Simultaneous calcium phosphate precipitation in anaerobic treatment of black water: a new approach to phosphorus recovery

Phosphorus recovery from wastewater by precipitation as calcium phosphate could reduce the depletion of scarce phosphate rock resources and the need for mining. This study will introduce simultaneous phosphorus recovery by precipitation of calcium phosphate granules in the anaerobic treatment of black water. The reduction of humic acids in tap water had a minor effect on the free calcium concentration, yet appeared to be the key for the occurrence of calcite seed crystals and subsequent precipitation of amorphous calcium phosphate granules. The granules formed in the Upflow Anaerobic Sludge Blanket (UASB) reactor were inspected with Scanning Electron Microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX), Inductively Coupled PlasmaAtomic Emission Spectroscopy (ICP-AES), and direct spectral analysis using Raman spectroscopy. The granules had a diameter of 1-2mm and a thin organic layer on the outside of the granule. The phosphorus content of the amorphous calcium phosphate granules was 15-17 wt%. Phosphorus recovery from the black water UASB reactor with these granules has to be further quantified.