GB2375761A

GB2375761A - Grey water recycling method

Info

Publication number: GB2375761A
Application number: GB0108839A
Authority: GB
Inventors: Christopher Jon Shirley-Smith; Metropolitan Water Co The
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-04-07
Filing date: 2001-04-07
Publication date: 2002-11-27
Anticipated expiration: 2021-04-07
Also published as: GB0108839D0; GB2375761B

Abstract

A method to recycle grey water in situ by using the roof space on urban blocks of flats to maximum advantage. Used wash water (grey water) is collected from domestic baths, basins and showers in the block to a sump, is filtered and pumped to the roof where it is allowed to trickle through root zone of a native plant sward 2 as a cleansing medium. The water enters the system by filtered grey water inlet 5 and passes through a series of descending, parallel, waterproofing channels in which the plants are rooted. The channels being laid across the width of the roof. During passage through the channels the water may encounter a number of physical barriers or weirs 7 to ensure maximum exposure to the medium. A waterproof membrane 1 may be secured to the upper surface of the channelled area, through which the plants are inserted so that the roots are below the membrane, while the foliage remains above. This membrane forms a barrier against the infiltration by the majority of ambient rainwater, which is collected in a gutter 3 at the lower edge of the roof, which is filtered and blended with the treated grey water, and re-supplied as a disinfected resource for the flushing of toilets and the subsurface irrigation of gardens and green spaces. Solar panels 4 may be used to power the pumps.

Description

Green Roof Water Recycling System-GROW Background-Why Recycle ? Water is the stuff of life. But water is also a bulky commodity which uses considerable amounts of energy to move about, requires an expensive network of pipes to be laid and maintained, and does not, in itself have a very high intrinsic value.

In the UK we are fortunate to be endowed with sufficient water, which if husbanded carefully, will meet all our current needs. The cost of high quality water to the customer at the tap is still, compared to many countries in the world, relatively cheap.

However, from an environmentally-conscious point of view, the use of treated drinking water for a number of industrial and domestic functions is increasingly being questioned. Often, a lower grade of water would suffice for the purpose.

For example, our society takes for granted that the flushing of a toilet with water is the accepted way of removing human biological waste. In urban environments, it is indeed a perfectly reasonable method of collecting material for central disposal which could otherwise be hazardous to health.

This element of sewage transport accounts for between 30-40% of the water consumption of a domestic household. Because this water is provided through the town main, no distinction can therefore be made between the grades of water actually required for different uses.

'Green Roof'System The philosophy behind the'Green Roof'water treatment system is that it is perfectly possible to locally treat a sufficient volume of the'grey'water collected from baths, basins and showers of households, which is not highly contaminated by soaps, greases and oils, to an acceptable'green'standard suitable for on-site re-use for toilet flushing, and a variety of other non-contact domestic and garden uses.

The'Green Roof'Water Recycling system is primarily intended for new build or refurbishment schemes of multi-storey housing stock in urban or peri-urban situations. It is therefore particularly suited to the requirements of Local Authorities, Housing Associations or other intense development where significant numbers of units are accommodated in a single block under one roof.

The biological system, employing no chemicals, relies on the constant availability of 'wash'grade (grey) water being collected from a number of adjacent sources to maintain the viability of the plants on the roof.

There are a number of advantages and unique characteristics in using this system: - Cheaper, lower grade water, fit for the purpose No requirement for extra land - Visual amenity to surrounding neighbourhood - Thermal insulation qualities - Ease of maintenance - Marketing with'green'credentials Unique feature-blending with collected rain water

Cheaper, lower grade water The recycling of water is becoming more commonplace. There are a number of proprietary systems for individual households on the market but which have not yet been proven with time. These are largely aimed at the new-build, single home domestic market on green field sites.

The'Green Roof'system is designed to recycle sufficient quantities of water on site in urban settings to provide a significant saving in cost to the water consumption of all contributing residents. In the case of Social Registered Landlords, savings on the basic necessities of life are to be greatly appreciated.

No requirement for land The price of land in the inner city-where it is available-makes other external forms of water recycling an expensive option. Where better therefore than to utilise space which otherwise remains more or less unused, and that is the roof.

Visual Amenity Given the attractive range of low growing flowering native plants whose roots can perform the same function as a reed bed, the'Green Roof'guarantees an attractive appearance at many times of the year. This uplifts the view of the neighbourhood from overlooking properties. It can be used as an amenity roof garden for the occupants of the block, although it should be stressed that the unit is a working element and should only be accessed by skilled persons.

Thermal Insulation Qualities The thermal characteristics of the green roof are enhanced. There is a depth of some 120mm of medium filled with water which remains-due to constant recharge-at approximately 5-8 C. This provides insulation in the winter and acts as a coolant in the summer.

Ease of Maintenance The'Green Roof is essentially a garden, and much of the maintenance is concentrated in care of the upper parts of the plants. Frequent access is discouraged, but basic maintenance can be carried out by the caretaker of the block or a'green fingered'volunteer under supervision.

Occasional backwashing of the filter medium may be required which will be carried out under expert supervision.

Available as a Modular Unit MWC are intending to build the green roof sections as a modular unit capable of being customised for each application. Each section would contain the treatment medium, pipework, collection and distribution tanks and sufficient photovoltaic capacity to power the circulatory pumps.

Claims

CLAIMS-Patent Application GROW-Green Roof Water Recycling System 1. GROW is an integral system for treating and cleansing collected household 'grey'water by passing it through a series of descending parallel, waterproofed channels laid across the width of the roof and filled with medium into which a variety of predominantly aquatic plants are rooted.
2. The plants, which should be'native'to the location of the built system, should be selected for their efficacy in uptake of water borne nutrients and inorganic material, their relatively low growing profile, and their generally pleasant appearance, including, where appropriate, flowering.
3. The medium is not specified but must contribute to the filtering of the water, the rooting of the plants and provide sites for the microbial fauna to live which are responsible for the digesting of the water borne solid organic material in the grey water.
4. During the passage of the water along the channels, it will encounter a number of physical barriers or weirs, placed across the channels which it should pass alternately over and under to ensure maximum exposure to the medium.
5. This cleansed water, having passed along the full length of the channels is collected at the lower edge of the roof and piped to a collecting tank.
6. Across the upper surface of the channelled area is spread, and tightly secured, a waterproof membrane, through which the plants are inserted into the medium, in such a way that the roots are below the membrane, whilst the foliage remains above the membrane. This latter forms a barrier against infiltration by the majority of ambient rainwater. As the plants mature the stems fill the perforations hence eliminating further orifices for rainwater penetration.
7. The rainwater remaining above the membrane is collected separately in a gutter at the lower edge of the roof, filtered, piped to the same holding tank as the cleansed grey water and hence blended with it. Here the blended water is dosed (1: 20,000) with a green vegetable dye to produce'green water' suitable for toilet flushing, subsurface irrigation and other non-potable uses for the same households to which it is then distributed.
8. The exact dimensions of the system together with the precise depth of the medium in the channels will vary according to the roof space available, the numbers of residents in the building, the pitch of the roof, hence the residence time of the water within the system. Further variations will be modelled according to the permeability of the selected medium.

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Green Roof Water Recycling [GROW] Key to Drawing 1) Geomembrane 2) Foliage of Plants 3) Rainwater Collector 4) Solar Panel 5) Inlet for coarsely filtered'grey water' 6) Cascade to lower channel 7) Weirs-alternating'over'and'under'at 1. 00m spacing 8) Filtration Medium in channels 9) Collection point for filtered water 10) Blending tank for rain and filtered water and site of'green'dosing equipment