Biomineralisation of metals in soil – effect of metal toxicity and precipitation as a protective mechanism

Biomineralisation offers the potential for in-situ sequestration and subsequent reduction in the bioavailability of heavy metals and radionuclides in the subsurface environment. Calcium carbonate minerals are known to sorb and form solid solutions with a range of target elements, and are readily produced by the actions of common microorganisms on simple chemical precursors. The ability of a commonly used urea-degrading, calcium carbonate-precipitating bacterium, Sporosarcina pasteurii, to tolerate the presence of a model contaminant, strontium, was determined in aqueous solution, with reduction in growth only seen at concentrations of 10 mM. Its ability to remove strontium from solution via calcium carbonate precipitation was then determined, and here S. pasteurii was shown to be able to remove 99% (+/- 1%) strontium from solution at concentrations up to 30 mM. This suggests that biomineralisation of metallic elements may afford a protective mechanism for the bacteria through providing a means to reduce the overall concentrations to tolerable levels. Finally, we explored the effects of ground conditions on mineralisation and strontium sequestration in different sand fractions (fine, medium and coarse), in a series of batch experiments. Almost all (97-99%) strontium present was removed from aqueous solution after three days, whereas no precipitation was observed in control samples over the same period. The amount of strontium removed increased with coarseness of sand grains under these static conditions, although over a very small range

Uncovering the true impacts of remediation

This bulletin investigates the sustainability of remediation through the development and use of a sustainability assessment methodology. It is one of the products of the Sustainable Urban Brownfield: Integrated Management (SUBR:IM) research consortium. The objective of this work was to identify and compare the wider impacts of a range of remediation technologies in use in the UK. A methodology was developed based on multi-criteria and detailed impact analyses, both of which incorporated life-cycle approaches. This was used to compare three options on a particular site, and highlighted the major impacts from each

The case for examining fluid flow in municipal solid waste at the pore-scale - A review

In this paper, we discuss recent efforts from the last 20 years to describe transport in municipal solid waste (MSW). We first discuss emerging themes in the field to draw the reader’s attention to a series of significant challenges. We then examine contributions regarding the modelling of leachate flow to study transport via mechanistic and stochastic approaches, at a variety of scales. Since MSW is a multiphase, biogeochemically active porous medium, and with the aim of providing a picture of transport phenomena in a wider context, we then discuss a selection of studies on leachate flow incorporating some of the complex landfill processes (e.g. biodegradation and settlement). It is clear from the literature survey that our understanding of transport phenomena exhibited by landfilled waste is far from complete. Attempts to model transport have largely consisted of applying representative elementary-scale models (the smallest volume which can be considered representative of the entire waste mass). Due to our limited understanding of fluid flow through landfilled waste, and the influence of simultaneously occurring biogeomechanical processes within the waste mass, elementary-scale models have been unable to fully describe the flow behaviour of MSW. Pore-scale modelling and experimental studies have proven to be a promising approach to study fluid flow through complex porous media. Here, we suggest that pore-scale modelling and experimental work may provide valuable insights into transport phenomena exhibited by MSW, which could then be used to revise elementary-scale models for improved representation of field-scale problems

Application of enzymatic and bacterial biodelignification systems for enhanced breakdown of model lignocellulosic wastes

This paper explores the extent to which enzymatic and bacterial biodelignification systems can breakdown lignocellulose in model wastes to potentially enhance biogas generation. Two representative lignocellulosic wastes (newspaper and softwood) commonly found largely undegraded in old landfills were used. A fungal peroxidase (lignin peroxidase) enzyme and a recently isolated lignin-degrading bacterial strain (Agrobacterium sp.) were used. Tests were conducted in stirred bioreactors with methanogens from sewage sludge added to produce biogas from breakdown products. Addition of lignin peroxidase resulted in ~20% enhancement in cumulative methane produced in newspaper reactors. It had a negative effect on wood. Agrobacterium sp. strain enhanced biodegradation of both wood (~20% higher release of soluble organic carbon and enhanced breakdown) and newspaper (~2-fold biogas yield). The findings of this paper have important implications for enhanced breakdown in old landfills that are rich in these wastes, and anaerobic operations utilising lignocellulosic wastes for higher degradation efficiencies and biogas production

