Anaerobic digestion of shea waste for energy generation

Abstract

In search for an alternative source of energy and also in order to utilize the shea waste in an appropriate way and to reduce its negative impact on the environment, the waste was investigated to identify its potential in methane generation through anaerobic digestion. The basic raw materials for the study were shea waste and cow dung. Input substrates were prepared with addition of predetermined amounts of water to bring the substrates to the required organic dry matter (odm) concentrations. The experiments were conducted on continuous feed system and under varying hydraulic retention times (HRT) and odm concentration of the waste. The experimental treatments were carried out in the following phases: cow dung fermentation at 30, 45 and 60 days HRT in 3 %, 5 % and 7 % odm; mono fermentation of shea waste at 30, 45 and 60 days HRT in 3 %, 5 % and 7 % odm; co-fermentation of shea waste with cow dung in proportions of 50:50, 75:25 and 90:10 by volume, at 7 % odm and 30 days HRT; and co-fermentation of substrate 50:50 at 7 % odm and 20 days HRT. The result of the experiments showed that process stability in anaerobic digestion of the shea waste could only be achieved through co-fermentation with cow dung in the ratio of 50:50 by volume at 7 % odm concentrations at 30 days HRT. Anaerobic digestion of shea waste was therefore found to be feasible in the generation of methane. It is recommended that the design and construction of the biogas digester must be located below ground level to promote an even temperature regime.