Woodchip-sulfur based heterotrophic and autotrophic denitrification (WSHAD) process for nitrate contaminated water remediation

•A woodchip-sulfur based mixotrophic denitrification is first studied.•Ammonium salts can enhance the metabolic activity of the Thiobacillus bacteria.•Better denitrification performance of the mixotrophic process is achieved.•Little sulfate is observed in the mixotrophic denitrification process.•No artificial alkalinity supplement is needed in the mixotrophic denitrification.

Nitrate contaminated water can be effectively treated by simultaneous heterotrophic and autotrophic denitrification (HAD). In the present study, woodchips and elemental sulfur were used as co-electron donors for HAD. It was found that ammonium salts could enhance the denitrifying activity of the Thiobacillus bacteria, which utilize the ammonium that is produced by the dissimilatory nitrate reduction to ammonium (DNRA) in the woodchip-sulfur based heterotrophic and autotrophic denitrification (WSHAD) process. The denitrification performance of the WSHAD process (reaction constants range from 0.05485 h−1 to 0.06637 h−1) is better than that of sulfur-based autotrophic denitrification (reaction constants range from 0.01029 h−1 to 0.01379 h−1), and the optimized ratio of woodchips to sulfur is 1:1 (w/w). No sulfate accumulation is observed in the WSHAD process and the alkalinity generated in the heterotrophic denitrification can compensate for alkalinity consumption by the sulfur-based autotrophic denitrification. The symbiotic relationship between the autotrophic and the heterotrophic denitrification processes play a vital role in the mixotrophic environment.

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