Photocatalytic discolouration of Reactive Black 5 by UV-A LEDs and solar radiation

Abstract

A B S T R A C TOne of the most important disadvantages of photocatalytic treatments is the high cost associated with the use of UV lamps. In this work, the efficiency of two UV-A LEDs (ultraviolet-a light emitting diodes) photosystems as a low cost alternative to conventional UV lamps was tested. The efficiency of the two UV-A LEDs photosystems was compared to that of the most economical UV source-solar radiation. To this end, the oxidative discolouration of Reactive Black 5 (RB5) aqueous solutions was studied using photocatalysis with different concentrations of TiO 2 (0.5-1 g/L) and H 2 O 2 (1.76, 4.41, 8.82 and 17.64 mM), exposed to different radiation sources: UV-A LEDs and solar radiation. The use of H 2 O 2 increased the discolouration rate of RB5; however, an excessive dosage reduced the yield of the treatment, and the best results were attained with a concentration of 8.82 mM of H 2 O 2 . Strong differences were observed between the use of UV-A LEDs (23 W/m 2 ) and solar radiation. In both cases total discolouration was observed, but the discolouration rate was considerably higher with solar radiation. However, the use of a more powerful UV-A LED photo-system (85 W/m 2 ) allowed the achievement of higher discolouration rates (k = 0.284 min À1 ) than those obtained with solar radiation (k = 0.189 min À1 ) using only 0.5 g/L of TiO 2 . Therefore, UV-A LED radiation is a serious alternative to conventional UV lamps, since they are ecofriendly, have a low operational cost and high energy efficiency.

Disinfection of simulated and real winery wastewater using sulphate radicals: Peroxymonosulphate/transition metal/UV-A LED oxidation

“…The treatments were carried out with an RMS current intensity of 240 mA, corresponding to a UV irradiance of 23 W/m 2 and a photon flux of 5.53 Â 10 À7 E/s. The application of this UV-A LED photo-system with successful results in the degradation of organic compounds has previously been reported (Rodríguez-Chueca et al, 2015, 2016aFerreira et al, 2016).…”

Treatment of Agro-Industrial Wastewaters by Coagulation-Flocculation-Decantation and Advanced Oxidation Processes—A literature Review

“…(3) Conventional UV-C lamps (primarily mercury lamps) present several problems: overheating, short lifetime, low photonic efficiency, and environmentally-unfriendly properties. LED lights appear to be a viable alternative since they present longer lifetimes, lower energy consumption, higher efficiency, do not overheat, and are less harmful to the environment [12].…”

“…Two additional reactions take place in the photo-Fenton process: (1) photoreduction of Fe 3+ to Fe 2+ ions (Equation ( 2)) [10] and (2) hydrogen peroxide photolysis via shorter wavelengths (Equation ( 3)) [11] + hv → 2HO • ; ʎ < 310 nm (3) Conventional UV-C lamps (primarily mercury lamps) present several problems: overheating, short lifetime, low photonic efficiency, and environmentally-unfriendly properties. LED lights appear to be a viable alternative since they present longer lifetimes, lower energy consumption, higher efficiency, do not overheat, and are less harmful to the environment [12].…”

Treatment of winery wastewater by sulphate radicals: HSO 5 − /transition metal/UV-A LEDs

“…The photo-assisted PMS/metal reactions were carried out in a lab-scale batch reactor which was illuminated with two different UV-A LED photo-systems [30,31]. The applied UV radiation in the first photo-system was generated by a matrix of 96 Indium Gallium Nitride (InGaN) LEDs lamps (Roithner RLS-UV370E) which illuminated an area of 11 x 7 cm 2 .…”