Acceleration of sand filtration start-up for manganese-containing groundwater treatment: microbial-mediated autocatalytic oxidation of manganese oxides

Abstract

The lengthy start-up period remains a bottleneck in treating manganese-polluted groundwater with rapid sand filters (RSFs). Manganese-oxidizing bacteria (MnOB) and biogenic manganese oxides (BioMnOx) are significant in accelerating the start-up of RSFs, while their interaction mechanism remains unclear. This study investigated four microbial start-up strategies for their effects on manganese (Mn) removal, microbial communities, and BioMnOx characteristics. All filters were matured within 120 days, possessing up to 95% Mn removal rate. In particular, seeding BioMnOx exhibited the fastest accelerated start-up, with a start-up period as short as 26 days, one-third that of the penicillin G injection filter (88 days), attributed to the multi-Mn species system and highly catalytic oxidation capacity of birnessite-type BioMnOx. Specifically, MnOB functional genera were involved in the construction of BioMnOx and elevated the content of the highly reactive Mn(III). The equilibrium ratio of Mn(IV)/Mn(III)/Mn(II) in BioMnOx determined the electron transfer and thereby influenced the multi-step conversion of Mn(II) to Mn(IV).The two accelerated start-up modes (inoculation with MnOB and seeding with BioMnOx) were more favorable for the growth of specific genera (Rhodococcus and Ruminococcus_1). At the same time, no significant correlation was observed between the amount of MnOB and Mn removal efficiency. In short, in RSFs, the Mn redox cycle relied more on the adsorption and autocatalytic oxidation of BioMnOx, whereas the MnOB were crucial in maintaining the BioMnOx properties.