Study On The Recognition Of Nitrogenous Disinfection By-products Precursorsand The Control Mechanism By Pre-oxidation In High Algae-containing Water

The occurrence of dissolved organic nitrogen in drinking water and formation of chlorined N-DBPs have been becoming a focus of people’s concern. The eutrophication of water bodies is still serious in our country,causing the vigorous growth of algae and the release of alage organic matter. Alage organic matter was indicated rich in organic nitrogen, containing the main precursors of N-DBPs. In this study, releae of algae-derived precursors of N-DBPs and change of structure have been studied; impacts of pre-oxidation process by chlorine, potassium permanganate and ozone on water quality parameters of AOM and the formation of N-DBPs and 1,1,1-TCP have also been studied.DON concentration of EOM shows a growing tendency during the growth of Microcystis aeruginous, the yield of which is less than 0.05 mg DON per 107 cells in the early groeth phase, around 0.40 mg DON per 107 cells in the late growth phase, respectively; molecular weight distributions of EOM during exponential phase and decline phase mainly concentrate in range of less than 1 k Da and more than 100 k Da, while organic matter less than 30 k Da dominating EOM in stationary phase;molecular weight distributions of IOM concentrate in range of more than 1 k Da and less than 100 k Da in the three phases. The main fluorescence regions of EOM occur at the fluorescence region of humic acid-like materials and soluble microbial products. By contrast, the region of aromatic proteins and soluble microbial products dominate the main region of EEM spectra of IOM. The components order of EOM of algae in the decline phase is hydrophilic organic matter> strong hydrophobic organic matter> weak hydrophobic organic matter, and the formation potential order of N-DBPs is strong hydrophobic organic matter> weak hydrophobic organic matter> hydrophilic organic matter. For IOM, the components order is strong hydrophobic organic matter> hydrophilic organic matter> weak hydrophobic organic matter, and the formation potential order of N-DBPs is hydrophilic organic matter > strong hydrophobic organic matter> weak hydrophobic organic matter.No siginificant destruction of alage cells and change of fluorescent characteristics of EOM have been found during pre-chlorination of alage suspensions under low dosages; when the chlorine dosage comes to 2.10 mg/L, destruction of some algae cells occurs, and there appear two remarkable fluorescence characteristic peaks at the region of humic acids-like compounds. Pre-chlorination in the acidic condition causes the release of IOM,at the same time, it can also remove parts of humic acid-like organic compounds. Total N-DBPs precursors decrease when the dosage of chlorine is low,and a slight increase with the high dosage. With the increase of the dosage of chlorine, TCAN precursors are controlled wel, but precursors of DCAN and 1,1,1-TCP increase. More TCNM and TCAN, fewer DCAN precursors are produced in the acidic conditions; 1,1,1-TCP precursors of the TCP decrease with the increase of p H.No siginificant destruction of alage cells and change of fluorescent characteristics of EOM have been found during pre-chlorination of alage suspensions when the dosage of potassium permangenate is less than or equal to 3.95 mg/L; when the dosage of potassium permangenate comes to 10.31 mg/L, destruction of some algae cells occurs, and there appear two remarkable fluorescence characteristic peaks at the region of humic acids-like compounds. The formation of nascent Mn O2 in the neutral condition improve the performance of settlement of alage cells; the pre-oxidation of potassium permangenate in the acidic and alkaline conditions has little effect on the removal efficiency of algae cells. The rate of change of fluorescent characteristic values from more to less is acidic condition> neutral condition> alkaline condition. Total N-DBPs precursors decrease when the dosage of potassium permanganate is low,of which precursors of TCAN can be well controlled,precursors of DCAN,TCNM and 1,1,1-TCP,however,increase; Precursors of total N-DBPs increase about 11.5% when algae suspension oxidized by potassium permanganate of high dosage, of which the precursors of TCNM and 1,1,1-TCP increase significantly. Formation of total N-DBPs precursors from more to less is neutral condition> alkaline condition> acidic condition. More DCAN, fewer TCAN and 1,1,1-TCP precursors are produced with the increase of p H; no significant change of precursors is found with different p H values.Pre-oxidation of algae suspension by low dosage of ozone has certain control of total N-DBPs precursors, the reason of which is that ozone can convert some nitrogenous organic matter into carbonaceous organic matter. In that case, precursors of TCAN and DCAN decrease, but that of TCNM and 1,1,1-TCP increase. N-DBPs and 1,1,1-TCP precursors have increased significantly with the increase of dosage of ozone. Algae removal efficiency is relatively the best in the acidic condition, at the same time,UV254, DOC have increased with the increase of p H value, though the change is not very significant. Less of humic acid-like compounds form with the increase of p H value; ozonation can degrade the SMPs-like compounds with little effect of p H value. TCAN, DCAN precursors have decreased with the increase of p H value; precursors of TCNM after oxidation by ozone in the alkaline condition and 1,1,1-TCP precursors in the neutral oxidation condition are produced the most.