Editing Microfiltration (section)

===Fundamental design heuristics===

A few important design heuristics and their assessment are discussed below:

* When treating raw contaminated fluids, hard sharp materials can wear and tear the porous cavities in the micro-filter, rendering it ineffective. Liquids must be subjected to pre-treatment before passage through the micro-filter.<ref>Water Treatment Solutions. 1998, Lenntech, accessed 27 September 2013 < http://www.lenntech.com/microfiltration.htm</ref>  This may be achieved by a variation of macro separation processes such as [[Mechanical screening|screening]], or granular media filtration.
* When undertaking cleaning regimes the membrane must not dry out once it has been contacted by the process stream.<ref>Cheryan, M 1998, ''Fouling and Cleaning''. 2nd edn. ''Ultrafiltration and Microfiltration Handbook'', CRC Press, Florida p. 237-278</ref>  Thorough water rinsing of the membrane modules, pipelines, pumps and other unit connections should be carried out until the end water appears clean.
* Microfiltration modules are typically set to operate at pressures of 100 to 400 kPa.<ref>Baker, R 2012, ''Microfiltration, in Membrane Technology and Applications'', 3rd edn, John Wiley & Sons Ltd, California p. 303-324</ref> Such pressures allow removal of materials such as sand, slits and clays, and also bacteria and protozoa.
* When the membrane modules are being used for the first time, i.e. during plant start-up, conditions need to be well devised. Generally a slow-start is required when the feed is introduced into the modules, since even slight perturbations above the critical flux will result in irreversible fouling.<ref>Cheryan, M 1998, ''Fouling and Cleaning.'' 2nd ed. ''Ultrafiltration and Microfiltration Handbook'', CRC Press, Florida p 237-278</ref>

Like any other membranes, microfiltration membranes are prone to fouling. ''(See Figure 4 below)'' It is therefore necessary that regular maintenance be carried out to prolong the life of the membrane module.

* Routine '[[backwashing]]', is used to achieve this. Depending on the specific application of the membrane, backwashing is carried out in short durations (typically 3 to 180 s) and in moderately frequent intervals (5 min to several hours). Turbulent flow conditions with Reynolds numbers greater than 2100, ideally between 3000 - 5000 should be used.<ref>Cheryan, M 1998, ''Fouling and Cleaning. in Ultrafiltration and Microfiltration Handbook'' 2nd edn., CRC Press, Florida, p. 237-278</ref>  This should not however be confused with 'backflushing', a more rigorous and thorough cleaning technique, commonly practiced in cases of particulate and colloidal fouling.
* When major cleaning is needed to remove [[Entrainment (engineering)|entrained]] particles, a CIP (Clean In Place) technique is used.<ref>Baker, R 2012, ''Microfiltration, in Membrane Technology and Applications'', 3rd edn, John Wiley & Sons Ltd, California. pp. 303–324</ref>  Cleaning agents/[[detergent]]s, such as [[sodium hypochlorite]], [[citric acid]], [[caustic soda]] or even special enzymes are typically used for this purpose. The concentration of these chemicals is dependent on the type of the membrane (its sensitivity to strong chemicals), but also the type of matter (e.g. scaling due to the presence of calcium ions) to be removed.
* Another method to increase the lifespan of the membrane may be feasible to design two microfiltration membranes in [[wikt:Special:Search/series|series]]. The first filter would be used for pre-treatment of the liquid passing through the membrane, where larger particles and deposits are captured on the cartridge. The second filter would act as an extra "check" for particles which are able to pass through the first membrane as well as provide screening for particles on the lower spectrum of the range.<ref>Baker, R 2000, Microfiltration, in Membrane Technology and Applications,  John Wiley & Sons Ltd, California. p. 280</ref>