Electrochemical degradation of aqueous metformin at boron-doped diamond electrode: kinetic study and phytotoxicity tests

The present study explores the galvanostatic electrolysis of synthetic solutions containing the antidiabetic metformin with different support electrolytes, using a boron-doped diamond anode in an undivided electrochemical cell to test the possibility of the reuse of the treated water in the field of agriculture. It also investigated the effects of the main operating parameters, including applied current density, supporting electrolyte nature and concentration, initial chemical oxygen demand, initial pH, temperature, and NaCl concentration. This was realized considering the chemical oxygen demand removal, current efficiency, energy consumption and phytotoxicity. The experimental results showed that metformin concentration, measured by the square wave voltammetry technique and the chemical oxygen demand decay, follows a pseudo-first-order kinetics. At the beginning of the electrolysis, the electrochemical efficiency was limited by a charge-transfer process. For an initial chemical oxygen demand of 900 mg L-1 and under optimal conditions (current density of 30 mA cm(-2), pH 2, Na2SO4 2 g L-1, NaCl 0.8 g L-1 and T 343.15 K), the removal of organic matter was about 90% and the complete elimination of metformin was reached after 2 h of electrolysis. Concerning the phytotoxicity tests of the treated water, they were carried out using Fenugreek and Lucerne seeds. The results indicated a positive effect on seeds germination due to the production of nitrate ions from the metformin molecules.