ENVIRONMENTAL BENEFITS AND TRADE-OFFS OF PRODUCING BIO-ENERGY AND BIO-MATERIALS FROM AUSTRALIAN SUGARCANE.

Transcription

1 ENVIRONMENTAL BENEFITS AND TRADE-OFFS OF PRODUCING BIO-ENERGY AND BIO-MATERIALS FROM AUSTRALIAN SUGARCANE By MA RENOUF 1,3, RJ PAGAN 1, MK WEGENER 2,3 1 School of Geography, Planning and Environmental Management, and 2 School of Integrated Systems, The University of Queensland, St. Lucia 3 Cooperative Research Centre for Sugar Industry Innovation through Biotechnology m.renouf@uq.edu.au KEYWORDS: Environmental Impact, Life Cycle Assessment (LCA), Diversification, Ethanol, Cogeneration, Plastic. Abstract THIS PAPER reports the findings of a project that examined the environmental implications of producing bio-energy and bio-materials from Australian sugarcane. Life cycle assessment (LCA) was used to quantify some of the environmental impacts of a diversified sugar industry relative to a conventional sugar-producing model. The entire life cycle of the sugarcane agro-industrial systems was considered, from the extraction of resources, through to the end-of-life disposal of products, wastes and emissions. A number of scenarios considered the utilisation of mill by-products from existing sugarcane processing (ethanol from molasses, from, and ethanol from ). These were found to result in some significant environmental gains, reducing non-renewable energy use and greenhouse gas emissions (GHG). These benefits come with few trade-offs. Of the three by-product utilisation scenarios, generation from provided the best gains if all impacts are considered. Other scenarios considered expanded cane for of ethanol and PLA plastics from cane juice. These scenarios yielded very high gains in non-renewable energy use and GHG emissions, but came with trade-offs the additional environmental impacts of expanded agricultural (land use, water use and potential water quality impacts). Introduction It has been suggested that product diversification in the Australian sugar industry through greater by-product utilisation or alternative systems is needed to ensure the future viability, and sustainability, of the sugar industry (Hildebrand, 2002). Product diversification can be argued on economic grounds by reducing the industry s exposure to sugar price volatility, and on social grounds 28

2 through the establishment of new rural industries. It could also be argued on environmental grounds since the energy, fuel and bio-materials derived from sugarcane displace products originating from non-renewable, fossil-fuel sources. However the environmental implications have not previously been tested for Australian sugarcane. The hypothesis is that sugarcane systems that incorporate greater product diversification can result in environmental benefits. To test this, the objectives were to: 1. quantify the life-cycle environmental impacts of conventional sugarcane systems in Australia, which principally have a sugarproducing function 2. quantify the life-cycle environmental impacts of some diversified sugar industry scenarios, whose products also include bio-energy, biofuels and bio-materials 3. compare the predicted change in environmental impacts from each scenario to determine whether, and to what extent, product diversification provides environmental benefits. The results from the first objective have been reported elsewhere (Renouf and Wegener, 2007) and subsequently updated by Renouf et al. (2010a, b). This paper reports the results from the objectives 2 and 3, focusing on the environmental benefits and trade-offs of a diversified sugar industry relative to the conventional sugarproducing model. Environmental life cycle assessment (LCA) was used to quantify the environmental impacts of the sugarcane systems. Past LCA work has evaluated individual products from sugarcane (sugar,, ethanol, plastics) (Almeida, 2005; Contreras, 2009; Macedo et al., 2008; Nguyen and Gheewala, 2008; Ramjeawon, 2004, 2008; Smeets et al., 2008). This work evaluates the agro-industrial system rather than the products, to provide a more predictive assessment of the implications of diversification. Method Diversification scenarios The diversification scenarios selected for the assessment were those considered to be the most viable in the medium-term, based on industry interest and the research priorities of the Cooperative Research Centre for Sugar Industry Innovation through Biotechnology (CRC SIIB) at the time. The intent was to represent scenarios that were either: I. based on continued raw sugar from existing cane, but with greater utilisation of mill by-products (s 1 3) or II. based on expanded cane to produce products other than sugar from the cane juice (s 4 5). The descriptions of the scenarios are as follows: The base case, representing no product diversification, is based on conventional Queensland sugarcane and milling operations 29

