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Feature: Power from people

Current attitudes to sanitation are based on the notion of human excreta as unwanted and unusable waste - something that we must get rid of because it is smelly and potentially dangerous.

With this approach we pollute our environment and also miss opportunities for turning human waste into resources that can create jobs, revitalise agriculture and provide a recycled product used as fertiliser in land reclamation as well as an energy source.

Most of the sewage in England and Wales is treated, leaving a substance called sewage sludge or biosolids. Because dumping sewage sludge at sea was banned in 1998, it has traditionally been disposed of in three ways: farmland, incineration and landfill.

The practice of recycling biosolids to land is recognised by the Government and the EU as often being the best practical environmental option.

Examples of former Scottish collieries where the use of sewage sludge has aided successful land restoration include Drumbow, North Lanarkshire and Skares, and East Ayrshire. The Skares site won the Wildlife Champions Award from the Scottish Environment Protection Agency in 2003 for the innovative approach to reclaiming a derelict brownfield site to create a community woodland. At the site, sewage sludge was used to regenerate poor quality soil, which was then planted with mixed woodland and grass, providing a rich habitat for a wide range of animals and birds.

Using recycled sewage sludge restores derelict land to a useful purpose. The sludge can be used to stabilise spoil and other waste materials prone to erosion and to re-contour disturbed land, such as former collieries, to blend in with the surrounding landscape.

Mixing sewage sludge in with colliery spoil and other materials that lack nutrients creates a medium capable of sustaining plant life.

Biosolids contains nutrients and valuable trace elements essential to animals and plants such as boron, calcium, copper and zinc. One of the most valuable properties of sewage sludge is that it
can be used as a substitute for peat, thus conserving valuable natural peatland in the UK and Ireland. Sewage sludge is a sustainable resource for use in place of peat in land reclamation projects.

In Northumbria, the regional sludge treatment centre at Bran Sands is the largest operational sludge drying facility in Europe. It is particularly interesting because it dries unprocessed rather than treated sewage. This maxi- mises the potential for dried sludge to be used as a fuel by maintaining a higher calorific value in the final product and also eliminates the need for an expensive sewage purification plant.

Biosolids are pumped into storage tanks for thickening. Here the waste is warmed and bacteria in the sludge breathe anaerobically and breed.

This creates gases that can be burned in a combined heat and power plant - the heat is used to warm more sludge and the power is used to drive the works.

The sludge is fed into massive tumble driers and hot air removes virtually all the remaining water. The dried sludge, in granular or pellet form, is then ready for use in agriculture and land reclamation. As it has the same calorific value as brown coal, it can also be used as a non-fossil coal replacement or carbon source in manufacturing.

Recycled sewage can also be used to create electricity. The Wanlip sewage works in Leicester deals with 185 million litres of sewage every day from more than 600,000 people across Leicester and

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