Skip to main content

[Greywater Treatment] Preliminary Research and Documentation

The following research and documentation is meant to get this project started. Please consider this a work in progress. Significant work is needed to move this project forward.

Grey Water

Grey water is all the water generated from bathrooms, showers, washing machines, kitchen sinks and does not contain water from toilets. It contains less harmful chemicals from soaps, non-fecal human waste like saliva ,sweat and mucous. It makes up about 60% of waste water generated in a standard household. Grey water is separated at source and treated in various stages to remove harmful germs and bacteria and hazardous chemicals. Grey water is easier to treat and recycle than sewage because of lower levels of contaminants. Grey water is often used immediately after treatment. If stored for more than 24 hours, the organic matter in the treated water begins to putrefy or decay producing a foul smell.

Parts of a grey water treatment system

  • Collection chamber
  • Solids filter chamber
  • Flocculation and coagulation chamber
  • Primary clarifier chamber
  • Aeration chamber
  • Membrane bioreactor chamber
  • Clean water chamber


Figure 1 - Schematic diagram of a grey water treatment plant

Collection Chamber

 Drain pipes from showers, bathrooms, and kitchen sinks are all connected to the grey water collection chamber. This stores the water before the treatment begins.

Solids filter

A solids filter removes visible solids from grey water. These solids may include unused pieces of soap, shampoo sachets, bottle caps, match sticks, cigarette butts, and items like that which may have inadvertently escaped the drain pipe trap. The resultant of this is only grey water with unsettled or floating solids that pass through the filter.

Flocculation and Coagulation Chamber

Flocculation and coagulation is the process of separating microscopic undissolved solid particles from grey water. Grey water is treated with coagulation and flocculation reagents to separate out suspended particles and colloidal particles. These reagents cause finely suspended particles to join together and form larger and denser particles  called flocs. These flocs settle at the bottom of the flocculation and coagulation chamber and can be removed periodically. Isolating these particles first using this process reduces the volume of grey water that is pumped into the primary clarifier chamber.

Primary Clarifier Chamber

Primary clarification is the process of removing floating solids before grey water is sent for biological treatment. Grey water enters the clarifier chamber and floating solids are removed by skimmers. Solids that settle at the bottom can be collected using a mechanical rake and pushed into a sludge chamber. This sludge can be removed periodically and disposed off.

Aeration Chamber

An aeration chamber is a tank where air is blown in to the grey water.  The oxygen in the air is used by bacteria in the grey water to break down any organic matter containing carbon to form carbon dioxide and water. As a result, the organic matter decomposes and settles at the bottom of the aeration tank. This can be removed periodically. 

Membrane bioreactor chamber

The resulting water is then pumped into the Membrane Bioreactor (MBR) chamber. A membrane bioreactor is a low-pressure microfiltration (MF) or ultrafiltration (UF) membrane that filters out micro organisms, animal cells , germs and bacteria that can be harmful. These particles form a sludge that can be periodically removed, or incinerated and finally disposed off.

Clean Water Chamber

After these multiple levels of purification, clean water is collected in the clean water chamber. It is then pumped to a storage tank for reuse in toilets and other applications like irrigation and cleaning.


This project is being developed as an open-source project with the following licensing: