Photocatalytic activity in titanium dioxide (TiO₂) has been extensively studied because of its potential use in sterilization, sanitation, and remediation applications. The aim of the study reported here was to assess the feasibility of “fixed” TiO₂ as the photocatalyst for inactivating pathogenic bacteria selected, Staphylococcus aureus and Escherichia coli, from a water stream. The investigation was undergone in a properly designed laboratory-scale evaluation. Using the system reported here, we obtained an effective bactericidal capability for E. coli and S. aureus with 90.0% and 98.0% after 30 and 10 min ultraviolet-A light irradiation with fixed TiO₂, respectively. Parameters such as the various initial bacteria concentration, TiO₂ concentrations, interruption of illumination, turbidity, and coexisted organic matters were examined to identify the removal efficiency in the photocatalytic reaction. Results indicated the negative effect by high bacteria concentration, coexisted organic matters, and turbidity on inactivation of bacteria, and positive effect on disinfection was associated with higher TiO₂ concentration. Furthermore, our results indicated that under the same experimental conditions, the removal efficiency of the system in synthetic water was performed better than that of crude water. This inferior removal capability in crude water is mainly caused by the negative effect from the unknown coexisted factors.

This paper investigated the influence of low-intensity ultrasound in biological nitrification and denitrification. The results showed that the nitrification activity of activated sludge could not be promoted significantly by ultrasound in 5-40 min with intensities ranging from 0.1 to 1.2 W cm⁻². It suggested the fact that nitrifying bacteria were insensitive to ultrasound, possibly related with their specific structures of cell membrane and ways of metabolism. Whereas, biological denitrification was enhanced quite remarkably by ultrasound and the optimal results were achieved at the ultrasonic intensity of 0.2 W cm⁻² and the irradiation time of 10 min. Compared with the control without ultrasonic irradiation, it took 5 h for the enhancement of denitrification rates induced by the optimum ultrasound to reach its peak level (16%). Therefore, ultrasound with intensity of 0.2 W cm⁻² could be employed in the biological denitrification system for 10 min every 5 h to obtain the optimal effect theoretically.

Background, aim and scope Photochemical processes can decontaminate the aqueous environment from xenobiotics, but they also produce secondary pollutants. This paper presents field and laboratory evidence of the transformation of 4-chlorophenol (4CP) into 2-nitro-4-chlorophenol (2N4CP). Materials and methods Field monitoring of 4CP and 2N4CP was carried out by solid phase extraction coupled with liquid chromatography-multiple reaction monitoring mass spectrometry. Laboratory irradiation experiments were carried out under a UV-Vis lamp, and the time evolution of the compounds of interest was followed by liquid chromatography. Purpose The purpose of this study was elucidating the pathways leading to 2N4CP from 4CP in paddy field water. Results and discussion The field monitoring results suggest that 4CP can be transformed into 2N4CP in the paddy field water of the Rhône delta (Southern France). The laboratory study indicates that the transformation can take place via photonitration by •NO₂. The nitration process is inhibited by bicarbonate, possibly due to basification that favours the occurrence of the 4-chlorophenolate. The latter could consume •NO₂ without being nitrated. Photonitration in the presence of bicarbonate could account for the observed transformation in the field. Conclusions Photonitration of 4CP to 2N4CP by •NO₂ could account for the observed interconversion of the two compounds in paddy fields. The results are of concern because 2N4CP is biorecalcitrant and toxic. Recommendations and perspectives Bicarbonate can modulate the photonitration of 4CP into 2N4CP, which can be very significant in bicarbonate-poor waters.

Introduction In the present work, we explored the kinetics of dichlorvos (2,2-dichlorvinyl dimethyl phosphate, DDVP) decay through UV-A light-induced TiO₂ photocatalysis at pH 4 and 9, and the formation of degradation intermediates and final products under specific experimental conditions. Experimental observations and theoretical considerations allowed us to suggest the degradation mechanism of DDVP by the UV/TiO₂ process in aqueous solution. Methods The irradiation experiments were carried out in a photoreactor using a 228-W medium-pressure Hg vapor lamp. The concentration of DDVP, phosphate ion and formaldehyde as reaction intermediate, are determined spectrophotometrically. Chloride ion concentration was measured potentiometrically. Results The photocatalytic degradation rate of dichlorvos (DDVP) under UV irradiation (360-380 nm) was optimized with respect to the flow rate of O₂ gas sparged into the solution and photocatalyst concentration for a constant dichlorvos concentration (1.66×10⁻⁴ M) at pH 4. Kinetic data were obtained at pH 4 and pH 9 for dichlorvos and the inorganic species released through its photo-induced degradation. The proposed mechanism which assumes the formation of some toxic intermediates resistant to mineralization is supported by theoretical calculations and the observed inorganic mass balances. Conclusions The calculated pseudo-first-order rate constants were dependent on the dissolved oxygen level at low O₂ flow rate, but somewhat independent on the initial pH. The decrease of pH during the irradiation suggests the formation of organic acids. The presence of organic intermediates was confirmed also by TOC measurements. A plausible reaction mechanism of DDVP degradation through the UV-A/TiO₂ process was proposed.

Background, aims, and scope Heavy metal contaminants in environment, especially in drinking water, are always of great concern due to their health impact. Due to the use of heavy metals as catalysts during plastic syntheses, particularly antimony, human exposure to metal release from plastic bottles has been a serious concern in recent years. The aim and scope of this study were to assess metal contaminations leaching out from a series of recycling plastic bottles upon treatments. Methodology In this study, leaching concentrations of 16 metal elements were determined in 21 different types of plastic bottles from five commercial brands, which were made of recycling materials ranging from no. 1 to no. 7. Several sets of experiments were conducted to study the factors that could potentially affect the metal elements leaching from plastic bottles, which include cooling with frozen water, heating with boiling water, microwave, incubating with low-pH water, outdoor sunlight irradiation, and in-car storage. Results Heating and microwave can lead to a noticeable increase of antimony leaching relative to the controls in bottle samples A to G, and some even reached to a higher level than the maximum contamination level (MCL) of the US Environmental Protection Agency (USEPA) regulations. Incubation with low-pH water, outdoor sunlight irradiation, and in-car storage had no significant effect on antimony leaching relative to controls in bottle samples A to G, and the levels of antimony leaching detected were below 6 ppb which is the MCL of USEPA regulations. Cooling had almost no effect on antimony leaching based on our results. For the other interested 15 metal elements (Al, V, Cr, Mn, Co, Ni, Cu, As, Se, Mo, Ag, Cd, Ba, Tl, Pb), no significant leaching was detected or the level was far below the MCL of USEPA regulations in all bottle samples in this study. In addition, washing procedure did contribute to the antimony leaching concentration for polyethylene terephthalate (PET) bottles. The difference of antimony leaching concentration between washing procedure involved and no washing procedure involved (AC) was larger than zero for samples A to G. This interesting result showed that higher antimony concentration was detected in experiments with no washing procedures compared with those experiments with washing procedures. Our study results indicate that partial antimony leaching from PET bottles comes from contaminations on the surface of plastic during manufacturing process, while major antimony leaching comes from conditional changes. Conclusion The results revealed that heating and microwaving enhance antimony leaching significantly in PET plastic bottles. Plastic bottle manufacturers should consider the contaminations during manufacturing process and washing bottles before first use was strongly recommended to remove those contaminants.