Study And Project Application On Simultaneous Nitrification And Denitrification In Medicine Chemical Industry Wastewater

In this work,the carbon and nitrogen removal efficiency of simultaneous nitrification and denitrification(SND) process in medicine chemical industry waste water was investigated.Sequencing batch reactor(SBR) was used for lab experiment and project application experiment respectively.The influences of dissolved oxygen(DO) and pH to carbon and nitrogen remove in SND process were researched,and the effects of COD,NH₄⁺-N,TN removal rate in project application were studied as well.Meanwhile,the changs of indexes of sludge were tested.This work provides data reference and developing direcation of SND project application,and proposes the direcations and emphasis of SND research in the future,such as the reaction mechanism and dynamics model of SND, screening and traning of aerobic denitrifiers,combination of simultaneous nitrification-denitrification,shortcut nitrification-denitrification and denitrifying dephosphorization.The major results are summarized as follows:(1) The sequencing batch reactor was used in lab experiment and the best condition of carbon and nitrogen removal efficiency of SND was DO:1～2 mg/L and 8h aeration time. In this condition,COD removal rate was 76%～78%;NH₄⁺-N removal rate was 78%;TN removal rate was 74%～77%.Ammonia-oxidizing bacteria(AOB) abundances of sludge in various DO conditions were different.AOB abundance of sludge was only 9.533×10² in DO:0.5 mg/L,but 10⁴ in DO:1,2,4 mg/L conditions.This was consistent with NH₄⁺-N removal rate.(2) Under the condition of DO:1 mg/L,the best influent water pH of SND should be controlled between 7 and 7.5.In this condition,COD removal rate was above 80%, NH₄⁺-N removal rate was 80%～82%and TN removal rate was 74%～78%.Excessive high or low pH would influence carbon and nitrogen removal efficiency.In single reaction cycle, pH fluctuated just between 7.49 and 7.15,and didn't show partition-change phenomenon; the concentrations of NO₂^--N and NO₃^--N didn't accumulatie massively,only 2.87 mg/L and 1.21 mg/L in effluent water.Denaturing gradient gel electrophoresis(DGGE) profile showed that influence of pH on sludge AOB microbial community structure and richness index was obvious.Microbial diversity of AOB was the highest under pH 7.5 and the lowest under pH 6.5.The reason of high NH₄⁺-N removal rate in high pH condition was various of AOB population,but not ammonia-nitrogen desorption.The influence of pH on denitrifying bacteria in SND process is a valuable research direction in the future.(3) The carbon and nitrogen removal efficiency of SND in project application was excellent.Under condition of DO:1～2 mg/L,influent water pH:7～7.5 and water temperature:28～32℃,the average COD,NH₄⁺-N and TN removal rate was 78.8%,78.4% and 74.5%respectively.Meanwhile,the aeration intensity,acid-base dosing quantity and treatment cost of SND process was much less than that in traditional biological nitrogen removal technology.SND denitrification technology has bright future in project application.(4) Excessive high water temperature and salt ion concentration could decrease COD, NH₄⁺-N and TN removal rate in simultaneous nitrification and denitrification process.In the late experiment period,water temperature rose up to 40～42℃,the concentrations of SO₄^2- and Cl^- reached 8512 mg/L and 8031 mg/L respectively,and the average COD,NH₄⁺-N and TN removal rate was just 66.9%,56.8%and 44.9%respectively.DGGE profile showed that,although new AOB strain appeared in different environment conditions, species and abundance of sludge ammonia-oxidizing bacteria decreased under the effect of influence factors.The decrese of AOB microbial diversity caused NH₄⁺-N,TN removal rate of SND process fall down.