Converting agricultural by-products into a carbon-neutral CO2 capture system: Biomass-ash-enhanced biogas slurry for plant and soil carbon sequestration

This study develops a regeneration-free CO₂ capture system by integrating alkaline biomass ash with biogas slurry to achieve multiphase carbonation. The process produced three CO₂-rich materials—CO₂-enriched biogas slurry (CRBS), bicarbonate-rich liquid (CRML), and carbonate-rich solid (CRMS)—with dissolved inorganic carbon contents of 150.1 mmol L⁻¹, 230.4 mmol L⁻¹, and 3176.5 mmol kg⁻¹, corresponding to CO₂ capture capacities of 6.6 g L⁻¹, 10.1 g L⁻¹, and 140 g kg⁻¹. When applied to tomato cultivation, CRML and CRMS increased yield by 27.7–35.8% and enhanced root activity and fruit quality. Stable-isotope analysis showed that bicarbonate-derived carbon assimilation increased 3–4 fold, with the fraction of plant carbon from soil bicarbonate ( f B ) rising from 0.135 (control) to 0.412–0.500 and soil-derived carbon fixation reaching 32.77 g-C per pot under CRMS. In soil, CRML and CRMS increased inorganic carbon (TIC up to 26.25 g kg⁻¹) and organic carbon (TOC up to 48.60 g kg⁻¹) through carbonate deposition and strengthened organo-mineral associations. These results demonstrate that biomass-ash–enhanced biogas slurry provides a by-product-based, zero-energy CO₂ capture pathway that simultaneously improves plant performance and soil carbon sequestration.