The increasing generation of hazardous waste presents a significant challenge to environmental and public health. This chapter explores various chemical methods and strategies for reducing the toxicity of waste, focusing on both industrial and municipal contexts. We examine advanced oxidation processes, chemical precipitation, neutralization, and other innovative chemical treatments designed to mitigate harmful substances. The effectiveness, advantages, and limitations of these methods are critically analyzed to provide a comprehensive understanding of their potential applications. By integrating recent advancements in chemical engineering and environmental science, this chapter aims to offer practical solutions for minimizing the adverse impacts of toxic waste for smart cities. Through detailed case studies and comparative analysis, we highlight successful implementations and identify areas that need further research. The insights gained from this study are intended to guide policymakers, researchers, and industry professionals in developing more sustainable and effective waste management practices.