Elemental sulfur-driven autotrophic denitrification process for effective removal of nitrate in mariculture wastewater: Performance, kinetics and microbial community

Abstract

To date, there is a lack of systematic investigation on the elemental sulfur-driven autotrophic denitrification (SDAD) process for removing nitrate (NO3−-N) from mariculture wastewater deficient in organic carbon sources. Therefore, a packed-bed reactor was established and continuously operated for 230 days to investigate the operation performance, kinetic characteristics and microbial community of SDAD biofilm process. Results indicate that the NO3−-N removal efficiencies and rates varied with the operational conditions including HRT (1–4 h), influent concentrations of NO3−-N (25–100 mg L−1) and DO (0.2–7.0 mg L−1), and temperature (10oC–30 °C), in the ranges of 51.4%–98.6% and 0.054–0.546 g L−1 d−1, respectively. Limestone could partially neutralize the produced acidity. Small portions of NO3−-N were converted to nitrite (<4.5%) and ammonia (<2.8%) in the reactor. Operational conditions also influenced the production of acidity, nitrite and ammonia as well as sulfate. Shortening HRT and increasing influent NO3−-N concentration turned the optimal fitting model depicting the NO3−-N removal along the reactor from half-order to zero-order. Furthermore, the NO3−-N removal was accelerated by a higher temperature and influent NO3−-N concentration and a lower HRT and influent DO concentration. Microbial richness, evenness and diversity gradually decreased during the autotrophic denitrifier enrichment cultivation and the reactor start-up and operation. Sulfurimonas constituted the predominate genus and the primary functional bacteria in the reactor. This study highlights the SDAD as a promising way to control the coastal eutrophication associated with mariculture wastewater discharge.