Augsburg model for sewage sludge recycling

The City of Augsburg wants to break the mould and to take charge of recovery of the sewage sludge produced. To do this the City of Augsburg's wastewater company plans to recover sewage sludge on site on its own wastewater treatment plant grounds in Augsburg using the so-called "Augsburg model".

Sewage sludge in Augsburg and recycling

Each year between 35,000 and 40,000 tonnes of mechanically dewatered sewage sludge are produced in Augsburg's wastewater treatment plant. At present it is disposed of by co-incineration in 7 different coal-fired power stations spread throughout the whole of Germany. In particular, the expensive and emissions-intensive truck transport and associated "sewage sludge tourism" are to be replaced by autonomous mono-incineration. This appears to make sense for the City of Augsburg's wastewater company, not only ecologically but also economically. After the project and planning resolution was passed by the city council, the bifa environmental institute was engaged in advance, to carry out an emissions comparison with the disposal variant currently implemented in relation to climate relevance and dust loading, and to check the pilot character of the Augsburg model.

Pilot project: Augsburg model

In this combination the "Augsburg model" is novel and has pilot character due to its regional approach. Apart from the familiar and tried and tested fluidised bed technology used in sewage sludge mono-incineration plants, a central component of the concept is the off-gas system. In addition to state-of-the-art flue gas cleaning, instead of passing the off-gas through a chimney stack it is fed through the existing aeration tank of the wastewater treatment plant, which the plant designers hope will achieve additional cleaning effects for dust and other constituents. A further special feature worth mentioning is that, due to the high degree of mechanical preliminary dewatering in Augsburg's wastewater treatment plant, there is no need for energy-intensive thermal drying before incineration and therefore the odour problems often associated with drying are also excluded.

Energy-autonomous concept

By using sewage gas as a backup firing system, the "Augsburg model" produces an energy-autonomous concept, so that no additional fuels or energy have to be added. In addition, the low-calorific energy contained in the off-gas in the form of residual heat is converted into electricity by a so-called ORC (organic Rankine cycle) plant. A further component of the Augsburg model is the potential option of phosphorus recovery at a later date. The planned sewage sludge recovery will be approved according to the Federal Immission Control Act ("Bundesimmissionsschutzgesetz" - BImSchG).