In order to study the remediation of complex wastewater from the groundwater polluted by the electrolytic manganese slag field, biochar was made from agricultural waste grapefruit peel as the raw material for the strain Acinetobacter baumannii AL-6 immobilized carrier (MBC), and the strain biochar coupling system (MBC) was obtained. The comprehensive treatment capacity of the coupling system for composite wastewater containing manganese, ammonia nitrogen and high calcium and magnesium ions was explored, and a Sequential Batch Reactor (SBR) was constructed to explore its application potential in wastewater treatment. The experimental results showed that MBC removed 98.46% of manganese within 48 h. Compared with two independent experimental groups (biochar group, strain AL-6 group), MBC has an excellent synergistic effect on the removal of manganese, and the average removal rate of manganese is 15.87 mg L-1 h-1, which is 1.09 times of that of the strain AL-6 and 14.33 times of that of the biochar group. In addition, MBC has a maximum removal ratio of 71.92% for ammonia nitrogen, and also has a certain removal effect for calcium and magnesium ions, with removal ratios of 41.46% and 26.95%, respectively. In the SBR, 90.1% of manganese and 85.44% of ammonia nitrogen are removed. The results show that immobilized strain AL-6 on grapefruit peel biochar has great application potential and can be used to treat wastewater polluted by electrolytic manganese slag.