Dyestuffs from textile industry wastewaters: Trends and gaps in the use of bioflocculants

Regarding environmental impact, the textile industry is one of the most relevant sectors. Worldwide, it is estimated that 700,000 tons of dyes are generated annually, and 12 % of them are inappropriately disposal into aquatic resources. In this sense, flocculating systems can be a cost-effective treatment of dye-containing wastewater. One route that has attracted attention to this researching field is the flocculating effect of biological components. Known as bioflocculants, these extracellular molecules, mainly polysaccharides and proteins, are produced by microorganisms and present relevant effects on precipitating suspended particles or diluted substances from solutions. However, the flocculating phenomena related to bioflocculants and dyes are not fully comprehended. The complex structure of extracellular substances and the variance in dye molecules make their interactions hard to predict. This review aims to critically discuss the current state of the art and future trends related to bioflocculants and dye-containing wastewaters from the textile industry. It includes biological systems of bioflocculant-producing strains, chemical properties of bioflocculants and dyes, and physical parameters employed on flocculation processes. This review would lead to a better understanding of challenges and corresponding strategies to open up new ways of bioflocculation in wastewater treatment.