Effect of straw on microbial community composition and degradation efficiency of polycyclic aromatic hydrocarbons in sludge digester

The main aim of this study was to investigate the effect of straw on microbial community composition and the degradation efficiency of polycyclic aromatic hydrocarbons (PAHs) in a sludge digester. In this study, three straws and four different ratios were assessed using identical semi-continuous-fed anaerobic digestion bioreactors; VSsludge/VScorn = ratio of 1:1.5 (C3) was observed to produce the highest biogas yield (2303.08 mL/d, with a methane content of 52.49 +/- 2.74%). The latter yield was approximately three times greater than that of the control (536.15 mL/d, with a methane content of 37.07 +/- 1.41%). However, the associated removal efficiency of PAHs was higher for other VSsludge/VScorn ratios apart from VSsludge/VSrice = 1:0.5 (R1) and VSsludge/VSwheat = 1:1.5 (W3). The highest removal rates were observed for 4-ring PAHs, especially BbF and BkF, which exhibited average removal rates of 60.87% and 67.74%, respectively. 16S rRNA gene sequencing demonstrated that Bacteroidetes, Proteobacteria and Chloroflexi were the dominant operational taxonomic units during co-digestion, and Christensenellaceae_R-7_group and unclassified_f_Ruminococcaceae increased to 2.33-15.73% and 0.61-1.74% following the addition of straw, respectively. In addition, the abundance of acetotrophic methanogens (Methanosaeta) varied with the addition of straw. Methanomassiliicoccus, which is the main methylotrophic methanogenic genus, increased in abundance from 1.00 to 8.07%.