Degradation of Textile Dyes Employing Advanced Oxidative Processes: Kinetic, Equilibrium Modeling, and Toxicity Study of Seeds and Bacteria

Abstract

The textile industries’ production of effluents with a high content of organic matter and coloration is notorious, particularly as regards their effect on the aquatic environment. This occurs in the presence of dyes that inhibit light penetration, thus affecting the biodegradability of the medium. This study evaluates the advanced oxidative processes (AOP) for use in the degradation of the reactive red 195 and direct black 22 textile dyes using bench reactors. The photo-Fenton/sunlight process was efficient, achieving a degradation of over 99% for the chromophore groups after 150 min when utilizing [H2O2] = 60 mg L−1, [Fe] = 1 mg L−1, and a pH of between 3 and 4. The kinetic model into which the experimental data best fitted was the non-linear model which employs wavelength monitoring. The COD study indicated an organic matter conversion rate of 94.96%, with a good kinetic adjustment (R2= 0.9927. A mathematical model was proposed to estimate the degradation (%) according to the variables [H2O2], [Fe], pH, and λ. In addition, the present study evaluated the toxicity of the solution, both before and after the treatment, and was verified that the treated solution was toxic by using a concentration of 10% of Lactuca sativa and Syzygium aromaticum seeds. The toxicity analysis using microbiological techniques showed that, after the treatment, the percentage of inhibition was reduced considerably, dropping to 46.0% for the sample without dilution and inhibiting only 33.4% for SPT1%.