Oil adsorption systems

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Woolspill ™

Woolspill™, a natural wool product, is an effective and highly efficient oil sorbent material able to adsorb up to 36 times its own weight in oil. Hydro-Carbon Filtration & Separation offers solutions to remove efficiently free and slightly emulsified oil from water. The Woolspill is used as final stage in our oil-water separators or used in stand-alone pressure vessels according your requirements. Depending on the application tailor made solutions for the removal of oil, suspended solids and other contamination can be made available.

Woolspill has the following advantages:

  • Woolspill utilises the natural affinity of wool for oil adsorption.
  • Woolspill has been independently evaluated to be the best performing natural sorbent available (S.L. Ross – Environment Research Ltd, for Environment Canada).
  • Woolspill is effective for all hydrocarbon types, particularly high viscosity oils.
  • Woolspill is biodegradable.
  • Woolspill is available in a number of versatile forms permitting tailoring of oil filtration and clean-up solutions.
  • A continuous filtration system has been developed to effectively remove total petroleum hydrocarbons (to 5 ppm), suspended solids and heavy metals. These machines have been successfully applied to many industries.
  • A gravity fed system, capable of handling virtually unlimited water flows has been developed. A feature of the system is its flow rate dependence on only the capacity of the pipe work. A system has been commissioned at Auckland International Airport to treat stormwater runoff from the aircraft arrival and departure gates.

Woolspill™ is the registered trade mark and name given to manufactured small spherical shaped wool fibres known as knops, which were developed principally for use as a sorbent for hydrocarbon based products. Woolspill has been extensively tested both in laboratory trials and actual hydrocarbon clean-up situations. The laboratory studies have indicated Woolspill ranks among the best adsorbents commercially available, and is certainly the best-performing natural adsorbent.

Oil adsorption mechanism

Wool fibres naturally have an oleophilic outer cuticle and a hydrophilic epicuticle. The wool fibre has evolved having these properties; the oleophilic outer cuticle tends to be covered in natural greases commonly known as lanolin. The lanolin is required in order for the sheep’s fleece to repel water and insulate the body. The fibre also has a hydrophilic central structure which allows moisture to be absorbed and dissipated, which helps the sheep to control its body temperature. It is the oleophilic outer cuticle that helps to make Woolspill so efficient as an oil sorbent. The other aspects are engineered into the physical design of Woolspill. Woolspill consists of small spheres of up to 300 fibres entangled and wrapped around each other forming a fibre structure, hollow in the centre, and about the size of a pea, known as a knop.
It is the spherical shape that complements the oil adsorbing nature of Woolspill as the fibres adsorb the oil into the structure using capillary action. The wool fibres are typically around 30-38 microns in diameter and thus each sphere is very porous, compared with most other sorbent. The fibre density of wool is approximately 1.31 g/ml and a sample of typical Woolspill has a density of around 0,33 g/ml. This allows the oil to quickly penetrate a mass of Woolspill. In effect the oil adsorption process can be described as a drop of oil bound up by wool fibres. Being of a particulate nature also allows Woolspill a number of advantages over continuous or semi-continuous forms, eg. it can be easily spread at different densities over waterways or housed in purpose-built netting receptacles to make boom or filters of various shapes and sizes.

Hydrocarbon adsorption efficiency

D4-secfilt2Woolspill knops were submitted to S.L. Ross – Environment Research Ltd on behalf of Environment Canada, a world leading oil spill response laboratory, for an independent evaluation of its performance against other sorbent materials. Woolspill and 15 alternative sorbents were evaluated in terms of initial and maximum sorbent capacities, water pick-up and re-use potential. Testing utilised three oils of widely varying viscosity – crude (1- and 7-day aged), bunker C and diesel – and two solvents – Cyclohexane and Toluene.
Environment Canada’s test results confirmed that wool in the knop form adsorbed considerably more oil, weight for weight, than any other natural sorbent, and it performed in a similar manner to the top four synthetic sorbents. Subsequent trials with oils of varying viscosity and knops of various size and density have allowed optimisation of the wool knop structure and hence oil adsorbing performance. Woolspill has proved most capable when adsorbing viscous oils such as heavy fuel oils and heating oils. If Woolspill is accidentally left in the marine environment there are naturally occurring bacteria, which will break down the wool fibres and residual hydrocarbons. There have been a number of environmental studies investigating the aftermath of the Exxon Valdez incident where there were mountains of polypropylene melt blown oil sorbent fabric saturated with oil left behind after the clean up. The fabric now poses an even greater environmental threat as the oil was not removed.

Forms of Woolspill

woolspillknopsWoolspill takes two forms:

  • Loose granulated product or knop, capable of adsorbing over 36 times its own weight in oil.
  • A continuous non-woven material which can be manufactured into a range of densities and widths, and can therefore be specially tailored to specific oil and situation types. This matting is capable of adsorbing up to 15 times its own weight of oil.

From the two forms of Woolspill, a range of spill response products including booms, pillows and mats are available, as are several filtration media products designed for use in a twin chamber filtration system. More recently, gravity-fed systems capable of large volume storm water treatment have been developed.
A commercial filter has been developed for use in industrial applications as a continuous flow system to remove total petroleum hydrocarbons, suspended solids. The system not only removes free floating hydrocarbons, but effectively removes the mid-phase suspended hydrocarbons that traditional separation systems fail to deal with.


Depending on the application tailor made solutions for the removal of oil, suspended solids and other contamination can be made available. The systems can include (but are not limited to) plate separators for gravity pre-separation, pre-filters for solids removal, pumps, controls, tanks and pressure vessels.

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