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Soil Aquifer Treatment (SAT) is a robust technology to increase groundwater recharge and to improve reclaimed water quality. SAT reduces dissolved organic carbon, contaminants of emerging concern, nutrients, and colloidal matter, including pathogen indicators, but little is known about its ability to reduce loads of antibiotic resistance genes (ARGs) from reclaimed waters. Here we test six pilot SAT systems to eliminate various biological hazards from the secondary effluents of a wastewater treatment plant (WWTP), equipped with reactive barriers (RBs) including different sorptive materials. Using flow cytometry, qPCR and 16S rRNA gene amplicon sequencing methods, we determined that all six SAT systems reduced total loads of bacteria by 80 to 95 % and of clinically relevant ARGs by 85 to 99.9 %. These efficiencies are similar to those reported for UV/oxidation or membrane-based tertiary treatments, which require much more energy and resources. The presence and composition of reactive barriers, the season of sampling (June 2020, October 2020, and September 2021), or the flow regime (continuous versus pulsating) did not affect ARG removal efficiency, although they did alter the microbial community composition. This suggests that an adequate design of the SAT reactive barriers may significantly increase their performance. Under a mechanistic point of view, we observed an ecological succession of bacterial groups, linked to the changing physical-chemical conditions along the SAT, and likely correlated to the removal of ARGs. We concluded that SAT is as cost-efficient technology able to dramatically reduce ARG loads and other biological hazards from WWTP secondary effluents., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The regeneration of wastewater has been recognized as an effective strategy to counter water scarcity. Nonetheless, Wastewater Treatment Plant (WWTP) effluents still contain a wide range of contaminants of emerging concern (CECs) even after water depuration. Filtration through Soil Aquifer Treatment (SAT) systems has proven efficient for CECs removal although the attenuation of their associated biological effects still remains poorly understood. To evaluate this, three pilot SAT systems were monitored, two of them enhanced with different reactive barriers. SATs were fed with secondary effluents during two consecutive campaigns. Fifteen water samples were collected from the WWTP effluent, below the barriers and 15 m into the aquifer. The potential attenuation of effluent-associated biological effects by SATs was evaluated through toxicogenomic bioassays using zebrafish eleutheroembryos and human hepatic cells. Transcriptomic analyses revealed a wide range of toxic activities exerted by the WWTP effluents that were reduced by more than 70% by SAT. Similar results were observed when HepG2 hepatic cells were tested for cytotoxic and dioxin-like responses. Toxicity reduction appeared partially determined by the barrier composition and/or SAT managing and correlated with CECs removal. SAT appears as a promising approach to efficiently reduce effluent-associated toxicity contributing to environmental and human health preservation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Submarine Groundwater Discharge (SGD) is recognized as a relevant source of pollutants to the sea, but little is known about its relevance as a source of chemicals of emerging concern (CECs). Here, both the presence and distribution of a wide range of CECs have been evaluated in the most comprehensive manner to date, in a well-characterized Mediterranean coastal aquifer near Barcelona (Spain). Samples from coastal groundwater and seawater allowed for the unique spatial characterization of the pollutants present in the land-ocean interface, an outstanding research gap that required attention. The main goals were (1) to determine CECs in the aquifer, so as to evaluate the SGD as a relevant source of marine pollution, and (2) to identify new tracers to improve our understanding of SGD dynamics. To this end, 92 CECs were located in the aquifer by using wide-scope analytical target methodologies (>2000 chemicals). Among them, the perfluoroalkyl and polyfluoroalkyl substances (PFAS), along with the pharmaceuticals carbamazepine and topiramate, were revealed to be good markers for tracing anthropogenic contamination in ground- and seawater, in concrete situations (e.g., highly contaminated sites). Additionally, non-target analysis expanded the number of potential tracers, making it a promising tool for identifying both the source and the fate of pollutants., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

The need and availability of freshwater is a major environmental issue, aggravated by climate change. It is necessary to find alternative sources of freshwater. Wastewater could represent a valid option but requires extensive treatment to remove wastewater-borne contaminants, such as contaminants of emerging concern (CECs). It is urgent to develop not only sustainable and effective wastewater treatment techniques, but also water quality assessment methods. In this study, we used polar organic chemical integrative samplers (POCIS) to investigate the presence and abatement of contaminants in an urban wastewater treatment plant (WWTP) and in soil aquifer treatment (SAT) systems (a conventional one and one enhanced with a reactive barrier). This approach allowed us to overcome inter-day and intraday variability of the wastewater composition. Passive sampler extracts were analyzed to investigate contamination from 56 pharmaceuticals and personal care products (PPCPs). Data from the POCIS were used to estimate PPCPs' removal efficiency along the WWTP and the SAT systems. A total of 31 compounds, out of the 56 investigated, were detected in the WWTP influent. Removal rates along WWTP were highly variable (16-100 %), with benzophenone-3, benzophenone-1, parabens, ciprofloxacin, ibuprofen, and acetaminophen as the most effectively removed chemicals. The two SAT systems yielded much higher elimination rates than those achieved through the primary and secondary treatments together. The SAT system that integrated a reactive barrier, based on sustainable materials to promote enhanced elimination of CECs, was significantly more efficient than the conventional one. The removal of the recalcitrant carbamazepine and its epoxy- metabolite was especially remarkable in this SAT, with removal rates between 69-81 % and 63-70 %, respectively., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Wormholes are highly conductive channels that develop in high solubility rocks. They are especially important for environmental and industrial sustainability in saline karst aquifers (e.g. Salar de Uyuni, Salar de Atacama). Wormholes dynamics (i.e., the space and time evolution of these preferential flow paths) depends on the hydrodynamic and geochemical conditions during formation, as well as on wormholes competition for flow. Despite the importance of wormholes interaction for their development, experimental efforts have focused on the evolution of a single flow-path. Direct observation and quantification of wormholes dynamics is still lacking. We propose an experimental set-up to visualize and characterize the dynamics of multiple wormholes, which may help to understand the changes in flow and transport behaviour of aquifers. We performed a dissolution experiment in a 2D synthetic evaporitic aquifer, and simultaneous fluorescent tracer tests before and during wormhole growth. We visualized the growth by sequential photographs, with the fluorescent tracer highlighting the evolving structures. We quantified wormholes dynamics by measuring pressure and mass changes of the aquifer, and by image analysis. On the one hand, results show that wormholes tend to form along areas where flux was fastest prior to dissolution. They also show clear evidence of competition for water between wormholes and represent the first quantitative evidence of the amplifying factor that drives the self-organization in wormhole growth. On the other hand, we found that the competition is slower than predicted by current analytical and numerical theories, but consistent with other laboratory results. We conjecture that the discrepancy between theory and experiments can be attributed to the combined effect of non-linear kinetics and particle dragging during dissolution. We then compared experimental tracer breakthrough curves before and during the formation of preferential flow paths. They reflect wormhole growth by an accentuated non-Fickian behaviour, with reduced first arrival and increased tailing., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Daniel Fernandez Garcia reports financial support was provided by SQM SA., (Copyright © 2022. Published by Elsevier B.V.)

