Clean-up provides stormwater as alternative supply

Helping Melbourne keep its urban river and water systems healthy is the underlying objective of Dr David McCarthy's research at the internationally renowned Monash University Centre for Water Sensitive Cities. At the top of his agenda is the need to tackle pollution to make sure stormwater is safe for reuse and discharge to downstream recreational water bodies.

Population growth and climate change are both expected to place pressure on existing water supplies. Stormwater provides an alternative source of supply, provided it can be effectively treated to remove pollutants.

David's research is rising to this challenge. He has two project areas. One is identifying the pollutants that accumulate in stormwater. The other is improving stormwater harvesting and reuse by developing sustainable, low-cost, low-energy treatment systems to remove those pollutants. He is seeking simple, sustainable solutions that reduce our environmental impact.

Stormwater is not just rainwater, David says. Rainwater is relatively uncontaminated when it is harvested. But stormwater collects any number of exotic pollutants as it rushes across roads and footpaths. Leaking septic tanks and misaligned domestic and trade sewers add to the contamination. 

He says many of the systems being installed to treat stormwater for reuse are highly engineered, energy-hungry and expensive to build and operate. These kinds of systems are difficult to sustain in the long term.

Treatment is usually based on 'indicator' organisms. However, stormwater can contain a whole host of more exotic disease-causing organisms, some of which are potentially deadly. 'If we're going to reuse this water we need to better understand the risks and eliminate the actual contaminants, not just indicator organisms. And it is as important for the rivers and creeks, where much of the stormwater ends up, as it is for potential urban reuse.'

One of the simplest stormwater treatment approaches is biofiltration. Stormwater is collected and processed through a 'vegetated filter'. This could be something like a swale that has been planted with shrubs. The plants help to take up nutrients and other specific pollutants from the stormwater. The sand or soil media lining the swale removes pollutants in several different ways. It can physically strain out pollutants, absorb them, or transform them into something less harmful through various chemical or biological processes. The treated water can then be redirected for discharge to downstream water bodies or for reuse.

David says biofiltration treatment of common stormwater pollutants is well recognised. Less well understood is how these systems perform in removing some of the more exotic pollutants. Improving this understanding is essential if stormwater is to be reused - whether that is for backyards, public parks or toilets.

He says there is potential to develop stormwater harvesting systems for use at the individual property level - on gardens and for flushing toilets. Rainwater harvesting is already common practice at the household level. Adding stormwater collected from other surfaces would simply be an extension of this. 

At a street level, stormwater could be used for trees and nature strips. At a precinct level, there could be more widespread watering of community parks and gardens and stormwater could even be introduced into the household for non-drinking uses. 

Not surprisingly, David's research has drawn cooperation from a wide range of water agencies in Melbourne and industry partners. He collaborates with leading national and international universities in much of his research. He enjoys the sense of being part of a much larger effort to better understand Australia's aquatic systems, especially those in urbanised areas.

David's research area is the movement of pollutants within urban water systems and the subsequent treatment of storm- and waste-waters for the protection of downstream ecosystems and, most importantly, human health.

His PhD involved the collection and uncertainty analysis of urban stormwater microorganism datasets, and the development of a new model to predict microbes in urban stormwater. He is a project leader in the CRC for Water Sensitive Cities, with a focus on how to effectively remove pathogens from various water sources using passive (or natural) treatment technologies. More recently, he studies the sources, sinks and processes of pathogens in the Yarra River estuary. He is a member and the treasurer of the Joint Committee on Urban Drainage, and the Chair of the International Data and Models Working Group, both of which fall under the International Water Association (IWA) and the International Association for Hydro-Environment Engineering and Research (IAHR). He was the deputy-chair and scientific chair of the 7th International Conference on Water Sensitive Urban Design (2012) and is the Chair of the upcoming International Conference on Urban Drainage (2020). He is a Churchill Fellow (2009), FASIC Fellow (2012) and a Victoria Fellow (2014), and also won a 2014 Young Tall Poppy Science Award.

David is a founding member of the Monash Centre to Impact AMR, and is a member of the Environmental Engineering strategy group.