Ozonation Of Typical Pollutants In Eutrophic Water In Taihu Lake

Organic pollution in water gradually become a serious threaten to water environment and human health. Especially, the eutrophication of water in Taihu Lake Basin leads to excessive growth of algae and formation of blooms. These bring out many problems in water ecosystem such as humic substance from the death of vegetable substances, odorous organic compounds and microcystins from metabolism of algae. They are difficult to be eliminated with routine processes of water treatment. Ozonation and AOPs, which could produce ?O H, perform powerfully in the removal of these pollutions. The investigation focused on the effect of ozonation to NOM and algae with its metabolites in surface wates, which mainly includes mechanism study and condition optimization of humic acids (HAs) degradation, algae killing, odorous compounds removal and microcystins (MCs) detoxification. Finally, a surface water treatment system powered by solar energy was designed and developed for eutrophication water. Research results of this thesis are as follows.(1) Ozonation with its direct and indirect reaction pathways can not only rearrange molecular structures of HA and convert it to more hydrophilic forms but partition the HA macromolecules into small fractions. The reaction of HA ozonation followed a pseudo-first order model, rate constant of HA bought from Sigma is 3.6×10-3 s-1 and HA extracted from Taihu Lake 2.9×103 s-1. The proper condition of ozonation of HA was optimized as 25℃and pH 7.0. The contributions of two pathways (molecular ozone attack and .OH attack) to HA ozonation could be traced using tert-butanol as the radical scavenger at different pH, temperature, and the results showed that .OH oxidation are more sensitive to operating variables than molecular ozone oxidation and exerted a contribution of approximately 50-60% to the overall reaction at the different operating parameters. And molecular ozone attack was found followed Arrehenius equation under different temperature, Catalytic ozonation of HA by different catalyst was further investigated, enhancement factor was calculated as follows: f(Mn2+)=1.31;f(Fe2+)=1.09;f(H2O2)=1.69.(2) The ozonation of M. Aeruginosa led to the damage of cell wall and celluar cytoplasm release from the cells, which caused the DOC increase in solution and odorous organic compounds production. A the ozone dosage of 3 mg L-1 and reaction time of 30 min could seriously damage the cells, which led to the death of algae. Further investigation found out that DOC and radicals scavenger (NaHCO3) exerted an important influence on the ozonation of algae. High concentration of these compounds leds to low efficiency of algae killing.(3) Ozonation was applied to investigate the removal efficiency of 6 odorous organic compounds in eutrophic water from Taihu Lake. The results showed that the ozonation process could be described by first order kinetic model and the overall kinetic rates of the odorous compounds were determined by their chemical characteristic and structure, which could be ranked:β-Ionone (3.3×10-3 s-1)﹥β-Cyclocitral (2.8×10-3 s-1)﹥2,4-Decadienal (2.7×10-3 s-1)﹥Neryl Acetone (2.2×10-3 s-1)﹥Geosmin (1.4×10-3 s-1)﹥2-Methylisoborneol (5.6×10-4 s-1). Ozonation of eutrophic water led to the formation of a series of aldehydes, ketones, alcohols and esters. The influence of DOC and radicals scavenger (NaHCO3) on odorous compounds ozonation were further investigated, results showed that the radicals scavenger could restrain the effect of ozonation by cutting down the radical pathway and DOC in the water by competition with target compounds.(4) The decomposition of MCs by ozonation appears to involve substitution and cleavage of the Adda conjugated diene structure, cleavage of the peptide bond between Mdha and Ala, and attack of the Adda benzene ring. The degradation rate of MC-RR was a little slower than that of MC-LR, which lead to more byproducts from Adda side chain cleavage in our study. The Adda moiety, which is important in MCs toxicity, is readily oxidized and destroyed by ozonation. It is apparent from this study that Adda degradation pathway is the major destruction pathway of both MC-LR and MC-RR. The heptotoxity of MCs expressed as inhibition of PP1 and damage in mouse liver was greatly reduced or eliminated by the ozonation process.(5) The surface water treatment system was developed as the output of equipment was 3 t h-1. The system was applied to eutrophication water in Taihu Lake and obtained the results as COD removal of 78.9%, Chl-a 49.0%, NH3-N 50.6%. Simultaneously, DO of water increased to 6.2 mg L-1. The device was equipped with the solar cell array of 3.24 KW, an inverter of 48 V/5 KW and 24 parallel connection of 48 V storage battery.In conclusion, the results indicate that ozonation was found an innovative and prospective method in surface water treatment. The application of ozonation was including organic compounds decomposition, algae and its metabolites killing and removal for dringking water security.