Influence of COD/sulfate ratios on the integrated reactor system for simultaneous removal of carbon, sulfur and nitrogen

An integrated reactor system was developed for the simultaneous removal of carbon, sulfur and nitrogen from sulfate-laden wastewater and for elemental sulfur (S⁰) reclamation. The system mainly consisted of an expanded granular sludge bed (EGSB) for sulfate reduction and organic carbon removal (SR-CR), an EGSB for denitrifying sulfide removal (DSR), a biological aerated filter for nitrification and a sedimentation tank for sulfur reclamation. This work investigated the influence of chemical oxygen demand (COD)/sulfate ratios on the performance of the system. Influent sulfate and ammonium were fixed to the level of 600 mg SO₄ ^2-L^-1and 120 mg NH₄ ⁺L^-1, respectively. Lactate was introduced to generate COD/SO₄ ^2-= 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 3.5:1 and 4:1. The experimental results indicated that sulfate could be efficiently reduced in the SR-CR unit when the COD/SO₄ ^2-ratio was between 1:1 and 3:1, and sulfate reduction was inhibited by the growth of methanogenic bacteria when the COD/SO₄ ^2-ratio was between 3.5:1 and 4:1. Meanwhile, the Org-C/S^2-/NO₃ ^-ratios affected the S⁰reclamation efficiency in the DSR unit. When the influent COD/SO₄ ^2-ratio was between 1:1 and 3:1, appropriate Org-C/S^2-/NO₃ ^-ratios could be achieved to obtain a maximum S⁰recovery in the DSR unit. For the microbial community of the SR-CR unit at different COD/SO₄ ^2-ratios, 16S rRNA gene-based high throughput Illumina MiSeq sequencing was used to analyze the diversity and potential function of the dominant species.