Palm tree mulch as substrate for primary treatment wetlands processing high strength urban wastewater.

The life span of subsurface flow treatment wetlands is determined by the clogging of the substrate. Thus, the influent should undergo primary treatment to reduce loadings of suspended solids and dissolved organic matter. An-organic based substrate should be less prone to clogging because of its remarkably higher porosity and plasticity. Mulch obtained from branches of the Canarian palm tree (Phoenix canariensis) has been tested as substrate for mixed flow, intermittently fed treatment wetland mesocosms processing high strength urban wastewater. The effect of the presence of plants (Phragmites and Cyperus), influent pressure and hydraulic loading rate was studied. The best removals (SS: 89%, COD: 77%, turbidity: 82%) have been obtained with planted reactors treating highly concentrated influents at the lower hydraulic loading rates tested. The palm tree mulch units achieved similar removals of SS, COD and turbidity to one having gravel as substrate and planted with common reed. Mulch obtained from stems of giant reed (Arundo donax) provided similar removals of SS and turbidity but that of COD was lower. The combination of organic-based TWs with gravel-based ones provided high removals (SS: 95%, COD: 78%, turbidity: 95%) while the risk of clogging was strongly reduced.

Effect of additives in photocatalytic degradation of commercial azo dye Lanaset Sun Yellow 180.

The photocatalytic degradation of the commercial dye Lanaset Sun Yellow 180 was studied in the presence and absence of the different additives used in the dye's formulation. The experiments were performed with Degussa P25 as received and doped with Fe (Fe-TiO2) and a new catalyst synthesized by our research group (ECT-1023). The best efficiency was achieved with Fe-TiO2. With this catalyst, the formation of a photoactive complex was observed between the dye and Fe atoms of the catalyst surface that accelerated degradation. FTIR studies revealed that the complex was formed by interaction between the dye's carbonyl groups and the atoms of the metal. In mixtures of the dye containing citric acid or acetate, degradation was notably inhibited with the catalysts Fe-TiO2 and ECT-1023 because of the formation of carboxylates on their surface. This inhibitory effect was neutralized when all the additives were present in the solution. Toxicity analyses indicated that intermediates were not toxic. Thus, the photocatalytic methods seem to be optimal for the decolourization of wastewaters containing this dye.

Degradation and detoxification of 4-nitrophenol by advanced oxidation technologies and bench-scale constructed wetlands.

The degradation and detoxification towards the duckweed Lemna minor of 4-nitrophenol (4NP) was studied by means of bench-scale constructed wetlands (CWs), TiO(2)-photocatalysis and Fenton + photoFenton reactions. The main goal of this work was to compare the three treatment techniques to evaluate their possible combination for the efficient, low cost treatment of 4NP effluents. In CWs, adsorption on the substrate of 4NP was found to achieve 34-45%. Low concentrations (up to 100 ppm) of 4NP were successfully treated by CWs in 8-12 h. The microbial degradation of 4NP started after a lag phase which was longer with higher initial concentrations of the pollutant. The greatest degradation rate was found to occur at initial concentrations of 4NP between 60 and 90 ppm. Solar TiO(2)-photocatalysis was faster than the CWs. The greatest removals in terms of mass of 4NP removed after 6 h of irradiation were found to occur at 4NP concentrations of about 200 ppm. Fenton reaction provided complete 4NP degradation up to 500 ppm in only 30 min but TOC was removed by only about 40%. The resulting toxicities were below 20% for initial 4NP concentrations below 300 ppm. It was the Fenton + photoFenton combination (180 min in total) that provided TOC reductions up to 80% and negative L. minor growth inhibition for almost all the 4NP concentrations tested. The combination of solar TiO(2)-photocatalysis (6 h) with CWs (16 h) was able to completely treat and detoxify 4NP effluents with concentrations as high as 200 ppm of the organic.

Combining TiO2-photocatalysis and wetland reactors for the efficient treatment of pesticides.

In the present work the photocatalytic and biological degradation of two commercial mixtures of pesticides (Folimat and Ronstar) and two fungicides (pyrimethanil and triadimenol) has been studied. The evolution of some components of these commercial products (dicofol, tetradifon and oxadiazon) and that of the two fungicides has been monitored by means of HPLC, GC-MS, TOC and toxicity (Lemna minor toxicity test) measurements. The photocatalytic method was able to degrade dicofol, tetradifon, pyrimethanil, triadimenol and the components of Ronstar with the exception of oxadiazon. In addition to this, the photocatalytic method eliminated pyrimethanil toxicity and reduced that of triadimenol by a 90%, Ronstar by a 78% and Folimat by an 87%. Nevertheless, the wetland reactors alone could reduce the toxicity of only the former. Finally, the proper dosage of the water containing the pesticides to a photocatalytic reactor followed by a wetland reactor resulted to be the most successful strategy for the detoxification of the studied compounds and their mixtures.

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.

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.

Photocatalytic degradation of formaldehyde containing wastewater from veterinarian laboratories.

The photocatalytic destruction of methanol, formaline (mixture of formaldehyde, methanol and water) and formaline wastes from the preservation of vertinarian physiologic samples has been attempted by two different processes, at high concentrations of reagents and by dossification of reagents, varying pH in both. Experiment evolution has been monitored by measuring the organic matter such as TOC and formaldehyde concentrations [H2CO]. Also, methanol and methanol-formaldehyde interactions with the TiO2 surface have been analysed by FTIR spectroscopy. Results indicate that at high concentrations the catalyst surfacial alterations given by methoxy, formates or carbonates, according to the pH of the sample can profoundly affect catalyst behaviour. It has been established that reagent dossification is advantageous for enhancing photonic efficiency as it minimizes the adsorbate presence that hampers the photocatalytic process.