Degradation of Glyphosate in Water by Electro-Oxidation on Magneli Phase: Application to a Nanofiltration Concentrate

This study evaluates the efficiency of sub-stoichiometric Ti₄O₇ titanium oxide anodes for the electrochemical degradation of glyphosate, a persistent herbicide classified as a probable carcinogen by the World Health Organization. After optimizing the process operating parameters (pH and current density), the mineralization efficiency and fate of degradation by-products of the treated solution were determined using a total organic carbon (TOC) analyzer and HPLC/MS, respectively. The results showed that at pH = 3, glyphosate degradation and mineralization are enhanced by the increased generation of hydroxyl radicals (^●OH) at the anode surface. A current density of 14 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mrow><mi>mA</mi><mo> </mo><mi>cm</mi></mrow></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup></mrow></semantics></math></inline-formula> enables complete glyphosate removal with 77.8% mineralization. Compared with boron-doped diamond (BDD), <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>Ti</mi></mrow><mn>4</mn></msub><msub><mi mathvariant="normal">O</mi><mn>7</mn></msub></mrow></semantics></math></inline-formula> shows close performance for treatment of a concentrated glyphosate solution (0.41 mM), obtained after nanofiltration of a synthetic ionic solution (0.1 mM glyphosate), carried out using an NF-270 membrane at a conversion rate (Y) of 80%. At 10<inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mrow><mo> </mo><mi>mA</mi><mo> </mo><mi>cm</mi></mrow></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup></mrow></semantics></math></inline-formula> for 8 h, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>Ti</mi></mrow><mn>4</mn></msub><msub><mi mathvariant="normal">O</mi><mn>7</mn></msub></mrow></semantics></math></inline-formula> achieved 81.3% mineralization with an energy consumption of 6.09 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mrow><mi>kWh</mi><mo> </mo><mi mathvariant="normal">g</mi></mrow></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula> TOC, compared with 90.5% for BDD at 5.48 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mrow><mi>kWh</mi><mo> </mo><mi mathvariant="normal">g</mi></mrow></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula> TOC. Despite a slight yield gap, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi>Ti</mi></mrow><mn>4</mn></msub><msub><mi mathvariant="normal">O</mi><mn>7</mn></msub></mrow></semantics></math></inline-formula> demonstrates notable efficiency under demanding conditions, suggesting its potential as a cost-effective alternative to BDD for glyphosate electro-oxidation.