Study On The Effectiveness And Mechanism Of Nitrate Removal From Groundwater By Biochar Electrodes

In recent years,nitrate pollution of groundwater resources has become increasingly serious.Long-term consumption of nitrate-polluted groundwater can cause a series of diseases,such as methemoglobinemia.Therefore,it is crucial to develop effective remediation techniques for nitrate pollution in groundwater.In this study,biochar was prepared from disposable bamboo chopsticks.Through characterization and adsorption kinetics analysis,the electrode material of biochar with the best nitrate removal performance was screened out,and the removal effect of biochar cathode driven by electric field was investigated.In the electrode biofilm reactor,the competition and synergy mechanism of electron donors in the reduction process of nitrate were studied,and the electrochemical reduction mechanism of nitrate was explored.The surface structure of the biofilm attached to the biochar particles and the microbial community structure were analyzed to elucidate the enhancement and regulation mechanisms of the bioelectrochemical process.The main conclusions of this dissertation are as following.（1）Bamboo chopstick biochar bio char was prepared at different pyrolysis temperatures and carbonization time.By means of elemental analysis,scanning electron microscope,specific surface area,resistivity and Raman spectrum,it was found that biochar prepared from disposable bamboo chopsticks pyrolyzed at 600℃for 2h（A-600-2）had the best comprehensive properties and was an ideal biochar electrode material.The carbonization time had little effect on the overall performance of biochar,but temperature has a significant effect,especially when the pyrolysis temperature rises from 500℃to 600°C,the specific surface area of the biochar increased from 2.18 m²·g^-1 to 179.21 m²·g^-1,and the resistivity decreased from 39900Ω·cm^-1 to 112.75Ω·cm^-1.（2）The adsorption kinetics experiment further confirmed the excellent adsorption performance of A-600-2,with a maximum adsorption capacity of 16.39 mg/g for nitrate.Under electric field driving（voltage of 4V,hydraulic retention time of 4h）,the removal rate of nitrate reached 76%when biochar was used as the cathode,while the removal rate of nitrate without voltage was only 32.7%,which indicated that biochar electrodes can fully utilize the coupling effect of adsorption and electrochemical reduction processes to achieve a stronger ability to remove nitrate.In addition,biochar electrodes can inhibit the accumulation of nitrite and improve the selectivity of electrochemical reduction.（3）In the electrode biofilm reactor,it is found that cathode electrons are the dominant electron donor for reduction of nitrate according to the comparison of reduction rates with glucose and cathode electron as sole electron donor.The addition of an appropriate amount of glucose can inhibit hydrogen autotrophic behavior,thus releasing the reduction potential of the cathode electrons.When the concentration of glucose is 1000 mg/L and applied current is 0.04 A,nitrate can be completely removed within 3 hours.At the same time,hydrogen autotrophic bacteria and bacteria with electrochemical activity exist in the electrode biofilm reactor,which can promote hydrogen autotrophy and microbial synergistic denitrification.Through extracellular electron transfer,the reactor can promote nitrate reduction,thereby improving the processing efficiency and electron utilization of the reactor.