Study On The Removal Of Oscillatoria Sp. And Its Odorous Compounds By Ozone Oxidation

Cyanobacteria bloom in water environment is becoming a pervasive global issue.The extensive proliferation of cyanobacteria algal bloom has caused the hazardous endanger to the water ecosystem and also threatened the safety of population.The odor compounds secreted by some odor-producing algal species have seriously affected the quality of water and increased the cost of water treatment plant.The most significant steps for the water treatment procedure includes coagulation sedimentation and post-oxidation sterilization.The former can remove most of the algal blooms including the odor substances in the cells,while the latter can degrade the dissolved odor substances,some soluble organic compounds and the bacterial viruses.However,enormous areas of high-concentration algal blooms,the traditional coagulation sedimentation and post-oxidation process cannot meet the national standards.Therefore,it is necessary to add pre-oxidation treatment before coagulation to improve the coagulation efficiency and reduce the dosage of coagulant.Advanced oxidation is applied in the post-oxidation process to improve the removal efficiency of dissolved odors and dissolved organic matter and reduce the generation of disinfection by-products.The purpose of this thesis is to explore the effect of growth characteristics and the ability of odorous compounds producing by Oscillatoria sp.and to determine the algal cell characteristics by removal of odorous compounds on ozone pre-oxidation process and to analyze the effect of algal cells and algal organic matter on the degradation of odorous compounds by ozone oxidation.The main research contents and results are as follows:（1）The growth characteristics and the ability of odor-producing compounds were studied.The growth rate was 0.192 d^-1 in logarithmic stage.The production of odorous compounds increased in both the adaption and logarithmic stages,reaching 12745 ng/L and 1888 ng/L respectively.After entering a stable period,the output of odorous compounds began to decline.However,the yield of odorous compounds of flab increased in the adaptation period,but decreased in the logarithmic period and stable period.The average secretion rate of the odorous compounds of the flutter algae decreased with the development of the growth cycle.There was a significant positive correlation between the production of odorous compounds and the number of cells in the adaptation phase and logarithmic phase,while there was a negative correlation in the stable stage.（2）After exploring the effect of ozone on the characteristics of algae cells and the mechanism of ozone enhanced coagulation followed by the ozone pre-oxidation enhanced coagulation procedure,it was found at 0.25 mg/L and 0.5 mg/L,the coagulation efficiency could be improved.When the ozone dose reached the concentration of 1 mg/L,the coagulation efficiency started declining significantly.Under the condition of low dose ozone,the structure of algal cells was relatively complete,and the absolute value of Zeta potential decreased,resulting in cell aggregation and particle size increase.That results in the formation of more compact structure and enormous volume flocs and considerably higher sedimentation rate.Under the high state dose of ozone pre oxidation,the algal cells were damaged,some intracellular organic substances overflowed,and the absolute value of Zeta potential on the surface of algal cells increased,consequence reduce the coagulation efficiency.The concentration of dissolved organic carbon（DOC）in the algal solution after ozone pre-oxidation increased with the pre-ozone concentration;And simultaneously,the removal rate of DOC increases with the higher dosage of coagulant.The best ozone reception per unit cell is 9.61×10^-11 mg/cell.Ozone pre-oxidation can significantly promote the removal of UV₂₅₄,and also has certain removal effect on soluble microbial by-products,which are further separated after coagulation and sedimentation.However,the removal effect of humic acids in the coagulation process is not ideal.（3）The study on how the characteristics of algae cells release and degrade odorous compounds in pre-oxidation process found that the higher concentration of algal cells subsequently increase the odorous compounds in the water bodies after the pre-oxidation treatment,however the proportion of odorous compounds released outside the cell is decreasing.Increased Extracellular organic matter（EOM）of algae derived organic substances produced by algae metabolism will reduce the risk of releasing of odor substances.Ozone has a certain great effect on the odor removal,and the advanced oxidation method of ozone and hydrogen peroxide treatment is more effective than ozone solely.In addition to the this,the reaction rate has been greatly improved with the increased rate odor removal.GSM（Geosmin）has faster oxidation removal efficiency than 2-MIB.The presence of EOM in the water body will seriously affect the oxidation and removal efficiency of odorous substances.The EOM should be reduced to the great extent along the removal of odorous compounds.