국내 하수처리시설의 악취 배출특성 및 바이오필터에 의한 악취 저감효율에 관한 연구

Abstract

The objectives of this work is to examine the emission characteristics of odor and major contributors of odor at each unit process of domestic sewage treatment facilities and to evaluate odor removal efficiency by biofilters which are in operation as odor preventive facilities there. For these purposes, the concentrations of composite odor and 22 designated malodorous compounds are measured at each unit process of 62 sewage treatment facilities and at inlet and outlet of 62 biofilters. From these results, the emission characteristics of composite odor and malodorous compounds at each unit process and of composite odor with season are studied. Major malodorous compounds affecting the composite odor are examined closely from the relation of composite odor and malodorous compounds. From the biofilters, their removal efficiency is evaluated by the ratio of outlet concentration to inlet concentration for each of composite odor and malodorous compounds and is also examined with inlet loading of malodorous compounds and with their type and capacity for composite odor. The results obtained are summarized as follows. The geometric mean value of composite odor concentration is the highest at the sludge holding tank with the value of 8,020 DT, followed by the gravity thickener, the 1st settling chamber and the dewatering building, with the value of 6,979 DT, 1,498 DT and 1,381 DT, respectively, among the unit process. The composite odor concentration of each unit process varied according to the season, but there was little tendency. Hydrogen sulfide has the highest emission concentration among 22 designated malodorous compounds at every unit process. Its average concentration is the highest at the sludge holding tank with the value of 188.88 ppm, followed by the gravity thickener, the dewatered sludge cake bin and the 1st settling chamber, with the value of 53.967 ppm, 23.706 ppm and 7.847 ppm, respectively. Its average concentration at the excess sludge holding tank is 0.603 ppm, which is the lowest among all the unit process of sewage treatment facilities. Sensitivity analysis shows that the concentration of hydrogen sulfide and methyl mercaptan affects the composite odor concentration from sewage treatment facilities by 79.1% and 20.0%, respectively. The correlation analysis of odor index from sewage treatment facilities shows that there is no significant difference in explanation ability between composite odor concentration and each of SOQ (sum of odor quotient), hydrogen sulfide with methyl mercaptan and hydrogen sulfide which are 83.0%, 78.9% and 76.0%, respectively. It is considered that hydrogen sulfide alone or along with methyl mercaptan can be used as a single or a combined index with the composite odor concentration to evaluate the odor emission characteristics of sewage treatment facilities. Removal efficiency of the composite odor and of the malodorous compounds by biofilters highly depends on each biofilter and the group of malodorous compounds. Wilcoxon signed rank tests indicate there are significant differences(p=0.000<0.05) of composite odor concentration and hydrogen sulfide concentration between the inlet and outlet of biofilters surveyed. Odor removal efficiency and maximum elimination capacity by biofilters are examined against inlet loading of 4 types of sulfur compounds, ammonia, acetaldehyde and toluene. The maximum elimination capacity (against inlet loading) of hydrogen sulfide, methyl mercaptan, dimethyl sulfide, dimethyl disulfide, ammonia, acetaldehyde and toluene is 12.1 g-H2S/m3/hr (28.1g-H2S/m3/hr), 1.1 g-CH3SH/m3/hr (1.97g-CH3SH/m3/hr), 4.0 g-DMS/m3/hr (4.2-DMS/m3/hr), 0.19 g-DMDS/m3/hr (0.49g-DMDS/m3/hr), 4.05 g-NH3/m3/hr (4.26g-NH3/m3/hr), 0.07 g-CH3CHO/m3/hr (0.15 g-CH3CHO/m3/hr), and 3.54g-C6H5CH3/m3/hr (3.79g-C6H5CH3/m3/hr), respectively. Trickling biofilters show slightly higher compliance rates of effluent quality standard than hybrid biofilters. It is because of difference in management and operation regarding nutrients, pH, circulating water, etc. The compliance rates of effluent quality standard are different depending on biofilter's capacities, but a tendency was not found.