Research Article Subcritical Water Extraction of Chlorella pyrenoidosa: Optimization through Response Surface Methodology Selvakumar Thiruvenkadam , Shamsul Izhar, Yoshida Hiroyuki, and Razif Harun Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang, Malaysia Correspondence should be addressed to Razif Harun; mh razif@upm.edu.my Received 30 June 2018; Accepted 21 October 2018; Published 7 November 2018 Guest Editor: Mohamed H. Abd-Alla Copyright © 2018 Selvakumar Tiruvenkadam et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Subcritical water extraction (SCW) was used to extract oil from Chlorella pyrenoidosa. Te operational factors such as reaction temperature, reaction time, and biomass loading infuence the oil yield during the extraction process. In this study, response surface methodology was employed to identify the desired extraction conditions for maximum oil yield. Experiments were carried out in batch reactors as per central composite design with three independent factors including reaction temperature (170, 220, 270, 320, and 370 ∘ C), reaction time (1, 5, 10, 15, and 20 min), and biomass loading (1, 3, 5, 10, and 15%). A maximum oil yield of 12.89 wt.% was obtained at 320 ∘ C and 15 min, with 3% biomass loading. Sequential model tests showed the good ft of experimental data to the second-order quadratic model. Tis study opens the great potential of SCW to extract algal oil for use in algal biofuel production. 1. Introduction Te rapid depletion of fossil fuels, together with the uncertain global climate in the past decade, has inevitably led to an increased commercial interest in renewable fuels. Biodiesel is viewed as an attractive potential solution to alleviate the exist- ing dependency on petroleum-based fuels [1]. Current pro- duction of biodiesel involves methanolic transesterifcation of extracted plant lipids, while bioethanol is presently syn- thesized via anaerobic yeast fermentation of sugar molecules found in the biomass of diferent food crops [2]. Algae are identifed as a promising alternative feedstock for both biofuels due to its high biomass productivity, perceived rapid lipid accumulation, and the suitability of its carbohydrate biochemistry for fermentation process [3]. Additionally, unlike other fuel-producing crops, algae can be grown with saline water in nonagricultural lands, thereby exempting their large-scale cultivation from placing addi- tional demands on precious freshwater and arable lands required for food production [4]. Although algal-based bio- fuels generate approximately 13% CO 2 lower emissions from combustion relative to CO 2 emissions from petroleum diesel [5], in terms of absolute emission levels, algal biofuels can be signifcantly high for full-scale applications. Te development of biofuels from algal biomass has been signifcantly suc- cessful under lab-scale conditions. However, opportunities for commercial-scale applications should focus on addressing related environmental, technological, and economic draw- backs. Te conventional biodiesel production from microalgae has downstream demands such as the moisture content which should not be more than 10%. Since the biochemical products used in the synthesis of biofuel (neutral lipids for biodiesel and simple sugars for bioethanol) are encapsulated within the algal cellular structures, disintegrating the cells to liberate these intracellular products will render them more readily accessible and subsequently enhance production yield. Te oil from algae is usually extracted with organic solvent and then converted into biodiesel using a catalyst. Te energy intake during drying and solvent extraction processes contributes to two-thirds of the total energy consumption of the entire process [6]. Numerous studies have been reported on diferent methods available for algal oil extraction [7, 8]. Tough these methods were found to be efective in Hindawi BioMed Research International Volume 2018, Article ID 1931634, 10 pages https://doi.org/10.1155/2018/1931634