Improving the biomethane yield of Xyris capensis through pretreatment methods and co-digestion

¹ Department of Mechanical Engineering Science, Faculty of Engineering and the Built Environment, University of Johannesburg, South Africa.
² Process Energy and Environmental Technology Station, Faculty of Engineering and Built Environment, University of Johannesburg, South Africa.

Abstract

The most common substrates for the anaerobic digestion process that release biomethane, a renewable energy source, are lignocellulose materials. Total energy recovery from lignocellulose substrates is challenging due to their recalcitrant nature. Therefore, pretreatment techniques are required for these feedstocks to enhance biomethane yield. This research investigates the impacts of pretreatment methods and co-digestion on the biomethane generation from Xyris capensis. Oxidative pretreatment using 75:25% of H₂O₂: H₂SO₄, the addition of 20 mg/L Fe₃O₄ nano additive, and combined oxidative and Fe₃O₄ nano additive were considered as pretreatment methods, and anaerobic co-digestion of duck waste and Xyris capensis at 50:50%. The substrates were subjected to anaerobic digestion under mesophilic conditions in a batch anaerobic digester to investigate the effect of the treatments on the biomethane production. Biomethane yields of 212.18, 216.41, 251.20, 309.52, and 143.21 mLCH4/g VSadded were recorded for oxidative, nano additive, combined, co-digestion, and control, respectively. The highest total biomethane generated was 309.52 mLCH₄/g VS_added, 116% higher than the untreated feedstock, and was achieved when duck waste and Xyris capensis were co-digested at a 50:50 % mixing ratio. Therefore, the pretreatment of substrates and anaerobic co-digestion of Xyris capensis and duck waste produce cost-effective renewable energy that replaces fossil fuels and promotes a circular economy.