In coastal aquifers, two opposite but complementary processes occur: Seawater intrusion (SWI), which may salinize heavily exploited aquifers, and Submarine groundwater discharge (SGD) which transports oligo-elements to the sea. Aquifers are expected to be chemically reactive, both because they provide abundant surfaces to catalyze reactions and the mixing of very different Fresh Water (FW) and Sea Water (SW) promote numerous reactions. Characterizing and quantifying these reactions is essential to assess the quality and composition of both aquifer water, and SGD. Indeed, sampling SGD is difficult, so its composition is usually uncertain. We propose a reactive end-member mixing analysis (rEMMA) methodology based on principal component analysis (PCA) to (i) identify the sources of water and possible reactions occurring in the aquifer and (ii) quantify mixing ratios and the extent of chemical reactions. We applied rEMMA to the Argentona coastal aquifer located North of Barcelona that contains fluvial sediments of granitic origin and overlies weathered granite. The identification of end members (FW and SW) and the spatial distribution of their mixing ratios illustrate the application procedure. The extent of reactions and their spatial distribution allow us to distinguish reactions that occur as a result of mixing from those caused by sediment disequilibrium, which are relevant to recirculated saltwater SGD. The most important reaction is cation exchange, especially between Ca and Na, which promotes other reactions such as Gypsum and Fluorite precipitation. Iron and Manganese are mobilized in the SW portion but oxidized and precipitated in the mixing zone, so that Fe (up to 15 μEq/L) and Mn (up to 10 μEq/L) discharge is restricted to SW SGD. Nitrate is reduced in the mixing zone. The actual reaction amounts are site-specific, but the processes are not, which leads us to conjecture the importance of these reactions to understand the SGD discharge elsewhere., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Jesus Carrera reports financial support was provided by Ministry of Science Technology and Innovations. Albert Folch reports financial support was provided by Ministry of Science Technology and Innovations. Tybaud Goyetche reports financial support was provided by Ministry of Economy, Industry and Competitiveness. Albert Folch reports financial support was provided by Catalan Water Agency., (Copyright © 2022. Published by Elsevier B.V.)

A paradigm shift is needed in wastewater treatment plants (WWTPs) to progress from traditional pollutant removal to resource recovery. However, whether this transformation produces overall environmental benefits will depend on the efficient and sustainable use of resources by emerging technologies. Given that many of these technologies are still being tested at the pilot scale, there is a lack of environmental assessments quantifying their impacts and benefits. In particular, an integrated approach to energy and nutrient recovery can elucidate the potential configurations for WWTPs. In this study, we conduct a life cycle assessment (LCA) of emergent wastewater treatment technologies aimed at increasing resource circularity in WWTPs. We focus on increasing energy self-sufficiency through biogas upgrades and a more radical circular approach aimed at nutrient recovery. Based on a case-study WWTP, we compare its current configuration with (1) implementing autotrophic nitrogen removal in the mainstream and deriving most of the organic matter for biogas production, which increases the quality and quantity of biogas available for energy production; (2) implementing struvite recovery through enhanced biological phosphorus removal (EBPR) as a radical approach to phosphorus management, offering an alternative to mineral fertilizer; and (3) a combination of both approaches. The results show that incremental changes in biogas production are insufficient for compensating for the environmental investment in infrastructure, although autotrophic nitrogen removal is beneficial for increasing the quality of the effluent. Combined phosphorus and energy recovery reduce the environmental impacts from the avoided use of fertilizers and phosphorus and the nitrogen release into water bodies. An integrated approach to resource management in WWTPs is thus desirable and creates new opportunities toward the implementation of circular strategies with low environmental impact in cities., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

