PULSE PROCESS: RECOVERY OF PHOSPHORUS FROM SLUDGE AND ITS PRODUCT QUALITY ASSESSMENT

In the framework of the Phos4You (P4Y) project funded by Interreg North West (NW) Europe 6 different Phosphorous(P)-recovery technologies will be demonstrated. The University of Liège is developing one of the processes, called PULSE (Phosphorus ULiège Sludge Extraction) process, to recover P from fully or partially dried sewage sludge. The PULSE process is a modification of the PASCH process developed at RWTH Aachen to extract P from sewage sludge ashes [1]. In the PULSE process P is recovered from partially or fully dried sludge using acidic leaching. Purification of the leach liquor will be carried out by reactive extraction to separate P and other nutrients from co-leached metals. Finally, depending on the leaching and extraction approach used above, the final product of the PULSE process can either be obtained as phosphate salt or phosphoric acid. Nevertheless, production of novel P products requires a novel standardized methodology for its quality assessment and valorisation on the market. In the first part of the research, the experiments for the unit operations of the PULSE process are conducted at lab-scale and metals, P and other macronutrient content in each step of the process sequence is monitored and benchmarked against the legislative limits. Comparison of the standardized sludge digestion method with nitric acid and/or aqua regia with modified sulphuric and hydrochloric acid will be conducted in order to establish a standard for sludge characterization especially for heavy metals determination. The data obtained for the different process options of each unit operation are evaluated using the methodology of ‘Cascaded Option Trees’ [2] to select the most feasible and optimum option. A solid-liquid equilibrium speciation model developed in MATLAB is further used for optimizing process parameters. In the second step, the PULSE process will be demonstrated on a pilot-plant scale at 4 different locations in NW Europe. The novel P product will be thoroughly analysed using quality methods selected by project partners responsible for quality assessment in the P4Y project for P availability and inorganic characterization, which provides feedback to the technology producer for improvement.
In the presentation, the concept of the PULSE process will be explained along with the results from the lab experiments and evaluation of process options. The concept of solid-liquid equilibrium speciation model and its application to optimize the PULSE process operation will also be presented. The relation between the quality of the P source and P product will be showcased. Further comparison of the quality of PULSE product with the regional and EU regulations on P fertilizers will also be presented.