Assessment of indoor airborne contamination in a wastewater treatment plant.

The main objective of this work was to quantify and characterize the major indoor air contaminants present in different stages of a municipal WWTP, including microorganisms (bacteria and fungi), carbon dioxide, carbon monoxide, hydrogen sulfide ammonia, formaldehyde, and volatile organic compounds (VOCs). In general, the total bacteria concentration was found to vary from 60 to >52,560 colony-forming units (CFU)/m(3), and the total fungi concentration ranged from 369 to 14,068 CFU/m(3). Generally, Gram-positive bacteria were observed in higher number than Gram-negative bacteria. CO(2) concentration ranged from 251 to 9,710 ppm, and CO concentration was either not detected or presented a level of 1 ppm. H(2)S concentration ranged from 0.1 to 6.0 ppm. NH(3) concentration was <2 ppm in most samples. Formaldehyde was <0.01 ppm at all sampling sites. The total VOC concentration ranged from 36 to 1,724 µg/m(3). Among the VOCs, toluene presented the highest concentration. Results point to indoor/outdoor ratios higher than one. In general, the highest levels of airborne contaminants were detected at the primary treatment (SEDIPAC 3D), secondary sedimentation, and sludge dehydration. At most sampling sites, the concentrations of airborne contaminants were below the occupational exposure limits (OELs) for all the campaigns. However, a few contaminants were above OELs in some sampling sites.

Bacteria and fungi inactivation by photocatalysis under UVA irradiation: liquid and gas phase.

In the last decade, environmental risks associated with wastewater treatment plants (WWTPs) have become a concern in the scientific community due to the absence of specific legislation governing the occupational exposure limits (OEL) for microorganisms present in indoor air. Thus, it is necessary to develop techniques to effectively inactivate microorganisms present in the air of WWTPs facilities. In the present work, ultraviolet light A radiation was used as inactivation tool. The microbial population was not visibly reduced in the bioaerosol by ultraviolet light A (UVA) photolysis. The UVA photocatalytic process for the inactivation of microorganisms (bacteria and fungi, ATCC strains and isolates from indoor air samples of a WWTP) using titanium dioxide (TiO2 P25) and zinc oxide (ZnO) was tested in both liquid-phase and airborne conditions. In the slurry conditions at liquid phase, P25 showed a better performance in inactivation. For this reason, gas-phase assays were performed in a tubular photoreactor packed with cellulose acetate monolithic structures coated with P25. The survival rate of microorganisms under study decreased with the catalyst load and the UVA exposure time. Inactivation of fungi was slower than resistant bacteria, followed by Gram-positive bacteria and Gram-negative bacteria. Graphical abstract Inactivation of fungi and bacteria in gas phase by photocatalitic process performed in a tubular photoreactor packed with cellulose acetate monolith structures coated with TiO2.

Synthesis and characterization of N-modified titania nanotubes for photocatalytic applications.

The modification of titanate nanotubes (TiNT) with nitrogen (NTiNT) was accomplished through impregnation method. TiNT were synthesized via hydrothermal treatment of titania powders in NaOH solution at 130 °C for 48 h. The obtained samples were characterized by UV-Vis absorption spectroscopy, Brunauer-Emmett-Teller (BET) surface area, XRD, TEM, XPS, and TG analysis. Structure, morphology, composition, and visible light absorption property of nitrogen-modified TiO2 nanotubes are found to depend on the nitrogen content and not on the calcination temperature for the range used in this work. The photocatalytic activity of these nanotubes was investigated for the degradation of methylethylketone (MEK) and hydrogen sulfide (H2S) under ultraviolet and solar light radiation. MEK is very resistant to photocatalytic degradation with the prepared materials;, however, the results show that modification of the TiNT with nitrogen in a proportion of 1 to 1 (TiNT to urea weight ratio) and calcination at 400 °C lead to materials with high photocatalytic activity under ultraviolet radiation and moderate photocatalytic activity under solar radiation for degradation of H2S.

Solar photocatalytic gas-phase degradation of n-decane--a comparative study using cellulose acetate monoliths coated with P25 or sol-gel TiO2 films.

Cellulose acetate monoliths (CAM) were used as the substrate for the deposition of TiO2 films to produce honeycombed photoactive structures to fill a tubular photoreactor equipped with a compound parabolic collector. By using such a setup, an efficient single-pass gas-phase conversion was achieved in the degradation of n-decane, a model volatile organic compound. The CAM three-dimensional, gas-permeable transparent structure with a rugged surface enables a good adhesion of the catalytic coating. It also provides a rigid structure for packing the tubular photoreactor, and maximizing the illuminated catalyst surface. The efficiency of the photocatalytic oxidation (PCO) process on n-decane degradation was evaluated under different operating conditions, such as feeding concentration (73 and 146 ppm), gas stream flow rate (73, 150, and 300 mL min(-1)), relative humidity (3 and 25 %), and UV irradiance (18.9, 29.1, and 38.4 WUV m(-2)). The results show that n-decane degradation by neat photolysis is negligible, but mineralization efficiencies of 86 and 82 % were achieved with P25-CAM and SG-CAM, respectively, for parent pollutant conversions above 95 %, under steady-state conditions. A mass transfer model, considering the mass balance to the plug-flow packed photoreactor, and PCO reaction given by a Langmuir-Hinshelwood bimolecular non-competitive two types of sites equation, was able to predict well the PCO kinetics under steady-state conditions, considering all the operational parameters tested. Overall, the performance of P25-CAM was superior taking into account mineralization efficiency, cost of preparation, surface roughness, and robustness of the deposited film.