Mesophilic anaerobic co-digestion of sewage sludge and orange peel waste

Mesophilic anaerobic digestion is a treatment that is widely applied for sewage sludge management but has several disadvantages such as low methane yield, poor biodegradability and nutrient imbalance. In this paper, we propose orange peel waste as an easily biodegradable co-substrate to improve the viability of the process. Sewage sludge and orange peel waste were mixed at a proportion of 70:30 (wet weight), respectively. The stability was maintained within correct parameters throughout the process, while the methane yield coefficient and biodegradability were 165 L/kg volatile solids (VS) (0°C, 1 atm) and 76% (VS), respectively. The organic loading rate (OLR) increased from 0.4 to 1.6 kg VS/m3 d. Nevertheless, the OLR and methane production rate decreased at the highest loads, suggesting the occurrence of an inhibition phenomenon.