Photochemical UVC/H2O2 oxidation system as an effective method for the decolourisation of bio-treated textile wastewaters: towards onsite water reuse

Abstract

A photochemical UVC/H₂O₂ oxidation system was applied for the decolourisation of two real textile wastewaters, textile wastewater A – TWA and textile wastewater B – TWB – collected after biological oxidation from two different textile wastewater treatment plants. The photochemical oxidation assays were performed in a lab-scale photo-reactor, where a borosilicate tube is associated to an internal concentric quartz tube filled with a UVC lamp (6 W). Photochemical reaction rates were determined under different operational conditions: H₂O₂ dosage (0–40 mM), pH (3, 5 and 9) and temperature (15, 23 and 35 °C). For both TWA and TWB, it was observed a positive influence on the UVC/H₂O₂ efficiency at higher hydrogen peroxide dosages and wastewater temperature. However, the pH conditions differently affected each wastewater. Although the dissolved organic content remained almost similar during the UVC/H₂O₂ reaction period, the biodegradable organic fraction increased for values higher than 40%. To achieve the colour discharge limits imposed by the Brazilian regulations, it was necessary 180/75 min of UVC irradiation (8.3/3.4 kJ_UVC L⁻¹) using an H₂O₂ dose of 25.0 mM, natural pH of 8.1/7.7 and T = 23 °C, respectively for the TWA/TWB. The photochemical-treated textile wastewater – PTWB was used as bathwater during bleaching and dyeing of cotton fibres in order to assess its onsite reuse in the textile manufacturing process. Compared with the same bleaching process made with distilled water, all quality indicators monitored showed small differences, which demonstrate the possible reuse of PTWB in this process. Finally, reuse of PTWB mixed with 50% distilled water as bathwater in the dyeing process with Direct Blue 71 resulted in similar samples (ΔE* = 0.76) when compared with standard dyeing process.