Integrating electrochemical processes with electrodialysis reversal and electro-oxidation to minimize COD and T-N at wastewater treatment facilities of power plants

Novel integrating electrochemical processes with electrodialysis reversal (EDR) and electro-oxidation were designed as advanced water treatment equipment to meet the most rigorous specifications for the existing wastewater treatment facility of secondary nonradioactive system. Pilot tests of these processes were carried out. Secondary chemical wastewater was treated using EDR, and the EDR concentrate was discharged into the sea after being purified through an electro-oxidation process. From the results of the analysis of the EDR product, it was found that it is possible to reuse water with less than 2 ppm COD and 8 ppm T-N. The possibility of scale formation by calcium carbonate was considered from the Langelier Index (LSI). In the case of the EDR process, the possibility of scale formation was excluded because the LSI value was less than zero. Foulants such as CaSO4, Mg(OH)2, Ca(OH)2, and Ca(Cl)2, however, were considered as the major causes for turbidity, and were identified as suspended solids through elemental analysis and ion chromatography. In the electro-oxidation process, the possibility of scale formation through the addition of sodium hydroxide was determined. It was likewise found that electro-oxidative treatment leads to the formation of halogenated by-products. Although the effluents are discharged into the sea, the possible toxicity of such compounds has an aesthetic influence on those residing near the site. Because the value of the THMs was determined to be within the range of 6–29 ppb (the THMs regulation for drinking water is less than 100 ppb, whereas the regulation for wastewater has not yet been established), it was proven to be of a negligible quantity. High T-N and COD removal efficiency (3.6 ppm COD and 5.1 ppm T-N) was predominantly achieved by the electro-oxidative process through indirect hypochlorite bulk oxidation. *Corresponding author. Presented at the conference on Wastewater Reclamation and Reuse for Sustainability (WWRS2005), November 8–11, 2005, Jeju, Korea. Organized by the International Water Association (IWA) and the Gwangju Institute of Science and Technology (GIST). 0011-9164/06/$– See front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.0000.00.000

The electrochemical treatment of real wastewater was investigated using electrodialysis reversal and the electro-oxidation system as an advanced water treatment system. From the results of the analysis that was conducted in this study, it was found that the integrated process allows the simultaneous removal of COD and T-N in the secondary wastewater treatment facility of the power plant. The results of the Langelier saturation index for the ANT process were positive. This indicates the possibility of greater precipitation for calcium carbonate in the electrolysis reactor and on the electrode surface. This is attributed to the addition of NaOH which improves the removal efficiency of COD and T-N. Therefore, the removal of the insoluble hardness materials in the ANT reactor should be considered to prevent the subsequent precipitation of the calcium and magnesium compounds. Through EA, SEM, IC, and ICP analyses, it was revealed that the major species for SS were CaSO4, Mg(OH)2, Ca(OH)2, and Ca(Cl)2 for EDR and CaCO3, CaSO4, Mg(OH)2, Ca(OH)2, and Ca(Cl)2 for ANT. From the analysis data of the EDR product, it was confirmed that it is possible to reuse the EDR product in the power plant. The ANT product met the water quality standard for COD and T-N, but exceeded the regulation for SS. This is due to the high SS concentration of EDR feedwater and the scale formation in the ANT process. When the THMs were measured to address the public complaints, it was found that they were of a negligible quantity (6–29 ppb THMs). Therefore, the ANT process, which has been proposed as a novel treatment strategy for EDR concentrates, has been successfully implemented in this study for the removal of hardto-treat wastes such as EDR concentrates.