Textbook in PDF format This book offers a comprehensive examination of the rotary drum composter as an effective solution for managing organic waste. With a focus on decentralized systems, it emphasizes the benefits of on-site composting to reduce waste transportation's environmental and economic costs. The book explores the underlying science and engineering principles behind the rotary drum composter, highlighting its ability to create high-quality compost in a controlled environment. Various studies are presented, detailing its successful application in handling municipal solid waste, sewage sludge, agricultural residues, and weeds. Additionally, the text delves into key factors such as temperature control, aeration, and microbial dynamics that influence the composting process