하수처리장 해양방류수역의 수질개선을 위한 해조장 조성에 관한 연구

Abstract

South Korea’s sewage treatment method is effective at removing suspended solids and organic matters, but it is not for removal of nutrient. So, huge quantities of effluence that include nutrients are discharged into the coastal area. In Busan, as the annual discharged amount of sewage and wastewater that released into outfall area from sewage treatment plant after activated sludge process and advanced treatment, as of 2008, are 504 million cubic meters within 20 ppm of the quality standards in effluent for total nitrogen, the pollution episodes like eutrophication have occurred frequently in the neighboring waters. For the water quality improvement in the ocean outfall area of sewage treatment plant, this study tried to control the water quality of outfall area using the biofilter method through seaweeds, a way of ecological engineering treatment that is applicable in the marine. Therefore, this research made an attempt the main factors necessary for creating seaweed bed to improve water quality in the outfall area of sewage treatment plant, and the results are as follows. First, it showed that the physic-chemical data, analyzed in the ocean outfall area of sewage treatment plant, water temperature(winter and summer) and salinity were suitable for a habitable environment of Ecklonia cava. In the COD and nutrient, the region for exceeding grade Ⅱ of environmental standard for water quality appeared frequently according to the time of investigation, and the exceeding grade Ⅲ of environmental standard for water quality revealed intermittently in the region installed effluent pipes. A change in the seaweeds showed that overall, standing crop decreased compared to that of 10 years ago, and a component ratio of seaweeds changed from the polar or temperate seaweeds to mixed things near to temperate. Second, in case of making the seaweed bed in the ocean outfall area of sewage treatment plant, Habitat Suitability Index of Ecklonia cava per all survey points, considered physical and physico-chemical factors in 5~10 meters below sea level, was 50~93 %(average 80 %), so this seaweed, Ecklonia cava, was suitable for making the seaweed bed. Third, calculating the range of the making seaweed bed to improve water quality of the ocean outfall area of sewage treatment plant, the area considered the range of dilution and diffusion after discharging sewage water into sea, using EFDC model, worked out the 214,726 square meters around the effluent pipes. In the selected area as the range of making seaweed bed, considering the light intensity in one year and the extent of diffusion of sewage water, I thought that making the seaweed bed in 5~10 meters depth under water was suitable for Ecklonia cava that inhabit the region, as well as it was effective for water quality improvement of ocean outfall area. Fourth, the results of nutrient uptake kinetics in experimenting indoors showed that Km and Vmax of nitrate were 41.87 μM and 54.70 μmol․g-1 dw․h-1, and Km and Vmax of ammonium were 39.41 μM and 52.32 μmol․g-1 dw․h-1. In addition, to satisfy grade Ⅱ of environmental standard for water quality of the sea as reducing untreated nitrogen within sewage water that discharged through making seaweed bed, in cases of DIN, it showed that each of Ecklonia cava per one square meter unit area was as much required as 31 g. Fifth, also we confirmed that the transplanted Ecklonia cava after creating artificial seaweed bed had a smooth condition of inhabitation. Through finding the new juvenile of Ecklonia cava in attachment substrate, I made sure that these seaweeds reproduced successfully. This means that the transplanted Ecklonia cava can inhabit the ocean outfall area of sewage treatment plant that turbidity and concentration of nutrient are relatively higher than the other. If swarm spores of Ecklonia cava spread by reproduction move to the attachment substrate like natural bedrock and then they are sessile and create the colonies of seaweeds, I expect the water quality improvement through absorbing nutrient. Furthermore, I am convinced that it can create the seaweed bed that is able to the roles like primary producer of sea, absorbing carbon dioxide that is major causing matter of greenhouse effect and a spawning ground.