Evolution of biogenic Fe-Mn binary oxide physicochemical properties during biofilter start-up for sustainable urban groundwater treatment

The declining freshwater resources due to climate change, population growth, and urbanization evoke the increasing demand for groundwater to replenish drinking water, while excess manganese (Mn) in groundwater poses a critical threat to drinking water safety. Biofiltration enables convenient and facile purifying of Mn-rich groundwater and its start-up process is crucial to efficacy. In this study, biogenic Fe and Mn binary oxides (BioFMBO) effects on the mid and late start-up of biofilter were investigated and compared with the role of bio-oxidation. The results showed that the dominant role of BioFMBO on Mn removal was more pronounced in the late start-up (85%) as compared to the mid-start-up (50%), reaching 2.5–11.2 times of the bio-oxidation effect. Besides, the biofilter regeneration period after BioFMBO disruption was 1.5–2 folds that of bio-inactivation. These phenomena were due to the continuous conversion of Mn and Fe to amorphous BioFMBO during filtration, characterized by mixed Mn(II)/(III)/(IV) species and abundant reactive oxygen vacancies with high catalytic oxidation ability to expedite single electron transfer during Mn oxidation. Additionally, the mixed Mn species ratio and reactive oxygen vacancies content changed with the enhanced catalysis capacity of BioFMBO, improving the Mn removal performance and regeneration ability of the biofilter.