Wastes: Solutions, Treatments and Opportunities II contains selected papers presented at the 4th edition of the International Conference Wastes: Solutions, Treatments and Opportunities, that took place 25-26 September 2017 at the Faculty of Engineering of the University of Porto, Porto, Portugal. The Wastes conference, which takes place biennially, is a prime forum for academics and industry representatives from the waste management and recycling sectors around the world to share their experience and knowledge with all in attendance. The published papers focus on a wide range of topics, including: Wastes as construction materials, Wastes as fuels, Waste treatment technologies,MSW management, Recycling of wastes and materials recovery, Wastes from new materials (nanomaterials, electronics, composites, etc.), Environmental, economic and social aspects in waste management and Circular economy.