Anaerobic digestion and gasification hybrid system for potential energy recovery from yard waste and woody biomass

There is a rapid growing interest in using biomass as an alternative source for clean and sustainable energy production. In this work, a hybrid system was developed to combine anaerobic digestion (AD) and gasification for energy recovery from yard waste and woody biomass. The feasibility of the proposed hybrid system was validated experimentally and numerically and the energy efficiency was maximized by varying energy input in the drying process. The experiments were performed in two stages. At the first stage, AD of yard waste was conducted by mixing with anaerobic sludge. At the second stage, co-gasification was added as post-treatment for the AD residue for syngas production. The co-gasification experiments of AD residue and woody biomass were conducted at varying mixing ratios and varying moisture contents of AD residue. Optimal energy efficiency was found to be 70.8% at mixing ratio of 20 wt% AD residue with 30 wt% moisture content. Two kinetic models were then adapted for prediction of biogas produced in AD process and syngas produced in gasification process, respectively. Both experimental and numerical results showed that full utilization of biomass could be realized to produce energy through the combination of these two technologies. •The feasibility of the proposed two-stage hybrid system was validated experimentally and numerically.•The proposed hybrid system could effectively improve the quality of produced gas.•The operating parameters were optimized to improve the overall energy efficiency of the system.•Drying process was found to play an important role in determining overall energy efficiency.•Optimal moisture content of AD residue was investigated for maximizing energy efficiency.