AWWA JAW50173

Design criteria were developed for nonmechanical dewatering of water treatment residuals. First, certain physical properties were determined for residuals high in alum, ferric chloride, or polyaluminum chloride, Laboratory tests that characterized these properties showed that capillary suction time and time to filter correlated very well; either could be used in the laboratory to test residuals' drainage characteristics. Pilot- and full-scale evaluations at five utilities followed. Drainage characteristics predicted by pilot tests using 2-in.-(50-mm-) diameter columns and measured in full-scale sand drying beds correlated closely. This work showed that pilot tests can allow good prediction of full-scale performance and, thus, the development of useful design parameters. Three models illustrate the proper sizing of sand drying beds, solar drying beds, and dewatering lagoons. These models allow a utility to determine the area required for each dewatering method on the basis of pilot data, local climatological data, and - most important - monthly residuals production. This article presents the test procedures and modeling required for utilities to size and design nonmechanical dewatering systems. Includes 3 references, tables, figures.