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Query: UMLS:C0016382 (flushing)
 6,387 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Seasonal (October 1997 and May 1998) concentrations of dissolved (< 0.45 micron) trace metals (Ag, Al, Cd, Cu, Fe, Mn), inorganic nutrients (NO3, PO4, Si), DOC and DON were measured at seven wells during periods of low and high groundwater flow, in the aquifer around Flanders Bay in Eastern Long Island, New York. Similar measurements were made in surface waters of Flanders Bay, a shallow coastal embayment with restricted water flushing and river input. Dissolved constituents in the groundwater were classified according to their behavior under different flow conditions as follows: (1) peak during high flow (DOC, pH, Si, NO3, Al and Cu); (2) peak during low flow (salinity, DON, Ag, Cd, Mn); and (3) concentrations independent of flow conditions (PO4 and Fe). The primarily urban and agricultural land use on the North Fork of Long Island was reflected in higher concentrations of nutrients, Cu and Cd in groundwater, compared to samples from the South Fork which is mostly open parkland. Principal component analysis indicated that groundwater seepage could influence the chemical composition of Flanders Bay with respect to the major geochemical carriers (e.g. Fe and Mn). However, mass balance estimates for Cu indicated that, during low flow conditions, net groundwater Cu input was about 10% of the total input. In contrast, during high flow, net groundwater flow could account for up to 58% of all Cu inputs. Nevertheless, a large imbalance, which accounted for up to 70% of the outflux during low aquifer recharge, suggested that the Cu budget of the Bay was not adequately described by the inputs considered (river, net groundwater flow, atmospheric deposition, and tidal exchange). Important missing components of the Cu mass balance in Flanders Bay may include groundwater circulation driven by tides and waves as well as diffusive benthic fluxes.
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PMID:Influence of net groundwater discharge on the chemical composition of a coastal environment: Flanders Bay, Long Island, New York. 1135 17

A solid-phase extraction method based on an ion-exchange retention mechanism has been used for in-line preconcentration of inorganic anions prior to their separation by capillary electrophoresis (CE). A single capillary containing a preconcentration and a separation zone has been used in a commercial CE instrument without instrumental modification. Analyte anions were retained on a preconcentration zone comprising an adsorbed layer of cationic latex particles, while separation was achieved in a separation zone comprising fused silica modified by adsorption of a cationic polymer. Elution of the adsorbed analytes was achieved using an eluotropic gradient formed by a transient isotachophoretic boundary between a fluoride electrolyte and a naphthalenedisulfonate electrolyte. Optimization of the electrolyte concentrations, sample injection times, and back-flushing times allowed the successful separation of sub-ppb levels of inorganic anions using a 100-min injection at 2 bar pressure, introducing over 40 capillary volumes of sample. A method based on a 10-min injection allowed a 100-fold increase in sensitivity over conventional hydrodynamic injection for Br-, I-, NO3-, CrO4(2-), and MoO4(2-) with a total analysis time of 25 min. Detection limits were dependent on the injection time but were in the range 2.2-11.6 ppb for a 10-min injection time. This approach was used to determine NO3- in Antarctic ice cores where the analysis could be performed using a sample volume 100 times less than that used for ion chromatography.
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PMID:On-column ion-exchange preconcentration of inorganic anions in open tubular capillary electrochromatography with elution using transient-isotachophoretic gradients. 3. Implementation and method development. 1203 14

Water quality measurements of surface runoff have been carried out in selected residential and industrial zones in urban areas, in which yearly mean precipitation is 1,225 mm. The concentrations of constituents in the surface runoff were measured at sampling sites categorized by land use type in the residential zone, and by industry type in the industrial zone. The water quality constituents of BOD5, COD, SS, NO3-N, TKN, PO4-P, TP, n-Hexane extracts, Cr, Cu, Pb and Fe were analyzed. The event mean concentrations (EMCs) of COD, SS, TKN and TP in the residential zone were 313 mg/L, 279 mg/L, 8.45 mg/L, 1.98 mg/L, and those in the industrial zone were 80 mg/L, 106 mg/L, 5.07 mg/L, and 1.93 mg/L, respectively. Cumulative load curves were created to analyze the first-flushing effect of each pollutant related to the pollutant, the rainfall event, and the land use type. No general relationship between the cumulative load and runoff has been established. The degree of first-flushing effect by constituents was in the following order; TKN>COD>SS>HEM>TP>PO4-P. The correlations between SS and other constituents were analyzed to evaluate the efficiency of the physical treatment process to control the surface runoff in urban areas. Based on the correlation of constituents with SS, high treatment efficiency of SS, heavy metals, organic matter, and TP was expected. The unit pollutant loading rates of COD, SS, TKN, TP, Cr and Pb in the residential zone were 2,392, 2,130, 64.6, 15.1, 0.31, and 1.83 kg/ha/yr, and those in the industrial zone were 612, 812, 38.7, 14.8, 0.51 and 0.82 kg/ha/yr, respectively.
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PMID:Characterization of surface runoff in urban areas. 1207 10

