| Emissions of nitrogen compounds have increased dramatically in recent years, with the development of industry and agriculture as well as the population growth. This fact leads to the increasing concentration of nitrate in the groundwater, which has caused continuous deterioration of the water quality. The contamination of nitrate in groundwater has become an ever-increasing and worldwide environmental problem.The bio-electrochemical denitrifying technology combines electrochemical process and autotrophic biological denitrification. Autotrophic denitrification reactions occur in the biofilms attaching on the cathode by using hydrogen as electron donors and nitrate as electron acceptors. It is a new technique which makes good use of the redox potential of the electricity and the high efficiency of mass transfer between electrodes and the autotrophic denitrifying biofilms, and it needs no addition of organic carbon source. It can remove nitrate from the water completely without any by-products that affect the water quality, so it is a cleaner way for the nitrate removal of drinking water.However, electric fields generated by electric currents inhibit the diffusion of the NO3- towards the cathode, and the repulsion increased with the raise of current intensity, thus reducing the mass transfer efficiency of the reactor. In addition, the denitrifying bacteria in the reactor are mainly autotrophic, and the microbial biomass is rather low, thus the disposal ability of the reactor is limited.In order to develop a bio-electrochemical reactor which is more powerful for nitrate removal, reinforcements of magnetic fields and sustained-release organic carbon source on the bio-electrochemical denitrification were studied in this dissertation, and main results were as follows:(1) Nitrate pollution of groundwater in Hangzhou was investigated. The results showed that, groundwater in vast areas of Hangzhou was polluted by nitrate, and it was particularly bad in some areas.(2) A biofilm-electrode reactor (BER) was developed, and the influencing factors on the nitrate removal of the BER were investigated. Optimal operating parameters were found as follows:optimum current applied from 80 mA to 102 mA, optimum pH between 6.5 and 8.5, optimum HRT of 9 h, optimum temperature of above 25℃Nitrate removal efficiency reached more than 85% when the reactor was operated in these proposed cases.(3) Experiment results of BER coupled with magnetic field (MBER) showed that the coupling improved the TN removal efficiency by 13 percent to 35 percent. Existence of the magnetic fields improved the mass transfer efficiency as well as the current efficiency, thus promoting the denitrification performance of the reactor. The MBER achieved better performance with lower current intensity compared with the BER.(4) The novel SHD-EHD reactor attained high nitrate removal efficiency. It combined electrochemical hydrogen autotrophic denitrification and solid-phase heterotrophic denitrification in a single reactor. The application of the sustained-release organic carbon source starch-based PLA cleared up problems such as the low processing capacity of autotrophic denitrification and out of control of the addition of organic carbon source. Starch-based PLA acted as the electron donors for denitrification, and provided carrier for microorganism. The treatment capacity of the SHD-EHD reactor could be operated ideally at the operation parameters:I=40mA;T=30℃0;HRT=3.5h;C(NO3--N)= 70 mg/L.The effluent of SHD-EHD was between 7.0-8.1, the concentration of effluent was below 10 mg/L,and no nitrite accumulation.
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