This book provides the information on the application of nanotechnology in cleaning wastewater and the impact of microbial ecosystem to solve environmental problems has been critically reviewed in the chapters. It also gives detailed reviews about the conversion of wastewater nutrients into a biofertilizer using microalgae, as well as the applications of Biochar for heavy metal remediation from water. Most importantly, this book contains critical review on microbial fuel cells and highlights the emerging risks of bioplastics on the aquatic ecosystem.