Reduction of environmental and energy footprint of microalgal biodiesel production through material and energy integration Raja Chowdhury a , Sridhar Viamajala a,⇑ , Robin Gerlach b a Department of Chemical and Environmental Engineering, The University of Toledo, Toledo, OH 43606, United States b Department of Chemical and Biological Engineering, Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717, United States article info Article history: Received 11 August 2011 Received in revised form 17 December 2011 Accepted 19 December 2011 Available online 31 December 2011 Keywords: Algae Life cycle assessment Nutrient recycling Anaerobic digestion Biofuel abstract The life cycle impacts were assessed for an integrated microalgal biodiesel production system that facil- itates energy- and nutrient- recovery through anaerobic digestion, and utilizes glycerol generated within the facility for additional heterotrophic biodiesel production. Results show that when external fossil energy inputs are lowered through process integration, the energy demand, global warming potential (GWP), and process water demand decrease significantly and become less sensitive to algal lipid content. When substitution allocation is used to assign additional credit for avoidance of fossil energy use (through utilization of recycled nutrients and biogas), GWP and water demand can, in fact, increase with increase in lipid content. Relative to stand-alone algal biofuel facilities, energy demand can be lowered by 3–14 GJ per ton of biodiesel through process integration. GWP of biodiesel from the integrated system can be lowered by up to 71% compared to petroleum fuel. Evaporative water loss was the primary water demand driver. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Concerns over rapidly depleting fossil energy sources and esca- lating greenhouse gas emissions have resulted in an increased inter- est in alternative energy sources. Biofuels are a renewable alternative to fossil fuels that are compatible with existing automo- bile- and fuel-infrastructure. However, first-generation biofuels such as ethanol from corn and biodiesel from oil seeds, are unlikely to replace a significant fraction of the US petroleum demand without adversely affecting food production due to the low yields (per unit land area) of feedstocks from traditional agriculture (Chisti, 2007). In addition, corn and oil-seed crops require significant resources of fertile land, fertilizer, pesticides, and irrigation water. The potential for increase in agricultural run-off from extensive cultivation of these dedicated energy crops also poses significant environmental concerns (Donner and Kucharik, 2008). Overall, net greenhouse gas (GHG) emissions, energy demand and water demand are not favorable for first-generation biofuels (Clarens et al., 2010). Microalgae-derived biodiesel is a promising renewable fuel (Yazdani and Gonzalez, 2007) and studies suggest that oil productiv- ities (per unit area) from microalgae can be nearly 8–20 times higher than those of plant oils (Chisti, 2007). However, algal fuel production involves more energy intensive processes for cultivation, harvesting and lipid recovery than conventional agriculture. Thus, overall energy and environmental impacts of algal biodiesel can only be determined through detailed life-cycle analyses of the fuel produc- tion processes. In addition, such analyses can also assist the develop- ment of more sustainable production options through identification of process steps that result in severe environmental effects. Several recent LCA studies have reported on environmental im- pacts of algal biodiesel production relative to fossil- or other alter- native-fuels (Batan et al., 2010; Clarens et al., 2010; Collet et al., 2010; Lardon et al., 2009; Sander and Murthy, 2010; Yang et al., 2011). The life-cycle global warming potential (GWP) of algal bio- diesel has been assessed to be lower than that of petroleum diesel as well as of biodiesel derived from soy or canola (Batan et al., 2010; Lardon et al., 2009). However, studies also estimated that the GWP of algal biodiesel was likely higher than that of biodiesel from palm- or rapeseed oil (Lardon et al., 2009). One of the poten- tial methods of reducing GWP associated with algal biodiesel is through generation of multiple by-products in the biorefinery. In such systems, the life-cycle burden can be distributed among all the products (commonly calculated through allocation procedures) thus lowering the life-cycle burden of biodiesel alone. Batan et al. (2010) used this approach to distribute overall process GWP to the two products in their system – biodiesel and algae residue. Sander and Murthy (2010) allocated their GWP to biodiesel and ethanol (derived from algal carbohydrates). A more direct approach for lowering life-cycle energy demand is through minimization of external fossil energy inputs or fossil- derived raw materials. External energy needs could be reduced if the energy contained in the non-lipid portion of algal biomass (not utilized for biodiesel production) was recovered and utilized 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.12.099 ⇑ Corresponding author. Tel.: +1 419 530 7417. E-mail address: sridhar.viamajala@utoledo.edu (S. Viamajala). Bioresource Technology 108 (2012) 102–111 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech