The Treatment Of Slightly Polluted Algae-containing Surface Water By Ozone Pre-oxidation And Co-coagulation With Diatomite And PAC

In recent years, cyanobacteria blooms have seriously affected the water security. Theconventional water treatment processes to remove the algae and organic matter from highalgae water are not effective and cannot meet the requirement. Therefore, the search formore efficient and safer method remove to algae and other pollutants from raw water isbecoming more important.The treatment of slightly polluted algae-containing surface water by ozone preoxidationand co-coagulation with diatomite and PAC was studied in this work.The effect of preozoneon the cytoactive of Anabaena flos-aquae was researched. Anabaena flos-aquae and organicmatter were treated by both the enhanced coagulation of ozone and PAC only, and theremoval rates were compared. The influencing factors of the enhanced coagulation for algaeremoval were studied. The effects of the different coagulation process and ozone dosage onthe removal of different molecular weight organic matter were also investigated.Thefollowings are the main research contents and conclusions.（1）Researching the effect of preozonation on cytoactive of Anabaena flos-aquae,results showed that preozonation restrained the cytoactive of Anabaena flos-aquae, whichcould be controlled for8d when the dosage of ozone was1.0mg/L, met the time of watertreatment. The Anabaena flos-aquae was killed, the cell structure of Anabaena flos-aquae wasdestroyed, and anatoxins released when the dosage of ozone was3.0mg/L.（2）The feasibility of using diatomite and PAC for advanced treatment of slightlypolluted algae-containing surface water by ozone preoxidation was investigated in this study.Results showed that Anabaena flos-aquae and organic matter were effectively removed byozone preoxidation with diatomite and PAC, and the effect of algae and organic matter wasbetter than that by ozone preoxidation with PAC.The reduction of the PAC dosage requiredfor satisfactory treatment of algae. It could mostly save about58%of PAC dose. Throughorthogonal experiment, the optimum coagulation conditions were worked out asfollows:ozone of1.0mg/L, diatomite of0.4g/L, PAC of2.5mg/L, and the remove rates of Chl-a,turbidity, TOC and UV254were96.05%,90.57%,27.59%and50%respectively.（3）The influencing factors of the enhanced coagulation combining diatomite and PAC by ozone preoxidation, such as temperature, pH value, addition sequence, preozonation timeon Anabaena flos-aquae and organic matter removal were investigated. It showed that exceptthe addition sequence greatly influenced the removal of algae and organic matter, thecombined technology is less sensitive to other influencing factors, reflecting its excellentperformance. Diatomaceous should be added before the coagulant in practical application.（4）The experiment of molecular distribution showed that the fractions with molecularweight <1kDa was predominant component in raw water from the Pearl River, accounting forabout42.35%of TOC; The removal of organic matter with different molecular weight can beimproved on varying degrees by diatomite, mainly to remove larger molecular organics. Partof the small molecule organics were completely oxidized by low doses of ozone, andimproved the removal rate of organic. High doses of ozone maked part of large organicmolecules transformation into small organic molecules, and increased content of smallmolecules organic, and resulted in total TOC increase.