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.     

The environmental impact of shrimp aquaculture: a global perspective

A global perspective on the environmental impacts related to the establishment and operation of shrimp aquaculture is presented. Alternatives to reduce the impacts are considered and research priorities are recommended.     

Solar photocatalytic mineralization of commercial pesticides: acrinathrin

A comparative study of the degradation of commercial acrinathrin spiked in water using TiO2 photocatalysis and photolysis under sunlight was performed. Samples were analysed by liquid chromatography-diode array detector (HPLC-DAD) and gas chromatography-ion trap-mass spectrometric detector (GC-ITMS). Additional total organic carbon (TOC) analyses were carried out to evaluate the mineralisation rates. One photoproduct, 2-phenoxy benzaldehyde, was unequivocally identified and evaluated by GC-ITMS during the processes. Although acrinathrin is almost destroyed when exposed to irradiation for more than 400 h, photocatalysis with TiO2 noticeably reduced degradation to a few hours. In this case, with the additional presence of peroxydisulphate, in less than 2 h acrinathrin is completely destroyed. Mineralisation of acrinathrin, without catalyst, was only around 50% after 400 h of irradiation.     

Mercury levels in muscle of two fish species and sediments from the Cartagena Bay and the Ciénaga Grande de Santa Marta, Colombia

Mercury (Hg) content in sediments and muscle from two fish species were determined in Cartagena Bay and Ciénaga Grande de Santa Marta, an industrialized bay and an unpolluted estuary in the Caribbean coast of Colombia. Sampling was conducted four times during March-November 1996, including both the dry and rainy seasons. Significant differences in Hg concentration were detected both for fish and sediments between the two waterbodies. Hg values ranged from 94 to 10,293 microg/kg dry weight (dw) in sediments from Cartagena Bay and between 20 and 109 microg/kg dw in Ciénaga Grande de Santa Marta. Highest Hg concentrations were observed for the omnivorous species Eugerres plumieri, and lowest concentrations were found in the detritivorous Mugil incilis. High Hg concentrations in sediments of Cartagena Bay were detected in front of the sewage discharge of an extinct chlor-alkali plant, with decreasing concentrations in stations far from the source. Our results suggest that Hg can be persistent in the sediments of previously exposed ecosystems and that the use of their biological resources should be avoided until decontamination programs guarantee safe levels of the metal in the environment.     

Ozone exposure among Mexico City outdoor workers

In researching health effects of air pollution, pollutant levels from fixed-site monitors are commonly assigned to the subjects. However, these concentrations may not reflect the exposure these individuals actually experience. A previous study of ozone (O3) exposure and lung function among shoe-cleaners working in central Mexico City used fixed-site measurements from a monitoring station near the outdoor work sites as surrogates for personal exposure. The present study assesses the degree to which these estimates represented individual exposures. In 1996, personal O3 exposures of 39 shoe-cleaners working outdoors were measured using an active integrated personal sampler. Using mixed models, we assessed the relationship between measured personal O3 exposure and ambient O3 measurements from the fixed-site monitoring station. Ambient concentrations were approximately 50 parts per billion higher, on average, than personal exposures. The association between personal and ambient O3 was highly significant (mixed model slope p < 0.0001). The personal/ambient ratio was not constant, so use of the outdoor monitor would not be appropriate to rank O3 exposure and evaluate health effects between workers. However, the strong within-worker longitudinal association validates previous findings associating day-to-day changes in fixed-site O3 levels with adverse health effects among these shoe-cleaners and suggests fixed-site O3 monitors may adequately estimate exposure for other repeated-measure health studies of outdoor workers.     

A practical method for quantification of phosphorus- and glycogen-accumulating organism populations in activated sludge systems.

Enhanced biological phosphorus removal (EBPR) from wastewater relies on the enrichment of activated sludge with phosphorus-accumulating organisms (PAOs). The presence and proliferation of glycogen-accumulating organisms (GAOs), which compete for substrate with PAOs, may be detrimental for EBPR systems, leading to deterioration and, in extreme cases, failure of the process. Therefore, from both process evaluation and modeling perspectives, the estimation of PAO and GAO populations in activated sludge systems is a relevant issue. A simple method for the quantification of PAO and GAO population fractions in activated sludge systems is presented in this paper. To develop such a method, the activity observed in anaerobic batch tests executed with different PAO/GAO ratios, by mixing highly enriched PAO and GAO cultures, was studied. Strong correlations between PAO/GAO population ratios and biomass activity were observed (R2 > 0.97). This served as a basis for the proposal of a simple and practical method to quantify the PAO and GAO populations in activated sludge systems, based on commonly measured and reliable analytical parameters (i.e., mixed liquor suspended solids, acetate, and orthophosphate) without requiring molecular techniques. This method relies on the estimation of the total active biomass population under anaerobic conditions (PAO plus GAO populations), by measuring the maximum acetate uptake rate in the presence of excess acetate. Later, the PAO and GAO populations present in the activated sludge system can be estimated, by taking into account the PAO/GAO ratio calculated on the basis of the anaerobic phosphorus release-to-acetate consumed ratio. The proposed method was evaluated using activated sludge from municipal wastewater treatment plants. The results from the quantification performed following the proposed method were compared with direct population estimations carried out with fluorescence in situ hybridization analysis (determining Candidatus Accumulibacter Phosphatis as PAO and Candidatus Competibacter Phosphatis as GAO). The method showed to be potentially suitable to estimate the PAO and GAO populations regarding the total PAO-GAO biomass. It could be used, not only to evaluate the performance of EBPR systems, but also in the calibration of potential activated sludge mathematical models, regarding the PAO-GAO coexistence.     

