Heterotrophic cultivation of Paracoccus denitrificans in a horizontal rotating tubular bioreactor

Abstract

In this work, the heterotrophic cultivation of bacterium Paracoccus denitrificans has been studied in a horizontal rotating tubular bioreactor (HRTB). After development of a microbial biofilm on the inner surface of the HRTB, conditions for one-step removal of acetate and ammonium ion were created. The effect of bioreactor process parameters [medium inflow rate (F) and bioreactor rotation speed (n)] on the bioprocess dynamics in the HRTB was studied. Nitrite and nitrogen oxides (NO and N2O) were detected as intermediates of ammonium ion degradation. The biofilm thickness and the nitrite concentration were gradually reduced with increase of bioreactor rotation speed when the medium inflow rate was in the range of 0.5–1.5 l h−1. Further increase of inflow rate (2.0–2.5 l h−1) did not have a significant effect on the biofilm thickness and nitrite concentration along the HRTB. Complete acetate consumption was observed when the inflow rate was in the range of 0.5–1.5 l h−1 at all bioreactor rotation speeds. Significant pH gradient (cca 1 pH unit) along the HRTB was only observed at the highest inflow rate (2.5 l h−1). The results have clearly shown that acetate and ammonium ion removal by P. denitificans can be successfully conducted in a HRTB as a one-step process.