Recovery of Phosphorus from Biofilm-Enriched Sewage by Fluidized Bed Crystallization of Vivianite

Existing techniques to recover phosphorus from urban sewage in the form of vivianite face difficulties in separating the crystals from the sludge. The present work proposes a new process for the efficient online recovery of phosphorus by growing vivianite crystals through fluidized bed crystallization (FBC) from biofilm-enriched phosphorus solution (up to 179.5 mg·L −1 ). The impact of process parameters on the phosphors recovery (PR), the crystallization ratio (CR), and the crystal size were examined. Under optimized conditions, i.e., 140 mg·L −1 phosphorus in the raw water, 15 m/h liquid up-flow velocity, and 5 h hydraulic retention time, a single batch of the FBC reaction could attain a high PR of 95.30% and a high CR of 88.23%. After seven consecutive batches of the FBC reaction, large vivianite crystals (d 50 = 270.52 mm) could be recovered. The identity of the collected vivianite crystals was verified by X-ray diffraction (XRD), scanning electron microscopy (SEM-EDS), and X-ray photoelectron spectroscopy (XPS). The proposed process shows very good potential as it can turn urban sewage into a valuable resource from which phosphorus can be efficiently recycled