Greywater: Difference between revisions

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Greywater, grey water or gray water, is water that has been polluted with (non-)biodegradable soaps and detergents.

Sources

Greywater can be found in the effluent pipes from all rooms in our house, except for the flush toilets (if present). This as the latter carries blackwater.

Both the water itself aswell as the nutrients inside the greywater is of value. This as water is an increasingly limited resource especially in dry climates.

Redirecting the pure water we use for tasks such as showering allows us to reclaim some of that value to grow plants and recharge the water table. It may be necessary to choose our soaps and detergents more carefully (opting for bio-degradable soaps/detergents), if we use the greywater for watering and fertilizing plants (see Water recycling systems without purification).

Recycling

It is important to treat greywater seperatly from blackwater, as the first is less polluted and so requires less treatment steps. By having less quantity of water going trough less treatment steps the treatment procudure becomes more efficient and less costly.

Systems

At present, several water recycling systems exist which can be used to:

• recycle the water without purifying it
• recycle the water while purifying or decontaminating it

Water recycling systems without purification

Water recycling without purification is used in certain agricultural companies (e.g., tree nurseries) and dwellings for applications where potable water is not required (e.g., garden and land irrigation, toilet flushing). It may also be used in dwellings when the greywater (e.g., from rainwater) is already fairly clean to begin with and/or has not been polluted with non-degradable chemicals such as non-natural soaps (thus using natural cleaning products instead). This water system also needs a supply of water to recycle and reuses water as well. It is also not recommended to use water that has been in the greywater filtration system for more than 24 hours or bacteria builds up affecting the water that is being reused.

Water recycling with purification

Water purification/decontamination systems are used for applications where potable water is required (e.g., to allow drinking, and/or for other domestic tasks as washing, showering).

For filtering the water to become potable (or near-potable), there are numerous systems based on soft processes. These include natural biological principles such as

• mechanical systems (sand filtration, lava filter systems and systems based on UV radiation)
• biological systems (plant systems as treatment ponds, constructed wetlands^[1], living walls) and Bio reactors or compact systems as activated sludge systems, biorotors, aerobic and anaerobic biofilters, submerged aerated filters, biorollsTemplate:Vague ^[2]

Finally, "hard", direct processes, such as distillation (evaporation) or mechanical processes such as membrane filtration, (typically ultrafiltration and reverse osmosis, which are capable of treating high volumes of grey water) can create potable, or near-potable water. There seem to be no commercially available "hard" greywater recovery devices suitable for on-site use in the individual household, even though a number of such technologies exist.

In order to purify the potable water adequately, several of these systems are usually combined to work as a whole. Combination of the systems is done in two to three stages, using a primary and a secondary purification. Sometimes a tertiary purification is also added.

Some municipal sewage systems recycle a certain amount of grey and blackwater using a high standard of treatment, providing reclaimed water for irrigation and other uses.

Minimizing health risks from greywater

Template:Portal box It may also contain pathogens, and/or harsh chemicals and care should be taken with it; although it is not as great a health risk as blackwater (sewage), it should be handled with great care and human exposure to greywater should be avoided.

• Wash yourself after contacting greywater.
• Install signage around greywater irrigation systems or areas.
• Do not drink or play with greywater.
• Do not allow anything that may be eaten to come into contact with greywater.
• Do not allow greywater to pond or run off the property.
• Do not wash domestic pets in greywater or allow pets to drink greywater.
• Do not use greywater in public places such as children's play areas or playgrounds, BBQ areas or recreation facilities.

Suggested projects

• What is the effect of various detergents and soaps in a greywater system? Consider the receiving soil and plant types - the answer may vary.^{[expansion needed]}

Organizations

• Water Conservation Alliance of Southern Arizona

Projects

• The old greywater system at CCAT

See also

• Earthship: domestic water system

External links

• Knoxfield greywater system - application of greywater treatment in a house in Knoxfield, in the suburbs of Melbourne, Australia. - Greenlivingpedia
• Wikipedia:Greywater
• Oasis Designs
• The graywater guide book from January 1995 (pdf)

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