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Mn2+and NH4+-N contamination in water by Mn slag leakage is urgent to be resolved. Biochar synergistic strains is considered to be a promising approach to remove pollution with high concentration, however, the specific oxidation and electron transfer processes are rarely elucidated in detail. In this study, under different biochar (BC) additions, NH4+-N concentration and pH ranges, removal efficiency of Mn2+, NH4+-N and COD had reached at 99.7 %-100 %, 100 % and 90.3–96.2 % by the BC & strain AL-6 system (co-system), respectively, and the nitrification processes was completed. Meanwhile, the electrochemical analysis showed that BC had strong tendency to donate, accept and transfer electrons, and electrons transfer property was more responsible for the removal process. Further, the electrical conductivity of co-system was enhanced upon reaction with Mn2+and NH4+-N, suggesting that co-system promoted the electron transfer processes for pollutants removal. Concretely, Raman spectroscopy specified that conductive graphite region of biochar accelerated electron transfer behavior in the system. As well as, 2D-COS and characterization analyses indicated that C-C and CC functional groups, O2•−radicals, and semiquinone radicals could promote the oxidation of manganese. Eventually, manganese presented 2+ and high valence state was adsorbed on the surface of the co-system. In addition, BC facilitated strain AL-6 to convert organic carbon into CO2and transfer electrons for N metabolism, and over time, CO2and N2O could also be absorbed by BC. This study further dissected the efficiency on the Mn-contaminated water bodies and mechanism process by co-system and provided potential value in mitigating climate change.

Mixed electroplating wastewater is in urgent need of eco-friendly and effective treatment. In this study, Pseudomonas hibiscicola L1strain (strain L1) immobilized in peanut shell biochar (PBC) was effective in the simultaneous removal of Ni(II), Zn(II), Cu(II), Cr(VI) and ammonia nitrogen from mixed electroplating wastewater. PBC improves the biological activity of strain L1. Compared with single PBC and free strain L1, the biochar-immobilized strain L1 had higher removal ratios. The biochar immobilized strain L1 showed excellent removal of Cu(II) (94.92%) > Zn(II) (91.46%) > ammonia nitrogen (79.90%) > Ni(II) (77.02%) > Cr(VI) (34.40%). Scanning electron microscopy (SEM) results showed that strain L1 was well immobilized on PBC with strong bioactivity. X-ray diffractometry (XRD) showed the formation of crystals of Zn(OH)2, Cu(OH)2, CrO(OH) and Ni(OH)2,etc. Fourier transform infrared spectroscopy (FTIR) revealed the formation of multiple functional groups on the surface of the biochar immobilized strain L1. In addition, the highest removal ratios for Ni(II), Zn(II), Cr(VI), Cu(II) and ammonia nitrogen in the sequencing batch reactor (SBR) were 78.70%, 94.57%, 59.70%, 92.50% and 98.81% by biochar immobilized strain L1, respectively. Therefore, biochar immobilized strain L1 has good application potential in treating mixed electroplating wastewater.