Conversion of Cu(II)-polluted biomass into an environmentally benign Cu nanoparticles-embedded biochar composite and its potential use on cyanobacteria inhibition

Abstract

Disposal of heavy metal-polluted biomass obtained from bioremediation through harmless approaches is a big challenge. In this work, we investigated the effects of pyrolysis temperatures on the conversion of exhausted Cu(II)-laden biomass into Cu nanoparticles (NPs) embedded biochar composite (CBC), Cu(II) chemical form and behavior variation, and associated ecotoxicity evolution. The potential of the resulted biochar products on the growth inhibition of harmful cyanobacterium species Microcystis aeruginosa was also evaluated. At the present study, the increase of pyrolysis temperature from 350 °C to 750 °C increased the pH value, surface area, total pore volume, and Cu concentration of CBC. Ecotoxicity test based on germination and root growth of Chinese cabbage showed that pyrolysis temperature >550 °C relived the ecotoxicity of biomass waste. The further analysis revealed that the Cu in the CBC existed in CuO, CuO/Cu2O/Cu0 mixture, and Cu0 crystal forms when they were produced at pyrolysis temperatures of 350, 550 and 750 °C, respectively. The embedded Cu NPs in the CBC decreased from nanosize 28.7 nm–5.8 nm with the temperature increase. Compared with the biochar without Cu, CBC-550 and CBC-750 significantly inhibited the growth of Microcystis aeruginosaalgae. Overall, this study demonstrated that the pyrolysis of Cu(II) laden biomass at ≥ 550 °C produces Cu NPs in-situ embedded biochar nanocomposite, which had the potential to be used as blue-green algae inhibitor with low ecotoxicity.