Integration of heterogeneous photocatalysis (TiO2/UV) and activated sludge system operated in air lift reactor for the treatment of industrial effluent red water.

In the industrial production of the explosive 2,4,6-trinitrotoluene (TNT), purification steps are required to ensure the quality of the product, procedures that generate wastewater of a complex nature and with eco-toxicological potential, called red water, which consists of soluble sulfonates, TNT isomers, and other typical nitro aromatic compounds. The present work aimed to study the effects of integrating heterogeneous photocatalysis based on commercial TiO2, with a biological process, based on activated sludge, for red water treatment. For the photocatalytic treatment, a 72% reduction in the typical absorption of nitro aromatic compounds (the region between 195 - 275 nm), a 36% reduction in chemical oxygen demand (COD), and a 68% reduction in total phenols were obtained. In the biological treatment, there was a 60% reduction in absorbance in the typical nitro aromatics region (NA), 10% reduction in COD, and 36% reduction in total phenols (FT). The integration of photocatalytic and biological treatments showed promising results compared to the individual processes. Having 94% reduction in NA absorbance, 72% reduction in FT, and 89% reduction in COD with an association of photocatalytic pretreatment followed by biological, and reductions of 88% in NA absorbance, 62% in FT, and 87% in COD for a biological pretreatment followed by the photocatalytic process. In general, when comparing the chemical and biological processes, isolated and integrated, both types of integration showed significantly superior results. They were able to remove the main nitro aromatic constituents of the Red Water effluent.

Factorial design application in photocatalytic wastewater degradation from TNT industry-red water.

In trinitrotoluene (TNT) purification process, realized in industries, there are two washes carried out at the end of the procedure. The first is performed with vaporized water, from which the first effluent, called yellow water, is originated. Then, a second wash is performed using sodium sulfite, generating the red water effluent. The objective of this work was to get the best conditions for photocatalytic degradation of the second effluent, red water, in order to reduce toxicity and adjust legal parameters according to regulatory agencies for dumping these effluents into waterways. It has used a statistical evaluation for factor interaction (pH, concentration) that affects heterogeneous photocatalysis with titanium dioxide (TiO2). Thus, the treatment applied in the factorial experimental design consisted of using a volume equal to 500 mL of the effluent to 0.1 % by batch treatment, which has changed TiO2 pH and concentration, according to the design, with 20 min time for evaluation, where it was used as response to the reduction of UV-Vis absorption. According to the design responses, it has obtained optimum values for the parameters evaluated: pH = 6.5 and concentration of 100 mg/L of TiO2 were shown to be efficient when applied to red water effluent, obtaining approximately 91 % of discoloration.