Pavers to Collect Their Own Water

by Anna Salleh

Car parks, patios and other paved areas could one day collect rainwater, purify it then channel it to underground

tanks for reuse, say

researchers. Special porous pavers made of concrete containing specific additives would purify the polluted

run-off, says Professor Simon Beecham, a civil engineer from the University of South Australia.

The water could then be captured in large underground tanks and be used for irrigation, cleaning and flushing the toilet, he says.

"We're trying to harvest a resource that we've not been able to tap into before," says Beecham.

Roads, driveways, pathways and the like make up 60% of impervious urban surfaces. And run-off from them causes flooding and pollutes our waterways.

Until now harvesting rainwater from them has proved more difficult than from roofs, says Beecham.

His team is developing a system in which porous concrete pavers allows run-off to seep into underground tanks made of galvanized metal or a flexible plastic lining filled with gravel.

A special bonding material ensures the porous pavers are strong enough to withstand the heavy weight of cars and trucks.

And additives mixed into the pavers, or into the sand and gravel bedding material beneath them, enables the system to trap pollutants.

A paver injected with ferrous hydroxide, for example, traps toxic and persistent heavy metals like lead, zinc and cadmium that come from sources such as car tires, brake-linings and exhaust.

A layer of microbes on fabric beneath the pavers can trap and degrade hydrocarbons such as oil.

And a layer of granulated activated carbon traps dissolved organic matter from leaf litter that is responsible for algal blooms in rivers, says Beecham.

He says the pollutants can accumulate in the pavers over 25 to 30 years, allowing usable water to be caught and pumped above ground for reuse.

He says the pavers could also allow trees, which themselves soak up and recycle water, to grow more freely because their roots have access to more water and air.

Problem tree roots could be avoided by using a special concrete device that directs the roots away from the pavers, he says.

And the pavers could be seeded with low maintenance native vegetation including sedges.

Beecham says one of his PhD students Baden Myers is about to construct a full-scale prototype of the complete water harvesting and reuse system, which he predicts will cost 10 to 30% more than conventional paving.

Part of the research has been submitted to Water Management, a journal of the UK's Institution of Civil Engineers.

The South Australian government water authority SA Water is a major source of finance for the research.

Monday, 25 September 2006

Australian Broadcasting Corporation

www.abc.net.au

Reprinted by permission of the author

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