| Conventional water treatment process adopts flocculation,sedimentation,filtration and disinfection.Flocculation is one of the most important steps,which has a significant impact on the following treatment processes and effluent quality.High-efficient,high performance and multifunctional flocculants are in great demand with the increasing standards of water treatment over the years.The sterilization of flocculant has attracted the wide attention by many researchers.But the sterilization process,sterilization mechanism,and the broad-spectrum sterilization of flocculant remain to be further explored.In addition,this paper also focus on the efficient and accurate discrimination of bacterial species in water after flocculation.Herein,the synergistic effect of inorganic and organic flocculants in the bacterial removal was studied.The sterilization process and sterilization mechanism of inorganic and organic flocculants in the process of bacterial removal were emphasized.And then,ultrasonic initiated polymerization and self-assembly technology were used to synthesize the novel flocculant with the sterilization function.The removal and sterilization efficiency of flocculant were improved.Floccualnt combining with surfacing enhanced Raman(SERS)labels developed a water treatment technology integrating flocculation,discrimination and sterilization of multiple bacteria.The key research contents were described as follows.1)The removal efficiencies of bacteria were investigated by traditional polyaluminum chloride(PAC)combining with polydimethyl diallyl ammonium chloride(PDMDAAC).2)Sterilization process,sterilization mechanism and tthe different roles of PAC with PDMDAAC were further studied.3)Flocculation and sterlization performance of flocculant were improved through introducing bacitracin,template polymerization and ultrasonic initiation in its preparation.The novel flocculant,B-g-PAMDAC,with cationic microblock structure and enhanced sterilization performed well in flocculation and sterilization of four kinds of bacteria,Escherichia coli,Pseudomonas aeruginosa,Bacillus cerevisiae and Enterococcus faecalis.4)A new SERS labels were prepared via modifying and optimizing sulfhydrylation graphite oxide and silver coated gold nanocomposite(GO-Au@Ag NPS).5)Flocculation,discrimination and sterilization of multiple bacteria in water treatment were achieved by combination of B-g-PAMDAC flocculant and SERS labels.And the fingerprints of four bacteria were obtained in Raman spectra.Main work and conclusions of this paper were summaried as follows:(1)Kaolin and Escherichia coli were well removed from water by traditional PAC flocculant with PDMDAAC flocculant.The optimal removal rates of turbidity and bacteria,93.2%and 96.1%,were achieved after respectively dosing two flocculants with the total dosage of 90 mg/L(the dosage of PAC was 20 mg/L,and the dosage of PDMDAAC was 70 mg/L).The weakly acidic water(p H=6-7)conduced to the best removal rate of bacteria.PAC excessively hydrolyzed at the alkaline condition and transformed to aluminum hydroxide gels and precipitation.It decreased the treatment efficiency of PAC.The 95%confidence intervals of Z*add and Z*mix calculated by contour method are(19.0515,20.1511)and(17.1426,17.9774),respectively.There is no overlap between the two intervals.The results showed that the removal efficiency of combination PAC and PDMDAAC was greater than that of the sum of the removal effects that can be achieved by adding separately.The two flocculants have synergistic effect in the sterilization process.(2)The different roles of PAC and PDMDAAC in removal bacteria and sterilization were studied via XPS analysis,disinfection kinetics,detection of?-galactosidase and detection of bacterial exopolysaccharides.Sterilization process and mechanisms of flocculants were further discussed.PAC played a key role of flocculation of bacteria,which contributed to sterilization of PDMDAAC.PDMDAAC played an essential role of sterilization due to its quaternary amine groups.And charge neutralization and attraction of these cationic groups caused the aggregation of flocs.They also made up for the deficiency of PAC in bridging.PDMDAAC sterilized bacteria via changing membrane permeability of bacteria,causing the release of cytoplasm and disturbing metabolism of bacteria.The process of sterilization mainly divided into two steps,fast adsorption and slow killing.The former only cost half hour,but the latter cost 4 h for complete sterilization.(3)After the research of bactericidal functional groups,sterilization process and sterilization mechanisms,a novel flocculant,B-g-PAMDAC,was prepared via copolymerization of acrylamide,2-trimethylammonioethyl methacrylate chloride and bacitracin under the initiation of supersonic wave.The sterilization capacity of flocculant was strengthened.The microblock structure of cationic functional groups was found on B-g-PAMDAC with the aid of self-assembly in the preparation.The microblock structure improved charge neutralization and briding of B-g-PAMDAC.Characterization analysis,such as 1H NMR,TG/DSC and SEM,confirmed that B-g-PAMDAC was successfully synthesized and there were microblocks on B-g-PAMDAC.B-g-PAMDAC performed well in coagulation-flocculation and sterilization of four bacteria.Their removal rate was above 96.2%,and their sterilization rate was above 99.64%.B-g-PAMDAC with cationic functional groups had the higher coagulation efficiency in the treatment of gram negative bacteria than in the treatment of gram positive bacteria.The microblock structure on B-g-PAMDAC contributed to low turbidity of treated water,decreasing for 31 NTU,and short settlement time of flocs,decreasing for 19 min,compared with B-g-PAMDAC without microblock at the same dosage.Bacitracin on B-g-PAMDAC enhanced sterilization rate for 48%and reduced the contact time to 3 h for completely killing bacteria.(4)SERS labels were prepared via preparation optimization and modification of GO-Au@Ag NPs.Rhodamin 6G(R6G)with the concentration of 10-9 mol/L was used to detect the signal amplification capability of SERS lables.The results indicated that GO prolonged the storage time of SERS labels,prevented oxidation of SERS labels and improved their sensitivity and stability.The highest intensity and sensitivity of SERS labels were achieved at the ratio of GO to Au@Ag NPs of 30:1(m L/mg)and the shell thickness of Au@Ag NPs of 5 nm.(5)The modified SERS labels was applied to discriminate bacteria in wastewater containing bacteria for the strong interaction between 4-MPBA on SERS labels and bacteria.The composite flocs of flocculant/bacteria/SERS labels were generated after coagulation.The different SERS spectra of four bacteria were detected in Raman spectrum,even at low bacterial concentration of 1×103 CFU/m L.Five characteristic peaks of Escherichia coli were discovered at 545 cm-1,688 cm-1,757 cm-1,1186 cm-1and 1283 cm-1.The peak at 1283 cm-1 was related to Pseudomonas aeruginosa.The peaks of 622 cm-1,1249 cm-1 and 1284 cm-1were corresponding to Bacillus cerevisiae.The peaks of Enterococcus faecalis were detected at 439 cm-1,622 cm-1,699 cm-1 and1368 cm-1.The fingerprint of four bacteria were stable and repeatable according to the standard deviation of characteristic peaks of four bacteria.SERS labels combining flocculant were able to be applied in efficient removal and discrimination of bacteria in water. |
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