(313f) Designing Synergies Between Technological and Ecological Systems for Chemical Manufacturing

Design of new industrial processes has typically relied on identifying an optimal design for a system from a set of alternative pathways. Design objectives for environmentally friendly processes usually include economic goals such as maximizing profit and net present value while simultaneously reducing impact from processes by choosing raw materials that are least toxic and identifying pathways that result in minimum impact. A more holistic and system wide approach towards design considers systems at the supply chain and life cycle scale and by combining principles of life cycle assessment and multi-objective optimization results in designs that are optimal from the cradle to grave of products [1] . Industries are also working towards reducing the impact of their current activities by improving process efficiency or by developing new designs from more ‘sustainable’ materials.  However, efforts to design new processes or enhancing system efficiency for existing processes focus primarily on the technological sphere.

Establishment of closed loop production systems with energy- and mass- integration and encouragement of cyclic material flow are more advanced steps in the direction of sustainable systems development resulting in a symbiotic system [2].  Yet, design and development are still confined only to the technological sphere while ignoring larger aspects of interactions with systems in the ecological sphere.

On the other hand, pressure from governmental policies and society has resulted in advances in the field of ecological engineering. Ecologists have focused on the reclamation of wastelands and restoration of ecological systems to address the issue of ecological degradation. In parallel to this, industries are realizing the importance of ecosystem services in supporting human activities and business decisions are slowly incorporating the value of natural capital into their planning. Recent study by Kroeger et.al 2014 [3] and Nowak et.al 2006 [4] have highlighted the economic and environmental benefits of reforestation as an air quality compliance strategy.  Several companies have implemented wetlands on manufacturing sites to meet water regulatory issues while saving costs compared to conventional water treatment systems.  Such systems may also be environmentally friendlier and provide various services to society such as flood regulation and carbon sequestration [5]. While such efforts help in moving towards the goal of sustainable development, they treat ecological systems as end-of-pipe solutions to treating pollutants.  Most of these advances are discrete, lacking integration with systematic design procedures resulting in suboptimal solutions with very little effort to bridge the gap between design efforts in technological and ecological spheres. Besides, these methods do not account for the fact that currently engineering and human activities demand significantly more goods and services from ecological systems than what can be supplied sustainably.

This presentation introduces a framework for designing engineering processes alongside designing the landscape around industrial facilities. The resulting network of technological and ecological systems establishes synergies between both spheres since the ecosystems provide services demanded by technological systems, while technological systems provide nutrients to ecosystems.  Ideally, such a design would result in situations where operation of industrial system is within the ecological carrying capacity and the ecological systems can generate enough ecosystem services to support plant operation.

This approach towards design relies on integration of models from various disciplines. The TES system comprises of process models of manufacturing systems that are integrated with pollutant transport models from point sources and of trees that take up pollutants such as particulate matter, nitrogen oxides and sulfur oxides.  Processes are represented by detailed engineering models that capture the non-linear behavior of production systems while pollutant transport is captured by means of Gaussian plume models for a selected region.  Gaussian models predict the maximum diffusivity of particles from point sources and are used to identify the most optimal location for restoring land around industrial facilities. Trees and forest ecosystems have the ability to take up pollutants from the atmosphere, significantly reducing atmospheric pollutant concentration and can store carbon in their biomass for decades. Besides, they also play a vital role in increasing groundwater filtration capacity in addition to reducing energy usage in buildings. Pollutant uptake by trees is modeled as a function of air pollutant concentration and deposition velocity of particles on trees species which varies spatially with changes in meteorological conditions. A mixed forest ecosystem model having multiple trees species is setup along with wetland models that are analogous to a simple CSTR systems. The index of sustainability for the integrated system is based on the TES metrics developed by Bakshi et.al 2015 [6] calculated as the overshoot in demand for ecosystem services over the supply, per unit demand of ecosystem service. The entire network is setup as a nonlinear program and the model is optimized to maximize the net present value and the index of sustainability for the system. To bring in time dynamics into the framework and to account for the development of ecosystem services through the operating life of a facility, each period of interest is modeled as discrete time periods accounting for a change in key parameters that change with time. Thus the framework considers designing a forest ecosystem and wetland ecological system analogous to unit operations along with process models so as to increase the overall supply of ecosystems services to offset most of the demand created by processes.

This TES design is applied to a biofuel production plant with an on-site utility generation systems in mid-western US. A biodiesel production plant in Ohio with soybean as its main feedstock with a coal combined heat and power plant to meet the utility demand is considered. Most of the land around this facility is almost barren and plume models identify a range of diffusivity distances for particles from the stack. A horizontal subsurface flow wetland is designed to treat the wastewater from the production plant to reusable standards while a mixed forest with the most common tree species in Ohio is designed to take up most of the pollutants generated by the process.

Preliminary results indicate that the TES design is more cost effective compared to conventional systems in that, to be able to reach the goal of zero emissions and pollution neutrality, ecological systems are more cost effective options than conventional pollutant control equipment. In addition, it was observed that within a period of less than 15 years of establishment of the ecological systems, the forest ecosystems have the ability to completely offset the demand for criteria air pollutants with a positive return on investment and shorter payback time compared to conventional systems design.

Thus the TES approach towards integrated design supports the development and restoration of local ecological systems to ensure continuous provisioning of ecosystem services that support functioning of human activities while simultaneously reducing the impact created by industrial processes resulting in a more sustainable techno-ecological system that is also more economical.  

References

[1] Azapagic, A., & Clift, R. (1999). The application of life cycle assessment to process optimisation. Computers & Chemical Engineering, 23(10), 1509–1526. doi:10.1016/S0098-1354(99)00308-7

[2] Jacobsen, N. B. (2006). Industrial symbiosis in Kalundborg, Denmark: a quantitative assessment of economic and environmental aspects. Journal of industrial ecology, 10(1‐2), 239-255.

[3] Kroeger, T., Escobedo, F. J., Hernandez, J. L., Varela, S., Delphin, S., Fisher, J. R., & Waldron, J. (2014). Reforestation as a novel abatement and compliance measure for ground-level ozone. Proceedings of the National Academy of Sciences, 111(40), E4204-E4213.

[4] Nowak, D. J., Crane, D. E., & Stevens, J. C. (2006). Air pollution removal by urban trees and shrubs in the United States. Urban forestry & urban greening, 4(3), 115-123.

[5] DiMuro, J. L., Guertin, F. M., Helling, R. K., Perkins, J. L., & Romer, S. (2014). A financial and environmental analysis of constructed wetlands for industrial wastewater treatment. Journal of Industrial Ecology, 18(5), 631-640.

[6] Bakshi, B. R., Ziv, G., & Lepech, M. D. (2015). Techno-Ecological Synergy: A Framework for Sustainable Engineering. Environmental science & technology.