Effect of zero-valent iron on biological denitrification in the autotrophic denitrification system

This study investigated nitrate removal using biological denitrification by the iron-reducing bacteria strain CC76 combined with zero-valent iron (ZVI) in simulated groundwater under anaerobic conditions. The mechanism of nitrate reduction as well as the process of iron cycling by strain CC76 and ZVI were studied. During growth experiments, the strain CC76 showed the ability to utilize Fe2+ (electron donor) produced from the stimulated corrosion of ZVI for the nitrate removal. ZVI exerted inhibitive effects on the growth of strain CC76 in the early stage. However, the strain CC76 was able to tolerate the presence of ZVI in the long term. Moreover, three factors (temperature, initial pH, and ZVI concentration) were selected as effective factors and were optimized using a central composite design of response surface methodology. Based on the statistical analysis, a temperature of 30.44 degrees C, initial pH of 6.11, and ZVI concentration of 5.89g/L were determined to be the optimum values. The effect of Fe2+/ZVI ratio was also explored and compared with ZVI alone, a certain amount of a mixture of Fe2+ and ZVI showed a higher nitrate removal ability. Moreover, scanning electron microscopy and X-ray diffraction analyses showed the corrosion of ZVI occurred after reaction in the autotrophic denitrification system.