Removal of nitrate and pesticides from groundwater by nano zero-valent iron injection pulses under biostimulation and bioaugmentation scenarios in continuous-flow packed soil columns.

This study evaluates the NO3- removal from groundwater through Heterotrophic Denitrification (HDN) (promoted by the addition of acetate and/or an inoculum rich in denitrifiers) and Abiotic Chemical Nitrate Reduction (ACNR) (promoted by pulse injection of zerovalent iron nanoparticles (nZVI)). HDN and ACNR were applied, separately or combined, in packed soil column experiments to complement the scarce research on pulse-injected nZVI in continuous-flow systems mimicking a Well-based Denitrification Barrier. Together with NO3-, the removal of two common pesticides (dieldrin and lindane) was evaluated. Results showed that total NO3- removal (>97%) could be achieved by either bioestimulation with acetate (converting NO3- to N2(g) via HDN) or by injecting nZVI (removing NO3- via ACNR). In the presence of nZVI, NO3- was partially converted to N2(g) and to a lower extent NO2-, with unreacted NO3- being likely adsorbed onto Fe-(oxy)hydroxides. Combination of both HDN and ACNR resulted in even a higher NO3- removal (>99%). Interestingly, nZVI did not seem to pose any toxic effect on denitrifiers. These results showed that both processes can be alterned or combined to take advantage of the benefits of each individual process while overcoming their disadvantages if applied alone. With regard to the target pesticides, the removal was high for dieldrin (>93%) and moderate for lindane (38%), and it was not due to biodegradation but to adsorption onto soil. When nZVI was applied, the removal increased (generally >91%) due to chemical degradation by nZVI and/or adsorption onto formed Fe-(oxy)hydroxides.

Removal of nitrate from groundwater by nano-scale zero-valent iron injection pulses in continuous-flow packed soil columns.

Injection of zero-valent iron nanoparticles (nZVI) into aquifers has gained increasing attention of researchers for in-situ treatment of NO3--contaminated groundwater. nZVI has proved efficient in chemically reducing NO3- and, according to recent research efforts, in supporting biological denitrification under favoured conditions. Given the scarce research on nZVI pulsed injection in continuous-flow systems, the objective of this study was to evaluate the effect of nZVI pulses on the removal of NO3- from groundwater in packed soil columns and, more particularly, to elucidate whether or not biotic NO3- removal processes were promoted by nZVI. Three identical columns were filled with aquifer soil samples and fed with the same nitrate polluted groundwater but operated under different conditions: (A) with application of nZVI pulses and biocide spiked in groundwater, (B) without application of nZVI pulses and (C) with application of nZVI pulses. Results showed that the application of nZVI (at 30 mg/L and 78 mg/L doses) resulted in an immediate and sharp removal of NO3- (88-94%), accompanied by an increase in pH (from 7.0 to 9.0-10.0), a drop in redox potential (Eh) (from +420 mV to <100 mV) and a release of Fe(II) and Total Organic Carbon (TOC) in the effluent (to 200 mg/L and 150-200 mg/L, respectively). The released TOC came from the organic polymer used as stabilizer of the nZVI particles. Comparison against the sterilized control column revealed that, under the experimental conditions, no biological denitrification developed and that the removal of NO3- was due to chemical reduction by nZVI. The main by-product of the NO3- removal was NH4+, which at the prevailing pH was partially converted to NH3, which dissipated from the aqueous solution resulting in a net removal of total dissolved N. A mass balance of Fe permitted to quantify the percentage of injected nZVI trapped in the column (>98%) and the NO3- retention capacity of the nZVI particles (13.2-85.5 mg NO3-/g nZVI).

Removal of Transition Metals from Contaminated Aquifers by PRB Technology: Performance Comparison among Reactive Materials.

