Hydrogenotrophic Denitrification For The Removal Of Nitrate In Groundwater

Groundwater has been severely contaminated with nitrate, presenting a great threat to the human health. To remove the nitrate from groundwater and achieve the requirement of Standards for Drinking Water Quality, autotrophic denitrification with hydrogen as the electron donor was investigated by using a sequencing batch reactor in an attached growth system.Reduction kinetics of nitrate followed a double Michaelis-Menten model. The kinetics of nitrate and nitrite reduction could be approximately descibed by a zero order kinetic model when both concentrations were higher than 10 mg/L. The zero order kinetic coefficients measured in the test were 13.8~25.0 mg/(g·h) and 12.3~18.7 mg/(g·h) respectively.Nitrate was removed efficiently with hydrogenotrophic denitrification. The removal rates of nitrate and TN could achieve 6.45 mg/(L·h) and 4.86 mg/(L·h) respectively. In the denitrification process, pH value was increasing until it achieved 10.56, causing the formation of insoluble deposition of calcium and magnesium ions. This affected the capability of diffusing hydrogen with gas permeable membrane and the activity of the biofilm, resulting in an unstable performance of the denitrification system. The organic contaminants introduced by biological denitrification were less, with an increase of DOC 0.91 mg/L.Hydrogen pressure and pH value were the main effect factors for the nitrate removal. The removal rates of nitrate and TN were not affected with the hydrogen pressure higher than 40 kPa, while decreased remarkably when the hydrogen pressure was lower than 25 kPa. Denitrification reaction was inhibited at lower pH value. The removal rate of nitrate was 1.8 mg/(L·h) when pH value of the influent was 6 while 3.13 mg/(L·h) when pH value of the influent was 8. Temporary deficiency of phosphate showed a negligible effect on denitrification.Nitrite was accumulated in the reactor with the maximum concentration 11.32 mg/L. Denitrification coefficientαcould be used as the index of nitrite accumulation. Whenαwas lower than 1, there was nitrite accumulation in the reactor; while nitrate could be exactly converted to nitrogen gas whenαwas 1. Nitrite accumulation and pH increase were the main problems to solve. Solutions for the problems and suggestion were proposed to further improve the performance of hydrogenotrophic denitrification technology.