Study of Anaerobic digestion of Brewery Spent Grains

Abstract

Beer brewing is a biotechnological process whereby agricultural products such as barley and hops are converted to beer by control of biochemical reactions in malting, mashing and fermentation. Breweries produce significant amounts of solid and liquid wastes from the production process. About 200 g of brewery wet spent grains and 11 Litres of wastewater are discharged per Litre of beer produced. The spent grains are disposed in a wet state with 70 % - 80 % moisture content. In this state spent grains deteriorate fast and becomes mouldy within hours, and unless controlled and properly managed, cause problems to the environment. Because solid waste that comes from the brewery industry is mainly organic in nature and highly biodegradable, it is quite suitable for anaerobic digestion. The objective of this study was to ascertain possibility of treating brewery spent grains in the process of anaerobic digestion and it was achieved by carrying out a series of  experimental trials using spent grains as the feed substrate and varying process conditions in a high-rate digester unit. Study indicates that the anaerobic digestion of brewery spent grains could be accomplished with careful control of the process by adjusting certain parameters such as pH, temperature and volatile acid concentration. It could be further shown that the degradation of brewery solid waste generate substantial quantity of biogas with methane content around 65 % i.e. burnable gas. Experimental trials using high rate reactor showed that the maximum gas yield of brewery waste was 0.596 m3/kgVS added under mesophilic condition. This means very high degree of degradation with the substrate showing amenability to the anaerobic digestion process. The study thus indicates the potential for recycling of this waste stream as an energy stream back into beer production process.