Non-ferrous metal mining is considered one of the largest sources of toxic metal released to the environment and may threaten ecosystems, notably biota. We explored how birds that inhabit non-ferrous metal mining sites are exposed to mercury, lead, and other trace elements by analyzing their feathers and verifying which factors may influence element concentrations in feathers. We sampled a total of 168 birds, representing 26 species, with different feeding habits and migration patterns in a non-polluted reference site and two historical metal mining areas: Almadén, which is considered one of the most heavily mercury-contaminated sites worldwide, and the Sierra Madrona mountains where lead has been mined since ancient times. The quantification of aluminum (Al), arsenic (As), barium (Ba), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), mercury (Hg), magnesium (Mg), manganese (Mn), molybdenum (Mo), nickel (Ni), lead (Pb), selenium (Se), thorium (Th), thallium (Tl), uranium (U), vanadium (V) and zinc (Zn) was performed by inductively coupled plasma mass spectrometry (ICP-MS). Feather analysis revealed contamination by Hg and Pb, in Almadén and Sierra Madrona, respectively. We found that granivorous birds had the lowest feather Hg levels compared to those found in omnivorous, insectivorous, and piscivorous species, whereas feather Pb was about twice as high in granivores and omnivores, than in insectivorous and piscivorous birds. We also found differences among study sites in 13 elements and confirmed the influence of feather age, migratory patterns of the birds, and external deposition of elements, on metal concentrations in the feathers. Our results highlight that despite the cessation of metal mining in the study areas, local avifauna are being exposed to Hg and Pb from abandoned mines and old tailings sites, indicating that appropriate measures are needed to protect biota from overexposure to these toxic metals., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Objectives: The main objective of this study was to compare the efficacy of 3 hemostatic methods for the prevention of early radial artery occlusion (RAO): standard patent hemostasis, patent hemostasis with ulnar compression or the ulnar artery transient compression facilitating radial artery patent hemostasis (ULTRA) method, and facilitated hemostasis with a hemostatic disc., Background: There are no prospective randomized studies that compare early RAO rates with the 3 most used nonocclusive hemostatic methods., Methods: This was a prospective, longitudinal, comparative, and randomized study. The final population analyzed was 1,469, and they were randomized into 3 groups: 491 patients in group 1 with standard patent hemostasis, 490 patients in group 2 with the ULTRA method, and 488 patients in group 3 with facilitated hemostasis with a hemostatic disc., Results: The RAO rate at 24 hours of the total population analyzed was 4.6%. By hemostasis groups, it was 3.6% for patent hemostasis, 5.5% for the ULTRA method, and 4.7% for facilitated hemostasis with a hemostatic disc, with no statistical difference among the 3 groups (P = 0.387). At 30 days, the overall rate of RAO was 1.8%, and by groups, it was 1.4% for the patent hemostasis group, 1.8% for the ULTRA method group, and 2.2% for the facilitated hemostasis with a hemostatic disc group, respectively (P = 0.185)., Conclusions: The rates of RAO at 24 hours evaluated by plethysmography oximetry and confirmed by ultrasound among 3 current radial hemostasis methods (ie, patent hemostasis, the ULTRA method, and facilitated hemostasis with a hemostatic disc) are not different., Competing Interests: Funding Support and Author Disclosures The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2022 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Coastal aquifers are a vital water source for the more than one billion people living in coastal regions around the globe. Due to the intensity of economic activities and density of population, these aquifers are highly susceptible not only to seawater intrusion, but also to anthropogenic contamination, which may contaminate the aquifer and submarine groundwater discharge. Identification and localization of contaminant source characteristics are needed to reduce contamination. The techniques of contaminant source identification are based on numerical models that require the knowledge of the hydrodynamic properties of aquifers. Thus, the challenging topic of contaminant source and aquifer characterization (CSAC) is widely developed in the literature. However, most of the existing studies are concerned with inland aquifers with relatively uniform groundwater flow. Coastal aquifers are influenced by density-driven seawater intrusion, tidal forces, and water injection and abstraction wells. These phenomena create complex flow and transport patterns, which render the CSAC especially challenging and may explain why CSAC has never been addressed in coastal settings. The presented study aims to provide an efficient methodology for the simultaneous identification of contaminant source characteristics and aquifer hydraulic conductivity in coastal aquifers. For this purpose, the study employs numerical modeling of density-dependent flow and multiple-species solute transport, to develop trained and validated artificial neural network metamodels, and then employs these metamodels in a version of the ensemble Kalman filter (EnKF) termed the 'constrained restart dual EnKF (CRD-EnKF)' algorithm. We show that this variant of the EnKF can be successfully applied to CSAC in the complex setting of coastal aquifers. Furthermore, the study analyzes the influence of common issues in CSAC monitoring, such as the effect of non-ideal monitoring network distributions, measurement errors, and multi-level vs. single level monitoring wells., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The chronic exposure of livestock to lead (Pb) pollution in historical mining areas may represent significant and unnecessary costs for farmers and primary producers, in addition to important food safety risks. Here, we evaluate the effect of mineral supplements, in the form of a commercial mineral block (MB), to reduce Pb bioavailability and toxicity in sheep through an experimental approach under real farming conditions in an abandoned mining area. Blood, fecal Pb levels, and soil ingestion, along with different blood and plasma biomarkers were studied. Experiment 1 was carried out with 3-months-old female lambs, n = 54, fenced in two contiguous MB and non-MB-supplemented plots. After 20 days of treatment, blood Pb level was lower in MB-supplemented sheep than in those that were non-MB-supplemented. Experiment 2 was carried out with 2-months-old female lambs, n = 34, fenced in a single plot and MB-supplemented during the first 20 days of experiment. After MB supplementation, blood Pb level in sheep was also reduced by almost half, falling below the threshold of subclinical intoxication, and then increased again after 20 days without MB. Experiment 3 was carried out with adult rams, n = 10, fenced in a single MB-supplemented plot during the first 20 days of experiment. In this case, blood Pb level decreased by day 40. Soil ingestion was not reduced by MB supplementation in any of the experiments. MB supplementation favored antioxidant status by increasing SOD activity and reducing GPX activity and MDA levels. In conclusion, the MB supplementation seemed to reduce Pb bioavailability by increasing its fecal excretion, but renal excretion and bone deposition may also have favored the reduction of blood Pb concentration. Mineral supplements may be a new easy-to-apply and cost-effective way to reduce livestock exposure in Pb polluted sites., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Here we characterize the bioaccumulation of mercury (Hg) and lead (Pb) in red swamp crayfish (Procambarus clarkii) from two river courses in Central Spain that are impacted by historical Hg and Pb mining activities, respectively. We estimate the absolute oral bioavailability of metals in crayfish tissues by means of in vitro bioaccessibility simulations, and assess whether their consumption may imply a health risk for humans by estimating target hazard quotients and safe consumption rates. We also study the