F.D. Moeschler

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.

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 comparative study of the magnetic separation characteristics of magnetotactic and sulphate reducing bacteria

Many microorganisms have an affinity to accumulate metal ions onto their surfaces which results in metal loading of the biomass. Microbial biomineralization of iron results in a biomass which is often highly magnetic and can be separated from water systems by the application of a magnetic field. This article reports on the magnetic separation of biomass containing microbial iron oxide (Fe3O4, present within magnetotactic bacteria) and iron sulphide (Fe1−XS, precipitated extracellularly by sulphate reducing bacteria) in a single wire cell. Since such bacteria can be separated magnetically, their affinity to heavy metal or organic material accumulation render them useful for the removal of pollutants from waste water. The relative merits of each bacterium to magnetic separation techniques in terms of applied magnetic field and processing conditions are discussed.

Continuous Cultivation and Recovery of Magnetotactic Bacteria

Magnetotactic bacteria (MTB) may be manipulated by the application of magnetic fields. This effect enables motile, magnetic field susceptible MTB to be utilised in the removal of contaminants, such as heavy metals, from wastewater. This paper discusses a process designed for continuous cultivation and extraction of metal loaded MTB. The performance of this recovery system is characterized here with respect to bacterial motility, the number of passes through the separator and the processing rate.

Efficiency enhancements through the use of magnetic field gradients in orientation magnetic separation

Magnetotactic bacteria [ l ] can take up heavy metals and be successfully removed from water systems in a process termed Orientation Magnetic Separation (OMS) [2], HM removal paper]. In OMS, a magnetotactic bacteria (MTB) culture is allowed to flow in a standard channel which is placedinavery lowmagnetic field. The bacteria, duethe presence ofmagnetitecrystal within their s t~~cture , sense the magnetic field and onentate themselves to swim along magnetic field lines to the channel walls where they accumulate. Revious work [3] has shown that the flow through the channel caused dislodgement of accumulated bacteria. A new approach, described in this paper, has been developed utilising magnetic gradients not only to reduce this effect but also to enhance separationefficiency and retention ofthe bacteria at the walls ofthe OMS separator. Acomparison of the standard channel separator with three new designs containing nickel wire mavices was undertaken. The effect on separator efficiency 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 Comparative Study of the Magnetic Separation Characteristics of Magnetotactic and Sulphate Reducing Bacteria

Many microorganisms have an affinity to accumulate metal ions onto their surfaces which results in metal loading of the biomass. Microbial biomineralization of iron results in a biomass which is often highly magnetic and can be separated from water systems by the application of a magnetic field. This article reports on the magnetic separation of biomass containing microbial iron oxide (Fe3O4, present within magnetotactic bacteria) and iron sulphide (Fe1?XS, precipitated extracellularly by sulphate reducing bacteria) in a single wire cell. Since such bacteria can be separated magnetically, their affinity to heavy metal or organic material accumulation render them useful for the removal of pollutants from waste water. The relative merits of each bacterium to magnetic separation techniques in terms of applied magnetic field and processing conditions are discussed.