Dear Emmanuel,

The recovery process involves the following steps: concentrating the sludge from 5% to 20% solids, acidification with sulfuric acid, separating the supernatent liquid, decolorizing it using charcoal, filtration, concentrating the solution by evaporation, and finally crystallization to obtain nearly pure alum crystals.

With my best regards

Prof. Bachir ACHOUR

But recovery process is expensive. Sludge contains a lot of phosphorus and can be used as fertilizer in agriculture. But in this case we have other problem - low bioavailability of P.