Buried dams help clean recycled water

Disease-causing microbes can effectively be eliminated from recycled water by storing it underground, new research by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) scientists has found.

Researchers at CSIRO Land and Water have for several years been investigating the feasibility of diverting urban stormwater and treated effluent into underground aquifers, where it can be recycled for use on parks, gardens, ovals and farms.

The idea is to harvest surplus water during the wet part of the year, store it underground for some months, then bring it to the surface again for irrigation during the dry season.

Researchers consider these underground dams offer a uniquely Australian solution to the problems of water storage, water conservation and recycling. The water will be injected into appropriate aquifers, where it is protected from evaporation or pollution - and does not submerge valuable land or habitat, as does a surface dam.

Now, microbiologist Dr Simon Toze is said to have produced the clear evidence that storing water underground also purges it of disease-causing organisms, making it clean enough to recycle as irrigation.

'We've been studying the behaviour and fate of various microbes in groundwater taken from different parts of the country,' he said. 'We've looked at enteric (gut) viruses, the protozoan Cryptosporidium, and disease-causing bacteria like Salmonella and Aeromonas.

'If we are to store large volumes of water underground for recycling, we need to know exactly what happens with these bugs, and whether they can survive in reclaimed water.'

Once underground, the disease-causing organisms face a hostile array conditions such as temperature changes, lack of oxygen, lack of nutrients and a whole army of naturally occurring groundwater micro-organisms that kill or inactivate them.

In experiments undertaken in aquifers and under controlled conditions in the laboratory simulating conditions of an underground aquifer, results have shown that the disease-causing microbes can last less than one month, he has found.

'This makes underground storage one of the most promising ways to cleanse and recycle water.

'Australia is naturally a dry continent, and in many areas our groundwater resources are being heavily exploited. This appears to offer a safe, clean way to recharge them.'

Dr Toze has tested the antiviral activity of indigenous microbes in groundwater taken from South Australia, the Northern Territory, Victoria, Queensland and Western Australia. In every case the large numbers of virus added to the water disappeared in less than six weeks.

'Since water injected into an aquifer is likely to remain underground for several months before being re-used for irrigation, it looks as if there will be a comfortable safety margin.'

Dr Toze said that, for many of Australia's more arid towns and cities, reclaiming water will soon be an essential practice.

'At present people still describe this as 'waste water' - but that is a bad term, and it shows how limited our thinking still is towards water. Instead, Australians need to focus on the productive uses of reclaimed water.

'This sort of water is not intended for drinking, but for the irrigation of parks, gardens, farms, ovals and street verges.

'I believe that in pioneering this sort of water re-use, Australia is showing the world a lead in a field that will be increasingly vital to the human and environmental future,' Dr Toze said.