Study on biogas production from coffee wastes and cow-dung fermentation and its use towards reducing emissions from coffee roasting

Abstract

The production of high-quality coffee for export is an important industry in Indonesia. However, coffee processing produces unavoidable waste and emissions to the environment; 1 kg of cherry beans (CB) needs 3 kg of water for processing (2 kg for CB selection by floating, 1kg for wash-fermentation). One kg CB generates several waste and product streams: cherry skin (44%), beans (20%), parchment (5%), pulp (4%), silverskin (0.5%), and volatiles (26.5%). This study utilized the wastewater from the washed-coffee processing such as fermentation wash water and coffee pulp. The materials were mixed with cow dung from local farms for anaerobic processing in a one-gallon digester. This research took into consideration three variations: cow dung mixed with water in the same amount (1:1); cow dung and fermentation washing wastewater (1:1); and cow dung and pulp (1:1). The resulting biogas was analyzed with gas chromatography for comparison. Biogas yield was used to estimate the potential for supplying heat and electricity for use in the coffee roasting process. Alternative energy sources were also considered in the following combinations: biogas-electricity (solar panels) and LPG-electricity (fossil). A life cycle assessment was performed on scenarios to calculate global warming potential (GWP). This study will be used as a pilot project toward a zero-waste and zero-emission coffee industry. The scenario with the lowest GWP can be used as a reference for the sustainability of coffee production.