Spreading MBT output on farmland goes on trial

Organic material made from mixed waste is being spread on a farm near Leicester in a two-year trial. But no discussions have yet been held over its public acceptability.

Organic outputs from mechanical-biological treatment (MBT) of municipal solid waste are being spread on farmland in Leicestershire in a two-year trial.

The trial, which started in October at Loddington Farm near East Norton, is being carried out by environmental consultancy ADAS UK for Leicester City Council and waste firm Biffa.

It intends to quantify the nitrogen release from the organic fraction of MBT residues to show it has a beneficial effect on crop yield. Up to six tonnes of the compost-like outputs will be spread on 0.2 hectares of land during the trial.

Leicester City Council and Biffa have been investigating the spreading of MBT outputs on farmland since 2005, following changes to the waste management licensing regulations (ENDS Report 393, pp 19-20 ). These meant that compost from processes such as MBT or anaerobic digestion could only be spread on agricultural land if made from source-segregated waste. But Leicester wants the spreading of MBT residues from mixed wastes to be a permitted operation.

At the time, the council was planning to spread the 5,000 tonnes of organic material produced each year by Biffa’s MBT plant in Leicester on farmland through Severn Trent’s sewage sludge network. Currently, the material is being used in land restoration.

The plant treats 100,000 tonnes of mixed municipal waste a year to make a refused-derived fuel for use in cement kilns, as well as the compost-like fraction.

ADAS has been testing the organic outputs from the Leicester plant and other MBT plants for over three years. This has shown the material has a similar composition to treated sewage sludge and green compost, said Paul Gibbs, principal scientist at ADAS (see table). It does not pose a risk to the environment or human health, he added.

The outputs analysed appear to have higher levels of lead compared with green compost and sewage sludge at an average 730 milligrams per kilogram. However, Brian Chambers, senior principle scientist at ADAS, said at typical agricultural application rates the lead applied would be less than 15kg per hectare over ten years - the level allowed under the code of practice for agricultural applications of sewage sludge. The high lead content is potentially due to batteries going through MBT plants, and Leicester is considering introducing a separate collection for them.

The trial is the first to take advantage of an Environment Agency position statement on regulating trials of waste management activities.1 The Agency will allow trials without an environmental permit or exemption when the operator can satisfy the Agency "the proposal is a genuine trial of a previously untested process" and that "it would be disproportionate to require an environmental permit".

In such cases, the Agency will issue a regulatory position statement, which will outline the details of the trial including how much waste can be used and where. Trials should last no more than six months, although the Agency will consider exceptions.

The Agency intends to pilot this approach for six trials before deciding whether to adopt the system permanently. A regulatory position statement for the ADAS trial was issued in October.2 Once the trial is completed, ADAS intends more studies looking at metals and organic compounds released to soil. In the longer term, Leicester City Council is seeking an environmental permit to spread the organic output from the MBT plant.

However, it is uncertain whether the public would be willing to accept the application of MBT outputs to land. During the summer, several articles appeared in daily newspapers claiming sewage sludge spread on land could be a health risk - much to the water industry’s concern (ENDS Report 404, p 19 ).

"Public perception is something we need to address with supermarket buyers at a later date once we’ve shown the output is safe and of a benefit to the environment," Dr Gibbs said. However, the British Retail Consortium said in a statement: "Any MBT material put on land would need to be approved by Assured Food Standards and we’d need to be assured it’s acceptable to the public."

Other waste firms and councils will be following the trial’s results closely. An MBT operators group - the BioCompost Alliance - is pushing for outputs to be spread on land. The group includes Biffa, Sita, Premier Waste Management, Global Renewables, Shanks, Viridor, Sterecyle and technology provider Bedminster.

Quality Meat Scotland has ended a ban on its members spreading green waste compost on their farms.

Last October the certification body for cattle and sheep farms placed a moratorium on its members using waste derived compost due to concerns about the presence of viruses such as foot and mouth and noxious weeds such as ragwort (ENDS Report 396, pp 18-19 ).

In July, it ended the ban on green waste following research into the presence of weeds. However, the compost needs to be ploughed into land rather than spread on top of it.

There is still a moratorium on compost made from food waste. The government’s Waste and Resources Action Programme is conducting a risk assessment and is due to report in March. The Open University has also been commissioned to investigate public attitudes to food waste compost. It will report in October.

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