The Engineer

Biodegradable products 'harm environment' during disposal

News

Research from North Carolina (NC) State University shows that so-called biodegradable products are likely doing more harm than good in landfills, because they are releasing a greenhouse gas as they break down.

‘Biodegradable materials, such as disposable cups and utensils, are broken down in landfills by micro-organisms that then produce methane,’ said Prof Morton Barlaz, head of NC State’s Department of Civil, Construction and Environmental Engineering. ‘Methane can be a valuable energy source when captured, but is a potent greenhouse gas when released into the atmosphere.’

The US Environmental Protection Agency (EPA) estimates that only about 35 per cent of municipal solid waste goes to landfills that capture methane for energy use. The EPA predicts that another 34 per cent of landfills capture methane and burn it off on site, while 31 per cent allow the methane to escape.

‘In other words, biodegradable products are not necessarily more environmentally friendly when disposed of in landfill,’ said Barlaz.

The problem may be exacerbated by the rate at which these man-made biodegradable materials break down. Federal Trade Commission (FTC) guidelines call for products marked as ‘biodegradable’ to decompose within ‘a reasonably short period of time’ after disposal.

But such rapid degradation may actually be environmentally harmful, because US federal regulations do not require landfills that collect methane to install gas collection systems for at least two years after the waste is buried. If materials break down and release methane quickly, much of that methane will likely be emitted before the collection technology is installed. This means less potential fuel for energy use and more greenhouse gas emissions.

As a result, the researchers found that a slower rate of biodegradation is actually more environmentally friendly, because the bulk of the methane production will occur after the methane collection system is in place. Some specific biodegradable products — such as bags that hold garden waste that are always sent to composting or anaerobic digestion facilities — were not included in the research.

’If we want to maximise the environmental benefit of biodegradable products in landfills, we need to both expand methane collection at landfills and design these products to degrade more slowly — in contrast to FTC guidance,’ said Barlaz.