Recent years have seen increasing positive interest in recycled nutrients. At the same time, the most advanced methods of nutrient recovery have gradually matured into technically production-scale processes. However, the available technological solutions for recovery have been strongly attached to current sludge streams and have not provided a comprehensive approach to nutrient recovery and recycling at wastewater treatment plants of different types and sizes.

HSY’s development work related to nutrient recovery has been based on the separation of the phosphorus nutrient fraction from the sludge fraction, which allows maximum and cost-effective nutrient recovery while also enabling more efficient wastewater treatment. We are developing a treatment method for post-precipitation chemical phosphorus sludge, the end product of which is phosphoric acid suitable for industry as a raw material or, alternatively, ammonium phosphate to be used directly as a fertiliser. Phosphoric acid is a valuable and versatile chemical, while ammonium phosphate is suitable for use as fertiliser as such.

A RAVITA DEMO pilot plant, size class 1,000 PE, has been built at the Viikinmäki wastewater treatment plant for the development work. The aim of the pilot plant is to coordinate and optimise the sub-processes of the RAVITA process. Additional objectives include studying the quality and quality of the side streams generated and assessing the cost of the process at full scale.