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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK; Malden, USA : Blackwell Science Inc
    Ground water 43 (2005), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A nitrate-reactive porous media layer comprising wood particles with very high hydraulic conductivity (K∼ 1 cm/s) was used to successfully treat nitrate in a shallow sand-and-gravel aquifer in southern Ontario. Nitrate concentrations of 1.3 to 14 mg/L as N in the aquifer were attenuated to 〈0.5 mg/L as N in the reactive layer. Borehole dilution testing indicated that ground water velocities in the reactive layer, although variable, averaged five times higher than in the surrounding aquifer, suggesting that the layer was capturing ground water flow from deeper in the aquifer. The use of high-K reactive media opens up the possibility of installing permeable reactive barriers as horizontal layers in the shallow water table zone that do not necessarily have to penetrate the full depth of a contaminant plume to be effective. Model simulations show that the depth of capture of a high-K layer increases as the layer width in the direction of flow increases. Shallower emplacement could decrease barrier costs at some sites.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 38 (2000), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Nitrate is now recognized as a widespread ground water contaminant, which has led to increased efforts to control and mitigate its impacts. This study reports on the long-term performance of four pilot-scale field trials in which reactive porous barriers were used to provide passive in situ treatment of nitrate in ground water. At two of the sites (Killarney and Borden), the reactive barriers were installed as horizontal layers underneath septic system infiltration beds; at a third site (Long Point), a barrier was installed as a vertical wall intercepting a horizontally migrating septic system plume; and at the fourth site (North Campus), a barrier was installed as a containerized subsurface reactor treating farm field drainage water. The reactive media consisted of 15% to 100% by volume of waste cellulose solids (wood mulch, sawdust, leaf compost), which provided a carbon source for heterotrophic denitrification. The field trials have been in semicontinuous operation for six to seven years at hydraulic loading rates ranging from six to 2000 L/day. Trials have been successful in attenuating influent NO3- (or NO3-+ NH4+ at Borden) concentrations averaging from 4.8 mg/L N at North Campus to 57 mg/L N at Killarney, by amounts averaging 80% at Killarney, 74% at Borden, 91 % at Long Point, and 58% at North Campus. Nitrate consumption rates were temperature dependent and ranged from 0.7 to 32 mg L N/day, but did not deteriorate over the monitoring period. Furthermore, mass-balance calculations indicate that carbon consumption by heterotrophic denitrification has so far used only about 2% to 3% of the initial carbon mass in each case. Results suggest that such barriers should be capable of providing NO3- treatment for at least a decade or longer without carbon replenishment.Reactive barriers have now been used to treat nitrate contamination from a variety of sources including septic systems, agricultural runoff, landfill leachate, and industrial operations. This demonstration of successful long-term operation should allow this technology to become more widely considered for nitrate remediation, particularly at sites where passive treatment requiring a minimum of maintenance is desired.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 41 (2003), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Review of phosphate behavior in four mature septic system plumes on similar textured sand has revealed a strong correlation between carbonate mineral content and phosphate concentrations. A plume on calcareous sand (Cambridge site, 27 wt % CaCO3 equiv.) has proximal zone PO4 concentrations (4.8 mg/L P average) that are about 75% of the septic tank effluent value, whereas three plumes on noncalcareous sand (Muskoka, L. Joseph, and Nobel sites, 〈1 wt % CaCO3 equiv.) have proximal zone phosphate concentrations (〈0.1 mg/L P) that are consistently less than 2% of the effluent values. Phosphate attenuation at the noncalcareous sites appears to be an indirect result of the development of acidic conditions (site average pH 3.5 to 5.9) and elevated Al concentrations (up to 24 mg/L), which subsequently causes the precipitation of Al-P minerals such as variscite (AlPO4. 2H2O). This is supported by scanning electron microscope analyses, which show the widespread occurrence of (Al+P)—rich secondary mineral coatings on sand grains below the infiltration beds. All of these septic systems are more than 10 years old, indicating that these attenuation reactions have substantial longevity.A field lysimeter experiment demonstrated that this reaction sequence can be readily incorporated into engineered waste water treatment systems. We feel this important P removal mechanism has not been adequately recognized, particularly for its potential significance in reducing P loading from septic systems in lakeshore environments.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 37 (1999), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Long-term monitoring of two well-characterized, oxidizing septic system plumes (Langton and Long Point 2 sites) over periods extending two to four years after decommissioning, has revealed that ground water PO 43− concentrations (0.4 to 5 mg/L P) have persisted at levels virtually unchanged from those observed during active sewage loading. In addition, the frontal part of the PO43− plume at the Long Point 2 site can be observed to continue to advance during the decommissioned period. At the Langton site, where an active regional ground water flow system is present, all major plume solutes (Na+, Ca2+, Cl−, NO 3−) returned to background values within one year of decommissioning, with the exception of PO43−.This evidence suggests that phosphate behavior in the ground water zone at these sites is dominated by sorption reactions that are both rapid and reversible. Thus, if septic system phosphorus is not retained in the vadose zone, but is transported into the ground water zone, it has the potential to be persistent and to be mobile enough to constitute a threat to downgradient surface water environments. This evidence also shows that when a septic system is decommissioned, if an oxidizing PO43− plume is present, downgradient P loading is not likely to diminish for many years thereafter.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 19 (1999), S. 0 
