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Objective & Scope
1. Evaluate of adsorption performance of Zeolite 2. Evaluation of Airlift BZ system 3. Evaluation of Airlift BAC system Main Contents The quality of surface water is worsening due to the increase of wastewater containing various pollutants discharged from industrial and domestic sources. It was now almost impossible to satisfy the stringent drinking water standards by using a conventional water treatment system (CWTS) which consists of coagulation, sedimention, sand filtration and chlorination. In contrast, the demand for clean and pleasant water is increasing according to the improvement of living conditions. Recently, an advanced water treatment system (AWST) centering around the ozone treatment and biological activated carbon (BAC) filtration has been developed to remove recalcitrant dissolved organic and inorganic compounds by oxidation and adsorption. The AWTS is also proved to be very effective in removing precursors of carcinogenic trihalomethane (THM) compounds which are formed during the chlorination process in the conventional water treatment system. However, the AWTS with ozone and BAC also has limitation such as the low removal efficiency of ammonia from the raw water especially upon seasonal or external shock loading. In this study, a novel AWTS was developed with the special object of removing ammonia more efficiently compared to the previous conventional AWTS. In the new AWTS, an additional filtration column packed with granular zeolite was installed prior to the BAC column in order to remove ammonia by adsorption onto zeolite. The ammonia adsorbed onto zeolite via ion-exchange with sodium ion was then oxidized and desorbed by nitrifying bacteria grown on the surface of zeolite. However, large amount of oxygen is required for the biological nitrification but the conventional packed-bed column cannot satisfy this requirement. Therefore, an air-lift system was designed to increase the oxygen supply for both of zeolite and BAC columns where the heterotrophic bacteria also required considerable amount of oxygen for the removal of dissolved organic carbon (DOC) including THM precursors adsorbed on BAC. The distribution of microorganism population was measured by MPN method and it was found that heterotrophs occupied most the surface of BAC while nitrifiers covered that of zeolite. This phenomena could be deduced from the fact that the BAC adsorbs DOC while zeolite adsorbs ammonia. The total amount of biomass attached on the zeolite was far less than BAC since the surface area of zeolite available for the bacterial growth is far less than BAC which has many macropores available for bacterial growth. However, the amount of nitrifying bacteria on the zeolite particles was enough to completely oxidize up to 5 mg/L of ammonia in the raw water. References 1) Development of novel advanced water treatment system by biological processes Kyu Kap Cho, Thesis of Master (1998), POSTECH, KOREA Related Patents 1) Reactor system with multi-layer matrices immobilized by microorganisms and its application to drinking water treatment J.M. Park and S.L. Lim, Korea Patent (1999) |
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