Development of biochar as fuel and catalyst in energy recovery technologies M. Waqas a, b , A.S. Aburiazaiza a , R. Miandad c , M. Rehan b , M.A. Barakat a, d , A.S. Nizami b, * a Department of Environmental Sciences, Faculty of Meteorology, Environment and Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia b Center of Excellence in Environmental Studies (CEES), King Abdulaziz University, Jeddah, Saudi Arabia c Department of Environmental Sciences, University of Peshawar, Peshawar 25120, Pakistan d Central Metallurgical R & D Institute, Helwan 11421, Cairo, Egypt article info Article history: Available online 3 April 2018 Keywords: Anaerobic digestion (AD) Biochar Biomass Pyrolysis Transesterification Energy recovery technologies abstract This study aims to (1) convert agricultural waste to biochar through pyrolysis, (2) examine its physi- ochemical characteristics, and (3) investigate its potential role as fuel and catalyst in energy recovery technologies. The produced biochars at 250, 350, and 450  C showed a wide range of mineralogical composition, high porosity, and thermal stability, and alkaline pH that make biochar suitable for improving the processes of energy recovery technologies such as anaerobic digestion (AD), trans- esterification and pyrolysis. The alkaline pH of biochars can neutralize the acidic condition and increase the digestibility of the feedstock in AD process for enhanced methane (CH 4 ) production. Biochar favors the transesterification process for biodiesel production due to products separation and high stability under basic and acidic conditions. In pyrolysis process, biochar can act as a catalyst to increase the degradation rates of plastic or biomass wastes or can be used as an adsorbent material during the post- treatment to improve the quality of the liquid oil. The high heating values (HHV) of biochars produced at 250, 350 and 450  C were 24, 23.64 and 23.08 MJ kg 1 . This characteristic of biochar along with the high tendency of slagging indicate that biochar could be used itself as a source of energy. Biochar can also act as a promising low-cost adsorbent for capturing carbon dioxide (CO 2 ) due to its highly porous structure and sorptive capacity and subsequently the conversion of absorbed CO 2 to fuel. Research is yet required on the application of biochar in pyrolysis and capturing and catalyzing the conversion reactions of CO 2 to fuels. © 2018 Elsevier Ltd. All rights reserved. 1. Introduction The global energy consumption in 1990 was about 1 billion gigawatts (GW) that have reached up to 13,371 Mtoe (million tonnes of oil equivalent; 1 toe ¼ 11,630 GWh) and further projected to increase up to 44,600 Mtoe by 2050 (IEA, 2014). This rise in energy demand is primarily due to the threefold increase in world population along with high industrialization and urbanization growth (Bilgen, 2014). The Kingdom of Saudi Arabia (KSA) is the 12th largest primary energy consumer country in the world with energy consumption rate of 9 quadrillion Btu (British thermal units) (Nizami et al., 2016). The current electricity demand is about 55 GW that is estimated to exceed 120 GW by 2032 (Ouda et al., 2015). The fossil fuels are the primary source of energy in the country (Miandad et al., 2017a). KSA has launched several programs, including the King Abdullah City of Atomic and Renewable Energy (KACARE) and Vision 2030 to utilize the indigenous resources such as wind, geothermal, waste and solar to meet the future energy demands (KACARE, 2012; Vision2030, 2016). Energy recovery technologies such as anaerobic digestion (AD), pyrolysis, refuse derived fuel (RDF), transesterification, and gasifi- cation have emerged as promising solutions to treat and convert waste materials to electricity, fuel, fertilizers, chemicals, and heat (Rehan et al., 2016). The selection of energy recovery technologies mainly depend on the type and amount of waste, process capital and operational costs, labor skills and technological requirements, end-products market, and the conversion efficiency of the tech- nology (Szarka et al., 2013). Ouda et al. (2016) and Nizami et al. (2017) have recently examined the energy recovery technologies including AD, pyrolysis, and transesterification in comparison to * Corresponding author. E-mail addresses: nizami_pk@yahoo.com, anizami@kau.edu.sa (A.S. Nizami). Contents lists available at ScienceDirect Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro https://doi.org/10.1016/j.jclepro.2018.04.017 0959-6526/© 2018 Elsevier Ltd. All rights reserved. Journal of Cleaner Production 188 (2018) 477e488