Electrochemical oxidation for the rapid degradation of emerging contaminants: Insights into electrolytes and process parameters for phytotoxicity reduction

Abstract

Atrazine (ATZ), carbamazepine (CBZ), and sulfamethoxazole (SMX) are contaminants of emerging concern (CECs) commonly detected in water sources, posing a risk to health, sanitation, and the ecosystems. This study evaluates the degradation, mineralization, and phytotoxicity reduction of a solution containing these three CECs using an electrochemical advanced oxidation process (EAOP). Key operational parameters – pH, flow rate (Q), current density (j), and type and concentration of supporting electrolytes (NaCl and Na₂SO₄) – were systematically investigated. The results showed that pH had minimal impact on the process. Higher flow rates (250 L h⁻¹) improved mineralization due to enhanced mass transfer to ^•OH on the anode surface. However, the flow rate had less effect on degradation, as the dominant degradation mechanisms involved chlorine- or sulfate-based oxidants. Current densities of 1 and 10 mA cm⁻² produced the most favorable results, leading to efficient degradation and mineralization, along with satisfactory mineralization current efficiency (up to 47 %) and energy consumption values (91,76–3142,88 kW h kg⁻¹). When NaCl was used as supporting electrolyte, the degradation of CECs was twice as fast as with Na₂SO₄, achieving over 88 % degradation in 5 min and 40 % mineralization within 60 min. While chlorinated and sulfate species enhance process efficiency, excessive electrolyte concentration should be avoided to prevent scaling and ^•OH scavenging. Phytotoxicity tests with Allium cepa revealed an unexpected reduction in toxicity in samples treated with NaCl, suggesting that Na₂SO₄ may be more phytotoxic under the tested conditions.