The development of the energy, water and food nexus systems model

The sustainability of natural resources is vital in the light of a rapid population growth and the associated ever increasing demand for services and products. Critical to this growth is the question of energy, water and food (EWF) security. The systems representing the three resources are intrinsically interdependent in what is known as the EWF Nexus. As such, there is a need to develop assessment tools that adequately quantify the inter-dependencies between EWF systems and the surrounding environment in order to identify and evaluate the trade-offs and synergies between them. Existing assessment methodologies do not explicitly identify and quantify the inter-linkages between EWF resources throughout product systems. As a result, decision making regarding the allocation of resources towards the development of a product or service, and the subsequent impact on resource sustainability and environmental degradation, is obscured. Furthermore, earlier approaches translate product system inputs into outputs through the use of generic databases. As such, analysis of product systems operating within varying spatial and temporal scales is hindered. The EWF Nexus tool is a culmination of well-established theories related to system engineering such as Industrial Ecology and LCA. With emphasis on the inter-linkages between EWF resources, the EWF Nexus tool quantifies material flow and energy consumption at component unit process level. The tool is distinguished from previous assessment tools in that it aggregates product systems in terms of the constituting processes identified as sub-systems. Representing complex systems in this manner offers advantages to conventional gate to gate representation. For instance, consideration of process variability and dependencies alleviates flexibility limitations associated with generic databases. Furthermore, with the inter-linkages between EWF resources adequately represented in sub-system design, the respective consumption of resources can be accurately accounted for in product systems. Considering the flexibility and modularity embedded within the EWF Nexus tool, the identification of environmental pressures can be computed for product systems operating within varying spatial settings utilising different technology options and in multiple configurations. The objective of this thesis is to present the details and function of the EWF Nexus environmental assessment tool, and illustrate its implementation through a specific food security scenario in Qatar. The EWF Nexus tool aggregates a proposed food system into its agriculture, water and energy components represented by sub-systems and is used to evaluate the different pathways for which a hypothetical 40 % food self-sufficiency target in Qatar can be achieved. As part of the LCA, sub-system LCI models representing the EWF systems have been developed. The food nexus element includes sub-system LCI models for the production of fertilizers and agricultural activities such as the application of fertilizers and the raising of livestock. The water nexus element includes sub-system LCI models for two desalination processes; Multi-Stage Flash (MSF) and Reverse Osmosis (RO) for the production of fresh water. The energy nexus element includes sub-system LCI models for power generation from two sources; a combined cycle gas turbine plant (CCGT) and renewable energy from solar Photovoltaics (PV). Furthermore, a sub-system for a biomass integrated gasification combined cycle (BIGCC) is integrated to recycle solid waste into useful forms of energy to be re-used within the EWF Nexus. Finally, a sub-system representing carbon capture (CC) technology is integrated to capture and recycle CO2 from both the CCGT and the BIGCC. The integration of CC with the BIGCC transforms the carbon neutral BIGCC process to a negative GHG emission technology with carbon capture and storage (BECCS). For the different scenarios and sub-system configurations considered, the results indicate that the largest global warming potential (GWP) originates from the non-energy related emissions within the food sub-systems. Within this category, emissions from the enteric fermentation processes present in livestock species represent the overwhelming majority of the GWP. Emissions from the power generation are reduced as power from PV technology is integrated as a substitute for the CCGT. The GWP is further reduced by 45 % as the BIGCC is integrated to supplement PV’s. The complete roll out of PV and the BECCS (BIGCC +CC) to power the water and food sub-systems can almost completely balance the GWP from the non-energy related emissions by reducing the total GWP by 98 %, attributed to a theoretical achievable maximum negative emission of 1.15×109 kg CO2/year. In the same scenario, the PV land footprint required calculated is a maximum of 660 ha accompanied by a 127 % decrease in natural gas consumption (27 % credit).