Sludge Waste Could Self-Heal Sewer Pipe Concrete
Described as a “world-first,” a project from the University of South Australia will look at using water treatment sludge to prevent sewer pipes from cracking in the form of self-healing concrete.
Led by sustainable engineering expert Professor Yan Zhuge, the research team is trialing the novel solution to halt “unprecedented levels of corrosion” in the country’s aging 117,000 kilometers of sewer pipes. The university reports say that this research could help save $1.4 billion in annual maintenance costs.
About the Research
According to the university’s release, corrosive acid from sulphur-oxidizing bacteria in wastewater, along with excessive loads, internal pressure and temperature fluctuations are cracking pipes and reducing concrete pipeline life span in Australia. This reportedly costs hundreds of millions of dollars to repair every year across the country.
The researchers say that self-healing concrete, in the form of microcapsules filled with water treatment sludge, could present a solution.
The team will reportedly develop microcapsules with a pH-sensitive shell and a healing agent core containing alum sludge, which is a by-product of wastewater treatment plants, and calcium hydroxide powder. The combination is anticipated to be highly resistant to microbially induced corrosion (MIC).
“Sludge waste shows promise to mitigate microbial corrosion in concrete sewer pipes because it works as a healing agent to resist acid corrosion and heal the cracks,” Zhuge said.
These microcapsules will then be embedded inside the concrete at the final step of mixing to protect it from breakage. When the pH value changes as acid levels build up, microcapsules will reportedly release the healing agents.
“This technology will not only extend the lifetime of concrete structures, saving the Australian economy more than $1 billion, but it will promote a circular economy as well by reusing sludge that would normally end up in landfill,” said Zhuge.
The university also reports that existing repairs are expensive and often short-lived, with 20% failing after five years and 55% failing after 10 years. While chemicals can be added to wastewater to stop corrosion, they are also costly and contaminate the environment.
Other options reportedly involve increasing the speed of sewage flow by amending the pipe hydraulics or adding surface coatings. However, these methods are not always effective, are time-consuming and their effects are temporary.
“Improving the concrete mixture design is the preferred method for controlling microbially induced corrosion. Using self-healing concrete that can seal cracks by itself without any human intervention is the solution,” said Zhuge.
Additionally, he notes that the construction industry is being forced to transition to a circular economy to be carbon-neutral by 2050.
“Industry by-products or municipal wastes that would normally be discarded in landfill sites, potentially generating pollution, may now be reused in the construction production chain,” he said.
“Mainland Australia alone has about 400 drinking water treatment plants, with a single site annually generating up to 2,000 tons of treated water sludge. Most of that is disposed of in landfill, costing more than $6 million each year, as well as causing severe environmental issues.”
Drinking water treatment sludge (DWTS) generally accounts for 1-3% by volume of the raw water and disposal accounts for a significant part of the total cost of water treatment. One ton of sludge disposed in a landfill also reportedly releases approximately 29.4 tons of carbon dioxide emissions and leaches aluminum into the soil and water.
By replacing sand and cement with DWTS, the team anticipates effectively eliminating stockpiled sludge to improve water operation system efficiency.
“We are confident this novel self-healing concrete based on advance composite technology will address issues of sewer pipe corrosion and sludge disposal in one hit,” said Zhuge.
The project is being partially funded by a grant from the Australian Research Council totaling $501,504. It also involves researchers from the University of South Australia and University of Queensland.
Other Sewer Concrete Research
Back in May 2020, engineering researchers from RMIT University explored a zero-waste approach that both treats wastewater and makes stronger concrete. In the study, researchers took steel slag used to absorb contaminants like phosphate, magnesium, iron, calcium, silica and aluminum, among others found in wastewater, and upcycled the remaining slag as an aggregate material for concrete.
“The global steel making industry produces over 130 million tons of steel slag every year,” said water engineer Biplob Pramanik at the time. “A lot of this by-product already goes into concrete, but we’re missing the opportunity to wring out the full benefits of this material."
In taking the steel slag used in wastewater treatment, civil and water engineers found that the new chemical properties caused that slag to perform better in concrete, making the new form stronger than its traditional steel slag counter-version.
“While there are technical challenges to overcome, we hope this research moves us one step closer to the ultimate goal of an integrated, no-waste approach to all our raw materials and by-products,” said Pramanik. He added that the study is the first to investigate potential applications for “sewage-enhanced” slag in construction material.
Later that year, in October, RMIT University engineers announced that they developed an eco-friendly, zero-cement concrete that can withstand corrosive acidic environments, commonly observed in sewage pipes and other types of wastewater infrastructure.
In an attempt to combat build-ups of fat, oil and grease—often referred to as “fatbergs”—in sewers and pipelines, lead RMIT researcher Rajeev Roychand and his team developed a concrete that eliminates the chemical compound that promotes corrosion and fatbergs, free lime.
According to RMIT, the material consists of manufacturing by-products including a zero-cement composite of nano-silica, fly-ash, slag and hydrated lime. In using the industrial by-products, the end result is reported to surpass sewage strength standards set by ASTM International and is more durable than ordinary Portland cement.
Additionally, the final product is also environmentally friendly, reduces concrete corrosion by 96% and totally eliminates residual lime that is instrumental in the formation of fatbergs.
While RMIT said replacing underground concrete pipes is a tedious task, the study proved certain by-products could help to reduce the annual costs of maintaining sewage networks and greenhouse gas emissions. Roychand and his team were looking to collaborate with manufacturers and government to develop more applications for their zero-cement concrete at the time.