The aim of this study was to evaluate the efficacy and safety of oral sildenafil to treat erectile dysfunction (ED) in chronic renal failure in patients on hemodialysis (HD). A double-blind, randomized, placebo-controlled study of oral sildenafil (50 mg) administered as required in HD patients with ED was designed. Patients on HD for at least 6 mo and who had a stable relationship with a female sexual partner were included. Patients older than 70 yr with penile anatomic abnormalities, cirrhosis, diabetes, angina, severe anemia, and those who were on nitrate treatment or with a recent history of stroke or myocardial infarction were not included. The International Index of Erectile Dysfunction (IIEF) was employed to evaluate ED and treatment response. Forty-one patients were evaluated (21 received placebo, and 20 sildenafil). Baseline clinical and demographic parameters were similar in both groups. Sildenafil was associated with improvement in the score of all questions and domains of the IIEF, except those related to sexual desire. Using the erectile function domain to evaluate primary efficacy, improvement was observed in 85% of the sildenafil patients compared with 9.5% of placebo patients. Sildenafil use resulted in normal EF scores in 35% of sildenafil patients. Sildenafil was well tolerated. Headaches and flushing occurred in both groups. Dyspepsia was reported by two patients in the sildenafil group. In conclusion, oral sildenafil seems to be an effective and safe treatment for ED in selected patients with chronic renal failure on hemodialysis.
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PMID:Efficacy of oral sildenafil in hemodialysis patients with erectile dysfunction. 1239 48

The process performance of the two largest activated sludge processes in Hong Kong, the Sha Tin and the Tai Po Sewage Treatment Works (STW), deteriorated in the initial period after the introduction of seawater flushing in 1995 and 1996, respectively. High effluent ammonia nitrogen (NH4-N) and total suspended solids (TSS) in excess of the discharge standards resulted from incomplete nitrification and changes in floc characteristics. A desktop study on the inhibitory effects of salinity, particularly on nitrification, was subsequently conducted using the Tai Po STW operating data. To assist the upgrade of the Sha Tin STW a five-month extensive bench-scale investigation on a simple but flexible modified Ludzack-Ettinger configuration with bio-selector was conducted to quantify the inhibitory effects due to the saline concentration. The Sha Tin STW upgrade consists of restoration of its original design capacity (conventional process) of 205,000 m3/day from its currently much reduced capacity as a Bardenpho process. Only the volume of the existing biological process and clarifier is to be utilized. The saline concentration ranges from 3,500 up to 6,500 mg Cl-/L, both daily and seasonally. High and greatly fluctuating saline concentrations have been known to inhibit nitrification. Design consideration should also be given to the peak daily and seasonal TKN loading of up to three times the average. Although the nitrifiers maximum specific growth rate was significantly reduced to a low 0.25 day(-1), the inhibition was considered to be tolerable with effluent NH4-N and NO3-N consistently at < 1 and < 6 mg/L. The bio-selector was demonstrated to be efficient in control of sludge foaming and bulking with SVI consistently < or = 125 mL/g. Results from the IAWO Model No. 1 and the hydraulic model of the secondary clarifiers allowed overall process capacity maximization. With an anoxic mass fraction of 25-30%, operating sludge age of 9-14 days and SVI < or = 125 mL/g, both the design requirements and the effluent discharge standards could be met. Without these investigations, an unnecessarily large reaction basin and secondary clarifier volume, and hence capital investment, would have resulted.
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PMID:The impact of sea water flushing on biological nitrification-denitrification activated sludge sewage treatment process. 1252 56

