SETTLING CHARACTERISTICS OF INDUSTRIAL SLUDGES

Abstract

Sedimentation is one of the most widely used unit operations in wastewater treatment, specifically in the case of sludge thickening. Design of a sludge sedimenta-tion tank is of pr nfluence the perfonnance of the entire treatment plant. For proper and efficient designing of sedimentation tanks, a study of the settling characteristics of the sludges becomes essential. In the present work studies on settling characteristics of three different sludges were carried out. The three sludges studied were phosphogypsum sludge from the phosphate fer- tilizer industry and `t,■.&,. sludge from the phosphate fertilizer industry and sugar mill sludge from the sugar industry. Extensive column settling tests were carried out with the three sludges. With the phosphogypsum sludge, four batch settling tests were done with initial SS concentrations of 83.3 mg/cc, 50mg/cc, 30mg/cc and 20mg/cc. With the lime sludge, the initial SS concentration were 58.67 mg/cc, 50mg/cc, 41.67mg/ cc and 33.33 mg/cc. With the sugar sludge, three batch tests were done with initial SS concentration of 146mg/l, 200ing/1 and 240mg/l. From the experimental data, settling characteristic curves were then used to develop families of curve between overall per-centage removal Vs. overflow rate and overall percentage removal Vs. retention time. From these curves, three simple models were then evolved for the three different slud-ges which correlated the overall percentage removal with the overflow rate and the initial suspended solids concentration, which are two important parameters required for the rational designing of sedimentation tanks.