The Study On The Origin Of The Nitrite In Waterworks And Control

According to the nitrogen contamination in surface and ground water, nitrite became a problem of drinking water safety. Though the nitrite concentration was limited in the last standards for drinking water quality in our country, it was just a reference. It's still necessary to study the fate of nitrite in drinking water treatment for drinking water safety.First part of this thesis was about the study on the occurrence and changes of NO₂^--N in the drinking water distribution system. The main results of the experiment showed that the NO₂^--N concentration hadn't been raised by simulating pre-chlorine disinfection. Keeping a dosage of the residual chlorine could make the NO₂^--N concentration stabilize at a low level. The supposition of nitrification existing in water pipeline was proved. It was found that the amount of nitrite-oxidizing bacterium had been far larger than that of ammonia-oxidizing bacterium. The factors making nitrite-oxidizing bacterium become a dominant species included the temperature, pH, ammonia, residual chlorine etc.The second part of this thesis was about the experiment in the removal of the NO₂^--N in raw water from the fifth waterworks in Xi'an. The removal efficiency of the NO₂^--N was researched by using different general oxidants such as chlorine, potassium permanganate, chlorine dioxide, and the synergistic treatment of chlorine and potassium permanganate. The sequence of those chemical agents' removal rate on nitrite from high to low respectively was chlorine dioxide, the synergistic treatment of chlorine and potassium permanganate, chlorine and potassium permanganate. The respective optimal dosages were 3mg·L^-1, 2+2mg·L^-1, 6mg·L^-1 and 3mg·L^-1. The increase of pH value made the removal rate decrease. However, pH value had little influence on the removal effect of chlorine dioxide and the synergistic treatment of chlorine and potassium permanganate. Reaction time also had little influence on the removal because the oxidation reaction carried out quickly, and most of the NO₂^--N was oxidized in the first 0.5h. The result of the experiment showed the removal effect of using the synergistic treatment of chlorine and potassium permanganate was better than that of using both respectively.In respect that there were problems of low removal efficiency or increase of nitrite in the drinking water treatment, the result of this thesis can help to ameliorate the water standard and technology of water treatment.