Study On Treating Nitrogen Contained High Salinity Wastewater By Using Microbial Fuel Cells (MFCs)

Nitrogen contained high salinity wastewater contains a large amount of inorganic ions,organic matter and nitrogen contained compounds.It is differcult to treat with a wide range of sources,complex composition and great harm.The present treatment methods have problems such as high energy consumption,poor system stability,existing secondary pollution and disable recycle energy contained in wastewater.Based on this,microbial fuel cell?MFC?technology was introduced to realize high-efficiency,low-cost and harmless treatment of nitrogen contained high salinity wastewater.The effects of non-buffer solution and PBS buffer,three anodes and three cathodes,salinity?NaCl concentration?and salinity shock,pollutants concentrations on MFC electricity generation and removal of nitrogen-contained pollutants were investigated in this study.And nitrogen contained high salinity raw wastewater was successfully treated by this MFC.The results of this study are as follows:The electrolyte solution had no significant effect on removal of nitrogen contained pollutants,but affected electricity production performance of MFC.When treating nitrate/nitrite nitrogen contained wastewater,the pH of non-buffer was increased due to denitrification in anode region.Thus,the maximum power production of MFC in non-buffer runs was higher than that in buffers.When treating ammonia contained wastewater,the pH of non-buffer was lowered due to nitrification of ammonia nitrogen in anode region,resulting in a decrease in power production of MFC.The three-dimensional carbon brush and graphite felt anode had higher electricity generation and pollutants removal performances than the planar carbon fiber cloth anode due to there higher specific surface area.Stainless steel cathode and graphite felt cathode had higher oxygen reduction rate,so their electricity generation performances were higher than those of nickel foam cathode.The denitrification performance of three cathode MFCs were similar,while MFC with graphite felt cathode had the best nitrification performance since its oxygen permeability was higher.Because of high salinity and pH change,carbon brush anode of stainless steel core,nickel foam cathode and stainless steel cathode corroded in varying degrees during long-term operation,which reduced stability of MFC.The results showed graphite felt was a more suitable electrode material for MFC treating nitrogen contained high salinity wastewater.MFC could operate steadily at NaCl concentration range from 0 to 70 g·L^-1.With salinity increase,output power,denitrification rate and COD removal efficiency of MFC increased first and then decreased,reaching the maximum at NaCl concentration of 20 g·L^-1.However,the removal efficiency of ammonia nitrogen decreased with increase of solution salinity.Salinity shocks reduced electricity generation and pollutants removal performances of MFC.However,when initial NaCl concentration was 20 g·L^-1,the effect of low salinity impact(<10 g·L^-1)on MFC performances of electricity generation and pollutants removal were small and could recover after the impact was removed,while the effect of high salinity shock(>20 g·L^-1)on performance couldn't be restored.Therefore,MFC was suitable for treating nitrogen contained wastewater with NaCl concentration range from 0 to 30 g·L^-1.When denitrifying,denitrification rate of MFC increased with increase of nitrogen concentration and COD concentration,but output power increasesd first and then maintained.When nitrifying,ammonia nitrogen removal efficiency of MFC decreased as ammonia nitrogen concentration and COD concentration increase.The MFC output power first increasesd and then remained unchanged with increase of COD concentration,but decreased with increase of ammonia nitrogen concentration.MFC could efficiently and stably treat high sanility raw wastewater with nitrate nitrogen concentration of 1510 mg·L^-1.Its nitrogen removal efficiency was higher than99.5%,average nitrogen removal rate was up to 137.3 mg·?L·h?^-1,and maximum output power density was 231.2 mW·m^-2.Also,average COD consumption of MFC for denitrifying was 3.72 g COD·?g NO₃-N?^-1 which was 25%lower than conventional biological methods.