Effect of organics on Cu and Cr in recovered struvite from synthetic swine wastewater

Abstract

The fast development of struvite precipitation provides an excellent opportunity for cost-effective removal and recovery of nitrogen and phosphorus in swine wastewater. Meanwhile, swine wastewater is rich in heavy metals and organic matters, whose interaction might change heavy metals' distribution and toxicity in recovered struvite. This research investigates the effect of organic matter on heavy metals' speciation variation during phosphorus (P) recovery. The results demonstrate that when the concentration of citric acid, humic acid, and tetracycline increases from 0 to 500 mg/L, the P recovery efficiency decreases from 95.14% to 85.39%, 81.76%, and 74.28%, respectively. When the concentration of ammonium citrate, tetrasodium iminodisuccinate, and ethylenediaminetetraacetic acid vary from 0 to 100 mg/L, the P recovery efficiency decreases from 95.14 to 83.21, 85.97, and 81.32 mg/L, respectively, while the Cr in recovered struvite is increased from 1.88 to 2.92 mg/kg, 1.58–2.64 mg/kg and 0.86–12.6 mg/kg, respectively. It could be concluded that the pH increase promotes Cr and Cu's toxicity shifting to a stable state under the presence of citric acid, while Cr and Cu with humic acid or tetracycline shift to an active state. Besides, chelating agents can reduce heavy metal contents in the recovered struvite, but they also significantly inhibit the P recovery efficiency.