Christian Maurice

Impact of water saturation level on arsenic and metal mobility in the Fe-amended soil

The impact of water saturation level (oxidizing-reducing environment) on As and metal solubility in chromium, copper, arsenic (CCA)-contaminated soil amended with Fe-containing materials was studied. The soil was mixed with 0.1 and 1 wt% of iron grit (Fe(0)) and 1, 7 and 15 wt% of oxygen scarfing granulate (OSG, a by-product of steel processing). Solubility of As and metals was evaluated by a batch leaching test and analysis of soil pore water. Soil saturation with water greatly increased As solubility in the untreated as well as in the Fe-amended soil. This was related to the reductive dissolution of Fe oxides and increased concentration of As(III) species. Fe amendments showed As reducing capacity under both oxic and anoxic conditions. The cytotoxicity of the soil pore water correlated with the concentration of As(III). The Fe-treatments as well as water saturation of soil were less significant for the solubility of Cu, Cr and Zn than for As. The batch leaching test used for waste characterization substantially underestimated As solubility that could occur under water-saturated (anaerobic) conditions. In the case of soil landfilling, other techniques than Fe-stabilization of As containing soil should be considered.

LFG emission measurements in cold climatic conditions: seasonal variations and methane emissions mitigation

Landfill gas (LFG) emissions were measured at three landfills in Northern Sweden and Northern Finland. Several strategies for measuring gas emissions in winter conditions (i.e., a snow-covered surface and frozen ground) were tested. Static chambers appeared to be the most suitable measurement technique. The study results showed that winter measurements should be done directly at the soil surface and that any snow cover should be removed beforehand. A seasonal variation of the emissions was observed. Methane emissions were measured during late winter at the three sites and during late summer at two of the same three sites. Monitoring performed during the different seasons yields a better estimation of the annual LFG emissions. Variations in methane oxidation are likely sources of any differences as low temperature and low soil water content both reduce methane oxidation activity. At low emission rates, the main methane emission may occur during wintertime because of the mitigation effect landfill cover has on methane oxidation during summertime. A reduced methane oxidation activity was observed during the late summer at two of the sites. A combination of summer dryness and heat from methane oxidation is believed to have dried the soil, which then caused a subsequent decrease in methane oxidation. To use landfill covers for the management of methane emissions in cold climates, special consideration must be given to the moisture and extreme low temperature factors.

Hydraulic conductivity of fly ash : sewage sludge mixes for use in landfill cover liners

Secondary materials could help meeting the increasing demand of landfill cover liner materials. In this study, the effect of compaction energy, water content, ash ratio, freezing, drying and biological activity on the hydraulic conductivity of two fly ash-sewage sludge mixes was investigated using a 2(7-1) fractional factorial design. The aim was to identify the factors that influence hydraulic conductivity, to quantify their effects and to assess how a sufficiently low hydraulic conductivity can be achieved. The factors compaction energy and drying, as well as the factor interactions material x ash ratio and ash ratio x compaction energy affected hydraulic conductivity significantly (alpha=0.05). Freezing on five freeze-thaw cycles did not affect hydraulic conductivity. Water content affected hydraulic conductivity only initially. The hydraulic conductivity data were modelled using multiple linear regression. The derived models were reliable as indicated by R(adjusted)(2) values between 0.75 and 0.86. Independent on the ash ratio and the material, hydraulic conductivity was predicted to be between 1.7 x 10(-11)m s(-1) and 8.9 x 10(-10)m s(-1) if the compaction energy was 2.4 J cm(-3), the ash ratio between 20% and 75% and drying did not occur. Thus, the investigated materials met the limit value for non-hazardous waste landfills of 10(-9)m s(-1).

Techniques for the Stabilization and Assessment of Treated Copper-, Chromium-, and Arsenic-contaminated Soil

Abstract Remediation mainly based on excavation and burial of the contaminated soil is impractical with regard to the large numbers of sites identified as being in need of remediation. Therefore, alternative methods are needed for brownfield remediation. This study was conducted to assess a chemical stabilization procedure of CCA-contaminated soil using iron (Fe)-containing blaster sand (BS) or oxygen-scarfing granulate (OSG). The stabilization technique was assessed with regard to the feasibility of mixing ameliorants at an industrial scale and the efficiency of the stabilization under different redox conditions. The stability was investigated under natural conditions in 1-m3 lysimeters in a field experiment, and the effect of redox conditions was assessed in a laboratory experiment (10 L). The treatments with high additions of ameliorant (8% and 17%) were more successful in both the laboratory and field experiments, even though there was enough Fe on a stochiometric basis even at the lowest addition rates (0.1% and 1%). The particle size of the Fe and the mixing influenced the stabilization efficiency. The development of anaerobic conditions, simulated by water saturation, increases the fraction of arsenic (AsIII) and, consequently, As mobility. The use of high concentrations of OSG under aerobic conditions increased the concentrations of nickel (Ni) and copper (Cu) in the pore water. However, under anaerobic conditions, it decreased the As leaching compared with the untreated soil, and Ni and Cu leaching was not critical. The final destination of the treated soil should govern the amendment choice, that is, an OSG concentration of approximately 10% may be suitable if the soil is to be landfilled under anaerobic conditions. Alternatively, the soil mixed with 1% BS could be kept under aerobic conditions in a landfill cover or in situ at a brownfield site. In addition, the treatment with BS appeared to produce better effects in the long term than treatment with OSG.

