Measurement of growth rate of ammonia oxidizing bacteria in partially submerged rotating biological contactor by fluorescent in situ hybridization (FISH)

Optimization of the nitrification processes in biofilms is important for effective nitrogen removal because nitrification in an aerobic biofilm is considered to be a less than reliable process. Thus, one of the main factors to improve biological nitrogen removal processes is a better understanding of the microbiology and population dynamics of ammonia oxidizing bacteria (AOB) in wastewater treatment biofilms. Although the AOB in wastewater treatment have been qualitatively and quantitatively studied, information on their actual populations and activities is still limited. Therefore, the areal cell density of AOB in domestic wastewater biofilms on a partially submerged rotating biological contactor (RBC) was determined by fluorescent in situ hybridization (FISH) with a set of 16S rRNA-targeted oligonucleotide probes. The growth kinetics of the in situ AOB was also studied. Although low numbers of AOB were found at the deeper layers where oxygen was depleted, they were primarily detected in the upper and middle layers of the biofilm. The maximum specific growth rate (µ_b,max) and half saturation constant (K_s) of AOB in the biofilm were 0.32 d^–1 and 1.7 mM/L of NH₄⁺, respectively. Key words: ammonia oxidizing bacteria (AOB), fluorescent in situ hybridization (FISH), growth rate, rotating biological contactor (RBC).