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Water, Engineering and Development Centre

Water, Engineering and Development Centre. Household use of grey water, wastewater and rainwater. Mike Smith. 1. Operating principles 2. Experience Grey-water recycling Rainwater collection 3. Water quantities 4. Water quality issues Grey-water Rainwater 5. Economic aspects

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Water, Engineering and Development Centre

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  1. Water, Engineering and Development Centre Household use of grey water, wastewater and rainwater Mike Smith

  2. 1. Operating principles 2. Experience Grey-water recycling Rainwater collection 3. Water quantities 4. Water quality issues Grey-water Rainwater 5. Economic aspects 6. Summary People-centred solutions for sustainable development since 1971

  3. Top-up water if needed Overflow Washbasins, showers, washing machines Piped water Storage Toilets Rainwater Treatment unit Treatment wastes Schematic principles of a domestic grey-water recycling system To sewers

  4. Treated grey-water could be used for: • Non-potable domestic purposes • Irrigation * * See, for example, “Draft guidelines for the reuse of Greywater in Western Australia” (2002)

  5. Examples of domestic re-use Loughborough University (UK) Treated grey-water and rainwater used for toilet flushing in a student accommodation block. Annecy (France) Treated grey-water used for toilet flushing in an apartment block, and landscape irrigation. Hockerton Housing project (UK) Rainwater used for drinking water. Treatment is by filtration and UV disinfection. Nottingham Eco-home (UK) Rainwater used for toilet flushing and laundry. Storage is the only treatment provided.

  6. Water quantities Percentages of water used for toilet flushing: Typical domestic range 29% to 47% Millennium Dome 48% Typical office 63% Four UK universities 39% to 54%

  7. Typical water usage at LU student accommodation block

  8. Data from a study, by Thames Water and Cranfield University, of grey-water re-use in five homes House 1 2 3 4 5 % of total 36% - 21% 9% 17% water saved Mean per capita 43 102 181 125 79 consumption (lpcd) Source: Hills, Birks, Diaper, Jeffrey, (2003)

  9. Water quality issues

  10. Grey-water is similar in quality to settled sewage. (Better than Raw sewage.) • BOD, Suspended solids and bacterial numbers are high, and grey-water will quickly smell unless treated. • Treatment is needed to: • Minimise health risks from contact and aerosols; • Improve appearance; • Reduce odour; • Minimise biological growth, scaling and corrosion.

  11. Handling of grey-water • 1. Storage of Greywater. Including storage capacity to accommodate sludge accumulation. • 2. Balancing and screening: pH correction, and screening to remove suspended solids, including hair. • 3. Aerobic treatment: This may include aeration, sedimentation, flotation, dilution, and addition of chemicals such as alum, lime, or chlorine. • 4. Slow filtration: Filters may use foam, slow sand filters, carbon filters or membranes. • 5. Storage of partially-treated grey-water.

  12. Rainwater quality The quality of rainwater depends upon the cleanliness of the collecting surface. Recent studies show that storage, and flow through a series of tanks, significantly improves the bacterial quality of rainwater.

  13. Loughborough University 2005

  14. Tank 1 Tank 3 Tank 2 Tank 4 Typical thermotolerant coliform count in tank series

  15. Valley Road, Loughborough (2005)

  16. Nottingham Eco-home (2005)

  17. Nottingham Eco-home (2005)

  18. Economics and justification For individual houses, grey-water recycling offers negligible economic benefits. For Loughborough University, retrofit costs could be recovered in 8 or 9 years. Benefits can be considered in terms of reduced demand on limited water resources, and reduced sewage flows. Full benefits depend on specific social, technical, economic and climatic conditions.

  19. Perceptions of users Surveys suggest that users generally have a positive attitude to using recycled water for toilet flushing. Householders want a simple, reliable, facility, requiring little or no maintenance. (They want a ‘fit and forget’ unit.) Re-use of grey-water and rainwater for toilet flushing is more attractive where a maintenance team is available.

  20. Summary • Currently, the cost and convenience of piped water supplies in UK does not encourage recycling of grey-water. • Incentives for recycling could include: • Personal or ethical preferences • Environmental concerns • Legislation • Tax incentives

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