Anaerobic digestion: reducing landfill waste
Leicester is a very urban city with limited pavement space for kerbside containers. But Leicester City Council was determined to cut its waste sent to landfill. So the council commissioned a collection and treatment service that included anaerobic digestion through the Private Finance Initiative (PFI).
There is a kerbside collection of glass, paper and plastic bottles. Wheelie bin waste is taken to a mechanical cascade mill, or ball mill, where the waste is separated into:
- organic waste - food and any garden waste
- plastic film, plastics and cardboard
The organic fraction is transported to an anaerobic digestion plant at a local sewage treatment works.
The financial model is based on tonnage. Biffa Waste Management get a fixed payment for a year, which covers the collection, treatment and disposal. This only varies if the tonnage varies.
Biffa make money by selling:
- scrap metals
- electricity from the anaerobic digestion plant back to the national grid
- liquid digestate for use as a soil conditioner
- plastic film, plastics and cardboard for cement making when there is a market for it.
They build this income into their bid so that it is reflected in the overall contract price paid by the council.
Leicester became Britain's first ‘Environment City' in 1990. In 1992, it was one of 12 world cities invited to attend the Earth Summit in Rio de Janeiro. Since then it has always been keen to adopt sustainable policies. Waste management is a big part of that and Leicester was keen to extract value from black bin waste.
The council wanted to divert waste from landfill to avoid incoming landfill taxes.
There were some teething problems initially because it was a new technology.
Bio-digestate - a by-product of the anaerobic digester - was originally sold to farmers as a fertiliser. In 2005, the Department for Environment Food and Rural Affairs (Defra) introduced new regulations that made this no longer possible. So Leicester and Biffa have been working with Defra and the Environment Agency for five years to show the material is safe for agricultural use. This has taken a long time and been very expensive.
The bio-digestate is currently being used as a soil conditioner on brownfield sites for land reclamation. However, recent field trials have produced favourable results for agricultural use. So Leicester and Biffa are now negotiating with the Environment Agency for a permit to use the digestate on a local farm.
Ensure the public are made aware of what is going on and what to expect. Leicester and Biffa placed a great deal of emphasis on public consultation. Throughout the procurement process they:
- publicised all council reports
- gave details of the scheme
- had a road-show around the area where the mechanical ball mill was built
- involved local press and radio
- involved the local tenants' associations.
A sewage treatment works is a good place for an anaerobic digestion plant because:
- it allows the digestate to go along the same route as sewage sludge to agriculture
- any odours associated are nullified by the sewage treatment works.
Whenever you put in a planning application, objections and comments will come in from a wide spectrum of people. So involve third parties like the Environment Agency and Friends of the Earth as well as the planning authority. Encourage them to talk to you about the development.
There is a weekly service for kerbside recycling and wheel bin contents. The scheme is popular among residents. Comments from the satisfaction survey 2010 include:
- "Staff do a good job and work very hard."
- "Have never had problems with recycling,everyone should do it."
- "Teams are friendly - when my little boy stops to watch them work if they spot him they give him a wave and it makes his day."
Leicester has a recycling and composting rate of just over 40 per cent, roughly half of which is derived from the organic material processed by anaerobic digestion.
The anaerobic digester processes about 20,000 to 25,000 tonnes of waste a year and the plant generates enough electricity to power 1,500 homes every hour. This is fed back into the National Grid.
Councillor Sarah Russell, Cabinet Lead for the Environment, says:
"We have significant parts of the city where the communities are quite transient - such as student areas and others. The big advantage of the system is that it's not only effective on street recycling, but also for those communities where you're never going to get very high recycling levels, you can still ensure a significant diversion from landfill and get the environmental benefits associated."
Head of Waste Management, Leicester City Council
Telephone. 0116 2161904
1 May 2012