Using support media to assist in the growth of purifying micro-organisms is a technique which has attracted renewed interest in recent years. The advantages of biofilm reactors - smaller than traditional reactors, often not requiring settlers, etc - have motivated research into the fundamentals of biofilms and vigorous development programmes for reactors, leading to the successful introduction of large-scale plant. In this volume forty-two papers from over a dozen countries offer authoritative accounts by international experts of the latest research results plus detailed descriptions of full-scale case studies. This book will be of value to scientists, development and design engineers and plant managers who need thorough and unbiased knowledge of one of the most modern and effective techniques of biological water treatment.