Water conservation Recycling
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recycling system to serve the whole site; a centralised dock-water recycling system (with water being taken from the adjacent dock); and a centralised black-water recycling system for toilet wastewater (see Factfile box). The first option, centralised grey water, brought with
it the problem of lack of riser space to accommodate the additional drainage required, together with the long, horizontal, gravity-fed pipework runs needed to connect each parcel to a centralised plant. When it became apparent that the largest commercially available plant could only treat 50 cu m per day and that a system to treat the estimated 375 cu m per day would have to be bespoke, a centralised grey-water solution was rejected. The second option was the result of a detailed study
by Hoare Lea of a model (originally worked on by Hilson Moran and Atkins) into the viability of using abstracted dock water as part of the cooling strategy. The advantage of this centralised dock-water recycling system was that additional drainage pipework would not be needed and that, as infrastructure to take the water for cooling was to be implemented, all we would need to do would be to divert some off into centralised storage and treatment, and distribute it to the parcels.
The downsides of dockwater recycling were: • The brackish water quality of 4psu (practical salinity units), which meant energy intensive reverse-osmosis (RO) treatment would be needed;
• the fundamental question of whether an abstraction license would be granted; and
The Council House 2 scheme in Melbourne, Australia, uses membrane bioreactor (MBR) technology to treat black water
• the restrictions that may be imposed during periods of low rainfall, as the dock in question is a closed one, using pumping to maintain water level if there is insufficient use of the locks. The third, black-water option came about because
Hoare Lea was aware that, internationally, there were examples of this technology being used successfully in buildings (see Technology box) . Our proposal involved installing a single centralised black-water recycling plant, which would treat the foul water generated on site to a standard where it could be re-used as non- wholesome water. There were a number of benefits to this option, which were mainly that no additional collection >
Table 1: Proposed volumes and uses for recycled black water Recycled black-water use
Wood Wharf building/ use
Buildings WW01 – WW06
Buildings WW07B – WW07D
Cooling tower Irrigation
40 • WC flushing
• Urinal flushing • WC flushing
• (possibly washing machines)
Cooling tower make-up External irrigation
CIBSE Journal October 2010
Factfile
Making use of waste black water
Black-water recycling is essentially the same process as any traditional municipal sewage treatment works. The difference is that instead of discharging the treated water to an estuary or similar water body, the water treatment is to a specified standard to suit whatever the re-use is.
There are various technologies, but the process stages are the same:
Screening to remove large solid items such as rags and plastics;
Sedimentation to allow solids to settle and oils and greases to be decanted;
Aeration to reduce the organic content in the water;
Clarification to further remove organic sludge; and,
Tertiary treatments to further improve (polish) the water quality, such as sand filtration, UV treatment and chlorination.
Because black-water recycling is a relatively new concept in the UK, there is currently no guidance regarding appropriate water quality for differing uses.
Estimated volume required
300 cu m/day 60 cu m /day
(100 cu m /day if water can be supplied to washing machines)
100 to 140 cu m /day As required
Not applicable Not applicable
Estimated volume discharged
470 cu m /day 330 cu m /day
Our research suggested that a document published by the Environment Protection Agency (EPA), Victoria, Australia, entitled Guidelines For Environmental Management – Use of Reclaimed Water, 2003, was a sound basis. It contains four classes of water quality, ranging from urban use with uncontrolled public access, to the irrigation of non-food crops. These classes of use are expressed as A to D, with A being the highest quality – the one we selected as the most appropriate for Wood Wharf.
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City of Melbourne
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