More resources to rise from ashes

Instead of ending up in the Semakau Landfill, more metals found in incinerator ash will be recovered and given a new lease of life from the second half of next year.

That is when a metal recovery facility for incinerator bottom ash (IBA) — or ash collected in pits at incineration plants — could be up and running in Tuas, according to the National Environment Agency (NEA). 

The agency recently called a tender to develop and operate the facility, which will recover ferrous metals — those with iron content and magnetic properties — and non-ferrous metals, such as aluminium and copper, from bottom ash generated at the four incineration plants here.

Over 1,500 tonnes of bottom ash are generated a day, and the NEA projects that the figure could rise to about 2,100 tonnes by 2023. Metals make up about 8 to 15 per cent of the bottom ash by weight.

Currently, ferrous pieces up to 30 centimetres are removed from the ash stream by magnetic separators at the incineration plants.

The facility is part of the Government’s plans to put incinerated ash to greater use and prolong the lifespan of the Semakau Landfill beyond 2045.

It is developing environmental standards and application guidelines for ash reuse over the next few years but is, in the meantime, “looking at initiatives to recover metal from IBA as part of resource recovery”, the NEA stated in its tender. When the standards and guidelines for ash reuse are developed, the residue after metal recovery can be processed “to make it suitable for safe application”.

Putting bottom ash to good use is not a new concept; it has been used here as a foundation layer for new roads on a trial basis, and is used in roads and car parks as foundation material, and in concrete and cement in places like Denmark, the Netherlands and Taiwan.

Sustainable Energy Association of Singapore Chairman Edwin Khew said much research is taking place to ensure products made from bottom ash do not leach out toxic substances, like heavy metals, that may be embedded in the ash.

Research is also being done in some countries to recover a higher proportion of metal from bottom ash. Delft University of Technology, for instance, has developed technology to treat bottom ash, so that the bulk of moisture and particles smaller than 0.5 millimetres — which make the ash so sticky and clumpy that it is difficult to recover all non-ferrous particles — are removed, wrote Dr Peter Rem on the “Resources and Recycling” blog of Delft’s Faculty of Civil Engineering and Geosciences.

Delft researchers aim to create a low-cost process that recovers “so much metal and mineral value from IBA that even relatively small incinerators will be tempted to install it into their plant”.

Mr Khew said recovering and recycling valuable products from waste is “always good” and will attract investments in treating and extracting metals from bottom ash.

According to the NEA tender, which closes on Sept 24, the metal recovered from bottom ash will belong to the facility’s operator, which is expected to “apply the optimal technology necessary”.

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