Preoxidation And Enhanced Coagulation For The Water From The Miyun Reservoir

Miyun reservoir is the main source of drinking water for Beijing; however, the quality of this water has been deteriorated in recent years, resulting in the trend of eutrophication and the increase of the concentrations of organic compounds. In order to meet the requirements of the stringent water quality of Beijing Olympic Games in 2008, and to deal with the latent problems caused by the South to North Water Division Project, related research is necessary to improve and modify the current technologies of water treatment. Disinfection by-products (DBPs) badly impact the security of drinking water. Ozone oxidation and enhanced coagulation are two kinds of important techniques to control DBPs. The technology of ozone oxidation and enhanced coagulation to treat the water from Miyun reservoir is studied in the dissertation.The source water of Miyun reservoir is investigated, especially in the aspects of polarity and molecular weight of organic matter. The apparent molecular-weight (MW) distribution of DOC by ultra-filtration method (UF) showed that DOC less than 1k Dalton has the largest percent in the total DOC of the raw water, corresponding to average 48%. The resin fractionation showed that hydrophobic acids (HoA) and the hydrophilic matter (HiM) are the main components in the DOC of the raw water, which account for 40% and 45% DOC respectively. The chemical fractional character of DOM changes not half with the seasons, which indicats that the fractional characterization of organic matter in the water is stable with the time changing. The research on the UV absorption capacity of fraction showed that HiM and HoA have strong UV absorption capacity.Through jar tests and pilot tests aiming at Miyun reservoir water quality, major operation parameters were obtained which including the use of HPAC as optimum coagulant, increasing of coagulant dosage and pH control. The function about electric charge neutralization and adsorption and bridging of HPAC is significantly better than the Polymeric Aluminium Chloride and the traditional flocculant of ferric chloride. HPAC is not only strengthened the ability of Alb which can make the particle pollutants of water destabilization, but also improved the separation ability of flocs. Basicity (B) and pH significantly affect the hydrolysis patterns of PAC1, thus affecting the coagulation effect.Preozonation process can significantly reduce the turbidity value and particles number of the sand filter effluent. Ozone can kill E. coli effectively, and the removal efficiency is as high as 95%. Preozonation process has a positive impact to improve the water quality, which can reduce the probability causing safety hazards. Compared withconventional technology, preozonation process could greatly improve removals of COD_Mn, UV₂₅₄ and THMFP, but has at the same time also brought negative effect on removal of DOC. In addition, preozonation could reduce the increasing rate of head loss of the sand filter; therefore, preozonation process has the important acceptation to improve net water production rate and lower operating costs.