High-speed rainwater treatment system (new solid-liquid separation system for all weather conditions)

Outline

Example of application with primary sedimentation tank

• This system can be installed at a final treatment plant and/or pump yard for the sophistication of simplified treatment for confluence type sewage or for simplified treatment of untreated wastewater.
• It can handle the removal of oil balls and other contaminants, BOD reduction and SS removal at the same time.
• As a means to reduce BOD and outflow load, its construction costs are about a half of those required for a holding pond with the same function.
• This system is certified with MLIT’s SPIRIT 21 Technology Assessment as a technology for confluence improvement.
• Awarded a METI Minister Award (34th Excellent Environment System Award Project sponsored by the Japan Society of Industrial Machinery Manufacturers)

Features

• Can be installed by modifying existing facilities (primary sedimentation tank, rainwater sedimentation tank).
• Since natural downflow is used both for the treatment process and the washing process, stability of operation is maintained by responding to any fluctuation in flow rates.
• Since the filter medium is very fine, no coagulation is required for the treatment. For that reason, there is no need to have any work done in rainy weather and the maintenance costs are as low as 0.1 yen/m3 (excluding pumping costs) for electricity.
• Neither pretreatment screens nor bottom screens for the preventing any outflow of filter medium are needed, making operational management easier.
• Operational management is easier since the number of in-tank devices and auxiliary devices is low.
• No auxiliary tank is required since the time required for the washing of filter media is short (1 min.).
• Suspended solids (SS) are efficiently removed, so the dose of disinfectant in the filtrated water is reduced by 40% when compared with the conventional, simplified treatment.

Construction and function

Construction

The mechanism is based on upward flow filtration taking place through the use of a float type filtration medium.
The filtration speed is as high as 1,000 m/day on average (1,500 m/day maximum). The system is comprised of an inflow channel, multiple high rate filtration tanks, and washing thickener.

Function

The raw water fed by the lifting pump overflows from the upstream channel and flows into the system, being filtered in an upward flow. This is followed by overflow and discharge of the filtrated water.

Special filter media

Filter medium of a material specially developed for rainwater treatment

• Windmill-shaped for extended filtration time
• Sized 7.5 mm or less, requiring no coagulant
• Durable material with excellent resistance against acid, alkali and friction
• No SS or oil stays in the filter medium as it is made of non-water-absorbing material

Treatment flow

The filtration speed varies depending on the flow rate of raw water flowing into the system and any clogging of the filter medium is cleared by automatic cleaning that is conducted based on the detection of levels on the raw water side. Therefore, it can handle the treatment of wastewater in rainy weather, where fluctuations tend to be seen in terms of quantity and quality.

By opening the high-speed washing system at the bottom, washing is conducted with a natural downflow based on the water level difference using the filtrated water reserved at the top of the filtration tank.

Example of installation

• It can be used as an alternative solution for a primary sedimentation tank. Effects are also expected in terms of a reduction in the installation area and in the amount of CO2 produced.
• This system can be installed in a rectangular or circular primary sedimentation tank and rainwater sedimentation tank.
• It is designed for tanks of an effective depth of 2.5 m or deeper.