Synergistic effect of alkaline pretreatment and Fe dosing on batch anaerobic digestion of maize straw

Abstract

The synergistic effect of alkaline pretreatment and Fe dosing on anaerobic digestion of maize straw was investigated using mesophilic batch reactors. Three straw treatments were investigated as follows: NaOH (4% and 6%) pretreatment, Fe dosage (50, 200, 1000 and 2000mg/L), and combined NaOH pretreatment and Fe dosage. Compared to the control, NaOH pretreatment alone increased methane yield by 3.5% (313.3mL CH4/gVS) and 22.5% (370.9mL CH4/gVS) and shortened the technical digestion time (TDT) from 48days to 19days and 10days in 4% NaOH and 6% NaOH pretreatment respectively. Moreover, Fe dosing (200–1000mg/L) alone gave a methane yield higher (9.4%) than that obtained from 4% NaOH and 7.5% less than the methane yield from 6% NaOH pretreatment; however, the TDT was 10days longer. Combining NaOH pretreatment and Fe dosage (200–1000mg/L) significantly increased the methane yield even further to 21.8% (368.8mL CH4/gVS) and 56.2% (472.9mL CH4/gVS), and shortened TDT from 48days to 13days and 7days in 4% NaOH and 6% NaOH pretreatment respectively. This synergistic effect may be attributed to the fact that the alkaline treatment improved accessibility of the biodegradable fraction of the straw while Fe contributed to increased microbial enzyme activity.