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Electro-oxidation of a Commercial Formulation of Glyphosate on Boron-Doped Diamond Electrodes in a Pre-pilot-Scale Single-Compartment Cell

Abstract:

Kinetic and environmental aspects related with the mineralization of a commercial glyphosate (GP) formulation in a pre-pilot-scale reactor were assessed. Assays were performed at an acidic pH using Na2SO4 as support electrolyte at five different current densities. GP removal can be achieved in 60 min and is not dependent on the applied current density; however, the reduction of organic carbon (TOC) and chemical oxygen demand (COD) from the sample evidence the impact of the limitations of mass transfer in aspects like energy consumption, effluent quality, and sustainability of the process. Assays at 120 and 240 mg L−1 revealed that it is feasible to improve the biodegradability of the effluent after 300 min of treatment using higher current densities (80 and 100 mA cm−2). At 360 mg L−1, neither the current density nor the time of treatment had an impact on the biodegradability of the effluent at all the assessed current densities. GP removal could have an environmental footprint (1.3 kg CO2 Eqv/kg TOC) in countries where the energy matrix depends on hydropower. In countries where electricity is generated from non-renewable raw materials, like gas or coal, the emissions of greenhouse gasses (GHG) could increase 170% and 439%, respectively. The use of renewable energy sources, like wind power or solar, could reduce the GHG emission to 0.3 kg CO2 Eqv/kg TOC. The cost of treatment ranged between US$ 0.7 and 2.1 g TOC−1 removed; this variability is due to the selected energy source and the subsidies established in each country.