Operational and Environmental Conditions for Efficient Biological Nutrient Removal in an Urban Wastewater Treatment Plant

Abstract

This paper examines correlations and processes related to nutrient removal in a wastewater treatment plant (WWTP), verifying the efficiency of plant improvements and the extent that public awareness campaigns have had on treated water quality. Increases in water pH value resulted in a decrease in nitrate nitrogen and phosphate phosphorus levels in treated wastewater, demonstrating a better performance of microorganisms with higher pH values. On the contrary, both nutrients proved to increase with increasing temperatures, although there were no significant differences in the nitrogen loading rate, representing a good behavior of the WWTP despite the considered season. This fact can be explained by a new storm tank located at the sewage plant that cushions sharp‐point organic loads, allowing a more stable performance of the WWTP. An increase in electrical conductivity resulted in higher phosphate phosphorus levels in the effluent, indicating a special sensitivity of phosphorus accumulating organisms (PAOs) to high osmotic pressures. High C/N ratios, both chemical oxygen demand and biochemical oxygen demand resulted in lower nitrification rates, indicating the favored growth of heterotrophs over slow‐growing nitrifying bacteria. Sludge age proved to have a strong effect on nutrients removal, increasing the diversity of ammonia oxidizing bacteria but worsening the nitrogen removal efficiency with older solids residence time. In order to meet the requirements of the Council Directive (91/271/CEE) for phosphate phosphorus removal, an anaerobic selector for PAOs growing should be implemented.