Contamination toxicity and remediation of stable dyes and oils in aquatic wastewater systems

Abstract Water resources are currently becoming increasingly scarce, and most of them are polluted by human activities such as domestic, industrial, and agricultural waste. Therefore, wastewater requires water treatment before it gets into the natural water bodies. The most significant role of wastewater treatment is the removal of different dyes and even oil pollutants that are found in wastewater, including suspended matter, organic carbon, fertilizers, inorganic salts, heavy metals, pathogens, etc. The last goal of wastewater treatment processes is the protection of human health and the environment. The present study reviews types of water contamination and the application of wastewater treatment technology to remove the major pollutants from wastewater, such as diverse oils, heavy metals, dyes, pesticides, and herbicides. Integrating the data about the sources, toxicity, environmental fate, and treatment performance, the review identifies the specific difficulties in dealing with chemically stable dyes and petroleum-derived oils, particularly when both of them coexist in the actual effluents. The practical implications of this review are also placed to inform the industrial practice to encourage the adoption of methods of clean production, recovery methods of resources and waste-to-wealth strategies and can also influence future wastewater management and policy formulation by supporting the design of integrated trains of treatment, realistic discharge of dye-oil mixes, and incentives to the use of advanced adsorbents and photocatalysts in the treatment of industrial wastewater. Health and the environment are the final objectives of wastewater treatment processes. We focus on physical, chemical, and biological remediation approaches, with particular emphasis on adsorption using Expanded Graphite (EG) and photocatalytic degradation using TiO₂ nanoparticles.