Engineers make a big splash, turning water treatment sludge into sustainable concrete

Concrete is widely used for making sewage pipes due to its availability, affordability and structural strength, but it is highly susceptible to acid and microbial corrosion in sewers, requiring ongoing repairs and maintenance that cost Australian taxpayers close to $70 billion each year.

Australian researchers are tackling this expensive problem facing our nation’s infrastructure by developing an eco-friendly alternative solution to traditional cement sewer pipes that are prone to cracking and corroding.

By combining sludge—a byproduct of the drinking water purification process—and blast-furnace slag, University of South Australia (UniSA) engineers have demonstrated that a new, corrosive-resistant material is more than 50% stronger than cement and resistant to acid-induced degradation.

Their new study published in the Journal of Building Engineering evaluates the effectiveness of the alkali-activated materials (AAMs) and demonstrates why they could revolutionize sewage infrastructure worldwide.

Samples containing 20% to 40% of alum-based water treatment sludge (AWTS) retained more than 50% higher compressive strength compared to 100% ground granulated blast furnace slag (GGBS), which is used in the production of cement.

The new material also limited the penetration of sulfur-oxidizing bacteria and slowed acid-reduced degradation.

UniSA civil engineering Ph.D. candidate Weiwei Duan, whose research is based on this project, says there is another major benefit: finding a cost-effective and environmental use for water treatment residue.

“Sludge is usually disposed of in landfill sites, which not only reduces available land for other uses, but also harms the environment, creating CO₂ emissions from transporting the waste,” Weiwei says.

Principal supervisor and lead researcher on the project, Professor Yan Zhuge, says the findings suggest that partially replacing the blast furnace slag with 20%–40% of water treatment sludge makes them “promising candidates” for use in sewers.

“This has the potential to extend the service life of sewage pipes, reduce maintenance costs, and promote the reuse of water treatment byproducts, thus contributing to the circular economy.

“The construction industry is one of the world’s biggest greenhouse gas emitters, so if we can cut down on the need for cement, we will be helping to lower carbon emissions,” Prof. Zhuge says.

In May, Weiwei Duan received the 2025 Australian Water Association’s Student Water Prize for his research—the first UniSA student to receive this national honor in 60 years.