Dra. Yeber-Ortiz, Maria

Arsenic (III) is a common by product of mining activity. This contaminant can have a high environmental impact because it might accumulate in the food chain and seriously affect human health. The purpose of this study is to develop a method to remove arsenic (III) using the photo catalyst TiO2-N activated by visible light. The catalyst TiO2 Degussa P-25 was doped with nitrogen in order to narrow the energy gap and to work with radiation in the visible range. A multi variable approach was used in order to optimize the removal of arsenic, varying the concentration of the catalyst and the pH, maintaining the initial concentration of As (III) in 3 mg L–1. Two optima were determined, in one of which As (III) was reduced by 96.7% at pH 2, and in the other As was reduced by 80% at pH 7. Furthermore, the toxicity of the As (III) solutions was determined using Daphnia magna before and after the photochemical treatment. Mortality in the initial concentration was 87%. After the treatment at pH 2.0, a significant reduction in toxicity was recorded, with a mortality of only 30%.

Dyes used in the textile industry have varied and complex structures are designed to resist degradation by external agents. Most are water soluble, resistant to chemical agents and not biodegradable, so they cannot be easily removed by wastewater treatment plants. Remazol Brilliant Blue R (RBBR) is one of the most important colorants in the textile industry, and it is frequently used as a starting material in the production of polymer dyes. This work studied the degradation of a textile dye by a heterogeneous photocatalysis process, using a titanium dioxide catalyst doped with nitrogen from urea, in the presence of visible light irradiation. For the optimization of the process a Box-Benhken experimental design was performed. Where, the TiO 2 was varied from 0.1 gL ⁻¹ (-1) to 1.0 gL ⁻¹ (+1), and the pH between 2.0 (-1) to 11(+1). With the optimal response it was possible to remove 86.3% of the dye (R ² = 0.987 and Q ² = 0.873, p < 0.001). The mineralization grade was determined through TOC analysis, which reached 50%, and the toxicity was evaluated with Daphnia magna nematodes, which was reduced considerably after photocatalytic treatment.

The possibility of using electrocoagulation for efficient removal of pollutants in the industrial liquid waste of a textile industry was studied. The performance of the process was evaluated through the analysis of color, turbidity, and chemical oxygen demand (COD). The analysis was first done with the wastewater coming from the process of dyeing linen, which is the most polluting of all effluents that reach the residual effluent pool (REP). For the analysis, the MODDE 7.0 software was used to construct a statistical model. With the results obtained from this model and the experimental measurements, response surfaces were obtained. These response surfaces predicted the behavior of electrocoagulation for different values of the studied variables (pH, current density, and treatment time). Based on the obtained results, the wastewater coming from the REP was treated using the optimum values for the operational variables. After the treatment it was possible to remove 86% color, 82% turbidity, and 59% COD. It was demonstrated that reusing the treated water in the process of wool dyeing does not have a negative effect on the quality of the dyed fabric. Thus, it is possible to implement the process in the textile industry to reduce the consumption of water.

The combination of persulfate, zerovalent iron, and UV radiation is an advanced oxidation process which allows for the degradation of high concentrations of organic dyes. This process is based on the generation of transient species with high oxidizing power, mainly the hydroxyl radical (HO•) and the sulfate radical (SO•-4). The reaction was carried out in a cylindrical glass reactor using potassium peroxydisulfate as an oxidant and zerovalent iron as a catalyst. The reaction was performed in a radiation chamber using a Philips HP-120 W lamp (λ ≥ 254 nm). A Box–Behnken design and response surface methodology were employed to evaluate the effect of persulfate dosage (0.01 (−1)–0.05 (+1) g L−1), iron dosage (0.01 (−1)–0.05 (+1) g L−1), pH (2 (−1)–11 (+1)), and reaction time (10 (−1)–120 (+1) min) on the reduction of 100 mg L−1 of Kraft Lignin. Optimization of the process determined that optimal experimental conditions were acidic pH (3.5), a persulfate concentration of 0.05 g L−1, a zerovalent iron concentration of 0.01 g L−1, and 60 min of reaction time, which resulted in 92% removal of Kraft Lignin, 96% chemical oxygen demand, 94% phenols, and 61.1% total organic carbon. The results indicate that the photocatalytic system was efficient in degrading a high concentration Kraft Lignin, and experimental design allowed determination of the maximum efficiency, with a 95% confidence interval.