Tag Archives: water treatment

Water resources

Oceans of wealth

As the driest inhabited continent, and the country with the sixth largest coastline, Australia is poorly endowed with freshwater but fringed by huge expanses of ocean.

We often take it for granted but access to clean drinking water is a critical issue in a growing number of regions around the world. In Perth, drinking water has traditionally been sourced from surface water dams and groundwater reserves. But these supplies have significantly diminished since the 1980s through the combined impacts of rapid urban growth and protracted drought conditions. And with the southwest of Australia expected to suffer more severely than other parts of the continent from the impact of climate change, the situation is only expected to worsen.

The Water Corporation of Western Australia has been intensively exploring diversified options for boosting Perth’s drinking water, focusing on climate-independent sources. The most innovative option has been to use advanced treated wastewater to replenish groundwater resources impacted by the drying climate.

To help with their investigations, they turned to Curtin experts, including water chemist Dr Cynthia Joll. As Deputy Director of the Curtin Water Quality Research Centre (CWQRC), Joll is part of a team that researched the performance of the wastewater treatment procedures to make the process both safe and viable. Joll explains there are a large number of potential micropollutants that might need to be removed from a city’s wastewater before it can be safely recycled as drinking water. These include residual pharmaceuticals such as antibiotics, hormones and pain relief medications found in urine.

“The Centre developed the vast majority of the analytical methods for detecting these chemicals in treated wastewaters and then looked to see whether they were in secondary and tertiary – or advanced – treated wastewater,” says Joll.

The research ensured the WA Department of Health approved a pilot water recycling plant. The plant produced advanced treated wastewater of drinking quality, which was pumped into the groundwater aquifer. As a result, they completed a successful groundwater replenishment trial by the end of 2012, which was dubbed a “highly viable” option for securing WA’s drinking water supplies in the drying climate.

In late 2013, the WA government announced that groundwater replenishment was to go ahead as a major new climate-independent water source for Perth. It’s predicted that, by 2060, as much as 20% of Perth’s drinking water is likely to be supplied using this approach. The advanced treated wastewater will be used to replenish groundwater supplies that won’t be drawn for drinking purposes for decades. By the time it is added to Perth’s water supply and subjected to the drinking water treatment process, it will have been naturally filtered by passing through groundwater aquifers, Joll explains.

The CWQRC is also involved in a wide range of fundamental and applied research into other water quality issues. For Joll, who’s been fascinated by water quality chemistry for many years, it’s been particularly thrilling as a scientist to be involved in work of such high public significance. “To help bring it to full scale has been fabulous,” she says, adding that the success of the research means the work of the CWQRC is creating interest in other regions around the world that are already, or are anticipating, experiencing drinking water limitations.

Water resources
Ocean colour image from the MERIS instrument, European Space Agency (ESA).

Engineers at Curtin are also working on a water supply issue. As drinking water is pumped into cities, or wastewater is pumped out, small bubbles can form as the result of a drop in pressure from falling supplies in reservoirs or fluctuations in wastewater usage. These bubbles can damage the pumps that control supply.

Dr Kristoffer McKee, a lead researcher in Curtin’s rotating machine health monitoring project, and colleagues are analysing the vibrations made by the bubbles as they form. When the bubbles enter a pump, the pump applies pressure to the liquid, causing the bubbles to pop (implode) which releases energy. At its peak, millions of bubbles pop within milliseconds of each other.

“This popping eats away at the metal on the ‘impeller’ blades in the pump,” says McKee. As a result, this phenomenon decreases the pump’s ability to apply pressure and push the liquid in the desired direction. “It sounds like you’re pumping gravel.”

The process makes holes in the impeller blades, causing the pumps to seize up. But by the time technicians can detect the telltale sounds, the damage has already begun, says McKee. “It can cost many thousands of dollars to take a pump offline and change an impeller.” He says their approach has been to try to detect the start of the process, called cavitation, before damage becomes significant.

Building on the results of work by a University of Western Australia colleague, and in collaboration with Queensland University of Technology researchers, the Curtin University engineers placed accelerometers (sensors which measure acceleration associated with vibrations) on pumps in Queensland towns. They found they could use the data to map cavitation in 3D to show how a pump changes as cavitation occurs, says McKee.

“Once you see cavitation starting, you can stop your pump and make sure the pressure is correct,” he adds. It’s early days yet and the work needs more field testing, but the research could cut industry costs significantly.

“By 2060, as much as 20% of Perth’s drinking water is likely to be supplied by groundwater replenishment.”

Water resources
Ocean colour image from the MODIS instrument, NASA.

The push to apply research outcomes is strong across Curtin, including in the field of marine and freshwater research. Much of this work is carried out at the university under the auspices of the Australian Sustainable Development Institute, which brings Curtin researchers together on research proposals that relate to sustainable development.

“It’s all about tackling the key issues facing society,” explains the Institute’s Executive Director, Mike Burbridge. “We know that there’s increasing pressure on water and water resources. The cross-disciplinary approach is hugely important at Curtin, but especially in the sustainability space. Major innovations have come about by taking ideas from one area and applying them in another.”

An interdisciplinary approach to solving oceanographic problems has become a hallmark of Curtin’s Centre for Marine Science and Technology (CMST), which fosters research connections across the university’s Departments of Imaging and Applied Physics, Applied Geology, and Environment and Agriculture, as well as with external organisations such as the Western Australian Energy Research Alliance, the Integrated Marine Observing System and the Australian Maritime College.

“It sets us apart from other marine science groups around Australia. We seem to have carved quite a niche for doing that within the Southern Hemisphere and beyond,” says Dr Christine Erbe, Director of the CMST. Erbe is working with a multidisciplinary team at the CMST within Curtin’s physics department in the area of bioacoustics to monitor and analyse the sounds made by marine animals and people at the beach (see News, p6).

Water resources
Perth drinking water will be replenished with reclaimed and treated wastewater.

In one project, researchers are looking at how to detect sharks in the water using off-the-shelf sonar systems – the type used by private and commercial fishermen that work by emitting acoustic signals reflected off objects in the water. “Many of us have engineering and physics backgrounds and apply that to biology,” says Erbe.

Professor David Antoine, head of Curtin’s Remote Sensing and Satellite Research Group, applies his expertise in the opposite direction, combining his background as a biologist with the use of highly sophisticated physics techniques to interpret changes in ocean colour.

Ocean colour activity is affected by the amount and type of particulate matter present – from phytoplankton to sediment. This matter affects how light penetrates into, and is scattered by, water. It can be expressed in physical terms such as the absorption (how much light is taken in by the water itself, as well as the particles or dissolved substances it contains) and reflectance (how much light is being scattered back compared to how much enters at the surface).

“If you have strong absorption, the water will look darker and you will have less light coming out of the water,” explains Antoine. Less absorption results in more scattering of light and different ocean hues. Understanding the changing spectral signatures that result from this play of light enables scientists to quantify, for example, amounts of phytoplankton – the tiny plants that float in ocean surface waters and drive marine food chains.

“Like terrestrial plant life, phytoplankton contains many pigments, particularly chlorophyll,” says Antoine. “And chlorophyll absorbs preferentially in the blue range on the visible light spectrum.”

As phytoplankton concentration increases in an area of ocean, the spectral signature of the water shifts from deep to light blue, then to green or brown, indicating a very large concentration of phytoplankton and highly productive waters. This can be measured in surface waters using an instrument called a radiometer – deployable from a ship, for example, or across huge areas via satellites.

While referred to as ‘satellite imagery’, it involves more than looking at nice pictures, Antoine says. His team is doing a rigorous quantitative analysis of the measured signal on each pixel of the image to look at geophysical properties and determine attributes such as phytoplankton concentration. “That can mean millions of individual observations on just one image, and billions of them when many years of observations are collected over the entire planet.”

This kind of understanding can be applied, for example, in the local and global management of fish stocks, which rely on patterns of phytoplankton production. And because phytoplankton carry out photosynthesis – absorbing CO2 and releasing oxygen – understanding where, when and how much of this resource there is can provide vast amounts of information about the global carbon cycle. This, in turn, has major implications for managing climate change.

The potential significance of phytoplankton in this area is enormous, says Antoine, explaining that huge numbers of tiny plants floating across the world’s oceans act as a major sink for atmospheric carbon, sequestering around 50 gigatonnes of carbon per year. This is as much carbon fixation as is carried out by terrestrial plants, and the plankton uses about 500 times less biomass because it is more efficient at photosynthesis. A significant part of the CO2 released in the atmosphere by human activity is absorbed by this process and eventually sinks to the deep ocean and is buried in the ocean floor.

There’s perhaps no better indicator of how all of Earth’s habitats – marine, freshwater and terrestrial – are all intimately linked.

Karen McGhee