RO Membrane Protection
Reverse Osmosis (RO) plants are extensively used throughout manufacturing and industry to improve water quality, so that it is suitable for a huge range of uses in food, beverage or pharmaceutical use, oil & gas, municipal water. A small sample of applications water treatment plants for ultrapure water production in electronics, sea water purification for drinking water uses on cruise ship and wastewater purification. It is important that in all these applications RO plants operate as effectively as possible because of the huge quantities of water that are processed every day and the energy that is used in their operation.
Read our INFOGRAPHIC on the 3 most common problems that cause RO Membranes to operate poorly.
Handling Variable Sea Water Quality in SWRO.
Use PurePore PP cartridges designed to cope with plankton or algae blooms, silts, or other sediments.
Chlorine Removal From Mains Water
CleanPore Carbon will lower residual chlorine levels ensuring extended RO membrane life.
Ensuring SDI Readings are Below 5
PurePore PP cartridges ensure you are well below RO membrane SDI limits.
HighFlow Cartridge Filter Housings
Fouling prevents long service life and optimum performance
Fouling of RO membranes can be a frequent problem, if insufficient pre-treatment is provided, which causes the service life of RO membranes to be dramatically reduced and increases running costs as replacement membranes are expensive. Cartridge and bag filtration both play their parts as the last stages of pre-treatment trains that ensures nothing impacts their operation of the plants or their service life.
Fouling is caused by contaminants found in the feed water being purified. If these are allowed to build up over time on and inside the RO membranes then there will be a reduction in membrane flux rate, which will see the production capacity decline over time without action.
Salt density index (SDI) is a measure of potential colloidal or particulate fouling of RO membranes and a feed water SDI of less than 5 shows low fouling of membranes. The use of pleated depth filters will help ensure SDI values below this value.
The correct design of pre-treatment train can prevent fouling and allow designers to minimise the size of RO plants and reduce the outlay in initial capital cost of the project. The other obvious benefit is that RO membrane life is maximised, running costs will be lowered.
The design of an RO pre-treatment is dependent on the water’s source (bore hole, municipal or sea water) and is designed specifically to counter the challenges found. However, the ultimate step is always cartridge filtration, typically 10 or 5 micron that often has a prefiltration step that uses bag filtration of 30 or 20 micron.
There are three main RO pre-treatments:
Activated Carbon (AC) for chlorine removal
Chorine is another danger for RO membranes and has long been an essential component in municipal, industrial and wastewater treatment due to its ability to eliminate most pathogenic microorganisms. RO membranes are though easily damaged by chlorine in the feed water. To prevent this damage carbon filters will be included in the pre-treatment train and ensure chlorine levels are reduced in the feed water.
Large flow systems
Originally when flowrates over 50 m3/hr were specified then normally standard size cartridges were used, which are typically 65mm in diameter. However, to match these flows caused for substantial numbers of cartridges to be installed in housings and this leads to large changeout times when cartridges are changed and a significant volume of cartridges to be disposed of. The solution was the development of the high flow cartridge and housing. Containing the same media as standard cartridges these cartridges are 6” (15cm) in diameter and significantly higher surface areas, hence the number of cartridges was reduced. This is turn leads to a simpler design of filter housing which again leads to lower initial capital cost.
SWRO applications
The use of cartridges to ensure SDI levels in sea water reverse osmosis (SWRO) has unique challenges. No longer can we use st.st housings as they suffer corrosion and therefore alternative materials need to be used. On lower system flowrates it is common to find either plastic or GRP housings used that hold a single cartridge. However, if the need is for a higher flowrate multi-round housing, such as the oil & gas industry, then a custom-built C-22 Hastelloy or glass lined housing will be required.
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