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Water good idea

Letters

Hats off to Yorkshire Water which won the Atkins Environmental Award in this year's British Construction Industry Awards (NCE last week) for its ecological wastewater treatment system at Scrayingham.

It was a brave decision by Yorkshire Water to adopt a natural treatment process, but a decision consistent with the need for civil engineers to put sustainability in the forefront of our thinking. The use of waste stabilisation ponds (WSP) and constructed wetland systems (CWS) for wastewater treatment is at last gaining momentum in the developed world, offering low energy and low whole life costs in comparison to the ubiquitous and electrical energy-thirsty variants of activated sludge, Though the unit cost of the Scrayingham system is very high, I am sure that in the future these natural treatment systems will look increasingly competitive with energyintensive processes as we put more value on amenity and when we take into account the full environmental costs of imported energy.

It is disingenuous however, to think WSP and CWS systems are 'ultra low tech'. The anaerobic, anoxic, aerobic, photosynthetic and plantcentred processes at work in natural treatment systems are complex and there are many challenges ahead for process designers to understand and simulate them in mathematical models and thereby design more efficient systems.

Further, the civil engineering designs for these systems pose novel problems in geotechnics, foundations, hydraulics and the use of vegetation. In fact it brings to mind that oft-quoted definition of the work of civil engineers - 'harnessing the forces of nature for the use of mankind'!

Michael Norton (M) director, Halcrow Group nortonmr@halcrow. com

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