This study has cross checked the change of internal sludge-recycle in Anaerobic-Digestion, and researched about not only the improvement of Bio-gas production from the digested sludge but also the efficient method of sludge minimization. Ultimate object of the study is to reduce the amount of sludge by the improved efficiency of contact with the organic-matter and the microbes in Anaerobic-Digestion. The sludge-recycle fluidized sludge layer and raised the activity of the sludge, the optimal sludge-recycle ratio, VS and COD removal ratio were 1,000%, 28.2% and 27.7%, respectively. Through these results of this study, it may be of use to treat waste sludge by the sludge-recycle ratio in terms of minimization and circulation of resources.

Abstract
 1. 서 론
 2. 재료 및 방법
  2.1. 실험장치
  2.2. 실험재료 및 방법
 3. 결과 및 고찰
  3.1. pH 및 알카리도 변화
  3.2. 고형물 감량
  3.3. 유기물 제거 및 메탄발생량 변화
 4. 결 론
 참 고 문 헌

• 권구호(경북대학교 환경공학과) | Kooho Kwon (Department of Environmental Engineering, Kyungpook National University)
• 민경석(경북대학교 환경공학과) | Kyungsok Min (Department of Environmental Engineering, Kyungpook National University) Corresponding author
• 이태우(대구광역시 환경시설공단) | Taewoo Lee (Daegu Metropolitan City Environmental Installations Corporation)
• 정용준(부산가톨릭대학교 환경공학과) | Yongjun Jung (Department of Environmental Engineering, Catholic University of Pusan)