A review of dye biodegradation in textile wastewater, challenges due to wastewater characteristics, and the potential of alkaliphiles

Thousands of synthetic dyes are used in the textile industry for fabric manufacturing. During the dyeing process, more than one-third of the dyes are not absorbed by the fabric and end up in wastewater. These dyes are toxic and carcinogenic, leading to significant environmental pollution, diminishing the aesthetic value of natural water bodies and posing threats to human health and aquatic biodiversity. Physicochemical treatment methods have been used to remove dyes but are neither economically feasible nor environmentally friendly. In contrast, biological treatment methods are cost-effective, efficient, and environmentally sustainable. This review aims to provide a comprehensive overview of textile dye biodegradation, the challenges posed by the characteristics of textile wastewater, and the potential of alkaliphilic microbes to address this issue. Additionally, it discusses the underlying mechanisms of dye biodegradation, the advantages of mixed cultures or microbial consortia over single microorganisms in dye degradation, and the factors affecting the degradation efficiency of microorganisms. Dye concentration and type, incubation temperature, pH, and time are identified as influential factors in the dye biodegradation process. Studies confirm that the standard biological treatment process using non-alkaliphilic microorganisms is ineffective for complete dye degradation and detoxification, as textile wastewater is alkaline and saline in nature. Therefore, alkaliphilic microbes are a potential alternative for textile dye wastewater treatment. These microorganisms can function under extreme conditions and produce various oxidoreductive enzymes, including azoreductase, laccase, lignin peroxidase, and manganese peroxidase, which can be involved in the biodegradation process. Alkaliphilic microbes play a crucial role in dye biodegradation through their alternative metabolic pathways and adaptive response mechanisms, enabling them to survive under harsh conditions and making them highly efficient. Although these microbes have been studied in laboratory and pilot-scale experiments, further research is needed to assess their practicality in real-world applications.