Anaerobic Naphthalene Biotransformation Coupled to Sulfate Reduction

Polycyclic aromatic hydrocarbons (PAHs) are a diverse group of hazardous and toxic pollutants widely distributed in the environment. The anaerobic degradation is a promising technique for the removal of recalcitrant aromatic hydrocarbons from waste stream. In this study, anaerobic degradation of naphthalene (NAP) was investigated by using cow dung-enriched mixed microbial consortia with varying NAP and sulfate concentrations. The maximum removal of NAP (99.8%) and sulfate (68%) was achieved while varying the sulfate concentration from 50 to 500 mg/L in 500 mg/L NAP influent concentration. 41.9 mg/L of sulfate was generated during this study. Similarly, when NAP concentration was varied from 100 to 1000 mg/L, 84% of chemical oxygen demand (COD), 74% of sulfate, and 92% of NAP were observed at constant sulfate concentration of 250 mg/L. This result reveals that sulfate concentration had no significant effect on NAP degradation. NAP mineralization was evidenced by the formation of sulfide and production of metabolites with decreasing NAP concentration. Gas chromatography–mass spectrometry (GC–MS) confirmed the formation of metabolites like naphthol and 1,2-dihydroxynaphthalene due to monooxygenation at C-1 as part of the metabolic pathway. The rate of NAP, COD, and sulfate removal followed the first-order kinetics with high regression coefficients while varying the influent NAP concentrations.