A mixotrophic denitrification composite for treatment of nitrate-contaminated water: Performance, microbial community and functional genes

Abstract

A mixotrophic denitrification composite was prepared with sulfur, pyrite, sawdust and calcium carbonate (SPSC) for the treatment of nitrate-contaminated wastewater. As a homogeneous integrated composite, fast mass transfer, convenient operation and transportation and easy attachment for microorganisms were obtained in the SPSC-based denitrification system. The long-term operation result showed that SPSC bioreactor exhibited strong resistance to the fluctuations of influent nitrate load, and 98.3% of the nitrate in the influent was reduced even under low hydraulic retention time (HRT). The SPSC system achieved an average nitrate removal rate of 4.59 mg-N/L/h, which was nearly triple the rate of sulfur autotrophic denitrification (SAD) system that utilized sulfur as its sole electron donor. The sulfate yield of the SPSC system (4.52mg SO42-/ mg NO3--N) was significantly lower than those of the SAD system (9.36mg SO42-/ mg NO3--N). Heterotrophic and autotrophic denitrifiers coexisted in the SPSC system, which was beneficial for the denitrification process. Metagenomic analysis indicated that the SPSC composite enriched the functional genes, which encoding key enzymes (nitrate reduction, sulfur oxidation and energy generation) involved in nitrogen, sulfur and carbon metabolism. Collectively, the SPSC composite synthesized in this study has provided a high efficiency, low-cost and promising technology for the treatment of nitrate-contaminated water.