MORE than 10,000 tonnes of dried human sewage and grease trap waste is being used each year as fertiliser on Hunter farms and coalmine rehabilitation sites.
Although state government regulators insist the practice is safe, some environmental activists say otherwise, citing the cumulative effects of heavy metals present in much of the material, together with other toxins and risks such as viruses and bacteria in the sludge.
Senior Environment Protection Authority staff told the Newcastle Herald that recycling the nitrogen-rich material as fertiliser was better than dumping it in landfills, which was what had happened before the practice began.
Authority staff confirmed the practice was made legal by exemptions to pollution laws granted to the recycling industry, but they say these exemptions mean the government has an ‘‘audit trail’’ to follow every load of sewage sludge or grease trap waste used as fertiliser.
Evidence of the scale of the practice emerged after the Herald investigated a tipoff from someone in the industry.
Grease trap waste is collected from drainage points in the sewage systems of commercial cooking operations and other businesses using oils and fats, while sewage sludge, also known as biosolids, is obtained from sewage treatment plants operated by government-owned water authorities including Hunter Water.
Hunter Water said this week it produced between 5000 and 6000 ‘‘dry tonnes’’of biosolids a year.
‘‘In the Hunter, approximately 40per cent of biosolid production is used for mine site rehabilitation and the remaining 60per cent is used for agricultural reuse,’’ a Hunter Water spokeswoman said.
A major collector and supplier of grease trap waste in the Hunter is Black Hill company Enviroking, licensed to handle 20,000 tonnes of waste a year.
A 2010 Department of Planning report on an expansion of the Enviroking plant said it would produce between 6000tonnes and 9000tonnes a year of grease trap waste in solid or sludge form.
In its application to the department, Enviroking said it had been supplying grease trap sludge to the nearby Bloomfield open-cut mine for rehabilitation.
A Bloomfield Collieries spokesman confirmed using the grease trap waste in a trial a few years ago.
The spokesman said the process had stopped because it had not resulted in any noticeable improvement to the land in question.
Enviroking declined to comment to the Herald last week, beyond saying everything it did was approved under the relevant legislation and guidelines.
Although the practices are legal, environmentalists contacted by the Herald questioned them.
Total Environment Centre spokesman David Burgess said exemptions from authority regulations implied the processes ‘‘exceed normal limits’’.