What Is Ultrafiltration Membrane And How Does It Work? - Waterdrop

Ultrafiltration(UF) is a physical filtration process that uses home water pressure to push water through the semipermeable membrane to get rid of particles larger than membrane pore size in water. The ultrafiltration membrane utilized during the filtration process is a kind of hollow fibers with pore size ranging between 0.01 to 0.1 micron, which is several thousand times smaller than a human hair. While water feeds in, the particles larger than the pore size would be retained on the surface of the membrane, whereas water and beneficial minerals that are smaller than the pore size would pass through and become the drinkable water. One highlight of the ultrafiltration membrane is that it does not remove all the dissolved minerals. This could be considered a pro if the home water TDS is at a good level since a certain amount of the retained minerals are beneficial to our health. Yet, it would be a shortcoming if the source water has a high TDS level, as overmuch TDS would significantly affect the water taste. So, you’d better check your home water TDS level before you buy a UF system. According to an authority review conducted by the United States, Canadian, World Health Organization (WHO) and European Community (EC), the US recommended maximum TDS level is 500 mg/L. If your home water TDS level has already exceeded this value, we suggest you choose a reverse osmosis system that could significantly reduce TDS.

What contaminants does the UF membrane remove?

The UF membrane is very effective in reducing rust, sediment, chlorine taste and odor, benzene, crypto, bacteria; it could also partially reduce algae, chloride, copper, lead, mercury; whereas it has no effect on chemicals and TDS.

Frequently asked questions about the UF membrane

Does Ultrafiltration Need Electricity?

Unlike the reverse osmosis filtration that needs a pump to push water past the membrane by increasing water pressure, ultrafiltration could work well with standard home water pressure. Therefore, most of the ultrafiltration system does not require electricity.

What’s the difference between ultrafiltration and reverse osmosis?

Ultrafiltration and reverse osmosis are all physical filtrations that use pressure to push water through the semipermeable membrane, and block impurities larger than the membrane pore size at the outer surface of the membrane. The main difference between them is filtration accuracy. The ultrafiltration membrane pore size ranges from 0.01 to 0.1 microns, whereas the reverse osmosis membrane has a more fine pore size of 0. microns. Thus the RO membrane could remove impurities that are much finer, such as TDS. Given the difference in pore size, RO systems usually need a pump to increase pressure, while ultrafiltration systems can work well with standard home water pressure. That explains why most RO systems need electricity supply but UF systems don’t need it.

What’s the difference between UF filtration and UV filtration?

UF removes impurities larger than the pore size by filtering them out. UV only works for microorganisms like viruses and bacteria in water by killing them with UV light.

Different types of ultrafiltration systems

There are many kinds of UF filters on the market to meet different customers’ needs, like the whole house filter, which installed at the point of entry where water comes into your home from a municipal supply. As well as point of use filter, like under-sink UF water filter and portable water filter straw.

Whole House Ultrafiltration Systems

The whole house ultrafiltration system is a point-of-entry water filtration system that serves the entire home, including the water tube, faucet, shower head, etc. With the 0.01-micron UF filter, it could eliminate different kinds of impurities and contaminants for the whole home and greatly increase the service life of the tubes, faucets, and any other filters present down-line. But the drawbacks of the whole house systems are that they usually need to be installed when you build the house. Furthermore, they are not comparatively affordable, most of which cost several thousands of dollars. However, point-of-use ultrafiltration systems only take a few hundred dollars or even less.

Under-sink Ultrafiltration System

Under-sink UF membrane filters are very popular for homes and families for the budget-friendly price and excellent filtration performance. Let's take Waterdrop smart under-sink UF system and inline under-sink UF water filter for example.

Smart Under-Sink UF System

The smart under-sink filter smart under-sink ultrafiltration system has a very similar appearance to the RO system. It also takes multi-stage filters and has a smart filter life indicating system on the front panel. It uses polypropylene, activated carbon as pre-filters to remove most of the large eye catchable impurities including colloids, sediments, rust, absorb chlorine taste and odor, fluoride as well as most VOCs in water. After that, the water would be filtered by the UF membrane filters with a pore size of 0.01 micron, where the bacteria, superfine rust and sediments, lead and other heavy metals would be removed. The filtered water then followed by another activated carbon filter to improve the taste and eventually flow to a dedicated faucet for home drinking, cooking, etc. The main difference between the smart UF under-sink system and the modern RO system is the filtration efficiency——the UF filter cannot remove the superfine dissolved minerals in water as discussed above.

