Investigation of geometric properties of media particles and operating conditions on floating media filtration

Abstract

Filtration is an effective process in removing particles that are present in water. Floating medium filter has been used in direct filtration because of its flexibility, cost savings gained by less land requirements, and less water and energy required for backwashing. The aim of this work was to investigate the effect of geometric properties of a floating medium in upflow filtration mode. A pilot plant was designed and constructed to evaluate the filtration process. Effect of physical parameters on filtration performance was also investigated. The experiments were carried out using a commonly available polypropylene floating medium. Four median grain sizes (2.28, 3.03, 3.30, and 4.07 mm) of polypropylene plastic pellets were used. Two media shapes (cubic and disc) were evaluated. Bentonite (250 mg/L ≈ 60 NTU) was used to make up the raw feed water. Three parameters that could influence the filtration performance were identified, namely: filtration velocity, media depth, and coagulant dose. The results showed that the best conditions to remove turbidity were found to be: low filtration rate (36.8 L/m2 min), longer media depth (600 mm) and optimum coagulant dose (23 mg/L). The results also indicated that the smaller plastic medium (2.28 mm) was more efficient in terms of turbidity removal than the larger medium. However, headloss development associated with smaller media was higher (109 mm of water) than that associated with larger medium (42 mm of water).