Sewage treatment plants remove the pollutants and nutrients in our waste water in a number of different treatment phases. What remains is known as sewage sludge, and it contains all the "waste" from the treatment process – heavy metals, organic pollutants, drug residues, pathogens, nanomaterials and plastic residues.
Not least of all because of the many pollutants in sewage sludge has its use in agricultural declined steadily and shifted more to thermal disposal. Today more than half of all municipal sewage sludge is treated in (co-)incineration plants.
The legislation has changed a great deal in recent years, resulting in further restrictions on the agricultural use of sewage sludge. Fertiliser law has established limit values for sewage sludge used as fertiliser which have been in effect since 2015. In addition, the Sewage Sludge Ordinance was re-enacted in 2017. The ordinance allows large-scale sewage treatment plants responsible for more than 100,000 or 50,000 inhabitants to use sewage sludge on soil (as fertiliser) up to 2029/2032 only. Sewage sludge which contains at least 20g phosphorus/kg dry matter and ashes from sewage sludge incineration must be processed for phosphorus recovery upon expiration of the transition period. This is to ensure that this valuable resource remains in the cycle.
Future treatment and disposal of sewage sludge must take account of these developments as sewage treatment operators and disposal businesses must also do. New techniques, in particular for the recovery of the phosphorus in sludge and incineration ash, are in development and must become established in the next few years. The waste management chain must be adapted and adjusted to changing costs accordingly. The German Environment Agency advocates a complete phase-out of sewage sludge use as fertiliser in the long term. A combination of targeted measures can help realise a sewage sludge disposal system that is both sustainable and resource-efficient. The new brochure provides an overview of the current situation and developments as well as of the options in sewage sludge treatment and disposal in Germany.