Homage to Bob Ayres (1932-2023)

When I first contacted Bob in 2001 inquiring how I could include Industrial Ecology in my PhD thesis, he taught me how to apply the principle of Material Flow Analysis to track chemical substances and assess chemical process in terms of efficiency, dissipative losses, and recycling opportunities throughout their life cycle. This has been the foundation of more than two decades of research, not only in the field of the chemical industry but now more recently in determining urban metabolism. Early on, Bob and I co-authored a series of substance flow analysis such as “Global Phosphorus Flows and Environmental Impacts from a Consumption and a Production Perspective, “all published in JIE. In that study we found that human activity had quadrupled the natural P flow, we had less than 100 years’ worth of P if we maintained current practices given known reserves, and that huge quantities of byproduct phosphogypsum were available for sulfuric acid recovery and could also useful as a fertilizer for calciumand sulfur-deficient soils. Later we applied MFA to chemical processes to quantify and report emissions of “confidential” processes and included exergy accounting to determine thermodynamic efficiency of the chemical industry of the US. Moving from chemical processes to critical metals, other MFA studies followed such as “Material and Energy Requirement for Rare Earth Metal Production.” I have continued applying MFA to nutrients (N, P, K) in urban areas from food, to waste, to recovery and application in agriculture to produce crops- to find opportunities for closing the nutrient cycle, using MFA not only to track the nutrients but also all the stakeholders involved, the drivers and obstacles along the way.

Gara Villalba Méndez

ICTA, Autonomous University of Barcelona