Capture and recycling of ammonium by dolomite-aided struvite precipitation and thermolysis.

The capture and reuse of NH is an ideal solution to treat NH-containing wastewater. The capture and reuse process needs to be clean and cost-effective. Currently, however, there are many obstacles, particularly in the availability, cost, and recovery of the chemical sources required. Here, we demonstrate a clean and efficient method to capture and recycle NH by a dolomite-aided struvite precipitation process. Dolomite calcined carefully in CO atmosphere was used as a Mg source to react with PO (KHPO) and NH in model wastewater (2000 mg L NH). The precipitation was performed at nMg:nNH:nPO = 1:1:1.2 and pH = 8.0 for 2 h; 89.7% of NH was recovered in the form of struvite precipitate. The competition between K and NH in the model wastewater led to the formation of K-struvite (MgKPO·6HO) and struvite (MgNHPO·6HO). The formation of K-struvite resulted in a decrease in the NH removal rate. When struvite was heated at 110 °C for 4 h, the NH release rate from the thermolysis reached 75.7%. Thermolysis readily occurred as an unstable Ca-CO-NH system formed in the mixture of MgNHPO·6HO and CaCO. The elements Mg and P that were obtained during the struvite precipitation-thermolysis-reprecipitation process can be repeatedly used. After 6 cycles, under the conditions pH = 9.0, nMg:nNH:nPO = 1:1:1 and reaction time of 2 h, up to 78.3% of NH was removed from the model wastewater.