The effect of solids on the electrochemical treatment of olive mill effluents

The electrochemical oxidation of an olive mill effluent over Ti–Pt anodes was studied. The effluent had an average total chemical oxygen demand (COD) value of 234 g L^?1, soluble COD of 61 g L^?1, soluble phenolic content 3.4 g L^?1, total solids of 80 g L^?1 and pH = 5.1. Experiments were conducted in a 10 L vessel with the effluent recirculating at 1 L s^?1. The applied current was varied between 5 and 20 A, the salinity between 1 and 4% NaCl, and experiments were performed with the effluent diluted with water to achieve the desired initial concentration. Emphasis was given to the effect of the presence of solids as well as of varying operating conditions on process performance as assessed in terms of COD, color and phenols removal. In general, degradation of phenols occurred relatively fast with conversion increasing with increasing applied current and decreasing initial organic loading and this was accompanied by low COD removal levels and moderate decolorization. The presence of solids had practically no effect on phenols removal, which, in most cases, was complete in less than about 180 min of reaction. However, oxidation in the presence of solids resulted in a substantial solid fraction being dissolved and this consequently increased sample color and the soluble COD content. The solid content typically found in olive mill effluents may partially impede its treatment by electrochemical oxidation, thus requiring more severe operating conditions and greater energy consumption. Copyright © 2007 Society of Chemical Industry