Among the numerous issues confronting our world today, two significant challenges stand out: waste management and freshwater contamination. This study addresses these issues by developing innovative recycling and circular economy techniques. For the first time, steel slag waste was converted into slag nanocomposites using a solvothermal preparation technique for wastewater treatment in an advanced oxidation process. Additionally, agricultural and plastic waste were transformed into biochar, graphene, and activated carbon through thermal pyrolysis, which were then applied as adsorbents for the removal of heavy metals from wastewater. Furthermore, cigarette waste was converted into TiO2/Zr impregnated with graphene oxide derived from plastic waste for CO2 reduction. These approaches not only mitigate landfill shortages but also provide sustainable solutions for environmental remediation.