"Gutter oil" alleged to have been pumped out of sewers near food outlets in Jurong was not sent to hawkers but used for processing into biodiesel, the National Environment Agency (NEA) said yesterday.
Its investigations into two incidents there found the waste oil was taken from grease traps that collect waste, which is supposed to be disposed of at one of the national water agency PUB's water reclamation plants.
Members of the public spotted a couple extracting the oil in two separate incidents in Jurong.
The NEA said anyone who collects or disposes of such oil illegally can be fined up to $2,000.
It added that it is investigating another case in Toa Payoh earlier this week, which the police said involved two men.
The agency explained that food establishments in Singapore are required to provide grease traps and maintain them regularly by hiring licensed general waste collectors.
These traps are installed as part of the sewerage system to prevent grease from clogging it.
The collectors are supposed to use vacuum trucks to empty the traps and dispose of the waste at a designated reclamation plant.
The NEA said it carries out checks at food outlets to ensure that ingredients used, including cooking oil, are from approved and licensed sources.
"There have been no previous incidents or person caught by NEA for illegal clearing of grease traps, or instances of food shops or food stalls using cooking oil from illegal sources in the past five years," a spokesman said late last month.
The Agri-Food and Veterinary Authority added that it checks licensed food manufacturing establishments, including those that produce or use cooking oil, and takes oil and food product samples for testing.
It also inspects and tests samples of imported food, including cooking oil. To date, it has not come across any use of waste oil in its checks.
"We also have not received any feedback on the use of waste oil in imported cooking oil or food manufacturing establishments," a spokesman added.
But biodiesel producers said that the illegal siphoning of waste oil has been going on for years.
The opportunists who siphoned such oil would later sell it.
A company director with more than 10 years' experience in the industry, who declined to be named, admitted that he occasionally buys four to seven tonnes of the waste oil to produce biodiesel.
"Sometimes the sellers will tell us it's good oil but we have a test kit because third parties may mix the oil," he said. "We pay about 30 cents for 1kg of grease trap oil."
Another veteran who has been in the industry for more than a decade said some illegal collectors sell the oil in Malaysia. The buyers blend the cheaper, toxic gutter oil with crude palm oil and sell the mix to unsuspecting customers in Third World countries.
"You can mix up to 50 tonnes of the gutter oil with 5,000 or 10,000 tonnes of crude palm oil and nobody will know," said the veteran, who also declined to be named.
Mr Allan Lim, chief executive of Alpha Biofuels, which works with companies such as Marina Bay Sands to recycle used cooking oil into biodiesel, said more regulation is needed to prevent such illegal, cross-border sales.
"I've seen the effects in Cambodia, where children in remote villages become very ill because street hawkers sell french fries and sweet potato fries with oil that contains a lot of gutter oil," he said.
These illegal "exports" could also haunt Singaporeans, he added. "If foreign manufacturers use the toxic gutter oil to make food products like love letters and pineappple tarts, Singaporeans who go overseas could eat them or bring them back to Singapore."
People who have information on the unauthorised collection of waste from grease traps should contact NEA on 1800-2255632 or Contact_NEA@nea.gov.sg