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

•BC and strain AL-6 removed Mn2+ (99.3%) and NH4+-N (97.7%) in complex water body.•The metabolism of N and C were mutual promotion by BC and strain AL-6.•BC and strain AL-6 immobilized Mn2+ and NH4+-N, and increased soil fertility.•BC and strain AL-6 increased abundance of functional bacteria.