Nutrient recovery as struvite from aquaculture wastewater by bipolar membrane electrodialysis with magnesite tailings

In this study, the feasibility of simultaneously recovering Mg, nitrogen (NH₄-N) and phosphorus (P) from magnesite tailings and freshwater aquaculture have been confirmed through the bipolar membrane electrodialysis with a processing unit for the first time. The H⁺ required for Mg²⁺ leaching and OH^– needed for struvite formation can be provided by the BMED system. The results indicate that adding 0.3 mol/L initial HNO₃ could enhance the Mg²⁺ leaching and reduce the energy consumption (EC). The recovery ratios of P and NH₄-N reached to about 97.9 % and 52.3 %, respectively, while the EC was about 0.051 kWh/L. Increasing the tailing dosage shortened the required treatment time and reduced the EC. Increasing the current density significantly enhanced nutrient recovery rate, but accompanied by an increase in EC. A longer treatment time is necessary for treating larger volumes of wastewater, while a P recovery ratio of approximately 99 % can be achieved. Calcium is the predominant impurity. The purity of struvite was enhanced through a multi-batch process, achieving a maximum of 97.1 % at the third time. This study provides new insights into the resourceful treatment of tailings and wastewater.