Home | Contact | Login
Find eco products and services e.g. solar hot water, house hold items and more
View photos and information on eco friendly homes or list your own eco house
Learn about sustainable living - info, events, news etc
Chat about sustainable living / eco living topics with other Ecobob users
Buy eco products online using our secure online shop

Search Eco Articles


 (Optional)

Category


Location

Avon Electric

What is grey water recycling?

Thursday, February 22, 2007
See full article on wikipedia.org

Greywater, sometimes spelled graywater, grey water or gray water and also known as sullage, is non-industrial wastewater generated from domestic processes such as washing dishes, laundry and bathing. Greywater comprises 50-80% of residential wastewater. Greywater is distinct from blackwater in the amount and composition of its chemical and biological contaminants (from feces or toxic chemicals). Greywater gets its name from its cloudy appearance and from its status as being neither fresh (white water from groundwater or potable water), nor heavily polluted (blackwater). According to this definition wastewater containing significant food residues or high concentrations of toxic chemicals from household cleaners etc. may be considered "dark grey" or blackwater.

In recent years concerns over dwindling reserves of groundwater and overloaded or costly sewage treatment plants has generated much interest in the reuse or recycling of greywater, both domestically and for use in commercial irrigation. However, concerns over potential health and environmental risks means that many jurisdictions demand such intensive treatment systems for legal reuse of greywater that the commercial cost is higher than for fresh water. Despite these obstacles, greywater is often reused for irrigation, illegally or not, in older rural construction, simple construction old and new, often consisting of nothing more than a "drain out back" (pipe pointed down the nearest hill). In droughtzones 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 is poorly understood compared with elimination.
Domestic wastewater plumbing is usually combined at the sewer, so that grey and black waters are removed together using a shared sewerage system. Sewage water can then be treated to limit pollution and health risks, before being returned to the environment at large. The majority of greywater ends up as effluent in rivers and oceans in this way. Despite treatment, this arguably results in greater contamination of natural waters, as the natural purification capacity of surface water is millions of times less than that of soil. Simply dumping greywater on the soil, from an ecological standpoint, is less damaging than sending highly treated greywater directly into natural waters.
Most greywaters are much easier to treat and recycle than blackwaters, due to their lower levels of contamination. However, entirely untreated greywater is still considered to be a potential health and pollution hazard.

If collected using a separate plumbing system to blackwater, domestic greywater can be recycled directly within the home and garden. Recycled greywater of this kind is never clean enough to drink, but a number of stages of filtration and microbial digestion can be used to provide water for washing or flushing toilets; relatively clean greywater may be applied directly from the sink to the garden, as it receives high level treatment from soil and plant roots. Given that greywater may contain nutrients (e.g. from food), pathogens (e.g. from your skin), and is often discharged warm, it is very important not to store it before using it for irrigation purposes, unless it is treated first.

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 no commercially available "hard" greywater recovery devices suitable for on-site use in the individual household, even though a number of such technologies exist.

Some municipal sewerage systems recycle a certain amount of grey and black waters using a high standard of treatment, thus providing reclaimed water for irrigation and other uses.

See full article on wikipedia.org