The project "KLAR - Sewage Sludge Inorganic Recycling" aims to make sewage sludge usable as an urban resource and to provide nutrients such as phosphorus (P) and nitrogen (N) as well as other inorganic valuable materials. The research project aims to develop an innovative recovery concept across the process path from gasification and purification to efficiently recover secondary recyclables for further recycling. The KLAR project deals with the optimization of operation management of the Dual Fluidized Bed (DFB) process at a 1 MW gasifier (Syngas Platform Vienna) to improve the inorganic outputs. These outputs will be characterized and the plant availability evaluated. Potential recycling from Vienna sewage sludge can recover up to 1,500 t/a each of nitrogen and phosphorus. If the process is applied throughout Austria, it could be possible to cover up to 50 percent of the annual phosphorus requirement for mineral fertilizers. The project thus makes a significant contribution to CO2 savings as well as closing the loop in the city.

Current results

To be able to carry out the initial gasification operation with sewage sludge at the Syngas Platform Vienna, a detailed literature review on the inorganic components that typically occur was conducted. The data on the distribution of phosphorus, nitrogen, and other inorganic compounds in the material streams that arise during gasification were then used to set up an extensive analysis plan. This plan was implemented for gasification with sewage sludge in May 2024. It was possible to achieve successful operation for 14 hours until the ash, generated from sewage sludge, caused a blockage in auxiliary aggregates. Based on the analyses performed, current material balances are being created for the inorganic material streams, and a life cycle analysis has also begun.

Additionally, a literature review is currently being conducted on further recovery of phosphorus and other valuable inorganics from the gasification ash, and based on this, a techno-economic evaluation of the entire process chain will be performed.

Outlook

Currently, an optimised operation scheme to further increase the gasification performance towards increased recoverability of inorganics is being developed. Optimised operation is planned for fall 2025.