Assessment and accumulation of microplastics in sewage sludge at wastewater treatment plants located in Cádiz, Spain.

Sludge from Wastewater treatment plants (WWTPs) have been determined as a sink of microplastics (MP) removed from wastewater. The aim of this research work has been to evaluate the presence of these pollutants in the sludge of seven WWTPs (five urban and two industrial), located in southern Spain. Samples were collected in the primary, secondary and digested sludge matrixes, MPs were extracted following wet peroxide oxidation and the removal of cellulose, finally the samples were analyzed according to their abundance, size (from 100 µm to 5 mm), shape, colour, and polymer type. Subsequently, the data obtained on the WWTPs were compared, the main difference among the WWTPs and different sample points showed high heterogeneity in terms of abundance of microplastics, due to the differences in the sludge loaded, the processes and the type of sludge. The results from this study established that the most abundant shape was fibers; regarding the size, 100-355 µm fraction was the most abundant, showing that the amount of MPs increased when the size decreased. Regarding the type of polymers, 23 were identified by ATR-FTIR. Further, Acrylate, PE, EAA and PP were the most abundant found polymers. The presence of MPs in the digested sludge varied from 0.02 ± 0.006 MP g DW-1 to 57.18 ± 20.69 MP g DW-1 in the WWTP 6 (food industry) and WWTP 3 (urban city over 212,000 inhabitants), respectively; higher abundance of MPs found in the primary sludge in respect to secondary sludge; in concordance with the removal from wastewater line reported in other studies. The results obtained showed that MPs were widely present in sludge, becoming a sink of these pollutants, estimating that among 8.05 · 104 and 1.77 · 109 MPs · day-1 were loaded to sludge; therefore, these facilities act as a significant source of MPs into agriculture when sludge is used as soil amendment.

Ventilación mecánica en España, 1998-2016: cambios en la desconexión de la ventilación mecánica / Mechanical ventilation in Spain, 1998-2016: changes in the disconnection of mechanical ventilation

Objetivo Evaluar los cambios en la desconexión de la ventilación mecánica en España desde 1998 hasta 2016. Diseño Análisis post-hoc de 4 estudios de cohorte. Ámbito Un total de 138 UCI. Enfermos Un total de 2.141 enfermos extubados de forma programada. Intervenciones Ninguna. Variables de interés principales Demográficas, motivo de ventilación mecánica, complicaciones, métodos para la desconexión, fracaso del primer intento de desconexión, duración de la desconexión, reintubación, traqueotomía post-reintubación, estancia y mortalidad en la UCI. Resultados Se observa un aumento significativo (p<0,001) en la presión de soporte como técnica de desconexión. Ha aumentado, a lo largo del tiempo, la probabilidad ajustada de utilizar la presión de soporte progresivamente decreciente frente a una prueba de ventilación espontánea, tanto para el primer intento de desconexión (referencia estudio de 1998: odds ratio 0,99 en 2004, 0,57 en 2010 y 2,43 en 2016) como para la desconexión difícil/prolongada (referencia estudio de 1998: odds ratio 2,29 en 2004, 1,23 en 2010 y 2,54 en 2016). La proporción de extubación tras el primer intento de desconexión ha aumentado con el tiempo. Hay una disminución del tiempo dedicado a la desconexión (desde un 45% en 1998 hasta un 36% en 2016). Sin embargo, no ha disminuido la duración en la desconexión difícil/prolongada (mediana 3 días en todos los estudios, p=0,435). Conclusiones Ha habido cambios significativos en el modo de desconexión de la ventilación mecánica, con un aumento progresivo del uso de la presión de soporte. Se han observado mínimos cambios en los desenlaces (AU)

