Study On Biotransformation Of Nitrate In Groundwater By Permeable Reactive Barrier

With the rapid development of society,the problem of nitrate pollution in groundwater has become increasingly serious,which has a negative impact on human health.The Permeable Reactive Barrier(PRB)technology has achieved good results in nitrate treatment of groundwater.Fe0 in PRB is transformed into a series of iron minerals.Organic matters which naturally occur in polluted groundwater will enter the PRB with groundwater,thus affecting the treatment of pollutants.Therefore,the study of nitrate reduction in complex systems has important research significance for repairing groundwater environment and protecting human health.In this paper,the microorganism Shewanella oneidensis MR-1,which can participate in iron reduction,nitrate reduction and humic reduction,was selected.PPHA(Pahokee Peat Humic Acid)was used to simulate the presence of humic substances in groundwater,and Fe3O4 was used instead of the traditional Fe0 in PRB.The biological reduction of nitrate by PRB in an anaerobic environment was investigated by measuring the amount of Fe2+ produced and the amount of nitrate reduction.The experimental results are as follows:In the static experiment of nitrate reduction by MR-1,the inhibition of PPHA on nitrate reduction mediated by MR-1 was enhanced with the increase of TOC concentration.The rate of nitrate reduction by MR-1 increased as the nitrate concentration increased.When the pH is 6-8,the removal rate of nitrate can reach 100%.The rate of nitrate reduction by MR-1 was accelerated with the increasing temperature in the range of 10-30℃.In the static experiment of Fe3O4 reduction by MR-1,PPHA accelerated the reduction of Fe3O4 by MR-1 regardless of the presence or absence of an applied magnetic field.In the experiment of reducing nitrate and Fe3O4 by MR-1 involved in PPHA,the addition of Fe3O4 prevented PPHA from inhibiting the nitrate reduction by MR-1.In the PRB reactor,the removal rate of nitrate by PPHA-MR-1-Fe3O4-KNO3 system is up to 99.9%,and the detected concentration of nitrate nitrogen is only 0.01 mg/L.The experimental results are beneficial to the improvement of PRB reactor.This paper is of great significance for evaluating the effects of iron reduction and humic reduction and their combined effect on nitrate reduction mediated by MR-1 in PRB,providing a good basis for simulating biochemical reaction in actual PRB projects.