The most common reactive material used for the construction of a permeable reactive barrier (PRB) is zero valent iron (ZVI), however, its processing can generate corrosive effects that reduce the efficiency of the barrier. The present study makes a major contribution to understanding new reactive materials as natural and synthetic, easy to obtain, economical and environmentally friendly as possible substitutes for the traditional ZHV to be used as filters in the removal of three transition metals (Zn, Cu, Cd). To assess the ability to remove these pollutants, a series of batch and column tests were carried out at laboratory scale with these materials. Through BACH tests, four of seven substances with a removal percentage higher than 99% were prioritized (cabuya, natural clinoptilolite zeolites, sodium mordenite and mordenite). From this group of substances, column tests were performed where it is evidenced that cabuya fiber presents the lowest absorption time (≈189 h) while natural zeolite mordenite shows the highest time (≈833 h). The latter being the best option for the PRB design. The experimental values were also reproduced by the RETRASO code; through this program, the trend between the observed and simulated values with respect to the best reactive substance was corroborated.

Concordance Between Rapid On-Site Evaluation and Final Cytologic Diagnosis in Patients Undergoing Endobronchial Ultrasound-Guided Transbronchial Needle Aspiration for Non-Small Cell Lung Cancer Staging.

OBJECTIVES: In patients with lung cancer undergoing mediastinal staging through endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA), decisions are based on rapid on-site evaluation (ROSE) findings. We aimed to analyze the concordance rate between ROSE diagnosis and final diagnosis. METHODS: A prospective study was carried out in patients undergoing EBUS-TBNA for lung cancer staging. Diagnosis concordance was defined as cases where lymph nodes (LNs) presented the same diagnosis in ROSE and final diagnosis. Determinants of concordance were analyzed. RESULTS: Sixty-four patients were included and 637 LNs sampled. ROSE diagnosis was concordant with final diagnosis in 612 (96.1%) LNs and nonconcordant in 25 (3.9%). Differences in the concordance rate were found between pathologists, ROSE diagnoses, presence of cell block, number of passes, and number of slides. The staging status was changed between ROSE and the final diagnosis in three (4.6%) patients. CONCLUSIONS: ROSE diagnosis has a high concordance with the final diagnosis.

Performance of a field-scale biological permeable reactive barrier for in-situ remediation of nitrate-contaminated groundwater.

We report the performance of a field-scale permeable reactive barrier (PRB) for the biological treatment of nitrate-contaminated groundwater. The reactive material of the PRB consisted of a mixture of gravel and mulch as a carbon source for denitrifying bacteria. The PRB was equipped with a delivery system that allowed injecting NO3- at controlled rates from the surface directly into the up-gradient layer of the PRB. This way, NO3- concentration entering the PRB was varied (from 1 to 530 mg/L) with the purpose of evaluating the ultimate efficiency of the PRB under different NO3- loadings. The PRB was successful at removing NO3- from groundwater at inlet concentrations up to 280 mg/L (with NO3- removal percentages ≥97%). Monitoring of groundwater at different depths within the PRB provided evidence that NO3- underwent denitrification preferably at the deepest part of the PRB, where more favourable reducing conditions were achieved. Among the shortcomings of the PRB were the fluctuations of groundwater fluxes caused by intense rainfalls during the study period, although they generally did not pose concern for the denitrification capacity of the PRB. Emission fluxes of gases (CO2, CH4 and N2O) from the PRB to the atmosphere were also measured. The results are finally compared with the few others reported existing PRBs for nitrate-contaminated groundwater worldwide.

Selection of organic substrates as potential reactive materials for use in a denitrification permeable reactive barrier (PRB).

The aim of the present study was to select a suitable natural organic substrate as a potential carbon source for use in a denitrification permeable reactive barrier (PRB). A number of seven organic substrates were first tested in batch tests. The materials attained varying degrees of success at promoting denitrification. Some of the organic substrates performed very well, achieving complete nitrate removal (>98%), while others were considered unsuitable for a variety of reasons, including: insufficient nitrate or nitrogen removal, excessive release of leachable nitrogen from the substrate or excessive reduction of nitrate to ammonium rather than removing it as gaseous N2. The top performing substrate in terms of denitrification extent (>98%) and rate (0.067 mgNO3(-)-N dm(-3)d(-1)g(sub)(-1)) was then selected for two bench-scale column experiments in an attempt to simulate the PRB. The inlet concentration was 50 mg dm(-3) NO3(-)-N and the columns operated at two different flow rates: 0.3 cm3 min(-1) (Column 1) and 1.1cm3 min(-1) (Column 2). The two columns showed different general patterns, making it clear that the flow rate was a key factor at the nitrate removal. Nitrate was completely removed (>96%) by the passage through Column 1, while only partially removed in Column 2 (66%). The results indicated that the selected organic substrate (Softwood) was applicable for further use as a filling material for a PRB.

