Abstract
One of the main limitations related to the industrial utilization of a photocatalytic process is the use of UV lamps that have several disadvantages such as the low quantum efficiency (QE). One of the approaches to increase the QE consists in the use of controlled periodic illumination (CPI). In this regard, Light Emitting Diodes (LEDs) are the best choice as light sources, since they can be electronically controlled by using LED dimming techniques, allowing variable turn-on and turn-off times on a microsecond time-scale.
The aim of this work is to investigate the influence of controlled modulation of LEDs light on the performances of a photocatalytic reactor for wastewater treatment using TiO2 immobilized on glass spheres (TiO2/GS).
The experiments were realized with a pyrex cylindrical batch photoreactor irradiated by three power UV-LEDs and placed surrounding the external body of the cylindrical photoreactor.
The system adopted for the controlled modulation of LEDs light is composed by a photovoltaic panel (PV), a dc–dc converter dedicated to the maximum power point tracking of the PV panel and a dc–dc converter dedicated to drive the UV LEDs. A system controller is also included, whose goal is to ensure matching between the maximum available PV power, the LED power and the resulting low-frequency LEDs dimming modulation. The experimental results showed that the use of certain types of duty-cycle dimming modulation waveforms, including periodic and non-periodic waveforms and combinations of them, have been discovered to improve the photo-catalytic reactor performances. In particular, the use of a modulation of LEDs dimming like sinusoidal and pseudo-sinusoidal waveforms is more effective than the fixed dimming. The best results in terms of methylene blue degradation (about 25% in less than 1 h) have been achieved with a pseudo- sinusoidal waveform.
