We often throw around the word “contamination” and how dangerous it can be in a cleanroom. And if you work in or around cleanrooms, you know how true this is. But to the everyday consumer, products being free from contamination is often taken for granted. We often don’t even think about contamination control! For many, we know that the water coming out of our tap is clean enough to drink and that’s the end of it.
But how does that water get clean? How do we get water clean enough to be feedwater for ultrapure water systems? What does that process look like?
While this process doesn’t take place in a cleanroom, per say, it does take place in a clean environment where the water is protected from additional contamination. And the water treatment process contains many similar elements that ultrapure water goes through. It might look a little different in every plant, but there are some basic essentials!
Ideally, water is collected near the treatment plant to keep transportation costs low. It is usually pulled from lakes, rivers, reservoirs, or any body of freshwater. Seawater is not used for water treatment because the process is too expensive.
Once the water has been collected, it needs to be screened to remove large debris. This can include debris like leaves, sticks, and other contaminants. Usually this screening is done at the intake point with two types of screens: coarse or bar screens and fine screens.
In coarse or bar screens, 25 mm bars are placed 75 to 100 mm apart. These are sturdy screens that traps large particles and debris.
Fine screens are further down the system and consist of a finer mesh material. In some cases, there is an automatic device on the screen that removes the trapped materials on its own. In this situation, it is referred to as an automatic strainer.
Sedimentation is the process where heavy particles sink to the bottom of the water and are removed. A sedimentation tank is specially designed to reduce the velocity of the water to allow for sedimentation. There are two types of sedimentation: plain and coagulation with chemicals, also called clarification.
Plain sedimentation is purely physical. Gravity does its job and pulls the sediment to the bottom of the tank, so the water can be carefully whisked away from it.
On the other hand, sedimentation with coagulation - or clarification - uses chemicals to speed the process along. Coagulates are added to the water which causes the sediment to stick together and create larger, heavier particles that sink more rapidly.
This is often the preferred method as plain sedimentation requires too much time and is, thus, too costly.
For clarification, you could use any number of chemicals, like alum, ferrous sulfate and lime, magnesium carbonate, polyelectrolytes, or sodium aluminate. Alum is the most commonly used chemical.
During clarification, many particles are formed that do not settle to the bottom. Thus, filtration is the most important step in the process to remove these particles. There are 3 primary types of filters used: slow sand filters, gravity type rapid sand filters, and pressure filters.
Slow sand filters have been in use since the early 1800s. This technology is the basis for other filters, but is so named because it is very slow. It takes much more time than the more modern, rapid options.
A slow sand filter is made up of an enclosure tank, filter media, base material, underdrainage system, and appurtenances. The water is run through the sloped enclosure tank and through the filter media and over the base material.
A gravity type rapid sand filter is made up of the same components but is smaller and it uses air compressors. The idea is the same: to filter the water through the components, but they become logged frequently. Thus, it requires frequent cleaning.
Lastly, a pressure filter is also built as a rapid sand filter; however, the container is closed and water is pressurized. This filter is either horizontal or vertical, depending on the flow direction.
Disinfection involves deactivating any pathogenic bacteria or microorganisms that present a danger to health, such as water-borne illnesses. This part of the process requires skilled operators to deploy a disinfectant that is effective, easily available, affordable, and safe.
This can be done through applying gamma radiation, metal ions, alkalis, or oxidants. In some cases, a physical treatment might be used in the form of ultrasonic waves or heat.
Most commonly, though, the water is chlorinated, which works as an effective disinfectant.
Can water be hard? Yes, it can! People who live on wells know the troubles that come with hard water, which means there are minerals present in the water. It can hurt appliances and is hard on human skin and hair over time.
Surface water is not typically very hard, but water retrieved from underground sources, surrounded by rocks and soil, is usually harder. Thus, a softening process is sometimes needed.
Depending on the minerals present, there are different processes. A common one is the addition of lime or boiling. The water might need an additional lime soda or zeolite process. It might require more deionization or demineralization.
If the water color or taste is off, the water might require additional treatment. This does not mean that the water is necessarily unsafe as it is, but just unpleasant to look at and taste.
There might be additives put into the water, or the water might be aerated.
How Can You Learn More?
Contamination control impacts all of us in everyday life - over and over again. From the water we drink to the phones we use, somewhere along the way, someone had to be concerned about contamination. We even practice contamination control in our everyday lives when we cough into our elbows, wash our hands before we eat, and wear a mask.
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