Distribution of polycyclic aromatic hydrocarbons (PAHs) and tributyltin (TBT) in Barcelona harbour sediments and their impact on benthic communities.

Sediments have long been recognised as a sink for many contaminants like polycyclic aromatic hydrocarbons (PAHs) and tributyltin (TBT), which by virtue of their nature can strongly adsorb onto sediments affecting the benthic community inhabiting them. Using geographical information systems, this study reports and combines the results of several already existing studies along Barcelona harbour in order to assess the potential ecological impacts of these contaminants on the benthos of the harbour ecosystem. Chemical analysis indicated low to moderate contents of PAHs and high contents of TBT in sediments in Barcelona harbour. Comparison against existing sediment quality guidelines (SQGs) indicated that acutely toxic effects would not be expected for PAHs but for TBT, which represents a serious environmental threat for the benthic community. Benthos surveys revealed a deterioration of the benthic community throughout the harbour, especially in the inner port.

Recovery of nutrients (N-P-K) from potassium-rich sludge anaerobic digestion side-streams by integration of a hybrid sorption-membrane ultrafiltration process: Use of powder reactive sorbents as nutrient carriers.

Here, an alternative nutrient (N-P-K) recovery route from potassium-rich sludge anaerobic digestion side-streams using powder reactive sorbents (PRSs) is presented. In the first step, the optimum PRS system was determined in batch experiments with mixtures of: a) a sodium zeolite (NaP1) to facilitate the NH4+ and K+ sorption; b) a Ca-zeolite (CaP1) to facilitate the removal of P by formation of Ca-phosphates (e.g., CaHPO4(s)), and c) caustic magnesia containing mixtures of MgO to facilitate the formation of Mg/NH4/PO4 minerals (e.g., struvite and magnesium phosphates). Evaluation of the continuous and simultaneous N-P-K removal with mixtures of PRSs was carried out using a hybrid sorption/filtration system with ultrafiltration (UF) hollow-fibre membranes. The dosing ratios of the PRS mixtures were optimised on the basis of the equilibrium and kinetic sorption data, and a PRS dose (<2-5gPRS/L) was selected to ensure the hydraulic performance of the system. Under such conditions, and with synthetic anaerobic side-stream removal capacities (qt) of 220±10mgN-NH4/g, 35±5mgP-PO4/g, and 8±2mgK/g, removal efficiencies of 32±3, 78±5, and 26±3% for ammonium, phosphate, and potassium, respectively, were obtained for the binary mixtures of NaP1/CaP1 zeolites. Contrary to the batch results, the use of tertiary mixtures of NaP1/CaP1/MgO only improved the K removal capacity and efficiency to 18±2mgK/g and 55±4%, respectively, while the phosphate removal capacity and efficiency remained unchanged (ca. 35±3mgP-PO4/g; 80±5%) and the ammonium capacity and efficiency were reduced to 185±12mgN-NH4/g and 20±2%, respectively, due to the competing Mg2+ ion effect. Nutrient removal trials with real anaerobic side-streams using binary mixtures of Na/Ca zeolites showed a reduction of both the hydraulic performance and the nutrient removal ratios due to the presence of dissolved organic matter. However, constant removal ratios of N, P, and K were recorded throughout the filtration experiments. The loaded PRSs exhibited suitable nutrient release rates and bioavailability as co-substrates for soil quality improvement. Chemical analyses detected the formation of Ca/P/O and Mg/N/P/O neo-minerals; however, the mineralogical data revealed only the formation of struvite, even when no magnesium oxide was used.