    ISSN: 1745-6592
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Treatment of nitrogen in landfill leachate has received considerable attention recently because of the relatively low levels at which some nitrogen species (i.e., NH3) can be toxic to aquatic life forms. This study reports on the results of a three-year, pilot-scale field trial demonstrating the use of infiltration bed and nitrate barrier technology to achieve nitrogen removal in landfill leachate. The infiltration bed comprises an unsaturated sand layer overlying a saturated layer of waste cellulose solids (sawdust), which acts as a carbon source for heterotrophic denitrification. When loaded at a rate of 1 to 3 cm/day, the infiltration bed was successful at lowering leachate inorganic nitrogen (NH4++ NO3-) levels averaging 24.8 mg/L N by 89%, including 96% in the third year of operation. The surface water discharge criteria for un-ionized ammonia (NH3) were met on all occasions in the treated leachate during the second and third years of operation. Nitrogen attenuation is presumed to occur by a two-step process in which leachate NH4+ is first oxidized to NO3- in the unsaturated sand layer and then is converted to nitrogen gas (N2) by denitrification occurring in the underlying sawdust layer. Mass balance calculations suggest that the sawdust layer has sufficient carbon to allow denitrification to proceed for long periods (1.0 to 30 years) without replenishment. Because this technology is simple to construct and is relatively maintenance free, it should be attractive for use at smaller landfills where the installation of conventional treatment plants may not be feasible.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water 36 (1998), S. 0 
    ISSN: 1745-6584
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: Phosphate distribution was reviewed in 10 mature, highly monitored septic system ground water plumes in central Canada. It was shown that six plumes (primarily those on calcareous sands) of enriched P concentrations (0.5 to 5 mg/L P) exceeding 10 m in length are present. In each case, phosphate migration velocity is highly retarded (retardation factor, 20 to 100) compared to the ground water velocity, hut migration rates remain sufficiently fast (−1 m/a) to the of concern when considering long-term operation and the normal setback distance of septic systems from adjacent surface water bodies (∼ 15 m). Much smaller scale phosphate plumes (〈 3 m in length) are present at the acidic sites on noncalcareous sands and on silt- and clay-rich sediments.At all of the sites, ground water concentrations are lower than effluent values by amounts ranging from 23 to 99%, suggesting that P accumulation has occurred in the vadose zone. This was confirmed by sediment analyses at four of the sites which, in each case, showed that zones of Penrichment were present within 1 m of the infiltration pipes (Wood 1993; Zanini et al. 1998). Also, observed phosphate concentrations are generally consistent with values expected based on the solubility constraints of the minerals vivianite in reducing zones (including the septic tank), and strengite and variscite in oxidizing zones, providing further evidence that min-eral precipitation reactions play a role in limiting P concentrations. Strengite and variscite have the potential to limit P to low con-centrations (co.1 mg/L) under acidic conditions, but oxidation of sewage efiluent leads to acidic conditions only in noncalcareous terrain or beneath old septic systems where calcium carbonate has been depleted. Overall, phosphate plume migration velocities in ground water appear to be controlled by sorption processes, but the phosphate concentrations that are present in the plumes appear to be strongly controlled by mineral precipitation reactions that occur in close proximity to the infiltration pipes.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Hydrology 158 (1994), S. 123-134 
    ISSN: 0022-1694
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Architecture, Civil Engineering, Surveying , Geography , Geosciences
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Comparative Biochemistry And Physiology 36 (1970), S. 387-393 
    ISSN: 0010-406X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 15 (1995), S. 0 
    ISSN: 1745-6592
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Geosciences
    Notes: A small-scale field experiment was carried out to demonstrate the effectiveness of using septic system -type infiltration beds for on-site treatment of landfill leachate. Using an infiltration bed with a 3-m-thick vadose zone of medium sand, and loaded at a rate 01 18 cm/day, a treatment efficiency of 〉99 percent was obtained for Fe, 94 percent for NH4+, and 54 percent for dissolved organic carbon (DOC). Attenuation occurred during one- to two-day residency in the aerobic vadose zone (pore gas O2 〉 12 percent by volume) as a result of oxidation reactions that caused nitrification of NH4+, convened Fe2+ to Fe3+ allowing subsequent precipitation of sparingly soluble Fe oxyhydroxide minerals, and biodegraded DOC. Attenuation of an aerobically degradable trace volatile organic compound (dichlorobenzene) was also noted, although other less degradable compounds (trichloroethylene and tetrachloroethylene) persisted.Fe mineral precipitation caused a discontinuous hardpan layer to occur in the zone immediately below the infiltration pipes. However, this layer did not become impermeable or continuous enough to significantly impede infiltration during the 82-day experiment.Advantages of this technology for leachate treatment are that it is low cost, it is simple to construct and operate. and treatment occurs on-site, avoiding the cost of transporting leachate off-site for treatment.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Estuarine, Coastal and Shelf Science 39 (1994), S. 185-200 
    ISSN: 0272-7714
    Keywords: Decapoda ; South Africa ; crabs ; mating ; maturity ; reproduction ; spawning seasons
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Geography , Geosciences
    Type of Medium: Electronic Resource
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