Investigation into pyrite autotrophic denitrification with different mineral properties.

Pyrite autotrophic denitrification (PAD) is considered a promising method for nitrate removal from wastewater and groundwater. However, the results of PAD studies have been contradictory for two decades, and the mechanism is unclear. Here, we investigated mineral properties of two kinds of natural pyrite (YP and TP), their PAD performances, and microbial community shift in their column reactors in parallel. Both pyrite are highly pure crystalline pyrite, but their other mineral properties are quite different. Both batch and column experiments found that PAD of YP occurred but that of TP did not. Thus, the contradictory results of PAD were presented for the first time at the same study. The dominant bacteria in YP and TP columns finally were Thiobacillus (24.55±8.67%) and Flavobacterium (21.11±10.59%), respectively, though their initial microbial communities cultured were similar. Reduced sulfur species and oxide impurities on the surface of pyrite, and small DO in water did not change autotrophic denitrification characteristic of the pyrite itself. This research indicates that mineral property of pyrite caused the contradictory result of PAD. Among pyrite properties, the main crystal plane exposed and chemical state of surficial sulfur and iron were considered the decisive parameters for PAD. The study provides guidelines for selection of pyrite minerals for PAD applications.