E. Tello Rendón

The photocatalytic disinfection of urban waste waters

In this paper we present the results of the photocatalytic disinfection of urban waste water. Two microbial groups, total coliforms and Streptococcus faecalis, have been used as indexes to test disinfection efficiencies. Different experimental parameters have been checked, such as the effect of TiO2, solar or UV-lamp light and pH. Disinfection of water samples has been achieved employing both UV-lamp and solar light in agreement with data shown by other authors. The higher disinfection rates obtained employing an UV-lamp may be explained by the stronger incident light intensity. Nevertheless no consistent differences have been found between TiO2-photocatalysis and direct solar or UV-lamp light irradiation at natural sample pH (7.8). At pH 5 the presence of TiO2 increases the relative inactivation rate compared with the absence of the catalyst. After the photocatalytic bacterial inactivation, the later bacterial reappearance was checked for total coliforms at natural pH and pH 5, with and without TiO2. Two h after the photocatalytic treatment, CFU increment was almost nill. But 24 and 48 h later an important bacterial CFU increment was observed. This CFU increment is slower after irradiation with TiO2 at pH 5 in non-air-purged samples.

TiO2 activation by using activated carbon as a support: Part I. Surface characterisation and decantability study

In the present work, the effect of mixing TiO2 with different portions of activated carbon (AC) has been studied. Transmission electron microscopy (TEM), scanning electron micrograph (SEM), laser scattering, FTIR and UV spectrophotometric analysis have shown changes of some of the TiO2 physico-chemical characteristics in catalysts containing an AC concentration lower than 15% in weight. Changes in the catalyst colour, the vibration bands of the hydroxylic groups from FTIR studies and the UV absorption spectrum have been observed. It seems that these changes correspond with TiO2 acid–base changes. SEM and TEM studies show a perfect TiO2 particles distribution on the AC surface in catalysts with lower AC contents, that also yields a homogeneous particle size distribution. One of the most interesting features of the resulting catalysts is their fast decantability in comparison with that of TiO2. This way one of the most important drawbacks of photocatalysis, the catalyst separation from the solution, may be overcome. The present study shows that the AC not only exerts a synergistic effect when is combined with TiO2 as some authors suggest, but it also modifies the catalyst characteristics.

TiO2 activation by using activated carbon as a support: Part II. Photoreactivity and FTIR study

Abstract It has been demonstrated that the modification of the TiO2 acid–base properties by the presence of activated carbon (AC) considerably modify the interaction of some molecules with the catalyst surface and hence its photocatalytic characteristics. FTIR studies have shown that while phenol interacts with TiO2 yielding a phenoxide, in the catalyst low AC containing catalysts mixtures the surfacial hydroxylic groups are inserted in the aromatic ring in the symmetric position to the –OH group. Additionally, the 4-aminophenol study shows that the molecule interacts with the TiO2 surface by means of the amino group, while in the catalyst containing AC the interaction takes place through the hydroxylic group. These results have confirmed the catalyst acid–base properties changes determined by the characterisation studies already performed. Also, it has been observed that catalysts with the lowest AC content show better catalytic behaviour than the untreated TiO2 and those with higher AC load. Another interesting result is the efficiency of these catalysts under solar irradiation.

Highly concentrated phenolic wastewater treatment by the Photo-Fenton reaction, mechanism study by FTIR-ATR

Phenol degradation by Photo-Fenton reaction has been studied in highly concentrated wastewaters and most intermediate species have been identified by Fourier Transform IR-Spectroscopy with ATR device. During the photodegradation of highly concentrated phenol solutions, the formation of dissolved and precipitate tannin has been observed. The possibility of a Fe3+-Pyrogallol complex formation, previous to the tannin formation, has been proposed too. The complex formation involving Fe3+ ions could be related to the observed Photo-Fenton activity decrease. Tannin formation inhibits the complete mineralization of phenol because *OH radicals attack will produce further condensation steps and the polymer size increase. This fact limits the applicability of the process for highly concentrated phenolic wastes mineralization. However, the tannin precipitation allows its separation from the solution by conventional filtration, and reduction of the corresponding dissolved organic carbon. These observations have been proved from the identification of primary degradation products, catechol and hydroquinone. Catechol is considered to be the first step for the formation of tannins. Degradation process for phenol, catechol and hydroquinone have been monitored by total organic carbon (TOC) measurements along the reaction time span. From these results, a global mechanism for the Photo-Fenton degradation of phenol is proposed.

