Enhanced biomethane production by 2-stage anaerobic co-digestion of animal manure with pretreated organic waste

Anaerobic co-digestion (AD) of different organic wastes is a promising technique to enhance clean energy (bioenergy) and manure (slurry) production, reducing stress on the environment. This is an experimental study aimed to investigate 2-stage co-digestion of pretreated organic wastes mixed with fresh animal manure (BD) and digester’s operation conditions (digester temperature and pH) to enhance biomethane production. To increase lignocellulose digestibility and biomethane (BM) production, fruit + vegetable waste (FVW) and corn stalks + wheat straw (CR) in ratio (1:1), respectively, were pretreated with inoculum taken from an anaerobic digester of poultry manure at 35 °C. This AD experiment was performed in a fixed dome biodigester with volumetric capacity of 2.3 m3. Biomethane potential (BMP) tests were conducted for biomass treatments and inoculum used (T1, T2, Ti) at 35 °C. In this study, the temperature of biodigester material was measured in mesophilic (30–40°C) and thermophilic (40–50°C) ranges and pH of fresh feed and slurry feed digesters was in optimum methane production range (7.01–7.52). The total daily methane productions from T1 and T2 were 125.13 ml/g VS and 104.89 ml/g VS in mesophilic range (30–40°C) while these values were 148.41 ml/g VS and 132.74 ml/g VS in mesophilic range (40–50°C), respectively. The 2nd stage digestion of slurry from fresh feed digester added 39–45% and 35–38% more methane production in T1 and T2 respectively. On calibration with BMP tests, experimental data have shown the synergetic effect on methane production and its thermal characteristics promoted by co-digestion of pretreated organic waste and BD. The economic and feasibility analysis proved the biomass co-digestion project viable and adoptable with positive (5.39 $) net return value (NRV), 2.92 years payback time (PBT), and 1.34 benefit cost ratio (BCR).