P.A.B. James

ADSORPTION OF RADIOACTIVE METALS BY STRONGLY MAGNETIC IRON SULFIDE NANOPARTICLES PRODUCED BY SULFATE-REDUCING BACTERIA

The adsorption of a number of radioactive ions from solution by a strongly magnetic iron sulfide material was studied. The material was produced by sulfate-reducing bacteria in a novel bioreactor. The uptake was rapid and loading on the adsorbent was high due to the high surface area of the adsorbent and because many of the ions were chemisorbed. The structural properties were examined with high-resolution imaging and electron diffraction by transmission electron microscopy. The adsorbent surface area was determined to be 400–500m2/g by adsorption of heavy metals, the magnetic properties, neutron scattering, and transmission electron microscopy. The adsorption of a number of radionuclides was examined at considerably lower concentration than in previous work with these adsorbent materials. A number of ions studied are of interest to the nuclear industry, particularly the pertechnetate ion (TcO4 −). 99Tc is a radionuclide thought to determine the long-term environmental impact of the nuclear fuel cycle because of its long half-life and because it occurs normally in the form of the highly soluble pertechnetate ion, which can enter the food chain. This bacteria-generated iron sulfide may provide a suitable matrix for the long-term safe storage of the pertechnetate ion. Also, because of the prevalence of the anaerobic sulfate-reducing bacteria worldwide and, in particular, in sediments, the release of radioactive heavy metals or toxic heavy metals into the environment could be engineered so that they are immobilized by sulfate-reducing bacteria or the adsorbents that they produce and removed from the food chain.

Continuous radionuclide recovery from wastewater using magnetotactic bacteria

Magnetotactic bacteria (MTB) can be magnetically removed and harvested from samples collected from ponds and streams. This is achieved by placing a permanent magnet at the sediment/water interface of a sample container. The bacteria swim along field lines, accumulating at regions close to the pole of the magnet. This is the basic principle of Orientation Magnetic Separation (OMS), where the applied magnetic field is utilised to orientate the bacteria to swim in a specific direction. This paper describes the use of MTB for bioaccumulation and radionucleide removal from wastewater using an OMS system.

Low magnetic-field separation system for metal-loaded magnetotactic bacteria

Magnetotactic bacteria (MTB) offer a unique approach to metal accumulation and separation from water systems. This paper proposes an integrated separator design, for the production of MTB, the metal uptake phase and their subsequent separation. Applied magnetic fields are used to orientate the bacteria, so that they swim in a direction resulting in their removal.

Evaluation of domestic Energy Performance Certificates in use

Since October 2008, Energy Performance Certificates (EPCs) have been a mandatory requirement for all dwellings sold or rented in England and Wales. Having now been in place for some time, it is of interest to assess the scheme’s impact and effectiveness. This paper presents the results of a questionnaire survey, targeted at almost 2000 homeowners in Southampton on the South coast of England, who bought their home within the first year of the scheme’s introduction. The survey had a response rate of 17% and established homeowner awareness of EPCs, but highlighted that they had little impact on decision-making or price negotiation. Where retrofitting measures have been undertaken, results are inconclusive as to whether retrofitting was done as a result of EPCs. Energy efficiency was not found to be a priority for homebuyers. Practical applications: The survey presented in this paper highlights that further refinement of EPCs and the certification process appear to be needed, in order for the scheme to become a widespread success in the domestic sector. Whilst there is an awareness of the scheme in general, there appears to be limited recognition of its potential. This poses a challenge for the building industry and certification bodies, which need to seek ways to better communicate the benefits of the scheme, in order to instigate the refurbishment works that are required to meet the national carbon emissions reduction targets in the UK.

Characterization and growth of magnetotactic bacteria: Implications of clean up of environmental pollution

Magnetotactic bacteria possess a magnetic moment due the presence of membrane bounded crystals of magnetite, (Fe3O4) called magnetosomes within their structure. Through manipulation in an applied magnetic field it is possible to determine the size, speed, and magnetic moment of individual bacteria, and hence an average for a culture. Variations in these characteristics with growth have been measured, indicating the suitability of this particular magnetic spirillum for metal loading. A correlation between the increase in magnetic moment and iron uptake of this bacterium leads us to propose a new mechanism for the biomineralization of magnetite. This paper describes the characterization of a magnetotactic spirillum and the implications these results have for its use in the clean up of environmental pollution.

