Comparison of various pretreatment techniques to enhance biodegradability of lignocellulosic biomass for methane production

Abstract

This study investigated the anaerobic digestion (AD) of garden waste (GW), which is a lignocellulosic type of biomass produced in large scale worldwide. Different pretreatment techniques were applied and their effect on the hydrolysis rate and methane production potential were evaluated. The pretreatments included alkaline (AP), thermal alkaline (TAP) and alkaline followed by solid/liquid phase-separation. A new strategy was proposed using fruit and vegetable waste (FVW) as an acid catalyst for breaking lignocellulosic biopolymers during co-storage with GW before the batch test. The biochemical methane potential (BMP) was evaluated following VDI 4630 [1] and a kinetic study was applied using the first-order and modified Gompertz models. The BMP of the untreated GW ranged from 255 to 323 LN CH4 kg VS–1. Alkaline pretreatment followed by solid/liquid phase separation showed to be the best technique, with a BMP increased by 70% when compared to the untreated GW. However, a liquid effluent with high soluble COD was produced. Co-storing FVW with GW prior to AD proved to be an alternative to increase the BMP of lignocellulosic biomass. After 7 days of co-storing GW with FVW at room temperature the BMP was increased by 13% (498 LN CH4 kg VS–1), indicating good capacity to enhance speed of degradation with no addition of chemicals and no generation of effluents. The best fit for predicting the BMP was observed for the first-order kinetic model, with R2 ≥ 0.992 and RMSE ≤ 11.3 L CH4 kg VS–1 for all pretreatments applied.