Updated: July 2002

1. Outline of the Rapid Filtration Equipment

The rapid filtration method is one of the basic water treatment methods and is widely used for various treatment. It includes various types such as up flow, down flow, immobilized bed, mobile bed, gravitational systems and pressurized systems, and has merits and demerits depending on the processing scales and applications.
Among these systems, the up flow filtration is frequently used as it is excellent at an appearance because the treated water spouts onto the visible filter layer.

2. Outline of the Up Flow Filtration Equipment

The up flow filtration equipment filters the water upward through the filter layer and hence the turbid matter is captured at the lowest part of the filter layer which is naturally the part very difficult to be washed. Thus, washing is a serious problem. There-fore, the water-collecting and dividing device at the lower part needs to be contrived where raw water is divided, washing water and washing air are blown. For the purpose, the perforated block is equipped with an air pipe, as shown in Fig.1. The perforated block is of the extremely low pressure loss type and so the washing can be performed by a level of washing water higher than the level of the filtration level which is approximately same as the raw water level by 3m, as shown in Fig.2.
Usually, in a filtration equipment a number of large diameter automatic valves are needed, but the present equipment used syphons in place of them. The standard filtering velocity is 200 to 300m/d.

Fig.1 perforated block equipped with air pipes

Fig.2 fundamental flow diagram

3. Features

1) As it uses syphons in place of large diameter valves, it is simple in structure to cut the equipment cost and the maintenance cost.
2) In the case the washing can be performed by natural flow-down, the washing pumps is unnecessary to make the equipment very simple.
3) As a perforated block of the low pressure loss type is used in the water-dividing device, the structure is simple to decrease the height of the filtration tank.

4. Washing Method

To wash the up flow filtration equipment, some ideas are necessary as the most dirty part of the filter layer is at the bottom, the most difficult part to be washed.
Fundamentally, the following method is adopted.

(Water discharge -> Air washing -> Water discharge -> Air washing -> Water filling -> Air washing -> Water washing)×2 or 3 Repeated.

5. Filter Layer Constitution

The constitution of the filter layer is as follow as a rule.
Sand layer (1-2mm diameter) : 150cm thick
Gravel layer, upper layer (3-5mm diameter) : 45cm thick
Middle layer (8-12mm diameter) : 15cm thick
Lower layer (40-50mm diameter) : 15cm thick