Nutrients removal from swine wastewater by struvite precipitation recycling technology with the use of Mg3(PO4)2 as active component

• Sodium alginate and bovine albumin have a slight effect on struvite precipitation.
• It is feasible to use magnesium phosphate as struvite precipitation precursor.
• Magnesium phosphate could be obtained from the pyrolysis of struvite and brucite.
• Recycling struvite pyrolysate can stably remove nutrients from swine wastewater.
• Recycling struvite pyrolysate could effectively reduce the cost of precipitation.

The recovery and removal of nutrients from swine wastewater was investigated by employing a struvite recycling process, which used magnesium phosphate (MP) as the active component. In this study, the effect of organic matters (sodium alginate, bovine albumin and acetic acid) in swine wastewater on the crystallization of struvite and the feasibility of MP as the phosphate and magnesium sources of struvite precipitation were first evaluated. The results demonstrated that sodium alginate and bovine albumin could slightly influence the crystallization of struvite while acetic acid did not. Using MP as the phosphate and magnesium sources of struvite precipitation could achieve a removal efficiency of the total ammonia nitrogen (TAN) close to that of using pure chemicals (MgCl2∙6H2O and Na2HPO4∙12H2O). The results of struvite pyrgenation revealed that the optimal pyrogenation condition of struvite was at Mg(OH)2:NH4+ 1:1 and temperature 150 °C for 3 h, at which the main pyrogenation product was MP. Recycling the pyrolysate at pH 8.5 could achieve a TAN removal of 78%. When the pyrolysate was recycled for six cycles, the TAN removal efficiency could be maintained above 70%, and 67% of the struvite precipitation cost could be reduced compared to using pure chemicals.

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