Fundamental Research On Ion Exchange Membrane Processes For Typical Industrial Wastewater Recycling

With the rapid development of chinese economy and the accelerating of industrialization,the pollution of industrial wastewater to the water environment is becoming more serious,which is endangering the homes on which people depend for survival.Therefore,it is urgent to treat the industrial wastewater and to recycle the wastewater.Membrane separation technology is a new chemical separation technology.Different particle size,different molecular weight and different ions can be separated or concentrated by the membrane separation technology under a driving force of pressure difference,electric potential difference or concentration difference.Also,the insoluble and soluble substances in feed can be separated or concentrated.Besides,molecules and ions in solution can be separated selectively by the membrane separation technology.Ion exchange membrane process can realize various ions separation.According to different driving force,it can be divided into diffusion dialysis(DD)process driven by concentration difference and membrane electrolysis(ME),electrodialysis(ED)and bipolar membrane electrodialysis(BMED)driven by potential difference.In this paper,the ion exchange membrane process was proposed to recycle ammonia-nitrogen wastewater,to achieve the "zero discharge" of high-salinity wastewater and recycle the alkaline wastewater,.Firstly,the ammona capture was carried out from the ammonia nitrogen wastewater by the integration or coupling of BMED and hollow fiber membrane contactor(HFMC).Secondly,the multistage ED was proposed to concentrate the high-salinity solution,and the theoretical analysis of the multistage ED was given.Lastly,the intergration of DD with ME was proposed to recover alkali from the alkaline wastewater.This dissertation comprises six chapters,and the contents are detailed.In chapter one,the harm of industrial wastewater to the environment was briefly introduced,then ion exchange membrane technology was introduced,and the ion exchange membrane and its related application process were discribed.Subsequently,The problems of wastewater in industrial production are introduced,including recycling the high-salinity wastewater with ammonia nitrogen and the alkaline wastewater.Finally,the research ideas and contents of this paper are put forward.In chapter two,a novel hybrid system of BMED and HFMCs for in-situ ammonia capture without the consumption of acid and base was proposed.In this system,the wastewater can be basified in-situ in BMED process;and acid solution,as stripping solution for ammonia capture by HMFCs,can be produced continuously in BMED process.Only one kind of cheap chemical(Na2SO4)should be applied in BMED process rather than the consumption of expensive chemicals of base in traditional single HFMC ammonia capture process.In BMED process,effects of ammonia nitrogen concentration,feed flow rate and current density on the pH of the basified wastewater.Results indicate that the normalized current density should be applied at~0.29 mA cm-2(mg/min)-1 to basify wastewater to a pH of~11.0.With an increase in C0 and Q,the applied current density should be increased and thus energy consumption increases accordingly.The minimum energy consumption is only 63.59 kJ/(mol NH4+-N)for a typical test(CO of 200 mg/L and Q of 0.034 L/min).The ammonia capture ratio can be achieved as high as 65.2%if four stages HFMCs were combined with BMED.In the practical application,the ammonia capture ratio can be increased to>98%by increasing the stages of HFMC modules.In chapter three,a coupling process of BMED and HFMCs was proposed,in continuous batch mode,for high-efficient ammonia capturefrom the wastewater with high ammonia nitrogen concentration.In BMED process,due to the co-ion transport and concentration diffusion,the acid leakage from the acid compartment to the salt compartment was investigated in various current densities and initial acid concentration.Results indicate that the current density and initial acid were optimised as 20 mA/cm2 and 0.01-0.05 mol/L H2SO4 respectively in consideration of low energy consumption(1.08-1.09 kWh/kg H2SO4)and high current efficiency(80.0%-82.3%).Then,coupling of BMED and HFMC was carried out for continuous batch ammonia capture.Results indicate that during the ten batches operation,the ammonia capture ratios all can reach to>99%,the CNH4+-N in the wastewater can be decreased to as low as<10 mg/L,and the concentration of by-product(NH4)2SO4 can reach to as high as 139.07g/L.In chapter