Primary and secondary waste in (bio)catalysis: What matters is not what is produced but what permanently remains!

Abstract

(Bio)catalysis creates waste, composed of wastewater and an organic fraction. Different metrics are used for the environmental impact of processes, being E-Factor and process mass intensity (PMI) the prominent ones. These metrics are typically applied to wastewater and spent organic fraction, which is the process “Primary Waste.” However, “Primary Waste” is industrially treated before it is released to the environment. When treating “Primary Waste,” CO₂ is generated, from the wastewater treatment plant and from the organic fraction incineration. That CO₂, coined as “Secondary Waste,” remains in the planet and thus should be the target for environmental assessments. When E-Factor and PMI calculated from “Primary Waste” are compared to the values of produced CO₂, results mismatch because the CO₂ depends on the proportion wastewater/organic fraction since incineration leads to higher CO₂ production than wastewater treatment. Sustainable options for (bio)catalysis would be process intensification, incorporating renewable energy and biogenic solvents (neutral carbon), and developing (new) wastewater treatment strategies to deliver pure(r) water effluents to the environment.