Influences of Naphthalene Concentration on Starch Anaerobic Digestion: Focusing on Digestion Performance, Extracellular Polymeric Substances and Function Microbial Community

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed in the sludge environment due to activities such as oil extraction and pose a serious threat to deep-seated anaerobic microorganisms. Thus, in this study, we discussed the dose–response efficiency of naphthalene (Nap, a typical PAH) on anaerobic digestion (AD) through co-metabolic degradation via batch experiments. The batch results showed that 30 mg/L Nap promoted the AD with the accumulation of CH4 18.54% higher than the control (without Nap) by increasing the efficiency of hydrolysis and acetogenesis 99.49% and 61.95%, respectively. However, adverse effects were observed with an excessive dosage of Nap (higher than 100 mg/L) with a decrease of methane production (37.16) with 2000 mg/L Nap. Interestingly, the concentrations of the polysaccharide and protein reached the highest at 138.76 mg/L and 400.41 mg/L, respectively, in 1000 mg/L Nap. Furthermore, the high activities of hydrolase and transmembrane ATPase were acquired in 30 mg/L Nap. In addition, Nap significantly affected the methanogenic microbial abundance and diversity, especially diminishing Methanolinea and Syntrophobacter. Furthermore, the enrichment of Bacteroides in 30 mg/L Nap showed moderate Nap could facilitate hydrolysis. The genes relevant to cellular processes were activated by Nap. This research provided a reliable basis for the anaerobic microbial response under Nap stress.