Beware of 'miracle' waste composters, scientist says

PUBLISHED : Monday, 19 September, 2011, 12:00am
UPDATED : Monday, 19 September, 2011, 12:00am


Property owners and managers should be sceptical of the allegedly fast-performing waste composters they are considering renting or buying under a HK$50 million government subsidy scheme, an expert warns.

Some waste composter suppliers claim their machines are able to turn food waste into compost suitable for organic fertilisers, or reduce the food waste volume by as much as 90 per cent within 24 hours.

'Unless there is a miracle, it will take at least three weeks for the waste to decompose thoroughly,' said Professor Jonathan Wong Woon-chung, head of Baptist University's Hong Kong Organic Resource Centre.

'As a scientist, I am not aware of such a fast-track process of composting.' Under the scheme launched in July, residential estates can seek funding from the Environment and Conservation Fund to install composting machines in an effort to encourage residents to dispose of food waste separately from other rubbish.

Wong, who established a quality standard for solid compost in 2005, said immature compost - food waste that is not fully decomposed - would be less useful as fertiliser or soil conditioner than true compost, and might even damage vegetation if it was improperly applied.

A consultant who works for one of the composter suppliers said the claims for speedy composting could be misleading. 'It is not a composting process using bacteria. Rather, it is just a dehydrating process that dries out food waste in a very high-temperature environment,' he said. However, there are many different composting technologies, and some might use both high temperature and bacteria for a fast composting process, the consultant said.

Food waste accounts for about a third of the 9,000 tonnes dumped daily at landfills, and an average Hong Kong household of four generates about 1.37kg of food waste daily.

There are few recycling channels, although the government plans to build two organic waste treatment plants in Fanling and Siu Ho Wan.

Friends of the Earth, which surveyed eight of the 13 composter suppliers listed on the Environmental Protection Department website, said information on waste composters - including size, purchase or rental price, post-sale service, power consumption and lifespan - varied considerably. The government said the scheme would initially subsidise 10 selected housing estates before more are allowed to join.