Sulphur-based autotrophic denitrification of wastewater obtained following graphite production: Long-term performance, microbial communities involved, and functional gene analysis

Abstract

Sulphur-based autotrophic denitrification is an energy-efficient NO3–-N removal process; it does not require carbon and may potentially replace traditional denitrification processes. This process was used to treat graphite production-derived wastewater and achieved almost complete removal of NO3–-N (concentration in effluent: 5.2 mg/L; concentration in influent: 606 mg/L) at a salinity of 15 g/L with a 30 h hydraulic retention time. A unique microbial community was established, in which the abundance of Thiobacillus increased with the increase of the NO3–-N concentration and salinity. Metagenomic analysis revealed that the denitrification metabolic pathway in the bioreactor was active. It also revealed the increased activation of nhaH, a gene encoding Na+/H+ antiporters; proA, proB, and proC, genes encoding proline; and Trk and Kdp systems during the treatment of graphite production-derived wastewater to maintain cell function, providing valuable information about utilizing the sulphur-based autotrophic denitrification process to treat graphite production-derived wastewater.