Could hybrid biological-inorganic systems be an environmentally friendly alternative to conventional wastewater treatment?

Wastewater treatment plants (WWTPs) have the potential to go beyond conventional treatment and become resource recovery platforms. The hybrid biological-inorganic (HBI) system can recover nitrogen from wastewater (WW) for several purposes including microbial protein (MP) production. The MP production process involves the use of hydrogen-oxidizing bacteria (HOB), which consume nitrogen along with hydrogen (H₂) and carbon dioxide (CO₂) to facilitate the process. A life cycle assessment (LCA) study was conducted to evaluate whether the HBI system is a more environmentally friendly alternative to conventional WW treatment processes. Since the process requires additional carbon from external sources, the assessment includes two CO₂ supply modes: amine-based carbon capture (CC) using monoethanolamine (MEA) and direct air capture (DAC), considering both biogenic/atmospheric and fossil sources. A dynamic IPCC Shared Socio-economic Pathways (SSPs)-aligned LCA study was conducted, incorporating a prospective assessment of background and foreground changes and applying the principles of consequential life cycle assessment (pCLCA). The assessment considered three SSP scenarios (i.e., SSP1, SSP2, and SSP5) as key inputs for climate models, focusing on three distinct time frames: 2030, 2040, and 2050. The proposed platform can reduce global warming potential (GWP) by up to 54 % compared to conventional WWTPs. However, to optimize efficiency, a sensitivity analysis was conducted on the electricity used for the electrolyzers in the HBI system, as the highest emissions are associated with electricity consumption during electrolysis. By adopting these innovations within a circular bioeconomy framework, we can significantly improve the sustainability of WW treatment practices.