Comparative Study of Phenolics Degradation Between Biological and Photocatalytic Systems

Phenol and phenol compounds are toxic organics that can be found in many industrial wastewaters. Biological wastewater treatments are considered to be the most convenient methods owing to their efficiency and low economic cost. Nonetheless, many organic pollutants are refractory to bacterial degradation. Photocatalytic methods can be an interesting alternative as pretreatment to improve biodegradability and reduce toxicity of industrial effluents. The goal of this study was to compare and combine TiO 2 -photocatalysis with constructed wetlands to obtain a low-cost method for the treatment of phenolic wastewater. The degradation of phenol was studied by means of Ti0 2 -Photocatalysis (solar and UV-lamp) in batch reactors. The degradations of phenol and two of its photocatalytic degradation intermediates, catechol and hydroquinone, were studied in wetland reactors with and without two wetland plants: common reed (Phragmites australis) and papyrus (Cyperus alternifolius). The application of pseudo first-order kinetics to the elimination of phenol in the wetland reactors provided high correlation coefficients (R 2 = 0.85 _ 0.99 ), allowing the comparison of the biological and photocatalytic methods. Although higher concentrations of phenol (250-400 mg/l ) could be treated, the elimination of 50 ppm was usually accomplished in batch experiments in less than 15 h, the time in which low or nil solar radiation is available for TiO 2 -photocatalysis. As a consequence, this concentration can be considered to be the upper limit for the wetland influent. The degradations of catechol and hydroquinone showed higher rate constants (0.2-0.4 h- 1 ) than that of phenol (about 0.15 h -1 ), particularly in the reactor with common reed (1-2 h -1 ). The degradation of phenol by the photocatalytic methods was three to four times faster than those obtained with the wetland reactors. By using solar TiO 2 -photocatalysis, concentrations of phenol up to 100 ppm were reduced down to 16 ppm and 27 ppm of phenol and hydroquinone, respectively, in about 7 h. However, it was toxic. When this sample was continuously (38 ml/min) added to wetland reactors with common reed, phenol and hydroquinone concentrations were below their detection limits (J ppm and 2 ppm, respectively). Solar Ti0 2 -Photocatalysis is a promising technique for the treatment of phenol but its application is limited to daytime periods with appropriate weather conditions. Constructed wetlands can also eliminate phenol and phenolic compounds without these limitations, but the toxicity of the influent must be as low as possible. The combination of both methods can provide a low-cost method for the treatment of phenolic wastewater.

FTIR study of the photocatalytic degradation of NH4+ determination wastes

In this work we present the results of the application of photocatalytic techniques to organic pollutants in water. Such aqueous wastes are produced during the UV-Vis spectrophotometric determination of the NH 4 + ion in water. Processes taking place during the photocatalytic degradation of such organics have been studied by using FTIR, HLPC and TOC measurements. The obtained results suggest that in the presence of light, air and a catalyst (TiO 2 or Fe 2+ ) one of the existing organics, nitroprusside is decomposed to C≡N - , NO 2 - and NO 3 -. Free C≡N - ions react with other intermediates yielding nitrogen-containing compounds such as acetaloximes and acetamides. The photocatalytic degradation of this kind of N-containing compounds seems to be more complicated than the corresponding alcohols and carboxylic groups generated during the individual degradation of phenol, citrate or ethanol. A remarkable affinity of those nitrogenated species in adsorbing onto the TiO 2 surface has been observed. This may be the cause of the reduced catalyst activity observed in the process. It has been also determined that C≡N - ions tend to react with Fe 3+ ions to give complexes like [C≡N-Fe] 2+ and [R-C≡N-Fe] 2+ inhibiting this way the photo-Fenton reaction. In fact, no organic carbon reduction was observed during the application of the photo-Fenton reaction or TiO 2 photocatalysis. Toxicity of the samples was determined before and after the application of the photo-Fenton reaction and TiO 2 photocatalysis. Toxicity as determined by using the algal species Phaedactylum tricornutum after the photocatalytic treatment was higher. This suggests the possible above mentioned recombination of chemical species during the degradation of the samples.

Conventional and photocatalytic degradation of aromatic amines from nitrite determination wastes

Different methods such as KMnO4 oxidation, TiO2-photocatalysis and photo-Fenton reaction have been employed for the degradation of wastes from the spectrophotometric determination of in seawater. The optimisation of the degradation process was determined by total organic carbon (TOC) measurements. Experimental parameters such as pH, TiO2, H2O2, Fe3+ or Fe2+ concentrations have been checked. The highest TOC reduction was achieved by applying the photo-Fenton reaction with 0.02 g of FeSO4 and 3 mL of H2O2 for every 100 mL of sample. Mean TOC reductions of about 78 and 47% were achieved by photo-Fenton reaction and TiO2-photocatalysis, respectively. The addition of potassium oxalate to the photo-Fenton reaction enhanced the mineralisation efficiency. The mineralisation of individual components of the samples by photo-Fenton reaction was also attempted. Sulphanilamide was degraded to a large extent since TOC reductions of about 83% were achieved. In contrast N-(1-naphtyl-)-ethylenediamine degradation was negligible and TOC reduction was never larger than 6%. Degradation of N-(1-naphtyl-)-ethylenediamine by KMnO4 yielded a TOC reduction of 40.89%. The application of a KMnO4 pretreatment enhances the oxalate--photo-Fenton reaction efficiency by greatly reducing the irradiation time. The solar photo-Fenton reaction of the sample gave a TOC reduction of about 70%. After the treatment wastes lose their characteristic pink colour becoming nearly transparent or showing a very subtle yellowish colour.