Optimization of biogas production from ethanol distillation waste stillage using molasses as the raw material.

Abstract

Background One of the final stages of ethanol production is distillation, in this process pure ethanol is separated from other by-products which are then disposed as waste. These contaminants are collectively known as distillery waste, also termed as stillage. Stillage is a highly polluting substance if disposed to the environment which is the case with most industries in the country. This distillery waste can be made of value by using it as a substrate for biogas production. Biogas production produces a double advantage since it recovers energy from waste and also its output is a very good farm fertilizer hence reducing the pollution problem. This would make ethanol production a green activity. Biogas production from waste stillage is already being performed in some parts of the world though that's not yet the case with Uganda. The incense of this project was to optimise gas production using this waste so as to make it more profitable.

Results There are many ways to accomplish biogas optimization. We centred our research on the co-digestion method. We applied four different co-digestion substrates for this research, cow-dung, chicken droppings, biochar and glycerin. Optimization was to be achieved by studying HRT graphs for the different samples. Peak gas production for distillery waste alone was achieved on day 32. The sample that produced its peak on the earliest day was taken as the best option for optimization. Biochar was the best co-digestion sample with samples containing 70g/L producing their peak on day 21, it was followed by cow-dung then chicken droppings. Glycerin produced the worst result and methane content was very poor. The poor gas yield by this sample was attributed to the chemical composition of the glycerine we used. Since it was of synthesized type, it created in-hibition of methane production

Conclusion Biogas production using distillery waste as the substrate can be optimised by co-digesting distillery waste with other substrates more so biochar. 1:1 TS ratio producing the best results.