불포화 사질토양을 이용한 도시하수의 3차 처리

Abstract

모래층 토양이 도시하수의 3차 처리에 이용될 경우 COD 제거율은 적용유량에 관계없이 약 70%에 이르는 것을 알 수 있었다. 적용유량이 증가함에 따라 COD제거에 필요한 토양 층의 깊이가 증가하여 50 L/day의 유량에서는 약 60 cm에 달하는 것을 알 수 있었다. 질산화는 매우 빨라서 표층토양 <TEX>$10{\sim}20\;cm$</TEX>에서 반응이 거의 완료됨을 알 수 있었다. 총 질소의 제거율은 유량에 상관없이 약 20%로 낮은 편이었으며, 이에 대한 보완책이나 추가적인 연구가 필요한 것으로 판단된다. 잔디를 식재할 경우 오염물의 처리효율에는 영향이 거의 없으나 투수능 유지에는 도움이 되는 것을 알 수 있었으며, 토양에 함유된 유기물로부터 상당한 양의 오염물이 용출되는 것을 알 수 있었다. 탈질과정에서는 아산화질소도 발생하므로 본 연구의 결과를 현장에 적용하기 전에 이에 대한 추가적인 연구도 필요할 것으로 판단된다. Treatment of secondary effluent was investigated using sandy soil as a possible alternative to the tertiary treatment of municipal wastewater. Secondary effluent was applied with three different flow rates to the surface of pilot scaled lysimeters, which were filled with sandy soil. Some of the lysimeters were covered with osd, while others were kept bare in order to investigate the role of plantation on the treatment. The concentration changes in COD and nitrogen were measured along the unsaturated soil depth. The same set of experiment as with the secondary effluent was performed using tap water to investigate the dissolution of the contaminants from the soil. from the results it was found that when sandy soil was used for tertiary treatment of municipal wastewater COD removal efficiency reached about 70% regardless of the application rate. The soil depth needed to obtain such efficiency increased along with the application rate, which was about 60 cm at the application rate of 50 L/day. Results also showed that nitrification occurred rapidly. The process was completed in soil depth of first <TEX>$10{\sim}20\;cm$</TEX>. Nitrogen removal efficiency was as low as about 20% regardless of the application rate. Some supplementary means should be considered to improve the efficiency. Sod on the soil surface had no significant influence on the contaminant treatment but was helpful to keep the infiltration rate undiminished. Finally, the organic soil was found to release significant amount of contaminants when it was in contact with soil water.