Contents lists available at ScienceDirect Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser Algal bioethanol production technology: A trend towards sustainable development Riaz Bibi a , Zulfiqar Ahmad b,f , Muhammad Imran c,g , Sabir Hussain d , Allah Ditta e , Shahid Mahmood b , Azeem Khalid b, ⁎ a Gwangju Institute of Science and Technology, Gwangju, South Korea b Department of Environmental Sciences, PMAS Arid Agriculture University, Rawalpindi 46300, Pakistan c Institute of Soil and Environmental Sciences, University of Agriculture, Faisalabad, Pakistan d Department of Environmental Sciences & Engineering, Government College University, Faisalabad, Pakistan e Department of Environmental Science, Shaheed Benazir Bhutto University Sheringal, Upper Dir, 18000 Khyber Pakhtunkhwa, Pakistan f Department of Environmental Sciences, University of California, Riverside CA 92521, USA g Soil and Environmental Sciences Division, Nuclear Institute for Agriculture and Biology (NIAB), Faisalabad, Pakistan ARTICLE INFO Keywords: Bioethanol Biofuel Algae Cultivation Bioreactors Sustainability ABSTRACT Fuel security, economics and climate change issues are creating a requirement for alternative renewable fuels. Bioethanol produced by algal biomass is becoming increasingly popular all over the world due to the sustainability of feed stock and environmentally friendly nature. This review paper describes the bioethanol production technology from algae using various cultivation, harvesting, extraction and commercialization techniques and its environmental perspectives. The economic sustainability of algae-derived bioethanol biofuel depends on the cost of production that could be minimized by producing valuable secondary by-products, which is the aim of current algal biofuel research. Future technologies with sufficient potential for maximum extraction capacity and minimal downstream processing using low cost feedstock will address the cost-effectiveness of renewable bioethanol biofuel. 1. Introduction Sustainable energy is a big challenge for the growing population of the world. The world's population will continue to grow for at least several decades. Demand for energy will probably increase even more rapidly and the proportion of fossil fuels will increase as rapidly to meet the demand for motor vehicles as fuels and industries. Fossil fuel resources are exhausting from day to day, which has ultimately increased the price of petroleum fuels [1]. Moreover, many environ- mental issues like global warming have emerged with the incredible use of fuel reserves. Elated energy demands and global climate change interests have brought biofuels in burst. To meet current and future energy needs, environmental-friendly energy sources that are capable of being irreproachable, efficient, substituting, inexhaustible, cost- effective and low-emitting greenhouse gases are the need for time [2,3]. Exploitation of renewable energy sources is an appropriate first consideration in sustainable development. Liquid fuels such as bioetha- nol, biodiesel and pyrolysis oils, gases such as biogas (methane) and solids such as charcoal and fuel wood pellets produced mainly from biomass are called biofuels [4]. A number of fuels such as methanol, ethanol, biodiesel, Fischer-Tropschdiesel, methane and hydrogen can be made from biomass [5]. Biofuels derived from biomass bring many local environmental benefits [6]. Biofuels are essential because they renew petroleum fuels [7]. Many developed and developing countries find biofuels important to reducing dependence on foreign oil, reducing GHG emissions and achieving rural development goals [8]. Increased energy security, exchange rate savings, reduced environmental impact and socio-economic problems are the main achievements of biofuels [9,10]. Many conventional biofuels are encumbered with higher production costs and therefore, uncompetitive retail prices [5,11]. However, political support through mergers and tax credit policies has allowed some types to penetrate the market for consumer fuels, with sugar ethanol in Brazil being an excellent example [12]. The production of bioethanol in the world has increased rapidly in the few years. In fact, production rose from 1 billion liters in 1975 to 86 billion liters in 2010, and production is expected to exceed 160 billion liters by 2020 [13]. However, the depletion of water sources and the use of arable land have put the viability of bioethanol under the scanner. The extreme use of arable land to produce biomass for bioethanol production may lead to a deficiency in basic food crops http://dx.doi.org/10.1016/j.rser.2016.12.126 Received 25 November 2015; Received in revised form 13 December 2016; Accepted 26 December 2016 ⁎ Corresponding author. E-mail addresses: azeem@uaar.edu.pk, azeemuaf@yahoo.com (A. Khalid). Renewable and Sustainable Energy Reviews 71 (2017) 976–985 Available online 30 December 2016 1364-0321/ © 2016 Elsevier Ltd. All rights reserved. MARK