Comparative evaluation of biochar, bone char, and conventional sorbents for arsenic removal from water: Performance and life-cycle carbon assessment

Abstract

Arsenic contamination of water poses a significant environmental and public health challenge, necessitating sustainable, low-carbon treatment technologies. This study aims to evaluate the carbon credit potential and arsenic removal performance of microwave-assisted (MW) biochar and MW bone char relative to conventional sorbents. Carbon emissions are quantified using life cycle assessment, and carbon sequestration is determined by elemental carbon analysis. Carbon credits are calculated for treating 1000 L of wastewater (0.3 to 0.01 mg·L−1). MW biochar achieves the only positive carbon credit (+0.0002 t CO2-eq·m−3) despite low arsenic sorption (0.78 mg·g−1), while MW bone char shows superior arsenic removal (2.78 mg·g−1) but incurs a net carbon debt (−0.00006 t CO2-eq·m−3). This trade-off reveals that higher sorption capacity does not guarantee lower carbon impact. MW biochar sequesters 1.7967 kg CO2-eq per kg versus 1.0882 kg CO2-eq emitted, making it the only carbon-negative option. These findings demonstrate that integrating carbon sequestration with remediation performance can guide the selection of low-carbon sorbents for sustainable water treatment.