Recovering phosphorus as struvite from the digested swine wastewater with bittern as a magnesium source

摘要

Recovering nitrogen and phosphorus through struvite (MgNH4PO4·6H2O) crystallization from swinenwastewater has gained increasing interest. However, swine wastewater contains complexncompositions, which may hinder the formation of struvite crystal and affect the purity of thenprecipitates by forming other insoluble minerals. In this work, experiments were carried out tonevaluate struvite precipitation in the anaerobically digested swine wastewater, with dosing bittern asna low-cost magnesium source. Exceeded 90% phosphate removal and 23–29% ammonium reductionnwere obtained. FTIR, XRD and mass balance analysis were combined to analyze the species ofnprecipitated minerals. Results showed that the precipitates were struvite, mixed with amorphousncalcium phosphate (ACP) and brucite. The presence of Ca2þ diminished the percentage of struvitenand gave rise to ACP formation. Controlling pH below 9.5 and bittern dosage above 1% (w/w) couldninhibit ACP precipitation and harvest a highly pure struvite crystal product.