Extraction of Arsenic from Soils Contaminated with Wood Preservation Chemicals

Three soil samples contaminated by chromated zinc arsenate (CZA) or chromated copper arsenate (CCA) were investigated in a laboratory scale to study As mobilization and to identify a chemical agent that could be used in soil washing to extract arsenic. Besides high As extraction, the cost, occupational health issues and technical aspects were considered when selecting the chemical. Arsenic is strongly bound to CZA/CCA soils; only ∼50% of the tot-As was removed from water-washed soils. High Fe or Al mobilization is not necessarily indicative of high As removal from CZA/CCA soils. A high Cu/As-ratio and a large amount of soluble Ca in the soil hampered As extraction. The high ratio can be an indication of stable Cu-arsenates in soil. Calcium can react with the extraction agent or with As during extraction. Sodium hydroxide, dithionite with citrate (and oxalate) (dithionite solutions), and oxalate with citrate were the most efficient chemicals for removing As from the soils. The disadvantages of using these strong chemicals are: a high cost (oxalate with citrate); damage to equipment (dithionite solutions); an adverse impact on occupational health (dithionite solutions); or a deterioration in soil quality after extraction (NaOH and dithionite solutons). Phosphate, solutions based on NH2OH·HCl, or citrate were not efficient in mobilizing As from the soils.

Assessment of the Methane Oxidation Capacity of Soils

Methane oxidation capacity of three soil matrices was assessed using a new method based on the pressure fall resulting from methane oxidation. The effects of incubation temperature, moisture and methane content on the oxidation capacity were studied. Parameters observed were non-methanotrophic oxygen consumption, methane assimilation, length of the lag period before steady pressure fall was reached, initial pressure fall and maximum pressure fall. Filling material taken from a biofilter was tested. The length of the lag period was an index of prior exposure of the soil to methane emissions. Incubation temperature of 30°C and soil moisture at the water-holding capacity were chosen to standardize the test. Oxygen depletion by non-methanotrophs varied between 40 and 60% of the total oxygen consumption while methane assimilation was at 40 to 50% of the total methane consumption.

Using Betula pendula and Telephora caryophyllea for Soil Pollution Assessment

The concentrations of available arsenic, copper, lead, and zinc in the soil, and the concentration of these elements in vegetal tissues were measured. The most common species at the sites were studied. All the species that were analyzed took up pollutants and could indicate polluted soil. However, all the studied species did not fit to map pollution. The birch (Betula pendula) and most of the fungi species had still quite low concentrations in their tissues compared with the available concentrations in the soil. No direct correlation between the pollution content in the soil and in the vegetation tissues could be observed. Specimens of Thlaspi caerulescens were accumulating zinc. Of the four fungi species collected, only Thelephora caryophyllea seemed to accumulate actively in the studied pollutants. Moreover, it was possible to use an arsenic test with the fungi, which is also interesting from the perspective of preliminary assessment of the degree of pollution. A qualitative judgement of the soil pollution is possible by examining the plant material. To obtain a more quantitative and complete mapping, the method has to be developed further and completed with other investigations when vegetation is missing.

Retention of Metals Leached From Municipal Solid Waste Incineration (MSWI) Bottom Ashes in Soils

Utilization of bottom ash in road construction may lead to a release of contaminants that can affect the soil of the swales constructed along these roads. Column tests were performed to evaluate the retention behavior of Cu, Cr, Zn, and Pb, originating from municipal solid waste incineration (MSWI) bottom ash leachate, in two substrates: peat and mould (a cultural soil). A chemical sequential extraction method was used to predict the risk associated with the release of the retained elements with modifications of environmental conditions. Apart from the dissolution of organic matter (OM), ash leachate properties hindered the metal transport from peat. Mould was efficient only in removing Zn, making it a less favorable substrate for the leachate control along the roads. Readily soluble forms made up a minor fraction of the retained metals in peat, reducing the risk of metal release due to ion exchange and pH drop. Changes in redox potential might be the main cause of Zn desorption from peat as the Fe-Mn oxides were the main scavengers for this metal. Oxidation of OM would be the primary reason of Cu and Cr release, while for Pb both fractions (Fe-Mn oxides and OM) might equally contribute to the metal discharge.

