Enhancing electrochemical crystallization for phosphate recovery from swine wastewater by alternating pulse current

The electrochemical crystallization of struvite offers the dual benefits of wastewater purification and phosphorus recovery. However, electrode passivation and high energy consumption restrict its applications. To address these challenges, this study uses alternating pulse current (APC) to replace the traditional direct current (DC). The operating conditions were optimized through single-factor variable experiments using simulated wastewater, and the electrode stability was examined through cyclic experiments under the optimal conditions. Various characterization methods were used to elucidate the purification mechanism, and the practical applications of this process were evaluated using real swine wastewater. The results indicated that under optimized APC operating conditions (pH = 8, current density = 3 mA cm 2, electrode gap = 4 cm, Mg:P = 1.4, duty ratio = 35 %, and frequency = 3500 Hz), the phosphate removal efficiency reached 94.72 %, with an energy consumption of 0.83 kWh m 3. After eight cycles, APC sustained a phosphate removal efficiency exceeding 94.28 % with energy consumption below 0.91 kWh m 3. This remarkable performance of the APC was primarily attributed to the periodic electric current, micro-capacitive structure on the electrode surface, and polarity reversal characteristics, which collectively mitigated electrode passivation and enhanced system stability. Notably, in treating swine wastewater, APC achieved a phosphate recovery efficiency of 82.41 %, markedly higher than DC at 62.83 %; its energy consumption was 0.77 kWh m 3, representing a substantial reduction of 93.05 % compared with DC. This study offers a reliable and economical method for obtaining phosphorus resources from swine wastewater, with implications for resource recovery from other aquaculture wastewaters.