Down the drain: Do Australian cities have the wrong approach to stormwater?
An inventor from Western Australia is on a mission to change the fate of urban stormwater with an at-source solution that helps transform the contaminated wastewater into a valuable resource.
The founder of Urban Stormwater Technologies Craig Rothleitner knew nothing about stormwater when he set out to solve a problem he noticed while working on dredging projects like the Sydney Harbour Tunnel. All he knew was what he saw.
“We were dredging the bottom of harbours to deepen them and there would be all this black ooze that we would put onto barges and dump out to sea,” he said.
This ooze was made up of the rubbish and rotting vegetation that collects in stormwater drains before being flushed out into waterways. The vegetation is particularly problematic as it begins to breakdown when moisture is present in a drain and releases nutrients that can be harmful to ecosystems.
“Stormwater infrastructure has been designed to prevent flooding with little or no regard for waterway contamination,” Rothleitner said.
“The drains are the first collection point for vegetation, cigarette butts, plastics, sediment, sand, building waste – everything that can go in the drains, will.”
Down the drain
There is no clear record of how much stormwater flows through Australian drains each year, but it has been estimated the country’s urban areas produce about 3000 GL of runoff annually. Less than 3% of this rainwater and stormwater is re-used.
Meanwhile, Australian cities draw an estimated 2100 GL of water from their catchments and groundwater sources annually.
In an era when governments around the world are attempting to climate-proof their water sources, Rothleitner said he believes stormwater should be recycled for use in water sensitive urban design (WSUD) projects or used to replenish groundwater supplies.
While there are notable examples of stormwater re-use in Australia – for example, South Australia’s successful use of managed aquifer recharge – he said this should be a matter of course rather than the exception.
“The most important thing we’re trying to get across is that stormwater is a valuable and substantial resource,” Rothleitner said.
“Currently stormwater is considered a contaminated wastewater, but it’s not contaminated when it comes out of the sky. It becomes contaminated when it lands on urban areas.”
Out of sight, out of mind
Rothleitner said one of the reasons stormwater has been ignored is the majority of the infrastructure is “out of sight, out of mind”.
“There is a public disconnect between the water that falls on our heads and on the roads, and what happens to this water and waste next,” he said.
“People think it goes down the drain and that’s it. That’s the last time they think about it.”
He said the lack of an at-source treatment capable of handling the sheer amount of water and waste that enters each drain has also prevented re-use, as it means water becomes contaminated the second it goes into a drain.
The problem is compounded by the fact that local councils generally take a reactive approach to managing stormwater infrastructure, unlike sewers or roads which they tend to actively maintain.
This means they remove tree roots and address waste when it builds up, but don’t proactively protect the drains.
“The tree roots we can’t do anything about, but the waste entering the drains we can,” Rothleitner said.
“Things like sediment and sand wear concrete stormwater pipes down, while the rotting vegetation becomes acidic and starts chewing them out at the same time … The day you stop waste going in is the day the infrastructure is protected.”
A catch-all solution?
Rothleitner spent more than 10 years developing a solution to the problem. He designed a catch basin insert made of a material that can filter particulate-rich water down to 63 micron – about one tenth the size of a grain of sand – at over 30 litres per second.
As his vision is to see councils across the country use the technology, Rothleitner knew he had to prove the science behind it.
He spent four years working with civil engineers from Curtin University to test the effectiveness of the insert. Their research, which was published recently in the Journal of Environmental Management, found the inserts now increased the overall quality of water entering the system by up to 80%.
With WA alone featuring more than a million drains, Rothleitner said it would be impossible to put one of his devices in each of them. Instead, he said the catch basin inserts should be used in conjunction with end-of-line treatments.
“It’s basic common sense. If you protect the system from the beginning, what happens at the end has got to be better than if you let all the rubbish go in it,” he said.
“But we don’t have a single solution – we’re here to work with everybody. Stormwater is too much of a resource to lose.”