Identification Of Disinfection By-products And Control Of Precursors During High Algae Laden Period In Water Source Ecological Purification System

The water source ecological purification system has a good removal efficiency for nitrogen,phosphorus and other nutrients in water,and can effectively improve dissolved oxygen and transparency of water.However,the deep purification area has the risk of algae outbreak in summer due to the hydraulic retention time,water depth and high transparency.Raw water containing a large number of algae cells will react with the disinfection process of water plant to produce teratogenic,carcinogenic and mutagenic disinfection by-products.In practical application,pre-oxidation is usually adopted to enhance the removal of algae cells and algae organic matter.On the one hand,what kind of pre-oxidation can remove algae cells and on the other hand,less disinfection by-products will be produced after pre-oxidation and subsequent disinfection process has become a hot research topic at home and abroad.In this study,the effect of temperature,light and nitrogen and phosphorus nutrients on algal cell density and algae filament were investigated by simulating the algal value-added process under different habitat conditions in the laboratory,using the water from the deep purification area of the Yanlong Lake water source ecological purification system as the research object.And to simulate the high algae water as object,study different pre oxidant（sodium hypochlorite,potassium permanganate and ozone）under the condition of different dosing quantity and different p H,algae organic nature change and disinfection by-products generated situation,explores the pre oxidant cancellation precursor disinfection by-products（algae control）of the organic matter and high algae water chlorination by-products,the influence mechanism.The research results are of great significance for the control of algae growth and disinfection byproducts in high algal period in water source ecological purification system.A single-factor rotation experiment showed that the optimum growth conditions for algae cells from the water source ecological purification system were:temperature=25°C,light intensity=2000lx,phosphorus to nitrogen concentration ratio=16mg/L:1mg/L.The chlorophyll a concentration increased from 81.52μg/L to 1879.79μg/L after 25 days of incubation.The dominant algal species changed from diatoms to green algae as the temperature increased,while light intensity and nitrogen to phosphorus concentration ratios did not have a significant effect on algal species composition.The low chlorine dosing rate caused less damage to the algal cells,the basic water quality parameters(DOC,DON,K⁺,UV₂₅₄,SUVA,DOC/DON)and fluorescence characteristics of the algal solution changed less,and the low chlorine dosing rate had some effect on the removal of carbon disinfection by-products and nitrogen-containing disinfection by-product precursors.At chlorine dosing levels≥2 mg/L,algal cell rupture occurred and the fluorescence characteristics peaks and area volumes varied considerably.The chlorine dosage was better at 1 mg/L.The algal solution was found to be more effective at 1 mg/L.Under acidic conditions,the basic water quality parameters of the algal solution varied considerably compared to the control sample,allowing the oxidation of fulvic and humic acids.Acidic conditions produced more carbonaceous disinfection by-products and alkaline conditions produced more nitrogenous disinfection by-products,on balance,chlorine pre-oxidation produced fewer disinfection by-products at p H=9.The basic water quality parameters and fluorescence characteristics of the algal solution changed little when potassium permanganate was added at≤2mg/L.At lower doses of potassium permanganate there was a control effect on carbonaceous disinfection by-product precursors and nitrogenous disinfection by-products increased with the addition of potassium permanganate.Overall,the best removal of disinfection by-product precursors is achieved at a potassium permanganate dose of 0.5mg/L.When potassium permanganate was added at≥3mg/L,some of the algal cells ruptured and the basic water quality parameters of the algal night changed significantly,with a large increase in the total fluorescence volume and the peak intensity values of each characteristic peak.The fluorescence of humic substances increased and dissolved microbial metabolites decreased under acidic conditions.Carbonaceous disinfection by-products were least produced under neutral conditions and nitrogenous disinfection by-products were less produced under acidic conditions.Disinfection by-product precursors were removed most efficiently under neutral conditions.The efficiency of algal cell removal increased with the increase of ozone dosing,and ozone was more efficient than chlorine and potassium permanganate in removing algal cells.When the ozone dosage was≤1mg/L,the basic water quality parameters of the algal solution decreased to a certain extent;when the ozone dosage was≥2mg/L,the basic water quality parameters of the algal solution showed a trend of increasing and then decreasing under the combined effect of ozone oxidation and intracellular organic matter release.When the ozone dosage was≥mg/L,the basic water quality parameters of algal solution showed a tendency to increase and then decrease under the combined effect of ozone oxidation and intracellular organic matter release.As the ozone dosage increases,humic acid substances are degraded and dissolved microbial metabolites are released.The carbonaceous disinfection by-products increase as the ozone dose increases.In contrast,nitrogenous disinfection by-products show an overall trend of increasing and then decreasing with increasing ozone dosing,with ozone pre-oxygenation increasing nitrogenous disinfection by-products compared to control samples.Ozone pre-oxidation increased the concentration of nitrogenous disinfection by-products compared to the control sample.Under acidic conditions,ozone pre-oxidation was most effective in removing algal cells,and UV254 values and DON concentrations were lowest under acidic conditions;while DOC concentrations were lowest under alkaline conditions,due to the higher indirect oxidation capacity under alkaline conditions.Humic acid species and dissolved microbial metabolites had the lowest peak intensity values under neutral conditions and the highest under acidic conditions;p H had a greater effect on humic acid species and a smaller effect on dissolved microbial metabolites.Ozone pre-oxidation produced the highest levels of carbonaceous disinfection by-products under neutral conditions and the highest levels of nitrogenous disinfection by-products under alkaline conditions.