Investigation of elevated process temperature on nitrification efficiency in leachate MBR plant using simulation tools

Abstract

The thesis explores the effect of temperature on the nitrification process in a Membrane Bioreactor (MBR) operating at a landfill. Nitrification, the first stage of nitrogen removal within activated sludge systems, involves the oxidation of ammonium nitrogen to nitrate and nitrite, whereas denitrification is the reduction of these oxidized forms to dinitrogen gas. The efficiency of these processes is significantly influenced by environmental factors, particularly temperature. To investigate this, both laboratory experiments and modeling were employed. In the laboratory experiments, a batch nitrification experiment was conducted using samples from the aerobic-activated sludge tank of a landfill's treatment plant operating at high temperatures. The primary objective was to measure nitrate and nitrite production rates. The laboratory setup involved carefully controlling the experimental conditions to simulate the high-temperature environment of the treatment plant and assess the impact on the nitrification process. The results from these experiments provided critical insights into how temperature variations affect the rate of nitrate and nitrite production. In addition to laboratory experiments, dynamic modeling was used to verify the kinetics of the nitrification process. This was accomplished through the utilization of the SUMO program, developed by Dynamita, employing the 2-stage nitrification-denitrification model (Sumo2). The dynamic modeling involved simulating the full-scale leachate MBR plant's performance under varying temperature conditions. Daily plant performance data were incorporated into the simulation studies to ensure that the model accurately reflected real-world operations. This comprehensive approach allowed for a detailed analysis of the nitrification process and the identification of key factors influencing its efficiency. It was concluded that cooling the membrane bioreactor is essential to enhance nitrification efficiency. The research indicated that the high temperatures observed in the plant (around 40°C) were detrimental to the nitrification process. To address this, minimum process temperatures were calculated by considering the measured values and operational conditions of the plant. These calculations provided a basis for determining the optimal temperature range for efficient nitrification. To implement the findings, surface aerators were installed to regulate the temperature within the bioreactor. These aerators helped to cool the bioreactor, thereby improving the conditions for nitrifying bacteria. The installation of surface aerators facilitated the start-up of the nitrification and subsequent removal of nitrogen. The study highlighted that temperature regulation was crucial for maintaining the efficiency of the nitrification process, especially in high-temperature environments typical of landfill leachate treatment plants. In conclusion, the thesis underscores the critical importance of temperature control in maintaining optimal nitrification rates in MBR systems treating landfill leachate, while also highlighting that pH levels also play a significant role in this process. By implementing cooling mechanisms, such as surface aerators, the efficiency of nitrogen removal processes may be greatly enhanced. This not only enhances the treatment efficiency but also contributes to better environmental protection. The study's comprehensive approach, combining laboratory experiments and dynamic modeling, provides a robust framework for optimizing nitrification processes in wastewater treatment plants operating under challenging environmental conditions.