Purpose To evaluate changes in the disconnection of mechanical ventilation in Spain from 1998 to 2016. Design Post-hoc analysis of four cohort studies. Ambit 138 Spanish ICUs. Patients 2141 patients scheduled extubated. Interventions None. Variables of interest Demographics, reason for mechanical ventilation, complications, methods for disconnection, failure on the first attempt at disconnection, duration of weaning, reintubation, post-reintubation tracheotomy, ICU stay and mortality. Results There was a significant increase (p<0.001) in the use of gradual reduction of support pressure. The adjusted probability of using the gradual reduction in pressure support versus a spontaneous breathing trial has increased over time, both for the first attempt at disconnection (taking the 1998 study as a reference: odds ratio 0.99 in 2004, 0.57 in 2010 and 2.43 in 2016) and for difficult/prolonged disconnection (taking the 1998 study as a reference: odds ratio 2.29 in 2004, 1.23 in 2010 and 2.54 in 2016). The proportion of patients extubated after the first attempt at disconnection has increased over time. There is a decrease in the ventilation time dedicated to weaning (from 45% in 1998 to 36% in 2016). However, the duration in difficult/prolonged weaning has not decreased (median 3 days in all studies, p=0.435). Conclusions There have been significant changes in the mode of disconnection of mechanical ventilation, with a progressive increase in the use of gradual reduction of pressure support. No relevant changes in outcomes have been observed (AU)

Mechanical ventilation in Spain, 1998-2016: Changes in the disconnection of mechanical ventilation.

PURPOSE: To evaluate changes in the disconnection of mechanical ventilation in Spain from 1998 to 2016. DESIGN: Post-hoc analysis of four cohort studies. AMBIT: 138 Spanish ICUs. PATIENTS: 2141 patients scheduled extubated. INTERVENTIONS: None. VARIABLES OF INTEREST: Demographics, reason for mechanical ventilation, complications, methods for disconnection, failure on the first attempt at disconnection, duration of weaning, reintubation, post-reintubation tracheotomy, ICU stay and mortality. RESULTS: There was a significant increase (p < 0.001) in the use of gradual reduction of support pressure. The adjusted probability of using the gradual reduction in pressure support versus a spontaneous breathing trial has increased over time, both for the first attempt at disconnection (taking the 1998 study as a reference: odds ratio 0.99 in 2004, 0.57 in 2010 and 2.43 in 2016) and for difficult/prolonged disconnection (taking the 1998 study as a reference: odds ratio 2.29 in 2004, 1.23 in 2010 and 2.54 in 2016). The proportion of patients extubated after the first attempt at disconnection has increased over time. There is a decrease in the ventilation time dedicated to weaning (from 45% in 1998 to 36% in 2016). However, the duration in difficult/prolonged weaning has not decreased (median 3 days in all studies, p = 0.435). CONCLUSIONS: There have been significant changes in the mode of disconnection of mechanical ventilation, with a progressive increase in the use of gradual reduction of pressure support. No relevant changes in outcomes have been observed.

Mechanical ventilation in Spain, 1998-2016: changes in the disconnection of mechanical ventilation. / Ventilación mecánica en España, 1998-2016: cambios en la desconexión de la ventilación mecánica.

PURPOSE: To evaluate changes in the disconnection of mechanical ventilation in Spain from 1998 to 2016. DESIGN: Post-hoc analysis of four cohort studies. AMBIT: 138 Spanish ICUs. PATIENTS: 2141 patients scheduled extubated. INTERVENTIONS: None. VARIABLES OF INTEREST: Demographics, reason for mechanical ventilation, complications, methods for disconnection, failure on the first attempt at disconnection, duration of weaning, reintubation, post-reintubation tracheotomy, ICU stay and mortality. RESULTS: There was a significant increase (p<0.001) in the use of gradual reduction of support pressure. The adjusted probability of using the gradual reduction in pressure support versus a spontaneous breathing trial has increased over time, both for the first attempt at disconnection (taking the 1998 study as a reference: odds ratio 0.99 in 2004, 0.57 in 2010 and 2.43 in 2016) and for difficult/prolonged disconnection (taking the 1998 study as a reference: odds ratio 2.29 in 2004, 1.23 in 2010 and 2.54 in 2016). The proportion of patients extubated after the first attempt at disconnection has increased over time. There is a decrease in the ventilation time dedicated to weaning (from 45% in 1998 to 36% in 2016). However, the duration in difficult/prolonged weaning has not decreased (median 3 days in all studies, p=0.435). CONCLUSIONS: There have been significant changes in the mode of disconnection of mechanical ventilation, with a progressive increase in the use of gradual reduction of pressure support. No relevant changes in outcomes have been observed.

