Design Analysis of a Pilot Scale Integrated Anaerobic Co-digestion Bioenergy System for Palm Agro-industrial Applications

Abstract

Medium-scale palm oil mills in Nigeria face increasing energy costs, inefficient biodegradable residue management and biogas-based bioenergy recovery systems. The non-utilization of palm mill wastes represents a loss of material and energy resources, under-exploiting waste as a bio-resource for energy and environmental challenges. The absence of pilot-scale systems with integrated digestion, purification, compression, and energy conversion has limited laboratory-scale biomethane studies' practical deployment. This study presents a theoretical design analysis and fabrication of an integrated pilot-scale biogas-to-electricity system for decentralized renewable energy. The system comprises a 0.101 m³ vertical continuous stirred tank reactor (CSTR) with biogas purification, compression, and bioelectricity generation subsystems for anaerobic co-digestion of palm oil mill effluent (POME), empty fruit bunches (EFB), mesocarp fibre (MF), and palm kernel shells (PKS). An analytical framework was developed based on engineering design standards. The system integrates a continuously stirred tank bioreactor for energy recovery from palm oil mill effluent and solid residues to optimize biogas production. The design considered palm mill energy requirements, waste volume, biomass availability, feedstock characteristics, C/N ratio, digester type and size, biogas production, feed rate, temperature control, total and volatile solids, gas yield, retention time, loading rate, mixing, pH, conversion efficiency, construction material availability, cost, and safety. The 0.101 m³ vertical CSTR was designed with a 76 L working volume, incorporating 25% gas and safety allowance, with biogas generation, purification, compression, and conversion subsystems, operated under mesophilic conditions at 35 °C with an organic loading rate (OLR) of 2.0 kg VS m⁻³ d⁻¹.The design framework outlined in this research offers a useful guide for enlarging decentralized biogas-to-electricity systems and aids in advancing sustainable and circular energy methods in the palm oil industry.