Republic Polytechnic (RP) boffins have made significant progress in solving what is looming as a major crisis - how to deal with mountains of trash once Singapore's only landfill runs out of space.
The Semakau Island landfill is expected to hit its limit by 2035, a deadline that has prompted an urgent search for other options, including assessing if piles of burnt rubbish can be used in construction and cars.
The idea of using incinerated ash to replace sand and stone in construction is not new, but its application has been delayed because of the risk of toxic heavy metals leaching into the environment.
But the RP researchers have created a chemical called GGBS-OPC that can bind heavy toxic metals like lead and arsenic to incinerated bottom ash so that they will not pollute the surroundings once exposed to water, sunlight and open air.
RP's project, which won $1.2 million in funding in April, was one of four that received grants under the National Environment Agency's (NEA) Closing The Waste Loop research and development initiative.
The $45 million fund was set up in 2017 to help academic and research institutes and companies that develop technology to convert waste to resources.
The same RP team developed a special chemical in 2014 that encapsulates toxic heavy metals within incinerated fly ash to stop leaching.
Dr Goh Chee Keong, the project's principal investigator, said a tonne of incinerated bottom ash can produce between 900kg and 950kg of material for construction.
About 1,500 tonnes of such ash is produced here a day, said the NEA last year.
RP, which has a patent pending for its research, is collaborating with construction firm EnGro Corporation, which provides the raw materials for making the GGBS-OPC liquid binders.
"The challenge of using incineration ash in construction materials is that, currently, Singapore does not have its own standards or environmental guidelines for the industry and, thus, adoption is quite limited," said Dr Goh.
He added that the NEA is working to develop such guidelines and that RP expects to expand the project to an industrial scale in three or four years.
The same round of grants is helping Nanyang Technology University (NTU) to develop ways to use incinerated ash to construct catalytic converters in cars.
Catalytic converters transform toxic gases produced during fuel combustion in car engines into non-toxic gases for release into the environment. Carbon monoxide, for example, turns into carbon dioxide when it goes through the converter.
Associate Professor Xu Zhichuan, principal investigator of the NTU project, said that about 2kg of incinerated ash would be needed to build what is called a ceramic substrate for a car's catalytic converter.
His team of four received a $1.5 million grant last month and is studying ways to build the substrate.
"Such an application can lead to high value creation while consuming considerable amount of ash to relieve the pressure on the landfill site," said Professor Hu Xiao, co-principal investigator of the team..
"It provides a waste management solution for land-scarce countries such as Singapore."
