Enhanced Biogas Production from Rice Husk Through Solid-State Chemical Pretreatments

Solid-state chemical pretreatment was carried out on rice husk (RH) for biogas production with hydrochloric acid (HCl), sodium hydroxide (NaOH) and ethanol (C2H5OH), at three concentrations i.e., 1, 3 and 5% at 100 and 120 degrees C for 60 min. Ethanol (organosolv) pretreated sample with 3% concentration and pretreatment temperature of 100 degrees C (3E100) had the highest biogas production of 5545 mL followed by NaOH pretreated substrate (3N100) with 4705 mL while acid pretreated sample (5H100) produced 700 mL which was lower than the control (raw RH) which was 2500 mL. The biogas yields values were 67.32, 60.89, 32.26 and 9.32 mL/gVS for 3E100, 3N100, RH and 5H100 respectively. Alkaline and organosolv pretreatments improved biogas quality with methane contents of 50.27 and 50.68%. A confirmation that solid state chemical pretreatment of RH with NaOH and C2H5OH could significantly enhance biogas production. The viability of the digestates as biofertilizer was evaluated with the conclusion that they could be used as low grade fertilizers based on their mineral contents and heavy metal concentrations.