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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.

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The high polluting potential and variable content of the landfill leachate makes it a significant source of environmental contamination. Advanced oxidation processes (AOPs) such as Fenton process, arises as leachate treatment. Application of response surface methodology (RSM) from previous literatures evaluates the synergistic effects of independent variables to optimize the Fenton process. This paper presents systematic review on articles published from 2005 to 2015 reported on optimum conditions of Fenton treatment landfill leachate treatment using RSM. Papers were selected from different database according to defined inclusion criteria and then, evaluated. The best conditions identified were: pH around 3, [H2O2]/[Fe2+] molar ratio from 2.38 to 24.00, [H2O2]/[CODraw leachate] mass ratio around 1 and reaction time from 30 min to 331.2 min. All models presented R2 > 0.75, indicating a good correlation between the experimental data and the values predicted by the models.