It goes without saying that the wastewater from the city’s households is treated before it is discharged back into the rivers. But at the end of the clearing process, there is something left over that few citizens think about eliminating. What happens to the clear sludge in rodental – and why it should stay that way – was explained by plant manager michael eckardt to the city council members.
Because of the high phosphate content, the residues from the clarification plants were long considered a sought-after fertilizer for agricultural land. But farmers’ interest in sludge has declined sharply. "In recent years, the public has become increasingly concerned about trace elements such as excreted pharmaceuticals and their decay products in clear sludge, said eckardt.
Therefore the stadtwerke rodental go for years another way. The clear sludge is first dewatered in a hose press. Then it was spread out in a kind of wax house. There it is dried with solar energy. "After that, the clear sludge is crumbed and automatically loaded into containers", eckardt explained. When these are full, they are taken to the sludge incineration plant and the dry sludge is burned there.
A process whose advantages convince eckardt: disposal remains under municipal control and is cost-efficient (currently 70 euros per ton). The disposal is safe, no long transports are necessary, and the environment is protected because of the MHKW’s external filters. The only disadvantage, he said, is the loss of the phosphorus it contains. There is currently no practical procedure for its recovery. But work is being done. If the raw material could be recovered once, this would provide further relief on the cost side, according to eckardt. He therefore advised the city council to stick to the proven method of clear sludge disposal.