Effective removal of organics from corn wet milling steepwater effluent by electrochemical oxidation and adsorption on 3-D granulated graphite electrode

Abstract

An electrochemical system was developed to successively apply electrochemical oxidation (EO) and electrochemical adsorption (EA) treatments. This coupled EO–EA treatment system was used for remediating steepwater effluent samples obtained from a commercial corn wet milling plant. The effects of system operating parameters such as pH, supporting electrolyte, current density, treatment duration, repeating EO–EA cycle etc. were investigated based on the amount of chemical oxygen demand (COD) removed. The effluent was also characterized for 5-day biological oxygen demand (BOD5), reduced sugars (as dextrose), lactic acid, protein, and phosphorus at different stages during electrochemical remediation. The initial EO treatment improved the system effectiveness during the subsequent EA treatment by enhancing the oxidation process, partially decomposing and creating new functional groups on the pollutants. This increased the affinity of the pollutant adsorbates with activated carbon particles filled within the EA cell, which served as both bipolar microelectrodes and enhanced adsorbents. By operating at pH 12, using NaCl as supporting electrolyte, the COD was reduced by 93.5% after 4h of EO followed by 16h EA. Repeating the EO–EA treatment (4h of EO followed by 4h of EA) further reduced the total COD by 99.2%, though with higher energy consumption. However, the total energy consumption for our process is much lower than that for other electrochemical treatments reported. The results show that our coupled EO–EA treatment process is very effective for remediating highly recalcitrant effluents such as corn wet milling steepwater. Furthermore, the treated water is very clear and is suitable for industrial reuse.