Citric acid application for denitrification process support in biofilm reactor

Abstract

The study demonstrated that citric acid, as an organic carbon source, can improve denitrification in Anaerobic Sequencing Batch Biofilm Reactor (AnSBBR). The consumption rate of the organic substrate and the denitrification rate were lower during the period of the reactor's acclimatization (cycles 1-60; 71.5 mgCOD L^-1 h^-1 and 17.81 mgN L^-1 h^-1, respectively) than under the steady state conditions (cycles 61-180; 143.8 mgCOD L^-1 h^-1 and 24.38 mgN L^-1 h^-1). The biomass yield coefficient reached 0.04 ± 0.02 mgTSS· mgCOD_re^-1 (0.22 ± 0.09 mgTSS mgN_re^-1). Observations revealed the diversified microbiological ecology of the denitrifying bacteria. Citric acid was used mainly by bacteria representing the Trichoccocus genus, which represented above 40% of the sample during the first phase of the process (cycles 1-60). In the second phase (cycles 61-180) the microorganisms the genera that consumed the acetate and formate, as the result of citric acid decomposition were Propionibacterium (5.74%), Agrobacterium (5.23%), Flavobacterium (1.32%), Sphaerotilus (1.35%), Erysipelothrix (1.08%).

Keywords: Biofilm reactor; Citric acid; Denitrification; External carbon source; Metagenomic analyses.