Comparison of electrocoagulation and chemical coagulation in removal of phosphonate chelators from water

In this study, the performances of electrocoagulation (EC) and chemical coagulation (CC) in removing phosphonate chelators (PCs) from water were explored and compared. As the representative of PCs, nitrilotri(methylphosphonic acid) (NTMP) could be efficiently removed in acid and neutral electrolyte by Fe-EC and at the pH range of 3.0-9.0 by Al-EC process. Precipitation pH had a slight impact on NTMP removal by Fe-CC, while Al-CC process could remove NTMP effectively only at the precipitation pH of 6.0. Fe-EC and Al-CC consumed much less iron or aluminum than the corresponding Fe-CC and Al-EC processes. Part of NTMP was degraded into phosphate during Fe-EC process, and high-valent iron (Fe(VI)O²⁺) was identified as the key active species responsible for its degradation through quenching experiments. Coexisting substances had no obvious impact on NTMP removal in Al-EC, Fe-CC and Al-CC processes, but NO₃^- and CO₃^2- inhibited significantly in Fe-EC process. The other PCs could be also removed efficiently in all EC and CC processes but 2-phosphonobutane-1, 2, 4-tricarboxylic acid. By comparison, Fe-EC process is considered as a promising technology for PCs removal from water due to its efficiency, easy accessibility and no addition of exogenous chemicals.