Enhanced decolorization of dyeing wastewater in a sponges-submerged anaerobic reactor

This study was conducted to assess the potential of a sponges-submerged anaerobic baffled reactor (SS-ABR) for enhancing the processing performance of azo dye-contaminated wastewater. A lab-scale four-compartment SS-ABR, with a total volume of 10 L, was operated at 30 °C for 180 days. A total of 14 polyurethane sponges were added in each compartment to treat synthetic wastewater including a commercial azo dye Hellozol HSR Reactive Black. During the entire operation, in synthetic wastewater, starch was used as a sole carbon source, and the true color level was maintained at 1050 ± 98 Pt/Co. Meanwhile, the hydraulic retention time (HRT) and total COD (T-COD) in the influent were changed to evaluate the SS-ABR treatment performance. After the start-up phase, true color and T-COD removal efficiencies were recorded as 65 ± 3% and 83 ± 2%, 68 ± 5% and 81 ± 4%, and 70 ± 5% and 84 ± 2% for HRT and influent T-COD concentration of 18.6 h and 260 mg L^-1, 14.6 h and 260 mg L^-1, and 14.6 h and 460 mg L^-1, respectively. The microbial community analysis showed that bacterial groups involved in dye degradation, such as Clostridium sp., and sulfate-reducing bacteria Desulfomonile sp. and Desulfovibrio sp. were detected prominently in the SS-ABR. Interestingly, the SS-ABR exhibited the dominance of both Geobacter sp. and Methanosarcina sp., and their occurrences in all columns were proportional to each other, revealing the formation of syntrophic relationships.