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

2015) Impact of loading rate and filter height on the retention factor in the model of total coliform (TC) removal in direct rapid sand filtration, Desalination and Water Treatment, 54:1, 140-146, A B S T R A C TAs 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.

The effect of high hydraulic loading rate on the removal efficiency of a quadruple media filter for tertiary wastewater treatment

“…In this study the removal efficiency of the top (anthracite) layer decreased quickly from 58 to 40% between 5 mh -1 and 10 mh -1 , a reduction of 3.5 %m -1 h (Figure 2c), a value similar to the literature values seen for a single media filter (4.4 %m -1 h in Li et al (2012) and 3.9 %m -1 h in Yu et al (2015)). The quicker change in removal efficiency across a single layer such as may be seen in conventional sand filters may be one of the key reasons why there has been reluctance to increase HLRs in conventional mono-media filters.…”

“…The average effluent turbidity increased from 1.9±0.1 NTU at 5.0 mh -1 to 6.8±0.5 NTU at 62.7 mh -1 ; resulting in removals of 80 and 40% respectively for the quadruple filter ( of 35 NTU when the HLR changed from 5 to 10 mh -1 (Li et al, 2012). A separate study saw reductions of 3.9 %m -1 h for an initial turbidity of 10 NTU when the HLR increased from 5 to 15 mh -1 (Yu et al, 2015). In an anthracite-sand dual-media filter removal reduced by 1.25 %m -1 h for an initial turbidity of 6.5 NTU and the HLR increased from 12.2 to 24.4 mh -1 (Williams et al, 2007).…”

The impact of filter bed depth and solids loading using a multimedia filter

“…More stringent discharge requirements for treated wastewater has become ever more important to improve water quality. In addition, the growing demand for water reuse in water stressed regions has driven the need for tertiary treatment of wastewater [1][2][3]. There are many different forms of tertiary treatment of wastewater, of which granular media filtration is a common choice due to its simplicity and its historical performance in drinking water treatment systems [3][4][5][6].…”

“…In addition, the growing demand for water reuse in water stressed regions has driven the need for tertiary treatment of wastewater [1][2][3]. There are many different forms of tertiary treatment of wastewater, of which granular media filtration is a common choice due to its simplicity and its historical performance in drinking water treatment systems [3][4][5][6]. However, the process design of granular filters is challenging as it involves a trade-off between various factors, such as the type and size of the filter media, the depth of media, the hydraulic loading rate, the headloss through the filter bed, the backwash hydraulics as well as the solids loading rate [7][8][9].…”