Greywater
From Wikipedia, the free encyclopedia
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.
[edit] Elimination of greywater
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.
[edit] Recycling of greywater
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.
[edit] Application of recycled greywater
[edit] Irrigation
Greywater typically breaks down faster than blackwater and has much less nitrogen and phosphorus. However, all greywater must be assumed to have some blackwater-type components, including pathogens of various sorts. Greywater should be applied below the soil surface where possible (e.g. in mulch filled trenches) and not sprayed, as there is a danger of inhaling the water as an aerosol.
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. If you are concerned about this, avoid using laundry powders; these often contain high levels of salt as a bulking agent, and this has the same effect on your soil as a drought.
[edit] Indoor reuse
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.
The level of treatment required in this case requires the water to have low or nil biochemical oxygen demand (BOD), but it is not necessary for it to be treated to the same standards as potable water. Greywater recycling for toilet flushing is currently considered to be uneconomical or environmentally unfriendly at most domestic levels. However, a Quebec company, Brac Systems, has recently patented a cost-effective system that uses a chlorine treatment, and is selling the system in the Americas, Europe, and Australia. As an alternative to treatment, a South Africa Company is manafacturing and distributing in South Africa and Australia a GardenResQ grey water diversion systems that allows all household grey water to be automatically diverted to the garden for irrigation.
[edit] Extreme living conditions
Greywater use promotes the ability to build in areas unsuitable for conventional treatment, or where conventional treatment is costly. The Mars Desert Research Station utilizes greywater recycling for this use, and might be used on trips to Mars to reduce water consumption and increase oxygen generation.
[edit] Heat reclamation
Devices are currently available that capture heat from residential and industrial greywater, through a process called "Drainwater Heat Recovery" or "Greywater Heat Recovery." Rather than flowing directly into a water heating device, incoming cold water flows first through a heat exchanger where it is pre-warmed by heat from greywater flowing out from such activities as dishwashing, or showering. Typical household devices receiving greywater from a shower can recover up to 60% of the heat that would otherwise go to waste.
[edit] Greywater and the environment
The potential ecological benefits of greywater recycling include:
- Lower fresh water extraction from rivers and aquifers
- Less impact from septic tank and treatment plant infrastructure
- Topsoil nutrification
- Reduced energy use and chemical pollution from treatment
- Groundwater recharge
- Plant growth
- Reclamation of otherwise misdirected nutrients
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.
[edit] Move towards ecologically sustainable development
Because greywater use, especially domestically, reduces demand on conventional water supplies and pressure on sewage treatment systems, its use is very beneficial. In times of drought, especially in urban areas, greywater use on gardens or in toilet systems helps to achieve Ecologically Sustainable Development by helping to meet its principles.
[edit] Dangers associated with greywater use
When treated properly, greywater is of sufficient quality to use on gardens and landscapes but it is important to remember that greywater contains impurites and microorganisms that are capable of causing disease and illness.
A recent study carried out by the Queensland Department of Natural Resources, Mines and Energy covering the quality of domestic greywater found that greywater has organic strength and harmful organisms equal to and in some instances greater than toilet waste.[citation needed]
Many substances used for cleaning and washing are designed to be treated in a sewage treatment plant. The term "biodegradable" means the product is able to be degrade in a wastewater treatment plant where the established bacterial community will quickly metabolize these compounds. However, such substances will still degrade elsewhere, but the timeframe may be longer. Laundry wastewater can contain harmful organisms such as E.coli and diseases such as Hepatitis, which can remain in the correct ground conditions for extended periods of time. [verification needed] In general, it is difficult for human pathogens to remain viable for long periods in the soil, owing to the existing competitive bacterial community.
Uncontrolled release of greywater, with its associated nutrient load, could find its way into storm water drainage systems and streams causing algal blooms and disruption of ecosystems.
Importantly, sensible precautions can mitigate almost entirely the risk associated with greywater use. In order for disease transmission, people have to contact (by aerosol or directly) the greywater. If the greywater is applied by dripper systems or by subsurface delivery, this cannot occur. Avoiding greywater use, particularly by spraying, on vegetables eaten raw is recommended.
[edit] Tips on how to minimise health risks associated with greywater
- 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.
[edit] See also
- List of waste water treatment technologies
- Ecological sanitation
- Sanitation
- Sewage
- Water conservation
- Water purification
- Water recycling
