Exergy Analysis of Biogas Production from Food Waste Through Anaerobic Digestion

The anaerobic digestion (AD) of food waste with different fat concentration was studied. The impact of hydraulic retention time (HRT) and organic loading rates (OLR) at thermophilic condition of 55 oC on CH4 concentration, CH4 yield, and exegetic performance of AD system was investigated using the model developed in Aspen Plus software. The CH4 concentration and yield decreased as fat concentration increased. The CH4 yield increased with increasing OLR while the CH4 concentration did not change for each fat concentration. The maximum CH4 yield of 1.36E-5 kmol/h was found at OLR 1.5 l/day and HRT of 15 days when food waste with 5% fat concentration was used. The exergy analysis indicated that the irreversibility of AD caused the highest exergy loss, followed by the biogas, liquid sludge and net waste heat released from the system. The highest exergy efficiency of 35.52% was derived when OLR and HRT were set at 0.5 l/day and 25 days, respectively, and food waste with 5% fat concentration was used. At this condition the exergy destruction of 1.34 kW was found.