3 producing raw sugar, C-molasses used as animal feed, and no export of. 1 ( generation) is as per the base case but with upgraded boiler efficiency and co-generation capacity, and any surplus directed to generation. 2 (ethanol from molasses) is as per 1, but with all C-molasses diverted to ethanol fermentation for blended fuels (). The ethanol process assumed conventional fermentation technology with the dunder concentrated for land application. 3 (ethanol from ) is as per 1, but with ~40% of diverted to ethanol fermentation for blended fuels (). The ethanol process was based on a detailed design for a cellulosic ethanol plant in the US employing dilute acid pre-hydrolysis (Aden et al., 2002). In this scheme the wastewater arising was treated anaerobically to recover methane and the treated effluent reused in the process. 4 (ethanol from cane juice) is as per 1, but with all cane juice directed to ethanol fermentation for blended fuels (). The ethanol process is as described in 2. 5 (PLA from cane juice), is as per 1, but with all cane juice directed to lactic acid fermentation and subsequent polylactate polymer (PLA plastic). The PLA process was based on that of Cargill Dow in the US (Vink et al., 2003). In this scheme the wastewater arising was treated and reused in the process. Energy for all the diversified scenarios is from in upgraded boilers with associated co-generation of steam and, and export of surplus. Modelling of energy balances was undertaken by Sugar Research and Innovation at Queensland University of Technology. The features of each scenario are summarised in Table 1 and quantities of products assumed to be derived are given in Table 2. A consequential LCA approach was taken, which is useful for assessing the consequential environmental impacts of changes to a system (Rebitzer et al., 2004 Section 3). For this approach the marginal changes associated with increased demand for the sugarcane products were assessed. This means that as well as the changes occurring to the sugarcane system, changes occurring in other systems are also included in the system boundary, i.e. displacement effects when the molasses byproduct is diverted from animal feed to fuel ethanol, and when sugarcane-derived, fuel ethanol and plastics substitute their fossil-fuel counterparts. The nature and quantities of the displaced products under each scenario are given in Table 2. 30

4 Table 1 Features of the product diversification scenarios. Primary product By-products Upgraded boiler efficiency and cogeneration capacity Surplus directed to Base case Feed molasses No No s based on greater by-product utilisation from existing raw sugar 1 Feed molasses Yes Yes 2 3 Ethanol from molasses, and dunder Feed molasses, and ethanol from s based on products other than sugar from expanded cane 4 Ethanol Dunder Yes Yes 5 Polylactate polymer (PLA) Yes Yes Yes Yes Yes Yes Table 2 Quantities of products, by-products and displaced products for each scenario (per 100 tonne cane). Unit Base case t Products Feed molasses (Cgrade) Exported (burning ) t MWh Ethanol (anhydrous) L 755 2,195 9,391 By-products Dunder m 3 3 Gypsum kg Polylactate (PLA) polymer pellets t 10.2 (1) 24 (1) Sorghum 3 t Displaced products Electricity (from coal) MWh L 542 1,574 6,735 Potassium chloride 4 kg Polyethylene (PET) polymer pellets 5 t In the source documents from which data were obtained for these processes, wastewaters are reported to be treated and reused. Therefore dunder is assumed not to be generated. 2 Gypsum is produced when acidic process streams are neutralised with lime. 3 Sorghum grain was assumed to be the substitute product for molasses in livestock feed applications. 4 When applied to cane land dunder is assumed to displace mineral potassium fertiliser (KCl). 5 PLA is assumed to displace PET (1:1) in packaging applications. 31

5 Figure 1 shows how the diversified scenarios differ from the base case, and also the expanded system boundaries for each. These boundaries represent the operations that change as a result of transforming the sugarcane system from the base case to the diversified scenarios. Boundaries for sugarcane systems are bold, expanded boundaries for displaced products are dashed. For scenarios 1 3 cane is not included in system boundaries, since there is assumed to be no change to cane for these scenarios. For s 4 5, cane is included since expanded cane is assumed to be a consequence, if they occur without displacing raw sugar. For simplicity, the expanded cane was assumed to occur in Queensland. However in reality expansion would more likely occur in countries with more capacity for expansion Brazil, China, India, etc. Data availability didn t allow for cane in other countries to be examined at this stage. Life cycle impact assessment (LCIA) results were generated for each diversification scenario per 100 tonne cane processed, using the method described by Renouf et al. (2010a). The results represent the consequential impacts of each scenario relative to the base case. The method adds together any increases in environmental impacts due to the altered sugarcane system, and subtracts any avoided environmental impacts associated with displaced products. Milling and sugar raw sugar C-molasses Livestock feed a) Base case Bagasse Milling and sugar raw sugar C-molasses Livestock feed Co-generation of Exported Qld black-coal b) 1 Milling and sugar raw sugar C-molasses Sorghum Livestock feed Co-generation of Exported Qld black-coal c) 2 Fermentation of molasses anhydrous ethanol dunder Fuel Potassium for agriculture KCl 32

6 Milling and sugar raw sugar C-molasses Livestock feed Co-generation of lignin Exported Qld black-coal Hydrolysis / fermentation of to ethanol anhydrous ethanol Fuel d) 3 dunder Potassium for agriculture KCl Milling juice Co-generation of e) 4 Ethanol fermentation of cane juice anhydrous ethanol Exported Fuel Qld black-coal Milling juice Co-generation of f) 5 Lactic acid fermentation of cane juice lactic acid PLA PLA resin PLA disposal in landfill Exported Plastic PET disposal in landfill Fig. 1 Base case and diversified sugarcane systems showing system boundaries. Qld black-coal PET The final result can be positive or negative. A positive result indicates a net increase in impacts of the system. A negative result indicates a net environmental benefit, where any increased impacts in the sugarcane system are offset by the environmental credits from displaced products. The impact categories reported are listed in Table 3. Eco-toxicity impacts were also assessed, but have not been reported here due to lack of confidence in the method. Further details about the scope of unit operations included in the assessment, and the data used, can be found in Renouf et al. (2010a, b). Results The changes in environmental impacts from each diversification scenario (relative to the base case) are reported in Table 3. Figure 2 provides a further breakdown of the impacts, showing the aspects that contribute to the final result. For brevity, the breakdown of water use and land use are not shown in Figure 2, as the vast majority of land use and water use are associated only with cane. 33

