| Water resources shortage and water pollution are the bottleneck problems that restrict the sustainable development of society and the economy.Membrane separation as an advanced water treatment technology has been widely used in recent years.Biofouling caused by microorganisms attached to the membrane surface is one of the main problems faced by membrane separation technology in water treatment.Quorum sensing(QS)is a mechanism of communication between microorganisms using signal molecules,which can regulate the formation of biofilms in biofouling.Quorum sensing inhibition provides a new way to control membrane biofouling.In this paper,the antifouling of water treatment membranes was studied based on the quorum sensing inhibition method.The acylase-modified polyacrylonitrile(PAN)ultrafiltration membrane and D-tyrosine-modified PAN ultrafiltration membrane with quorum sensing inhibition were prepared by surface modification,and quorum quenching bacteria with acyl homoserine lactones signal molecule degradation ability was isolated from activated sludge.The surface characteristics and water permeability of the modified membrane were investigated,the quorum quenching ability of the screened strains was tested,and the inhibition performance of the modified membrane and the quorum quenching bacteria on membrane biofouling of different bacteria groups was evaluated.The ultrafiltration experiment was carried out with domestic sewage as the feed liquid to further evaluate the antifouling effect of the modified membrane and the quorum quenching bacteria in membrane water treatment.The main research conclusions are as follows:(1)The surface of the PAN ultrafiltration membrane was modified by quorum quenching enzyme,and modified membranes with different acylase contents were prepared:ACY 0.1,ACY 0.5,ACY 1.0,and ACY 1.5.After modification,a continuous and uniform modified coating was formed on the surface of the modified membrane,and the pore structure of the modified membrane became denser,while the modified membrane still maintained a low surface roughness.The results of the FTIR analysis showed that acylase was stably fixed into the coating of the modified film.The contact Angle of the modified ACY membrane ranges from 78.71°±4.26oto 81.63°±1.86o,and the water permeability ranges from 156.43±7.25 L/(m~2·h·bar)to 192.14±11.09L/(m~2·h·bar).The modified ACY membranes are hydrophilic and have high water permeability.The results showed that the acylase could degrade AHLs signaling molecules and inhibit the quorum sensing pathway of bacteria.Acylase in the modified membrane can maintain high activity,which can effectively inhibit the adhesion of Escherichia coli,Agrobacterium tumefaciens,and mixed bacteria in sewage on the membrane surface and the formation of biofilm.With the increase in acylase concentration in the modified layer,the anti-biofouling performance of the membrane is enhanced.ACY 1.0 and ACY 1.5 with high acylase content maintained a slow growth level in 48 h culture.(2)The surface of the PAN ultrafiltration membrane was modified by D-tyrosine,and the modified membrane DTY 1,DTY 3,DTY 5,and DTY 7 with different contents of D-tyrosine were prepared.After modification,the pore structure of the modified membrane became relatively dense,and FTIR spectra showed that D-tyrosine was successfully fixed on the modified membrane.The contact angle of the modified DTY membrane ranges from 64.48°±0.2°to 67.81°±3.57°,and the water permeability ranges from 155.95±8.28 L/(m~2·h·bar)to 175.24±9.04 L/(m~2·h·bar).The modified DTY membrane still has good hydrophilicity and high water permeability.D-tyrosine modified membrane can effectively inhibit the adhesion of gram-positive Bacillus subtilis and gram-negative E.coli on the surface of the membrane and the formation of biofilms.After 24 h culture,the amount of bacteria and biofilms on the surface of the modified membrane is significantly reduced compared with that of the unmodified membrane,and the biofilms are sparse.The membrane samples were mixed with sewage for culture.The surface of the unmodified membrane was almost completely covered by biofilm containing bacteria at 24 h,and dense biofilm was formed at 48 h.In contrast,the contamination of D-tyrosine-modified membranes was significantly reduced,especially in DTY 5 and DTY 7 with high D-tyrosine content.The D-tyrosine-modified membranes could effectively inhibit the biofouling of different bacteria.(3)The bacterial strains in the sludge were separated by an inorganic salt medium with C8-HSL as the only carbon source,and a quorum quenching bacterial strain which could effectively degrade C8-HSL without producing AHLs was screened out by the biological chromogenic method.16S r DNA sequencing results showed that the QQ strain had 99%homology with Klebsiella pneumonia.LC-MS results showed that the QQ strain could degrade 82.23%±1.85%of 50μM C8-HSL within 24 h.To improve the feasibility of quorum quenching bacteria in water treatment,sodium alginate beads were prepared to immobilize the strain.The inhibition effect of quorum quenching bacteria and quorum quenching bacteria beads on the biofilm formation of different bacterial groups was tested using Escherichia coli,Bacillus subtilis,and actual sewage.The results showed that both quorum quenching bacteria and quorum quenching bacteria beads could effectively control the biofilm formation of E.coli and mixed bacteria in sewage on the membrane surface,but had no obvious inhibition effect on Bacillus subtilis.(4)The domestic sewage was used as an influent to conduct membrane fouling filtration and fouling-cleaning cycle experiment.In the membrane fouling filtration experiment,the modified membrane prepared by acylase and D-tyrosine at different concentrations showed higher water fluxes than the unmodified PAN membrane,and the water fluxes were 32%-46%and 38%-69%higher than those of the unmodified PAN membrane after 8 h operation,respectively.Adding the embedded quorum quenching bacteria of sodium alginate beads into the feed liquid can also effectively inhibit the decrease of water flux.In the membrane fouling filtration experiments of 4h and 12 h premixed culture of beads and feed liquid,the water flux after 8 h operation is 12%and 30%higher than that of the feed liquid without quorum quenching bacteria beads,respectively.The flux recovery rate of acylase modified membrane and D-tyrosine-modified membrane was still 6%-35%and 10%-26%higher than that of the unmodified membrane after four cycles in the membrane fouling and cleaning cycle experiment.In addition,the membrane flux recovery rate was 14%higher than that of the control group without the addition of the quorum quenching bacteria beads.After the membrane fouling filtration experiment,the biofilm on the PAN membrane was coated with a large number of bacteria,while the test using the quorum sensing inhibition method had fewer bacteria on the membrane surface.Compared with PAN membrane,the protein content on ACY 0.5,ACY 1.0,ACY 1.5,DTY 5,and DTY 7decreased significantly,which were 30.77%,28.96%,34.39%,19%,and 32.58%,respectively.Polysaccharide content also decreased by 11.75%,8.88%,12.27%,3.65%,and 13.05%,respectively.The modified membrane and quorum quenching bacteria have good anti-biofouling and stability in the process of water treatment membrane separation. |
PDF Full Text Request