Water quality models of urban systems have previously focused on point source (sewerage system) inputs. Little attention has been given to diffuse inputs and research into diffuse pollution has been largely confined to agriculture sources. This paper reports on new research that is aimed at integrating diffuse inputs into an urban water quality model. An integrated model is introduced that is made up of four modules: hydrology, contaminant point sources, nutrient cycling and leaching. The hydrology module, T&T consists of a TOPMODEL (a TOPography-based hydrological MODEL), which simulates runoff from pervious areas and a two-tank model, which simulates runoff from impervious urban areas. Linked into the two-tank model, the contaminant point source module simulates the overflow from the sewerage system in heavy rain. The widely known SOILN (SOIL Nitrate model) is the basis of nitrogen cycle module. Finally, the leaching module consists of two functions: the production function and the transfer function. The production function is based on SLIM (Solute Leaching Intermediate Model) while the transfer function is based on the 'flushing hypothesis' which postulates a relationship between contaminant concentrations in the receiving water course and the extent to which the catchment is saturated. This paper outlines the modelling methodology and the model structures that have been developed. An application of this model in the White Cart catchment (Glasgow) is also included.
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PMID:Application of a water quality model in the White Cart water catchment, Glasgow, UK. 1290 Oct 79

Results from the first multi-constituent dynamic modelling study of the Humber estuarine system over seasonal time scales are presented. The model, constructed within the ECoS3 simulation software, has been calibrated using data obtained from 27 surveys of the Yorkshire Ouse and Humber estuaries during 1994-1996. The model is tidally averaged, and is one-dimensional in the vertical and in cross-section. Daily-varying longitudinal concentration profiles of SPM, POC, nitrate, nitrite and ammonium have been simulated, and these have been compared with the observations used for model calibration (model confirmation). The fits are generally good. The model captures the marked seasonal variability in concentrations of the particulate constituents (SPM, POC), and places the turbidity maximum in approximately the correct region of the estuary. There was a high degree of scatter in the SPM and POC concentrations measured due to tidal resuspension, which was not reproduced by the tidally averaged model. Comparisons between measured and simulated nitrate+nitrite are satisfactory, although for a number of surveys the modelled values are systematically too low in the lower Yorkshire Ouse and upper Humber. These discrepancies are not readily explained, but may be linked to inadequately characterised source terms for this nitrogen. The general trends in the concentrations and distributions of ammonium are reproduced by the model, despite the plethora of external inputs of this constituent, and significant modifications to ammonium transport by in situ nitrification and benthic exchange. The simulated concentrations and distributions have also been tested against independent data encapsulating axial transects in the Trent and Humber estuaries, and temporal variations at fixed sites on the Trent and Yorkshire Ouse estuaries. With some exceptions, the fits between the model results and these data are also good. The model has also been used to construct constituent budgets (external/internal sources and sinks) for each estuary for 1994, 1995 and 1996. Riverine inputs of SPM, POC, nitrate, nitrite and ammonium decreased over the 3 years, presumably reflecting changing patterns of terrestrial runoff coupled to a reduction in effluent inputs. This trend was also observed in the point discharges of these constituents direct to the estuary. The simulated estuary was a source of sediments to the North Sea during 1994 and 1996, but a sink during 1995. The difference has been ascribed to the exceptionally dry summer and autumn of 1995, in which up-estuary tidal 'pumping' of SPM was dominant over down-estuary flushing by river water. Fluvial inputs represent an important external source of POC to the model estuary (27-55%), as does the North Sea (26-58%). These inputs are exceeded by POC loss via bacterial remineralisation, suggesting that the estuarine bed is a net source of POC. Riverine inputs account for 76-77% of the external inputs of nitrate. This constituent behaves quasi-conservatively in the estuary, reflecting the dilution of nitrate-rich river waters with low-nitrate coastal water, although nitrification is a significant input (approx. 21%). Denitrification is small, and consequently all nitrate added to the estuary is lost to the North Sea. External loads of nitrite are small and ammonium nitrification accounts for approximately 93% of its annual input. Practically all of the nitrite is oxidised to nitrate, and little escapes to the North Sea. The fluvial and direct waste inputs of ammonium to the estuary are of similar size. Most of the ammonium in the model is nitrified (98-100%) and only a few tons are exported to the North Sea. In 1996 the estuary appears to have been a sink for coastal water ammonium. Constituent budgets are compared with independently evaluated fluxes. There is good agreement in a number of cases, but the comparison highlights the main uncertainties in the simulated fluxes. It is concluded that the model as currently formulated provides an excellent basis for heuristic studies of the Humber estuarine system.
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PMID:The fluxes and transformations of suspended particles, carbon and nitrogen in the Humber estuarine system (UK) from 1994 to 1996: results from an integrated observation and modelling study. 1449 58

