Electrooxidation of aminomethyl phosphonic acid (AMPA) using a boron doped diamond anode

Abstract

Glyphosate, a commonly used herbicide, can transform into aminomethyl phosphonic acid (AMPA, CH6NO3P) in the aquatic environment. This AMPA can bioaccumulate in the food chain, damage living organisms at cellular and embryonic levels, and trigger eutrophication by releasing bioavailable phosphorus. Electrooxidation (EO) offers a promising strategy to neutralize organic pollutants, yet limited research has extended EO to manage AMPA in diluted water matrices. In this study, we determine EO’s kinetics in degrading low-concentration AMPA and evaluate operational strategies to boost EO’s performance under diffusion-limited conditions. Results of the batch systems indicate that AMPA can be degraded via direct and indirection oxidation under 2.5 V. The former takes place on an anode surface through direct electron transfer, while indirect oxidation is achieved via electrochemically generated reactive species such as •OH and H2O2. We find all degradation products to be inorganic ions, with no accumulation of organic intermediates. Further decrease of AMPA levels from 0.1 to 0.01 mM poses a diffusion-limited condition to our EO system, suppressing AMPA degradation efficiency from 97.2% to 84.2%. We subsequently increased the electric driving force from 2.5 to 3.0 V and obtained a 98.8% 0.01 mM AMPA removal. The long-term performance of a continuous-flow reactor reveals EO is governed by electrode surface area and hydraulic retention time (HRT), with the highest removal rate of 6.6 mg m−2 h−1 at 3.5-h HRT. Our results indicate that EO can efficiently remove diluted AMPA in water matrices and warrants future efforts in electrode and reactor design to effectively counter mass transfer constraints.