Effects of Retention Time and Substrate Type on Biogas and Alkalinity Productions from Anaerobic Digestion of Slaughterhouse Wastes

Anaerobic digestion of slaughterhouse solid wastes, such as rumen contents, is an appropriate treatment option for managing such residues, because of their significant role in reducing the environmental impacts as well as the potential for biogas production. The objective of this study was to investigate the effects of retention time and substrate type on the biogas and alkalinity productions during anaerobic digestion of rumen contents.
This study aimed to investigate the effects of retention time and substrate type on biogas and alkalinity productions of slaughterhouse wastes using one liter anaerobic digester with batch flow. Experiments were performed at temperature of 35°C and retention time of 30 days with three types of substrate: cattle rumen contents, sheep rumen contents and their mixture (mixing ratio 1:1) with total solids of 6.5, 9.1 and 8.0%, respectively.
Maximum alkalinity was found in the digester containing cattle rumen contents as it increased pH. Thus, the highest cumulative biogas and methane yields obtained for these digesters were 286.1 and 80.7 mL/g VSdegraded respectively.
In general, it can be concluded that in the process of anaerobic digestion of rumen contents (regardless of substrate type and retention time), pH of the reactors can play a major role in biogas and methane productions. Thus, to prevent pH drop and to provide a suitable environment for the growth and activity of microorganisms, addition of an alkaline substance is required.