In-situ removal of microcystin aeruginosa and microcystin-LR by biochar supported sulfide nZVI via persulfate activation: Performance, mechanism and degradation pathway

As a hepatotoxin generated by the excessive proliferation of Microcystis aeruginosa, Microcystin-LR (MC-LR) has posed serious threat to humans and wildlife. In this study, biochar supported sulfide nZVI and persulfate sustained-release agent (S-nZVI-BC/PSSA) were prepared to simultaneously remove MC-LR and Microcystis aeruginosa. Batch experiments showed that the removal efficiency of MC-LR (100 μg/L) by S-nZVI-BC/PSSA could reach 92.0 % when the BC pyrolysis temperature, the Fe/C mass ratio and the Fe/S molar ratio were 700 °C, 1:2 and 40:1, respectively. According to the results of EPR and density functional theory (DFT), the carbon–carbon conjugated diene bond (C = C-C = C) on Adda were most vulnerable to attack by the free radicals such as •OH and SO4-• generated by S-nZVI-BC/PSSA. The results of reactor experiments indicated that S-nZVI-BC/PSSA had good removal effect on MC-LR and Microcystis aeruginosa. According to the transcriptome analysis, S-nZVI-BC/PSSA led to the disorder of cell metabolic process by up-regulating ATP and pigment synthesis genes and down-regulating photosynthesis genes, eventually inhibiting the growth of Microcystis aeruginosa and even causing their death. In addition, the up-regulation of biological transport processes could enhance the release of MC-LR from Microcystis aeruginosa, which was completely removed by S-nZVI-BC/PSSA. Moreover, four degradation pathways of MC-LR were analyzed, and the final products were CO2 and H2O. Therefore, this S-nZVI-BC/PSSA system showed great promise for practical applications in the removal of Microcystis aeruginosa and MC-LR.