Updated: July 2002

1. Outline of equipment

Multi-module Uniflo sand filter is one that is scaled up to handle larger amount of water while retaining the features of Uniflo sand filter. Approximately 1,500 units of the latter are already in use in Japan. The multi-module type has been adopted as high-grade equipment in advanced sewage treatment facilities and lake-water purification plants where a large volume of water is treated.
The basic principle is similar to that of conventional Uniflo sand filter. The raw water flows upward as the solids are removed, and comes out as clean filtrate. The sand that catches the solids is sucked up by the air lift pump from the bottom, and is washed as it is mixed with air and water while rising. The sand then goes down the Sand washer where it receives final washing by a part of the upward-moving filtrate. The solids separated from the sand in the Separator are discharged from the filtration unit with backwash water.
Since the filtration and washing are performed continuously, the filter bed is kept clean, and the unit does not require the interruption of operator to wash, nor does it need such components of backwash as storage tank, backwash water tank and other accessories. Therefore, the system is simple, occupies small floor area, and reduces operation cost.
The difference from the Uniflo sand filter lies in the construction of filter surface and the design filtration rate. The filter surface is made up by the equilateral-polygon shaped Uniflo sand filters combined as a unit without spacers between the units. Each unit shares the piping and works as a single large filter.
The filtration rate is roughly half again as large as the conventional model, without excessive increase of the head loss at the filter bed. This reduces the power for lifting raw water to the extent that sometimes filtration can be accomplished without pumping raw water up.

2. Features

The filter bed is always kept clean by the continuous washing, bringing the following benefits.
(1) Head loss is very small and stabilized.
(2) The flocculant is injected directly, enabling coagulation-filtration. It has a high SS capture rate, and coagulation-filtration does not clog up the bed. It assures stabilized operation.
(3) Its structure is simple with just a small number of auxiliary equipment. The auxiliary units for running are only raw water pump, safeguard strainer/screen and air source for airlift.
(4) It can be designed for gravity flow.
If there is a head of roughly 1.5m between the inlet and outlet, the filter can be designed solely for gravity flow.

3. Performance

(1) Design filtration rate: 300m/d
(momentary maximum: 450m/d)
(2) SS concentration (for sewage treatment)
20mg/l influent -> 5mg/l effluent
(3) Objects of filtration:
SS, BOD, turbidity, phosphorus etc.

4. Applications

(1) Advanced sewage treatment facilities
(2) Reclamation and reuse facilities
(3) Purification facilities for lake and pond water
(4) Various wastewater treatment facilities
(5) Facilities for pretreatment of city water