After identifying species by collecting the suspended and attached algae mat inhabiting in the slow sand-filter, Spirogyra sp., Mougeotia sp. and Closterium sp. were main green algae and Synedra sp. was diatom algae. Among them green algae Spirogyra sp. was dominant species. A result of observing the life mode of apple snail for a month after introducing into the slow sand-filter, apple snail eggs were discovered on the filter walls 2 weeks after introducing, 4 weeks later lots of eggs were observed all of the slow sand-filter walls, it means there is no problem for apple snail to live in the slow sand-filter. The observation result for algae removal potential by introduced apple snail after 2 months later, slow sand-filter where apple snail were introduced, a few algal mat were observed. On the other hand, no introduced apple snail into the slow sand-filter, lots of suspended algal mats were formed in the water and attached algal mats on the sand surface as well, these algal mat induced much of operating problems.

Abstract
 1. 서 론
 2. 재료 및 방법
  2.1. 실험재료
  2.2. 실험방법
 3. 결 과
  3.1. 왕우렁이 투입 유무에 따른 여과지 내의 조류 형성특성
  3.2. 왕우렁이 투입 유무에 따른 완속 모래여과 처리수의수질 비교
 4. 결 론
 참 고 문 헌

• 손희종(부산광역시 상수도사업본부 수질연구소) | Hee-Jong Son (Water Quality Institute of Busan) Corresponding author