Simultaneous Di-oxygenation And Denitrification In An Internal Circulation Baffled Bioreactor

Phthalic acid(PA),an important organic industrial raw material,is widely used for production of phthalic aid esters(PAEs)that is presoma to produce dyes,polyester resins,polyester,drugs and plasticizer,etc.Because of the hugely produced and widely used in people's society,PAEs has been one of the environmental pollutant in our life.PAEs can not only have mutagenic and carcinogenic effects on human beings,the main impacts of PA and PAEs are as endocrine disrupters.The PAEs are readily bio-transferred into PA,since PA is the main intermediate product of PAEs,degradation of PA from water has became more important.Recently,the pollution of nitrate and nitrite has became more serious due to the abuse of nitrogenous fertilizer in agriculture and the emission from industry.Currently,the main degradation of PA we use commonly is aerobic biological treatment,and for the sewage which contains nitrate and nitrite,we use the method of denitrification reaction in anoxic environment.In this work,we employed a modified version of the internal circulation baffled bioreactor(ICBBR)in order to realize simultaneous di-oxygenation and denitrification in one unit.The ICBBR had co-existing aerobic and anoxic zones that allowed di-oxygenation and denitrification to occur simultaneously.In this study,we supplemented a modest concentration of succinate,a readily oxidized product of PA biotransformation,to test the hypothesis that adding an exogenous electron donor will accelerate di-oxygenation and denitrification.We also tested whether or not electron donors generated from UV/H2O2 advanced oxidation of PA had the same impact on accelerating di-oxygenation and denitrification.We also found that the nitrite was more easily to be removed than the nitrate in the reaction of denitrification.Here are the main results from our study:(1)A modified version of the internal circulation baffled bioreactor(ICBBR)in order to realize simultaneous di-oxygenation and denitrification in one unit.We control the range of dissolved oxygen is about 2mg/L.The ICBBR had co-existingaerobic and anoxic zones that allowed di-oxygenation and denitrification to occur simultaneously.(2)Adding an exogenous electron donor will firstly accelerate di-oxygenation,the downstream products which come from the di-oxygenation of PA are more easily used for denitrification.(3)Succinate was added at different initial concentrations to evaluate its kinetics for stimulating denitrification.Adding a little of succinate into the reactor supported a slow rate of denitrification.When the amount of the succinate reached 1.27mM/L,the rate of the denitrification grew rapidly.Comparing with the PA+succinate,their rates were almost the same.With the electron-equivalent balance,we are more sure that a little of exogenous electron donor will firstly accelerate di-oxygenation,then product more intracellular electron donor for the denitrification.(4)PA di-oxygenation and denitrification were accelerated by generation of electron donors generated by UV/H2O2 advanced oxidation of PA.The acceleration effect from UV/H2O2 advanced oxidation of PA was approximately the same as the effect of the exogenous electron donors.(5)As the nitrate need more electron donors than the nitrite in the denitrification reaction,we found that the nitrite was more easily to be removed,with the denitrification rate with nitrite being 3-fold greater than with nitrate.At the same time,the removal rate of the PA with nitrite being 2~3-fold greater than with nitrate.Therefore,the results of the study provides more evidence for shortcut nitrification and denitrification,as we can control the ammonia that in the nitratlon reaction transfer into nitrite directly to accelerate the rate of the denitrification.