First COSTECH scientific and technological conference: Science and technology for growth and poverty reduction in Tanzania

Sustainable energy production is one of the poverty reduction strategies which could dramatically Improve living standards rn developing countries. The development of anaerobic technologies to efficiently convert organic waste to methane is driven by the need for sustainable energy production and the need to reduce greenhouse gases emissions and nutrients leakage. A two-stage system, consisting of a solid-bed bioreactor for hydrolysis/acidification connected to methanogenic bioreactor packed with sisal fibre waste as biofilm carriers, was investigated with regard to methane production during anaerobic digestion of aerobic pre-treated sisal pulp waste. The solid-bed bioreactor was fed in batch mode with solid sisal pulp waste and operated with recirculation of the leachate through the bed. The leachate from this bioreactor was fed to the methanogenic bioreactor at organic loading rates which varied from 2 to 10 g CODL-1d-1 and the overflow recirculated through the solid-bed bioreactor. The hydrolysis/acidification and the methanogenic stage were reasonably well separated, as indicated by the high carbon dioxide production, high volatile fatty acids (VF As) concentration and low pH in the acidogenic bioreactor compared with high methane production, low VF As concentration and above neutral pH in the effluent of the methanogenic bioreactor. Digestion of sisal pulp waste gave energy yields of 2.45 kWh kg volatile solids-1 in the form of methane. The integrity of the methanogenic bioreactor packed with sisal fibre waste as biofilm carriers was maintained throughout the period of operation producing biogas with 51-70% methane content. A stable effluent pH range of 7.1-7.5 showed that the methanogenic bioreactor had good ability to withstand the variations in load and VF As concentrations that occurred in the two-stage process. The results of this study show that the two-stage anaerobic digestion system is suitable for effective stabilization and biomethanation of sisal pulp waste. (author)