Improving the energy balance of microalgae biodiesel: Synergy with an autonomous sugarcane ethanol distillery Henrique Leonardo Maranduba a, * , Sabine Robra c , Iracema Andrade Nascimento b , Rosenira Serpa da Cruz a , Luciano Brito Rodrigues c , Jos e Adolfo de Almeida Neto a a State University of Santa Cruz, Campus Soane Nazare de Andrade, Rodovia Jorge Amado, Km 16, CEP 45662900, Salobrinho, Ilheus, Bahia, Brazil b Institute of Biology, Federal University of Bahia, Campus Ondina, Rua Bar~ ao de Geremoabo, 147, CEP 40170290, Ondina, Bahia, Brazil c State University of Bahia Southwest, Campus Itapetinga, Rodovia BR 415, Km 03, CEP 45700000, Itapetinga, Bahia, Brazil article info Article history: Received 29 July 2015 Received in revised form 19 August 2016 Accepted 9 September 2016 Keywords: Biofuels Cumulative energy demand Net energy balance Fossil energy ratio Integrated biorefineries System expansion abstract This study analyzed the algal biodiesel production system via dry-route, based on Chlorella vulgaris cultivated in raceways, by comparing the Net Energy Balance (NEB) and the Fossil Energy Ratio (FER) of five scenarios: C0 (single system of biomass production); C1 (C0 þ pyrolysis of the microalgae press cake); C2 (C0 þ anaerobic co-digestion of the microalgae press cake); C3 and C4 (same conditions of C1 and C2, but integrating both scenarios into an autonomous ethanol distillery). Each scenario was analyzed under de perspective of energy allocation (a) and system expansion with avoided product (b). The results showed that with the energy allocation, only C3a and C4a improved the values of baseline scenario (C0a) for NEB, in 120% and 72% respectively. When the system expansion is considered, none of the scenarios was better than the respective baseline scenario (C0b), in relation to the NEB. Considering the FER, C3a increased in 3.4% the values of C0a, while C3b and C4b increased the values of C0b in 54.1% and 28.8%, respectively. In general, system expansion showed the best scenarios: for the NEB C0b showed the highest average values while C3b showed the highest average values for the FER. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Although projections indicate that, until about 2030, crude oil will remain the dominant source of transportation energy, over the last ten years, biofuels such as ethanol and biodiesel have been emerging in the global energy scenario as complete or partial substitutes for petroleum products [1]. According to the Brazilian National Agency of Petroleum, Nat- ural Gas and Biofuels (ANP),, Brazil has turned into a major player in the energy sector over the last years, due to a share of 43.5% renewable energy in its primary energy production, three times more than the world average [2]. Brazil is the world's second largest ethanol producer. Based on the use of sugarcane as feedstock, the Brazilian Government projected the production of 30.68 billion li- ters of ethanol for 2016, a substantial increase over the previous production peak of 24 billion liters [3]. Regarding biodiesel based on feedstocks such as soybean (77.4%), beef tallow (18.5%), and cotton oil (2.0%), Brazil became an important world player with a production around 3.94 billion liters per year [4]. The biodiesel industry is regulated by the government, with a current compul- sory biodiesel content of 7% in the diesel fuel being in effect, while the industry advocates an increase of 10% in the blend by 2020. However, the projections of an increasing demand of biofuels are now causing concern. Although important for reducing the atmo- spheric CO 2 impact resulting from the use of fossil fuels, these first generation biofuels, which are based primarily on edible com- modities as feedstock, may result in competition for food and the expansion of agricultural lands, causing the release of carbon (as CO 2 or CH 4 ) stored in soil and biomass, besides the indirect emis- sions caused by the increasing use of natural resources and fossil fuels, which tend to intensify the greenhouse gas (GHG) emissions [1,5]. Under these circumstances, compared to land crops, microalgae appear as potential biofuel feedstock, due to their positive charac- teristics. Microalgae can be cultivated in a variety of water sources, do not compete with food crops for arable land and have a higher * Corresponding author. Current address: Grupo Bioenergia e Meio Ambiente (BioMA), Universidade Estadual de Santa Cruz (UESC, Campus Soane Nazare de Andrade, Rodovia Jorge Amado, km 16, CEP 45662900, Salobrinho, Ilheus, Bahia, Brazil. E-mail address: henrique.leo@gmail.com (H.L. Maranduba). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2016.09.061 0360-5442/© 2016 Elsevier Ltd. All rights reserved. Energy 115 (2016) 888e895