Analysis of the characteristics of organic matter discharge in the Paldang Lake water system: focusing on the sewage treatment plant located in the inflow tributary

Paldang Lake is a major water source that supplies approximately 78 million tons of tap water to Seoul and the metropolitan area per day. Approximately 55% of the water flowing into Paldang Lake comes from the Namhan River, and 1.6% comes from the Gyeongancheon Stream. This study aimed to investigate the characteristics of organic matter discharge based on total organic carbon (TOC) in the Namhangang River and Gyeongancheon Stream. In particular, the characteristics and effects of organic matter discharge were investigated with a focus on sewage treatment plants located near the target water system. A total of 14 monitoring sessions were conducted. The concentrations of biodegradable (labile) and non-biodegradable (Refractory) organic matter in the influent and effluent of sewage treatment plants and water systems near the three sewage treatment plants in the study area were investigated. In addition, the effects of organic matter discharge characteristics from the sewage treatment plants and rivers were investigated based on the results of the concentration analysis. This confirmed that biodegradable organic matter was reduced by approximately 95% through sewage treatment. In addition, the results of the 14 monitoring sessions confirmed that the variability in the removal rate was also small, which confirmed that biodegradable organic substances can be stably removed using the current sewage treatment method. In the case of non-biodegradable organic substances, the average removal rate was approximately 63%. In other words, the removal rate of non-biodegradable organic substances is relatively low in sewage treatment plants where biological treatment processes using microorganisms are the main process, but it was confirmed that more than 50% was removed through sedimentation and filtration within the process. Accordinglhy it was concluded that management of non-biodegradable organic substances is necessary in order to manage organic substances present in water systems. In addition, it was revealed that the MBR (Membrane Bioreactor) method, which easily removes particulate organic substances through membrane separation, would be effective in managing non-biodegradable organic substances. This study provides basic information for managing organic substances in sewage treatment plants and water systems.