High gradient magnetic separation of motile and non-motile magnetotactic bacteria

Motile magnetotactic bacteria are normally separated from a solution by applying a low intensity (mT) orientating magnetic field. This constrains the bacteria to swim in the required direction. High gradient magnetic separation (HGMS) is a well established method for the extraction of magnetic particles from solutions. This paper reports on the separation properties of both motile and non-motile magnetotactic bacteria using both techniques. A comparison of HGMS separation with low field orientational magnetic separation is made and the conditions under which HGMS becomes beneficial are considered.

EFFICIENCY ENHANCEMENTS THROUGH THE USE OF MAGNETIC FIELD GRADIENT IN ORIENTATION MAGNETIC SEPARATION FOR THE REMOVAL OF POLLUTANTS BY MAGNETOTACTIC BACTERIA

Orientation magnetic separation (OMS) represents a simple method that permits motile, field-susceptible magnetotactic bacteria (MTB) to be separated from water. Such an approach can be used to decontaminate polluted water through uptake of contaminants by the bacteria and their subsequent removal by the application of magnetic fields. In OMS, a separation channel through which an MTB culture is flowing is subjected to a magnetic field perpendicular to the flow direction. The bacteria “sense” the magnetic field, orientating themselves parallel to the field lines and then swim to the channel sides where they accumulate. The fluid flow through such a standard separation channel has been shown to cause dislodgement of accumulated bacteria. To reduce this effect, a new approach has been developed utilizing magnetic gradients to retain the bacteria at the walls of the separator. A study comparing the operation of a standard channel separator with three new designs containing nickel wire matrices has been carried out. The resultant separation efficiencies and the effect on separation of varying both the flow rate and the applied magnetic field are described. The new separators enhance the separation efficiency by up to 300% over the standard separator.

A cation budget analysis for a coastal dune system in North-West England

Summary Input/output budgets for Ca, Mg, Na and K are estimated in a coastal, calcareous dune system for a one year period. An attempt is made to separate inputs via bulk precipitation from those via aerosol impaction. Output, by ground water discharge, is estimated from mean concentrations in ground water and from estimated ground water discharge. Outputs of Na, Mg and Ca are high; Klosses are average. Balances are negative for Ca and Mg and positive for K and Na.

Investigating the principal adaptive comfort relationships for young children

Thermal comfort surveys in school classrooms suggest that children have different thermal preferences to adults. This implies a need to revisit the current adult-based thermal comfort models. This paper investigates the principal adaptive comfort relationships that form the basis of adaptive comfort theory, using 2693 pupil thermal sensation responses and measured classroom temperatures from surveys in two naturally ventilated school buildings. The data were examined in two steps. Firstly, each survey set, obtained over one-day visits to the schools, was examined in order to derive the relationship between indoor temperature change and comfort vote with minimum impact of adaptation. Secondly, the data set was investigated over the entire survey period in relation to the weather experienced by the pupils in order to estimate their time for adaptation to outdoor temperature changes. The analysis shows that the basic adaptive comfort relationships are valid for children. However, a difference was found for the correlation coefficients of the comfort temperature to the outdoor running mean temperature between the schools, and a mismatch between their adaptive comfort equations. It is proposed that the difference in the consistency of the weather during the tests is the main reason for this discrepancy.

Influence of iron valency on the magnetic susceptibility of a microbially produced iron sulphide.

Microbial iron sulphide is well known as an adsorbent for the treatment of metallic ion polluted wastewater. Under certain culture conditions a highly magnetic iron sulphide can be produced which would enable a low cost biomagnetic separation process to be developed. This paper illustrates that by raising the ferrous content of a ferrous - ferric sulphate rich medium the magnetic susceptibility of the iron sulphide produced is increased.