Study On The Three Dimensional Complex Biofilm Electrode Reactor For Removal Of Nitrate Nitrogen From Micro-polluted Groundwater

Due to the intensification of groundwater pollution caused by industrial and agricultural production,the groundwater quality in many areas shows the phenomenon that nitrogen nitrate and trace organic matter exceed the standard at the same time.In order to effectively treat this combined pollution groundwater,common phenol was used as a representative component of trace organic matter in groundwater.According to the micro-polluted groundwater quality in a certain area of Shandong Province,a simulated contaminated groundwater containing nitrogen nitrate and trace organic matter was artificially prepared,and a new three-dimensional complex biofilm electrode reactor(3D-CBER)was constructed to conduct processing studies.3D-CBER had two layers of BER structure,stainless steel orifice plate was used as the cathode,and due to the different needs of nitrate and organic matter,the anode was in two forms in the experiment.One of the form was two layers of anodes were both graphite plates,and this reactor is called the same anode three-dimensional complex biofilm electrode reactor(3D-T-CBER).In the other form,the graphite plate was used as the lower anode,the titanium dioxide plated titanium plate was used as the upper anode and the corresponding reactor is called the different anode three-dimensional complex biofilm electrode reactor(3D-Y-CBER).The particle electrodes in the reactor were shell activated carbon.In order to investigate the removal process of nitrate nitrogen and trace organic matter in groundwater by three-dimensional complex biofilm reactor,the experiment studied on the removal effects and main influencing factors of micro-polluted groundwater containing nitrate nitrogen were studied by pure electrochemical action and electrochemical biofilm before and after inoculation of hydrogen autotrophic denitrifying bacteria.The main conclusions of the experiment were as follows:(1)3D-T-CBER and 3D-Y-CBER have certain removal effect on nitrate nitrogen and trace organic matter in groundwater.Under the optimal conditions,for 3D-T-CBER,the removal rate of nitrate nitrogen was 89.22%,the removal rate of phenol was 79.24%;for 3D-Y-CBER,the removal rate of nitrate nitrogen was 79.27%,the removal rate of phenol was 90.29%.Under the premise of ensuring the removal of nitrate nitrogen from the effluent,the 3D-Y-CBER had better removal effect of trace organic matter than 3D-T-CBER,so 3D-Y-CBER is the best form of three-dimensional complex biofilm electrode reactor.(2)The main influencing factors of the three-dimensional complex biofilm electrode reactor were hydraulic retention time(HRT),current intensity,influent nitrate nitrogen concentration and influent pH.The experimental results showed that with the extension of HRT,the removal effect of nitrogen nitrate and organic matter(phenol)in micro-polluted water was correspondingly improved.When HRT was 12 h,the removal rate of nitrate nitrogen by 3D-T-CBER was 85.6%,the degradation rate of phenol was 74.64%.By 3D-Y-CBER,the removal rate of nitrate nitrogen was 81%,and the degradation rate of phenol was 90%.It showed that 3D-Y-CBER was more conducive to the simultaneous electrochemical action of the anode and cathode.The experimental results of current intensity showed that when the current intensity was 40 mA,the removal rate of nitrate by 3D-T-CBER reached to 87.52%,and the degradation rate of phenol was 75.27% by 3D-Y-CBER,the removal rate of nitrate reached to 79% and the degradation rate of phenol was 90.64%.The surface current intensity had a more pronounced effect on the anodizing effect.Nitrogen nitrate concentration in the influent water was also a major influencing factor.When the influent nitrogen nitrate concentration was 20 mg/L,the removal rate of nitrate nitrogen by 3D-T-CBER reached to 86.61%;the removal rate of nitrate nitrogen by 3D-Y-CBER was 82.1%.The influent pH had a great influence on the activity of hydrogen autotrophic denitrifying bacteria and the reaction of the electrode.The neutral or weak alkaline environment of the influent water was more conducive to the removal of nitrate nitrogen and phenol by the double reactor.(3)According to the corresponding surface experiments,the degree of the four influencing factors on the removal rate of nitrate nitrogen in 3D-T-CBER and 3D-Y-CBER was as follows: current intensity>hydraulic retention time>influent nitrate nitrogen concentration>influent pH;the degree of influence on the removal rate of phenol was as follows: current intensity>hydraulic residence time>influent pH>influent nitrate nitrogen concentration.The optimal conditions for 3D-T-CBER to remove nitrate nitrogen from groundwater were that residence time was 10.88 h,current intensity was 41.70 mA,influent pH was 7.41 and influent nitrate nitrogen concentration was 29.57 mg/L;the optimum conditions for removing phenol from the reactor were as follows: HRT was 11.09 h,current intensity was 35.38 mA,influent pH was 7.06 and influent nitrate nitrogen concentration was 28.35 mg/L.The optimal conditions for 3D-Y-CBER to remove nitrate nitrogen from groundwater were that residence time was 9.44 h,current intensity was 39.68 mA,influent pH was 7.11 and influent nitrate nitrogen concentration was 21.61 mg/L;the optimum conditions for removing phenol from the reactor were as follows: HRT was 10.98 h,current intensity was 41.47 mA,influent pH was 6.51 and influent nitrate nitrogen concentration was 29.06 mg/L.The results showed that the newly constructed three-dimensional complex biofilm electrode reactor can simultaneously remove nitrate nitrogen and trace organic matter in groundwater without causing excessive accumulation of nitrite and ammonia nitrogen in the reactor,which is an efficient treatment.3D-CBER provides a solution to the problem of complex pollution containing both nitrogen nitrate and trace organic matter.