Results are presented from a campaign in which dissolved inorganic nutrients were measured in the Tweed Estuary, UK. The data utilised here were derived from surveys undertaken on a monthly basis from January to August 1997. There was consistency between the nutrient concentrations observed in the freshwater reaches of the tidal estuary and earlier measurements made several km upstream, in the freshwater river. Typically, nitrate was of the order of 100 microM and silicate approximately half this, whereas phosphate and nitrite were typically approximately 1 microM. Seasonal fluctuations in freshwater nitrate and silicate were very large, with concentrations exceeding (respectively) 300 and 100 microM in winter and less than 30 and 10 microM in summer. The estuarine nutrients surveyed followed this general seasonal pattern. A simple box model was used to investigate the temporal behaviour of a hypothetical estuarine nutrient. The model demonstrated that large deviations from the 'broad-brush' seasonal pattern for nitrate and silicate could be expected to occur within the estuary as a result of runoff and residence-time variations. The model also demonstrated that mid-estuarine peaks observed in the longitudinal distributions of phosphate could only have arisen as a result of non-freshwater, wastewater phosphate inputs to the estuary. Without this mid-estuarine input, rapid flushing rates would have ensured that transients due to changing freshwater phosphate concentrations, runoff and tides (via the residence time) would have had relatively little impact on the classic, linear 'conservative' mixing diagram for the estuary. Conservative mixing was largely applicable to the other nutrients.
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PMID:Dissolved nutrients in the Tweed Estuary, UK: inputs, distributions and effects of residence time. 1449 60

This study explores the effects of manure policy options for agricultural land in The Netherlands on nitrate leaching to groundwater, ammonia and nitrous oxide emissions to the atmosphere and on eutrophication of surface waters. The implementation of the farm gate balance MINAS at farm level, with levy-free N surpluses in the range of 300 to 40 kg per ha per year, and levy-free P surpluses in the range of 17.5 to 0.4 kg of P per ha per year, have been examined. Results indicate that nitrate concentrations in the upper groundwater are related to N surplus, land use, soil type and groundwater level. On dry sandy soils, the N surplus has to be below 60 to 140 kg of N per ha per year, depending on land use, to decrease the nitrate concentrations in the upper groundwater to below 50 mg nitrate per litre. Decreases of N and P concentrations in surface waters, upon lowering levy-free surpluses appear relatively small. For improving the ecological state of surface waters, we recommend a combination of low levy-free N and P surpluses with dredging P rich sediments, flushing of ditches, and decreasing discharges from other sources.
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PMID:Environmental effects of manure policy options in The Netherlands. 1505 4

The bioreduction of soluble uranium [U(VI)] to sparingly soluble U(IV) species is an attractive remedial technology for contaminated soil and groundwater due to the potential for immobilizing uranium and impeding its migration in subsurface environments. This manuscript describes a column study designed to simulate a three-step strategy proposed for the remediation of a heavily contaminated site at the U.S. Department of Energy's NABIR Field Research Center in Oak Ridge, TN. The soil is contaminated with high concentrations of uranium, aluminum, and nitrate and has a low, highly buffered pH (approximately 3.5). Steps proposed for remediation are (i) flushing to remove nitrate and aluminum, (ii) neutralization to establish pH conditions favorable for biostimulation, and (iii) biostimulation for U(VI) reduction. We simulated this sequence using a packed soil column containing undisturbed aggregates of U(VI)-contaminated saprolite that was flushed with an acidified salt solution (pH 4.0), neutralized with bicarbonate (60 mM), and then biostimulated by adding ethanol. The column was operated anaerobically in a closed-loop recirculation setup. However, during the initial month of biostimulation, ethanol was not utilized, and U(VI) was not reduced. A bacterial culture enriched from the site groundwaterwas subsequently added, and the consumption of ethanol coupled with sulfate reduction immediately ensued. The aqueous concentration of U(VI) initially increased, evidently because of the biological production of carbonate, a ligand known to solubilize uranyl. After approximately 50 days, aqueous U(VI) concentrations rapidly decreased from approximately 17 to <1 mg/L. At the conclusion of the experiment,the presence of reduced solid phase U(IV) was confirmed using X-ray absorption near edge structure spectroscopy. The results indicate that bioreduction to immobilize uranium is potentially feasible at this site; however, the stability of the reduced U(IV) and its potential reoxidation will require further investigation, as do the effects of groundwater chemistry and competitive microbial processes, such as methanogenesis.
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PMID:Bioreduction of uranium in a contaminated soil column. 1605 82


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