effect of cooking crayfish on the mobilization of the metal body burden in the context of the traditional Spanish cuisine. The results showed that crayfish from the mining districts accumulated a high level of Hg and Pb pollution in both the tail muscle and the carcass. The in vitro bioaccessibility of Hg and Pb in the edible part was 27.86 ± 4.05 and 33.73 ± 5.91%, respectively. Absolute bioavailability was estimated to be 38.31 for Hg, and 20.21 (adults) and 67.35% (children) for Pb. Risk indices indicated that, even after adjusting for bioavailability, it is not safe to consume crayfish from the mining-impacted rivers because of their high levels of Hg and Pb. Using the carcass as a condiment for flavouring should also be avoided. The cooking procedure extracted relatively small amounts of the total Hg (8.92 ± 2.13%) and Pb (1.68 ± 0.29%) body burden. Further research that will support human and ecological risk assessment, along with the implementation of advisory measures for the local population as regards crayfish consumption, are recommended., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Changes in the concentration of circulating essential elements in animals over life may be indicative of periods of vulnerability to deficiencies and associated diseases. Here we studied age-related variations in essential elements (Se, Cu, Zn and Mn) and some selected oxidative stress biomarkers (GPx, SOD, vitamin A and vitamin E) in blood of an Iberian red deer (Cervus elaphus hispanicus) population living in semicaptive conditions. Animals during their first year of life showed to be especially vulnerable to suffer Se- and Cu-related diseases and disorders. Older female deer had lower blood levels of Zn and Mn, which was accompanied by a lower blood SOD activity. On the contrary, GPx blood activity was elevated in older deer, which may help to compensate the reduction of other antioxidants with during aging. Age-related changes in GPx and SOD and their positive relationships with the essential elements suggest that the observed nutritional deficiencies at certain age stages may have a detrimental effect on the antioxidant system, increasing the risk of oxidative stress. Thus, the biomarkers used in the present study may be important tools for the subclinical diagnosis of nutritional disorders and diseases related to the generation of oxidative stress in both domestic and wild ungulates., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A reactive barrier that consisted of vegetable compost, iron oxide and clay was installed in an infiltration basin to enhance the removal of emerging organic compounds (EOCs) in the recharge water. First-order degradation rates and retardation factors were jointly estimated for 10 compounds using a multilayer reactive transport model, whose flow and conservative transport parameters were previously estimated using hydraulic head values and conservative tracer tests. Reactive transport parameters were automatically calibrated against the concentration of EOCs measured at nine monitoring points. The degradation rate of each compound was estimated for three zones defined according to the redox state, and retardation coefficients were estimated in two zones defined according to the organic matter content. The fastest degradation rates were obtained for the reactive barrier, and the estimated values were similar to or higher than those estimated in column and/or field experiments for most of the compounds (8/10). Estimated retardation coefficients in the reactive barrier were higher than in the rest of the aquifer in most cases (8/10) and higher than those values estimated in previous studies. Based on the results obtained in this study the reactive barrier seems to be able to enhance the removal of EOCs., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Groundwater management in urban areas requires a detailed knowledge of the hydrogeological system as well as the adequate tools for predicting the amount of groundwater and water quality evolution. In that context, a key difference between urban and natural areas lies in recharge evaluation. A large number of studies have been published since the 1990s that evaluate recharge in urban areas, with no specific methodology. Most of these methods show that there are generally higher rates of recharge in urban settings than in natural settings. Methods such as mixing ratios or groundwater modeling can be used to better estimate the relative importance of different sources of recharge and may prove to be a good tool for total recharge evaluation. However, accurate evaluation of this input is difficult. The objective is to present a methodology to help overcome those difficulties, and which will allow us to quantify the variability in space and time of the recharge into aquifers in urban areas. Recharge calculations have been initially performed by defining and applying some analytical equations, and validation has been assessed based on groundwater flow and solute transport modeling. This methodology is applicable to complex systems by considering temporal variability of all water sources. This allows managers of urban groundwater to evaluate the relative contribution of different recharge sources at a city scale by considering quantity and quality factors. The methodology is applied to the assessment of recharge sources in the Barcelona city aquifers., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Polyhydroxyalkanoates (PHA) are biopolymers that can be an alternative against conventional plastics. The study reported herein evaluated the enrichment of a mixed microbial culture (MMC) operated under feast/famine regime and different pHs in a sequencing batch reactor (SBR) using acetate as sole carbon source to produce polyhydroxyalkanoates (PHAs). The enrichment step was evaluated at controlled pH of 7.5 and also without pH control (averaged value of 9.0). The acetate uptake rate (-q S ) of both enrichments at the end of the experimental period exhibited similar behaviour being about 0.18CmolAcCmolX -1 h -1 and 0.19CmolAcCmolX -1 h -1 for SBR-A and SBR-B, respectively. However, the PHA-storing capacity of the biomass enriched without pH control was better, exhibiting a maximum PHA content of 36% (gPHAg -1 VSS) with a PHA production rate (q PHA ) of 0.16CmolPHACmolX -1 h -1 . Batch experiments were performed to evaluate PHA-storing capacity of the enriched culture at different pHs and nutrients concentrations. In the pH experiments (without nutrient limitation), it was found that in the absence of controlled pH, the enriched biomass exhibited a PHA content of 44% gPHAg -1 VSS with -q S and PHA to substrate yield (Y PHA/Ac ) of 0.57CmolAcCmolX -1 h -1 and 0.33CmolPHACmolAc -1 , respectively. Regarding the experiments at variable nutrients concentration (pH ranging 8.8 to 9.2), the results indicate that the PHA content in the enriched biomass is significantly higher being around 51% gPHAg -1 VSS under nitrogen limitation. This work demonstrated the feasibility of the enrichment of a MMC with PHA storage ability without pH control. Results also suggest that better PHAs contents and substrate uptake rates are obtained without controlling the pH in the accumulation step. Finally, this work also highlights the importance of understanding the role of nutrients concentration during the accumulation step., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Continuous feeding operation of an airlift reactor and its inoculation with mature aerobic granules allowed the successful treatment of a mixture of aromatic compounds (p-nitrophenol, o-cresol and phenol). Complete biodegradation of p-nitrophenol, o-cresol, phenol and their metabolic intermediates was achieved at an organic loading rate of 0.61 g COD L(-1)d(-1). Stable granulation was obtained throughout the long-term operation (400 days) achieving an average granule size of 2.0 ± 1 mm and a sludge volumetric index of 26 ± 1 mL g(-1) TSS. The identified genera in the aerobic granular biomass were heterotrophic bacteria able to consume aromatic compounds. Therefore, the continuous feeding regimen and the exposure of aerobic granules to a mixture of aromatic compounds make possible to obtain good granulation and high removal efficiency., (Copyright © 2015 Elsevier B.V. All rights reserved.)

A permeable reactive layer was installed at the floor of an infiltration basin. The reactive layer comprised 1) vegetable compost to provide a sorption surface for neutral organic compounds and to release easily degradable organic matter, thus generating a sequence of redox states, and 2) minor amounts of clay and iron oxide to increase sorption of cationic and anionic species, respectively. Field application of this design was successful in generating denitrification, and manganese-, and iron-reducing conditions beneath the basin. This, together with the increase in types of sorption sites, may explain the improved removal of three of the four selected pharmaceuticals compared with their behavior prior to installation of the layer. After installation of the reactive layer, atenolol concentrations were below the detection limits in the vadose zone. Moreover, concentrations of gemfibrozil and cetirizine were reduced to 20% and 40% of their initial concentrations, respectively, after 200 h of residence time. In contrast, prior to installation of the reactive layer, the concentrations of these three pharmaceuticals in both the vadose zone and the aquifer were more than 60% of the initial concentration. Carbamazepine exhibited recalcitrant behavior both prior to and after the reactive barrier installation., (Copyright © 2015 Elsevier B.V. All rights reserved.)

This work is motivated by a sound understanding of the chemical processes that affect the organic pollutants in an urban aquifer. We propose an approach to quantify such processes using mixing calculations. The methodology consists of the following steps: (1) identification of the recharge sources (end-members) and selection of the species (conservative and non-conservative) to be used, (2) identification of the chemical processes and (3) evaluation of mixing ratios including the chemical processes. This methodology has been applied in the Besòs River Delta (NE Barcelona, Spain), where the River Besòs is the main aquifer recharge source. A total number of 51 groundwater samples were collected from July 2007 to May 2010 during four field campaigns. Three river end-members were necessary to explain the temporal variability of the River Besòs: one river end-member is from the wet periods (W1) and two are from dry periods (D1 and D2). This methodology has proved to be useful not only to compute the mixing ratios but also to quantify processes such as calcite and magnesite dissolution, aerobic respiration and denitrification undergone at each observation point., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Livestock from the ancient mining area of Sierra Madrona and Alcudia Valley (Spain) is exposed to elevated levels of lead (Pb), as previous studies based on blood monitoring have revealed. Here we have studied blood, liver and muscle Pb levels in sheep in order to know if Pb exposure could represent a risk for human consumers of the meat and offal of these animals. A cross-sectional study was conducted with ≥4 years old (adults) ewes from the mining area (n=46) and a control area (n=21). Blood samples were taken before the sacrifice at the slaughterhouse, and liver and muscle samples were taken thereafter. At the same time, 2-3 year old rams (subadults, n=17) were blood sampled in the mining area. Blood, liver and muscle Pb levels were higher in the mining than in the control area. Blood Pb concentration in the mining area (n= 44, mean: 6.7μg/dl in ewes and 10.9μg/dl in rams) was above background levels (>6μg/dl) in 73.3 percent of animals. Liver Pb concentration in 68 percent of sheep from the mining area (n=32, mean: 6.16μg/g dry weight, d.w.) exceeded the minimum level associated with toxic exposure (5µg/g d.w.) and 87.5 percent of liver samples were above European Union Maximum Residue Levels (MRL) established for offal destined for human consumption (0.5µg/g w.w.~1.4µg/g d.w.). On the contrary, none of the muscle samples in ewes exceeded the EU MRL (0.1µg/g w.w.~0.34µg/g d.w.) established for meat, which may be related to the decline of blood Pb levels with age observed in the present study. These results suggest a potential health effect for sheep exposed to Pb pollution in this area and implications for food safety, but further research with lamb meat may be necessary to refine the risk assessment for human consumers., (Copyright © 2014 Elsevier Inc. All rights reserved.)

The occurrence and fate of UV filters (UV F) in an urban aquifer in correlation with (1) the spatial distribution of UV F in Barcelona's groundwater, (2) the depth of the groundwater sample, (3) the physicochemical properties of the target compounds, (4) the recharge sources, and (5) the redox conditions of the Barcelona aquifers, were studied for the first time. The highest groundwater concentrations and the largest number of detected UV F were observed in an aquifer recharged by a polluted river (around 55 ng/L in SAP-4). In contrast, the urbanized areas had lower concentrations (around 20 ng/L in MPSP-1). Two pathways can be identified for UV F to enter the aquifers: (1) leakage of row sewage from the sewage network in urbanized areas and (2) wastewater treatment plant (WWTP) effluents discharged into the river. Measured concentrations of UV F were significantly much lower than those estimated from the waste water proportion in groundwater samples suggesting that UV F might undergo transformation processes in both reducing and oxidizing conditions., (Copyright © 2014 Elsevier B.V. All rights reserved.)

This study presents a methodology using an end-member mixing analysis (EMMA) and MIX to compute mixing ratios and to identify hydrochemical reactions in groundwater. The methodology consists of (1) identifying the potential sources of recharge, (2) characterising recharge sources and mixed water samples using hydrogeochemistry, (3) selecting chemical species to be used in the analysis and (4) calculating mixing ratios and identification of hydrochemical reactions in groundwater. This approach has been applied in the Besòs River Delta area, where we have collected 51 groundwater samples and a long data register of the hydrogeochemistry of the Besòs River created by the Catalan Water Agency is also available. The EMMA performed in the Besòs River suggests that 3 end-members are required to explain its temporal variability, accounting for the species chloride, sulphate, sodium, bicarbonate, calcium, magnesium, potassium, ammonium, total nitrogen, and electrical conductivity. One river end-member is from the wet periods (W1), and two are from dry periods (D1 and D2). These end-members have been used to compute mixing ratios in groundwater samples because the Besòs River is considered the main recharge source for the aquifer. Overall, dry season end-members dominated over the wet season end-member, in a proportion of 4:1. Moreover, when departures from the mixing line exist, geochemical processes might be identified. Redox processes, carbonate dissolution/precipitation and ion exchange processes may occur in Besòs Delta aquifer., (Copyright © 2013 Elsevier B.V. All rights reserved.)

A sequencing batch reactor (SBR) was inoculated with p-nitrophenol-degrading activated sludge to biodegrade a mixture of monosubstituted phenols: p-nitrophenol (PNP), PNP and o-cresol; and PNP, o-cresol and o-chlorophenol. Settling times were progressively decreased to promote biomass granulation. PNP was completely biodegraded. The PNP and o-cresol mixture was also biodegraded although some transitory accumulation of intermediates occurred (mainly hydroquinone and catechol). o-Chlorophenol was not biodegraded and resulted in inhibition of o-cresol and PNP biodegradation and complete failure of the SBR within a few days. The biomass had very good settling properties when a settling time of 1 min was applied: sludge volume index (SVI₅) below 50 mL g(-1), SVI₅/SVI₃₀ ratio of 1 and average particle size of 200 μm., (Copyright © 2013 Elsevier B.V. All rights reserved.)

