Water conservation Recycling
L
ess than a decade ago the incorporation of a rainwater harvesting system into a project was seen as something of a novelty – a bit of green- wash to keep people happy. Nowadays, these
systems are included as a matter of course, and even recycling systems for grey water (recyclable waste water) are regularly given consideration. In 2008, when Hoare Lea was appointed as mechanical/electrical/ plumbing (MEP) and sustainability consultants to the infrastructure, residential and hotel elements of Wood Wharf, one of London’s largest waterside developments, the need for each of the proposed buildings to reduce water consumption was firmly on the agenda. Wood Wharf is a seven-hectare site adjacent to
Canary Wharf in London’s Docklands. The proposed masterplan for the site comprises a range of high- quality homes, offices, shops and community facilities, set within a waterspace and public realm. The main features of the proposed scheme are: • Six commercial buildings providing approximately 454,000 sq m of office space;
• Six residential buildings providing up to 1,668 homes, including 35% social rented housing and a significant proportion of affordable shared ownership family housing;
• A waterside hotel; • A retail mall; and • A new public park.
Emerging challenges The tall buildings and high density of the development makes the ratio of population to available water collection area very high – which means that rainwater harvesting was never going to have much impact. Conservation and re-use of water were going to have to be considered if our efforts were to be anything other than token. On a building-by-building level, (or ‘parcels’ in Wood
Wharf masterplanning terminology) the office teams, with MEP designers from Hilson Moran and AECOM,
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had already incorporated ‘per parcel’ grey water recycling facilities. However, both teams acknowledged that the effectiveness of these facilities would be limited by the fact that an office block could never yield enough grey water to meet its non-wholesome water needs. Within the residential and hotel elements of the scheme, the MEP designers from Hoare Lea found themselves blessed with more grey water (from all those baths and showers) than they could find uses for. Hoare Lea’s feasibility study showed that if centralised grey-water facilities were incorporated into each of the three marketable residential parcels, 7B, 7C and 7D there would be about 17,000 litres per day of excess grey water available to use elsewhere in the development (see diagram showing ‘Outline strategy for black-water recycling at Wood Wharf’). Unfortunately, unlike the office designers with
their well-defined cores and basement plant rooms, our residential designers were faced with limited riser space to accommodate additional sets of grey-water drain and vent stacks, and non-wholesome water risers. This, together with limited space for plant at basement level, led the team to conclude that only the hotel could accommodate a centralised system. Therefore the apartments would either have to rely
on flow-limited taps and showers, and reduced-volume bath tubs (which would not be seen as acceptable in the high-specification private residential accommodation), or they would need to install micro grey-water collection facilities for each of the 1,000 apartments. But such installations, at around £1,800 per unit, would be too costly overall. There was also the issue that such technology was largely an unknown quantity in the UK a couple of years ago.
Recycling options Given the unfavourable conclusions of the per-parcel solutions, Hoare Lea’s MEP infrastructure and sustainability designers were tasked to look at the idea of a ‘whole site’ approach. This led to a review of three centralised options: a single centralised grey-water
Depiction of the ZeeWeed membrane bioreactor (MBR) process flow
> October 2010 CIBSE Journal 39
Courtesy of GE
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