Sustainability of Land Remediation. Part 1: Overall Analysis

A comparative assessment was carried out of the technical and environmental sustainability of five different contaminated land remediation projects completed in the UK between 1997 and 2002. The remediation technologies employed were in situ stabilisation/solidification, soil washing, ex situ bioremediation, cover system and excavation, and disposal to landfill. A further objective of the assessment was to highlight areas of sustainability concerns for the individual technologies and projects. The assessment is based around four principal criteria defined by the authors. Each project was assessed using both an overall multi-criteria analysis, detailed in this paper (Part 1), and a study of the detailed impacts on an individual project basis, detailed in Part 2

Sustainability of Land Remediation. Part 2: Impact Assessment

A comparative assessment was carried out of the technical/environmental sustainability of five different contaminated land remediation projects completed in the UK between 1997 and 2002. The remediation technologies employed in those projects were in situ stabilisation/solidification, soil washing, ex situ bioremediation, cover system, and excavation and disposal to landfill. A further objective of the assessment was to highlight areas of sustainability concerns for the individual technologies and projects. The assessment is based around four principal criteria defined by the authors. Each project was assessed using both an overall multi-criteria analysis, detailed in Part 1 of this paper, and a detailed impact assessment, detailed here in Part 2

Electrokinetic biosparging of toluene in groundwater

Electrolysis of water occurs when electrokinetic techniques are used to remediate contaminated soils and groundwater. Under an electric field, generation of hydrogen and oxygen gases, and hydroxyl and hydrogen ions, occurs at the electrodes. By orienting electrodes vertically, oxygen has been generated at the base of aqueous solutions and saturated soil specimens, which then rises in the form of fine bubbles through the overlying media. Three sets of experiments were performed to explore the ability of this oxygen flow to encourage removal of dissolved-phase toluene by both sparging and biosparging. Low electric currents of 10 to 50 mA were found to be sufficient to generate appreciable quantities of oxygen. These, in turn, were found to stimulate more rapid growth of bacteria (Pseudomonas putida mt-2) in uncontaminated aqueous media with and without the presence of gravel. In addition, bubble generation was found to cause abiotic removal of the volatile toluene in coarse-grained soils (sand and gravel) but not in fine-grained sand. Finally, removal of toluene from aqueous solution was achieved through the combined action of sparging and enhanced biodegradation (biosparging)

Self-healing soil: Biomimetic engineering of geotechnical structures to respond to damage

The concept of self-healing, whereby materials such as polymers, composites and cementitious construction materials are able to sense damage or deterioration and regulate, adapt and repair themselves automatically, is applied here to natural and anthropogenic soil structures. Damage in such structures can be difficult to detect and monitor, and will have significant consequences, but maintenance and repair are costly and disruptive. This paper presents an overview of the self-healing concept, its potential within geotechnical engineering and results from preliminary experiments exploring the potential for self-healing through the actions of living organisms such as bacteria. We report a simple experimental example, which demonstrates the potential for bacterial activity in microbially induced calcium carbonate precipitation of coarse-grained soils to persist and heal damage. Sands stabilized through calcium carbonate precipitation effected by Sporosarcina pasteurii were sheared and rehealed with only additional supply of nutrients, recovering a proportion of the original strength. This example is a simple demonstration of the ability of living organisms to adapt and respond to damage, and suggests the potential for this ability to be harnessed by engineers to design structures that can heal themselves

Electrokinetic-enhanced bioremediation of organic contaminants: A review of processes and environmental applications

There is current interest in finding sustainable remediation technologies for the removal of contaminants from soil and groundwater. This review focuses on the combination of electrokinetics, the use of an electric potential to move organic and inorganic compounds, or charged particles/organisms in the subsurface independent of hydraulic conductivity; and bioremediation, the destruction of organic contaminants or attenuation of inorganic compounds by the activity of microorganisms in situ or ex situ. The objective of the review is to examine the state of knowledge on electrokinetic bioremediation and critically evaluate factors which affect the up-scaling of laboratory and bench-scale research to field-scale application. It discusses the mechanisms of electrokinetic bioremediation in the subsurface environment at different micro and macroscales, the influence of environmental processes on electrokinetic phenomena and the design options available for application to the field scale. The review also presents results from a modelling exercise to illustrate the effectiveness of electrokinetics on the supply electron acceptors to a plume scale scenario where these are limiting. Current research needs include analysis of electrokinetic bioremediation in more representative environmental settings, such as those in physically heterogeneous systems in order to gain a greater understanding of the controlling mechanisms on both electrokinetics and bioremediation in those scenarios