Republic Polytechnic team finds way to ‘clean’ incineration ash

LOUISA TANG Today online 9 Sep 17;

SINGAPORE — Fly ash produced from burning garbage could soon be used to make concrete, reducing the amount of waste that will have to be dumped in landfills.

A research team from Republic Polytechnic (RP) has come up with a new nano-silica product that “cleans” incineration ash, building on a similar product created in Europe to deal with waste management. Silica is a common mineral found in many materials, such as sand.

Last year, an average of 250 tonnes of incineration fly ash (IFA) and 1,350 tonnes of incineration bottom ash (IBA) were generated a day in Singapore’s four incineration plants.

While both types of ash contain toxic heavy metals such as zinc and lead, IFA has higher concentrations of such metals, and they tend to “leach out more”, or escape from the ash, said research project principal investigator Dr Goh Chee Keong.

The amount of metals in the ash is not high enough to offset the cost of extracting them, he added.

Hence, to stabilise the heavy metals in the ash, the RP team mixes its nano-silica product with the ash. The silica nanoparticles then bind and trap the heavy metals — a process that is about 20 to 30 per cent more efficient than current methods, Dr Goh said.

By doing so, the metals will not leach out of structures that are made of concrete containing treated IFA, when it rains. Such leaching could result in the toxic metals contaminating rainwater that runs into the reservoirs, which poses a serious health risk.

Treated IFA is considered to be a greener alternative to sand and cement, which are traditionally used to make concrete. The cement manufacturing industry is one of the primary producers of carbon dioxide, a major greenhouse gas.

The four-man RP team, who completed their research in January after three years, tapped the National Environment Agency’s (NEA) Environment Technology Research Programme grant scheme for their project.

First launched in 2009, the scheme aims to help Singapore-based companies and researchers develop and commercialise advanced technologies for making better use of waste.

The team has filed for a patent for their nano-silica product, and is in talks with several firms to explore how they can use it in their industry operations.

In response to TODAY’s queries, the NEA said that the RP project has shown positive results.

However, since it is a lab research project, further study will be required to produce the product “on a commercial scale for it to be viable, and to develop and optimise an integrated continuous process for the chemical stabilisation of incineration ash, and to recycle the water to minimise its usage,” it added.

Apart from being a greener alternative, the RP team noted that using treated IFA to make concrete will reduce pressure on the Semakau Landfill — Singapore’s only landfill that is expected to be filled up by 2035 — where all incinerator ash and non-incinerable waste are currently disposed of.

Waste generation in Singapore has increased steadily from 7.67 million tonnes in 2015 to 7.81 tonnes last year, said the NEA.

Dr Goh said the treated incineration ash produced by his team is expected to comply with current European standards.

The NEA added that it is working on the development of environmental guidelines for the use of IBA in land reclamation and construction.

Treated IBA has been used successfully in trials for road pavement construction in Singapore, while a S$15 million recovery facility to salvage metals from IBA opened in Tuas in 2015.