Every year 76,000 tonnes of sludge, rich with nutrients, is produced in the wastewater treatment process.
Wastewater becomes fuel
When the sludge is decaying, it emits gas that can be used to produce biogas, an environmentally friendly fuel for motor vehicles. Stockholm Vatten's sewage treatment works produce 4.1 million m³ of biogas annually, but have the capacity to double this amount.
The demand for biogas is growing and several of Stockholm's buses, taxis and private cars are run on biogas from the sewage treatment works.
Sludge as fertilizer in agriculture
The sludge is of high quality, satisfying the demands of the authorities, and can therefore also be used as fertilizer in agriculture. Stockholm Vatten continuously works to improve the quality, by reducing the amount of environmental toxins in the sludge. This is done by, among other measures, demanding pre-treatment of the wastewater by businesses such as car washing facilities and dentists, as well as urging the population to use environmentally friendly products.
Long-distance heating
The treated wastewater is around 14-15°C. Before it is discharged into the Baltic Sea, the heat is extracted from the water and used in district heating systems in Stockholm.
Land restoration
Today, the sludge is also used to restore land in mining areas as well as to cover up old waste disposal sites