[Movement and transformation of nitrate in soil by non-uniform electrokinetics]

Movement and accumulation of nitrate in soil and groundwater has become a serious threat in many cities and agricultural areas. At the same time, application of nitrate as bacterial nitrogenous nutrient in the in-situ bioremediation of some organics-polluted sites is often required. Laboratory experiments were conducted to examine the feasibility of using non-uniform electrokinetics (NUEK) to control the movement of nitrate in unsaturated soil-water system. A natural soil taken from woodland was used as experimental soil. Three electrokinetic processes were tested in bench-scale cells at a constant potential gradient of 1.0 V/cm: unidirectional NUEK, NUEK with periodic polarity-reversal, and conventional uniform electrokinetic (UEK). The tests showed that NUEK drove NO3- through the experimental soil at a rate of 13.5-20 cm/d depending upon the concentration of NO3- and the distribution of electric field density. Compared with UEK, NUEK process more effectively concentrated and retained NO3- close to the anode. Moreover, NUEK process maintained soil characteristics and consumed much less electric energy. Reversal the polarity of NUEK weakened the concentration of NO3- to electrodes, but it stimulated the transformation of NO3- to NO2- and further lowered the electric energy consumption.