Biofilms in Nitrogen Removal: Population Dynamics and Spatial Distribution of Nitrifying- and Anammox Bacteria

Efficient nitrogen removal at wastewater treatment plants (WWTPs) is necessary to avoid eutrophication of recipient waters. The most commonly used approach consists of aerobic nitrification and subsequent anaerobic denitrification resulting in the release of dinitrogen gas into the atmosphere. Nitrification is a two-step process performed by ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB) often grown in biofilms at WWTPs. Alternatively, anaerobic ammonium oxidation (anammox) where anammox bacteria convert ammonium and nitrite directly into dinitrogen gas may be utilized. These groups of recalcitrant bacteria grow very slowly and are sensitive to perturbations, which may result in decreased efficiency or even breakdown of the respective process. Thus, their ecology, activity and the structure of the biofilms in which they grow require detailed investigation to improve our understanding of the nitrification and anammox processes. This in turn will facilitate the design of more efficient nitrogen-removal strategies. To assess the population dynamics and spatial distribution of nitrifying and anammox bacteria, culture-independent methods are essential. Therefore, the application of methods such as quantitative PCR (qPCR), terminal restriction fragment length polymorphism (T-RFLP) and Fluorescence In Situ Hybridization (FISH) in combination with advanced microscopy techniques and digital image analysis for the study of nitrifying and anammox biofilms will be reviewed in this chapter.