Self-powered wastewater purification and phosphorus recovery systems with novel self-filtering Al-air batteries

Sustainable water treatment systems are crucial for water recycling and resource recovery. However, the existing self-powered water treatment technology for metal-air batteries has several challenges. This study proposed a new self-powered water treatment system concept by developing self-filtering aluminum-air (SF Al-air) batteries. The sandwich-shaped flexible air cell comprised an aluminum (Al) scrap anode, an inexpensive hydrophilic separator, and a graphite-coated titanium mesh cathode. By utilizing the capillary action and porous structure of the separator, the autonomous flow and filtration of electrolytes or wastewater were achieved inside the battery. Owing to the high Al purity of 95 % and the ultra-thin structure, the low-cost kitchen Al foil is a promising anode, with the highest power density of 23.02 mW g-1 (anode weight), 4.60 x 10-2 W $-1 (anode cost). Kitchen paper is the preferred separator facilitating electrolyte transfer and automatic renewal inside the battery owing to the strong water storage property. The SF Al-air cell can also efficiently removed 90% of phosphorus at an initial concentration of 100 mg P/L and initial pH = 7. Specifically, the cell converted phosphate pollutants and Al foil waste into a valuable AlPO4.2H2O flame retardant coating on kitchen paper, resulting in a first-class flame retardancy of the separators. Lake water treatment results showed that the self-powered SF-Al-air cell purified real surface water and obtained a stable power production of 146.7 mW g-1. Our study demonstrates a promising sustainable water treatment technology for simultaneous power generation, wastewater purification, phosphorus recovery, and waste Al disposal.