Biological Wastewater Treatment Plants Suitable for Domestic Wastewater Treatment in Cold Climatic Conditions

Treatment of wastewater with an activated sludge system is ideally completed in a central treatment plant, and treatment can occur in most climates. However, colder environments reduce the treatment capacity. According to literature on classical activated sludge systems, the most suitable systems for microorganisms work under ideal conditions between 20 and 40 °C. Treatment performance is affected by cold climatic conditions, reducing the microbial activity in the activated sludge and the efficiency of domestic wastewater treatment plants (WWTP). Biological wastewater treatment in cold climates can be a challenge due to the low reaction rates; however, the alternative of heating large flows of wastewater results in significant operating costs. To have a comprehensive understanding of current performance of wastewater treatment plants in a cold climate and water management action in the future, two different wastewater treatment plants were investigated. The operating conditions and treatment performance of Erzurum WWTP and Sarıkamış WWTP, in Turkey, were examined to suggest suitable processes for the wastewater treatment plant planned to be built in the city centre of Kars, where the winters are very harsh and cold. These two WWTPs are close to the planned Kars WWTP region and currently operating under similar cold climatic conditions in the region. Three treatment processes are recommended for the planned WWTP in Kars. The Moving Bed Biofilm Reactors (MBBR) is suggested, as the MBBR system is not affected by nitrogen and phosphorus removal at low wastewater temperatures and full nitrogen removal can be achieved at 4 °C of inlet water temperature. The Integrated Fixed-Film Activated Sludge System (IFAS) system, which is a hybrid version of the MBBR system and includes sludge recycling, is also considered recommendable. Moreover, it is considered that classical activated sludge systems can also be applied. Carbon removal achieved by activated sludge reactor, nitrogen removal is performed by using sequential reactors and phosphorus removal is performed by chemical additive in these processes.