An Approach Combined Electrochemical With Biological Denitrification For Nitrate Removal From Groundwater

The groundwater has been polluting by NO₃^--N in many countries,with waste discharges of industrial waste and agriculture waste.That resulted to different levels of groundwater NO₃^--N pollution in different cities.Electrochemical biofilm denitrification was a process combined electrochemical with biological denitrification.During this process,autotrophic denitrifiers obtained CO₂ and H₂ from electrochemical reaction,and then deoxidized NO₃^--N to N₂.It has attracted extensive attention,because H₂ was free of pollution as denitrifiers' electron donor and operated simply.The effect of various factors on NO₃^--N removal of the electrode biofilm reactor(BER) were studied in this paper.The reactor was optimized by rectifying the problems of the reactor druing running,and then,a novel approach was developed by combining heterotrophic with autotrophic denitrification.The main results as follow:1.The effect of current,temperature,influent NO₃^--N concentration,influent pH and hydraulic retention time on NO₃^--N and TN removal and effluent NO₂^--N accumulation of BER were investigated.The results showed that,a positive linear correlation was found between the current intensity and NO₃^--N removal efficiency, while the current intensity ranged from 0 mA to 110mA NO₃^--N removal rates declined,when current intensity was more than 110mA.TN removal efficiency increased with increasing current,until the current reach to 145mA.But TN removal efficiency decreased when current excess 145mA.The higher the temperature of the reactor was,the better the efficiency of the denitrification.For example,the efficiency at 31℃was twice more than that at 15℃.According to the dentrification efficiency effected by influent NO₃^--N concentration,we can saw that the limitation concentration removed by BER was 42.18 mg/L.NO₃^--N removal rate was shown negative linear correlated with the the influent NO₃^--N concentration.The best range of influent pH in the reactor was between 7.04 and 7.50,but generally,changes of influent pH did not have many infections on the dentrification efficiency of BER.The better dentrification efficiency contributed to the longer HRT and the HRT should be longer than 11.2h in order to achieve completely denitrification.In the experiment,the effluent NO₂^--N accumulation concentration was up to 12 mg/L,when the current,influent pH,HRT,temperature and influent NO₃^--N concentration were 100 mA,7.5,10 h,31℃and 100 mg/L respectively.2.A novel approach,combining solid-phase denitrification and electrochemical hydrogen autotrophic denitrification(SHD-EHD),for nitrate removal from groundwater was investigated.The results showed that,compared with BER, SHD-EHD showed the better denitrification efficiency,shorter HRT,and smaller current.When the current was 40mA and the HRT was 3.5h,the NO₃^--N concentration in the effluent decreased from 70mg/L to 10mg/L.No accumulation of NO₂^--N in the reactor was found,and the pH of the effluent was stable between 7.0 and 8.1.