This project had the potential to deal with different types of waste, municipal solid waste, chemical waste, clinical waste etc. but the waste that caught the eye was that of sewage waste.
Sludge production and disposal are entering a period of dramatic change, driven mainly by EC legislation. the Urban Waste Water Directive will result in at least 50% more sludge being produced by the end of 2005 and, during the next decade, sludge disposal to all the established outlets could become increasingly difficult or, in the case of sea disposal, will became illegal by the 1st Jan 1999.
West of Scotland Water
We had a real life problem which has to be tackled immediately. Contact was made with the West of Scotland Water Board and their answer for sludge disposal was to dump it at sea. This is no longer applicable and their next disposal option will be to landfill it, until it is possible to thermally dry the sludge in conjunction with Scottish Power and burn it with coal in Longannet coal fired power station. This decision was based on economics.
Energy from Waste (EfW)
Being an Energy from Waste project, we decided this was the ideal opportunity to look at the various disposal options that were available: dedicated incineration, anaerobic digestion and production of a refuse-derived fuel (RDF), and determine the best disposal option from an energy balance point of view.
The case study
It was a case study involving one of the treatment centres in the West of Scotland area, this particular area being the Glasgow area, where being an urban area it promotes large amounts of sewage to be disposed of. Because of the amount of sewage for disposal we could then look at all the disposal options already mentioned whereas if it were a small rural plant some of the options would not be viable simply on economic grounds.
For each of the investigated EfW technologies and investigated sludge disposal options a literature review was done. A general methodology was used to determine the thermodynamic boundaries involving each of the routes. Assumptions had to be made in calculating our energy balances for each route. The reasons why these assumptions were made are given in the investigated routes of disposal section. Having calculated the energy balances and considered the other peripheral issues we came to a proposed solution which in our opinion is the best disposal route for the Shieldhall Sludge Treatment centre.