Characteristics of Organic Matters in Influents and Effluents of Sewage Treatment Plants in Gyeongsanbuk-do

Objectives : This study aimed to provide scientific information on the characteristics of organic matters in influents and effluents of sewage treatment plants (STPs) in Gyeongbuk province, Korea, for better performance of treatment processes in the plants. Methods : We selected six STPs with each capacity over 30,000 m3/day in Gyeongbuk province, and analyzed water quality data in influents and effluents of the plants from 2013 to 2020. Also, the removal efficiencies of pollutants were assessed with the operational data. In 2020, characteristics and origins of dissolved organic matters (DOM) in influents and effluents were investigated using the fluorescence excitation emission matrix (FEEM) analysis. Results and Discussion : The average BOD5/CODMn ratios of influents and effluents from the STPs were 1.60 and 0.27, respectively. High variability in BOD5/CODMn ratios was observed for both influents and effluents. The CODMn/TOC ratios of the influents and effluents were the same with an average of 1.6. Although the biological treatment process was different for each STP, the organic matter removal efficiency was similar, and the TOC removal efficiency was 86.5~91.7%. The representative spectra of DOM identified through FEEM analysis was peak C (humic-acid like substance) region, and under the same carbon concentration (2 mg-C/L) the fluorescence intensity of effluents was stronger than influents possibly due to the influence of soluble microbial products (SMP). It was found that DOM of both influent and effluent originated from microorganisms, and the difference in water quality of DOM was statistically significant. Conclusions : The characteristics and fate of organic matters in influents and effluents of the six STPs were similar regardless of plant location. The results of this study can be used as basic information to efficiently control organic matters in the STPs.