Simultaneous removal of ammonia nitrogen and recovery of phosphate from swine wastewater by struvite electrochemical precipitation and recycling technology

• A coupled electrochemical process was developed to treat swine wastewater.
• Struvite of high purity can be obtained by electrochemical precipitation.
• About 93% nutrients were recovered from swine wastewater by the proposed process.

The removal of phosphorus and nitrogen from wastewater has been a matter of great concern for several decades. In this study, a coupled electrochemical process, involving the electrochemical recovery of phosphate as struvite, electrochemical decomposition of the struvite recovered, and removal of the ammonia nitrogen by recycling the struvite electrolysis product, was tested to simultaneously recover phosphate and remove the ammonia nitrogen from swine wastewater. The results demonstrated that when a magnesium alloy was electrolyzed as the magnesium source of struvite crystallization, the recovery efficiency of the phosphate was 99%, at a current density of 2 mA/cm2 for 45 min. When the struvite recovered was electrolyzed using seawater as a supporting solution, the ammonium in the struvite could be completely removed. The characterization analysis revealed that the active component of the electrolysis product was present as dissolved phosphate and magnesium and insoluble cattiite. An efficiency of >90% of ammonia nitrogen removal could be achieved by recycling the electrolysis product of struvite. A pilot-scale test performed for 30 recycle cycles demonstrated that approximately 93% of the recovery/removal efficiencies of the phosphate and ammonia nitrogen from swine wastewater could be achieved stably by the process proposed, which implied the presence of an important application value in the water eutrophication control and recovery of the phosphorus resources.