In the PULSE process, acidic leaching is used to dissolve P from dried sludge. By using dried sludge, the consumption of acid for leaching is reduced and the separation of the solid and liquid fractions even at very low pH is easier as compared to using dewatered sludge. Metals and heavy metals that are co-leached with P are then removed by a reactive-extraction step. P is then recovered as calcium phosphate by precipitation. A mobile demonstrator with capacity of treating about 100 kg of dewatered sludge/batch has been constructed in order to demonstrate the PULSE process in real environment. The demonstrator is currently being operated at ULiège, where P recovery from German sludge is being tested. In the next steps, the demonstrator will be operated at a waste-water treatment plant near Liège and then in Scotland.
PULSE demonstrator (all pictures: Z. Shariff, University of Liège)
A: Containers for housing equipment and for transportation
B: drying, crushing, leaching and precipitation units installed inside the container
C: mixer-settlers for solvent extraction of metals