digesters that are used for the purpose of production of biogas can be used in mesophilic conditions, which mean a temperature range of 20 to 25 degrees Celsius to 40 to 45 degrees Celsius. The digesters can also be run in thermophilic conditions, where the temperature range is from 50 to 55 degrees Celsius to 60 to 65 degrees Celsius. Both these conditions call for separate species of bacteria. It is thought that the mesophilic operations are more safe and stable than the thermophilic operations that are capable of inactivating the parasites of animals and the various pathogens.
° or + 60 u) conditions, but the optimum temperature range at which soil microorganisms can grow and function actively is rather narrow. Depending upon the temperature range at which microorganisms can grow and function, are divided into three groups i.e. psychrophiles (growing at low temperature below 10 °C) Mesophiles (growing well in the temp range of 20 ° C to 45° C) and thermopiles (can tolerate temperature above 45° C and optimum 45-60°C). Most of the soil microorganisms are mesophilic (25 to 40 °) and optimum temperature for most mesophiles is 37° C. True psychrophiles are almost absent in soil, and thermopiles though present in soil behaves like mesophiles. True thermopiles are more abundant in decaying manure and compost heaps where high temperature prevails. Seasonal changes in soil temperature affect microbial population and their activity especially in temperate regions. In winter, when temperature is low (below 50° C ), the number and
Hot water treat- taneous meat, respectively, to <10 CFU/cm2 ments at 82°C for 10 seconds may cause tem- (Avens et al. 2002). On scalded and/or pol- porary bleaching of the tissue, as the meat ished uneviscerated pork carcasses, the regains its redness after chilling (Barkate et maximum reported reduction of natural al. 1993). Other studies indicate that water microbial contamination (e.g., mesophilic temperatures of 85°C for 10–20 seconds may aerobic bacteria and E. coli) by commercial confer both substantial microbial reductions application of hot water ranged from 2 and acceptable appearance of carcasses (Gill to 3 log10/cm2 (Gill et al. 1995, 1997; et al. 1995, 1997; 1999; Gill and Badoni Eggenberger-Solorzano et al. 2002). Such 1997). Long carcass hot water-washing dura- 54 Chapter 3
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