•Falling head (PT) vs constant head (Kfs) hydraulic conductivities across Irish soils.•Reynolds (2008) solution should be used to determine Kfs in Irish context.•PT vs Kfs relationship for Irish ...soils matches more generic formulations closely.•Comparison of international standards for soil treatment units provided.•Irish threshold PT limits for on-site wastewater treatment converted to Kfs values.
The suitability of a location for an on-site wastewater treatment process (for areas which lack access to centralised wastewater treatment systems) requires an assessment of the permeability of the soil into which the effluent will be discharged. In many jurisdictions this is determined using some type of in-situ percolation test. Falling head percolation tests, which give a value of percolation time (PT) that is empirically related to the notion of hydraulic conductivity, are widely used as they are relatively simple to carry out, but the test does not have a sound theoretical framework and test methods are not standardised internationally. In comparison, the saturated hydraulic conductivity of a soil obtained from a constant head well permeameter test is independent of test conditions, and so is a more suitable metric for design. A database of over 900 falling head tests carried out across a range of different subsoil types in Ireland has been collated, all with the inherent limitations of the existing regulative framework regarding the percolation test and soil texture assessment. These tests were then modelled using Hydrus 2-D numerical modelling simulations to determine equivalent field saturated hydraulic conductivity (Kfs) values and thereby provide a correlation with PT values across the range of subsoil conditions. In addition, falling head tests have been carried out in parallel to constant head permeameter tests in the field and compared against the relationship derived from the broad dataset of simulated results. This revealed an optimal solution by which to determine Kfs from the field permeameter test (using parameters recommended for most structured soils from clays to loams). The trendline based on Irish data was also compared against more generic formulations of the relationship between PT, and Kfs and shown to match closely, particularly the Reynolds (2016) ‘unified’ methodology. Finally, the Irish threshold PT limits for on-site wastewater treatment have been converted to Kfs values and compared against other international standards.
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Soil “health” is becoming an increasing concern of modern societies, namely, at the European level, considering its importance to the fields of food, clean water, biodiversity, and even climate ...change control. On the other hand, human activities are contributing more and more to induce contamination in soils, especially in industrialized societies. This experimental work studies different additives (carbon nanotubes, clay, and Portland cement) with the aim to evaluate their effect on heavy metals, HMs (lead, cooper, nickel, and zinc) immobilization in a contaminated soil in conditions similar to a real scenario. Suspension adsorption tests (fluid-like condition) were performed aiming to supply preliminary information about the adsorption capacity of the soil towards the different HMs tested, while percolation tests (solid-like conditions) were performed aiming to evaluate the HMs immobilization by different additives in conditions similar to a real situation of soil contamination. Results showed that soil particles alone were able to retain considerable amounts of HMs (especially Pb and Cu) which is linked to their fine grain size and the soil high organic matter content. In conditions of good dispersion of the additives, addition of carbon nanotubes or clay can rise the HMs adsorption, except in the case of Zn2+ due to its low electronegativity and high mobility. Moreover, the addition of cement to the soil showed a high capacity to immobilize the HMs which is due to the chemical fixation of the HMs to binder hydration products. In this case, HMs immobilization comes associated with a soil stabilization strategy. The results allow to conclude that the additives, carbon nanotubes and clay, have the potential to minimize HMs mobility in contaminated soils and can be a valid alternative to the usual additive, Portland cement, when tested in conditions similar to a real on-site situation, if the objective is not to induce also soil stabilization, for instance, to enable its use for construction purposes. The results obtained can help designers and decision-makers in the choice of the best materials to remediate HMs contaminated soils.
Soil is a vital resource to humans and soil health is a concern of modern societies. One of the problems is the existence of heavy metals (HMs) pollution, which can affect food, water sources and ...biodiversity. This experimental work studies the effect of multiwall carbon nanotubes (MWCNTs) and surfactants characteristics on HMs immobilization in a contaminated soil. The testing program comprises the characterization of the MWCNTs and surfactants, followed by two distinct adsorption tests: suspension tests designed to supply preliminary information regarding the adsorption capacity of soil particles towards the different HMs, and percolation tests to evaluate the HMs immobilization in conditions mimicking a real in-situ scenario. The different HMs exhibit different affinities order to the soil studied: Pb > Cu > Ni > Zn. Results indicated that the inherent soil particles can immobilize significant quantities of HMs (especially Pb and Cu) due to their fine size and the existence of a substantial amount of organic matter content in the soil matrix. Molecular weight and charge density of the surfactant are characteristics with an impact on the MWCNTs dispersion and also on the adsorption capacity of the different HMs, namely in the case of Ni
2+
and even in the case of Zn
2+
possessing lower electronegativity and higher mobility. The findings of the study allow concluding that MWCNTs possess the potential to reduce the mobility of heavy metals in soil, even when employed at very low concentration (0.01% w/w), which is an important feature considering their cost.
Article Highlights
Effect of MWCNTS on the decrease of the mobility of heavy metals in a contaminated soil.
Influence of surfactant characteristics on the dispersion of the MWCNTs.
MWCNTs dispersion quality is correlated with the capacity of soil to retain heavy metals.
Laboratory leaching tests may be used for source term determination as a basis for risk assessment for soil–groundwater pathway (leachate forecast) on contaminated sites in Germany. Interlaboratory ...comparisons on the evaluation of the reproducibility of column percolation tests were conducted within the framework of an integrated R
+
D program using three waste reference materials.
The interlaboratory comparisons of column percolation tests showed good reproducibility of the results for inorganic and organic parameters as well as for the accompanying parameters. This is due to the stipulations concerning the time of contact between leachant and sample material as well as the sample placement in the columns. Different column dimensions used by the participants of the interlaboratory comparisons did not have any substantial influence on the column test results.
