Water footprint profile of crop-based vegetable oils and waste cooking oil: Comparing two water scarcity footprint methods
Introduction
Biofuels have been emerging as an alternative to meet the demand for transport fuel worldwide (REN21, 2015). The focus of research and policies on the sustainability of biofuels has been on the reduction of greenhouse gas (GHG) emissions (e.g., Camobreco et al., 2000; Bozbas, 2008; Fargione et al., 2008; Atabani et al., 2012), but there are other relevant aspects to consider when evaluating the environmental impacts of biofuels, such as the freshwater consumption impacts. Freshwater consumption refers to: “water removed from, but not returned to, the same drainage basin. Water consumption can be because of evaporation, transpiration, integration into a product, or release into a different drainage basin or the sea” (ISO, 2014).
The majority of biodiesel is produced from vegetable oil feedstocks (Eisentraut, 2010; Issariyakul and Dalai, 2014; OECD-FAO, 2013) such as soya, palm or rapeseed that can require large quantities of freshwater depending on the location where the crops are cultivated (Pfister and Bayer, 2014; Su et al., 2015). If those areas present high water scarcity, the freshwater consumption impacts can be significant (Chiu et al., 2011; Elena and Esther, 2010). Moreover, the use of fertilizers and pesticides in crop cultivation can also diminish freshwater quality (Emmenegger et al., 2011). Freshwater is related to fresh surface and groundwater; i.e., the freshwater in lakes, rivers and aquifers, and in the particular case of agricultural production, it refers to irrigation freshwater (Pfister et al., 2009).
Several studies on the water footprint (WF) of biofuel systems can be found in the literature. Some were performed according to the water footprint assessment (WFA) manual (Hoekstra et al., 2011, 2009) that provides a methodology to perform a water footprint audit (inventory level) (e.g., Gerbens-Leenes et al., 2009; Elena and Esther, 2010; Chiu and Wu, 2012; Gerbens-Leenes et al., 2012; Chiu et al., 2015). Others are focussed on WFs based on the life cycle assessment (LCA) methodology, quantifying impacts due to freshwater consumption and degradation (impact assessment level) using different methods (e.g., Emmenegger et al., 2011; Yeh et al., 2011; Chiu et al., 2011; Hagman et al., 2013).
Over the last seven years, the LCA-based WF impact methodology has progressed rapidly, resulting in a complex set of methods for addressing different freshwater types and sources, pathways and characterization models with different spatial and temporal scales. The need to ensure consistency in addressing the impacts from freshwater consumption and quality degradation led to the development of the international standard ISO 14046 (ISO, 2014) that provides guidelines on how to perform an assessment of freshwater-related environmental impacts (due to consumption and degradation) and to the water use in LCA (WULCA) group founded under the auspices of the Life Cycle Initiative of the United Nations Environment Programme (UNEP)/Society of Environmental Toxicology and Chemistry (SETAC) (WULCA, 2015).
As no study focussed on the freshwater impacts of biodiesel feedstooks following ISO 14046 has been perfomed, the main goal of this article is to present a comparative WF profile assessment of vegetable oils used for biodiesel production following the ISO 14046 guidelines (ISO, 2014). The profile includes the water scarcity footprint (impacts related to freshwater consumption) and water degradation footprint (impacts due to freshwater degradation). We performed a comparison of two water scarcity footprint methods: water stress index (WSI) (Pfister et al., 2009; Ridoutt and Pfister, 2013) and available water remaining (AWARE) (Boulay et al., 2017). As the AWARE method is new and still in its initial phase of application, we performed a sensitivity analysis on the AWARE characterization factors (CFs) based on different modelling choices.
The water degradation footprint was assessed through the following impact categories: freshwater and marine eutrophication (from the ReCiPe method; Goedkoop et al., 2009), aquatic acidification (from the IMPACT, 2002 + method; Jolliet et al., 2003) and human toxicity and freshwater ecotoxicity (from the USETox method; Rosenbaum et al., 2008).
Four feedstocks were analysed: three virgin oils typically used in biodiesel production obtained from rapeseed (cultivated in Germany, France, Spain, Canada and the United States), soya (cultivated in Argentina, Brazil and the United States) and palm fruit (cultivated in Colombia and Malaysia) and waste cooking oil (WCO), which has recently gained prominence in biodiesel production, collected and refined in Portugal. Palm oil is extracted at the cultivation site while the soya and rapeseed oils are extracted in Portugal. All virgin oils are refined in Portugal. For the case of WCO, two refining processes were considered depending on the WCO quality. In total, 12 oil systems were analysed: 10 virgin oil systems and 2 for WCO.
Section snippets
WF profile
According to ISO 14046 (ISO, 2014), the WF profile considers a range of potential environmental impacts associated with water, encompassing the consumption of freshwater (water scarcity footprint) and impact categories related to freshwater degradation (water degradation footprint – freshwater and marine eutrophication, aquatic acidification and human toxicity).
Water scarcity footprint
Fig. 2 depicts the water scarcity footprint calculated for the WSI and AWARE methods using country level CFs (left-hand side) and the contribution of each stage to the overall impacts (right-hand side). The water scarcity profile calculated following the WSI method ranges from 0.002 to 2.11 world m3eq kg−1 oil, whereas the water scarcity profile varies from 0.008 to 133.79 world m3eq kg−1 oil following the AWARE method. Although the ranges of values are different in magnitude, both methods lead
Conclusions
This article presents a WF profile of vegetable oils used for biodiesel production: palm, soya, rapeseed (assessing different cultivation locations) and WCO. In total, 12 oil systems were analysed. The differences obtained are due to the different characteristics of each system, namely: type of crop, cultivation location and fertilizer and pesticide scheme used. The Rapeseed_SP oil system presents the highest water scarcity footprint due to high water consumption and water scarcity of the
Acknowledgements
Carla Caldeira, Érica Castanheira and Paula Quinteiro and acknowledges financial support from the Portuguese Science and Technology Foundation (FCT) through grants SFRH/BD/51952/2012, SFRH/BPD/107883/2015 and (SFRH/BPD/114992/2016), respectively. Ana Cláudia Dias acknowledges the financial support from FCT (IF/00587/2013). Paula Quinteiro, Ana Cláudia Dias and Luís Arroja also acknowledge financial support from CESAM (UID/AMB/50017), to FCT/MEC through national funds, and the co-funding by the
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2021, Extractive Industries and SocietyCitation Excerpt :As the water-extensive activities, agricultural and forestry products draw much attention of WSF studies, such as food (Hess et al., 2015a; Kaewmai et al., 2020, 2015b; Silalertruksa et al., 2017; Payen et al., 2018; Usva et al., 2019), crops (Cao et al., 2018), forest (Musikavong and Gheewala, 2016; Roibás et al., 2018), etc. A small number of studies have also applied WSF to industrial products, such as biodiesel (Caldeira et al., 2018), hydropower stations (Scherer and Pfister, 2016), aluminum (Buxmann et al., 2016), etc. To summarize, the academic literature on WSF mainly concentrates on agricultural or industrial products.