Research On The Effect Of Different Pretreatment Methods On The Change Rule Of Microcystins And Disinfection By-products In Water

At present, there are many limitations in the conventional pre oxidation process in removing algae, removing microcystins from water and controlling disinfection by-products, which threaten the safety of water supply. This experiment through studying microcystins and disinfection by-products, caused by pressure, pro-oxidation and photocatalysis, analyzes and compares the adverse effects of algae in the water quality caused by different treatments, to provide certain reference for selecting safer and more reliable algae treatments. Principal results are as follows:(1) After water containing algae being pressurizedby0.3 to 0.8 MPa, the balloonruptured inside algal cells and the cyanobacteria sank, under the pressure of 0.7 MPa, pressurized mixed coagulation precipitation obtained better removal effect of algae and turbidity, algae removal rate reached 90.48%, turbidity removal rate reached93.48%.Water containing algae after adding the sodium hypochlorite,algal cells ruptured, and the balloon with the increase of concentration of sodium hypochlorite slightly reduced. After sodium hypochlorite oxidation coagulation precipitation, algae removal rate reached 42.79～68.38%, turbidity removal rate reached 47.62～ 66.67%, this shows that pressurized coagulation precipitations safe and effective to remove algae.(2) After water containing algae being pressurizedby0.3 to 0.8 MPa, the concentration of microcystins in water samples was 0.189～0.192μg·L-1, which was less slightly than0.197μg·L-1 the concentration of microcystins in the raw water, indicating that the pressurization does not rupturealgal cells andrelease microcystins. After 0.5～3 mg/L potassium permanganate oxidation, concentration of microcystins in water reduced by 6.1%～14.7%, because potassium Permanganate’s oxidation interacting with MC aqueous solution can destroy the unsaturated double bond of Adda in MCS. After 0.5～3 mg/L sodium hypochlorite pre oxidation, the highest concentration of MC increased to 0.442 μg/L, increased 2.24 times, thus it can be seen, with the increase of concentration of sodium hypochlorite, algal cells rupture, microcystins with intracellular algae fluid leak.(3) After the raw water is pressurized, the concentration of AOX in water has not changed obviously, which indicates that the pressure will not lead to the breakdown of algae cells and leakage of algae fluid. Potassium permanganate pre oxidation to remove humic acid and fulvic acid, which can remove against the AOX in a certain extent, therefore, after 0.5～3 mg/L potassium permanganate oxidation, AOX concentrations in water reduced by 11.8%～21.6%;And after 0.5～3 mg/L sodium hypochlorite oxidation, glial cells surface afterbirth fell off and algal cell liquid leaked, so the AOX concentrations increased gradually, the highest concentration increased 38.2%.(4) From the pressure,1 mg/L sodium hypochlorite and 1-2 mg/L potassium permanganate oxidation water after coagulatingsedimentation, concentrations of microcystins no significant changes can be judged that coagulatingsedimentationhas no functionto remove microcystins.(5) After the compression ofcyanobacteria water, the halogen acid precursors slightly reduced comparing with raw water, the concentration of THMFP had no obvious change; After coagulatingsedimentation, the concentration of halogen acid precursors decreased 34.3%, the concentration of THMFP decreased by 13.5%.And by 2mg/L sodium hypochlorite pre-oxidation, the concentrations ofHAAS and THMs were greatly increased by 12.7% and 34.7% comparing the raw water treatment.(6) After the compression ofcyanobacteria water, HAAS slightly reduced comparing with the raw water, THMs had no change; After coagulation and sedimentation filtration disinfection, HAAS slightly increased comparing with the raw water treatment, while THMs decreased by 48% comparing with the raw water treatment. THMs and HAAS in sodium hypochlorite treatment have the largest increasein the oxidation process.(7) 30 min before coagulant dosing or 7 min after coagulant dosing adding powdered activated carbon can havebetter effect of removing microcystins for pressurized water; And the additionof coagulant dosing and powdered activated carbon at the same time may have the best effect of microcystins for pre-oxidation.(8) Photocatalytic oxidation has the effect of degradation of microcystinsin water, and with the increase of reaction time, the degradation rate of microcystins lowers, finally tends to be stable, which conforms to the second-order attenuation index function. When the uv irradiation is 9 min, microcystin removal rate reached above 75%.