Influence of biogas digesters on faecal indicator organisms in digestate and around homesteads in Ethiopia

Abstract

It is important, prior to application of organic wastes to land, that pathogen loads are reduced sufficiently to minimize dissemination to the wider environment. Anaerobic digestion for biogas production is a low-cost method to reduce pathogens in agricultural wastes that provides the added benefits of energy generation. There have been claims of pathogen reduction following installation of biogas digesters in homesteads in Sub-Saharan Africa. Homestead pathogen levels following installation of the different designs of biogas digester were monitored using faecal indicator organisms within small rural farms in Ethiopia. However, different designs of digesters have registered varying levels of success. Of the three digester designs considered, fixed dome, floating drum and flexible balloon, the fixed dome design achieved the highest reductions in indicator organisms (coliforms, Escherichia coli and Enterococci) from feedstock to digestate; this is likely to be due its longer hydraulic retention time. Households with biogas digesters installed had significantly (p < 0.05) lower levels of coliforms, E. coli and Enterococci detected in the environment inside and outside the house area. However, in the same households, there was a significant (p < 0.05) increase in indicator organisms on the surface and handles of doors, indicating the potential for spread of pathogens on contaminated hands to door handles from handling the animal waste feedstock. This therefore, suggests the need for proper hand washing regimes after handling of feedstocks for biogas digesters.