Microfiltration
It is commonly used in conjunction with various other separation processes such as ultrafiltration and reverse osmosis to provide a product stream which is free of undesired contaminants.
More microscopic, atomic or ionic materials such as water (H2O), monovalent species such as Sodium (Na+) or Chloride (Cl−) ions, dissolved or natural organic matter, and small colloids and viruses will still be able to pass through the filter.
[3] The suspended liquid is passed through at a relatively high velocity of around 1–3 m/s and at low to moderate pressures (around 100-400 kPa) parallel or tangential to the semi-permeable membrane in a sheet or tubular form.
In that sense, both filtration and disinfection take place in a single step, negating the extra cost of chemical dosage and the corresponding equipment (needed for handling and storage).
MF membranes are employed in these industries as a method to remove bacteria and other undesired suspensions from liquids, a procedure termed as 'cold sterilisation', which negate the use of heat.
Furthermore, microfiltration membranes are finding increasing use in areas such as petroleum refining,[10] in which the removal of particulates from flue gases is of particular concern.
The key challenges/requirements for this technology are the ability of the membrane modules to withstand high temperatures (i.e. maintain stability), but also the design must be such to provide a very thin sheeting (thickness < 2000 angstroms) to facilitate an increase of flux.
Aside from the above applications, MF membranes have found dynamic use in major areas within the dairy industry, particularly for milk and whey processing.
Dead-end filtration; all of the process fluid flows and all particles larger than the pore sizes of the membrane are stopped at its surface.
Microfiltration systems do not require expensive extraneous equipment such as flocculates, addition of chemicals, flash mixers, settling and filter basins.
The design involves a pleated membrane which is folded around a perforated permeate core, akin to a spiral, that is usually placed within a pressure vessel.
[33] As separation is achieved by sieving, the principal mechanism of transfer for microfiltration through micro porous membranes is bulk flow.
[37] Where Rigorous design equations[38] To give a better indication regarding the exact determination of the extent of the cake formation, one-dimensional quantitative models have been formulated to determine factors such as See External Links for further details Although environmental impacts of membrane filtration processes differ according to the application, a generic method of evaluation is the life-cycle assessment (LCA), a tool for the analysis of the environmental burden of membrane filtration processes at all stages and accounts for all types of impacts upon the environment including emission to land, water and air.
In general, the potential environmental impact of the process is largely dependent on flux and the maximum transmembrane pressure, however other operating parameters remain a factor to be considered.
A specific comment on which exact combination of operational condition will yield the lowest burden on the environment cannot be made as each application will require different optimisations.
[39] In a general sense, membrane filtration processes are relative "low risk" operations, that is, the potential for dangerous hazards are small.
All pressure-driven filtration processes including microfiltration requires a degree of pressure to be applied to the feed liquid stream as well as imposed electrical concerns.
[40] Membrane microfiltration is fundamentally the same as other filtration techniques utilising a pore size distribution to physically separate particles.
Reverse osmosis is able to retain almost all molecules except for water, and due to the size of the pores, the required osmotic pressure is significantly greater than that for microfiltration.
[41] Similar research has been done into the construction high flux poly(trimethylene terephthalate) (PTT) nanofiber membranes, focusing on increased throughput.
Specialised heat treatment and manufacturing processes of the membrane's internal structure exhibited results indicating a 99.6% rejection rate of TiO2 particles under high flux.