Mechanical ventilation in Spain, 1998-2016: Epidemiology and outcomes. / Ventilación mecánica en España, 1998-2016: epidemiología y desenlaces.

PURPOSE: To evaluate changes in the epidemiology of mechanical ventilation in Spain from 1998 to 2016. DESIGN: A post hoc analysis of four cohort studies was carried out. SETTING: A total of 138 Spanish ICUs. PATIENTS: A sample of 4293 patients requiring invasive mechanical ventilation for more than 12h or noninvasive ventilation for more than 1h. INTERVENTIONS: None. VARIABLES OF INTEREST: Demographic variables, reason for mechanical ventilation, variables related to ventilatory support (ventilation mode, tidal volume, PEEP, airway pressures), complications during mechanical ventilation, duration of mechanical ventilation, ICU stay and ICU mortality. RESULTS: There was an increase in severity (SAPSII: 43 points in 1998 vs. 47 points in 2016), changes in the reason for mechanical ventilation (decrease in chronic obstructive pulmonary disease and acute respiratory failure secondary to trauma, and increase in neurological disease and post-cardiac arrest). There was an increase in noninvasive mechanical ventilation as the first mode of ventilatory support (p<0.001). Volume control ventilation was the most commonly used mode, with increased support pressure and pressure-regulated volume-controlled ventilation. A decrease in tidal volume was observed (9ml/kg actual b.w. in 1998 and 6.6ml/kg in 2016; p<0.001) as well as an increase in PEEP (3cmH2O in 1998 and 6cmH2O in 2016; p<0.001). In-ICU mortality decreased (34% in 1998 and 27% in 2016; p<0.001), without geographical variability (median OR 1.43; p=0.258). CONCLUSIONS: A significant decrease in mortality was observed in patients ventilated in Spanish ICUs. These changes in mortality could be related to modifications in ventilation strategy to minimize ventilator-induced lung injury.

Evaluation of a biological wastewater treatment system combining an OSA process with ultrasound for sludge reduction.

Sludge production is an undesirable by-product of biological wastewater treatment. The oxic-settling-anaerobic (OSA) process constitutes one of the most promising techniques for reducing the sludge produced at the treatment plant without negative consequences for its overall performance. In the present study, the OSA process is applied in combination with ultrasound treatment, a lysis technique, in a lab-scale wastewater treatment plant to assess whether sludge reduction is enhanced as a result of mechanical treatment. Reported sludge reductions of 45.72% and 78.56% were obtained for the two regimes of combined treatment tested in this study during two respective stages: UO1 and UO2. During the UO1 stage, the general performance and nutrient removal improved, obtaining 47.28% TN removal versus 21.95% in the conventional stage. However, the performance of the system was seriously damaged during the UO2 stage. Increases in dehydrogenase and protease activities were observed during both stages. The advantages of the combined process are not necessarily economic, but operational, as US treatment acts as contributing factor in the OSA process, inducing mechanisms that lead to sludge reduction in the OSA process and improving performance parameters.

Relative contribution of articular cartilage's constitutive components to load support depending on strain rate.

Cartilage is considered a biphasic material in which the solid is composed of proteoglycans and collagen. In biphasic tissue, the hydraulic pressure is believed to bear most of the load under higher strain rates and its dissipation due to fluid flow determines creep and relaxation behavior. In equilibrium, hydraulic pressure is zero and load bearing is transferred to the solid matrix. The viscoelasticity of the collagen network also contributes to its time-dependent behavior, and the osmotic pressure to load bearing in equilibrium. The aim of the present study was to determine the relative contributions of hydraulic pressure, viscoelastic collagen stress, solid matrix stiffness and osmotic pressure to load carriage in cartilage under transient and equilibrium conditions. Unconfined compression experiments were simulated using a fibril-reinforced poroviscoelastic model of articular cartilage, including water, fibrillar viscoelastic collagen and non-fibrillar charged glycosaminoglycans. The relative contributions of hydraulic and osmotic pressures and stresses in the fibrillar and non-fibrillar network were evaluated in the superficial, middle and deep zone of cartilage under five different strain rates and after relaxation. Initially upon loading, the hydraulic pressure carried most of the load in all three zones. The osmotic swelling pressure carried most of the equilibrium load. In the surface zone, where the fibers were loaded in tension, the collagen network carried 20 % of the load for all strain rates. The importance of these fibers was illustrated by artificially modifying the fiber architecture, which reduced the overall stiffness of cartilage in all conditions. In conclusion, although hydraulic pressure dominates the transient behavior during cartilage loading, due to its viscoelastic nature the superficial zone collagen fibers carry a substantial part of the load under transient conditions. This becomes increasingly important with higher strain rates. The interesting and striking new insight from this study suggests that under equilibrium conditions, the swelling pressure generated by the combination of proteoglycans and collagen reinforcement accounts cartilage stiffness for more than 90 % of the loads carried by articular cartilage. This finding is different from the common thought that load is transferred from fluid to solid and is carried by the aggregate modulus of the solid. Rather, it is transformed from hydraulic to osmotic swelling pressure. These results show the importance of considering both (viscoelastic) collagen fibers as well as swelling pressure in studies of the (transient) mechanical behavior of cartilage.

