Solving problem is one of the functions of an engineer. Text books in the field of wastewater engineering devote most of their pages to the development and explanation of the theory. This book is devoted to the pragmatic idea that performance and understanding of calculations should have more proportion in illustrating the principles. Special attention has been given to problems relating to sludges, nutrient removal, natural system of treatment, VOCs, economics and statistical method. In addition, ample notes have been given towards the end of each problems, ( salient point to ponder). This book will be useful to students, teachers, practising engineers, as also the researchers working in the field of wastewater treatment.