'Green' roads made out of rubbish

Ash is a by-product of incinerating tonnes of rubbish each day and the Ministry of the Environment is plotting to put the treated waste to better use

By Sharmilpal Kaur

ASH from incinerated rubbish is likely to be recycled and used in the making of roads.

This will help cut down on the amount of rubbish being dumped in landfill, which is filling up fast.

Acting Environment Minister Lim Swee Say saw how European countries turned the ash into roads during a recent trip there.

On his return, he announced the ministry would study how the technique might be applied here.

Singapore throws out 7,600 tonnes of rubbish a day and about 90 per cent of it is incinerated.

The ash is buried in landfill.

According to experts, the ash, if treated properly, can make for durable roads.

Mr Denis Gasquet, chief executive officer of Onyx - one of the world's largest waste management companies - said: 'Properly handled, you would have an excellent product.'

The bulk of the incinerated waste is known as bottom ash, which is the type normally used in road construction.

The rest is known as fly ash, which can be toxic because it contains more heavy metals and has a higher lime content.

According to Internet websites, countries in Europe have been using bottom ash for the past two decades.

In Denmark, Germany and the Netherlands, more than half of the bottom ash generated is used to build roads and in other similar applications.

US states such as Texas, Massachusetts and California have used the ash to build highways and carparks.

Some countries, including Japan, have also used the ash for land reclamation.

But bottom ash needs to be treated before it was used, said Mr Gasquet.

He said it should be properly stabilised.

This means that most of the toxic heavy metals, such as cadmium and lead, have to be removed.

He and other experts also recommended that the ash be piled up and left for several months, so normal chemical reactions, such as oxidation could occur.

Mr David Liang, section manager from Singapore's Environmental Technology Institute, explained that there were two kinds of ash generated from incinerators.

Several environmental studies have shown that using unstable fly ash to build roads could lead to leaching, where acid seeps into groundwater and contaminates the underground water supply.

But fly ash can be recycled for other uses after treatment.

Mr Gasquet said fly ash with low lime and metal content could be used in the manufacture of ceramics.

Mr Liang said fly ash could be also used to make cement.