The effect of loading rate on the development of early damage in articular cartilage.

Experimental reports suggest that cartilage damage depends on strain magnitude. Additionally, because of its poro-viscoelastic nature, strain magnitude in cartilage can depend on strain rate. The present study explores whether cartilage damage may develop dependent on strain rate, even when the presented damage numerical model is strain-dependent but not strain-rate-dependent. So far no experiments have been distinguished whether rate-dependent cartilage damage occurs in the collagen or in the non-fibrillar network. Thus, this research presents a finite element analysis model where, among others, collagen and non-fibrillar matrix are incorporated as well as a strain-dependent damage mechanism for these components. Collagen and non-fibrillar matrix stiffness decrease when a given strain is reached until complete failure upon reaching a maximum strain. With such model, indentation experiments at increasing strain rates were simulated on cartilage plugs and damage development was monitored over time. Collagen damage increased with increasing strain rate from 21 to 42 %. In contrast, damage in the non-fibrillar matrix decreased with increasing strain rates from 72 to 34 %. Damage started to develop at a depth of approximately 20 % of the sample height, and this was more pronounced for the slow and modest loading rates. However, the most severe damage at the end of the compression step occurred at the surface for the plugs subjected to 120 mm/min strain rate. In conclusion, the present study confirms that the location and magnitude of damage in cartilage may be strongly dependent on strain rate, even when damage occurs solely through a strain-dependent damage mechanism.

Meniscus replacement: Influence of geometrical mismatches on chondroprotective capabilities.

The chondroprotective success of meniscal transplantation is variable. Poorly controlled factors such as a geometrical mismatch of the implant may be partly responsible. Clinical data, animal studies and cadaver experiments suggest that smaller transplants perform better than oversized, but clear evidence is lacking. The hypothesis of this study is that smaller menisci outperform larger ones because they distribute stresses more effectively at those particular locations that receive the highest loads. Consequently, collagen in the adjacent cartilage is protected from damage due to overstraining. Experimentally it is not possible to measure load distribution and collagen strain inside articular cartilage (AC). Therefore, a numerical model was used to determine the mechanical conditions throughout the depth of the AC. Meniscus implants with different sizes and mechanical properties were evaluated. These were compared with healthy and with meniscectomized joints. To account for the time-dependent behavior 600s of loading was simulated; results were visualized after 1s and 600s. Simulations showed that AC's strains strongly depended on implant size and loading duration. They depended less on the stiffness of the implant material. With an oversized implant, collagen strains were particularly large in the femoral AC initially and further increased upon sustained loading. The severest compressive strains occurred after sustained loading in the meniscectomized joint. Strains with an undersized meniscus were comparable to a perfectly sized implant. In conclusion, these results support the hypothesis that an undersized implant may outperform an oversized one because it distributes stresses better in the most intensely loaded joint area.

Should a native depth-dependent distribution of human meniscus constitutive components be considered in FEA-models of the knee joint?

