Mixotrophic denitrification processes based on composite filler for low carbon/nitrogen wastewater treatment

Removal of nitrogen from wastewater with low carbon/nitrogen ratio was treated by using a denitrification packed bed reactor. Composite fillers with both autotrophic and heterotrophic denitrification capacity were prepared by mixing melted polycaprolactone and elemental sulfur at various alkalinity ratios (heterotrophic to autotrophic ratios of 1:2, 1:1, 3:2, and 2:1). Optimum denitrification was achieved at a ratio of 2:1. The diversity of the microbial community in the biofilm on the surface of the composite fillers showed that the increase of the elemental sulfur in the composite fillers has led to the increase of the microbial abundance. Furthermore, biofilm composition developed from a single dominant species to multiple species, and genes related to sulfur metabolism increased while those related to denitrification decreased slightly.