SBR treatment of raw and chemically pre-treated olive mill wastewaters

The olive-oil extraction industry is an economically important activity for many countries of the Mediterranean Sea area, with Spain, Greece and Italy being the major producers. This activity, however, may represent a serious environmental problem due to the discharge of highly polluted effluents, usually referred to as “olive mill wastewaters” (OMWs). They are characterized by high values of Chemical Oxygen Demand (COD) (80-300 g/L), lipids, total polyphenols (TP), tannins and other substances difficult to degrade. An adequate treatment before discharging is therefore required to reduce the pollutant load. The aim of the present paper was to study the combined treatment of olive mill wastewaters made by a Sequencing Batch Reactor (SBR) with a Granular Activated Carbon (GAC) adsorption pre-treatment. A deep characterization of the effluents from the different pre-treatment methods was carried out in order to select the most suitable process for the subsequent biological treatment. Based on both the results obtained from the fractionation and the different pre-treatment efficiencies, GAC adsorption was chosen to be used as a pre-treatment to the following biological process. The removal efficiency of COD and Total Phenol was investigated for different feeding conditions: diluted OMWs with dilution ratio of 1:50 and 1:25, and the pre-treated wastewater. The best performances were obtained with the lower dilution ratio: in this case, the removal efficiencies were 90% and 76%, as average, for COD and TP respectively. Feeding the SBR with the pre-treated or the diluted OMWs at 1:50 gave very similar performance of COD abatement (74%) but an improvement of TP removal. This indicated that GAC pre-treatment was capable of eliminating potentially inhibiting phenolic compounds by adsorption.