Environmental impacts and remediation of dye-containing wastewater

Synthetic dyes are used in various industries including textile processing, food production and the pharmaceutical sector. Yet, approximately 80% of the dye-containing wastewaters produced are often released untreated into waterways or used directly for irrigation, causing detrimental impacts on human health and ecosystems. In this Review, we discuss the environmental impact of dye-containing wastewater and explore the chemical, biological and physical mitigation strategies used to treat and decontaminate dye-containing wastewaters. Untreated synthetic dyes cause coloration of receiving water bodies, hindering the degree of visible light reaching the photic ozone, and have carcinogenic, mutagenic and teratogenic properties that have toxic impacts on plants, animals and humans. Chemical treatment methods such as coagulation are the most widely adopted treatment methods; however, they require careful sludge management to be effective. Biological degradation, involving the implementation of enzymes, microorganisms and plants, is an environmentally friendly and energy-efficient approach for dye degradation, but it requires lengthy reaction times and the use of selective bio-organisms for target dyes. Advanced membrane-based physical separation can achieve effective removal of dyes and inorganic salts from highly saline dye-containing wastewater, while also enabling their recovery and reuse. Strengthened regulatory requirements and development of non-toxic dyes are required in conjunction with these remediation treatments to effectively mitigate dye-related pollution.