Optimization of Solid/Liquid Separation Processes Using Particle Size Distribution Analysis

Abstract

A study was conducted to investigate the influence of the coagulant dosage, suspension pH, mixing intensity and time on the suspended solids particle size distribution during coagulation, flocculation and filtration of dilute suspensions. The coagulation/flocculation investigation consisted of laboratory experiments utilizing the jar test apparatus as well as a pilot plant mixing tank. Filtration experiments were conducted using 3-six inch inside diameter glass columns with different media sizes. The data generated were used to compute the distribution slope of the particles in each sample. The distribution slope was used as the pretreatment performance indicator. The distribution slope is influenced by both chemical and physical treatment parameters and it can be used in the treatment of dilute suspensions to optimize the coagulant dosage, mixing intensity, and mixing time. Both the total number of particles and the distribution slope of flocculated suspensions were found to follow a second order polynomial equation due to floe breakage after the optimum mixing time. The coagulant dosage was found to affect both the head loss development and the effluent quality of granular media filters. The mixing intensity and time were found to influence mostly the head loss development and not the effluent quality. The effluent quality improved with the increase in the coagulant dosage and mixing time and deteriorated with the increase in the mixing intensity. The filter's effluent particle size distribution was influenced by both the influent particle size distribution and media size. Fine media was sensitive to the influent changes whereas coarse media showed much less sensitivity to changes in the influent characteristics.