Pyrolysis of wetland biomass waste: Potential for carbon sequestration and water remediation

• Biochars prepared from twenty two species of wetland plant were investigated.
• Biochars varied in physicochemical properties and adsorption capacity.
• The biochars had a carbon sequestration potential of 19.4–28%.
• Hydrocotyle verticillata derived biochar had the largest adsorption capacity for PO43−.
• Canna indica derived biochar displayed the largest adsorption capacity for both NH4+ and Cd2+.

Management of biomass waste is crucial to the efficiency and sustainable operation of constructed wetlands. In this study, biochars were prepared using the biomass of 22 plant species from constructed wetlands and characterized by BET-N2 surface area analysis, FTIR, TGA, SEM, EDS, and elemental compositions analysis. Biochar yields ranged from 32.78 to 49.02%, with mesopores dominating the pore structure of most biochars. The biochars had a R50 recalcitrance index of class C and the carbon sequestration potential of 19.4–28%. The aquatic plant biomass from all the Chinese constructed wetlands if made into biochars has the potential to sequester 11.48 Mt carbon yr−1 in soils over long time periods, which could offset 0.4% of annual CO2 emissions from fossil fuel combustion in China. In terms of adsorption capacity for selected pollutants, biochar derived from Canna indica plant had the greatest adsorption capacity for Cd2+ (98.55 mg g−1) and NH4+ (7.71 mg g−1). Whereas for PO43−, Hydrocotyle verticillata derived biochar showed the greatest adsorption capacities (2.91 mg g−1). The results from this present study demonstrated that wetland plants are valuable feedstocks for producing biochars with potential application for carbon sequestration and contaminant removal in water remediation.