Strategies for sludge handling in the Stockholm region

The annual production of dewatered sludge from the municipal wastewater treatment plants handled by Stockholm Water Company is about 75,000 tonnes. The policy of Stockholm Water Company is to find methods to use the sludge as a resource by recovering its contents of nutrients and earth-forming substances. The most suitable sludge use is considered to be for agriculture. Intensive work has been done on reducing the sludge concentration of toxic metals and other pollutants by use of control of discharges of industrial waters into the sewer network, information campaigns to households, and improved management of storm water. The sludge quality is measured by automatic samplers for dewatered sludge and analyses of heavy metals and certain organic pollutants. Sludges with better quality than limiting values from authorities may safely be used in agriculture, while sludges not fulfilling stringent requirements must be handled by other methods. Due to resistance from the food industry and a number of interest organisations, it is important to find other handling methods also for high quality sludges. Such methods include the use of incineration together with municipal solid wastes or biomass or separation of the sludge into different products for internal or external use.