An Innovative Approach to Remove Nitrogen from Wastewater Using a Biological ANaerobic AMMonium OXidation (ANAMMOX) Process

Abstract

Nitrogen (N) is essential for life because it is one of the main constituents of organic molecules such as amino acids and proteins. However, at the same time it is a threat to both the environment quality and human health. To avoid the negative effects of N, recent worldwide regulations have been promulgated to limit the use of nitrogen based fertilizers and the amount of nitrogen discharged into water bodies from wastewater treatment plant (WWTP). An aerobic oxidation of reduced N either followed or preceded by an anoxic reduction of oxidized N are the most common systems used in WWTP to convert the reactive N (ammonium, nitrite and nitrate) to the harmless nitrogen gas (N₂). An alternative to the traditional systems is represented by the innovative biological process named Anammox that anaerobically converts ammonium into N₂. Compared to the traditional processes, this new process requires lower amount of oxygen, has no need of organic carbon supply and is highly efficient with any concentration of ammonium. However, a wide use of this process at full scale is hampered by the extremely slow growth rate of bacteria operating Anammox process and by the difficulty in the control of critical co-existence of different bacterial strains that compete for the same substrate and thrive in opposite environmental conditions. This work highlights the strategies to improve the enrichment of Anammox operating bacteria from two different biological sludge (activated and anaerobic) and to optimize the efficiency of two Anammox biological sequential batch reactors (SBR) by changing the operational conditions. The main results have shown that in an activated sludge the Anammox biomass grows faster than in anaerobic sludge and the performance of Anammox one-stage process can be regulated by controlling the stirring system as well as the oxygen and inorganic carbon (IC) concentrations in the system even if no one of the previous operating parameters has resulted to be decisive.