7 Non-renewable energy use Greenhouse gas emissions Eutrophication potential Acidification potential Respiratory organics Respiratory inorganics Table 3 Change in environmental impacts due to product diversification (per 100 tonne cane). Unit 1 (co-gen) 2 (ethanol from molasses) 3 (ethanol from ) 4 (ethanol from cane juice) 5 (PLA from cane juice) GJ t CO2(eq) kg PO4(eq) kg SO2(eq) kg ethylene(eq) kg PM10(eq) Water use kl ,751 3,767 Land use ha Discussion All the diversification scenarios bring benefits of reduced non-renewable energy consumption and greenhouse gas (GHG) emissions. These benefits arise from the avoided and use of fossil fuel-derived products which are displaced by sugarcane-derived, ethanol and plastics. a) Non-renewable energy use (MJ) b) Greenhouse gas emissions (kg CO 2(eq) ) 34

8 c) Eutrophication potential(kg PO 4(eq) ) d) Acidification potential (kg SO 2(eq) ) e) Respiratory organics (kg ethylene (eq) ) f) Respiratory inorganics (kg PM10 (eq) ) Fig. 2 Characterised life cycle impact assessment results (per 100 t cane) for each diversification showing changes in impacts relative to the base case). The scenarios that utilise the whole crop from expanded cane for of ethanol or plastic (s 4 and 5) bring considerable energy and GHG credits. These credits more than offset the energy and GHG impacts invested in cane and processing. For the PLA scenario ( 5), the energy and GHG credits for avoided PET are very large because PET is energy intensive. Under these scenarios, the ratio of energy avoided to energy consumed for ethanol and PLA is around 7 and 12, respectively, and for GHG emissions, the ratio of avoided to emitted is 4 and 3, respectively. However, the expanded cane required for dedicated bio- has trade-offs. The 35

9 additional agricultural brings with it the impacts of additional land use, water use and the potential for eutrophication, acidification and air pollutants. Ecotoxicity impacts from herbicide use are also expected, but have not been fully quantified at this stage. For dedicated ethanol ( 4), some of the impacts of expanded cane are partially offset by avoided petrol and coal- (see Figure 2c f). For PLA ( 5) many of the impacts of expanded cane are fully offset by the avoided impacts of PET (see Figure 2c f). However the avoided impacts from the displaced fossil-fuel products cannot offset the increased land use and water use required for expanded cane, and these may be the most significant impacts for these scenarios. In s 4 and 5 it was assumed that wastewaters (dunder) generated from ethanol and PLA is treated and reused in the process, as this was specified in the source documents from which data was derived. In the sugar industry context it is more likely that dunder streams will be applied to cane fields. However the impact associated with the land application, and the credits gained from the avoided potassium are insignificant and so this assumption does not influence the results or the conclusions drawn. The scenarios that utilise mill by-products (s 1 3) come with few trade-offs. The only potential trade-offs are those associated with additional sorghum assumed to occur when C-molasses is diverted from livestock feed to ethanol. It is difficult to accurately predict the displacement effects of molasses in the animal feed market, so there is uncertainty in this. Of the three byproduct utilisation scenarios, generation from provides the best overall gains if all impacts are considered. Conclusion This work has identified that there are considerable environmental benefits to be gained from the diversification of the Australian sugar industry into bio-energy and bio-materials. When assessed consequentially, the benefits can be seen to be strongly driven by avoided impacts that result when sugarcane products displace their fossil-fuel counterparts. Diversification based on utilisation of milling by-products from existing cane has clear environmental benefits with few or no trade-offs. Diversification based on expanded cane, however, needs to be carefully considered as some of the impacts of the increased agricultural cannot be fully offset by the displaced fossil-fuel and use. In particular, land use, water use, and possibly eutrophication and eco-toxicity need to be considered. Acknowledgements This work was undertaken as part of a PhD project in the School of Geography, Planning and Environmental Management at The University of Queensland. The authors are grateful for the support and funding provided by the CRC SIIB. Thanks also go to the organisations that contributed data and guidance including Queensland growers, harvesters, SRI at QUT, Mackay Sugar, Novozymes, Light Railway Research Society of Australia, CSIRO Sustainable Ecosystems, Queensland DPI&F, BSES Limited, Fertiliser Industry Federation of 36

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