A new inoculation method of sulfur autotrophic denitrification reactor for accelerated start-up and better low-temperature adaption

Elemental sulfur (S0) autotrophic denitrification (SAD) has been proved feasible for nitrate removal from aquatic environments. The long start-up period up to weeks of the SAD reactor impedes its industrial application. To accelerate the start-up process, this study employed S0 powder packed sequencing batch reactor operated for 10 days to obtain a seed biofilm, which was inoculated into a regular S0 flake packed bed reactor afterwards. Merely two days after inoculation, the reactor inoculated with seed biofilm was well started up and outperformed the control reactor, which was inoculated with regular anaerobic sludge and operated for more than 10 days, delivering much increased denitrification rate of 126 ± 0.68 mg N/(L·d) and a high nitrate removal efficiency of 93.0%. Batch tests during the start-up period showed that the seed biofilm developed well on S0 flakes and delivered improved nitrate removal performance than the control. Extracellular polymeric substance (EPS) analysis revealed an abundant content of protein in tightly bound EPS in the biofilm developed from the seed biofilm, which was recognized as a major contributor to facilitate the biofilm's attachment and growth onto S0 flakes. After operating under moderate temperature, the reactors were tested at a reduced temperature of 15 °C. Results indicated that the reactor inoculated with seed biofilm showed stronger adaptation ability towards low temperature and sustained better denitrification performance than the control, which was attributed to increased protein content in tightly bound EPS produced by the microbes against low-temperature. Determination of the microbial communities in tested reactors when the whole experiment was closing found that sulfur-related genera were dominating in the packed-bed reactor inculcated with seed biofilm, which played an important role in the S0-based denitrification process. [Display omitted] •Seed biofilm was obtained from S0 powder-packed sequencing batch reactor.•S0 flake-packed bed reactor inoculated with seed biofilm was rapidly started up.•Protein content in TB-EPS promoted biofilm's development on S0 flake.•Reactor inoculated with seed biofilm showed stronger adaptation to low temperature.•Thiobacillus played a major role in the reactor inoculated with seed biofilm.