| With the acceleration of industrialization and urbanization,the problem of water pollution is becoming increasingly serious.Compared with other sewage treatment technologies,membrane separation technology has the characteristics of low energy consumption,wide application range,and can realize water recycling,and is widely used in the field of water treatment.However,in the process of practical application,membrane fouling,especially biofouling,has greatly affected the treatment effect and limited its wide application.Adding media can effectively alleviate membrane fouling through adsorption,mechanical scouring,and formation of loose pollution layer.In the context of "double carbon",carbon-based media such as activated carbon have been widely used to alleviate membrane fouling.As a porous material produced by pyrolysis under oxygen-limited conditions,biochar had physical and chemical properties such as large specific surface area and rich functional groups.In addition,biochar is a good substitute for activated carbon due to its low cost,safety and environmental protection,and has great potential to alleviate membrane biofouling.In this context,this paper took Escherichia coli as a model microorganism,and explored the mitigation effect of biochar with different preparation temperatures on membrane biofouling through the combination of static adsorption and dynamic filtration experiments,using contact angle measuring instrument,scanning electron microscopy(SEM),atomic force microscopy(AFM),solid zeta potential meter,fourier transform infrared spectroscopy(FTIR)and laser confocal microscopy(CLSM)and other characterization methods were used to analyze the hydrophilicity,morphology,potential,chemical composition and pollutant distribution of the filtered membrane surface,combined with the analysis of the adsorption capacity of biochar on microorganisms,the impact on the extracellular polymer(EPS)secreted by them and the adsorption capacity,and the mechanism of alleviating membrane biofouling was analyzed by using the change of interface energy and filtration mechanism.It also studied its mitigation effect on membrane biofouling of anaerobic system.The main conclusions are as follows:(1)The physicochemical properties of corncob biochar under different preparation temperatures(300℃,500℃,700℃)were studied.The results showed that the density of corncob biochar increased and the hardness decreased with the increase of temperature;The specific surface area increased,the pores increased,and the adsorption increased;Surface potential decreased;The hydrophobicity was weakened;The surface functional groups were reduced;Graphite crystal with multi-layer stable microporous structure did not contain crystalline mineral components.(2)Through static adsorption and dynamic filtration experiments,the mitigation effect of adding biochar at different temperatures on membrane biofouling was studied.The results showed that the number of bacteria adhering to the membrane surface decreased by nearly30% when biochar was added at different temperatures;The addition of biochar alleviated the membrane biofouling in the filtration process and delayed the time of flux decay.The membrane flux at the end of filtration with 300℃,500℃ and 700℃ biochar was respectively3.3 times,3.7 times and 3.1 times of that without carbon,500℃ biochar has the best relieving effect.The analysis of the change of membrane surface performance showed that the addition of biochar increased the electrostatic repulsion between the pollutants and the membrane,effectively alleviated the adhesion of microorganisms on the membrane,and increased the hydrophilicity of the membrane surface,the roughness,the water area and the flux.Fourier transform infrared spectroscopy(FTIR)and laser confocal microscopy(CLSM)showed that biochar had obvious effect on protein substances.(3)Combined with the experimental analysis of the effect of biochar at different temperatures on microorganisms and EPS released.The results showed that the biochar had adsorption on Escherichia coli,and the adsorption performance was positively correlated with the preparation temperature;Biochar had an effect on the EPS released by Escherichia coli and was mainly adsorption.The adsorption effect of biochar on protein was better than that of polysaccharide.The results showed that the adsorption of Escherichia coli and its released EPS by biochar was an important reason for its mitigation of membrane biofouling.(4)The XDLVO theory and filtration model were used for analysis.The results showed that the electrostatic force energy and van der Waals force energy between the bacterial solution and the membrane in the control group and the group with biochar at different temperatures were both negative and small.It showed that these two interfaces can promote the membrane adsorption process of Escherichia coli,which was one of the reasons for membrane biofouling,but the effect was small.The Lewis acid-base interaction energy between different interfaces was positive,showing obvious hydrophilicity characteristics,and was in a dominant position compared with other interface interaction energies.Therefore,the Lewis acid-base interaction energy of the membrane-Escherichia coli interface was mainly caused by the hydrophilicity between the interfaces;The results of filtration model analysis showed that the membrane filtration process had an obvious transition stage from membrane pore plugging to cake filtration.The addition of biochar prolongs the time of its pore plugging model,and the time of 500℃ biochar pore plugging model was longer.(5)The mitigation effect of biochar at different temperatures on membrane biofouling caused by microorganisms in anaerobic system was studied.The results showed that 700℃biochar had a good effect on alleviating membrane biofouling in anaerobic system.By comparing and analyzing the surface properties(hydrophilicity,membrane potential,roughness,surface functional group)of the contaminated membrane after the addition of biochar,it was found that the reason for the different mitigation effects of 500℃ biochar and700℃ biochar on microbial contamination in different systems might be the difference of electrostatic repulsion between the pollutants and the membrane caused by them. |
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