A Lab Scale Optimization of Brewers Surplus Yeast Co-Digested with Brewers Wastewater for the Production of Biogas at Heineken Breweries, Addis Ababa, Ethiopia.

Abstract

Anaerobic digestion is a promising technology for recovering energy from brewery waste, sewages, and agricultural wastes. The brewing industry typically utilizes batch-type operations to process raw materials into the final beer product, with surplus yeast being recovered through natural sedimentation. The study aimed to investigate the optimum conditions for producing biogas through the anaerobic co-digestion of brewery wastewater and brewers surplus yeast in a lab-scale anaerobic batch reactors. A study was conducted to optimize the mixing ratio and hydraulic retention time for biogas production from brewers’ surplus yeast and brewers’ wastewater under mesophilic conditions (35℃). The physico-chemical characteristics of raw materials before and after digestion were analyzed using a laboratory scale anaerobic digester system. The study found that a mixing ratio of 75%:25% brewer’s wastewater to brewer’s surplus yeast resulted in the highest biogas production (2438 ml/800 ml sample) with a 20 days' retention time. In contrast, the lowest production was observed with 100% brewer’s surplus yeast (938 ml/800 ml sample) within the same retention time. The highest methane and chemical oxygen demand removal efficiency was achieved at a 3:1 mixing ratio of brewer’s wastewater to brewer’s surplus yeast (71.6% and 85.08%, respectively) with a 20 days' retention time. The results indicate that co-digestion of brewer’s wastewater with brewer’s surplus yeast can significantly improve biogas production, particularly at a 3:1 mixing ratio. This approach not only enhances energy recovery from brewery wastes but also helps mitigate disposal difficulties associated with surplus yeast.