Under-Sink Inline Ultrafiltration Water Filter

The inline ultrafiltration water filter is a more compact filtration system compared with the smart UF water filter. It takes an all-in-one design that puts different filter materials like a polyester membrane, activated carbon block, KDF, UF membrane all together in one composite filter to get rid of the harmful substances. Benefit from the all-in-one design, the inline filter takes very little space under the counter and especially fits for small apartments, RVs, etc. Just connect it between the tap water input and output faucet, you will be accessible to refreshing, clean water from the tap at the minute.

Portable Water Filter Straw

Ultrafiltration membranes can also be used in portable water filters for drinking water directly from rivers, lakes, and other water resources outdoors. Also takes an all-in-one design, the portable water filter straw is a four-stage filtration made out of pre-filter fabric, UF membrane, activated carbon filter and post polyester membrane. Though the filter itself has a smart frame, the filtration efficiency is powerful. Most of the harmful substances such as chlorine, rust, colloids, sediments, bacteria and heavy metals could be effectively reduced from the raw water. The compact design allows you to put it in your backpack and takes it everywhere, making it possible for you to access safe water anywhere, anytime.

Takeaway

It is important to understand the working principle of the filtration system before choosing a product. Only in this way, you could understand what kind of filtration works best for your water and whether the system could meet your needs or not. I hope this article would be useful in helping you make the right choice.

Water for Injection (WFI) is a critical utility with increasing demand for vaccines and therapeutics. Traditionally, WFI production uses distillation, but producers that use such systems want options with lower ownership costs and more sustainability. Reverse osmosis (RO) membrane-based systems with ultrafiltration can meet some of these challenges. 

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If you are a manufacturer of pharmaceutical or biologic medicines, you’ll want to evaluate all the pros and cons surrounding your design choice for a new WFI generation system.

Membrane-based production for WFI continues to be at the forefront of discussions as it presents a design alternative to the traditional distillation-based system. Membrane-based production of WFI has the potential to lower total cost of ownership and possibly provide a more sustainable solution long-term.

Regulatory and Quality Requirements for WFI

Producers implementing membrane-based WFI systems must first consider regulatory and quality requirements, including those from the United States Pharmacopeia (USP), European Pharmacopeia (EP), and Japanese Pharmacopeia (JP). 

Each set of regulatory standards differs slightly in the allowed WFI production processes. The standards require purification processes equivalent or superior to distillation, with some unique requirements, like no added substances. These equivalent systems can include membrane-based purification. 

USP Monograph outlines WFI must be purified by distillation or a purification process that is equivalent or superior to distillation and that it contains no added substances.

The European Pharmacopeia (Ph. Eur. Monograph 169) outlines a purification process that is equivalent to distillation. Reverse osmosis, which may be single-pass or double-pass, depending on water coming into your facility and other risk-based questions, coupled with other appropriate techniques such as electrodeionization, ultrafiltration or nanofiltration, is suitable. Notice should be given to the supervisory authority before implementation.

Japanese Pharmacopeia requires WFI by distillation or reverse osmosis and/or ultrafiltration. It’s important to know that the JP requires the molecular weight cut-off of your final membrane barrier to be at 6,000 Dalton.

The regulatory standards also set slightly different benchmarks for conductivity, total organic carbon, bacterial, and microbial levels.

Learn more about navigating global pharmacopeia standards for water quality here.

Operations of a Typical Membrane WFI System

Membrane-based WFI systems meet regulatory standards through comprehensive system design, including the following components:

• Pretreatment: The first subsystem that would see water is the pretreatment, which protects the final treatment (generation) from damage. It conditions the water so it is acceptable for feeding into the final treatment or generation subsystem. 
• Final treatment: This component forms the heart of the system that produces the final required quality and quantity of Water for Injection (WFI). The membrane gets implemented here. 
• Storage and distribution: After proper purification, storage and distribution systems ensure adequate water volumes with sufficient pressurization for point-of-use requirements. 

Before you implement a membrane-based system, there are four main areas to evaluate before designing your system. For example purposes, we’ll be using Water for Injection (WFI) to explain the importance of each.

1. Feed water quality and temperature: What’s your starting water quality? There are a number of different contaminant groups to evaluate to make sure each can be adequately treated to guarantee Water for Injection quality at the outlet of the system. This usually comes from a standard laboratory water analysis of whatever the local feed water source. The other area to consider is temperature and any seasonal variation of that temperature, which is a particular concern with surface water and parts of the world that have large temperature swings between seasons. This is important because membrane-based systems’ performance is affected by the feed water temperature.
2. Peak water usage: This will directly impact the storage tank size and also will inform what the flow rate will need to be.
3. Daily water usage: The total amount of water that will be used on any given day. You will also want to know worse-case scenario. This impacts the final treatment or generation system as it will have to make enough water safely to satisfy that total daily demand.
4. Point of use temperature required: There are some applications that use ambient water and others that require hot. MECO has designed a number a systems that have different temperature requirements at different points of use. This can all be accounted for in the storage and distribution design of a membrane-based Water for Injection system.

