Efficient remediation of Mn2+ and NH4+-N in co-contaminated water and soil by Acinetobacter sp. AL-6 synergized with grapefruit peel biochar: Performance and mechanism.

Electrolysis manganese slag produced in industrial manganese production causes massive leachate containing heavy metal Mn2+ and inorganic NH4+-N, which causes serious hazard to the water body and soil. A cost-effective alternative to address the multiple pollution is urgently needed. This study investigated the synergy of grapefruit peel biochar (BC) and strain AL-6 to remediate Mn2+ and NH4+-N in sequencing batch bioreactor (SBR) and soil column. The results showed that, in SBR, under the condition of C/N 5, temperature 30°C, BC and strain AL-6 showed fabulous performance to remove Mn2+ (99.3%) and NH4+-N (97.7%). The coexisting ions Mg2+ and Ca2+ had no effects on the removal of Mn2+ and COD, however, 23.3% removal efficiency of NH4+-N was curtailed. Characterization found that the presence of MnCO3 confirmed the adsorption of Mn2+ by functional groups action, and gas chromatography indicated that BC and strain AL-6 promoted the reduction of N2O and organic carbon. In addition, BC and strain AL-6 helped to immobilize 799.41 mg L-1 of Mn2+ and 320 mg L-1 of NH4+-N after 45 d in the soil column. And the determination of TOC, CEC, pH, Eh, soil enzymatic activity (catalase and urease), and microbial diversity and abundance confirmed that BC and strain AL-6 increased the soil fertility and bioavailability of pollutants. Totally, BC and strain AL-6 possess great potential to remediate Mn2+ and NH4+-N pollution in water and soil.