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            Filtration

Filtration typically separates a solid of interest from a liquid. Separation efficiency is expressed as the percentage of dry solids recovered during the separation. The moisture content of the solid fraction is calculated as a percentage of the masses of water and dry matter respectively. Choosing a suitable filtration method for a particular biomass is not trivial as the efficiency depends on how the solids in the biomass pack during the filtration. Examples of equipment for filtrations of forest biomass are sieves and filter presses. Alternatives to conventional filtrations are membrane filtrations such as micro-, ultra- and nano-filtrations. For smaller volumes microfiltration can be more cost effective but for larger volumes it is more economical to use centrifugation. (Grima, Belarbi, Fernandez, Medina, & Chisti, 2003).

         Centrifugation

Centrifugation separates materia by differences in density where the most dense particles settle first. Low density particles drift towards the axis whilst high density particles within the biomass travel away from the axis. There are a number of different types of centrifuges for example solid bowl centrifuges, disc stack centrifuges, decanter centrifuges and hydrocyclone  to mention a few. Centrifugation is generally not used for low value bulk products as the operating costs are high. Centrifugation is energy intensive and the fast moving mechanical parts leads to high maintenance costs. (Sharma, Garg, Li, Malekizadeh, & Schenk, 2013)