Mechanism And Technology Study On The Advanced Nitrogen Removal Of Tail Water From WWTP By The Coupling Process Between Catalyzed Fe-C Micro-electrolysis And Biological Processes

Advanced nitrogen removal for tail water from WWTP is a major task for cutting TN emission and achieving the TN emission control objective in the 13th Five-Years Plan of China.Advanced nitrogen removal of tail water remains among the hotspots and difficulties in wastewater treatment.Hence,it is of great significance to develop novel technologies and theories for advanced nitrogen removal from the tail water.In this thesis,an iron based material—catalyzed iron and activated carbon micro-electrolysis based carrier(CIA-MEC)was used as bio-carrier.Coupling process between catalyzed Fe-C micro-electrolysis and biological denitrification was developed to achieve simultaneous nitrification and autotrophic denitrification(SNAD)under microaeration(DO=0.46?1.69 mg/L).Firstly,the applicability of CIA-MEC as a bio-carrier in water treatment was evaluated.Then,nitrogen removal system was started utilizing CIA-MEC as bio-carrier and the optimization of process parameters was processed.Coupling mechanism was studied through jar tests,microbiological community analysis,iron compounds analysis and gaseous products analysis.Based on the mechanism,the migrations and transformations of nitrogen,carbon source,Fe and electrons were analyzed and quantified.The results showed that:(1)CIA-MEC possessed proper physicochemical properties as a bio-carrier,as well as reaction activity.The NO3--N reduction rate at pH of 3,7 and 9 were 104,105 and 106 times higher than that of Fe0,respectively.(2)Start-up of the nitrogen removal system took 26 days when influent NH4+-N,NO3--N,TP and C/N ratio were 10.0 ± 2.0 mg/L,15.0 ± 3.0 mg/L,1,0±0.1 mg/L and 0.6±0.2,respectively.The optimal HRT of 3.0 h,air to water ratio of 1.5,influent pH of 7.2±0.2 were obtained with NH4+-N,NO3--N,TN and TP removal efficiencies of 91.1%,94.3%and 92.6%,respectively.TN removal load of 0.255 kg N/m3 d for tail water and maximum TN removal load of 0.373 kg N/m3·d were obtained.This system achieved simultaneous NH4+-N,NO3--N and TP removal.The effluent quality was satisfactory with the A standard of DB 11/307-2013 for Beijing,and the effluent NH4+-N,TP and BOD was satisfactory with the ? standard of GB 3838-2002 of China.(3)Coupling mechanism was established(Figure 4.13),indicating that autotrophic denitrification was efficient processed using[H]/H2 and Fe2+ as electron donor with electron supplication rate of 1.07×102 mol e/m3·d.The denitrification load was 104 times higher than that of Fe0 corrosion based autotrophic denitrifUcation and higher than that of H2,S and biofilm electrode surported autotrophic denitrification.Additionally,the in situ production of[H]/H2 by CIA-MEC avoided the low utilization rate of H2 when immediately feeding H2 as electron donor.(4)Autotrophic denitrificans Hydrogenopha(13.1%),Denitratisoma(2.1%),Thermomonas(2.5%)and Pseudomonas(1.8%)utilizing[H]/H2 as electron donor and autotrophic denitrificans Sphaerotilus(9.7%),Thermomonas and Pseudomonas utilizing Fe2+ as electron donor were found dominant in this system.The aerobic and facultative anaerobic bacteria covered 24.6%OUTs of the system,indicating that an aerobic autotrophic denitrification system was obtained.(5)The main iron compounds produced in the system were FeOOH and Fe(OH)3,which were stored in the biofilms and suspended sludge.The results showed that immigration,transformation and storage of iron oxides were efficiently processed by Sphaerotilus and other genera in the system,which were essential for maintaining the electron donor supplication rate in the long term operation.(6)TN degradation model based on the Eckenfelder kinetics and SND model based on the Monod kinetics were established and calculated as respectively.The models consistently verified that biological denitrification proceeded effectively in this system under low C/N ratio and microaeration.(7)In this system,99.7%of COD removal was attributed to the assimilation of microorganisms.CIA-MEC was the main electron donor supplier.The mass balance equation for nitrogen,carbon source,Fe and electron was calculated as:37.02 Fe + 0.85 C6H12O6 + 6.27 NH4+ + 15.77 NO3-+ 11.93 O2?C5H7O2N1.1+0.14 Fe2++36.88 Fe3+ + 10.47 N2?+0.093 CH4?+0.016 C02?.This thesis pioneered the coupling between chemical reaction and microbial processes,providing a new idea for biological nitrogen removal.The research in this thesis supplied theoretic reference and tech support for cutting TN emission,as well as solving the problem of water shortage in China.