Solar TiO2 photocatalytic process assisted by a Fresnel lens was investigated for treating an azo dye wastewater of Acid Orange 10 (AO10). Response surface methodology (RSM) was employed to assess the effect of critical process parameters (including initial pH of wastewater, concentration of TiO2, and reaction time) on treatment performance in terms of COD and TOC degradation efficiency. Optimized reaction conditions based on the analysis of RSM were established under an initial pH of 6.0, a concentration of TiO2 of 1？g/L, and a reaction time of 2？h for reaching a 90% COD and TOC degradation of AO10 wastewater. With the assistance of Fresnel lens, the TOC degradation rate of AO10 wastewater increased significantly from 0.606？h？1 and 0.289？h？1 to 1.477？h？1 and 0.866？h？1 in summer (June) season (UV280–400？nm？nm: 39.9–44.8？W/m2) and winter (December) season (UV280–400？nm？nm: 23.9–26.9？W/m2), respectively. This could be mainly due to the concentrating effect of Fresnel lens for solar energy, resulting in an increase of 2~2.5 times of solar light intensity and a raising heat irradiation in terms of 10~15？°C of wastewater temperature. These results revealed that solar energy could be concentrated effectively by using Fresnel lens and showed a significant promoting effect on the TiO2 photocatalytic degradation of dye wastewater. 1. Introduction Over 100,000 different types of dyes are commercially available and 700,000 tons are produced yearly all over the world. Nearly 50% of these dyes are azo-type dyes . Azo dyes, aromatic moieties linked together by azo (–N=N–) chromophores, represent the largest class of dyes used in textile processing and other industries. The release of these compounds into the environment is undesirable, because the color matters and their toxic breakdown products can be mutagenic . In addition, due to the complex aromatic structure and stability of the azo-dyes, conventional biological treatments are ineffective for degradation and mineralization of the dye molecules . Instead, activated carbon adsorption or coagulation is commonly used. However, new environmental laws may consider the spent adsorbents or sludge as hazardous waste and require further treatment. Consequently, intensive research for novel technologies with higher efficiency and less amount of waste generated has been stimulated. Advanced oxidation processes (AOPs) have been previously described as a promising option to remove persistent pollutants from contaminated water . AOPs are able to produce a highly reactive, nonspecific oxidant, mainly hydroxyl
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