| With the development of wastewater treatment processes,membrane bioreactors(MBR)have been widely used in the past decades due to their unique wastewater treatment advantages,such as small footprint,short hydraulic retention time(HRT),long sludge retention time(SRT),high sludge concentration and low production rate,and stable effluent quality.However,membrane fouling has been an important obstacle that limited the further development and application of membrane bioreactors.In this article,by established anoxic-aerobic membrane bioreactor,two membrane modules were operated simultaneously in the MBR system to investigate the difference of membrane fouling formed by constant flux mode with constant flux and constant TMP mode with constant differential pressure across the membrane.The aim was to investigated the effect of different operation modes on membrane fouling mechanisms.At the same time,microplastic as an emerging source of pollution has gradually entered the public eye.Microplastic refers to plastic particles and fibrous materials less than 5mm in diameter,which mainly include polyethylene terephthalate(PET),polypropylene(PS)and polyethylene(PE),etc.The current wastewater treatment plants can remove microplastics at a rate of 98% or more,but a small amount of microplastics can enter the environment and cause pollution.To address the above problems,this study established two simultaneously operating membrane modules in the A/O-MBR reactor,maintaining high and low flux operation,respectively,and dosing different concentrations of PET microplastics to investigate the effects of microplastics on the biological system and membrane fouling in the MBR system.The effects of different concentrations of PET microplastics on membrane fouling mechanisms and microbial communities were investigated to provide theoretical support for the practical prevention and treatment of PET microplastics in wastewater.An A/O-MBR reactor was built,and two membrane modules were operated in the system in both constant flow and constant MP modes.During the experiment,the operating effect of the reactor was monitored for a long time,and the TMP variation data of the two membrane modules were collected.Meanwhile,when the pressure difference across the membrane modules reached about 25 kpa,the bio-cake layer on the membrane surface was collected and extracted and analyzed for extracellular polymeric substances,while the sludge sample of the cake layer was saved for subsequent biological information analysis.In this paper,membrane fouling was researched in two parts by building an A/O-MBR reactor.Experiment I,the difference in membrane fouling formed by constant flux mode and constant TMP mode was investigated by building two membrane modules operating simultaneously.Experiment II,,two membrane modules operating in parallel,maintaining high and low flux operation,were dosed with different concentrations of PET microplastics(mixed particle size)to investigate the effects of microplastics on the microbial communities system and membrane contamination.The reactors operated in constant flux mode and constant TMP modes had higher removal efficiencies for NH4+-N,、TN、COD and TP,which were maintained above 90%、92%、95% and 75%,respectively,but there was no significant difference between the removal effects of the two modes.By extracting EPS from the bio-cake layer,it was found that the levels of both PS and PN were higher in the constant flux mode than in the constant TMP mode.This indicated that the fouling was more serious in the constant flux mode.The fluorescence response intensity of protein-like substances and humic acid-like substances were found to be higher in the constant flux mode than in the constant TMP mode in three dimensional fluorescence spectroscopy(EEM).The results of Fourier infrared transform spectroscopy(FTIR)also showed that the absorbance of functional groups of polysaccharides was higher in the constant flux mode than in the constant TMP mode.By comparing the permeation amounts of the two different modes,it was found that the permeation amounts were lower in the constant flux mode than in the constant TMP mode.4.The TMP data of the four operation stages also showed that the constant flux mode reached25 kpa faster than the constant TMP mode,and the membrane cleaning cycle was shorter than that of the constant TMP mode.This indicated that the membrane fouling rate was higher in constant flux mode than in constant TMP mode.The operational efficiency of the MBR system and the changes of microbial community structure in the bio-cake layer were investigated when different concentrations of PET microplastics were added.There was no significant difference in the removal of NH4+-N、TN、COD and TP by the A/O-MBR reactor during the operation phase with different PET concentrations.As the increasing concentration of PET microplastics gradually increases,the content of PS and PN in the EPS of the filter cake layer keeps increasing.In the EEM measurement of the EPS of the bio-cake layer,it was found that the highest fluorescence intensity of protein-like substances and humic acid-like substances was observed in the PET dosing stage with a concentration of 50 mg/L,followed by the PET dosing stage with a concentration of 30 mg/L,and the concentration of The results of FTIR also showed the same trend,and the absorbance of functional groups of polysaccharides increased with the increase of PET dosing concentration.Real-time monitoring of TMP revealed that the membrane cleaning cycle was gradually shortened and the contamination rate was gradually increased with the increase of PET dosing concentration.This indicates that the membrane contamination rate tends to increase with the increase of PET dosing concentration.In conclusion,this research illustrates the impact of different operation modes on membrane fouling process,and provides a reference for the selection of energy-efficient operation modes in the actual wastewater treatment process.On the other hand,by studying the effect of microplastics entering the MBR system on membrane fouling,it provides a theoretical reference for how to deal with the aggression of microplastics on the MBR system in the actual wastewater treatment process... |
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