Sorption studies of Zn(II) and Cu(II) onto vegetal compost used on reactive mixtures for in situ treatment of acid mine drainage.

The efficiency of the sulphate reducing bacteria-based in situ treatment of acid mine drainage is often limited by the low degradability of the current carbon sources, typically complex plant-derived materials. In such non-sulphate-reducing conditions, field and laboratory experiences have shown that mechanisms other than sulphide precipitation should be considered in the metal removal, i.e. metal (oxy)hydroxides precipitation, co-precipitation with these precipitates, and sorption onto the organic matter. The focus of the present paper was to present some laboratory data highlighting the Zn and Cu sorption on vegetal compost and to develop a general and simple model for the prediction of their distribution in organic-based passive remediation systems. The model considers two kinds of sorption sites ( succeeds SO(2)H(2)) and the existence of monodentate and bidentate metal-binding reactions, and it assumes that only free M(2+) species can sorb onto the compost surface. The acid-base properties of the compost were studied by means of potentiometric titrations in order to identify the nature of the involved surface functional groups and their density. The distribution coefficient (K(D)) for both Zn and Cu were determined from batch experiments as a function of pH and metal concentration. The model yielded the predominant surface complexes at the experimental conditions, being succeeds SO(2)Zn for Zn and succeeds SO(2)HCu(+) and ( succeeds SO(2)H)(2)Cu for Cu, with log K(M) values of -2.10, 3.36 and 4.65, respectively. The results presented in this study have demonstrated that the proposed model provides a good description of the sorption process of Zn and Cu onto the vegetal compost used in these experiments.

Chemical characterisation of natural organic substrates for biological mitigation of acid mine drainage.

The current approach of the biological treatment of acid mine drainage by means of a passive remediation system involves the choice of an appropriate organic substrate as electron donor for sulphate reducers. Nowadays this selection is one of the critical steps in the performance of such treatment, as this depends to a great extent on the degradability of the organic substrate. Thus, a prior characterisation of the organic substrate predicting its biodegradability would be desirable before embarking on an extensive large-scale application. The aim of this study was to correlate the chemical composition (lignin content) of four different natural organic substrates (compost, sheep and poultry manures, oak leaf) and their capacity to sustain bacterial activity in an attempt to predict biodegradation from chemical characterisation. The results showed that the lower the content of lignin in the organic substrate, the higher its biodegradability and capacity for developing bacterial activity. Of the four organic materials, sheep and poultry manures and oak leaf evolved reducing conditions and sustained active sulphidogenesis, which coupled with the decrease in sulphate concentration indicated bacterial activity. Sheep manure was clearly the most successful organic material as electron donor (sulphate removal >99%), followed by poultry manure and oak leaf (sulphate removal of 80%). Compost appeared to be too poor in carbon to promote sulphate-reducing bacteria activity by itself. Column experiments emphasised the importance of considering the residence time as a key factor in the performance of continuous systems. With a residence time of 0.73 days, sheep manure did not promote sulphidogenesis. However, extending residence time to 2.4 and 9.0 days resulted in an increase in the sulphate removal to 18% and 27%, respectively.

Performance of a field-scale permeable reactive barrier based on organic substrate and zero-valent iron for in situ remediation of acid mine drainage.

A permeable reactive barrier (PRB) was installed in Aznalcóllar (Spain) in order to rehabilitate the Agrio aquifer groundwater severely contaminated with acid mine drainage after a serious mining accident. The filling material of the PRB consisted of a mixture of calcite, vegetal compost and, locally, Fe(0) and sewage sludge. Among the successes of the PRB are the continuous neutralisation of pH and the removal of metals from groundwater within the PRB (removals of >95%). Among the shortcomings are the improper PRB design due to the complexity of the internal structure of the Agrio alluvial deposits (which resulted in an inefficient capture of the contaminated plume), the poor degradability of the compost used and the short residence time within the PRB (which hindered a complete sulphate reduction), the clogging of a section of the PRB and the heterogeneities of the filling material (which resulted in preferential flows within the PRB). Undoubtedly, it is only through accumulated experience at field-scale systems that the potentials and limits of the PRB technology can be determined.

