Photocatalysis for Continuous Air Purification in Wastewater Treatment Plants: From Lab to Reality

The photocatalytic efficiency of TiO2–SiMgOx plates to oxidize H2S was first evaluated in a flat laboratory reactor with 50 mL min–1 synthetic air containing 100 ppm H2S in the presence of humidity. The use of the photocatalyst-adsorbent hybrid material enhanced the photocatalytic activity in terms of pollutant conversion, selectivity, and catalyst lifetime compared to previous H2S tests with pure TiO2 because total H2S elimination was maintained for more than 30 operating hours with SO2 appearing in the outlet as reaction product only after 18 h. Subsequently, the hybrid material was successfully tested in a photoreactor prototype to treat real polluted air in a wastewater treatment plant. For this purpose, a new tubular photocatalytic reactor that may use solar radiation in combination with artificial radiation was designed; the lamp was turned on when solar UV-A irradiance was below 20 W m–2, which was observed to be the minimum value to ensure 100% conversion. The efficient distribution of the opaque photocatalyst inside the tubular reactor was achieved by using especially designed star-shaped structures. These structures were employed for the arrangement of groups of eight TiO2–SiMgOx plates in easy-to-handle channelled units obtaining an adequate flow regime without shading. The prototype continuously removed during one month and under real conditions the H2S contained in a 1 L min–1 air current with a variable inlet concentration in the range of tens of ppmv without release of SO2.