Energy and phosphorus from wastewater sludge

Since 2005, a pilot plant has been in operation at the Waßmannsdorf wastewater treatment plant , which degrades the wastewater sludge more quickly and improves the energy-relevant production of digester gas. A further innovation will be the filtration of the phosphorus used for fertiliser production from the filtrate.

The aim of the project in the Waßmannsdorf wastewater treatment plant is to increase the digester load in order to degrade the organic dry matter in the sludge more completely and more quickly, and thus to increase the production of digester gas for energy use. The intensive digestion is achieved through a two-stage reactor cascade of the digesters. In addition, the digester sludge in the first digestion stage is filtered by a rotating membrane of a rotary disc filter and is therefore further drained of water and returned to the process.

A further innovation is to separate the phosphorus as a high-quality magnesium-ammonium phosphate (MAP) from the filtrate of the rotary disc filter. MAP is a valuable raw material used for the production of fertilisers. In addition, phosphorus is a non-renewable natural resource that could become scarce and expensive within a foreseeable period of time.

The process could now be successfully tested with continuous and discontinuous raw sludge feeding without additional sludge thickening by using a rotary disc filter.  In line with the objective, the maximum digester load for the two-stage intensive digestion, the resulting elimination of the organic dry mass and the gas production were determined.