Photocatalysis for continuous air purification in wastewater treatment plants: from lab to reality.

The photocatalytic efficiency of TiO(2)-SiMgO(x) plates to oxidize H(2)S was first evaluated in a flat laboratory reactor with 50 mL min(-1) synthetic air containing 100 ppm H(2)S 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 H(2)S tests with pure TiO(2) because total H(2)S elimination was maintained for more than 30 operating hours with SO(2) 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 TiO(2)-SiMgO(x) 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 H(2)S contained in a 1 L min(-1) air current with a variable inlet concentration in the range of tens of ppmv without release of SO(2).

Identification and photocatalytic destruction of malodorous compounds in sewage.

Malodorous compounds were identified in sewage samples using two different types of pre-concentration procedures: (a) pre-concentration onto adsorbent column (Tenax), (b) liquid-liquid extraction, in conjunction with sensory analysis. Sulphur and nitrogen containing compounds, hydrocarbons, substituted benzenes and components of essential oils and aldehydes were identified. These compounds were considered to be responsible for the septic and grassy/earthy odour described by sensory panellists. Studies on photodestruction of malodorous compounds present in the sewage samples showed that the main compounds were destroyed. This destruction was confirmed by both sensory analysis and gas chromatography through abatement in the intensity of odour as well as chromatogram peak areas. Comparing odour destruction using two processes, photocatalysis and loss due to mass transfer, the conversion rate was 71% at the beginning, later reaching a plateau of about 65%. Thus photocatalysis seems to be a promising technology in the degradation of malodorous compounds stripped to the atmosphere from sewage, especially when they are present at low concentrations.