UltraFiltration

18^th January, 2024.

In this post, we will see the concept of ultra filter (UF) membranes.

Filtration techniques are evolving in water treatment day by day. It is a must follow and without it, the basic process of water treatment will not work. There a wide range of technologies used for filtration of water. Out of them, one of the most used ones is ultra filtration. It is the one which removes very fine to fine bacteria and other impurities. Thus, it is a very effective way of treating water with greater accuracies. In this way, we will see the concept of ultrafiltration.

Ultrafiltration Meaning:

Refer the below image. You can see that it is a membrane first of all. Practically, there is not one membrane but multiple membranes housed in a single unit, depending on the flow of water at the inlet. Also, depending on the water flow, multiple such units are used in a row for filtering water. In this technique, water is passed through these membranes which are semi permeable. It is a filter which removes particles that are 5000 times smaller than a human hair. Surprised by this removal? Yes, because UF is specifically designed for ultra small particles which a normal filter cannot remove. This means that even the smallest of pathogens and viruses will not be able to pass through it. After ultrafiltration, the next stage which comes in water treatment is nano filtration and reverse osmosis (RO). For your information, RO is the last stage of water treatment and its outlet is always pure drinkable water. But many applications even do with UF, because it too provides a pure usable water. It all depends on the requirements of the user.

A single UF unit consists of multiple membranes, which can block small sizes of impurities. This is due to the pore size of the membrane, which is very thin. It requires water to be passed in such a pressure that all the suspended solids, bacteria, viruses and other pathogens are retained at the outside boundary of membrane; allowing only lower weight molecules like water components (hydrogen and oxygen) to pass through it. Practically, particles greater than 0.05 microns are blocked in this technique which provides a stringent quality of water.

Ultrafiltration Technology:

Let us now come to the main topic of its working. Refer to the below image. One membrane is very thin as discussed earlier. When water is passed around the membrane, only lower weight and molecules like water will pass through it. The other bigger size particles and molecules stick around the outer boundary of the membrane or just float nearby. But they cannot go inside the membrane. Due to this, only ultra-high pure water is present inside the membrane, which is then passed to the outlet. After some period of time, maybe one hour, this unit will be required to be cleaned to remove the floating or stuck particles around it. This is done through backwash process, which takes the outlet of UF and passes it in a reverse direction to the inlet of UF. This backward pressure immediately removes the particles and are flushed into the drain. Then again, service of the UF starts for filtering water.

There are many steps when working with a UF filter. Let us see each of them one by one.

1. Forward flush:

This is the first step in a UF process. Initially, the water from UF inlet is taken inside and flushed into the drain. This is done because when the plant is in stop mode, the stagnancy in water creates more pathogens. So, this step removes it initially to some basic level due to the turbulence created when water starts flowing. After this step, the water can then be passed to the outlet stage. It is to be noted that there are two valves at the outlet - flushing and service. For this stage, flushing valve will be open and service valve will be closed.

2. Service:

This is the second step. Here, the water at UF inlet is taken and passed through the membranes. The impurities are blocked around the membranes and the outlet passes pure water for use. Remember that here, the service valve will be open and the flushing valve will be closed.

3. Backwash:

After a certain amount of service time, backwash cycle will start where the water from the UF outlet will be passed through the inlet of UF in a reverse direction. This back force will remove the impurities around the membrane. For this step, both the flushing and service valves will be closed and there is a backwash valve in the inlet side which will be open for flushing the water. After backwash, service will start again and the cycle repeats. Forward flush runs only when the plant is started.

4. Chemical backwash:

Now this is an important stage. UF membranes are very sensitive and due to the task, it does for removing impurities, there will be a time when after some prolonged use, even normal backwash will not remove all impurities. It will also cause scaling, fouling or growth of microbiological agents like algae. So, to remove it, chemical backwash is done. This is performed after a certain cycle set of service and backwash have been performed. This is usually done after 2-3 days of usage. The chemicals are passed through the membranes or backwashed instead of normal water and this completely removes the impurities stuck inside. The chemical solutions used are acid, caustic and chlorine. They are passed sequentially after hours of usage. Means, first a set of service and backwash cycles will happen. Then, first chemical will be passed. Then again, the service and backwash cycles work. Then, second chemical will be passed. The same works for third chemical.

Benefits Of UF:

1. It efficiently removes bacteria, viruses, silt and other small pathogens. You can use it even without final RO process. Also, RO sometimes can remove the necessary minerals present in water, but UF retains it for use.

2. UF drains very less water. If you compare it with other filtration methods, then the rate of flush water outlet is very low. This makes the system more productive to use.

3. UF system can operate at low pressure of water. So, it is not always necessary to increase the speed of water flow for filtration.

4. UF system consumes very less space as compared to other filtration systems.

I have covered some general principles related to ultra filtration technology. I have also not attempted to cover all the methods, as it can vary from case to case and there is no end to it. Once you are familiar with this filter technique, you can easily tackle all types of problems in it.

Thank you for reading the post. I hope you liked it and will find a new way in this type of technology.