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.