Life-Cycle impacts of biochar, MOFs, and biomass adsorbents: A meta-analysis for wastewater and carbon management

Abstract

This study presents the first quantitative meta-analysis of life-cycle assessment (LCA) data on adsorbent-based wastewater treatment, integrating results from 52 peer-reviewed studies published between 2015 and 2025. Studies were selected based on explicit inclusion criteria: (i) reporting LCA results of adsorbents applied in wastewater treatment, (ii) providing comparable functional units or sufficient data for standardization, and (iii) covering at least one of the four targeted impact categories. Using standardized functional units (per kg adsorbent and per m³ treated water), we compared the environmental performance of biochar, biomass-derived adsorbents, and metal–organic frameworks (MOFs) across four impact categories: global warming potential (GWP), water footprint, cumulative energy demand, and carbon sequestration potential. Biochar demonstrated the lowest mean GWP (1.2 kg CO₂-eq/kg), especially when derived from agricultural residues through low-emission pyrolysis, while MOFs exhibited the highest values (up to 30 kg CO₂-eq/kg) due to energy-intensive precursor synthesis. Biomass-based adsorbents occupied an intermediate range (2.5–3.2 kg CO₂-eq/kg), with variation linked to feedstock type and activation methods. Water and energy use followed the same pattern, with MOFs requiring up to 1,200 L/kg and 80 MJ/kg, compared to <60 L/kg and <6 MJ/kg for biochar. End-of-life modeling further revealed that biochar can sequester up to 2.4 t CO₂-eq/ha/year when incorporated into soils, exceeding the benefits of energy recovery from MOFs or biomass ash. These findings highlight biochar’s relative advantages for carbon management and low-impact wastewater treatment, while underscoring the need for harmonized LCA protocols and region-specific data to optimize adsorbent deployment.