Impact of loading rate and filter height on the retention factor in the model of total coliform (TC) removal in direct rapid sand filtration

Abstract

As a promising technology for wastewater reuse, direct rapid sand filtration has been widely used throughout the world, especially in arid developing and emerging countries. Retention factor describing the equilibrium between retained and mobile total coliform (TC) bacteria plays an important role in the model of TC removal in direct rapid sand filtration. Little attention has been given to the relationship between retention factor and loading rate as well as filter height, two critical parameters impacting retention factor. Therefore, the influence of loading rate as well as filter height on retention factor was discussed. Results showed that retention factor decreased dramatically with loading rate ranging from 9 to 15 m/h, but increased slightly as loading rate ranged from 5 to 9 m/h, which is a little different with the variation of suspended solids and total phosphorus removal efficiency. Retention factor decreased significantly with filter height of 0–30 cm and 120–150 cm, but reduced uniformly with filter height of 30–120 cm. It was deduced that the optimum loading rate and filter height may be 9 m/h and 90–120 cm, respectively. Increasing flocculant could overcome retention factor reduction resulted from higher loading rate or smaller filter height.

Keywords:

• Direct rapid sand filters
• Filter height
• Flocculant dose
• Loading rate
• Retention factor
• Total coliform (TC)

Acknowledgments

The study was financially supported by the research fund provided by the Major Science and Technology Program for Water Pollution Control and Treatment (2012ZX07506-002-2), Jiangsu Environmental Monitoring Research Fund (20121105), and Foundation of Key laboratory of Environmental Engineering of Jiangsu Province of P.R. China (KF2012002).