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Dynamic responses of the blanket in full-scale flat-bottom type floc blanket clatters at the PingTsan Water Works, Taiwan Water Supply Corporation. were monitored given a step-change in coagulant (polyaluminum chloride, PACI) dosage. The blankets in the clarifiers were easily washed out using the conventional coagulation-clarification process (the 'single-stage process'), seriously threatening drinking water quality. Consequently, the PingTsan Water Works included a pretreatment stage before the single-stage process to enhance treatment efficiency. The performance of this full-scale 'two-stage process' for treating high-turbidity storm water was monitored on November 9 to 10. 2000. The two-stage process achieved a stable blanket and good quality clarified water that was insensitive to variation in raw water turbidity or PACI dose. Pilot tests were also conducted on October 6 to 7, 2001 to reveal performance differences between the single-stage and two-stage processes in dealing with high-turbidity water. The single-stage process yielded a blanket that was sensitive to PACI change, Not only was the produced blanket easily washed out when the PACI dose was step-decreased, it was also slow to recover when the chemical dosage was returned to its original value. The blanket yielded by the two-stage process was more robust to low coagulant dose, and recovered more easily when coagulant supply was increased. Applying the two-stage process to achieve the same effluent quality from single-stage process could significantly reduce total PACI dosage. DOI: 10.1061/(ASCE)0733-9372(2004)130:12(1481) CE Database subject headings: Water treatment; Taiwan; Water distribution; Flocculation; Potable water; Water quality.

In this work we investigated the use of a short time, low superheat boiling process to treat biological sludge. The treated sludge would exhibit a deteriorated filterability, and a marked increase in soluble organics content. A large portion of extracellular polymers was released from the solid phase by boiling. The microbial density levels of the total coliform bacteria and the heterotrophic bacteria were reduced after treatment. Dilution in sludge concentration could allow more organic compounds to be hydrolyzed and a greater fraction of microbes to be disinfected when compared with the undiluted samples. DOI: 10.1061/(ASCE)0733-9372(2002)128:11(1100) CE Database keywords: Thermal factors; Activated sludge; Dewatering; Waste treatment.

An experimental program was conducted to investigate the rewetting characteristics of liquid flowing through multiple layers of screen mesh covering a heated vertical plate. Data obtained for acetone and R-11 were analyzed and compared with previously developed theoretical expressions for the rewetting velocity, the maximum liquid rise height, and the maximum heat flux for which rewetting could occur. The experimental results indicate that the thickness of the screen mesh layer and the liquid thermophysical properties are the most important factors affecting the rewetting behavior. As predicted by the theoretical model, small increases in the thickness of the screen layer initially caused the maximum permissible rewetting heat flux to increase. Once the layer thickness had reached a critical value, continued increases resulted in a decrease in the maximum permissible rewetting heat flux.

A study on rewetting velocity as a function of fluid properties, film thickness and the applied heat flux is presented. This experiment utilized thin, surface tension driven liquid films over heated plates. The equations developed for both flat and grooved plates were compared with data from previous investigations. Although good agreement was derived for low film velocities, significant deviations from the theoretical predictions on high velocities were reported.