| In recent years,more and more organic-laden saline wastewaters especially phenol-laden saline wastewaters were discharged.Phenol is an important industrial raw material,and it is a cancerogen?level 3?recognized by WHO,which is hazardous to flora,fauna and human being.The common phenol treatment methods?physical-chemical process,membrane process,biodegradation process?suffer low separation accuracy,low degradation efficiency and secondary pollution under saline condition.To address these issues,extractive membrane bioreactor?EMBR?is developed for the phenol-laden saline wastewater treatment.A selectively permeable membrane divides EMBR into wastewater and microorganisms,phenol could permeate the membrane via solution-diffusion for biodegradation,while salt ions are rejected.In this way,the separation,recovery and degradation of phenol from saline wastewater are achieved.However,the common used silicone rubber tube in internal EMBR exhibited high mass transfer resistance,low mass transfer coeffieient,excessive biofilm formation,which inhibited the research,application and popularization of EMBR.Therefore,novel selectively permeable membrane with high mass transfer coefficient is fabricated via electrospinning in this study.Novel external EMBR is set up to isolate the microorganisms from membrane.As a result,the biofouling is avoided.The main conclusions of this study are listed as follows:1)Internal EMBR with silicone rubber tube was set up for phenol-laden saline wastewater.This study investigated the effect of wastewater circulation rate on phenol permeation and salt rejection.Results showed that the circulation rate of 1.8 L h-1 for wastewater and the HRT of 24 h for microorganism nutrient were the best candidates for EMBR operation.With the increase of phenol concentration(from 1.0 to 5.0 g L-1)in saline wastewater(35.0 g L-1NaCl),the permeated phenol increased from 55.6 to 273.9 mg L-1,meanwhile,the salt rejection was above 99.97%.The optimized mean phenol mass transfer coefficient was1.29×10-7 m s-1,and maximal phenol removal capacity was 136.9 mg L-1 d-1.2)Electrospun permeable porous membrane was fabricated using polydimethylsiloxane?PDMS,function polymer?and polymethyl methacrylate?PMMA,carrier polymer?.This study investigated the effects of polymer,solution and process parameters on membrane properties.Results showed that the membrane surface roughness was positive correlated with surface hydrophobicity.The optimized condition for superhydrophobic and superorganophilic electrospun PDMS/PMMA membrane was 10/1/10/50/50 of PDMS/cross-linking agent/PMMA/THF/DMF,0.6 mm of needle inner diameter,10.5 kV of positive voltage,1.0 kV of negative voltage,16 cm between needle tip to collector,1.0mL h-1 of injection rate,500 min of electrospinning,25oC of temperature and 35%of humidity.The surface water,phenol contact angle,fiber diameter,pore size,thickness and surface roughness of membrane were 162.0o,0o,1.28?m,4.74?m,78.7?m and 5.8?m.3)Superhydrophobic and superorganophilic electrospun PDMS/PMMA permeable porous membrane was used to set up an external EMBR without microorganism?membrane aromatic recovery system,MARS?for in-situ phenol separation from saline wastewater.This study investigated the effects of hydraulic condition,temperature,pH on phenol permeation and salt rejection.Results showed that 0.90 L h-1 of wastewater,1.26 L h-1 of receiving solution,40oC of wastewater temperature and 2.5 of pH were the best candidates for phenol recovery.The phenol permeation gradually increased from 427.4 to 2386.4 mg L-1 with the increase of phenol concentration(from 2.0 to 10.0 g L-1)in wastewater.Resultant phenol recovery in 24 h was stable?21.2-23.9%?.Meanwhile,the salt rejection still was above 99.96%,even the NaCl concentration increased from 10.0 to 50.0 g L-1 in wastewater.The phenol mass transfer coefficient was 6.7×10-7 m s-1 without using NaOH or HCl.The membrane performance was stable during 3 cycle.Membrane pore blockage was avoided due to the membrane adsorption,diffusion and desorption mechanism.4)Electrospun PDMS/PMMA permeable porous membrane was used to set up an external