Abstract
Struvite precipitation electrolyzers are interesting environmental electrochemical reactors with potential applications for efficient phosphate recovery from wastewater, such as swine wastewater. In this paper, effects of phosphate concentration and pH on the struvite precipitation reaction rate were investigated. When phosphate concentration decreased from 100 to 20 mg/L, the precipitation reaction rate decreased from 396.65 mg/L·h to 70.46 mg/L·h, indicating that the reaction rate of struvite crystallization can be controlled by adjusting pH according to the change of phosphate concentration. Numerical simulation of different currents and flow rates on pH in the electrolyzer was developed and validated, and pH in the electrolyzer was dynamically measured along the distribution point of the flow field. We aimed to test the treatment effect of the electrolyzer on actual swine wastewater. When the flow rate was 20 L/h and constant voltage was 4 V, the electrolyzer was run continuously for 5 hours with the volume of 50 L. The phosphate recovery efficiency reached 99.51%, and the time-space yield of the struvite precipitation electrolyzer was 0.0219 kg/m2·h. The harvested struvite particles were identified by XRD and SEM-EDS, which presented orthorhombic structure and high purity. Economic analysis demonstrated that the proposed electrolyzer was cost-effective and technologically convenient.
Highlights
The recovery of phosphorus in the form of struvite precipitation has been recognized by many domestic and foreign experts as one of the most promising technical methods
When the phosphate concentration increased from 20 to 100 mg/L, and solution pH increased from to 8.6 to 9.08, the reaction rate incereased from 70.46 to 396.65 mg·L−1·h−1. This reslut shows that the reaction rate of struvite crystallization can be controlled by adjusting pH according to the change of phosphate concentration
Based on the above research, we aimed to investigate the treatment of the actual swine wastewater by the electrolyzer, and the experiment was conducted with the following conditions: the feed volume of 50 L; reaction time of 300 min; and the feed flow rate of 20 L/h
Summary
The recovery of phosphorus in the form of struvite precipitation has been recognized by many domestic and foreign experts as one of the most promising technical methods. The struvite crystallization process and the recovery efficiency of the phosphate depended on concentration of phosphate, ammonium and magnesium ions, pH, the flow rate, and the N/P ratio[13,14,15]. Huang et al.[21] reported that the phosphorus in swine wastewater was recovered efficiently in the form of struvite precipitation by magnesium metal corrosion. By building a new type of electrochemical struvite precipitation of phosphorus recovery unit (especially magnesium board is used as the electrode), and Comsol software was used to simulate device performance and optimize reaction conditions, so as to obtain feasible process route and parameters.
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