Lighting promotes sulfate removal and improves microbial community stability in upflow anaerobic sludge bed reactors under low ratio of chemical oxygen demand to sulfate

Abstract

The anaerobic treatment of sulfur-laden organic wastewater is common; however, competition between sulfate-reducing bacteria (SRB) and methanogenic archaea (MA) can result in low removal efficiencies and unstable systems. Photosynthetic bacteria, capable of oxidizing reduced sulfides, can alleviate sulfide toxicity to microorganisms, thereby enhancing sulfate removal. This study compared the performance of anaerobic reactors under identical organic loads but with varying light conditions and different carbon-to-sulfur (C/S) ratios. The illuminated reactors outperformed the non-illuminated ones, achieving sulfate removal rates exceeding 85% when the light wavelength was optimized. Sludge analysis revealed that the illuminated group had larger particle sizes and higher protein and polysaccharide contents compared to the non-illuminated group. These findings suggest that light exposure enhances the removal of sulfate and organic matter, mitigates competitive inhibition, and promotes synergistic interactions among microbial populations, offering valuable insights for treating sulfate-rich wastewater using photosynthetic bacteria.