We have been awarded the Chartered Institute of Waste Management Award for Innovative Practice for developing a new, more sustainable way of stabilising our sludge so it can be used on land as a fertiliser.
We are not always able to digest our wastewater sludge before it is re-used so we often use lime to ensure germs are killed and it can be used safely on land as a fertiliser. But using lime in this way is unsustainable as it is produced by a highly energy intensive process that uses raw materials. Lime is also only found in a relatively few locations in the British Isles so it often has to be moved long distances.
With the help of the National Industrial Symbiosis Programme (NISP), we joined forces with waste management company Envar whose client, paper company UPM Kymmene (UK) Limited, produces large volumes of lime ash from the combustion of paper sludge in its combined heat and power plant.
Joint trials showed that the lime ash can be successfully used as a substitute for quarried lime in our sludge stabilisation. The benefits from its use are:
• Improved odour levels;
• A more attractive fertiliser product for farmers, as the ash contributes potash to the end product, improving its nutrient content;
• Reduction of carbon emissions by preventing virgin extraction of limestone and avoiding the high energy input used in converting it and transporting it.
Four of our existing lime treatment facilities in Lancashire and the South Lakes are now using this substitute material, comprising three quarters of all our liming needs.