A comparison of indigenous mosses and topsoils for use in monitoring atmospheric heavy metal deposition in Galicia (northwest Spain)

Samples of moss (Scleropodium purum or, in its absence, Hypnum cupressiforme) and of topsoil (0-5 cm) were collected in the spring of 1995, from 75 sites distributed throughout Galicia (northwest Spain) in order to compare the potential usefulness of each in evaluating the atmospheric deposition of contaminants. Analysis was made of the total content of various metals in the moss and of different soil metal fractions (including total metal content, labile metals and metals bound to organic material). We found that the labile fraction most closely resembled the metal content of the moss. Calculation of enrichment factors allowed us to show that the soil was not, except in the case of Cr, the main source of contamination in the moss. By comparing contamination factors of metals in moss and soil fraction samples we found that moss samples were more useful for evaluating the degree of contamination at different sites.     

Hydroxylated PCB metabolites in nonhatched fulmar eggs from the Faroe Islands

Thirty-six polychlorinated biphenylols (OH-PCBs) congeners were characterized in Fulmar (Fulmarus glacialis) eggs collected from the Faroe Islands. The seven most abundant congeners were quantified in 19 samples, and the sigmaOH-PCB concentrations ranged between 0.92 and 4.0 ng g(-1) fresh weight (f.w.). These eggs constitute a part of the traditional diet for at least a part of the population on the Faroe Islands and may contribute to the high levels of these contaminants found in the blood of pregnant Faroese women. Because the metabolites are present in the nonhatched fulmar egg, it is concluded that the OH-PCBs are transferred to the egg before laying. High levels, 3300-18,000 ng g(-1) l.w., of sigmapolychlorinated biphenyls (PCB) were determined in the fulmar eggs, which are a considerable source for human exposure. The high PCB levels are a source for metabolic formation of hydroxylated PCBs.     

Evaluation of relative photonic efficiency in heterogeneous photocatalytic reactors

The evaluation of photonic efficiency in heterogeneous photocatalysis remains elusive because the number of absorbed photons is difficult to assess experimentally. The photonic efficiency of heterogeneous photocatalytic reactors depends on the reactor geometry, irradiation source, and photocatalyst properties. In this work, the relative photonic efficiency of heterogeneous photocatalytic reactors to degrade an azo dye was evaluated using phenol as the standard system. The experimental tests were carried out in a batch reactor under different conditions of pH, catalyst dosage, initial concentration, and ultraviolet (UV) lamps. The kinetics of disappearance of both phenol and azo dye were studied using the initial rate method and were described according to the Langmuir-Hinshelwood (L-H) kinetic model. It was observed that the relative photonic efficiency depends on the adsorption/desorption properties of the photocatalyst.     

Levels of polychlorinated biphenyls and organochlorine pesticides in serum samples of Egyptian Vulture (Neophron percnopterus) from Spain

Concentrations of 23 polychlorinated biphenyls (PCBs), p,p'-DDT and two of its metabolites, p,p'-DDE and p,p'-TDE have been measured in serum samples of up to 1 ml of Egyptian Vulture (Neophron percnopterus) gathered from five populations in Spain. SigmaPCB concentrations were found to be in the range 3.2-97 ng/ml, while those of SigmaDDTs ranged from 0.93 to 38 ng/ml. p,p'-DDT/p,p'-DDE ratios higher than one were only found in the Segovia population, which could be an indication of recent use of p,p'-DDT in the area. In all cases, PCB profiles were dominated by congeners 52, 132 + 105, 138, 153 and 180. However, some differences among the five populations studied became evident when their profiles were compared with those of technical PCB mixtures by principal components analysis. The DDT and PCB levels detected in the serums analysed were lower than those previously reported for similar avian species and those reported to have deleterious effects on survival or reproduction of birds.