Evaluation of the removal status of organic micropollutants in urban biological wastewater treatment plant

Organic micropollutants are at the center of major concerns due to their trace levels of toxic, carcinogenic and mutagenic effects in natural environments. The aim of this thesis is to examine the behavior and fate of these pollutants in the treatment processes to improve the organic micropollutant removal performance of urban biological wastewater treatment plants (WWTP). For this purpose, micropollutants were monitored in the Tunceli urban biological WWTP, including seasonal variations. WWTP influent, effluent and biological process waters were sampled seven times in 2019 and 2020. Before the micropollutant monitoring study, the structural and functional properties of microbial life in the WWTP was monitored with the conventional parameters, and the facility influent, effluent and aeration basins were sampled twelve times between 2017 and 2018. As a micropollutant linear alkylbenzene sulfonates (LAS), nonylphenol mono-di-ethoxylates (NPEO1-2), nonylphenol (NP), polychlorinated biphenyls (PCB) and polyaromatic hydrocarbons (PAH) were monitored. During the organic micropollutant monitoring period, WWTP was operated in the endogenous respiration phase without sludge disposal. In this treatment environment, where aged microorganisms are intense, nitrogen removal in general decreased as a result of the slowing of nitrify activity. The highest NH3-N removal (41%) of the study period was realized in March, when the lowest mixed liquid volatile suspended solids (MLVSS) value (380 mg/L) and the lowest sludge age were observed. In this month, the highest micropollutant removal efficiency was obtained in relation to metabolic activity. On the other hand, in August, when the highest MLVSS value (1,750 mg/L) was observed, the lowest NH3-N removal (6%) and the lowest organic micropollutant removal were also recorded. Biomass with high adsorption capacity has lost yield due to lack of metabolic activity. It was observed that the removal of LAS and NPEO1-2 from the monitored micropollutants was high during the whole monitoring period, and microbial species were able to metabolize these pollutants easily. However, due to the fact that PCB and especially PAH species do not undergo metabolic degradation, they remain in the water and are found in high amounts at various stages of the treatment process. It has been understood that there is an increase in the level of wastewater micropollutants with the releases experienced in the last sedimentation process, and finally, a high amount of discharge to the environment. The results showed that micropollutant removal in biological treatment-based urban WWTPs can be enhanced by operating arrangements focused on sludge age and hydraulic retention time.