零价铁-反硝化菌在地下水硝酸盐污染修复中的应用

Review on nitrate removal from the groundwater by using zero-valent iron combined with denitrifying bacteria

综述了应用零价铁-反硝化菌复合体系去除地下水中硝酸盐氮污染的研究进展。脱氮技术主要包括物理化学法、化学还原法和生物反硝化法,但单独使用任何一种方法都无法得到令人满意的处理效果。以零价铁在水中厌氧腐蚀所释放的氢气供给微生物进行反硝化,可以同时解决这两种技术单独使用时所存在的弊端。在此复合体系中,主要反应包括产氨、析氢和反硝化,降低脱氮产物中的氨氮比例就要减少产氨反应的发生几率。此外,使用纳米铁代替零价铁和反硝化细菌复合,可以大大提高脱氮反应速率。然而,该技术的研究在国内外尚处于起步阶段,在反应机理、产物控制、条件优化等方面都存在不足,还需要深入研究。

The paper is aimed to provide a review on the nitrate removal from the subsurface water by using zero-valent iron combined with denitrifying bacteria. As is known, nitrate pollution of subsurface and surface water has become a serious environmental problem in many parts of the world. Popular methods used for nitrate removal for the time being include physical chemical method, chemical reductive method and biological denitrification method. However, physical chemical methods can only help to transfer the nitrate form of the groundwater with no help to reduce it. As to the chemical reductive methods, they may also lead to the generation of large amounts of ammonium, which may result in greater degree of toxicity than the nitrate itself. Biological denitrification, however, is also likely to lead to excessive biomass and soluble microbial products that make it necessary to do secondary treatment before using it, especially, when heterotrophic bacteria are involved. That is to say, no methods can be properly used for removal nitrate with no other treatment. The reason for this trouble comes from the fact that when iron metal is immersed in water, its oxidation tends to involve the reduction of water derived protons to form cathodic hydrogen, which can actually be applied for sustaining autotrophie denitrification. Therefore, it would be the only way to combine the microbial-Fe（0） treatment systems for them to display their comprehensive potential advantages over any individual approach when used alone. The dominating reactions may include ammonium generation, hydrogen release, biological denitrification, and so on. Furthermore, it is necessary to point out that the ammonium generation can contribute to the reaction between iron and nitrate, which tends to be the key problem to controlling ammonium generation and decrease of the liability of such reactions. Moreover, the substitution of zero-valent iron by iron nanoparticles can help to heighten the efficiency of denitrification. However, in this case, the problem may include a few difficulties of the technology in discussion for its in situ applications, which may include： （1） the combined system can only decrease ammonium generation, but cannot prevent it from happening, and, therefore, it is necessary to treat the residual ammonium for further application. （2） low temperature and high pH value can only result in low denitrification efficiency; （3） when the denitrification is completed, it is necessary to treat the residual Fe^2＋/Fe^3＋ ; （4） The efficiency of the denitrification process can also be affected by the complication due to the presence of denitrifying bacteria and other bacteria in the mixture of the groundwater and the soil.