Biological treatment of olive mill wastewater in a sequencing batch reactor

The olive mill wastewaters (OMWs) are among the more difficult wastewaters to be treated. Among the different solutions investigated up to now, the biological processes are capable of achieving complete degradation of the biodegradable compounds contained in the OMWs and therefore to significantly reduce the pollutant load. However, further studies still need to be performed in order to find out the optimal bioreactor and the best operating conditions. The aim of the present study was to investigate the efficiency of a sequencing batch reactor (SBR) in the biological treatment of OMWs. Different influent organic loadings (0.08, 0.11, 0.19 and 0.69 mg COD mg MLVSS-1 d(-1)) were applied and their effects on chemical oxygen demand (COD) and total polyphenols (TPPs) removal determined. Furthermore, it was evaluated the possibility to add a pre- or a post-treatment through different membrane separation steps, namely ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO). The SBR always showed high performances, achieving complete removal of the biodegradable organic content at all the investigated influent loadings, with average efficiencies constantly at about 90% and 60% for COD and TPPs, respectively. These values increased up to 92% and 78%, respectively, when the OMWs were added with nutrient. The membrane separation stage posed down flow the SBR process was capable of further improving the effluent quality and to comply with the limits posed on COD, pH and conductivity for discharge or reuse according to the Italian legislation. However, the residual polyphenols content was still above the concentration limit required for reuse. (C) 2014 Elsevier B.V. All rights reserved.