Swinburne University of Technology - Melbourne Australia

No waste spared for travel in the fast lane

Story by Robin Taylor

Whenever he drives on a freeway, Dr Atputharajah Arulrajah eyes the roadside embankments and pictures a not-too-distant future when such earthworks are all created from recycled waste, including sewage.

He hopes to broker a marriage between the vast amounts of fill material for new roads and their embankments, and the large volumes of biosolids (the products left over after domestic wastewater has been treated) being accumulated by water treatment plants.

Dr Arulrajah, a senior lecturer in civil engineering at Swinburne University of Technology’s Centre for Sustainable Infrastructure, believes biosolids would be an ideal material to recycle into such civil engineering applications.

In a project funded by the Smart Water Fund, an initiative of the metropolitan water businesses and the Victorian Government, and with the support of VicRoads, he is studying the properties of biosolids and their suitability for use as a stabilised fill.

Dr Arulrajah specialises in the sustainable use of recycled materials. His other projects involve re-use of brick rubble, crushed concrete and crushed rock. He thinks biosolids could become a useful resource for road construction and, when mixed with other substances, could become stable enough to use in embankments.

Manager of the Smart Water Fund Chris Lee says the project is an example of the innovative thinking that the fund seeks to support. "It is an exciting project. The idea of using treated biosolids as fill material in construction is one that has the potential to address a key challenge of the water industry, the disposal of biosolid waste from the water treatment process."

Dr Arulrajah is applying his skills and experience as a geotechnical engineer to the project. After working on major projects in Singapore and Malaysia over a period of 12 years, including Singapore’s Changi International Airport land reclamation project, he came to Melbourne in 2004 and joined engineering consultants Connell Wagner.

It was while working with Connell Wagner on a biosolids handling project at Melbourne Water’s western treatment plant that he began thinking about the potential for using these waste materials in civil engineering applications. He had the opportunity to put his ideas into practice when he joined Swinburne in 2006 and successfully applied for a research grant from the Smart Water Fund.

"A lot of my research nowadays is looking into recycled materials and how to use them in a sustainable manner in engineering applications," Dr Arulrajah says. "I knew there were biosolid stockpiles and I thought we could try to use it in geotechnical engineering applications, such as road embankment fills."

Senior environment officer for VicRoads Marianne Robertson says a huge amount of fill is used in major projects: "The Deer Park (Melbourne) bypass, for example, used three million cubic metres of fill."

However, there are strict engineering requirements for this material.

"Biosolids have a high organic matter content, which generally makes them unsuitable for a lot of our structural fill," Ms Robertson says. "The organic matter doesn’t allow it to compact properly to the required density."

This is where Dr Arulrajah’s research comes in. He is investigating what needs to be done for biosolids to meet these specifications.

Dr Arulrajah is looking at mixing biosolids with cement as a way of strengthening and stabilising them, but the research still has some distance to travel.

"It fits in with our move to try to minimise the use of virgin materials and increase the use of recycled materials," says Ms Robertson, who is hoping to trial biosolids as non-structural fill if Dr Arulrajah’s results give them the thumbs up.

So far the results are promising. "Field tests to determine the strength properties and bearing capacity of the material show great potential," Dr Arulrajah says.

The next phase of the project is to verify these results through laboratory tests, which are under way, and then to model embankments using biosolids.

Director of Swinburne’s Centre for Sustainable Infrastructure Professor John Wilson says the project is a typical one for the centre, which has a focus on sustainable materials and emerging technology.

"We see great growth in finding novel uses for materials that once would have ended up in landfill," he says. The emphasis is on recycling material in infrastructure-type applications.

Other projects that the centre is involved in include investigating the use of recycled brick rubble for road bases, and tyres for concrete. "In Melbourne alone, 500,000 tonnes of brick rubble from demolition jobs are being stockpiled," Professor Wilson says.

Sustainability Victoria is funding this project, which also involves a number of demolition companies and VicRoads.

The problem of tyre waste is also huge. "In developed countries, about one tyre for every person goes to waste each year," Professor Wilson says. In Australia, this equates to about 20 million tyres each year going to waste."

The Swinburne researchers are working with a commercial partner on crumbing tyres and using the crumbed material in concrete.