Enhanced anaerobic mono-digestion and co-digestion of crop residues by NaOH alkalı pre-treatment

Abstract

The main objective of the study was to determine the effect of different dosages of NaOH alkali pre-treatment on the lignocellulosic structures and the methane production of crops’ residues. In this regard, NaOH pre-treatment was implemented with different dosages on three different crops’ residues: wheat, rye, and rice straws. Substrates were soaked into NaOH solutions at different dosages with solid to liquid ratios of 100 and 200 gTS/L to investigate both conditions. Anaerobic digestion process was conducted using AMPTS II under mesophilic conditions. By 8 % NaOH pre-treatment dosage, the reduction of hemicellulose and lignin was 81 % and 62 % for rice straw, 86 % and 69 % for wheat straw, 80 % and 74 % for rye straw, respectively. The concentrations of CODs in the liquid fraction after pre-treatment were regarded as 3 times higher than untreated samples. Pre-treatment with 8 % NaOH dosage increased the methane yield of rice, wheat, and rye straws by 55 %, 40 %, and 46 % respectively. During the co-digestion test, an increase in VFA production was regarded by (rice/wheat) and (rice/wheat/rye) sets by values of 1930 and 1710 mg/L total acetic acid on the 5th day. Samples from digesters that produced the highest methane yield were chosen for further molecular analysis. Proteobacteria was found the most abundant bacterial phylum in the inoculum used, while Methanothermobacter and Methanoculleus were the major archaeal communities found. Compared to untreated digesters, 16S rRNA gene amplicon sequencing revealed more diverse microbial communities in NaOH digesters.