Effect of spent coffee grounds addition on biogas and methaneyield from anaerobic digestion of tannery solid waste

Abstract. Anaerobic digestion (AD) of organic waste can be greatly improved when carbonaceous ingredients are introduced to the anaerobic degradation process. The objective of this experimental work was to increase the amount of biogas and methane that could be produced from the AD of tannery solid waste (TSW) by adding spent coffee grounds (SCGs) in various proportions at a temperature of 38±1 0C. The results of this study showed that adding SCGs to TSW during AD has reduced the amount of time that anaerobic degradation takes to occur. This was demonstrated by the biogas production rising from 9 ml/gVS to 150 ml/gVS, associated with methane concentration also increasing from 17.6% to 68.7%. The optimum biogas generation of 150 mL/gVS with a methane concentration of 68.7% was achieved at a TSW to SCG mix ratio of 85:15. This shows that the addition of SCG synergistically increased the biodegradability of the TSW substrate as such. According to this study, the volatile solids content of the TSW was reduced by 49% when SCG was added indicating an improvement of 51.1%. The kinetic simulation with the Gompertz model offered a very good fit with the biogas yield data obtained from the experiment, with the goodness of fits (R2) ranging from 0.9656 to 0.989. SCG addition considerably raised the bio-methane output and maximal production rate during this experimental investigation. Therefore, it can be said that adding SCG to AD at various mix ratios to TSW is a successful and economical way to increase and speed up the production of bio-methane while promoting zero waste and also a circular economy for sustainable development by beneficially handling the two waste streams.