Study of the effect of biochar from spent coffee grounds on anaerobic digestion of food waste from the restaurant industry

Abstract

The uncontrolled and unsanitary disposal of food waste, which is a valuable raw material for Ukraine's energy independence, has led to a negative impact on the environment, public health and socio- economic development. Integration of food waste into an advanced closed-loop economy will allow for a significant increase in sustainable bioenergy production. The aim of the study was to evaluate the impact of biochar obtained from waste coffee sludge on the anaerobic digestion of food waste from the restaurant industry, which was done using biogas accumulation and digestate quality indicators, such as pH, sCOD, VFAs, NH 4+-N concentration. The results show that thermophilic anaerobic digestion with a higher degree of hydrolysis was prone to instability due to the accumulation of VFAs and a drop in pH. Biochar from spent coffee sludge effectively stimulates the consumption of VFAs and increases methane production, especially under thermophilic conditions. The biochar treatment achieved both higher maximum specific methane production rates and shorter retention times. As the amount of biochar increased from 0 to 15 g l-1, the cumulative methane production under thermophilic conditions increased from 296.7 ml g-1 VSadded to 476.1 ml g-1 VSadded, while the fermentation time decreased from 22 days to 14 days. pH, temperature and VFAs were important factors indicating that increasing the anaerobic digestion process rate leads to better performance in thermophilic digestion using biochar. The potential use of biochar from food waste (waste coffee grounds) in the anaerobic digestion of food waste can simultaneously address the pollution problem of several types of organic waste, including kitchen waste and restaurant food waste. The biochar increased the methane yield and also ensured stable operation with a short lag time in the thermophilic anaerobic digestion process. The methane produced can be used for biomass pyrolysis.