The removal of COD from coking wastewater using extraction replacement-biodegradation coupling

Using the extraction replacement-biodegradation coupling technique, the removal of chemical oxygen demand (CODcr) from coking wastewater was successfully carried out, and the appropriate extractant type, extractant/diluter ratio, extraction time, and the extractant/wastewater phase ratio were also determined. The results show that when n-octanol and cyclohexane, in a ratio of 1:1, were selected as the mixed extractant, nitrogen-containing heterocyclic compounds (NHCs), such as pyridines and quinolines, were effectively extracted and replaced by the extractant from coking wastewater. As a result, the biodegradable nature of coking wastewater could be improved significantly. After pretreating coking wastewater with the extraction replacement method for 5 min using a 1:1 ratio of extractant to wastewater and following with biodegradation treatment, the biochemical oxygen demand for five days (BOD5)/CODcr values and the CODcr removal efficiencies of the coking wastewater effluent were improved from 0.06 to 0.29 and from 68.81% to 88.63%, respectively. The result of economic feasibility analysis shows that, by controlling the treaded quantity and concentration of coking wastewater, the extraction replacement-biodegradation coupling process can become a profitable project. (C) 2012 Elsevier B.V. All rights reserved.