(426a) Nature in Engineering: Expanding the Engineering Design Space By Including Ecosystem Goods and Services

Currently, most engineering design methods ignore the role played by nature in supporting engineering systems. Analogous to economic systems, ecological systems also include limits on the stocks of ecosystems goods and services. These can include limits on the availability of ecological resources like fossil fuels, minerals, biomass, fiber and feed, as well as limits on the provisioning of ecosystem services like carbon sequestration, water provisioning, nutrient cycling etc. Ignoring these limits while designing systems have resulted in several unintended consequences, resulting in ecological degradation. For instance, switching farming practices to more intensive agricultural habits to increase crop yield has resulted in harmful algal blooms in Lake Erie due to fertilizer runoff from farms.

In the engineering context, the main focus of conventional design has been to maximize profitability while simultaneously minimizing environmental impacts. Accounting for the role of nature in engineering has been confined to ideas like Biomimicry [1] and Eco-technology [2] such as the use of wetlands for water treatment. However, these methods lack proper integration with concepts of engineering design and such methods do not necessarily identify possible synergies and trade-offs that exist between engineered systems and nature. In addition, all these approaches also neglect the ecological carrying capacity, thus resulting in an increase in disparity between the demand for ecological goods and services and their supply from nature.

The Techno-Ecological Synergy (TES) framework [3] was developed to account for the carrying capacity of ecosystems by quantifying the demand and supply of ecosystem services (ES). Resource inputs for operating engineering systems creates a demand for ecological goods while the emissions, waste and wastewater generated by engineering systems creates a demand for ecosystem services. The supply of ecosystem goods and services is based on the capacity of an ecological system, in the vicinity of an engineering system to provide the necessary ES demanded by the process. The sustainability index for this framework is based on the difference in the supply and demand for ES.

This work integrates the TES framework with concepts of engineering design, resulting in the design of integrated Techno-Ecological systems. The TES design framework accounts for both demand and supply of ecosystem services while designing systems and the objective is to maximize profitability and minimize the disparity between the demand and supply of ES. Thus, the problem focuses on reducing both demand and increasing supply by preservation and restoration of ecological systems, in contrast to conventional approaches of merely minimizing demand.

The presentation conveys the significance of including the role of nature in supporting engineering design. This is indicated by demonstrating that including nature in the design problem expands the solution space of conventional engineering design resulting in the identification of plausible â??win-winâ? scenarios. Design problems are formulated as multi-objective optimization problems, with the objective of maximizing the economic value of the system and maximizing the sustainability index. Trade-offs between these objectives are identified by scalarizing multiple objectives using the epsilon constraint methods. Tradeoff designs are obtained for different ecosystem services, depending on the type of service relevant to the system of interest and the spatial presence of ecological systems.

Four diverse case studies are discussed to demonstrate the significance of including nature in engineering. The first study describes the design of a residential system accounting for ecosystems like trees, lawn and a vegetable garden. While designing a residential systems, technological, ecological and behavioural variables are considered in the design. The objectives are to minimize both the cost compared to basecase and carbon emission. The problem is formulated as a simulation-based Mixed Integer Linear Program (MILP) using EnergyPlus as the simulation engine.

The second study discusses the design of a biosolids network flow system along with the design of ecological systems that supply carbon sequestration ecosystem services, like timberland, forest lands and geological sequestration. Superstructure of possible biosolid flow pathways along with possible pathways for carbon sequestration are identified, and optimal designs of these coupled Techno-Ecological networks are determined by minimizing the network cost and minimizing the difference between carbon sequestration service demand and supply. The entire problem is formulated and solved as a MILP in the Eco-Flow tool. In addition, feedback from ecosystems in terms of biomass from timberland is considered as a feedstock for supplying energy to the wastewater treatment sites.

Third study describes the benefits of including ecosystems in a process engineering design context whereby ecological systems are included in engineering design analogous to unit operations. An integrated design of a biofuel system with a wetland ecosystem is discussed wherein the system is design to maximize provisioning of ecosystem services like water provisioning service and water quality regulation service, while maximizing the net present value.The problem is formulated as an Non Linear Program implemented in GAMS.

The last study focuses on designing agricultural landscapes for producing energy and food, while accounting for services provided by agro-ecosystems. These services include carbon sequestration, water provisioning, and others. The trade-off between monetary objectives and costs are evaluated for various biofuel production alternatives.

Non-inferior pareto frontiers are generated for each ecosystem service for all case studies. Results indicate that including ecological variables in the design results in possible solutions that do not exist in the techno-centric solution space of conventional engineering methods. In addition to this, accounting feedback flows from ecosystems in terms of ecological goods shifts the Pareto frontier to a new range, revealing innovative and novel design solutions. These new solutions obtained from including ecological systems are economically superior compared to conventional solutions; they also have environmental benefits in terms of reduced overshoot.

References

[1] Benyus, Janine M. Biomimicry. New York: William Morrow, 1997.

[2] Straškraba, M. "Ecotechnology as a new means for environmental management." Ecological Engineering 2.4 (1993): 311-331.

[3] Bakshi, Bhavik R., Guy Ziv, and Michael D. Lepech. "Techno-ecological synergy: A framework for sustainable engineering." Environmental science & technology 49.3 (2015): 1752-1760.