Study On Simultaneous Nitrogen And Carbon Removal From Municipal Wastewater With Low C/N Ratio By Membrane Aerated Biofilm Reactor

Membrane aeration biological membrane reactor（MABR）technology has no bubble aeration high oxygen-transfer efficiency and low energy consumption of aeration,pollutants and dissolved oxygen reverse diffusion driven biofilm stratification,in turn,can be synchronized nitrogen in addition to carbon,oxygen,the advantages of easy to control,in turn,can adapt to the water load changes,the low carbon and nitrogen ratio has good potential applications in municipal wastewater treatment.In this study,the typical municipal wastewater with low concentration and low C/N ratio in South China was taken as the treatment target,and the hydraulic retention time（HRT）and aeration pressure of MABR process were optimized and regulated to achieve the best synchronous nitrogen and carbon removal efficiency.In addition,synchronous chemical phosphorus removal was used to meet the discharge standard of Grade A of urban sewage treatment plant（GB 18918-2002）.The main research results are as follows:A two-step biofilm enrichment strategy of nitrification and denitrification was adopted to realize rapid acclimation of MABR pilot plant,and the removal loads of COD and total inorganic nitrogen（TIN）reached 10.5 and 2.3 g/m²/d,respectively,in the treatment of simulated medium-concentration wastewater with low C/N ratio（COD and ammonia nitrogen were 495 and 103 mg/L,respectively）.By simulating municipal wastewater with low concentration and low C/N ratio（COD and ammonia nitrogen are 270 mg/L and 27.5 mg/L,respectively）in South China,and gradually reducing HRT and increasing aeration pressure,it is proved that when the aeration pressure is 10 k Pa and HRT is shortened from 24 h to 4 h,both COD and ammonia nitrogen of MABR effluent meet the discharge standard of Grade A.MABR can also achieve the same effect when HRT is shortened to 3 h and aeration pressure is increased to 14 k Pa.The sustainable HRT and influent load of MABR are 3-4 h,19.4-25.9 g COD/m²/d and 2.0-2.6 g N/m²/d,respectively.The COD and TIN removal loads are 22.8 and 2.2 g/m²/d,respectively.The removal processes of COD and ammonia nitrogen follow the quasi-first-order and zero-order kinetics respectively.Due to the rapid proliferation of heterotrophic biofilms,the COD removal rate constant increased from 0.226 h^-1 at startup to 0.511h^-1 at 3 h HRT.As the excessive growth of the outer heterotrophic biofilm increased the mass transfer resistance of ammonia nitrogen diffusing from the mainstream to the inner nitrifying biofilm,the removal rate constant of ammonia nitrogen decreased slightly from 8.01 mg/L/h at startup to 6.68mg/L/h at 3h HRT.In summary,MABR showed good simultaneous nitrogen and carbon removal efficiency in simulating municipal wastewater treatment with low concentration and low C/N ratio.The actual municipal sewage with low concentration and low C/N ratio（COD,ammonia nitrogen,total nitrogen and total phosphorus are 258.1 mg/L,30.5 mg/L,36.8 mg/L and5.35mg/L,respectively）,by shortening HRT simultaneously and increasing aeration pressure,It was proved that MABR under HRT 24 h and 4k Pa aeration pressure,HRT 12 h and 7k Pa aeration pressure,HRT 8 h and 8k Pa aeration pressure,HRT 6 h and 10 k Pa aeration pressure conditions,the effluent ammonia nitrogen and total nitrogen all meet the first-class A discharge standard,and the effluent COD is slightly higher than 50 mg/L.By further synchronous coagulation（polyaluminum chloride,Al:P mole ratio 2.27,concentration 48.19 mg/L）,the total phosphorus and COD of MABR effluent meet the discharge standard of Grade A.Experiments on oxygen mass transfer characteristics show that The oxygen flux,oxygen transport efficiency and aeration efficiency of clean and hollow fiber membrane with biofilm were 12.21-21.11 and19.60-40.49 g O₂/d/m²,11.00-17.09%and 20.74-31.87%,5.89-7.42 and 11.87-14.24 kg O₂/k Wh,the metabolic activity of the biofilm affected by ammonia nitrogen and organic matter load significantly improves the oxygen mass transfer efficiency of hollow fiber membrane,reflecting the adaptability of the biofilm.（According to the intake of organic matter and ammonia nitrogen oxygen consumption load automatically through the aeration film extraction required oxygen）.