The depth-dependent matrix composition of articular cartilage is important for its mechanical behavior. It is unknown whether the depth-dependent matrix composition of a meniscus is similarly important for its load-bearing function. The present objective was to determine whether it is necessary to account for the native distribution of matrix components in the cross-sectional plane of the meniscus, when studying its mechanical behavior in numerical models. To address this objective, measured depth-dependent distribution of matrix contents in the human meniscus, and fitted visco-elastic mechanical properties of the collagen were used as input in FEA simulations of a knee joint. The importance of including the depth-dependent matrix component constitution in the meniscus was determined by comparing simulations with an axisymmetric representation of the knee joint, which incorporated either the depth-dependent matrix composition or homogenized matrix. Depth-dependent differences in water, collagen and proteoglycan contents were observed, but these were not significantly different. The anterior region, with significantly higher collagen content, was statistically stiffer than the posterior region. However, depth wise, stiffness did not correlate to the constitution of the tissue. GAG content was significantly higher in the posterior than in the anterior region. Visco-elastic properties of meniscus collagen were fitted against tensile test data. Simulations show that the distribution of stresses and strains in the cartilage is slightly low when the meniscus contains a depth-dependent constitution, but this difference is only modest. Therefore, this study suggests that knee joint mechanics is rather insensitive to the distribution of constitutive components in the cross section of the meniscus, and that the depth-dependent matrix distribution of the meniscus is not essential to be included in axisymmetric computational models of the knee joint.

Ozonation of ibuprofen: a degradation and toxicity study.

This paper presents the results obtained in the degradation of ibuprofen by ozonation. This study aims to evaluate the degradation of ibuprofen by ozonation once the operating variables have been optimized, investigating the degradation and degradation efficiency of the compound and assessing the toxic effect of ibuprofen and of the intermediate compounds generated during oxidative treatment. Work was carried out to optimize the four operating variables: pH, conductivity, hydraulic retention time and the use of a maze of pipes to enhance contact between the ozone and the drug. All the trials were conducted in a purpose-built pilot-scale reactor. Analyses of the compound were carried out after solid-liquid phase extraction on high resolution liquid chromatography (HPLC). Working under optimal operating conditions (pH=9, HRT=20 min and 12 ± 2 gN/m(3)), a degradation value of 99% was obtained, although degradation efficiency or mineralization of the compound was not achieved. The toxicity of ibuprofen and its intermediate compounds formed during the oxidative process was likewise studied. This toxicity was found to increase with increasing initial concentrations of the compound, with the intermediate compounds thus formed being more toxic than the starting compound.

Use of microbial activity measurements for monitoring RBC biofilms.

Fixed biomass technologies, such as rotating biological contactors or biodiscs, have been applied for wastewater depuration both in large and medium-small-sized agglomerations. Biofilm's composition and microorganism activity are essential parameters for the successful operation and control of these systems. Biofilm's thickness and total dry weight have been widely used for biofilm's characterization but, actually, are not sufficient to describe biofilm activity. In fact, biofilm's activity is not proportional to the quantity of fixed biomass, but increases with the thickness of biofilm up to a determined level called the "active thickness". Above this level, the diffusion of nutrients through the film becomes a limiting factor. A stable, thin, and active biofilm thus offers numerous advantages in water and wastewater treatment. Different parameters have been used to evaluate biofilm's activity. The specific oxygen uptake rate, INT-dehydrogenase activity, and the ratio active/total cells have been applied for that purpose. These methods are not only simple and rapid but also sensitive, precise, and representative. The results obtained confirm the potential of the microbial activity measurements studied for an accurate biofilm's characterization and biomass activity estimation in fundamental research and for the practical operation and control of fixed biomass depuration systems.

Chemical degradation of PCB in the contaminated soils slurry: direct Fenton oxidation and desorption combined with the photo-Fenton process.

This paper reports the results of the direct treatment of PCBs sorbed to solid particles (glass beads and sand) employing the Fenton process. The results obtained with contaminated sandy soils show 98% removal of the original PCB structure and 82% dechlorination, all within a reaction time of 72 hours. The degree of removal was observed to be dependent on the level of congener chlorination. The optimized conditions were: 5% H(2)O(2); 100 ppm Fe(3+); sandy soil mass/volume of oxidizing solution ratio (m/V) of 1/3 g/mL, vigorous agitation and dispensed with the need for heat. Results obtained by applying an integrated desorption treatment followed by photo-Fenton oxidation to sandy soils contaminated with PCBs are also present in this paper. Desorption of PCBs with surfactant solutions took place to an extent of around 90% (92.2% with K-perfluoroalkyl sulfonate, FT800, and 87% with Lineal Alkyl benzene Sulfonate, LAS), while photo-Fenton oxidation at 254 nm achieved degradation percentages close to 100% in 30 minutes for PCBs in solution, both with FT800 (98%) and LAS (97%) surfactants.