This paper reviewed the presence of emerging organic contaminants (EOCs) that have been found in the groundwater in Spain in both, rural and urban areas. The list of compounds included pesticides, pharmaceutical active compounds (PhACs), selected industrial compounds, drugs of abuse (DAs), estrogens, personal care products and life-style compounds. The main sources of pollution and possible pathways have been summarised in this review. EOCs are likely to enter to the aquifer mainly through the effluents of waste water treatment plants (WWTPs) and are present in groundwater at concentrations of ng/L to μg/L. The most studied compounds in Spanish groundwater were pesticides followed by industrial compounds and PhACs. It is important to mention that compared to other water bodies, such as rivers, groundwater is considerably less contaminated, which may be indicative of the natural attenuation capacity of the aquifers. However, some EOCs have sometimes been detected at higher concentration levels in the aquifer than in the rivers, indicating the need for further research to understand their behaviour in the aquifers. For a wide array of compounds, their maximum concentrations show values above the European groundwater quality standard for individual pesticides (0.1 μg/L). Therefore, to preserve groundwater quality against deterioration it is necessary to define environmental groundwater thresholds for the non-regulated compounds., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Soil-aquifer processes have proven to work as a natural treatment for the attenuation of numerous contaminants during artificial recharge of groundwater. Nowadays, significant scientific effort is being devoted to understanding the fate of pharmaceuticals in subsurface environments, and to verify if such semipersistent organic micropollutants could also be efficiently removed from water. In this context we carried out a series of batch experiments involving aquifer material, selected drugs (initial concentration of 1 μg/L and 1 mg/L), and denitrifying conditions. Diclofenac and sulfamethoxazole exhibited an unreported and peculiar behavior. Their concentrations consistently dropped in the middle of the tests but recovered toward the end, which suggest a complex effect of denitrifying conditions on aromatic amines. The transformation products Nitro-Diclofenac and 4-Nitro-Sulfamethoxazole were detected in the biotic experiments, while nitrite was present in the water. Their concentrations developed almost opposite to those of their respective parent compounds. We conjecture that this temporal and reversible effect of denitrifying conditions on the studied aromatic amines could have significant environmental implications, and could explain at least partially the wide range of removals in subsurface environments reported in literature for DCF and SMX, as well as some apparent discrepancies on SMX behavior., (Copyright © 2012 Elsevier B.V. All rights reserved.)

This study is concerned with drugs of abuse (DAs) and their metabolites in urban groundwater at field scale in relation to (1) the spatial distribution of DAs in Barcelona's groundwater, (2) the depth of the groundwater samples, (3) the presence of DAs in recharge sources, and (4) the assessment of the fate of DAs in Barcelona aquifers. To this end, 37 urban groundwater samples were collected in the city of Barcelona and a total of 21 drugs were analyzed including cocainics, amphetamine-like compounds, opioids, lysergics and cannabinoids and the prescribed drugs benzodiazepines. Overall, the highest groundwater concentrations (around 200 ng/L in SAP-4) and the largest number of detected DAs were found in zones basically recharged by a river that receives large amounts of effluents from waste water treatment plants (WWTPs). In contrast, the urbanized areas yielded not only lower concentrations but also a much smaller number of drugs, which suggests a local origin. In fact, cocaine and its metabolite were dominant in more prosperous neighborhoods, whereas the cheaper MDMA was the dominant DA in poorer districts. Measured concentrations were consistently smaller than those estimated from the waste water fraction in groundwater samples, suggesting that DAs undergo removal processes in both reducing and oxidizing conditions., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Growth in production and use of nanoparticles (NPs) will result increased concentrations of these in industrial and urban wastewaters and, consequently, in wastewater-treatment facilities. The effect of this increase on the performance of the wastewater-treatment process has not been studied systematically and including all the microbial communities involved in wastewater treatment. The present work investigates, by using respiration tests and biogas-production analysis, the inhibitory effect of four different commonly used metal oxide (CeO(2) and TiO(2)) and zero-valent metal (Ag and Au) nanoparticles on the activity of the most important microbial communities present in a modern wastewater-treatment plant. Specifically, the actions of ordinary heterotrophic organisms, ammonia oxidizing bacteria, and thermophilic and mesophilic anaerobic bacteria were tested in the presence and absence of the nanoparticles. In general, CeO(2) nanoparticles caused the greatest inhibition in biogas production (nearly 100%) and a strong inhibitory action of other biomasses; Ag nanoparticles caused an intermediate inhibition in biogas production (within 33-50%) and a slight inhibition in the action of other biomasses, and Au and TiO(2) nanoparticles caused only slight or no inhibition for all tested biomasses., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The natural processes occurring in subsurface environments have proven to effectively remove a number of organic pollutants from water. The predominant redox conditions revealed to be one of the controlling factors. However, in the case of organic micropollutants the knowledge on this potential redox-dependent behavior is still limited. Motivated by managed aquifer recharge practices microcosm experiments involving aquifer material, settings potentially feasible in field applications, and organic micropollutants at environmental concentrations were carried out. Different anaerobic redox conditions were promoted and sustained in each set of microcosms by adding adequate quantities of electron donors and acceptors. Whereas denitrification and sulfate-reducing conditions are easily achieved and maintained, Fe- and Mn-reduction are strongly constrained by the slower dissolution of the solid phases commonly present in aquifers. The thorough description and numerical modeling of the evolution of the experiments, including major and trace solutes and dissolution/precipitation of solid phases, have been proven necessary to the understanding of the processes and closing the mass balance. As an example of micropollutant results, the ubiquitous beta-blocker atenolol is completely removed in the experiments, the removal occurring faster under more advanced redox conditions. This suggests that aquifers constitute a potentially efficient alternative water treatment for atenolol, especially if adequate redox conditions are promoted during recharge and long enough residence times are ensured., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Following on the accident occurred in Aznalcóllar in 1998, whereby a huge amount of acid mine drainage and heavy metal-bearing pyritic sludge was released to the Agrio river valley with the subsequent contamination of groundwater, a subsurface permeable reactive barrier (PRB) was installed to mitigate the long-term impacts by the spillage. The PRB material consisted of a mixture of limestone and vegetal compost. A particular characteristic of the Agrio aquifer is its high water flow velocity (0.5-1 m/d), which may pose difficulties in its remediation using PRB technology. The present study reports the 36-month performance of the PRB. Vertical differences in water velocity were observed within the PRB, with the deeper part being slower and more effective in neutralizing pH and removing heavy metals (Zn, Al, Cu). On the other hand, partial sulfate removal appeard to be restricted to the bottom of the PRB, but with no apparent influence on downgradient water quality. The results are finally compared with the other four reported existing PRBs for AMD worldwide., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Background Aims: Human multipotent mesenchymal stromal cells (hMSC) have become one of the main interests in regenerative medicine because of their ability to differentiate into different lineages. Human amniotic fluid is reported to contain MSC (hAMSC) and therefore may be a useful source of cells for clinical applications. However, our understanding of the behavior of these cells in indefinite in vitro culture conditions is very limited., Methods: We systematically evaluated and characterized, throughout their whole lifespan, the expansion potential, chromosomal stability, surface and intracellular phenotype and differentiation potential of fibroblastoid hAMSC (F-type hAMSC)., Results: Nine F-type hAMSC cultures could be expanded in in vitro culture conditions for 223.25 ± 24.44 days (mean ± SD), during which time 28.96 ± 1.5 passages were made giving rise to 54.95 ± 3.17 population doublings (PD) and an estimated number of accumulated cells of between 1.0 × 10(22) and 9.7 × 10(23), with no visible alterations in the chromosome during their lifespan. All the cultures showed unchanged percentages of strongly positive expressions of the surface markers CD29, CD44, CD73, CD90, CD95, CD105 and HLA-ABC, as well as the embryonic intracellular markers Nanog and Sox2, during their lifespan, whereas the expression of the embryonic surface markers SSEA3, SSEA4, TRA-1-60 and TRA-1-81 fell until it disappeared with progression of the culture. These cells retained their differentiation capacities to adipogenic, chondrogenic and osteogenic lineages throughout their lifespan., Conclusions: F-type hAMSC exhibit reproducible biologic characteristics, confirming that these cells are ideal candidates for use in regenerative medicine.

