ANIMAL MANURE AS SUBSTRATE FOR BIOGAS PRODUCTION

Lately, anaerobic fermentation of animal manure is considered a promising way for biogas production through the anaerobic digestion process. Anaerobic digestion technology is viewed as a method not only for solving environmental problems, but also for contributing to energy production and resolving economic and social issues. This paper investigated the potential of cow and pig manure for biogas production obtained through the anaerobic digestion process. The retention time in the digester was 20 days and the operating temperature was kept in mesophilic domain of 35 +/- 1.5 degrees C. The most important factors influencing the gas composition are the characteristics of the substrate. The samples of the tested substrates were collected and analysed for pH, total soluble solids (TSS), ash, the content of soluble proteins and sugar content. The results showed that the total biogas production derived from pig manure was higher (about 2.5 m(3).batch(-1)) compared to that derived from cow manure (about 2 m3.batch(-1)). During the anaerobic digestion, it was observed that the values of TSS and pH were slightly decreasing due to the growth and multiplication of bacterial cells, the consumption of substrate and the accumulation of metabolites. Reducing sugars and soluble proteins were found in a relatively stable range, between 0.4 and 0.9 mg.ml(-1) for proteins and the concentration of sugars was maintained between 2.8 and 4.6 mg.ml(-1).