Liz Wachs
Department of Agricultural and Biological Engineering, Purdue University
Liz is a second year PhD student. She holds a BA in Ancient History and Classical Civilization (University of Texas at Austin), BS in Chemical Engineering (Purdue University) and MA in Desert Studies (from Ben-Gurion University of the Negev) focused on environmental policy and livestock husbandry systems in Israel. Her research is focused on large-scale modeling of nitrogen flows for economic and ecological policy analysis. She is a member of the American Institute of Chemical Engineering (AIChE) and ISIE.
Physical Input-Output Tables (PIOTs) depict material flows in the economy using the input-output (IO) framework. PIOTs combine the strength of material flow analysis (MFA) and IO models by connecting material flows to the industrial production chain. PIOTs also incorporate waste streams; this helps in identifying waste with recovery value or high environmental impact, key for moving towards a circular economy. Several PIOTs have been developed in the past including a PIOT for nitrogen (N) [1]. The adoption of PIOTs has been limited, however, due to: a) the high cost of empirical development of these PIOTs and b) lack of validation and quality check on data. Most PIOTs compiled to date have not focused on environmentally important materials, or are highly aggregated. In this work, we overcome these limitations of PIOT development using a process modeling approach. We focus on N since management of the N cycle has been identified as a “grand challenge for engineering.” Process modeling provides a bottom-up methodology to connect material flows in the economy to production in industrial sectors while preserving information about the mechanisms of material transformations. This approach offers several advantages: once the models are in place, they should reduce the cost of creating PIOTs, their built-in mass-balances make reconciliation easier, and it provides a robust validation for empirical models. In this case study we build on previous work by Singh et al. [2] which developed an empirical N PIOT for Illinois. We build process models using Aspen Plus to follow the N flow in the economy through successive transformations into products beginning with raw materials. Each sector has a process model based on a true-to-scale representation of the industrial process used. Results from the models are then scaled to represent true economic flows based on empirical data of input flow numbers for the whole Illinois economy. Preliminary results from the model-based approach applied to three sectors [3] show a better mass balance between inputs and outputs (up to 2 % error in process based vs. up to 40 % in empirical based) and better accounting for residuals. A more comprehensive model for a process based N PIOT for Illinois will be presented along with the demonstration of an algorithm for the application of our methodology for PIOTs.
[1] Pedersen, OG. Physical Input-output Tables for Denmark: Products and Materials 1990: Air Emissions 1990-92. Danmarks Statistik, 1999.
[2] Singh, S., Compton, J., Sobota, D. & Hawkins, T. (2013). Utilizing Physical Input-Output Model to Inform Nitrogen related Ecosystem Services. Abstract for presentation at the International Symposium for Sustainable Systems and Technology, (ISSST), May 15-17, 2013, Cincinnati, Ohio.
[3] Wachs, E. and Singh, S. (2016). Computational Approaches in Systems Modeling for Environmental Impacts of Industries: Automating Physical Input-Output Tables (PIOTs) Via Aspen Process Modeling. Poster presented at the Annual Meeting of the American Institute for Chemical Engineers (AIChE), Nov 14-18, 2016, San Francisco, CA
• Environmentally and socially-extended input-output analysis , • Socio-economic metabolism and material flow analysis , • Circular economy
