| As an emerging pollutant（PPCPs）,antibiotics have been included in the focus control scope and are widely detected in water bodies.Due to its high stability,structural complexity and antibacterial activity,it is difficult to solve the problem by conventional water treatment processes.Although nanofiltration can effectively trap antibiotics,low flux and serious membrane pollution during operation make it unable to be widely used in the treatment of antibiotic wastewater.Therefore,it is urgent to develop a technology that can not only improve in situ treatment efficiency,but also effectively reduce membrane pollution.Micro-nano bubbles have been gradually used in wastewater treatment and membrane pollution control due to their strong stability and high interfacial potential.Based on this,the effect and mechanism of nano-bubble enhanced nanofiltration membrane on norfloxacin antibiotic wastewater treatment were studied.In this study,norfloxacin was separated from water by nanofiltration membrane,and air micro nano bubbles（AMNBs）were added to improve nanofiltration efficiency and reduce membrane pollution during nanofiltration operation,so as to increase the ubiquity of nanofiltration in the treatment of antibiotic wastewater.NF270 membrane was used as the test membrane,norfloxacin was used as the target pollutant,and antibiotic interception rate and membrane flux were used as efficacy indexes.Firstly,the treatment performance of nanofiltration membrane was investigated by orthogonal experiment,and the optimal conditions were determined as pressure of 1.0 Mpa,cross-flow rate of 100L/h and temperature of 25℃.The influence of norfloxacin concentration on nanofiltration efficiency was investigated under optimal conditions.It was found that with the increase of Norfloxacin concentration,the membrane flux gradually decreased at the initial stage of filtration and showed a slight decreasing trend with the change of time,indicating that with the increase of Norfloxacin concentration,the concentration polarization phenomenon intensified.Secondly,the influence of AMNBs on nanofiltration water flux was explored,and the mechanism of AMNBs strengthening nanofiltration membrane water flux was analyzed through bubble characteristics.It was found that the membrane flux of clear water with nanofiltration increased significantly after AMNBs was added.Mechanism analysis found that the nanoscale size made the bubbles relatively stable,which was not easy to burst directly,but more easy to self-pressurize and dissolve.When the bubble size was smaller than the membrane hole,it would pass through with the membrane hole and form slug flow,which increased the shear force on the membrane and led to the increase of flux.The enhancement effect of AMNBs on nanofiltration at different norfloxacin concentrations was further investigated,and the mechanism of AMNBs enhancement on Norfloxacin at different concentrations was analyzed by bubble characteristics.It was found that the membrane flux increased significantly after adding AMNBs,and with the increase of norfloxacin concentration,the increase effect of flux was more obvious.When Norfloxacin concentration is 100 mg/L,the absolute value of Zeta potential on the surface is almost 0m V,which is mainly due to the adsorption of norfloxacin on the bubble surface.At the same time,with the increase of norfloxacin concentration,the bubble size increases and tends to be stable.At this time,the proportion of micron bubbles increases,and bubbles are more likely to directly burst and form a vacuum region,which is conducive to the increase of flux.Finally,the mitigation effect of AMNBs on nanofiltration membrane pollution under the condition of multi-pollutant interaction was investigated,and the mitigation mechanism of membrane pollution was revealed through the analysis of membrane pollution characteristics combined with the changes of bubble characteristics.The results showed that the flux decreased with the increase of time,and the decrease of membrane flux was the most obvious when bovine serum protein interacted with antibiotics,and the recovery rate of membrane water flux was the lowest after physical cleaning.After the addition of AMNBs,the membrane fouling resistance decreased significantly,and the membrane flux increased significantly,especially in the interaction between bovine serum protein and antibiotics:the flux increased from 3.51 L·m-2·h-1 to 16.09 L·m-2·h-1 after 5 h filtration.According to the physical cleaning experiment,the surface of the physically cleaned membrane without AMNBs is obviously attached by pollutants,and its roughness is significantly improved compared with the original membrane.However,the surface roughness of the physically cleaned membrane is lower and the water flux recovery rate is higher after AMNBs is added.Through the analysis of bubble characteristics,it was found that the bubble size decreased significantly and the Zeta potential on the surface was positive and increased significantly when bovine serum protein interfaced with antibiotics,which was different from the change rule of bubble size under the condition of single antibiotic.Through electrostatic adsorption,positively charged bubbles are more easily adsorbed to the membrane surface,resulting in displacement,which makes it difficult to form a polluted layer on the membrane surface,thus slowing down the pollution of nanofiltration membrane.In conclusion,MNBs enhanced nanofiltration treatment of norfloxacin antibiotic wastewater can not only improve the efficiency of nanofiltration on the basis of in situ,but also reduce the pollution of nanofiltration membrane,which provides theoretical basis and data support for the application of this technology in engineering. |
