Nitrate contamination is one of the most important environmental problems in the world. It is a common contaminant in groundwater system. Recent research shows that there is nitrate contamination within the shallow aquifers of many countries (Colin 1995; Williams et al. 1998). Nitrate contamination is a potential health hazard to infants and pregnant women, and limiting direct use of such groundwater resource for human consumption is common in many parts of the world (WHO 1993; Shrimali and Singh 2001). Microbiological methods have been proposed for remediation and removal of the nitrate contamination in groundwater by: a) injecting organic matter into the aquifer to increase the reduction zone and activate organisms for denitrification through multiple or double boreholes (Hiscock et al. 1989; Dahab 1992); b) using sand tank circulation and gravel tank system (Volokita et al. 1996; Dejournett and Alvarez 2001); c) introducing nitrate contaminated groundwater into underground caves with a carbon source under pressure for denitrification (Gregory 1991). The first method uses existing organisms in the media to remove nitrate through pumping and injection. Limitations of this method are spatial variation of the underground environment, heterogeneity and non-cultivation of the denitrifying organisms, therefore the nitrate removal efficiency may be not satisfactory and the processes are not well understood (Liu et al. 1992; Gomez et al. 2000). The second and third methods are suitable for sites of small area and less contamination via engineering constructions; they are not necessarily cost-effective approaches (Bouwer 1994; Gomez et al. 2001; Schipper and Vukovic 2001). The main sources of nitrate in the groundwater environment include agriculture (manures, fertilizers, pesticides and wastewater irrigation) and improper disposals of urban industrial and domestic wastewater, which percolate through soil and flow into groundwater (Colin 1995). In the natural environment, the behavior of nitrogen is disturbed by human activity and microbiological activity (Shen et al. 1995; Yang et al 1999). Zhao and Yang (2002) have studied an efficient denitrifer for wastewater bio- treatment. Based on these research results, this paper has further applied the approach of bioremediation to a simulated contaminated porous media aquifer. A study for nitrate removal using microorganisms in a sand tank has been carried out based on the biochemical characterization and denitrifying mechanism of the micro-organism.

在河南境内黄河流域地下水系统划分的研究中，探讨区域地下水系统划分应依据两个基本条件：（1）依据地质环境因素确定含水层系统；（2）含水层系统是否具有独立的水循环流动系统，即拥有完整的补给、径流、排泄系统。河南境内黄河流域划分成5个区域地下水系统（3个孔隙地下水系统，2个裂隙岩溶水系统），都具有稳定的边界，便于对地下水资源做出准确评价、开发、规划和管理。