Greywater
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Greywater, sometimes also spelt as graywater, grey water or gray water and also known as sullage, is wastewater generated from processes such as washing dishes, laundry and bathing. Sometimes, the term excludes kitchen wastewater containing significant food residues. It is quite distinct from blackwater in the amount and composition of its chemical and biological contaminants. Greywater gets its name from its appearance and possibly also from its status as being neither fresh (white water from groundwater or potable water), nor heavily polluted (blackwater from feces or other toxic chemicals). From the point of view of treatment and pollution prevention, greywater decomposes much more quickly and is easier to treat and eliminate than blackwater, but is still considered to be a health and pollution hazard if released into the natural environment untreated.
In recent years concerns over dwindling reserves of groundwater and overloaded or costly sewage treatment plants has generated much interest in reusing or recycling greywater, particularly for use in irrigation. However, concerns over potential health and environmental risks means that many jurisdictions demand intensive treatment systems that are so expensive they usually cost more than simply treating and buying the tap water they save. Treatment methods and risks are poorly researched and understood by authorities. Despite this, greywater is often reused for irrigation, illegally or not, in drought zones or areas hit by hose pipe bans, typically by manual bucketting. In the third world, reuse of greywater is often unregulated and is common. At present, the recycling of greywater and its risks are poorly researched compared with its elimination.
Reuse of greywater
Greywater comprises 50-80% of residential "waste" water. It may be reused for other purposes, especially landscape irrigation (see http://greywater.net). The benefits of grey water reuse can include:
- Lower fresh water use
- Less strain on failing septic tank or treatment plant
- Grey water treatment in topsoil is highly effective
- Ability to build in areas unsuitable for conventional treatment
- Less energy and chemical use
- Groundwater recharge
- Plant growth
- Reclamation of otherwise wasted nutrients
Blackwater from the household and other venues can be eliminated via the application of commercially available composting or incinerating toilets in place of the classical flush toilet. Similar devices can be used to dispose of garbage from the kitchen sink disposal.
With appropriate plumbing, greywater can be used for irrigation without pretreatment (it receives high level treatment from soil and plant roots). However, long term research on greywater use on soil has not yet been done and it is possible that there may be negative impacts on soil productivity.
There are numerous "soft" processes based on natural biological principles such as using reedbed filter systems, the [wetpark] systems or the living wall that can be used to clean up greywater.)
There are also "hard", direct processes, such as distillation (evaporation) which need not necessarily be as energy intensive as they might initially appear. There seem to be as yet no commercially available "hard" greywater recovery devices suitable for on-site use in the individual household, even though a number of such technologies exist, thanks, for example, to the space programs.
Recycled greywater from showers and bathtubs can be used for flushing toilets, which saves great amounts of water. Many attempts at this have been made in Germany. However, untreated greywater cannot be used as flush-water as it will start to smell and discolor the flush toilet fixture if left for a day or more. Although the level of treatment required in this case requires the water to have low or nil BOD, it is not necessary for it to be treated to the same standards as potable water. Greywater recycling for toilet flushing is generally not economical at a residential scale.
In the water damage restoration industry, grey water is considered to be any water from the exterior of the home, or clean water that has been standing for more than 48 hours.
In the U.S. Southwest and the Middle East where available water supplies are limited, especially in view of a rapidly growing population, a strong imperative exists for adoption of alternative water technologies. See the Greywater Policy Center, http://oasisdesign.net/greywater/law/index.htm .
See also
| Topics related to waste | [http://encycl.opentopia.com/ edit] | |
| Anaerobic digestion | Compost | Dustbins | E-waste | Waste collection vehicle | Incineration | Landfill | Mechanical biological treatment | Radioactive waste | Recycling | Reuse | Sewage | Scrap | Sewage treatment | Waste | Toxic waste | Waste management | Waste management topics | Waste minimisation |
External links
- [Greywater Recycling Information] Url accessed May 11 2006
- [greywater.net]
- [Grey Water Central]
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