Increasing the availability of wastewater treatment is an important issue to preserve the environmental development. The sewage treated should be discharged safely to the water courses according to governmental standard or even to pave a way to the next treatment level in aiming for water reuse. Challenge of such treatment is to reduce the investment cost of the applied system. This book presents an effective design regarding the low investment and proposes a new system using a gradual concentric chamber (GCC) reactor for treating low-strength wastewater. A clear and odorless effluent for the purpose of reuse either in agriculture or in industrial process is an advantage compared to a treatment which only works anaerobically. Its simplicity is also valuable from the economical point of view thus the GCC technology would be of particular interest as an alternative solution for domestic sewage treatment. This book is primarily targeted to beginners as well as environmental professionals who are directly involved in water treatment. It is, therefore, written as a textbook for senior undergraduates and graduate students as well as a reference book for general reader.