Sewage sludge is a natural by-product of the wastewater treatment process. Our sewage treatment works now produce more sewage sludge than they did in the past because of improved wastewater treatment standards and an increasing population.
We expect this to continue, which means we must ensure we have beneficial and sustainable ways to manage sludge in the future.
Our economic regulator, Ofwat, this year altered the basis for reporting so that we no longer provide figures on how sludge is recycled. The figures in this section are consistent with the data we provide annually to the Environment Agency and show the actual dry solid weight recycled, which is more representative from an environmental perspective.
In 2009, 265,682 tonnes of dry solids were produced. We put 100 per cent of this to beneficial use, sending none to landfill. Most of this (56 per cent) was treated and recycled to agricultural land (as biosolids) in order to provide soils with a valuable source of organic matter and nutrients. This is recognised as the best practicable environmental option in most circumstances by the EU and UK government.
| Agriculture | Incineration | Land restoration | Other | |
|---|---|---|---|---|
| Percentage | 56% | 39% | 3% | 2% |
The production, treatment and recycling, reuse or disposal of sewage sludge is controlled by comprehensive legislation, with which we have maintained 100 per cent compliance. We have also voluntarily complied with tougher quality requirements since 2002. This helps to further reassure our stakeholders about the quality and safety of our biosolids and their use in agriculture.
In addition, sewage sludge has a high calorific content that we can use to generate electricity, in a process we call 'energy from waste'. We use two methods to create power from sewage:
In 'thermal destruction with energy recovery', sewage sludge – the solid content of the sewage – is dried into blocks of 'cake' and burned to generate power.
Methane derived from sewage sludge is burned to create heat, which in turn generates power. This is known as 'anaerobic digestion followed by CHP (combined heat and power)'.
Our 25-year Sludge Strategy, published in December 2008, provided the framework for our sludge investment proposals. During the period 2010 – 15, we are investing in increasing our sludge processing capacity and in new enhanced digestion technology. This technology will maximise energy recovery and lessen the quantity of sludge we need to recycle by reducing the amount of solids within it. Where there is suitable land available, recycling to land remains our favoured option.
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