Optimization of the solution parameters during the degradation of Orange II in a photo-reactor mediated by Fe-Nafion membranes.

The Fenton and photo-Fenton mediated degradation process of Orange II was investigated in a flow photo-reactor. The degradation was monitored as a function of the wavelength of the applied light, recirculation flow rate, amount of H(2)O(2) and the initial concentration of Orange II. Optimization of the photo-Fenton degradation mediated by Fe-Nafion membranes indicated that an Orange II (0.25 M) solution discolored above 95% within 2.5 hours at an H(2)O(2)/Orange II ratio of 20. A concomitant mineralization of 40% of Orange II was observed after 5 h reaction. Homogeneous photo-Fenton processes were able to fully discolore Orange II within 1 hour and concomitantly fully mineralize the dye in the presence of Fe(III) (2 ppm) and an H(2)O(2)/Orange II ratio of 20. Surfactants such as linear alkylbenzene sulphonates (LAS) and K-perfluoroalkyl sulphonate (FT 800) slowed down the Orange II abatement in photo-Fenton processes.

Comparison of four chemical uncouplers for excess sludge reduction.

A substantial part of the operating costs of wastewater treatment plants (WWTP) is associated with the management and treatment of the excess sludge generated during the treatment process. Different strategies have been applied for excess sludge reduction, such as the oxic-settling-anaerobic process, the high dissolved oxygen process, the uncoupler-containing activated sludge process, the ozonation-combined activated sludge process, control of sludge retention time and biodegradation of sludge in a membrane-assisted reactor. Chemical uncouplers have been shown to reduce excess sludge production, disassociating the energy coupling between catabolism and anabolism. These metabolic uncouplers may be organic compounds, such as 2,4-dinitrophenol (2,4-DNP) or 3,3',4',5-tetrachlorosalicylanilide (TCS), or heavy metals. In this paper, four different chemicals (2,4-DNP, TCS, copper (Cu) and zinc (Zn)) were chosen for short-term tests for studying their ability to reduce sludge yield (Y(x/s)) and, consequently, their potential for reducing excess sludge production. According to the results obtained, only TCS seems to be very effective in reducing sludge production from the activated sludge process. Compared with the control test, Y(x/s) can be reduced by over 30% at 0.8 mg/l TCS. It was also found that the substrate removal capability was not adversely affected by the presence of TCS. Furthermore, an increase in the microbial activity of the system was observed.

Non-ionic surfactant biodegradation in lab-scale activated sludge.

The biodegradation of a non-ionic surfactant was evaluated by the evolution of the microbial activity and the determination of the soluble surfactant present in the effluent. Two lab-activated sludge reactors/systems were fed with synthetic sewage, one of which received in addition different concentrations--5 and 10 mg/L--of nonylphenol ethoxylates (NPEO). The parameters employed in this assay were: control parameters (COD and SS) and activity microbial parameters (specific oxygen uptake rate and dehydrogenase activity). The removal of NPEO and the production of secondary metabolites were monitored. Solid-phase extraction and HPLC with fluorescence detection were employed for sample preparation and analysis. The results suggest that the microbial activity was not inhibited when 5 mg/L of NPEO was added. Nevertheless, an important inhibition of the general metabolism was observed for 10 mg/L of NPEO.

Ecotoxicity and biodegradability of an alkyl ethoxysulphate surfactant in coastal waters.

