Evaluation of aerobic and anaerobic co-digestion of Tetraselmis suecica and Oil Palm Empty Fruit Bunches by Response Surface Methodology Ashfaq Ahmad 1 , Syed Muhammad Usman Shah 1 , Azizul Buang 1 , Mohd Fariduddin Othman 2 , Mohd Azmuddin Abdullah 1,a 1 Department of Chemical Engineering, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750,Tronoh, Perak, Malaysia. 2 Fisheries Research Institute, Pulau Sayak, 08500, Kota Kuala Muda, Kedah, Malaysia. *Corresponding author. Tel: +605 3687636; Fax: +605 3656176 a E-mail address: azmuddin@petronas.com.my Keywords- Anaerobic digestion; biomethane; Tetraselmis suecica; Response Surface Methodology; Palm Oil Mill Effluent; Waste remediation Abstract. This study investigated co-cultivation of Tetraselmis suecica microalgae with Oil Palm empty fruit bunch (OPEFB) for anaerobic biomethane production and Palm oil mill effluent (POME) treatment. The highest specific biogas production (0.1162 m 3 kg -1 COD day -1 ) and biomethane yield (3900.8 mL CH 4 L -1 POME day -1 ) was achieved with microalgae at 2 mL mL -1 POME, and OPEFB at 0.12 g mL -1 POME. Without co-digestion of microalgae, higher specific biogas production (0.1269 m 3 kg -1 COD day -1 ) but lower biomethane yield (3641.8 mL CH 4 L -1 POME day -1 ) were observed. Second order polynomial model fits the data well with less than 5% error. Higher removal efficiency (62-95%) of COD, BOD, TOC and TN were achieved by aerobic and anaerobic treatment of POME with microalgae than without microalgal treatment after 3 and 7 days of hydraulic retention time (HRT). Introduction There is an increasing interest in alternative renewable sources of fuels due to increased demand for energy worldwide [1]. Palm oil industries are among the major contributors of the Malaysian economy, besides other commercial crops like rubber and cocoa. In common processing of palm oil, 1 tonne of crude palm oil requires 5-7.5 tonnes of water, where half of the used water ends up as a Palm Oil Mill Effluent (POME) [2]. POME is a voluminous thick brownish oily wastewater, containing highly concentrated colloidal dispersion of biological origin with an unpleasant odor. These are dissolved oil and fatty acids, glycerin, crude oil solids and short fibers and a wide range of biological substances from complex biopolymers such as proteins, starches and hemicelluloses to simple sugars and amino acids, as well as soluble materials that are harmful to the environment [3, 4]. The nature of POME can support the growth of microalgae. Algae adds an advantage to effluent treatment by increasing the performance of degradation, improving CO 2 balance and lowering energy demand for oxygen supply in aerobic treatment stage, by assimilating plant nutrients and supporting the bacteria with oxygen. Bacteria, in turn, are involved in the degradation of organic material in wastewater, the same process utilized in activated sludge [5]. Microalgal wastewater treatment has been shown to be a more cost-effective way to remove BOD, COD, phosphorus and nitrogen than activated sludge [6]. Scendesmus sp., Chlorella sp., and Chlamydomonas reinhardtii are among algal species capable of reducing COD and BOD [7-9]. The aim of this study was to investigate the effects of anaerobic co-cultivation of T. suecica with the addition of OPEFB and sludge as inoculum for biomethane production and POME treatment. The different parameters studied were substrate, co-substrate/inocula and T. suecica ratio. The responses evaluated were biomethane and specific biogas production rate, and the effects were estimated using a multilevel factorial experimental design. Advanced Materials Research Vol. 925 (2014) pp 243-247 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.925.243 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 115.135.67.111-09/04/14,12:18:11)