Contaminants in Water

There are a number of contaminant groups that need to be considered when designing your membrane-based system. The purpose of pretreatment is to condition the water before it is fed to the generation system. The typical three groups of contaminants are particulates (suspended solids), scalants/foulants (calcium/magnesium) and disinfectants (C12).

Our Membrane WFI System cannot tolerate high levels of particulates. Particulates can be removed through a variety of options in our pretreatment subsystem, such as bag filter cartridge or multimedia filter.

Scalants and foulants have to be removed or reduced during pretreatment as they produce chemical compounds that interfere with the membrane’s performance. This jeopardizes the output quality and quantity of the system.

Lastly, disinfectants must be removed. Disinfectants are added to public water to protect the public health but those disinfectants are damaging to the membrane by causing oxidative damages to membranes and EDI stacks.

Unit Processes in Membrane Based WFI System

In our pretreatment subsystem for membrane-based water purification systems we remove particulates through a multimedia filter composed of anthracite, sand, fine garnet, course garnet, medium or course gravel. The typical removal rate is about 10 microns, which is industry standard for media filters.

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For companies who want to cut down their water footprint, we can use pleated dev filter or bag filter for the pretreatment subsystem. The downside to these filters are they have higher maintenance as someone will consistently need to change the filters.

The filtrate will exit that vessel and move on to the next step of water softening. We use a resin bed in order to remove the calcium and magnesium from the feed water. The hardness must be removed so it does not scale the membranes. This will release sodium, since we are using salt to regenerate that bed.

Chlorine is then removed from the feedwater using activated carbon. Our membranes have about PPM hours of chlorine tolerance so you can run at 1PPM of chlorine for hours before you see damage to the membrane. The EDI stacks generally cannot handle chlorine, which is why this stage of chlorine removal from feedwater is so important.

Carbon filters are tried and true when it comes to removing chlorine. Chemical injections can be tricky to manage, for example you don’t have a good injection rate, your pump isn’t putting out what it needs or a bad batch got mixed up. Chemical injections are just not as reliable in removing chlorine as carbon filters. For UV chlorine removal, it is hard to get 100% kill of the chlorine guaranteed.

Dechlorinated water will then exit the carbon filter and proceed to final treatment.

First step is the RO, which will reduce the bulk of all contaminant groups (single or double pass depending on water quality). Next step is EDI stack, which uses a mix of electricity, membranes and resin in order to polish what comes out of the RO. This further reduces inorganics and some organics. The final barrier is the UF, which is where the Dalton membrane will be used in order to reduce biological contaminants.

After this step the system sends the water to a storage tank. 

Learn more about the cost differences between the four main system designs for Water for Injection here.

There are three types of sanitation methods for storage and distribution:

1. Thermal (most popular method)
2. Ozonation
3. Chemical (difficult to deal with, time consuming and hard to rinse out)

Risks of a Membrane-Based WFI System

Water for Injection (WFI) is one of the most critical pharmaceutical manufacturing ingredients and therefore extra precaution must be taken in identifying and preventing risks. Controlling risks involves:

• Identifying risks
• Considering their consequences
• Determining how often the risk could occur
• Setting up systems to detect risks
• Deciding how to take corrective action

Membranes can grow bacteria at any point in the system and the best way to deal with that is hot water sanitization. This is the most popular way to reduce risk of contamination of your membrane-based water purification system.

Since membrane systems operate at ambient temperatures, they require robust predictive maintenance, and their complexity can also influence reliability. In distillation water purification systems, you’re operating at self-sanitizing temperatures (65-80C). 

It’s important to have a preventative maintenance (PM) protocol set up for any membrane-based WFI system as well. 

Read more about WFI risk, reliability, and sustainability from our whitepaper here.

The MECO Membrane WFI System

The compact MASTERpak™ULTRA provides a complete solution for producing ambient WFI using membranes. The unit incorporates MECO’s pretreatment, RO, electrodeionization and ultrafiltration capabilities. Get in touch today to see how MECO can help with a membrane-based WFI system. 

Water our full webinar on Membrane WFI Systems below.

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