2008

Hydrocyclone/Filter for Concentrating Biomarkers From Soil

This apparatus could detect biomarkers or chemical waste in soil.

The hydrocyclone- filtration extractor (HFE), now undergoing development, is a simple, robust apparatus for processing large amounts of soil to extract trace amounts of microorganisms, soluble organic compounds, and other biomarkers from soil and to concentrate the extracts in amounts sufficient to enable such traditional assays as cell culturing, deoxyribonucleic acid (DNA) analysis, and isotope analysis. Originally intended for incorporation into a suite of instruments for detecting signs of life on Mars, the HFE could also be used on Earth for similar purposes, including detecting trace amounts of biomarkers or chemical wastes in soils.

Image
In this Prototype HFE, a soil/water slurry is pumped from a sample container through a hydrocyclone separator vessel and a filter and is recycled through the sample container. The hydrocyclone separates most of the soil particles into an underflow. The filter traps smaller particles in the overflow.

In addition to a conical separator vessel typical of a hydrocyclone, the HFE includes a pump, a sample container, an electropositive nanoparticle filter, and associated plumbing (see figure). The hydrocyclone serves to separate both cellular-sized particles (<5 μm) and dissolved organic compounds from the bulk soil (consisting mostly of particles larger than 5 μm). The electropositive filter serves to capture cellular biomass and remove particles from the extract with maximal capacity (that is, minimal clogging).

The soil sample is prepared by mixing it with sterile water or another suitable solvent to form a slurry, which is pumped to the hydrocyclone separator vessel in tangential streams at the top (wide) end to form two concentric opposing vortices at high hydrodynamic pressures to effect separation based on particle size. The spinning motion of the injected slurry is accelerated by the conical taper, creating a large centrifugal force that causes the larger particles to rapidly separate from the rest of the flow and leave the vessel as part of underflow through the bottom (narrow) end of the separator vessel. The liquid containing suspended particles smaller than 5 μm leaves the vessel as the overflow (which is larger than the underflow) at the top (wide) end of the vessel. The overflow is then fed through the filter.

The filter contains electropositive aluminum nanotubes embedded in a glass-fiber matrix. The filter has a nominal pore size of 2 μm, but can collect biological particles having sizes down to fractions of a micron, on the basis of electrostatic charge, without clogging. The combination of the hydrocyclone and the electropositive nanoparticle filter is capable of extracting 99 percent of particles smaller than 5 μm from the soil sample and retaining them for analysis. In the prototype HFE depicted schematically in the filter, the underflow and the effluent from the filter are fed back to the sample container. It is envisioned that the fully developed HFE could operate in a continuous-flow mode, making it possible to extract biomarkers from a large volume (e.g., 1 m3) of soil using a minimal amount (e.g., 1 L) of solvent.