Fractionation and removal of dissolved organic carbon in a full-scale granular activated carbon filter used for drinking water production.

The removal of natural organic matter (NOM) and, more particularly, its individual fractions by two different GACs was investigated in full-scale filters in a drinking water treatment plant (DWTP). Fractionation of NOM was performed by high performance size exclusion chromatography (HPSEC) into biopolymers, humic substances, building blocks and low molecular weight organics. The sorption capacity of GAC in terms of iodine number (IN) and apparent surface area (SBET), as well as the filling of narrow- and super-microporosity were monitored over the 1-year operation of the filters. Both GACs demonstrated to be effective at removing NOM over a wide range of fractions, especially the low and intermediate molecular weight fractions. TOC removal initially occurred via adsorption, and smaller (lighter) fractions were more removed as they could enter and diffuse more easily through the pores of the adsorbent. As time progressed, biodegradation also played a role in the TOC removal, and lighter fractions continued to be preferentially removed due to their higher biodegradability. The gained knowledge would assist drinking water utilities in selecting a proper GAC for the removal of NOM from water and, therefore, complying more successfully the latest water regulations.

Characterising biofilm development on granular activated carbon used for drinking water production.

Under normal operation conditions, granular activated carbon (GAC) employed in drinking water treatment plants (DWTPs) for natural organic matter (NOM) removal can be colonised by microorganisms which can eventually establish active biofilms. The formation of such biofilms can contribute to NOM removal by biodegradation, but also in clogging phenomena that can make necessary more frequent backwashes. Biofilm occurrence and evolution under full-scale-like conditions (i.e. including periodic backwashing) are still uncertain, and GAC filtration is usually operated with a strong empirical component. The aim of the present study was to assess the formation and growth, if any, of biofilm in a periodically backwashed GAC filter. For this purpose, an on-site pilot plant was assembled and operated to closely mimic the GAC filters installed in the DWTP in Sant Joan Despí (Barcelona, Spain). The study comprised a monitoring of both water and GAC cores withdrawn at various depths and times throughout 1 year operation. The biomass parameters assessed were total cell count by confocal laser scanning microscopy (CLSM), DNA and adenosine triphosphate (ATP). Visual examination of GAC particles was also conducted by high-resolution field emission scanning electron microscopy (FESEM). Additionally, water quality and GAC surface properties were monitored. Results provided insight into the extent and spatial distribution of biofilm within the GAC bed. To sum up, it was found that backwashing could physically detach bacteria from the biofilm, which could however build back up to its pre-backwashing concentration before next backwashing cycle.

In-situ remediation of acid mine drainage using a permeable reactive barrier in Aznalcóllar (Sw Spain).

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.

Performance of a sequential reactive barrier for bioremediation of coal tar contaminated groundwater.

Following a thorough site investigation, a biological Sequential Reactive Barrier (SEREBAR), designed to remove Polycyclic Aromatic Hydrocarbons (PAHs) and BTEX compounds, was installed at a Former Manufactured Gas Plant (FMGP) site. The novel design of the barrier comprises, in series, an interceptor and six reactive chambers. The first four chambers (2 nonaerated-2 aerated) were filled with sand to encourage microbial colonization. Sorbant Granular Activated Carbon (GAC) was present in the final two chambers in order to remove any recalcitrant compounds. The SEREBAR has been in continuous operation for 2 years at different operational flow rates (ranging from 320 L/d to 4000 L/d, with corresponding residence times in each chamber of 19 days and 1.5 days, respectively). Under low flow rate conditions (320-520 L/d) the majority of contaminant removal (>93%) occurred biotically within the interceptor and the aerated chambers. Under high flow rates (1000-4000 L/d) and following the installation of a new interceptor to prevent passive aeration, the majority of contaminant removal (>80%) again occurred biotically within the aerated chambers. The sorption zone (GAC) proved to be an effective polishing step, removing any remaining contaminants to acceptable concentrations before discharge down-gradient of the SEREBAR (overall removals >95%).