Tratamento de Águas Cinzas por Processos Alternativos: Estudo Comparativo entre Adsorção e Processos Oxidativos Avançados

Abstract

The growing pressure on water resources has encouraged the development of alternative technologies for the treatment and reuse of domestic wastewater, including greywater. In this context, the present study evaluated the performance of adsorption processes and photo-assisted oxidative processes applied to the treatment of the dissolved fraction of greywater. Initially, a hydrocalumite - type layered double hydroxide (Ca–Al LDH) was synthesized by coprecipitation and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and simultaneous thermal analysis (TG/DTA). The results confirmed the formation of the characteristic lamellar structure of the material, with a basal spacing d003 of approximately 0.87 nm and thermal behavior typical of layered double hydroxides. Adsorption tests were coducted using 20 mL of greywater and different masses of adsorbents (0 - 200 mg) of hydrocalumite and activated carbon, with a fixed contact time of 60 min., evaluating the removal of dissolved organic matter by UV-Vis spectroscopy. Hydrocalumite showed a reduction of approximately 60% in absorbance at 254 nm, as well as a significant decrease in absorbance in the visible region of the spectrum, indicating contribution to effluent clarification. Activated carbon showed superior performance, with removals greater than 90% of absorbance at 254 nm at the highest dosages evaluated. Oxidative processes involving UV radiation, hydrogen peroxide H2O2, and the combined UV/H2O2 system were also investigated. UV radiation alone promoted changes in the spectral profile of dissolved organic matter, suggesting structural transformation of the compounds present. Isolated hydrogen peroxide at 9.8 mol/L with different volumes (0.1 mL, 0.5 mL, 1.0 mL, 1.5 mL, 2.0 mL, and 2.5 mL) showed low reactivity under the evaluated conditions. The UV/H2O2 system, however, wasevaluated under two oxidant dosage conditions (1 mL and 10 mL) in 200 mL of effluent, promoting more pronounced spectral modifications, indicating partial degradation of chromophores and the formation of detectable intermediates in the ultraviolet region. The results demonstrate that activated carbon has high efficiency in removing dissolved organic matter, whereas hydrocalumite shows moderate performance with potential application as a complementary adsorbent material. The photoassisted oxidative processes proved capable of promoting chemical transformations in the organic matter present in the effluent, highlighting the potential of the UV/H2O2 system as a transformation step in greywater treatment processes.