Carbon sources influence the nitrate removal activity, community structure and biofilm architecture

Influence of the frequently used carbon sources in nitrate removal processes were evaluated in a lab-scale biofilm reactor. The NO3–N removal efficiency was in the order acetate > glucose > methanol > ethanol. Acetate-fed biofilm reduced nearly 100% NO3–N with negligible amount of NO2–N accumulation. Although 99% NO3–N was reduced in the glucose-fed biofilm, substantial NH3–N and NO2–N accumulated. Methanol-fed biofilm reduced 72% of NO3–N with accumulation of 2.2 mg L−1 of NO2–N, while biofilm formed in presence of ethanol showed 61% reduction in NO3–N although relatively higher ratio of denitrifiers were observed. Acetate and ethanol-fed biofilm displayed characteristic biofilm architecture with voids, but the former had relatively higher thickness and diffusion distance. In presence of glucose and methanol, a confluent biofilm without characteristic voids was formed. Pseudomonas sp. numerically dominated the acetate and ethanol-fed biofilm, while Enterobacter sp. and Methylobacillus sp., were abundant in glucose and methanol biofilms respectively.

► Nitrate removal process was efficient in acetate-fed biofilm.
► Denitrification-supportive structure was formed in acetate-fed biofilm.
► Nitrate ammonifying bacteria are abundant in glucose-fed biofilm.
► Methylotrophs are abundant in methanol-fed biofilm with a confluent biofilm.
► Nitrate removal was low in ethanol-fed biofilm though denitrifier abundance was high.