Microorganisms: A remedial source for dye pollution

Abstract Dyes, mostly organic compounds, are coloring substances used by several industrial production industries such as textile, leather, food, paper, pharmaceuticals, cosmetics, etc., as an identifier, a decorative or aesthetic agent, or for artistic purposes. They impart a better appearance to materials to which they have been applied. At present, more than 9000 coloring substances with more than 50,000 trade names are available on the market. Synthetic dyes have almost replaced natural dyes, as they have a higher resistivity toward washing, heat, light, oxidizing and reducing agents, pH, exposure to biological agents, solubility limits, or any other factors to which the dyed material is likely to be exposed. Moreover, they come with enhanced brightness, stability, and color range as well as a lower cost compared to natural dyes. Most of these dyes are not free from serious adverse effects on the environment. The natural properties of these dyes, when mixed with soil or water, are altered, rendering them unsuitable for jobs with which they have been prevalently used in the past. They have been reported as carcinogenic, teratogenic, or allergic toward humans. The Quinoline Yellow dye present in pharmaceutical products causes hives, wheezing, sneezing, or itching when consumed by the user; they may also cause hyperactivity in children. The intake of Sunset yellow is known to be associated with gastrointestinal intolerance, vomiting, abdominal pain, and indigestion. Dye removal methods can be classified into chemical (oxidation-reduction, photochemical degradation, ionic separation, neutralization, electrochemical degradation, etc.), physical (adsorption, filtration, precipitation, reverse osmosis, etc.), and biological (sorption by plants and microbial communities). Various strategies have been employed to remove dyes from the environment such as absorption of dyes by porous materials, nanostructures, clays, activated carbons, and others. Adsorbents such as magnetic nanoparticles, sugarcane pulp, activated sludge, powdered carbon, etc., have been used for dye removal from wastewater. Numerous studies conducted using plants and microbial populations for dye degradation or removal from the environment have been found to be effective and efficient strategies. In this chapter, we discuss various sources of dyes, their impact on the environment and human health, and strategies for their removal from the environment with a special focus on microbial degradation.