For photolytic experiments, the samples were irradiated with a UV lamp with an output of 254 nm operating at 50–60 Hz with a current intensity of 0.12 A at ambient temperature. The photolytic decolouration of carmine via UV radiation in the presence of H2O2 was optimized using response surface methodology (RSM) utilizing Design-Expert 7.1.
Carmine (C.I. Natural Red 4)
Under the optimized conditions of 62 M dye, 5.5 mM H2O2, and pH 4, the experimental values were as predicted, indicating the suitability of the model and the success of RSM in optimizing photooxidation conditions for carmine dye. In the optimization, and correlation coefficients for the quadratic model were evaluated quite satisfactorily at 0.998 and 0.997, respectively.
UV/TiO2/H2O2, UV/TiO2, and UV/H2O2 were compared as pretreatment processes to detoxification and treatment. The tubes were then irradiated for 40 h (initial concentrations of 50 mg/L) or 56 h (initial concentrations of 100 mg/L) at 300 W cm−2 with two 18 W UV bluelamps and an initial chlorophenol concentration of 50 mg/L.
4-Chlorophenol (4CP), 2,4-dichlorophenol (DCP), 2,4,6-trichlorophenol (TCP), and pentachlorophenol (PCP)
Chlorophenol photodegradation was well described by a first-order model kinetic ( > 0.94) and the shortest 4CP, DCP, TCP, and PCP half-lives were achieved during UV/TiO2/H2O2 treatment at 8.7, 7.1, 4.5, and 3.3 h, respectively.
A 60 W mercury vapour lamp (UV C, 253.7 nm) with a frequency of 50 Hz and a voltage of 240 V was used. The initial concentrations of H2O2 and melanoidin were manipulated while pH, flow rate, irradiated surface area, volume, lamp intensity, and temperature were kept constant. The relative change of each constituent was identified at various initial concentrations of H2O2 (up to 12000 mg/L) and melanoidin (263–5314 mg-Pt Co/L).
Melanoidin
UV/H2O2 was shown to remove the colour associated with melanoidin effectively. The process was less effective in removing the DON and DOC present in the melanoidin solution. At the optimum H2O2 dose (3300 mg/L), with an initial melanoidin concentration of 2000 mg/L, the removal of colour, DOC and DON was 99%, 50%, and 25%, respectively.
This study compared the efficacy of UV photodegradation with that of different advanced oxidation processes (O3, UV/H2O2, O3/activated carbon). Photo-irradiations were carried out using a merry-go-round photoreactor (MGRR), DEMA equipped with a 500 WTQ 718 Heraeus medium-pressure mercury lamp (239–334 nm) or a TNN 15/32 Heraeus low-pressure mercury lamp (254 nm). The temperature in the MGRR was kept at °C during all irradiations. The concentration of H2O2 used was 3 mM.
Naphthalene sulphonic acids
These results demonstrated that the treatment of naphthalene sulphonic acids with UV radiation is not effective in their removal from aqueous solutions. The presence of duroquinone and 4-carboxybenzophenone during the irradiation of naphthalene sulphonic acids increases their elimination rate. O3/activated carbon and UV/H2O2 based systems were found to be more efficient than the irradiation process in the removal of naphthalene sulphonic acids from aqueous solutions.
The reactor had a 1 L capacity and was equipped with a mercury medium-pressure steam UV lamp which was 110 mm in length and used 1000 W, 145 V, and 7.5 A. In the UV light/H2O2 flow reactor system, the initial concentration of sulphide was 6.34 mg L−1. The initial concentrations of sulphurous water were 6.34 mg L−1 of HS−, 1000 mg L−1 of , and 1.5 mg L−1 of . The amount of hydrogen peroxide added was of mL L−1.
Sulphurous water
In a batch reactor it was possible to demonstrate that the sulphur compounds of the sulphurous waters could be oxidized to sulphate in a UV light/H2O2 air system with very small concentrations of hydrogen peroxide ( mL L−1). In a flow reactor it was possible to obtain the same results by adding only mL L−1 of hydrogen peroxide.
Radiation energy was supplied by two lamps. Two different types of lamp were used: (1) two Philips TUV lamps with an input power of 15 W each and (2) two Heraeus UV-C lamps operated with an input power of 40 W each. Both types of lamp are low pressure mercury vapour lamps with one single significant emission wavelength at 253.7 nm. DCA concentration and radiation absorbing species concentration (H2O2) were 60 ppm, 145 ppm and pH and temperature were kept at 3.4 and 20°C, respectively.
Dichloroacetic acid (DCA)
The fastest degradation rate was obtained with the H2O2/UV40W system, followed by H2O2/UV15W. Although the photocatalytic process was effective in degrading DCA, the reaction rate was much slower when compared with the homogeneous processes. For the H2O2/UV40W reaction, the DCA conversion at s (ca. 4 h of reaction) is more than 80%, whereas the H2O2/UV15W system reaches half of this value. The DCA and TOC conversion values are similar in each process. This is in agreement with the fact that there are no stable reaction intermediates and DCA is rapidly converted into HCl and CO2.
Low pressure mercury vapour lamps with a maximum emission primarily at 253.7 nm were used as the light source. The changes in the pH of dye solutions as a function of the irradiation time for different initial pH values are carried out. The effect of the initial H2O2 concentration in a range of 10–100 mM on the rate of RO16 decolourization was investigated. The effect of the initial RO16 concentration in a range from 20 to 80 mg dm−3 on the efficiency of dye degradation was also investigated. The influence of UV light intensity on the decolourization of RO16 azo dye was monitored by varying the light intensity from 730 up to 1950 W cm−2.
Azo dye Reactive Orange 16
The UV/H2O2 process could be used efficiently for the decolourization of aqueous solutions of the azo dye Reactive Orange 16. It was found that the rate of decolourization is significantly affected by the initial pH, the initial hydrogen peroxide concentration, the initial dye concentration, and the UV light intensity. The decolourization follows pseudo first-order reaction kinetics. Peroxide concentrations in the range from 20 to 40 mM appear to be optimal. Colour removal was observed to be faster in neutral pH solutions than in acidic and basic ones. The hydroxyl radical scavenging effect of the examined inorganic anions increased in the order phosphate < sulphate < nitrate < chloride.
