Sewage sludge is a valuable resource. Direction Scotland, where sludge becomes green energy and fertilizer.
In Edinburgh, thanks to innovative processes implemented by Veolia to make the most of sewage sludge, they are no longer percieved as problematic waste, but as a useful and even profitable resource.
A circular approach
Veolia operates approximately 15 wastewater treatment facilities in Scotland’s Edinburgh and Lothian areas. The project was made to cover the sanitation needs of approximately 900,000 people and treats over 125 million m3 of wastewater per year.
Taking a circular approach, Veolia has a twofold objective - to reduce not only the environmental impact of the various facilities but also their operating costs. For example a cogeneration plant (which simultaneously produces electricity and heat) which converts the sewage sludge into a new resource.
In addition to providing significant energy self-sufficiency, excess electricity produced is sold to the National Grid, thereby producing a significant revenue stream. At the same time the volume of sludge is reduced by the process and this delivers savings worth several million pounds per year.
Great news for farmers
The Seafield wastewater treatment plant in Edinburgh, the largest managed by Veolia in Scotland, it has been equipped with a solution combining thermal hydrolysis and anaerobic digestion. The thermal hydrolysis technology, which consists of heating the sludge under special temperature and pressure conditions to hydrolise it, improves the efficiency of the anaerobic digestion process which both creates more energy whilst reducing the sludge to be disposed of. Not only is the volume of sewage sludge is further reduced, but it also produces even more new resources in the form of biogas and fertilizers.
Thanks to the process implemented by Veolia, these fertilizers add a very interesting dimension to the project, since several tonnes of biosolids are now produced per day at Seafield. Rich in nutrients such as nitrogen, phosphate, and sulfide, they can be used as fertilizer on farmland which helps improve productivity and stimulate plant growth – and means less chemical fertilizers too!
Consequently Veolia converts 60% of the sludge to energy generating enough electricity to supply 4,000 homes and produces 30,000 tonnes of organic fertilizer for agricultural use.
Main picture: Credit phototheque Veolia, Stéphane Lavoué