Characteristics of nitrifying biomass from sidestream process operated at various pH

The nitritation process, i.e., ammonia to nitrite oxidation, is effectively utilized in various methods for treating reject water. The impact of pH on characteristics of nitrifying biomass was investigated in three experiments performed at pH 6.0, 6.5, and 7.0 using real dewatering liquor from the Wrocław Wastewater Treatment Plant. A comprehensive analysis was conducted by applying both microscopic examination and digital imaging to assess the morphology of activated sludge flocs. The aim was to understand how process conditions impact the physical properties and functional performance of nitrifying biomass. The study revealed significant differences between the results of experiments, i.e., considerable changes occurred in the morphology of the activated sludge flocs, mainly their size and structure, as well as filamentous bacteria content. The most substantial changes occurred in the experiment at pH 7.0, which can be attributed to the combined effect of process conditions, i.e., the optimal pH, sludge retention time, and dissolved oxygen concentration as well as the lowest free nitrous acid and free ammonia concentration.