| The nitrate nitrogen in groundwater exceeds the environmental quality standard for groundwater and the emerging organic pollutants glucocorticoid(GCs)is frequently detected due to the impact of human production and life,which can bring health risks to residents who use groundwater as drinking water source.The purpose of this article is to study the simultaneous removal of representative fluorine-containing GCs,dexamethasone(DXMS)and nitrate nitrogen from groundwater by bio-electrochemical systems(BESs).A two-dimensional bio-electrochemical system(BES-2D)was constructed by selecting electrode materials and operating parameters,then the synergistic removal performance of BES-2D for DXMS and nitrate nitrogen was explored,furthermore,enhanced removal of pollutants was explored in the three-dimensional bio-electrochemical system(BES-3D)with activated carbon-loaded polyaniline(PANI/AC)as particle electrodes,and the changes of dominant functional bacteria and the metabolic mechanism and pathway of DXMS were also explored in BESs in order to provide technical support for drinking water safety.The experimental results of parameter optimization of BES-2D showed that the order of removal efficiency in BES-2D with different materials as electrodes was titanium plate>modified graphite rod>graphite plate>carbon brush.The removal efficiency of pollutants increased firstly and then decreased with the current intensity increasing under the current intensity of 0?30 m A,which were related to the activity of microorganisms,and the degradation percentages of DXMS and nitrate nitrogen were the highest at the current intensity of 3 m A.The removal efficiency of pollutants decreased with the increase of the electrodes'spacing.The removal efficiency of target pollutants showed an increasing trend with the extension of hydraulic retention time(HRT),but the increase of the removal efficiency was not significant after HRT was greater than 21 h.The optimized BES-2D can achieve effective and coordinated removal of two pollutants while the average removal percentages of DXMS and nitrate nitrogen reached87.9%and 76.6%,respectively,which was closely related to the evolution of microbial community structure.The enrichment of Pseudomonas,Desulfuromonas,Methylotenera,Thauera and other microorganisms with simultaneous denitrification and degradation of polycyclic substances played an important role in the degrading of pollutants.The removal efficiency of DXMS and nitrate nitrogen in the BES-3D with PANI/AC as particle electrodes increased by 6.5%and 5.2%compared with BES-2D,respectively,with significant difference,and the improvement of electron transfer efficiency significantly increased the defluorination percentage of DXMS in BES-3D,which was 11.0%higher than that in BES-2D.Meanwhile,the activity of microorganism and the expression of nitrogen conversion(nir S)and dehalogenation genes(rdh)were enhanced,and the functional degradation bacteria were further enriched due to particle electrode provided the attached carrier for microorganism.The metabolic pathways of DXMS in BESs mainly include reactions such as defluorination,demethylation,chain breaking and oxidation of hydroxyl groups to ketones and final ring opening.The removal of nitrate nitrogen was mainly converted into nitrogen.Based on the technological parameters of the experimental study,a 500 m~3/d drinking water bio-electrochemical pretreatment system was designed,which can provide domestic water for 1,000-peoson village. |
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