Alkyl ethoxysulphates (AES) are anionic surfactants widely used in numerous commercial and industrial applications. In spite of the high AES volume consumption a few data concerning the occurrence, fate and effects of AES in marine environments are reported in literature. The objective of this study is to evaluate the biodegradability and toxicity of AES in pristine sea water. Ultimate biodegradation was studied according to the guideline 835.3160 "Biodegradability in sea water" proposed by the United States Environmental Protection Agency (USEPA). Acute toxicity of AES was studied to the microalgae Nannochloropsis gaditana, Isochrysis galbana, Chaetoceros gracilis, Dunaliella salina and Tetraselmis chuii and the invertebrate Artemia franciscana, using culture growth inhibition and death, respectively, as effect criteria. During the degradative process two different stages were observed, which were better described with the first order and logistic kinetic models, respectively. Lag times were 3.3 (stage A) and 26.5 (stage B) days whereas half-lives were 18.6 (stage A) and 49.8 (stage B) days. AES inhibited the microalgae growth, with 96-h EC50 values ranging from 4.68 g L(-1) for D. salina to 24.02 mg L(-1) for I. galbana. Mean 48- and 72-h LC50 values for A. franciscana were 38.30 and 23.92 mg L(-1), respectively. The results indicate an extensive biodegradability of AES in sea water, although at a very slow rate. Acute toxicity was highly dependent on the species tested, being the green alga D. salina the most affected organism. The present study provides relevant data concerning the biodegradability and adverse effects of an AES surfactant on marine organisms, which are useful to establish water quality criteria in a regulatory framework.

Photoreactivation and dark repair in UV-treated microorganisms: effect of temperature.

Because of the lack of readily available information about the influence of temperature on microorganism reactivation processes subsequent to inactivation with UV radiation, a series of batch reactivation studies were performed at 5, 10, 15, 20, 25, and 30 degrees C. A special effort was made to model the reactivation process to enable the effect of the temperature variable to be quantified. Because an earlier-proposed kinetic model (K. Kashimada, N. Kamiko, K. Yamamoto, and S. Ohgaki, Water Sci. Technol. 33:261-269, 1996), a first-order saturation type, does not adequately fit the data obtained in experiments of reactivation in conditions of light and darkness, a modification of that model is proposed. The new model, which actually coincides with the classical logistic equation, incorporates two kinetic parameters: the maximum survival ratio (Sm) and the second-order reactivation rate constant (k2). In order to interpret correctly the reactivation occurring in conditions of darkness, a new term for the decay is added to the logistic equation. The new model accurately fits the data obtained in reactivation experiments, permitting the interpretation of the kinetic parameters Sm, k2, and M (for only repair in darkness), where M is mortality, a zero-order decay rate constant, and their relationship with various environmental conditions, such as microbial type, light, and temperature. The parameters Sm and k2 (and M for reactivation in conditions of darkness) show exponential dependence on the reactivating temperature, and it is possible to predict their values and hence the reactivation curve from the equations proposed in this work.

Thermal analysis in the evaluation of sediment pollution.

Characterization of organic matter in four sediments in the infuence area of wastewater discharges was carried out by both chemical and thermal analysis in order to assess their pollution level. Oxidisable organic carbon and organic matter were calculated by the standard methodology in laboratory. Thermogravimetry (TG), between 50 and 900 degrees C, was simultaneously performed in oxidizing conditions on ground sediments samples after three different pretreatments. Linear regression adjust of thermal analysis results versus chemical parameters provides the better Pearson's coefficients, leading to the best coefficients for weight loss in 250-400 degree C temperature range versus oxidisable organic carbon and organic matter at 360 degrees C, respectively. These results demonstrated the utility of thermoanalysis technique for the evaluation of the organic matter content of fresh sediments.

Using solar and ultraviolet light to degrade PCBs in sand and transformer oils.

The present study describes the effect of the operating variables in the sensitized solar photolysis of sandy sediments contaminated by polychlorinated biphenyls (PCBs) in alkaline isopropanol. PCBs were almost completely removed in two weeks with stoichiometric release of chloride and biphenyl (BP) by a mechanism of reductive dechlorination. The concentration of the sensitizer (acetone) was the variable found to have most influence on the process. Under the same conditions, only partial dechlorination of the PCBs (34%) was observed in dielectric fluids without generating biphenyl to any appreciable extent. Direct photolysis (ultraviolet light at 254nm) of dielectric oils dissolved in alkaline isopropanol lead to 92% removal of PCBs in 60min. The observed mechanism was again that of reductive dechlorination, with stoichiometric release of chloride, and the accumulation of biphenyl, quaterphenyl and condensation products of biphenyl with isopropanol.