Treatment Of High Concentrated Ammonia-nitrogen Wastewater By Membrane Absorption Process

At present physical and chemical methods are the commonly used methods to treat the high concentrated ammonia nitrogen wastewater characterized with strong biological toxicity.Currently,chemical precipitation method and catalytic oxidation method are relatively costly and not suitable for the large-scale industrial application.Stripping method is the most mature and widely used process in industrial for the treatment of high concentrated ammonia nitrogen wastewater.However it has the disadvantages of easy scaling,large area occupation,high temperature and gas-liquid ratio requirement.Membrane absorption method with broad application prospects overcomes the shortages of stripping method and is easy to enlarge.However,the current research on the treatment of high concentrated ammonia nitrogen wastewater by membrane absorption process is mainly focused on the study of simulated wastewater.The treatment of actual wastewater remains poorly understood,especially for the pretreatment method selection before the membrane absorption process.In present study,based on the results from the simulated wastewater treatment,the author studied the treatment of the two typical highly concentrated ammonia nitrogen wastewaters?etching solution and landfill leachate as examples?by the membrane absorption process.The pretreatment method and the key parameters of membrane absorption process were inveatigated in detail,and the corresponding integrated processes for the treatment of actual etching solution and landfill leachate were also proposed.For the simulated high concentrated ammonia nitrogen wastewater,the effects of processing mode,operating conditions,temperature and coexisting ions on the removal of ammonia nitrogen by membrane absorption process were studied.The results show that under the conditions of pH 11.0,feed liquid flow rate 3.6 cm/s,absorption liquid flow rate 1.1 cm/s,2 mol/L sulfuric acid solution as absorption liquid with the processing mode of continuous operation,preferable effect for the treatment of the high concentrated ammonia nitrogen wastewater?2 000 mg/L?was observed.At these conditions,removal rate of ammonia nitrogen,the mass transfer coefficient,and the transmembrane flux of the signle membrane component reached 70.0%,1.5×10^-5 m/s,and 17.9 mg/?m²·s?respectively.Meanwhile it was found that heating was beneficial to the removal of ammonia nitrogen and the effect of coexisting ions was mainly reflected in the salt effect.The efficiency of membrane absorption in treating etching solution was investigated by a small scale experiment.The integrated processes for the etching solution treatment was provided as pH adjustment with NaOH first,then ammonia removal by membrane absorption process,and decomplexation-percipitation for ammonia release followed by biochemical treatment with some other wastewaters.Based on the study of the optimal operation parameters for simulation wastewater treatment,the effect of key parameters of feed liquid si de and absorption liquid side on ammonia nitrogen removal in etching solution was studied.For the actual etching solution with an initial ammonia nitrogen concentration of 82 000 mg/L,when the pH value was 10.5,other parameters are the same as the simulated wastewater,the ammonia nitrogen content of the effluent reached about 100 mg/L.The mass transfer coefficient,and the overfilm flux reached 3.2?3.4×10^-6 m/s and 40?43 mg/?m²·s?,respectively.For the treatment of landfill leachate,the integrated process for the landfill leachate treatment was proposed as follows:foam separation,coagulation and precipitation,calcium removal,microfiltration and ultrafiltration,ammonia removal by membrane absorption process and final biochemical treatment.Also,the effect of key parameters of feed liquid side and absorption liquid side on ammonia nitrogen removal in landfill leachate was studied on the basis of the optimal operation parameters for simulation wastewater treatment.When the landfill leachate pH value was 11.5,other parameters are the same as the simulated wastewater,the ammonia nitrogen content of the effluent was stabilized at below 50 mg/L and the overfilm flux reached 3.0?3.2 mg/?m²·s?.