RESUMEN
This work investigated the impregnation of Nb2O5 into carbon black (CB) in different ratios and its effect in photocatalytic degradation of real wastewater from a dyeing factory by advanced oxidative processes (AOP). Synthesized catalysts were characterized regarding their crystalline structure (DRX, micro-Raman), morphology (MEV), textural (BET area) and optical properties (bandgap energy by diffuse reflectance) and pH at the point of zero charge (pHpzc). Preliminary tests showed better photodegradation results in the acidic medium after 5â h of irradiation with NCB-0.5 (Nb2O5:CB 0.5:1). Treatment parameters optimization was carried out using response surface methodology based on Box-Behnken experimental design. Catalyst concentration, solution pH and irradiation time were varied, analysing absorbance reduction (285 and 574â nm), COD and TOC removal after treatment as responses. The composite catalyst showed improved photocatalytic activity, attributed to an increase in adsorption capacity and the bandgap narrowing, redshifting the absorption edge wavelength to the visible region, brought by CB impregnation. Optimal conditions were found at 0.250â gâ L-1 of catalyst, pH 2.0 and 5â h of irradiation, removing 72.19% and 93.52% of absorbance in 285 and 574â nm, respectively, 51.29% of COD and 70.70% of TOC using NCB-0.5.
Asunto(s)
Niobio , Aguas Residuales , Catálisis , Hollín , TextilesRESUMEN
The present work investigated the degradation of a dyeing factory effluent by advanced oxidative process under UV irradiation. TiO2 and ZnO were used as catalysts and the influence of different concentrations of H2O2 added to the system was studied. The catalysts were characterized in terms of crystal structure (X-ray diffraction), textural properties (Brunauer-Emmett-Teller area and pore volume) and point of zero charge, which indicated the semiconductors had a positively charged surface in an acidic medium. After 8â h of irradiation at pH 3.0 and catalyst concentration of 0.0625â gâ L-1, the effect of H2O2 was evaluated by means of kinetic efficiency (rate constants), absorbance reduction (at 284, 621 e 669â nm), total organic carbon reduction and mineralization (in terms of the formation of ions such as NH4+ and NO3- ). Adding H2O2 to the photocatalytic system significantly increased pollutants' removal, highlighting tests with 1.0 × 10-2â molâ L-1, showing higher absorbance reduction and rate constants at 621 and 669â nm for TiO2 and best mineralization rates for ZnO. Ecotoxicity bioassays using Artemia salina L confirmed the treatment efficacy, with effluent lethal concentration (LC50) increasing from 65.68% (in natura) to over 100% after photocatalysis treatment.
Asunto(s)
Contaminantes Químicos del Agua , Óxido de Zinc , Catálisis , Peróxido de Hidrógeno , Textiles , Titanio , Rayos Ultravioleta , Aguas ResidualesRESUMEN
Leachate is a highly variable, heterogeneous and recalcitrant wastewater generated in landfills which may contain high concentrations of many organic and inorganic compounds, hampering the application of a single technique in its treatment. Therefore, this paper assessed leachate degradation through supercritical water oxidation (ScWO) as well as combined processes of ozonation and supercritical water oxidation (O3/ScWO and ScWO/O3), a yet innovative combination. Ozonation was carried out at different reaction times (30-120â¯min). ScWO was developed at 600⯰C, 23â¯MPa, and spatial time (τ) from 29 to 52â¯s. A combination of ozonation (30â¯min) and supercritical water oxidation process (O3-30'/ScWO) was the most efficient technique for the degradation of the leachate assessed. These conditions enabled to remove high values of apparent and true color (92% and 97%, respectively), biochemical oxygen demand (BOD5,20) (95%), chemical oxygen demand (COD) (92%), total organic carbon (TOC) (79%), nitrite (78%), nitrate (84%), total (96%), dissolved (96%) and suspended (94%) solids. In addition, the combined process presented significant decrease in electric conductivity (EC) (68%) and less leachate turbidity removal (43%). Except for ammonia and nitrite, all parameters of the leachate treated by O3-30'/ScWO met the specifications of Brazilian legislation (CONAMA Resolutions No. 357/2005 and No. 430/2011) for the disposal of wastewater in water bodies. Besides, both processes are considered to be clean technologies. This shows the great possibility of applying the O3/ScWO combination to landfills leachates.