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

• An electrochemical system is developed to remediate highly contaminated effluents.
• Electro-oxidation (EO) assists partial decomposition of organic contaminants.
• Further remediation is possible by subsequent use of electro-adsorption (EA).
• EA facilitates decomposition, adsorption, and regeneration on 3-D electrode.
• Successive EO–EA is simple, “green”, efficient, and enables large-scale treatment.

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 4 h of EO followed by 16 h EA. Repeating the EO–EA treatment (4 h of EO followed by 4 h 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.