Effect of Alkaline Pretreatment and Iron Oxide Nanoparticles on Biogas Production From Rice Straw

Abstract

One of the hurdles in the use of agricultural residues for biogas production is their recalcitrance to biodegradation. For this purpose, agricultural residues are pretreated before their anaerobic digestion. Furthermore, the use of nano additives has an extraordinary effect on biogas production. Trace metals as micronutrients play a very significant role on the performance and stability of anaerobic digestion process. This study focused on the enhancement of biogas production through alkaline pretreatment of rice straw (RS) and the use of magnetite (Fe3O4) nano particles (MNPs). The study was divided into four phases. In phase 1, effect of alkaline pretreatment with 2, 4, 6, 8 and 10% NaOH on chemical composition and structural changes of RS was analyzed. In phase 2, amino acid coated MNPs were prepared and characterized. In phase 3, effect of alkaline pretreatment performed in phase 1 on biogas yield and reactor stability was investigated. Finally, in phase 4, effect of 2% NaOH pretreatment and MNPs doses on biogas yield from RS was investigated. For this purpose, 60, 80, 100 and 120 ppm doses of MNPs were used. Effect of MNPs alone on untreated RS and the combined effect of 2% NaOH pretreatment and MNP doses were evaluated. Results of phase 1 showed that 2% NaOH pretreatment was most effective in removing lignin, reducing lignocellulosic bonds of RS and preserving holocellulose. The results of phase 2 indicated that the synthesized nanoparticles were pure magnetite and well coated. The results of phase 3 revealed that 2% NaOH yielded 53.5% more biogas as compared to control and has positive effect on reactor stability. The results of phase 4 showed that 120 ppm MNPs increased 27.20% and 30% biogas and methane yield respectively as compared to untreated RS without MNPs. Moreover, combined 2% NaOH pretreatment and 120 ppm MNPs increased 99.6% and 130% biogas and methane yield as compared to untreated RS. The combined effect of 2% NaOH pretreatment and 120 ppm MNPs was the most significant.