Once wastewater has been filtered by Stockholm Exergi’s treatment plant, converted into biogas, and dewatered, large amounts of sewage sludge are formed. The sewage sludge contains desired and finite substances but also excessive concentrations of environmental toxins and heavy metals that should not remain in the ecosystem. Through combustion, toxins can be removed. In a collaborative project, Stockholm Exergi develops methods for treating sewage sludge and studies the possibility of returning the nutrients that remain after incineration to agriculture.