Study On The Degradation Of Indole And Indole-like Nitrogen-containing Pollutants In Water By Ozonation

Indole compounds have been detected in the effluent of coking wastewatertreatment plant and wastewater treatment plant, and some natural water which waspolluted by domestic wastewater. As a kind of disinfection by-product precursors, theyhave high potentials of formating nitrogen-containing heterocyclic disinfectionby-products and chlorinated disinfection by-products. The researches about indolecompounds was focused on the synthesis of new materials, while the removal of indolecompounds got little attention.Four typical indole compounds, indole,3-methylindole, L-tryptophan and gramine,were investigated and the detection methods for single and mixed form were establishedin the study. The effects of ozonation on these compounds by separate and mixed formwere studied. The removal effect of ozonation on indole and3-methylindole oxidizationwas studied and the related rate constants were measured. The reaction rate constants ofmolecular ozone and overall reaction rate with indole and3-methylindole weredetermined. The pH value, the condition of water quality, water temperature andhydroxyl radical inhibitor were also taken into consideration for indole and3-methylindole in this study.The p（[O₃]₀/[M]₀） was used to describe the removal efficiency. The relative rates ofozone oxidation of these four compounds were compared. The removal was increasedwith the increase of p. The best mole ratio on removal of various compounds wasp=0.42（indole）, p=0.52（L-tryptophan）, p=0.74（3-methylindole） and p=1.04（gramine）,respectively. The order of these four compounds mixture in water degradation byozonation was3-methylindole, indole, L-trp, gramine.The kinetic rate constants for indole and3-methylindole degradation by molecularozone was k^In_O3=77.30L/（mol·s）,k^3-MIn_O3=833.30L/（mol·s）. The overall reaction rateconstants of indole and3-methylindole were103orders of magnitude and it was lessaffected by the concentration of·OH with the pH range of6.5to8.0. Through the studyof pH in the reaction system, it was found that the removal ratio was decreased with theincrease of pH, which proved that the direct reaction of ozone molecule was dominatedin all reactions. The addition of hydroxyl radical inhibitor only decreased the reaction efficiency a little, which proved that though·OH took part in the reaction, but thecontribution for the removal is little. There were both promotion and inhibition for thereaction when improving the temperature. The law of removal rate was not clear withthe temperature range of5℃to35℃. The compounds in tap water and raw water fromSonghua River were competitive with target compounds for O3, which could reduce theremoval efficiency.It was illustrated that ozonation could remove aqueous indole compoundseffectively.