Microbial community response reveals underlying mechanism of industrial-scale manganese sand biofilters used for the simultaneous removal of iron, manganese and ammonia from groundwater

Abstract

Most studies have employed aeration-biofiltration process for the simultaneous removal of iron, manganese and ammonia in groundwater. However, what's inside the "black box", i.e., the potential contribution of functional microorganisms behavior and interactions have seldom been investigated. Moreover, little attention has been paid to the correlations between environmental variables and functional microorganisms. In this study, the performance of industrial-scale biofilters for the contaminated groundwater treatment was studied. The effluent were all far below the permitted concentration level in the current drinking water standard. Pyrosequencing illustrated that shifts in microbial community structure were observed in the microbial samples from different depths of filter. Microbial networks showed that the microbial community structure in the middle- and deep-layer samples was similar, in which a wide range of manganese-oxidizing bacteria was identified. By contrast, canonical correlation analysis showed that the bacteria capable of ammonia-oxidizing and nitrification was enriched in the upper-layer, i.e., Propionibacterium, Nitrosomonas, Nitrosomonas and Candidatus Nitrotoga. The stable biofilm on the biofilter media, created by certain microorganisms from the groundwater microflora, played a crucial role in the simultaneous removal of the three pollutants.

Keywords: Canonical correspondence analysis (CCA); Groundwater; Industrial-scale biofilters; Iron, manganese and ammonia removal; Microbial community.

Fig. 1

Schematic and photograph of the enhanced water-dropping aeration and biofiltration process (a). Iron (b), manganese (c) and ammonia (d) removal effects and the DO variation (e) in the enhanced system

Fig. 2

SEM images of the mature manganese sand (×100 and ×2000) (A). Morphology (B) and EDS analysis (C) of biofilm on the media

Fig. 3

OTU networks of specific functional genera in the three bacterial communities (a). Genus level identification of the specific functional bacterial sequences (Unit: Number of OTUs) (b)

Fig. 4

Canonical correspondence analysis (CCA) between enriched genera and environmental variables (iron, manganese, ammonia, DO, temperature and layer height)