four,high-salinity solution was concentrated by one-,two-,and three-stage-batch ED,in which the operating parameters were optimized,the phenomenon of water transport in ED process was investigated,and the total energy consumption of multistage ED was calculated.First,in the one-stage ED,the operating voltage across the membrane stack and the volume ratio of the concentrate to dilute((Vc)in:(Vd)in)wer optimised to 6 V and 1:10 respectively to achieve a relatively low water transport(18.5%),high current efficiency(83.7%),low energy consumption(0.18 kWh/kg NaCl),and relatively high salt content(11.4%).Next,to achieve a high-salt-content concentrate,a two-stage ED,with a(Vc)in:(Vd)in of 1:10 in both stage-batches,was proposed.The salt content was increased from 3.5%to 17.9%.In addition,a three-stage ED with a(Vc)in:(Vd)in of 1:5 in each stage was developed to further increase the salt content.The results indicated that the salt content could be increased from 3.5%to 20.6%.The water transport in multistage ED was then investigated.In two-stage ED,the flux ratio of water to salt(?)decreases from 14.1-19.0 to 12.4-15.0 mol H2O/mol NaCl,as the stage advances.In three-stage ED,? decreases from 14.4-18.3 to 11.5-12.1 mol H2O/mol NaCl,as the stage advances.These results indicate that fewer water molecules,with the same amount of salt transport,were transported as the stage-batch number advanced,as well as the salt concentration increased.In view of the volume change,the water transport increased from 18.5%to 50%in two-stage-batch ED and from 17.8%to 42.5%in three-stage ED,as the stage-batch advanced.Finally,the material balance and total energy consumption were calculated in multistage ED.In two-stage ED,the total volumes of the dilute(Vd,total)and concentrated solutions(Vc.totai)were calculated as 0.84 and 0.16 m3,respectively,when treating 1 m3 of 3.5%NaCl solution.The total energy consumption was 0.3 1 kWh/kg.In three-stage ED,Vd,total and Vc,total were calculated as 0.86 and 0,14 m3,respectively.The total energy consumption was relatively high(0.45 kWh/kg),1.4 times that of the two-stage ED.Hence,high-salinity solutions can be concentrated by multistage-batch ED to a higher salt content,but consume more energy.In chapter five,alkaline sodium metavanadate solution containing NaOH and NaVO3,which is simulated from the production of vanadium pentoxide has been separated efficiently by integrating dynamic DD with ME process.Firsty,the membrane performance of PVA-I and PVA-II was evaluated.Results indicate that the PVA-II membrane is the optimal membrane due to the reason that this membrane has high selectivity(68.8)and high rejection ratio of vanadium(>91.48%).Meanwhile,the PVA-II membrane has high alkali-resistance(mass loss ratio of only 2-6%).Then,the effect of feed flow rate,water flow rate on DD performance were investigated.Results indicate that when Qfeed and Qwater are 0.75 mL/min and 1.5 mL/min respectively,the VO3-rejection ratio appeared as high as-92.56%with only 0.0102 mol/L residue in diffusate,the NaOH recovery ratio can stretch up to-66.59%with the concentration of~0.933 mol/L,and he residual concentration of NaOH in dialysate was 0.676 mol/L,which will be further treated by the membrane electrolysis process.The membrane electrolysis process reduced the pH of the dialysate side to-6,and enhanced the concentration of NaOH in diffusate side from~0.933 to~1.455 mol/L correspondingly.The leakage ratio of VO3~from the dialysate to the diffusate almost reached zero.The energy consumption is as low as 293.4 MJ/(m3 feed)under the optimized current density of 30 mA/cm2.The dialysate after the treatment of membrane electrolysis can be directly introduced to vanadium precipitation process rather than neutralizing with acid;the recovered alkali(diffusate)can be directly reused and recycled in the circuit of vanadium pentoxide production.Besides,H2 and O2 produced in ME process can be recycled as clean energy in the subsequent calcination process to save the production cost.Preliminary economic evaluation indicated that the running cost of the proposed method(integration of DD with ME,-24.18$/(m3 feed))is much lower than that of the traditional method(without membrane process,24.52$/(m3 feed)).Hence,integration of DD accompanied with ME process is a clean,energy-saving,efficient and sustainable method to separate and recovery of NaOH in the production of vanadium pentoxide.The chapter six is a summary of the full text of this dissertation,and the prospect of ion exchange membrane process in industrial wastewater recycling.