Synergistic Removal of Zinc and Copper in Greenhouse Waste Effluent by Struvite

Struvite (MgNH4PO4·6H2O) can be recovered from wastewaters for mitigation of phosphorus content. However, the interaction of dissolved constituents with struvite is rarely evaluated. Removal of heavy metals and total organic carbon (TOC) in a greenhouse wastewater (GW) by struvite was investigated. Presynthesized struvite was added to GW and removal of Zn (689 μg/L), Cu (151 μg/L), and TOC (51 mg/L) monitored from 1 to 26 d. Metal uptake in sodium nitrate solutions was used to assess competition, and the influence of other GW constituents on sorption. Struvite was also directly precipitated from GW (PPT). Recovered GW solids had 64–247 mg/kg Zn, 12–54 mg/kg Cu, and 1721–8806 mg/kg TOC, with lowest loadings for PPT and highest for 26 d solids. X-ray absorption spectroscopy detected polymerized Zn-phosphate, induced by dissolved phosphorus in GW, and Cu copolymerization, initially limited by aqueous Cu-organic complexation. Sorbed Cu shifts Fourier transform infrared-sensitive phosphate bands and changes the intensities of reflections in X-ray diffraction patterns of struvite more so than Zn. Struvite from GW is more susceptible to thermal decomposition than unreacted struvite, evolving CO­(g), CO2(g), NH3(g), and H2O­(g). Therefore, struvite from GW sorbs metals and organics, and can release sorbed and structural components to the aqueous and gas phases.