Impact of Iignocellulosic waste types and inoculum-to-substrate ratio on anaerobic co-digestion with sewage sludge under mesophilic conditions

Abstract

Currently, anaerobic digestion of agricultural waste to produce biogas and methane stands out as one of the most effective methods in utilization of renewable and clean resources. This study investigates the co-digestion of four types of lignocellulosic biomass (wheat straw (WS), barley straw (BS), corn straw (CS), and rice straw (RS)) with anaerobic sludge as an inoculum, across three varying inoculum to substrate ratios (ISR): 2, 1, and 0.5. For this purpose, single-stage one-liter reactors with a batch hydraulic regime were operated under mesophilic conditions at 36 °C, with total solids loading of 10% for a duration of 180 days. The results demonstrated that the co-digestion of various types of straw and sludge led to an increase in biogas production yield compared to mono- digestion of sludge. Additionally, the best performance of the digestion process was observed for corn straw with ISR = 2 and wheat straw with ISR = 1, with biogas production rates of 0.555 m³/kg-VS and 0.530 m³/kg-VS, respectively. Furthermore, ISR = 1 for WS, BS, and RS, and ISR = 2 for CS were recorded as the optimal ISR ratios with the highest biogas production. According to the kinetic modeling, increasing ISR led to a reduction in the lag time for all treatments.