EMBR with cultivated activated sludge for phenol separation and degradation from saline wastewater.Microorganisms were isolated from membrane to avoid biofouling.This study investigated the effect of hydraulic condition on phenol separation and degradation.Results showed that 0.188 L h-1 of flow rates for wastewater and nutrient were the best candidates for EMBR operation.Phenol permeation increased from 14.1 to 290.7 mg L-1and salt rejection was stable,when the phenol concentration in wastewater increased from2.5 to 20.0 g L-1.During 32 days,the phenol and ammonium removal efficiencies were99.2-100%and 30.4-83.6%,the maximal phenol removal capacity was 290.7 mg L-1 d-1.With the phenol concentration increase,protein content increased from 5.76 to 16.12 mg gSS-1 when polysaccharide content decreased from 18.22 to 4.19 mg gSS-1.Meanwhile,Proteobacteria and Saccharibacteria became the main phyla.Low phenol concentration promoted the proliferation of genes phe,amoA,narG,nirS,while high concentration inhibited.In conclusion,phenol was mainly biodegraded by denitrifiers and other carbon-consuming bacteria during nitrification-denitrification and other processes as carbon source.5)Part of PMMA was replaced by thermoplastic polyurethane?TPU?to fabricate electrospun TPU/PDMS/PMMA composite membrane?ETPPM?.This study investigated the effect of TPU on membrane properties.Results showed that the formations of hydrogen bond,self-bundled fiber yarns and point-bonded structure were promoted,which enhanced the membrane mechanical strength.Compared with the unmodified membrane,the pore size of ETPPM?3/4/1 of TPU/PDMS/PMMA weight ratio?reduced by 42.4%,thickness reduced by 68.0%,tensile strength increased by 637.5%,elongation at break increased by 89.9%.Meanwhile,the NaCl solution and phenol contact angle on ETPPM were 143.4o,0o,respectively.The hydrophobicity of ETPPM slightly decreased,but the phenol adhesion ability significantly increased.The corresponding phenol mass transfer coefficient was7.3×10-7 m s-1 and phenol recovery was 24.9%during 24 h,when the salt rejection reduced to 99.86%.6)Phase inversion was used to fabricate electrospun-phase inversion PDMS/PMMA composite membrane.The surface morphology was similar to phase inversion PDMS layer,and its cross-section was uniformly distributed electrospun layer and phase inversion layer.Compared with unmodified membrane,the hydrophobicity?116.7o of water contact angle?and organophilicity?93.0o of phenol contact angle?of composite membrane significantly decreased.However,its high phenol adhesion ability and hydrophobicity surface still achieved the phenol permeation and salt rejection.Results showed that the 8 h of wastewater HRT and 24 h of microorganism influent HRT were the best candidates for EMBR operation.With the increase of phenol concentration from 2.5 to 10.0 g L-1 in wastewater,the phenol permeation increased from 77.5 to 508.9 mg L-1.Resultant phenol degradation efficiency was above 96.7%,and the maximal phenol removal capacity was 508.9 mg L-1 d-1.Composite membrane exhibited high self-cleaning ability,and therefore,the attached biofilm thickness was lower than 10?m even in internal EMBR.The superhydrophobic and superorganophilic electrospun PDMS/PMMA permeable porous membranes exhibit low mass transfer resistance,low mass transfer pathway,high mass transfer coefficient.Solution-diffusion mechanism and external membrane configuration avoid the membrane fouling?pore blockage and biofouling?.The membrane modifications based on TPU and phase inversion further improve the mechanical strength and mass transfer of electrospun permeable porous membranes.The fabrications of novel electrospun permeable membranes and their applications in EMBR expand the research field and system of electrospinning and EMBR,provide reliable method for organic-laden saline wastewater treatment and organic recycling.The results of this study might be helpful to alleviate the organic-laden saline wastewater pollution in water environment,and to achieve the sustainable utilization of water source in China. |
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