Process Biochemistry 39 (2004) 1947–1951 The effect of pretreatment on anaerobic activity of olive mill wastewater using batch and continuous systems Isam Sabbah ∗ , Taisir Marsook, Sobhi Basheer The Regional Research & Development Center, The Galilee Society, P.O. Box 437, Shefa-Amr 20200, Israel Received 11 April 2003; received in revised form 4 August 2003; accepted 19 September 2003 Abstract This study was focused on several physico-chemical and biological treatment methods that may affect the reduction of the organic load in olive mill wastewater (OMW). In this study, removal of 95% of the phenolic compounds present in OMW was achieved using sand filtration and subsequent treatment with powdered activated carbon in a batch system. This pretreatment for OMW was found to enhance the anaerobic activity of the sludge in the batch system significantly. The efficiency of organic load removal achieved by the anaerobic treatment of untreated OMW in batch reactors with tap water dilution factors below 1:10, reached approximately 65% chemical oxygen demand (COD) removal. However, in the up-flow sludge anaerobic blanket (UASB) reactor, COD removal efficiency of 80–85% was reached at a hydraulic retention time (HRT) of 5 days with an influent COD concentration of 40 g l -1 and organic loading rate (OLR) = 8g -1 COD l -1 per day. © 2003 Elsevier Ltd. All rights reserved. Keywords: Olive mill wastewater; Anaerobic treatment; OLR; Polyphenol; UASB 1. Introduction Olive mill wastewater (OMW) generated by the olive oil extraction process is the main waste product of this industry. Approximately 1.8 × 10 6 t of olive oil are pro- duced annually worldwide where the majority of it is pro- duced in the Mediterranean basin [1]. The average amount of olive mill wastewater produced during the milling pro- cess is 1.2–1.8 m 3 t -1 of olives. OMW resulting from the production process surpasses 30 million m 3 per year [2] in the Mediterranean region. Treatment of OMW is becoming a serious environmental problem, due to its high organic chemical oxygen demand (COD) concentration, and because of its resistance to biodegradation due to its high content of phenolic compounds [3]. Due to the current lack of appropriate alternative tech- nologies to treat OMW, much of the OMW in the Mediter- ranean area is discharged directly into sewer systems and water streams or concentrated in cesspools despite the fact ∗ Corresponding author. Present address: Johns Hopkins University, 3400N Charles Street, Baltimore, MD 21218, USA. Tel.: +1-410-516-4255 (USA)/972-4-9504523 (Israel); fax: +1-410-516-8996 (USA)/972-4-9504525 (Israel). E-mail address: isabbah@jhu.edu (I. Sabbah). that such disposal methods are prohibited in many Mediter- ranean countries. Similarly, OMW is often concentrated in ponds and left to dry throughout the summer season [4,5]. OMW, which contains high concentrations of organic ma- terials, such as polyphenols, tannins, and lipids, negatively impacts the regional environment due to its toxicity to mi- croorganisms in domestic wastewater treatment plants, its strong and unpleasant odor after anaerobic digestion, and also due to its potential threat to surface and groundwater. OMW is comprised of water (83%), organic compounds (15%), and inorganic chemicals (about 2%). The color of the waste produced ranges from black to dark-red reflect- ing the presence of phenolic compounds. OMW is acidic and contains high concentrations of total suspended solids (TSS), total dissolved solids (TDS), and phenols. The OMW is characterized by high levels of COD and biochemical oxygen demand (BOD), in addition to having very high concentrations of fat, oil, and grease (FOG) [6]. Maximum BOD and COD concentrations in OMW reach 100,000 and 220,000 mg l -1 , respectively. This is one of the highest organic loads of known concentrated effluents, which is 100–150 times higher than that of domestic wastewater. Several methods have been proposed for treating OMW, such as evaporation ponds, thermal treatment, physico- chemical and biological treatments. Also, reuse of the OMW 0032-9592/$ – see front matter © 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2003.09.026