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Brief Overview

  1. Gravity transports greywater to the system.
  2. Preliminary filtration removes large debris (like hair).
  3. Greywater enters biological treatment tank for oxygenation.
  4. Oxygenation helps the growth of beneficial bacteria.
  5. Fine hollow fibers filter out bacteria and viruses.
  6. Treated greywater is stored in clean tank for distribution.

Technical Explanation

 greywater being collected from handwash basins


Greywater is collected from bathrooms across the building and transported via dedicated pipework to eliminate cross-contamination between the greywater and wastewater supplies.

Greywater can be collected from showers, handwash basins, and bathtubs. These outlets produce waste greywater which is ideal for reuse as contaminants can be easily filtered.

Wastewater from kitchens, toilets, or any other blackwater source cannot be connected to the greywater recycling system due to containing a significantly high pollutant load.

 preliminary filtration on a greywater recycling system

Pre Filtration

Before entering the main treatment tank, greywater passes through a pre-tank filter.

Preliminary filtration is designed to separate undissolved solids such as hair and textile fibres from the greywater supply.  

Preliminary filtration involves passing greywater through a mesh sheet. The mesh sheet contains small holes (rated to 1000 microns) which allow the greywater supply to enter the treatment tank whilst trapping undissolved solids.

Stormsaver pre-tank filters are supplied with a high-pressure backwash to remove excess debris when required. This is a key failure point on other systems available on the market as the backwash supply does not have sufficient pressure to remove debris efficiently.

 biological treatment process occuring within the greywater recycling system

Bilogical Treatment

Greywater enters the main treatment tank allowing the natural biological treatment process to begin.

Aeration supplies high volumes of oxygen into the treatment tank to naturally degrade dissolved contaminants such as shower gels and foam.

Aeration also assists with the sedimentation process whereby any remaining undissolved solids are allowed to settle on the base of the tank for removal via a sludge pump.

Growth bodies within the treatment tank allow biofilm to be easily separated from the greywater supply. Growth bodies are essential for increasing the surface area for biofilm to attach.  

 a diagram showing ultrafiltration on a greywater recycling system


Once the biological treatment process has been completed, greywater is then processed through a membrane filter.

Membrane filters contain bundles of hollow fibres where microbiological particles are trapped by the micropores to efficiently separate these particles from the greywater supply.

Any remaining traces of bacteria, viruses, or biofilm are removed in this process. The membrane filter is rated to ultrafiltration level (0.02 microns).

As the micropores become blinded by particles, the filter efficiency reduces. To prevent build-up from becoming an issue, automatic backwashing of the filters is completed daily by pushing a pressurised supply of air and water in the reverse direction.

 Clean water tank on a rainwater harvesting system


Treated greywater is transferred into a separate clean water tank for storage until required.

Treated greywater is made safe for extended storage due to the removal of solid particles and a low nutrient load during the biological treatment process.

Treated greywater is used to supply points of use, the backwash nozzle for the pre-tank filter, and backwash for the membrane station.

The mains water backup also enters the clean water tank via a WRAS-compliant air gap for periods of low greywater supply.

 greywater supplying points of use

Usage Points

Greywater can be used to supply

  • Toilets
  • Irrigation systems
  • Vehicle and train wash
  • Manufacturing processes
  • Dust suppression
  • Cooling

Greywater cannot be used to supply

  • Potable outlets
  • Showers

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