Statistical optimization of thermal pretreatment conditions for enhanced biomethane production from defatted algal biomass T. Sarat Chandra a,b,c , G. Suvidha a , S. Mukherji b , V.S. Chauhan c , S. Vidyashankar c , K. Krishnamurthi a , R. Sarada c , S.N. Mudliar c,⇑ a Environmental Biotechnology Division, CSIR-National Environmental Engineering Research Institute, Nagpur, Maharashtra, India b Centre for Environmental Science and Engineering, Indian Institute of Technology, Mumbai, Maharashtra, India c Plant Cell Biotechnology Department, CSIR-Central Food Technological Research Institute, Mysore, Karnataka, India highlights  Thermal pretreatment to biomass was optimised for improved biomethanation.  Pretreatment resulted in enhanced biodegradability of defatted algal biomass.  Methane yield enhanced up to 60% after pretreatment. article info Article history: Received 11 February 2014 Received in revised form 12 March 2014 Accepted 16 March 2014 Available online 26 March 2014 Keywords: Scenedesmus dimorphus Defatted algal biomass Thermal pretreatment Methane yield abstract The present study analyzes the effect of thermal pretreatment for enhancing the biomethane potential of defatted algal biomass of Scenedesmus dimorphus through statistically guided experimental design. To this end, defatted microalgal biomass at various concentrations (1, 3 and 5 g L 1 ) was pretreated at ele- vated temperatures (100, 120 and 150 °C) for 20, 40 and 60 min. The solubilised TOC was favourably enhanced up to 71 mg L 1 after pretreatment at a temperature of 150 °C for reaction time of 60 min. The methane yield was substantially enhanced (up to 60%) and could be correlated with an increase in organic matter solubilisation and enhanced biodegradability via thermal pretreatment. The optimisation of the integrated thermal pretreatment-biomethanation process resulted in up to 1.6-fold increase in methane yield. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Depletion of fossil fuel reserves and increase in greenhouse gas emissions has driven researchers in search of alternative renew- able fuel sources. Over the last few years, various kinds of biomass have been identified as a possible source for biodiesel production such as edible and non-edible oil seeds. Taking into account the problems associated with land-based fuel crops, photosynthetic aquatic species such as oleaginous microalgae have been suggested as more suitable for biofuel production (Chisti, 2007). Energy and life cycle assessments of algal biodiesel production have shown the high nutritional needs, usually in terms of fertilizers as well as the high energy demand of lipid extraction and harvesting pro- cedures (Lardon et al., 2009). The nutrient requirements can be minimized by recycling the media after harvesting the microalgae (Yang et al., 2010). Mineralization of defatted algal biomass by anaerobic digestion can also be a solution to minimize the nutrient requirements. Anaerobic digestion serves the dual purpose of – nutrient recycling and energy cogeneration through production of methane. The methane thus produced can be used to minimize the energy requirements for upstream processes of algal biofuel production – such as cultivation, harvesting and extraction (Chisti, 2007; Shifrin and Chisholm, 1980). Recent life cycle energy and carbon foot prints analysis of microalgal biodiesel production cou- pled with byproduct utilization via anaerobic digestion indicate that for producing 1 MJ biodiesel, the lifecycle energy inputs are re- duced from 4.3 MJ to 1.3 MJ (Gao et al., 2013). The integration of microalgal cultivation with waste water treatment and anaerobic digestion could serve the dual purpose of removal of chemical and biological contaminants from waste waters and energy cogen- eration by anaerobic digestion of defatted algal biomass. Also, the application of wastewaters for cultivation of algae would minimis- es the fresh water and nutrient requirements thereby improving the economics of the process (Yang et al., 2010). http://dx.doi.org/10.1016/j.biortech.2014.03.080 0960-8524/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: sandeepm@cftri.res.in (S.N. Mudliar). Bioresource Technology 162 (2014) 157–165 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech