The objective of this study is to analyze the photodegradation of the antibiotic tetracycline by the solar photo-Fenton process. The optimal conditions were obtained in a 2 2 (2 × 2) factorial design with the following input variables: reaction time and catalyst concentration (ferrous ion [Fe 2+ ]). After statistical analysis using the Statistica 7.0 software, the optimal conditions determined, time = 120 min and Fe 2+ = 166.81 mg/L, were applied in a pilot scale photoreactor, resulting in an 88.7% removal of the drug. In addition, in this stage we studied the reaction kinetics, biodegradability, and phytotoxicity of the products generated by the process. In the kinetic study, a constant of 1.82 × 10 −2 min −1 was obtained. For this constant, a reaction time of 38.16 min is required for the initial tetracycline concentration to be reduced by 50%. The biodegradability tests indicated a gradual increase in the five-day biological oxygen demand/chemical oxygen demand ratio over time. The phytotoxicity tests showed an 18.5% decrease in the inhibition rate of the root growth of lettuce seedlings, indicating that the treatment applied reduces the toxicity of the substance. K E Y W O R D Sbiodegradability, photo-Fenton, photoreactor, phytotoxicity, solar photocatalysis, tetracycline
Solar photocatalytic studies were carried out using zinc oxide (ZnO) as a catalyst for the removal of the cationic methylene blue (MB) dye, and the anionic dye reactive red 198 (RR198), from simple and binary mixed solutions. The following parameters were experimentally investigated: catalyst concentrations (50-250 milliliters [ml]), initial pH of the solution (5, 7, and 9), and time of exposure (20-120 minutes [min]). The catalyst concentration has been found to be the variable with the greatest significance of the three, leading to degradation rates of up to 98% and 100%, for MB and RR198 dyes, respectively. When it comes to the RR198 dye, considerable decolorization rates (up to 75%) were achieved even at the shortest time interval (20 min). The results indicated that, especially for the RR198 dye, the majority of the color removal during the photocatalysis process was due to the adsorption of the dye onto the ZnO surface. Batch scale experiments were performed by mixing both MB and RR198 dyes in order to simulate a synthetic effluent.Color removal rates up to 98% were achieved after 90 min of sunlight exposure. Experiments in a pilot-plant based on compound parabolic collectors were performed under the same conditions, and similar results were obtained. In addition, organic matter removal was investigated and rates up to 70% were achieved. The results showed the feasibility of the solar photocatalysis process with ZnO to achieve considerable rates of color removal from wastewater containing dyes from different classes.
O presente trabalho avaliou a eficiência do pré-tratamento do lixiviado bruto de aterro sanitário por coagulação/floculação seguido do processo oxidativo homogêneo solar (H2O2/UV). Foram realizados ensaios em Jar-Test, com o Al2(SO4)3 e o FeCl3, a fim de determinar as melhores condições para a coagulação/floculação, tendo como variáveis-resposta: a remoção de cor verdadeira e turbidez. Em seguida, a melhor condição de cada coagulante foi submetida ao processo H2O2/UV solar, sendo as amostras avaliadas quanto a cor verdadeira, turbidez e DQOtotal. Na combinação da coagulação/floculação com Al2(SO4)3 (600 mgAl2+L-1, pH 5), seguida pelo processo H2O2/UV solar, conseguiram-se remoções de 95,26% de cor verdadeira, 69,36% de turbidez e 53,92% DQOtotal. Já o processo com FeCl3 (450 mgFe3+L-1, pH 4) seguido por H2O2/UV solar obteve remoções de 97,01% de cor, 79,57% de turbidez e 62,85% de DQOtotal. Concluiu-se que o tratamento utilizado foi eficiente, podendo auxiliar na aplicação posterior de um tratamento biológico. Palavras-chave: Tratamento fisico-químico. Al2(SO4)3, FeCl3.
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