Photoactivation and photoregeneration of TiO2/PAC mixture applied in suspension in water treatments: approach to a real application

Environmental Science and Pollution Research - The process TiO2/PAC/UV-vis has been under study and compared with the isolated treatments of adsorption and photocatalysis determining possible...     

Performance comparison of commercial TiO2: separation and reuse for bacterial photo-inactivation and emerging pollutants photo-degradation

This research aims to compare the disinfection and degradation effectiveness in water of a commercial suspension of nano-TiO₂ (TiO₂Levenger) with the standard TiO₂Degussa P25. Photo-inactivation and photo-degradation experiments were conducted with UVA-vis light. Concerning the disinfection, the effects of TiO₂ dose (0–2 g/l), water matrix, bacterium type (Gram-positive or Gram-negative), and bacterial regrowth after the photo-treatments were studied for each catalyst. The experimental results show that Enterococcus sp. (Gram-positive) was more resistant to the photo-treatments than Escherichia coli (Gram-negative) for both catalyst; however, postirradiation trends showed similar behavior for both bacteria, favoring regrowth for short-treated cells and decay for longer-treated ones. Caffeine was selected as a model substance of pharmaceuticals and personal care products. In terms of caffeine removal, the effects of TiO₂ dose (0–2 g/l) and water matrix were analyzed. Besides, the comparison between mechanical coagulation-flocculation-decantation and simple decantation of TiO₂ was carried out. The results show that simple decantation allowed the recovery of 97.5% of TiO₂ Degussa P25 and TiO₂ Levenger within 1 day of simple decantation, while applying the proposed mechanical coagulation-flocculation decantation 99.7% of recovery of both catalysts was achieved in 2 hours. Finally, the subsequent reuse of both catalysts was proved with little loss of efficiency in terms of photo-disinfection during the four cycles. Nevertheless, the standard TiO₂ Degussa P25 photo-degradation efficiency of caffeine decreases considerably as compared to commercial suspension of TiO₂ Levenger concerning the reutilization.

     

Levels and distribution of DDT in the Cinca River (Spain).

The evolution over time of the levels and distribution of dichlorodiphenyltrichloroethane (DDT) in water, surface sediments, and fish from the River Cinca (Spain), a tributary of the River Ebro, during the period 1999 to 2004, was investigated by means of gas chromatography coupled with mass spectrometry. The sampling site corresponded to a point downstream from Monzón, a heavily industrialized town with drainage into the river. This river has historically been a source of emissions of DDT and its metabolites. The highest levels were found in 1999 and 2000, although the concentrations of organic compounds in sediments and fish have decreased since then. The levels of DDT in water were below the quantification limit during the period of study. The average composition of DDT isomers measured in sediments and fish showed the prevalence of p,p'-DDE, the product of aerobic degradation of p,p'-DDT. Concentrations in fish were compared with sediment samples, and high quotients indicate that they are highly bioavailable.     

Inactivation of <Emphasis Type="Italic">Escherichia coli</Emphasis> in fresh water with advanced oxidation processes based on the combination of O<Subscript>3</Subscript>, H<Subscript>2</Subscript>O<Subscript>2</Subscript>, and TiO<Subscript>2</Subscript>. Kinetic modeling

The purpose of this work was to study the efficiency of different treatments, based on the combination of O₃, H₂O₂, and TiO₂, on fresh surface water samples fortified with wild strains of Escherichia coli. Moreover, an exhaustive assessment of the influence of the different agents involved in the treatment has been carried out by kinetic modeling of E. coli inactivation results. The treatments studied were (i) ozonation (O₃), (ii) the peroxone system (O₃/0.04 mM H₂O₂), (iii) catalytic ozonation (O₃/1 g/L TiO₂), and (iv) a combined treatment of O₃/1 g/L TiO₂/0.04 mM H₂O₂. It was observed that the peroxone system achieved the highest levels of inactivation of E. coli, around 6.80 log after 10 min of contact time. Catalytic ozonation also obtained high levels of inactivation in a short period of time, reaching 6.22 log in 10 min. Both treatments, the peroxone system (O₃/H₂O₂) and catalytic ozonation (O₃/TiO₂), produced a higher inactivation rate of E. coli than ozonation (4.97 log after 10 min). While the combination of ozone with hydrogen peroxide or titanium dioxide thus produces an increase in the inactivation yield of E. coli regarding ozonation, the O₃/TiO₂/H₂O₂ combination did not enhance the inactivation results. The fitting of experimental values to the corresponding equations through non-linear regression techniques was carried out with Microsoft® Excel GInaFiT software. The inactivation results of E. coli did not respond to linear functions, and it was necessary to use mathematical models able to describe certain deviations in the bacterial inactivation processes. In this case, the inactivation results fit with mathematical models based on the hypothesis that the bacteria population is divided into two different subgroups with different degrees of resistance to treatments, for instance biphasic and biphasic with shoulder models.

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Pesticides removal in the process of drinking water production

The aim of this research work was to study the effectiveness of the treatments commonly used in drinking water plants in Spain to degrade 44 pesticides systematically detected in the Ebro River Basin. The pesticides studied are: alachlor, aldrin, ametryn, atrazine, chlorfenvinfos, chlorpyrifos, pp'-DDD, op'-DDE, op'-DDT, pp'-DDT, desethylatrazine, 3,4-dichloroaniline, 4,4'-dichlorobenzophenone, dicofol, dieldrin, dimethoate, diuron, alpha-endosulphan, endosulphan-sulphate, endrin, alpha-HCH, beta-HCH, gamma-HCH, delta-HCH, heptachlor, heptachlor epoxide A, heptachlor epoxide B, hexachlorobenzene, isodrin, 4-isopropylaniline, isoproturon, metholachlor, methoxychlor, molinate, parathion methyl, parathion ethyl, prometon, prometryn, propazine, simazine, terbuthylazine, terbutryn, tetradifon and trifluralin. The techniques applied are: preoxidation by chlorine or ozone, chemical precipitation with aluminium sulphate and activated carbon adsorption. Oxidation by chlorine removes 60% of the studied pesticides, although combining this technique with a coagulation-flocculation-decantation process is more effective. The disadvantage of this treatment is the formation of trihalomethanes. Oxidation by ozone removes 70% of the studied pesticides. Although combination with a subsequent coagulation-flocculation-decantation process does not improve the efficiency of the process, combination with an activated-carbon absorption process gives rise to 90% removal of the studied pesticides. This technique was found to be the most efficient among the techniques studied for degrading the majority of the studied pesticides.