Waste water treatment solutions in sewage sector

High-speed rainwater treatment system


■Application example for primary clarifier tank

Application example for primary clarifier tank

  • This system can be installed in a final treatment plant and pump yard as a high-speed solution for simplified treatment of confluence type sewage as well as a simplified treatment technology for untreated wastewater.
  • It addresses elimination of both contaminants such as oil ball and BOD and SS at the same time.
  • As a means to reduce BOD flow-out impact, its construction costs are about half those of a holding pond with the same function.
  • As a technology for confluence improvement, this system is certified with MLIT's SPIRIT 21 Technology Assessment.
  • This system was awarded a METI Minister Award. (The 34th Excellent Environment System Award Project sponsored by Japan Society of Industrial Machinery Manufacturers)


  • It can be installed by modifying the existing facilities (primary sedimentation tank, rainwater sedimentation tank).
  • Because natural down flow is used both for treatment process and washing process, stable operation depending on flow rate fluctuation is possible.
  • Because the filter media is very fine, a non-flocculation process is available. Because of this, the maintenance and management cost is needed only for electricity, which is as low as 0.1 yen/m3 (excluding pumping cost) without the need for working in rainy weather.
  • Neither a pretreatment screen nor bottom screen for preventing flowing out of filter media are needed, which makes the operation management easier.
  • Because the number of in-tank devices and auxiliary devices is fewer, operation management is easier.
  • Because the time for washing filter media is short (1 min.), no auxiliary tank is necessary.
  • Efficient elimination of SS makes it possible to reduce the dose of disinfectant in filtrated water by 40% compared to the water after simplified treatment in the conventional approach.

Structure and function


The mechanism is based on upward flow filtration by using a float type filtration media.
The filtration speed is very high, 1,000 m/day on average (1,500 m/day at the maximum). The system is comprised of a flow-in channel, multiple high-speed filtration tanks and washing thickener.


The raw water fed by water pump overflows from the upstream channel and flows into the system. Then, the water undergoes upward flow filtration. This is followed by overflow and discharge of the filtrated water.

Special filter media

The filter media is made of a material specially developed for rainwater treatment

The filter media is made of a material specially developed for rainwater treatment
  • Wind mill geometry to prolong filtration time
  • Coagulant is not necessary because of compact size (≦7.5 mm)
  • Durable material with excellent resistance to acid, alkaline and friction
  • Because it is non-water absorbing material, SS, oil or fat will not be retained in the filter media.

Treatment flow

The filtration speed varies depending on the flow rate of raw water flowing into the system, and clogging of the filter media can be automatically cleaned based on the detection of water level on raw water side. Therefore, it can treat wastewater during rainy weather that tends to fluctuate both qualitatively and quantitatively.

By opening the high-speed washing system in the bottom, washing can be achieved with a natural down flow based on the water level difference using the filtrated water reserved on the top of the filtration tank.

Filtration process,Washing process

Installation example

  • It can be used as an alternative solution for a primary sedimentation tank. Benefits such as saving of installation of space and CO2 reduction can be expected.
  • This system can be installed in a rectangular or circular primary sedimentation tank and rainwater sedimentation tank.
  • It is designed for the tank with an effective depth of 2.5m or deeper.

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