Want to clean up recycled water? Bury it in the dirt.
That''s the latest discovery by scientists at the Commonwealth Industrial Scientific Research Organisation (CSIRO) in Australia, who found that disease-causing microbes can effectively be eliminated from recycled water by storing it underground.
Researchers at CSIRO Land and Water are 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. In other words, to create underground dams.
The idea, say the scientists, 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. The water will be injected into appropriate aquifers, where it will be protected from evaporation or pollution. The underground aquifers do not submerge valuable land or habitat, as does a surface dam.
Microbiologist Simon Toze, Ph.D., has 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 explains. "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 microorganisms that kill or inactivate them, says Toze.
In experiments conducted in aquifers and under controlled conditions in the laboratory simulating conditions of an underground aquifer, Toze found that the disease-causing microbes generally last less than one month, with none lasting more 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," says Toze, making underground storage one of the most promising ways to cleanse and recycle water.
"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," Toze argues. "This sort of water is not intended for drinking, but for the irrigation of parks, gardens and farms."
by Sandy Smith ([email protected])