Uncertainty analysis in the measurement of nitrification kinetics in urban wastewater treatment plants in Türkiye

Abstract

In this study, relation between the maximum growth rate of nitrifiers and the initial amount of active biomass placed at the beginning of the nitrification experiment was investigated by using parameter estimation and uncertainity analysis for four different wastewater treatment plants, taking into account local conditions. By focusing on these parameters, critical importance of the effects of initial conditions on the nitfication experiment is investigated. To designing and optimising the performance of wastewater treatment plants, nitrification kinetics play a decisive role. Nitrification directly affects aerobic sludge age, which is one of the most important parameters to obtain volume calculations. Understanding of nitrification kinetics will enable predict and control the rates of these biochemical transformations with greater sensitivity and, in turn, increase the effectiveness of future nitrogen removal processes. Nitrification is important for the alleviation of aquatic eutrophication and the minimization of the toxic ammonia concentration to meet the ever-increasing stringent environmental discharge regulations. In addition, it has significant impacts on designed advanced treatment technologies and sustainable practices along the pathways to ensure minimal anthropogenic impact on the natural ecosystems. Four different advanced biological wastewater treatment plants across the Marmara Region of Türkiye are taken into account to highlight the importance of the local conditions. From these plants daily samples were taken and nitrification experiment was carried on, and with the results of the experiments and the data generated by the model are used in this study. Some assumptions such as assuming the respiration and growth as constant are made in order to reduce the complexity of the initial conditions and to improve practical identifiability and lesser uncertainity between the focused parameters. The nitrification experiment results of the plants, that were modeled using Microsoft Excel program, used and with the help of sum of squared method, parameter estimations are performed, and the effect of the initial conditions of the experiment, and uncertainties are investigated. According to the results, approximate confidence intervals were visualized as contour plots based on critical values calculated at a 95% confidence level for each plant. The effects of local conditions on nitrification kinetics experiments were discussed based on observed similar trends in approximate confidence intervals. Nitrifiers growth rates in Türkiye found to be lower than that of standard values, and errors in maximum growth rate of nitrifiers are calculated to be in the order of 5-10%, which is acceptable according to the general design margins which is typically range between 20% to 25%. Also, for the practical applications overdesign is very general approach for construction of wastewater treathment plant design and oftenly varies between 10-30%. Thus, the importance of factors that may arise from the initial conditions of the experiment was emphasized, and the most suitable experimental conditions were examined. In many studies, the significance test of the data can be overlooked; however, this study focuses on the uncertainty analysis between the maximum growth rate of nitrifiers and the initial active biomass placed at the beginning of the experiment. Meanwhile, it is important to acknowledge that this study may be one of the first investigations to explore this specific aspect.