Study On Preoxidation Applied For Drinking Water Treatment In Tianjin

In Chinese north cities, more than 70% of drinking water resource is surface water which has been seriously polluted by organic matters and algae. As a result, the conventional treatment processes can't guarantee the safety of drinking water, which makes advanced and efficient tretment techniques necessary. The quality of Tianjin resource water varies greatly with seasons and often worsens abruptly. The characteristic of Tianjin resource water is typical in north China. In this study, preoxidation applied on Tianjin resource water during different water quality periods was conducted to intensify the conventional treatment processes, enhance removal efficacy of organic matters and improve the quality of drinking water.The preoxidation by three chemicals, such as potassium permanganate, chorine and ozone, and its influence on the subsequent processes were analyzed. The results showed that proxidation could improve the quality of the water after followng treatment processes. As to Luan River water in Summer Period, after preoxidation by potassium permanganate, part of organic matters were removed and the amount of organic matters in the water after air-flotation and sand-filtration were reduced significantly. However, although prechlorination efficiently removed algae, its effect was directly related to the quantity of algae and was more obvious in the period of algae bloom. With regard to Yellow River water in winter with low temperature and low turbidity, it was discovered that preozonation did not result in a substantial removal of total organic carbon (TOC), but a remarkable UV254. It was further revealed that preozonation changed the characteristics and structure of organic matters and then enhanced removal efficiencies of them by subsequent processes.The effects of potassium permanganate, chorine and ozone were compared and theresults showed that although all of them could enhance coagulation and then reduce the turbidity of the water after subsequent treatment units, potassium permanganate and ozone were more effective to ensure the quality of the water after air-flotation and sand-filtration. High-performance liquid chromatography (HPLC) analyses demonstrated that all of these three chemicals could change organic matters in the water into those with lower molecular weight. Gas chromatography-mass spectrometry (GC-MS) analyses showed that both potassium permanganate and chlorine could oxidate the organic matters with unsaturated functional groups into those with carboxyl, hydroxyl and aldehyde. And it was further revealed that after preoxidation by potassium permanganate, the sorts of organic matters were reduced remarkably, however, chlorination leaded to increase of the sorts of orgnic matters and brought some chloro-organics such as chlorobenzene, chlorophenol, and trichloro-ethane.