Performance and microbial community profiles in pilot-scale biofilter for ammonia, iron and manganese removal at different dissolved oxygen concentrations

Dissolved oxygen (DO) is a significant operational parameter in biological systems. In this study, a pilot-scale biofilter was constructed to investigate the removal efficiency of ammonia, iron and manganese, as well as the microbial community structure evolution at different DO concentrations. Results indicated that when DO decreased from 8 to 4 mg/L, iron and manganese were still completely removed, however the concentration of ammonia in the effluent increased, and exceeded the permitted limit of 0.5 mg/L when DO was about 4 mg/L. The main functional microbes for ammonia and manganese removal were Nitrosomonas and Crenothrix, which was mainly distributed at 0.8 and 0.8 m of the filter bed with a corresponding abundance of 8.61% and 16.87% in sufficient DO considition, respectively; while iron was mainly removed by Crenothrix and Gallionella in 0 m with a corresponding abundance of 30.45% and 9.77%. With the decreasing of DO concentration, iron oxidizing bacteria (IOB, Crenothrix and Gallionella) was not affected, while the abundance of manganese oxidizing bacteria (MnOB, Crenothrix) increased to completely oxidize manganese. However, the amount of ammonia oxidizing bacteria (AOB, Nitrosococcus) at 0.4 and 0.8 m of the filter depth obviously decreased with increased ammonia in the effluent. Kinds of other bacteria which may be related to methane, hydrogen sulfide and organic matter removal, were also found. In addition, small part of archaea was also detected, such as Candidatus Nitrososphaera and Ferroplasma, which could oxdize ammonia and ferrous iron, respectively.