Efficiency And Mechanism Of Calcium Peroxide/ferrous Iron Combined With Membrane Process In Treating High Algae-containing Wate

Algal blooms in eutrophic water bodies such as lakes and reservoirs not only endanger human health,but also increase the operational burden of water plants.Membrane technology,represented by ultrafiltration（UF）and forward osmosis（FO）,can retain algae cells efficiently and has significant advantages in algae-laden water treatment,but the inevitable membrane fouling problem still limits its further application.Oxidation pretreatment is an effective solution to these problems as it can improve the effluent quality of the membrane while alleviating membrane fouling.Calcium peroxide is a mild oxidizer,which can slowly release hydrogen peroxide when reacting with water,and has the advantages of being safe,cheap and not easy to pollute the environment.The reaction between calcium peroxide and ferrous iron can produce hydroxyl radicals with oxidizing effect,trivalent iron with coagulation effect and calcium hydroxide with coagulation aid.Therefore,this study intends to apply the calcium peroxide/ferrite system to algae-laden water treatment and investigate its effects and mechanisms on UF and FO membrane fouling.In this study,we investigated the efficacy of calcium peroxide/ferrite in treating algae-laden water and explored the mechanism of its treatment.It was found that the calcium peroxide/ferrite system could remove 57.4%of algal cells,51.4%of UV₂₅₄,54.7%of DOC and most of fluorescent organic matter from algae-laden water,which effectively improved the water quality.The hydroxyl radicals generated by calcium peroxide/ferric oxide could oxidize large organic matter to lower molecular weight organic matter,while the in-situ generated trivalent iron and calcium hydroxide exerted coagulation effects,prompting algal cells to agglomerate into flocs.In addition,it was found that the algal cells still had high fluorescence activity after the calcium peroxide/ferrite treatment,indicating that the algal cells were not significantly damaged.In this study,we investigated the effect and mechanism of calcium peroxide/ferrite treatment on the efficacy of UF treatment of algae-laden water by constructing a coupled calcium peroxide/ferrite UF treatment process.It was found that the calcium peroxide/ferrite system could effectively improve the purification capacity of UF for algae-laden water,reduce the content of algal cells,UV₂₅₄ and DOC in the effluent water,and remove fluorescent organic matter from the water.The calcium peroxide/ferrite pretreatment increased the terminal specific fluxes of PES and PVDF UF membranes from 0.12 to 0.87 and 0.64,and reduced the total fouling resistance of PES and PVDF membranes by 97.9%and 95.5%,respectively.The membrane fouling mechanism analysis revealed that the calcium peroxide/ferric oxide treatment slowed down the transition from membrane pore blockage to cake filtration.Scanning electron microscopy and Fourier infrared spectroscopy revealed that the algal cells and algae-derived organic matter settled on the membrane surface were greatly reduced after the calcium peroxide/ferrite treatment,and the flocs formed a more sparse and porous cake layer on the membrane surface.This study investigated the effect and mechanism of calcium peroxide/ferrite treatment on the effectiveness of FO treatment of algae-laden water.It was found that calcium peroxide/ferrite treatment increased the specific flux at the end of filtration from 0.46 to 0.70 and the recovery flux after cleaning by 16.2%.The effects of both in-situ treatment directly in the feed solution and ex-situ treatment with pretreatment followed by filtration and the amount of calcium peroxide dosing on membrane fouling were then investigated,and it was found that both calcium peroxide/ferrite treatments mitigated the decrease in membrane flux and enhanced the recovery flux after cleaning.The reversible and irreversible fouling caused by algae-laden water was effectively controlled by the calcium peroxide/ferrite treatment at different draw solution concentrations and membrane orientations.The detection of fluorescent organics in the draw solution revealed that the calcium peroxide/ferrite treatment facilitated the removal of fluorescent organics by the FO membrane.After the calcium peroxide/ferrite treatment,the protein-like substances adhering to the membrane surface were significantly reduced,and the organic matter with molecular weight around 200,000Da had largely disappeared.Scanning electron microscopy and Fourier infrared spectroscopy analysis can reveal that the algal cells and organic matter deposited on the surface of the FO membrane after calcium peroxide/ferrite treatment were significantly reduced.The results of the interfacial free energy analysis indicated that the calcium peroxide/ferrite treatment weakened the adhesion between the contaminants and the membrane surface,and the interaction between the contaminants and the adhering contaminants on the membrane surface had changed to repulsion in the late filtration stage.In this thesis,calcium peroxide/ferrite was used to treat algae-laden water,and the transformation law of algae-derived pollutants in the treatment process and the effect of calcium peroxide/ferrite treatment on the fouling and water purification efficiency of UF and FO membranes were systematically studied,which can provide new ideas for the application of membrane combination process in algae-laden water treatment.