Availability of carbon sources on the ratio of nitrifying microbial biomass in an industrial activated sludge

Abstract Chemical industry wastewater is known to have disproportionate nutrient concentrations with varying C:N ratios, thereby individually affecting the growth of heterotrophs and autotrophs in activated sludge. The present study underlines the impact of the changing availability of organic and inorganic carbon on the ratio of nitrifying biomass in an industrial activated sludge. To quantify changes, oxygen uptake rates by nitrifiers were monitored using respirometry, while nitrifier abundance was determined by real-time PCR using 16S rRNA primers. The obtained results point to the prominent influence of the organic or inorganic carbon source, reducing or increasing the active nitrifying biomass ratio and AOB gene quantity respectively. When the active nitrifier ratio dropped below 10% of the total activity or when nitrifiers were limited for inorganic carbon, ammonia oxidation was compromised. Nitrifiers were able to recover sufficient activity after a carbon starvation period of 34 days through the supply of gaseous CO 2 or bicarbonate. The results of this study suggest a superior role of gaseous CO 2 over bicarbonate as carbon source for nitrifiers and the feasibility to operate a high performing nitrification without any COD.