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Hitachi Infrastructure Systems (Asia) Pte. Ltd.

This system plays a major role in conserving water.


Securing water for daily living is an important issue for any city. However, if rain doesn't fall or drought continues for a long time, there will inevitably be a water shortage. However, the current situation is that many buildings use the precious drinking and cooking water in toilets, etc. Our building gray water system is a system that purifies waste water that has been used once and re-uses it in building toilets and as non-potable water.

In buildings, this much water is used per person per day.

Image: Pie graph breakdown of 100 L

Image: Water flow illustration of building gray water

Equipment summary

Gray water equipment summary

  1. Large pieces of debris are removed with a screen
  2. Adjustment tank provides uniform water quality and water volume
  3. Biological treatment is done in an aeration tank
  4. Film treatment
  5. Color and odors are removed in an ozone reaction tank
  6. Sterilization

Photograph: MBR

Gray water quality

Gray water quality
Application Water for flushing toilets
PH 5.8-8.6
Odor There must not be any abnormal odors
Appearance Must be transparent and have almost no color
E. coli Must not be detected
Free residual chlorine 0.1 mg/L or more
BOD 20 mg/L or less
COD 30 mg/L or less

From the Waste Water & Rain Water Reuse System Plan Criteria and descriptions (2004 version)

System & device summary

Illustrated explanation of the role of AQUA UFO

(1) Use a screen to remove large debris ( (2) Homogenize water amount and water quality in adjustment tank ( Do biological treatment in aeration tank ( (3) Use the rotating flat membrane separator AQUA UFO to do membrane treatment ( (4) Remove colors and odors in the ozone reaction tower ( (5) Sterilize.

Photograph: Aeration tank
Aeration tank

Photograph: Ozone generator
Ozone generator

Photograph: Deodorizing device
Deodorizing device

AQUA UFO is a registered trademark of Hitachi Plant Technologies in Japan.

FAQ about gray water

Q. What can it be used for?
A. It can be re-used as toilet flushing water.

Q. What about holidays?
A. On holidays there is less waste water, but this system operates intermittently, operating and stopping according to the amount of waste water, so it is a streamlined treatment method. Operation can be restarted easily after a holiday is over.

Q. How is the removed debris processed?
A. It is separately incinerated and disposed of as industrial waste.

Q. Is there an odor or color?
A. We treat the water using ozone reaction devices and other devices, so there isn't enough color or odor to be a problem.

Q. How much tap water can be saved?
A. You can expect to save 30-50%. (Our test results)


  • Building gray water equipment