UF and DMF
Published on by AHMAD ALHARBI, Power and Water Utility Company of Jubail and Yanbua - Sr. Specialist, Water Planning in Technology
Dear All,
Can any one shade a light on thetechnical advantages of UF technology compared to DMF as well as the cost benefits.
Thank you for your help.
Taxonomy
- Desalination
5 Answers
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Very late reply here. For me DMF with media of a bio supporting type eg Pumice or Expanded Clay is nearly always better solution than UF/MF .
a) Are there really any large size UF SWRO plants that do not suffer bad biofouling of the RO . DMF with deep biosupport media and dechlorination before DWF should reduce the biofouling on RO to level with far fewer CIP annual actions
b) Claimed longer RO membrane life with UF/MF not reality due to biofouling needing frequent CIP actions. Biofouling causes of lack of RO membrane performance/life always excluded from RO membrane guarantees.
c) Membrane integrity a major problem for several UF/MF plants for seawater RO .
d) DMF tendency now to operate with no acid , and average iron dose of only around 1- 2 ppm. This the chemical saving/sludge treatment saving /Environmental argument is present but not very strong .
e) Gravity DMF needs only about 12-16 filter cells for a 150 MLD RO plant, there will be backwashing only once every 30-50 hours of each train using approx. 5 actuated valves . A UF/MF system will use 20-30 trains each with backwashing occurring every 30-45 mins using 5 actuate valves . UF/MF has to be far more mechanically unreliable.
f) UF/MF valves often have some leakage , thus needs constant dosing of the filtrate with SMBS to prevent oxidation of the RO.
g) Too often the spent chlorine and other chemicals used for CEB/CIP actions of the UF/MF are not neutralised to save cost and discharged to sea (yes neutralisation facilities provided but not used) if there is not effective environmental monitoring .
h) The UF/MF membranes life is very uncertain 3-7 years with many (but not all) of the suppliers. One UF/Mf supplier has a proper demonstrated 10 year life. This is also linked to the membrane integrity issue.
I) The UF/MF modules are often bespoke for the Rack systems of the supplier , this makes them more subject to issues when they become obsolete and also leads to sole source vendor issues, (price exploitation , and issue when they leave the business).
J) DMF plants do not need a building . Yes some designers put them in the building to prevent algae growth, but I believe why bother , let the algae grow on the top surface of the DMF and remove the nutrients needed for biofouling of the RO. The DMF will remove most (not all) of this additional algae any way, better to remove the soluble and fine colloidal nutrients.
k) The UF /MF needs to have effective pressure screen pretreatment . Some say 100 microns to protect against barnacles, other say 50 microns to protect against Mussels. Other are now allowing 150-300 microns , but it is very unclear the effect of fine sand /silt abrasion on the membrane. Perth II desal has published (San Diego 2015) a MF membrane integrity problem caused by very small spinicules .
1 Comment
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Dear Conor Kenny,
Good and informative answers are never too late!
Thank you for the precise and elaborate answer.Best regards,
Duško
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The main benefit of DMF over UF is that it is cheaper to install, replace and operate. We offer our Pumice Media for DMF pretreatment prior to UF as it gives the following filtrate quality when used with sand: - Suspended Solids
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Dear Mansoor & Matan, Thank you helpful comments. I asked this because i am preparing a report about both systems to change an existing DMF with UF or rehabilitate the former for one of our SWRO.
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Dear Ahmad, There matter of applications, some places DMF are move economical and beneficial then using UF. Some application are of DMF is used as Pre-Filtration to UF. DMF cheaper to replace than UF membranes DMF having filtration efficiency up to 50 - 100 microns. Whereas UF having Filtration Efficiency up to 0.02 - 0.03 micron. SDI most of the times unaffected by DMF whereas UF reduces SDI significantly. Overall Cost of DMF is cheaper than UF if we compare DMF you only need to change Media whereas you need to change UF membrane as a whole. DMF media life depends but normally Sand media up to 2 - 3 years whereas Activated Carbon Life 1 years max. UF acquire/occupy lesser space then DMF For me normally it is not appropriate to compare both as this is matter of application and normally you are very clear in the product water requirement so you choose which type of filtration is better/economical to apply.
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Main benefits of UF compared to DMF are: -higher filtrate quality, typically guaranteeing SDI