An Evaluation of Using Various Admixtures of Green Liquor Dregs, a Residual Product, as a Sealing Layer on Reactive Mine Tailings

Green liquor dregs (GLD), a residual product from sulfate paper mills, was blended with tailings, fly ash, and bark sludge with the aim of improving the material’s physical properties so that it could function as a sealing layer in dry covers on sulfidic mine waste. Geotechnical and geochemical investigations, including weathering cell tests, were carried out on GLD with admixtures to assess their effectiveness. Due to its alkaline character, GLD was shown to have the potential to improve leachate quality by decreasing metal mobility when blended with tailings. The admixtures showed favorable sealing layer properties such as high water retention capacity and low hydraulic conductivity. However, caution must be exercised when the dregs are blended with tailings containing large amounts of As and Mo, since increased leaching of these elements may be expected.ZusammenfassungGrünlaugenschlamm (GLD), ein Abprodukt der Papierherstellung nach dem Sulfatverfahren, wurde mit Tailings, Flugasche und Rindenschlamm mit dem Ziel gemischt, dessen physikalische Eigenschaften zu verbessern, um ihn als Dichtschichtmaterial beim Bau von Abdecksystemen für sulfidische Bergbaurückstände verwenden zu können. Hierzu wurden geotechnische und geochemische Untersuchungen, darunter ein spezieller Labor-Elutionstest, an Rezepturen von GLD mit verschiedenen Zusatzstoffen durchführt. Wird GLD mit Tailings verschnitten, ist er aufgrund seiner Alkalität grundsätzlich geeignet, die Sickerwasserbeschaffenheiten infolge verringerter Metallmobilitäten zu verbessern. Die untersuchten Rezepturen wiesen positive Dichtschichteigenschaften auf, so ein hohes Wasserrückhaltevermögen und eine geringe hydraulische Durchlässigkeit. Allerdings ist Vorsicht geboten, wenn GLD mit Tailings verschnitten wird, die hohe Gehalte an As und Mo aufweisen, da es hierdurch zu einer Mobilitätserhöhung dieser Elemente kommen kann.ResumenEl licor verde residual (GLD), un producto residual en las fábricas de papel por el método sulfato, fue mezclado con colas, cenizas volátiles y lodo de cortezas con el objetivo de mejorar las propiedades físicas del material para ser usado como una capa de sellado en cobertores secos sobre residuos de una mina de sulfuros. Investigaciones geotécnicas y geoquímicas, incluyendo los test de células de desgaste, fueron realizadas con GLD y diferentes agregados a fin de relevar su efectividad. Debido a su carácter alcalino, GLD mostró potencial para mejorar la calidad del lixiviado disminuyendo la movilidad de los metales cuando se mezcló con las colas. Los agregados mostraron propiedades favorables para ser usados como capas sellantes con una alta capacidad de retención de agua y baja conductividad hidráulica. Sin embargo, deben ser observadas ciertas precauciones cuando los residuos son mezclados con colas que contienen altas cantidades de As y Mo ya que puede esperarse un incremento de la lixiviación de estos elementos.抽象绿液渣(GLD)是硫酸盐造纸厂的固体废物。本文将绿液渣与尾矿、粉煤灰和树皮泥混合,旨在提高混合材料的物理性能,以作含硫化物尾矿堆的保护盖层。通过绿液渣(GLD)及其混合物的岩土力学试验、地球化学试验(包括模拟风化箱试验)评价其作为盖层材料的阻渗、防氧化效率。绿液渣呈碱性,与尾矿混合后能降低尾矿金属离子活性,减少滤出液离子含量,提高滤出液质量。绿液渣混合物表现出了高持水能力和低渗透性的良好盖层特性。但是,应当注意,当绿液渣与含有大量砷和钼的尾矿混合时,这些元素溶出量也会增加。

Improving Soil Investigations at Brownfield Sites Using a Flexible Work Strategy and Screening Methods Inspired by the US Environmental Protection Agency's Triad Approach

Abstract Investigations of polluted brownfield sites and sample analyses are expensive, and the resulting data are often of poor quality. Efforts are needed, therefore, to improve the methods used in investigations of brownfield sites to both reduce costs and improve the quality of the results. One approach that could be useful for both of these purposes is the triad strategy, developed by the US Environmental Protection Agency, in which managing uncertainty is a central feature. In the investigations reported here, a field study was conducted to identify possible ways in which uncertainties could be managed in practice. One example considered involves optimizing the uncertainty by adjusting the sizes of samples and the efforts expended in analytical work according to the specific aims of the project. In addition, the potential utility of several toxicity assessment methods for screening sites was evaluated. As well as presenting the results of these assessments, in this contribution we discuss ways in which a flexible work strategy and screening methods inspired of the triad philosophy could be incorporated into the Swedish approach to remediate brownfield sites. A tiered approach taking advantage of field and screening methods is proposed to assess brownfield sites focusing on the response and acceptable uncertainty that are required for the task.