One-step synthesis of easily-recoverable carboxylated biogas residues for efficient removal of heavy metal ions from synthetic wastewater

Simultaneous treatment of organic solid waste and heavy metal polluted water has drawn public attention, which can reuse solid waste resource and purify water body. However, regeneration efficiency and production cost limited the wide application of traditional biosorbents in practice. Herein, a recoverable and cost-efficient carboxymethylated biosorbent, named as CA-BR, was synthesized from biogas residues by an easy one-step method. The morphology properties of the CA-BR indicated that this novel biosorbent had a well-developed pore structure with abundant carboxyl functional groups, which contributed to the diffusion and chelation of heavy metal ions. Cu2+ uptake by CA-BR increased with the rising temperature, and the maximum adsorption capability was 76.92 mg/g. The preferential Cu2+ capture by CA-BR can also be achieved in the presence of co-existing cations (K+ and Na+, 200 mg/L), and adsorption capacity could still keep more than 67.69 mg/g. The CA-BR exhibited a good chemical stability and its adsorption capacity could still reach up to 92% after 8 continuous adsorption-desorption cycles, which indicated the feasibility of CA-BR in real applications. Furthermore, the treatment volumes of synthetic wastewater were 550 mL (275 BV) for Cu2+ (using 1 g of CA-BR), and several column adsorption-desorption cycles exhibited that there was no significant loss in Cu2+ capacity (<20%). The cost of CA-BR was approximately 3.99 $/kg lower than some reported biosorbents, indicating that the development and application production of biogas residue-based biosorbent is economically feasible. Overall, this study is meaningful for the combination of biogas residues reutilization and heavy metal ions removals, which according with the purpose of "Green" application and clean production.