Comparison of UV based AOPs using mercury lamp and LED diode as irradiation source: kinetic tests with spectroscopic parameters using different radical promoter agents

Aim of this study was to investigate and compare the production of radical species by two UV based Advanced Oxidation Processes using two different irradiation sources: a traditional mercury lamp and innovative LED diode. Production of radical species was evaluated by using UV absorbance and fluorescence measurements, which have been shown to be very effective parameters for online monitoring of very different wastewater treatment processes. In details, investigations were performed using wastewater effluents after filtration at 0.45 μm. The AOP technology applied were UV/H2O2 and UV/Cl2. Hydrogen peroxide was used in two different dosage (30 mg/L, 50 mg/L) and Chlorine in one dosage (5 mg/L). Results were analyzed monitoring three main parameters coming from Fluorescence (fluorescence indices at defined excitation/emission wavelengths: I3(245/440 nm), I4(275/345 nm) and I5(345/440 nm)) and UV absorbance at 254 nm (UV254) to have an understanding about the rate constant, degradation and also the electrical energy consumption. After carrying out all the experiments, results showed the lowest electrical energy consumption with highest reduction of fluorescence and UV254 signals when using 5 mg/L of Chlorine coupled with UV-LED instrument. In general, in terms of spectroscopic parameters removal, UV-LED lamp was more effective with Cl2, while with H2O2 mercury lamp allowed to reach higher degradation rate at the tested concentration of radical promoters (i.e.; H2O2 and Cl2). In terms of energy consumption LED lamp showed better results with lower consumptions when using chlorine as radical promoter. It has been concluded that the following research gaps need to be filled: optimization of radical promoter concentration to increase degradation kinetics and reduce energy costs, and testing of additional radical promoter such as sodium persulfate.