New pavers to purify run-off

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

His team is developing a system in which porous concrete pavers allows run-off to seep into underground tanks made of galvanised 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.

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 tyres, brake-linings and exhaust.

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

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

Long-term use

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.

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

Professor 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 per cent 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.