Evaluation of the environmental and economic scope of an electrocoagulation process for the treatment of wastewater from the instant coffee industry

Abstract

In this study, an industrial wastewater from instant coffee production was treated by electrocoagulation (EC). The effect of various EC operating parameters, such as electrode type, current density, support electrolyte concentration and stirring velocity, were investigated to determine the optimal operating EC conditions. The scope of electrocoagulation (EC) was assessed, in environmental and economic terms, for the treatment of industrial wastewater originated from the production of instant coffee. The evaluation included the effect of EC operating factors (electrode type, current density, supporting electrolyte concentration and stirring velocity) on Color removal, COD and TOC degradation, toxicity, molecular weight distribution, as well as the total operating cost. The following optimal operating conditions were established through a series of preliminary experiments, a Box-Behnken design of experiments, Response Surface Methodology application, and multi-objective optimization analysis: the pair of Fe (anode)-stainless steel (cathode) electrodes, supporting electrolyte = 1.78 g of NaCl/L; current density = 150 A/m²; electrode gap = 3 mm; stirring velocity = 350 RPM; and pH₀ = 4.7 (that of raw industrial effluent). Finally, the kinetic study allowed defining the electrolysis operation time of ca. 180 min required to comply with the maximum permissible discharge limits for the production of instant coffee the discharge of soluble coffee effluents, in terms of COD concentration, established by current Colombian legislation. The EC reached ca. 97% decolorization, as well as 72% and 65% of COD and TOC removal degradation, respectively, with total operating costs of 6.26 USD/m³. This yielded an oxidized (COS = 2.87), biocompatible (BOD₅/COD = 0.437) and non-toxic effluent, free of contaminants with molecular weight > 30 kDa. The EC appeared as an effective alternative for the treatment of industrial wastewater from the production of instant coffee within the framework of different Sustainable Development Goals (number 6 (Clean water and sanitation), number 7 (Clean and affordable energy), number 9 (Industry, innovation and infrastructure) and 13 (Climate action)).