Biological treatment in drinking water treatment plants

Water is one of the most fundamental needs for sustaining life. Efforts and methods developed by humans to ensure that water used is free from harmful substances or organisms have a long history. Recent studies in European countries have identified over 100 types of micropollutants in wastewater, effluents from treatment plants, surface waters, groundwater, and even drinking water. Due to their resistant structures, traditional treatment facilities often do not effectively remove these pollutants. Therefore, advanced treatment processes are applied to purify micropollutants from aquatic environments. When groundwater is used as drinking water, contamination by nitrogen compounds, such as nitrates from agricultural fertilizers leaching into groundwater, is a common concern. Nitrate, due to its low adsorption tendency, frequently contaminates groundwater. Another source of nitrate is untreated municipal and industrial wastewater discharged into receiving environments, where ammonium nitrogen can be converted to nitrate via nitrification. Nitrification converts ammonia's chemical form solely to nitrate. Denitrification, on the other hand, refers to the reduction of nitrate (NO3-), nitrite (NO2-), nitric oxide (NO), nitrous oxide (N2O), and ultimately to nitrogen gas (N₂). Biological denitrification, one of the methods used for nitrate removal, involves both autotrophic and heterotrophic bacteria. In autotrophic denitrification, microorganisms use inorganic carbon sources and inorganic electron donors. In heterotrophic denitrification, both the carbon and electron sources are organic substances. In both types of denitrification, other nutrients (such as phosphorus, sulfur, trace elements, etc.) must be present in the environment. Heterotrophic and autotrophic denitrification methods are employed in full-scale drinking water treatment plants. This research thesis investigates the adaptation of a pilot-scale facility, comprising four heterotrophic and one autotrophic denitrification processes, in laboratory conditions to real-scale drinking water treatment plants. Although high removal efficiencies are not always observed in biological treatment processes, nitrate removal rates of approximately 90-95% have been achieved with additional units (e.g., activated carbon adsorption, filtration). This thesis discusses various micropollutants found in drinking water and touches upon treatment methods used in some treatment plants. The acceptance of treatment methods by the public has been evaluated by examining full-scale biological drinking water treatment plants implemented in our country.