Spatial variability in a flow field leads to spreading of a tracer plume. The effect of microdispersion is to smooth concentration gradients that exist in the system. The combined effect of these two phenomena leads to an 'effective' enhanced mixing that can be asymptotically quantified by an effective dispersion coefficient (i.e. Taylor dispersion). Mixing plays a fundamental role in driving chemical reactions. However, at pre-asymptotic times it is considerably more difficult to accurately quantify these effects by an effective dispersion coefficient as spreading and mixing are not the same (but intricately related). In this work we use a volume averaging approach to calculate the concentration distribution of an inert solute release at pre-asymptotic times in a stratified formation. Mixing here is characterized by the scalar dissipation rate, which measures the destruction of concentration variance. As such it is an indicator for the degree of mixing of a system. We study pre-asymptotic solute mixing in terms of explicit analytical expressions for the scalar dissipation rate and numerical random walk simulations. In particular, we divide the concentration field into a mean and deviation component and use dominant balance arguments to write approximate governing equations for each, which we then solve analytically. This allows us to explicitly evaluate the separate contributions to mixing from the mean and the deviation behavior. We find an approximate, but accurate expression (when compared to numerical simulations) to evaluate mixing. Our results shed some new light on the mechanisms that lead to large scale mixing and allow for a distinction between solute spreading, represented by the mean concentration, and mixing, which comes from both the mean and deviation concentrations, at pre-asymptotic times., (Copyright © 2010 Elsevier B.V. All rights reserved.)

The correct characterization of the effective reactive transport dynamics is an important issue for modeling reactive transport on the Darcy scale, specifically in situations in which reactions are localized, that is when different reactions occur in different portions of the porous medium. Under such conditions the conventional approach of homogenizing only the porous medium chemistry is not appropriate. We consider here reactive transport in a porous medium that is characterized by mass transfer between a mobile and a distribution of immobile regions. Chemical and physical heterogeneities are reflected by distributions of kinetic reaction rate constants and residence times in the immobile zones. We derive an effective reactive transport equation for the mobile solute that is characterized by non-local physical mass transfer and reaction terms. Specifically, chemical heterogeneity is upscaled in terms of a reactive memory function that integrates both chemical and physical heterogeneity. Mass transfer limitations due to physical heterogeneity yield effective kinetic rate coefficients that can be much smaller than the volumetric average of the local scale coefficients. These results help to explain and quantify the often reported discrepancy between observed field reaction rate constants and the ones obtained under well mixed laboratory conditions. Furthermore, these results indicate that transport under physical and chemical heterogeneity cannot be upscaled separately., (Copyright © 2010 Elsevier B.V. All rights reserved.)

