Homogeneous and heterogeneous AOPs for rapid degradation of Triton X-100 in aqueous media via UV light, nano titania hydrogen peroxide and potassium persulfate.

Feasibility of degradation of Triton X-100 as a widely used and resistive surfactant in aqueous media was studied via some homogeneous and heterogeneous AOPs of UV/TiO2, UV/H2O2 and UV/S2O8 2-. For treatment of solutions containing 20 mg/L of Triton, the optimum obtained conditions are: 5.0 mg/L of nano TiO2, 270.3 mg/L of KPS, and 34.0 mg/L of H2O2 (1 mM of the oxidants), initial natural pH of 5.4 and temperature of 45 °C. Under these conditions, the degradation efficiency for the UV/TiO2, UV/H2O2 and UV/S2O8 2- processes exceeds 71.9% (in 60 min), 80.9% (in 60 min) and 98.5% (in only 30 min) respectively. It was found that simultaneous application of these heterogeneous and homogeneous AOPs (UV/TiO2/H2O2 or S2O8 2-) is not desirable due to some physico-chemical retarding effects. The influence of temperature on the reactions was examined in the range of 15-45 °C and a kinetic power law model jointed with the Arrhenius equation was introduced. A pseudo first order reaction rate is appropriate for UV/S2O8 2- and UV/TiO2 processes under optimum conditions, while this order for UV/H2O2 process is 2.27. Meanwhile, the initial rates of degradation in UV/TiO2 process can be described well by the Langmuir-Hinshelwood kinetic model. Analysis of energy consumptions (thermal and electrical) revealed that increasing in temperature is an effective factor for lowering the energy cost of the preferred process of UV/S2O8 2-.

Sono-assisted photocatalytic degradation of styrene-acrylic acid copolymer in aqueous media with nano titania particles and kinetic studies.

The ultrasonic irradiation (28 kHz, 50 W) in pre-cavitations regime was employed to enhance the degradation rate of styrene-acrylic acid copolymer in aqueous media with nano titania photocatalyst particles. A stainless steel cylindrical sono-photo reactor with capacity of about 1.25 L, equipped with a UV lamp (250 W) was used. The influence of operational parameters, i.e. catalyst concentration, pH and temperature was studied and the role of active species was also distinguished. For an initial substrate concentration of 30 mg L(-1), under mild applied conditions of 30 mg L(-1) of photocatalyst, 25 degrees C and natural pH, a degradation and mineralization conversion of 96% and 91%, respectively, was achieved using sono-assisted photocatalysis process in about only 60 min. These efficiencies are much higher than those obtained with only photocatalysis process. Meanwhile, the threshold of cavitations was found corresponded to catalyst concentration of about 70 mg L(-1). Kinetic studies based on Langmuir-Hinshelwood and power law models in addition to the results from radical scavenger usage revealed that for sono-assisted process, the substrate undergoes degradation mainly via electron-hole redox on the surface of titania particles. It is while for the only photocatalysis process, the reaction proceeds via hydroxyl radicals in the solution bulk.

Degradation of the fungicide carbendazim in aqueous solutions with UV/TiO(2) process: optimization, kinetics and toxicity studies.

An attempt was made to investigate the potential of UV-photocatalytic process in the presence of TiO(2) particles for the degradation of carbendazim (C(9)H(9)N(3)O(2)), a fungicide with a high worldwide consumption but considered as a "priority hazard substance" by the Water Framework Directive of the European Commission (WFDEC). A circulating upflow photo-reactor was employed and the influence of catalyst concentration, pH and temperature were investigated. The results showed that degradation of this fungicide can be conducted in the both processes of only UV-irradiation and UV/TiO(2); however, the later provides much better results. Accordingly, a degradation of more than 90% of fungicide was achieved by applying the optimal operational conditions of 70 mgL(-1) of catalyst, natural pH of 6.73 and ambient temperature of 25 degrees C after 75 min irradiation. Under these mild conditions, the initial rate of degradation can be described well by the Langmuir-Hinshelwood kinetic model. Toxicological assessments on the obtained samples were also performed by measurement of the mycelium growth inhibition of Fusarium oxysporum fungus on PDA medium. The results indicate that the kinetics of degradation and toxicity are in reasonably good agreement mainly after 45 min of irradiation; confirming the effectiveness of photocatalytic process.

Enhanced photocatalytic degradation of pollutants in petroleum refinery wastewater under mild conditions.

A circulating photocatalytic reactor was used for removing aliphatic and aromatic organic pollutants in refinery wastewater. The TiO(2) added wastewater samples, while saturating with air, were irradiated with an immersed mercury UV lamp (400 W, 200-550 nm). Optimal catalyst concentration, fluid pH and temperature were obtained at amounts of near 100 mgL(-1), 3 and 318K, respectively. A maximum reduction in chemical oxygen demand of more than 90% was achieved after about 4h irradiation and hence, 73% after about only 90 min; significant pollutant removal was also achievable in the other conditions. The identification of the organic pollutants, provided by means of a GC/MS and a GC analysis systems, equipped with headspace injection technique, showed that the major compounds were different fractions of petroleum aliphatic hydrocarbons (up to C(10)) and the well-known aromatic compounds such as benzene, toluene and ethylbenzene. The results showed a high efficiency degradation of all of these pollutants.

Degradation and mineralization of Direct Blue 71 in a circulating upflow reactor by UV/TiO2 process and employing a new method in kinetic study.

Direct Blue 71 (C(40)H(23)N(7)Na(4)O(13)S(4)), an azo dye with a high worldwide consumption and providing toxic effluents, can be highly degraded using TiO(2) catalyst suspension and irradiation with a UV-C lamp in a circulating upflow photo-reactor with no dead zone. An initial concentration of 50 mgL(-1) of dye, within the range of typical concentration in textile wastewaters, was used. The influence of catalyst concentration, pH and temperature were investigated. The results showed that degradation of this dye can be conducted in the both processes of only UV irradiation and UV/TiO(2); but with the aim of mineralization, the later process provides significantly better results. Accordingly, a degradation of more than 97% of dye was achieved by applying the optimal operational parameters with 40 mgL(-1) of catalyst, natural pH and 45 degrees C, during 120 min irradiation. A removal of about 50% of COD could also be obtained at the same time. In kinetic investigations, the effect of catalyst particles' turbidity was taken into account and the rate of degradation of the dye, under mild conditions, was expressed as the sum of the rates of individual photolysis and photocatalysis process branches, with mainly influence of the bulk hydroxyl radicals.