Study On The Fate Of Nitrite In Drinking Water Treatment

According to the nitrogen contamination in surface and ground water, nitritebecame a problem of drinking water safety. Because there is no uniform standard ofnitrite in the drinking water standard of our country, so it's necessary to study the fateof nitrite in drinking water treatment for drinking water safety .Fist part of this thesis was about the study on the fate of nitrite in traditionaldrinking water treatment. The main results showed that NH₄⁺-N, NO₃^--N and NO₂^--Ndidn't change during coagulation and sedimentation. When using filter material fromdrinking water plants, NO₂^--N was produced during filtration. The NO₂^--N was notproduced from NO₃^--N by denitrification but from NH₄⁺-N by nitrosation with thehelp of microbiology. During filtration the decrease of filter velocity, the increase ofresidence time and the increase of filter depth would all lead to the increase ofNO₂^--N product. In the chlorination and chloramine disinfection, the concentration ofHClO was the primary factor which influenced the removal rate of NO₂^--N and ClO^-could not remove NO₂^--N. Chlorination could easily remove NO₂^--N with traditionalcondition. During chloramines disinfection, the decrease of pH, the increase ofresidual chlorine and chlorine-ammonia ratio would lead to the increase of HClOconcentration which could increase the removal rate of NO₂^--N.The second part of this thesis studied the transformation of inorganic nitrogenwith UV irradiation. In the reaction, the effects of different organics on the formationof nitrite were also studied and compared. The experimental results showed that withUV irradiation NO₂^--N could not be formed from NH₄⁺-N but could be formed fromNO₃^--N. The addition of organics could accelerate the formation of NO₂^--N. Theeffects of some organics on the formation of NO₂^--N could be showed as following:for the organics with same carbon chain, the sequence is alcohol>aldehyde>acid>ketone and more functional groups have greater accelerating effect;for the organicswith same functional group , longer carbon chain have greater accelerating effect;normal butyl alcohol>isobutyl alcohol>sec-butyl alcohol>tert-butyl alcohol. In theQSAR studies, the stepwire regression(SR) method was adopted to establish QSARmodel. The model was applicable to most of the organics in the experiment, and wasnot well applicable to acetone and chloroacetic acid. Two molecular descriptorswhich were used in the model were energy of the highest occupied molecular orbital(EHOMO) and heat of formation (HF). According to the model, the acceleratingeffect of organics on the formation of nitrite mainly depended on the EHOMO of theorganics.Since there are problems of low removal efficiency or increase of nitrite in thedrinking water treatment and there is no standard for nitrite in our drinking waterstandard, the result of this thesis can help to ameliorate the water standard andtechnology of water treatment.