There are a number of publications in the literature that might indicate a connection between pH and the kinetics of the aerobic p-nitrophenol (PNP) biodegradation. In this study two hypotheses were postulated to elucidate the kinetics dependence on pH: (i) the substrate inhibition does not depend on the pH value, therefore the half-saturation coefficient and the substrate inhibition constant will be the same at any pH and (ii) the substrate inhibition depends on the pH value, therefore the half-saturation coefficient and the substrate inhibition constant will have a different value depending on the pH. A PNP-degrading activated sludge was used to carry out three batch respirometric experiments at different pH values: 6.5±0.1, 7.0±0.1, 8.0±0.1. The ability to describe the experimental results with the kinetic models derived from both postulated hypotheses was quantitatively evaluated through the norm of the prediction error array. The time course of specific oxygen uptake rate and PNP concentration was satisfactorily described by a Haldane kinetics that includes the pH effect, based on the PNP acid-base equilibrium, on the kinetic parameters. The results suggest that the nonionised form of PNP is the real substrate and also the inhibitor of the aerobic PNP biodegradation., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Water-soluble efflorescent salts often form on tailings in hyperarid climates. Their high solubility together with the high risk of human exposure to heavy metals such as Cu, Ni, Zn, etc., makes this occurrence a serious environmental problem. Understanding their formation (genesis) is therefore key to designing prevention and remediation strategies. A significant amount of these efflorescences has been described on the coastal area of Chañaral (Chile). There, highly soluble salts such as halite (NaCl) and eriochalcite (CuCl(2).2H(2)O) form on 4km(2) of marine shore tailings. Natural occurrence of eriochalcite is rare: its formation requires extreme environmental and geochemical conditions such as high evaporation rate and low relative air humidity, and continuous Cl and Cu supply from groundwater, etc. Its formation was examined by means of reactive transport modeling. A scenario is proposed involving sea water and subsequently a mixture of sea water/freshwater in the groundwater composition in the formation of these efflorescences. The strong competition from other halides (i.e. halite and silvite (KCl)) for the Cl may inhibit the precipitation of eriochalcite. Therefore, the Cl/Na ratio trend >1 is a key parameter in its formation. Cation-exchange between Na(+) and other major ions such as K(+), Ca(2+), Mg(2+) and Cu(2+) in the clay fraction of tailings is proposed to account for realistic Cl/Na ratios. With regard to preventing the formation of eriochalcite, a capillary barrier on the tailings surface is proposed as a suitable alternative. Its efficiency as a barrier is also tested by means of reactive transport models.

Active gas control systems are commonly used in municipal solid waste (MSW) landfills and the design of such systems requires thorough understanding of the gas flow pattern. A model is developed to predict the two-dimensional radial transient gas flow to a vertical gas extraction well in deformable MSW landfills. Variations of gas storage include time-dependent compression of the refuse, dissolution of gas components and porosity enlargement due to organic matter degradation. Mechanical compression of solid skeleton is coupled with gas pressure using K-H rheological model which is capable of reproduce the evolution of settlement for MSW landfills. The new analytical solution obtained in Laplace transform domain can be used to determine excess gas pressure fields, gas fluxes in the well and through the top cover as well as landfill settlements. The solution is validated by comparison with field measurements and numerical simulations. It demonstrates that the gas storage variation term becomes predominant only during early times. Long-term gas flow is controlled by the gas generation rate and the quasi-steady solution is valid. Parametric studies indicate that the solution given in this paper is useful for the prediction of gas fluxes, for the choice of the optimum spacing between wells, and for the determination of the final cover properties as well as appropriate vacuum pressure imposed in the extraction well.

We review the current status of expression of heterologous systems for bioenergy and bioproduction in bacteria using a model-based approach. As an aim for synthetic biology, it requires mathematical models of genetic modules that could be characterized independently of their context. This fastens the design of metabolic circuits using a combinatorial design approach, where given pathways could be optimized for maximal bioproduction, while being nontoxic for the chassis. We show how recent characterization of genetic parts, such as promoters, RBS or sRNAs could be used to fine-tune the expression of individual genes to achieve that goal. We also present lists of enzymes that are used for bioproduction, enlarging such set of biological parts.

We report a patient in Automatic Peritoneal Dialysis (APD) with tuberculous peritonitis by possible peritoneal infection due to the proximity between fallopian tube and the left ovary, a peritoneal liquid culture was constantly negative. The patient presented a bad clinic evolution. Her only medical history was hypercalcemia six months before developing a peritonitis and occasionally nausea and vomits To confirm the diagnosis it was needed a peritoneal biopsy by means of a laparoscopy with a removal of the peritoneal catheter and left anexectomy. Now, the patient is asintomatic in daily home hemodialysis.

Wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) were investigated as suitable precursors for the biological treatment of industrial wastewater containing sodium dodecylbenzene sulfonate (DBS). Two hours WAO semi-batch experiments were conducted at 15 bar of oxygen partial pressure (P(O2)) and at 180, 200 and 220 degrees C. It was found that the highest temperature provides appreciable total organic carbon (TOC) and chemical oxygen demand (COD) abatement of about 42 and 47%, correspondingly. Based on the main identified intermediates (acetic acid and sulfobenzoic acid) a reaction pathway for DBS and a kinetic model in WAO were proposed. In the case of CWAO experiments, seventy-two hours tests were done in a fixed bed reactor in continuous trickle flow regime, using a commercial activated carbon (AC) as catalyst. The temperature and P(O2) were 140-160 degrees C and 2-9 bar, respectively. The influence of the operating conditions on the DBS oxidation, the occurrence of oxidative coupling reactions over the AC, and the catalytic activity (in terms of substrate removal) were established. The results show that the AC without any supported active metal behaves bi-functional as adsorbent and catalyst, giving TOC conversions up to 52% at 160 degrees C and 2 bar of P(O2), which were comparable to those obtained in WAO experiments. Respirometric tests were completed before and after CWAO and to the main intermediates identified through the WAO and CWAO oxidation route. Then, the readily biodegradable COD (COD(RB)) of the CWAO and WAO effluents were found. Taking into account these results it was possible to compare whether or not the CWAO or WAO effluents were suitable for a conventional activated sludge plant inoculated with non adapted culture.

Two families of approaches exist to simulate reactive transport in groundwater: The Direct Substitution Approach (DSA), based on Newton-Raphson and the Picard or Sequential Iteration Approach (SIA). We applied basic versions of both methods to several test cases and compared both computational demands and quality of the solution for varying grid size. Results showed that the behavior of the two approaches is sensitive to both grid size and chemistry. As a general rule, the DSA is more robust than the SIA, in the sense that its convergence is less sensitive to time step size (any approach will converge given a sufficiently small time step). Moreover, the DSA leads to a better simulation of sharp fronts, which can only be reproduced with fine grids after many iterations when the SIA is used. As a consequence, the DSA runs faster than SIA in chemically difficult cases (i.e., highly non-linear and/or very retarded), because the SIA may require very small time steps to converge. On the other hand, the size of the system of equations is much larger for the DSA than for the SIA, so that its CPU time and memory requirements tend to be less favorable with increasing grid size. As a result, the SIA may become faster than the DSA for very large, chemically simple problems. The use of an iterative linear solver for the DSA makes its CPU time less sensitive to grid size.