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The effectiveness of UV-A Light emitting diodes (UV-A LEDs) for decolourization of Reactive Black 5 (RB5) solutions in a continuous photoreactor and the effect of different operational parameters on the photocatalytic decolourization of RB5 were investigated in the present work. The operational parameters included catalyst load, initial dye concentration, irradiance and solution flowrate. Photocatalytic experiments were conducted in a self-designed photoreactor with a matrix of 96 UV-A LEDs (375 nm) and Evonik P-25 TiO 2 was used as a photocatalyst. The optimum experimental conditions that allowed the highest decolourization of RB5 (89%) were an irradiance of 40 W/m 2 , 1.0 g/L of TiO 2 , 50 mg/L of RB5 and a flowrate of 0.8 mL/min.A continuous stirred tank reactor (CSTR) design equation, subsequently simplified to a pseudo-first order rate equation, was used to analyse the kinetics of the experimental results. From the kinetics it is possible to observe that high TiO 2 concentrations (1.0 g/L) and light irradiances (40 W/m 2 ) positively affect the reaction rate (r, 2.483 Â 10 À7 mol/L min) and the reaction rate constants (k, 7.351 Â10 À3 min À1 ).The figure-of-merit electrical energy per order (E EO ) was calculated for the photoreactor, and values of 220 kWh/m 3 /order were reached for an electric power consumption of 0.0129 kW and a solution flowrate of 4.8 Â 10 À6 m 3 /h. Results demonstrated that a UV-A LED/TiO 2 process can effectively decolourize RB5 dye solutions within the selected optimum conditions.

This contribution investigates the effect of solar activated persulfate and solar mild thermal heating for water disinfection (PS/solar). The basic effects of solar ultraviolet (UV) and thermal increase were separately studied for the inactivation of E. coli and E. faecalis. The process was studied in isotonic water (IW) and synthetic urban wastewater (SUWW) at bench and pilot scale (60 L-solar compound parabolic collector reactor). The thermal inactivation at 40 ºC and 0.5mM-PS shows a 3 log reduction value (LRV) for E. coli without lag phase and 5-LRV for E. faecalis with a lag phase of 1h, in 4 h of exposure. At 50 ºC the mere effect of temperature, overlaps the thermal activation of PS, being markedly fast. Effective accelerated disinfection effect by PS/solar (UVA and thermal) was observed. 6-LRV in E. coli and E. faecalis was determined for solar exposure periods of 20 min (solar dose), using 0.5 and 0.7 mM of PS in isotonic water, respectively. Longer solar exposure times were required to attain similar LRV in synthetic urban wastewater, in the presence of 25 mg/L of organic matter, i.e. 80 and 100 min (solar dose) for E. coli and E. feacalis, respectively. These results were confirmed at pilot scale, where 60 L of isotonic water were treated with 0.5 mM of PS in 50 min (solar dose). The PS/solar uses low cost chemical reagents (0.5 mM-PS) and a free source of energy (solar) to treat wastewater and achieve the high removal (6-LRV) of two model faecal indicators of water contamination, which opens a clear alternative to treat polluted water with organic matter and pathogens with implications in water-energy reclamation field.

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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.