Installation, commissioning and preliminary microbiological and operational investigations of full-scale septic tank digestion of sewage.

Abstract

This study investigated the commissioning and maintenance of a Pennells two-tank bioreactor system with specific reference to its application in rural areas of KwaZulu- Natal, South Africa to treat sewage and generate biogas. The septic tank configuration was installed in a community which lacked electricity and domestic waste disposal. An artificial wetland was constructed at the outlet of the system to facilitate further treatment. Inefficient operation and maintenance of the system occurred due to various social/community-related problems which are typical of a field- and community-based project of this nature in a rural region of a Third World African country. These problems affected both maintenance and digester performance. The Pennells system was characterized by incomplete anaerobiosis which limited methanogenesis. Despite this, and attendant problems of low temperatures and elevated pH values, COD removal resulted. Laboratory-scale batch cultures, in conjunction with fluorescence and scanning electron microscopy, were used to identify a suitable anaerobic digester sludge for inoculation purposes. Perturbation experiments with locally used detergents and toxic compounds demonstrated the inimical effects of these agents. In contrast, low concentrations of penicillin and tetracycline promoted methanogenesis. Further analysis with light, fluorescence and scanning electron microscopy identified the acidogens as the predominant bacterial species, whilst fluorescence microscopy confirmed the absence of methanogens in the bioreactor.