Nitrate removal efficiency of a mixotrophic denitrification wall for nitrate-polluted groundwater in situ remediation

Sand tank experiments were conducted to evaluate a mixotrophic denitrification process for nitrate contaminated groundwater in situ remediation. Nitrate removal efficiency reached up to 86.6% when the nitrate loading rate was <= 522mgNd(-1) kg(-1) WS (woodchip-sulfur), while 58.7% of the reduced nitrate was heterotrophically removed and 41.3% was autotrophically removed. Nitrite accumulation was only observed at the experimental phases with relatively low nitrate removal efficiency. Ammonium accumulation in the present mixotrophic bio-system was overwhelmingly less than that in heterotrophic denitrification wall (DW). The sulfate produced by the autotrophic bacteria could be effectively controlled under the mixotrophic environment, and a minimum water contact time of 5.64 d was required for the growth of microorganisms which were closely related to sulfate-reducing bacteria. No alkalinity supplement was needed to adjust the pH. The mixotrophic DW could maintain more superior permeability than the heterotrophic DW, and the longevity of the present DW was estimated as 935 d when it operated effectively. The present study revealed the operational mechanism of the mixotrophic DW and could provide reference significance for field applications. (C) 2017 Elsevier B.V. All rights reserved.