Research Of Urban Reclaimed Water For Chlorine Disinfection Experiment

At present, the shortage of water resources is increasingly serious. The reuse of urban reclaimed water is an effective way to ease water pollution, save fresh water, and solve the water shortage. The key problem is the safety of reclaimed water quality, of which disinfection is the precondition. Disinfection can kill the pathogenic microbes, prevent the dissemination of epidemic disease, and guarantee the security of water quality. However, there are fewer researches about the disinfection of reclaimed water, the disinfection theory mainly focuses on drinking water, and this may lead to an unsatisfactory disinfection effect. Combined with the actual problem of chlorine dosage unstable in production, this paper used NaClO instead of chlorine as the disinfectant to do laboratory experiments. The study have determined the chlorine dose under different conditions, analyzed influence factors for chlorine decay, established chlorine decay model, and studied thecharacteristics of disinfection by-products, THMs and HAAs, the HAAFP for different molecular weight organic.Results show that ammonia nitrogen is the main factor for the unstable chlorine dosage. According to the experiment results and the chlorination break point curves, the water samples can be classified into four kinds as the difference of ammonia nitrogen to discuss the relationship between chlorine and ammonia nitrogen: when CNH3-N<1mg/L, the Cl/N for peak point is between 4.2~5.2, for break point is between 6.5~8.3, and a chlorine dose of 7mg/L may be fit for both winter and summer in case of unforeseen circumstances; When 1mg/L≤CNH3-N≤2mg/L, a chlorine dose of 4mg/L may has a good fit no matter in winter or summer; When CNH3-N>2mg/L, in order to attain a perfect result for chlorination, while consider the effect of residence time, we make the chlorine dose of 3mg/L for winter and 5mg/L for summer as the best result.A model to predict chlorine demand has been developed, the decay process use t=30min as the boundary, first-order decay model for the second interval. According to the residual chlorine(Ct) that calculated from the decay model and the initial chlorine dose(C0), the chlorine demand will be forecasted. The effects of initial chlorine dose, TOC, temperature and ammonia nitrogen for chlorine decay have been studied with the experimental datas were fitted with first-order decay model. Results indicate that the decay rate has a negative correlation with initial chlorine dose and ammonia nitrogen, and a positive correlation with TOC and temperature, and the influence of temperature on the decay rate can be described with Arrhenius equation. In addition, the disinfection way has been changed to optimize the disinfection process and the way that first ammonia nitrogen and then chlorine has the best effect.The analysis method of THMs and HAAs has been established using the liquid extraction. The factors affecting the kinds of DBPs have been study. The main types of HAAFP in reclaimed water are DCAA and TCAA, and the most of HAAFP is formed by the organic whose molecular weight<4KDa. Water samples from different water treatment processes have different HAAFP in different organic molecular weight interval. At last, the paper introduce some methods to control disinfection by-products, by removing precursor or changing disinfection way.