Phosphorus recovery in aerated systems by MAP precipitation: optimizing operational conditions.

An attractive way of recovering essential phosphorus from digested sludge of a WWTP is the precipitation in the sludge directly, as part of the continuous treatment process. For optimizing the precipitation, 1 litre-batch tests were performed in a model system to examine the MAP-crystallization kinetics. Different parameters such as e.g. the aeration flow rate were investigated. The aim was to find an optimized setting for a pilot reactor for the continuous production of MAP. This reactor performed as an airlift reactor for an improved mixing and stripping the dissolved CO2 and separating the MAP-crystals. The optimal condition for the airlift pilot reactor is given when the air flow rate for mixing the system and for stripping CO2 for a maximum MAP precipitation is aligned with the particle size distribution.