Ranking of energy potentials of agro-industrial wastes: Bioconversion and thermo-conversion approach

The rising amount of organic wastes (biomasses) generated annually constitute serious environmental concerns but hold enormous potentials in solving the increasing global energy demand. When properly harnessed, they are good renewable energy sources with capabilities of bridging the energy demand gaps and ameliorating environmental concerns of developing climes. In this study, the mixed-method approach of anaerobic digestion and thermogravimetry were used in the ranking of eighteen selected agro-industrial biomasses based on their energy (biomethane or thermochemical) conversion potentials. The ultimate and proximate properties of the substrates were determined, then the experimental biomethane potentials (BMP) were carried out via anaerobic digestion of feedstocks at mesophilic conditions for 30 days. The biomasses were also degraded thermally within a temperature range of 50 and 800 degrees C, torrefaction and the pyrolysis char yields were determined. The calorific values and the theoretical biomethane potentials (TBMP) were calculated from the elemental compositions of substrates. From the results obtained, lignocellulosic plant materials and the animal manures recorded lower methane yields and biodegradability. Although the animal manures had appreciable high heating values (HHVs), their BMP yields were poor with biodegradability as low as 25.8%. Consistent with agro-based biomasses, most of the biomass had low H/C-eff, high H/C and O/C atomic ratios. Based on ranking criteria, waste samples from animal carcasses and oil crops were ranked topmost in both thermochemical and biochemical energy conversion. Co-digestion/degradation of high ranked biomass with others and enhancements of the substrate before energy conversion is recommended. Thermal upgrade of biomasses and co-pyrolysis with coal is also recommended. (C) 2020 The Authors. Published by Elsevier Ltd.