This study is conducted in order to find more improved solidifying effects than the former converter slag solidification technology. The converter slag is used as a solidifying agent, and the quick lime and the gypsum are used as solidifying aids. Several tests are performed for the purpose of investigating the solidifying effects and the applicability of the solidified sludge as a daily or intermediate landfill cover. The unconfined uniaxial compressive strength, pH and leaching of heavy metal are investigated. In the case of using both quick lime and gypsum as solidifying aids, the compressive strength of specimen has significantly increased that of specimen which used quick lime only. The compressive strength of each specimen cured for 7 days which is mixed with quick lime and gypsum as mixing ratios 7:1, 5:1 and 3:1 are $0.59kg/cm^2$, $1.18kg/cm^2$, and $1.25kg/cm^2$, respectively. The results of all the leaching tests of specimen cured for 7 days show that the concentrations of leachate heavy metals(Cu, Pb, Cd and $Cr^{6+}$) are lower than the Korea toxic waste criteria. The microstructure analysis by SEM shows that needlelike crystals appear as the solidification proceed. The analysis of these crystals by EDS confirms that these main components are Ca. Si etc. Also, XRD analysis shows that the main solidification products are CSH and Ettringite; in addition, $Ca(OH)_2$ CAH are observed. When the added gypsum is used as a solidifying aid, more improved solidifying effects are obtained and the solidified sludge may be appropriately used as a daily or intermediate landfill cover.

The operation of flocculation process and the evaluation thereof have been mainly based on G, t and $G{\times}t$ values which are available from design guidelines and texts. However, their suggested ranges are too wide to find the optimum condition specific to a particular water treatment plant and none of the existing method can be used to evaluate and suggest the optimum operational condition. Recently, a commercially available particle counter is found to be useful in determining the flocculation process based on the particle dynamics. The optimum condition is defined as one that best suits the purpose of flocculation; the number of small particles should decrease, while that of large particles should increase. The experiments were performed at two conventional water treatment plants in Korea, one with horizontal mechanical flocculators, and another with vertical type mechanical flocculators. In this paper, experiences to evaluate the flocculation process and to suggest the optimum operation condition will be presented. Although particle counting method is found to be beneficial compared to any other existing methods, the optimum condition is very much site-specific and should be evaluated at each water treatment plant for different conditions.

Sludge production from water treatment plants is increasing each year because water resources deterioration is proceeding and water supply facilities are growing due to water demand increase. Water treatment plant sludges can be modified to soil cover in sanitary landfilling site through the lime treatment and other alternatives. The compression strength of $1.0kg/cm^2$ is necessary for the dozer operation on soft son cover material at municipal landfilling site. Modified sludge was experimentally produced in this study with lime, bentonite, loess, and activated loess dosing. X-ray diffraction patterns of the limed water treatment plant sludge confirmed the presence of calcium carbonate and ettringite. Unconfined compression strength properties of modified sludges showed material property improvement applicable for soil cover alternatives. When adding 20-30% activated loess to water treatment plant sludges. the modified sludges could reach the compression strength for cover soil after 7 days solidification reaction, but decrease of compression strength was intentioned in 28 days reaction period. Solidification effect of the modified sludge with activated loess was observed through the scanning electron microscope.

In order to compare the effect of water quality on two service systems, tank and direct connection service, we selected randomly 30 rooftop tanks installed in the buildings with five or fewer floors, and collected water samples from each tank as well as tap water by direct service. At the same time each tank was investigated on their cleanliness and sanitary control. 30 water samples from direct service met Korean Drinking water quality standard. But 5 tank water samples(17%) were not able to meet Coliform or Total Colony Counts standard and free chlorine of 12 tank water samples(40%) were less than 0.2mg/L. Also Fe, Turbidity, TOC, Total Algae in tank water were higher than tap water on direct service. We concluded that thorough health control of water tank is necessary and conversion into direct connection service results in improving tap water quality importantly.

In water treatment plants, open channel is used to distribute incoming flow to parallel treatment unit, such as flocculation basin and sedimentation basin. These control devices must be designed so that the incoming flow evenly distributed to the process unit. this is important in the view of optimizing process unit. In the recent past. significant insights into the sedimentation process have been developed. In this study, the 2-D computer program is developed to investigate fluid flow field and velocity vectors in flocculation sedimentation inlet distribution weir and calculate flow rates in each inlet weir. The specific purpose of this study is to analyze physical design factors, such as now rates, shape of channel, tapered angle in tapered type channel and main channel width.

Techniques such as dissolved air flotation and electroflotation, which utilize micro bubbles, are increasingly used for water and wastewater treatment. Most studies have concentrated on particle characteristics. Pretreatments that manipulate particle size and zeta potential were considered important. A recent study, which modeled the collision mechanism between micro bubbles and particles in dissolved air flotation, suggested bubble characteristics should also be important. Hydrogen micro bubbles were generated electrolytically and their zeta potentials measured under various conditions using a novel electrophoresis method. Effects of several parameters were investigated. Bubble zeta potentials were found to be pH dependent, and to have a negative value around neutral pH, becoming zero or positive at lower pH. The pH at zero zeta potential was 5.0 under study conditions. Using artificial solution and tap water, at fixed pH, bubble zeta potentials varied with solution composition. Zeta potentia]s of bubbles were affected by the types of cations and anions in solution but not by the voltage applied. These findings will help improve efficiencies of particle removal processes that utilize micro bubbles. As bubble zeta potential varies with solution composition, it needs to be measured for each composition to understand those effects, which increase removal efficiency.

Powdered activated carbon(PAC) is widely used to control 2-MIB와 geosmin causing earthy-musty odor in water supplies. It was known that chlorine is one of the chemicals often come into contact with activated carbon. But activated carbon react with chlorine and surface oxide accumulate on carbon surface. As result, adsorption capacity of activated carbon is reduced. To investigate the effect of chlorine on the PAC's ability to adsorb 2-MIB and Geosmin, a series of experiments was carried out to show (1) the effect of aqueous chlorine doses on the ability of PAC to adsorb 2-MIB and Geosmin from Lake Heodong water. (2) the effect of delaying the chlorine addition after PAC had been added (to simulate the effect of using an alternative point of chlorine addition). As a result of experiment, as chlorine dose increased correspondingly decreased the capacity of activated carbon to adsorb 2-MIB and geosmin. Even though previously adsorbed 2-MIB and geosmin released, as result of the application of delaying the chlorine adding was more beneficial than simultaneous adding chlorine with PAC.