LECTURE

NEW WATER FOR OLD

Professor J. Howell, University of Bath, on 24 November 1999

A Joint Lecture with the British Association for the Advancement of Science (West of England Branch)

In September a UN report revealed that over the last forty years Arctic ice has decreased from ten to six feet in depth. Global warming will radically change water availability, pollution situations and usage. Rainfall figures vary, but in many countries irrigation is needed for food, and evaporation exacerbates problems. UN studies indicate that while some currently use up to 40% of their rainfall, many will take more in future. Some already use over 100%, through tapping rivers - e.g. the Danube and the Rhine. Border disputes over water rights involving irrigation and pollution will develop, as now between Jordan and Israel.

Professor Howell detailed figures on water usage in the UK and elsewhere. Although we use only 1% for irrigation and 36% for power generation, we use 51% for industry and domestic purposes, also extracting from rivers, whereas in Australia domestic use dominates, irrigation is significant and industrial use is relatively low. In Mexico, irrigation dominates but in the US and the UK its use varies widely locally. For example, in Britain while the north-west is relatively wet, East Anglia is now classified as a `semi-arid zone', with fertiliser pollution treatment adding to water costs. Since the Israeli population had been forecast to rise by 50% between 1985 and 2000, sophisticated irrigation measures had been adopted, to ensure food supplies, including the use of greenhouses to limit transpiration.

The US uses ten times the average UK consumption of water and in such developed countries re-use of industrial and municipal water supplies is widespread. Japan now re-uses 80% of its water and requires water-recycling in all large buildings. Pulp and paper industries aim to re-use up to 95% of their water. Los Angeles plans to meet rising demand through recycling waste water first to aquifers, then reed bed percolation, then to the fresh and salt water boundary of its water-table, then (with treatment) to food crops. Sydney is now testing a system which converts sewage to potable water at all required standards. In our Dome, washbasin `grey' water, rain and borehole water is biologically filtered and treated, using reed beds for rainwater and back-flushed membrane treatment, which yields 72% reuse, for toilets and washing. Wessex Water uses membrane treatment to meet EU bathing standards at Porlock.
The speaker gave a desktop demonstration of membrane filtration while he talked, later revealing that his unfiltered liquid was beer. He then explained that beer filtration poses problems, since loss of colour, aroma and `head' is unacceptable. He provided many illustrations of a variety of installations using digesters, reverse-osmosis membrane systems, etc. but acknowledged that some polluting bacteria are now resistant to treatments, so that while membrane filtration will remove them, standard treatments need skilled use to be effective.

In the subsequent discussion period there were queries on reed bed systems and desalination. If two reed beds are run alternately and reeds replaced annually water-logging may be avoided, although bacteria growth threatens blockage if waste is uncontrolled. Similarly, salination problems arising from irrigation and over-abstraction, as in the Aral Sea, can be overcome at a cost. When questioned finally on overall progress Professor Howell observed that time is short and problems are complex. UK water costs are relatively low, but re-use for low-quality needs could be economic if usage required that. Saudi Arabia will use membrane rather than distillation and evaporation treatments for desalination, for example. Although membrane plants produce less sewage sludge, they do produce more carbon dioxide than traditional methods. However, small-scale membrane systems which may be used reliably in remote areas, such as in Africa and Australia, are being developed. Many developed countries, including Britain, could meet water problems arising from global warming through suitable investment, but many others lack both financial and technical resources. The UN now forecasts large-scale armed conflicts over water problems.

Geoff Catchpole