Can the performance of Al electrocoagulation for phosphate removal be regulated via cathode material selection?

An innovative Al electrocoagulation (EC) technology for phosphate removal was proposed via cathode regulation using typical cathodes (Al, Ti, Cu, stainless steel, and graphite). At a current density (CD) of 2.5 A/m², all EC systems displayed excellent phosphate removal (>99 %, 20 min). The graphite cathode had the lowest electrochemical resistance, reducing the costs by 68 %−79 % than the Al cathode (1.25−5 A/m²). The addition of NaCl effectively reduced the energy consumption of Al EC. SO₄^2– and NO₃^– showed non^-significant effects on the costs of Al-G EC (p > 0.05). Ca²⁺ and Mg²⁺ at 50 mM increased the costs of Al-Al EC by 17 % and 20 %, respectively. Al-G EC reduced the costs by 67 % than Al-Al EC in the presence of HA. The nanosized flocs from Al-G EC showed higher zeta potentials and smaller pore diameter (8.98 nm), beneficial for phosphate adsorption. The lower HER activity of graphite cathode effectively prevented a rapid pH increase during Al-G EC, thereby regulating the formation of medium and large polymeric species (Al_b and Al_c). The continuous-flow test (120 h) further demonstrated the advantage of Al-G EC regarding phosphate removal and operating costs. Overall, this study provided a cost-effective strategy for Al EC via selecting suitable cathodes.