Debugging recycled water

Forget costly desalination plants and plans to tap into liquid aquifers - water recycling is the only commonsense, sustainable option for conserving our most valuable resource. The task facing a team of Macquarie University scientists is to convince us all that it's safe.

In the past few years, water restrictions in most Australian capital cities finally brought home to the urban population what our farmers have known for a long time - water is an extremely valuable, but limited, resource.

Faced with extensive droughts and increasing demand, our governments have considered a range of ways of accessing more water, or - through gardening restrictions and subsidies for the installation of rainwater tanks, for example - to reduce our consumption. While there is undoubtedly logic behind some of these moves - after all, Australia has the third-highest per capita consumption of water among OECD countries - the recycling or re-use of waste and storm water has by far the greatest potential in terms of easing the pressure on our ever-shrinking dams.

The biggest barrier to widespread recycling, according to Dr Belinda Ferrari of Macquarie University's Research Institute for Biotechnology, is a stigma that recycled water is less safe, or palatable, than dam water.

"Water recycling is increasing, but there's still a stigma attached, which needs to change," she says. "One of the major points is that we actually drink less than 1% of the water we use, so most recycled water doesn't need to be potable-quality."

It makes sense then that before tackling the difficult task of trying to convince the community that they should drink treated wastewater, its applications in other areas should be increased. Irrigation alone accounts for 75% of Australia's total water use and there are countless manufacturing and domestic functions - from heating industrial boilers to flushing toilets - that currently use up vast amounts of drinking-quality water.

In order to help these commercial users ensure their recycled water remains free of disease-causing organisms, Ferrari and her Water Pathogen Team at Macquarie University are developing a suite of tools to rapidly and accurately identify potentially dangerous bugs in a range of wastewater sources. Made up of postdoctoral fellows and PhD students, the team comes under the umbrella of the multi-organisation Environmental Biotechnology Cooperative Research Centre (EBCRC), which is using biotechnology to overcome a variety of environmental problems.

The team's initial focus is two parasites not unknown to Sydneysiders - Cryptosporidium and Giardia. Cryptosporidium in particular is environmentally robust and is capable of surviving standard chlorine disinfection practices. Because the infectious organism can be transmitted via human and animal effluent entering water sources, it is a threat to public health worldwide, and gave Sydneysiders a scare in 1998 as Ferrari remembers only too well.

"I was here at Macquarie, doing my PhD," she recalls. "We actually developed the antibody and the test that was used then, so we had to convert our lab and work 24 hours a day just to pump samples through for the authorities."

Despite finding high levels of Cryptosporidium in the samples, Ferrari has doubts as to whether the water would have actually been harmful to Sydney residents. Back in 1998, scientists knew of around 10 species of Cryptosporidium, including one called Cryptosporidium parvum which was able to infect humans and animals. Since then, however, they have discovered a further four species - including Cryptosporidium hominis that only infects humans - as well as around 30 genotypes identified in a range of mammals, from cows to kangaroos, and little is known as to how many are dangerous to humans.

Authorities were right to be cautious, though, given a 1993 US outbreak of cryptosporidiosis, which can lead to heavy bouts of diarrhoea and potential fatalities among immuno-compromised patients. An estimated 403,000 individuals were infected by a dangerous strain of Cryptosporidium via Milwaukee's water supply system.

"In that case it was a false negative because they tested for some bugs but not Cryptosporidium and in our case it was a false positive," Ferrari says. "Which would you rather?"

Scientific understanding of the biology of Cryptosporidium is increasing rapidly, demonstrated by the recent publication of the genome of two human infective species. However, traditional contamination detection relies largely on laboratory-based methods which are too slow and too expensive for routine use in the field.

"Our aim is to get rapid, one-day turnaround results targeting specific organisms," says Ferrari. "Our focus so far has been on Cryptosporidium and Giardia, and we're developing the platform technologies to those organisms, and then we should be able to adapt them for any other pathogens that are out there."

Already a prototype is being developed for the first of these tests - a simple dipstick test for the bacteria E. coli, which will take less than half an hour. If the inexpensive, credit-card sized dipstick changes colour, confirming that the bacteria is present, field operators will be able to take a sample for use in more complex, but still rapid, laboratory-based tests to get an idea of what numbers are present and whether they have the potential to be dangerous to humans.

These second-tier tests take advantage of a range of new biotechnologies, including nanotechnology, flow cytometry and quantum dots in order to detect pathogens using fluorescent molecules that glow when struck by a laser. A separate test using the science of proteomics is attempting to identify differences between cattle and human-infective strains of Cryptosporidium by targeting proteins expressed by each of these strains.

"The ultimate dream scenario is that water will come through a pipe, they'll get a real-time, online signal which says it's abnormal, and they'll know straight away that there could be a problem and will divert that stream," Ferrari says.

"The EBCRC also wants to get people out there in industry and in the community in general to understand the issues, from a risk point of view. People need to understand that even if something is detected, it may not be a problem, rather than getting scared. There have been research papers looking at infectivity of different Cryptosporidium strains, in some instances you only need one organism to cause disease, in others you may need hundreds."

Recent government regulations aimed at increasing the reuse or recycling of wastewater suggest that perceptions are beginning to change. Ironically, if these initiatives are embraced by industry and individual consumers, the traditional assumption that water is an endless resource may actually have a ring of truth to it.

Story reprinted from Macquarie University News, August 2006