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| Credit: Silicon Valley Advanced Water Purification Center |
When : All year (preference is given to Santa Clara and San Jose groups, plan ahead)
Who : 4th grade and up
Cost : Free
Notes: Wear closed-toe shoes. Photos are allowed but not videos
It's hard to miss the Silicon Valley Advanced Water Purification Center. As you exit the freeway, the huge water tank (2.25 million gallons!) looms in the horizon. The signage to the visitor center is clear, and there is a small parking lot (additional spots are available in a different area).
When we arrived, we first watched a presentation to understand the reason for investing in water purification - of the water on earth, only 3% is drinkable and some is locked up in forms we cannot access, e.g. glaciers, or inconvenient to access. Santa Clara county gets over half of its water from reservoirs that are far away, which makes for a vulnerable water supply. Water reuse (currently 5% of water use) can reduce that vulnerability.
To see water reuse in action, students can start looking for purple pipes when they are outside. In Santa Clara county, these carry recycled water - wastewater that has been treated so it is safe for irrigation and industrial use. Recycled water is non-potable, i.e. it is not suitable for drinking.
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| Purple pipe = recycled water Credit: Silicon Valley Advanced Water Purification Center |
Purified water is wastewater that has additionally treated and disinfected, towards a goal of being potable. Students were tickled to hear that purified water is being used in other parts of California including Anaheim (Q: Does Disneyland make its own water? A: Purified water is not made at Disneyland but when you run a drinking fountain there, you may be drinking some). This purification was the subject of our tour, and we were eager to begin.
We first walked past some pumps where water was brought up to 40 psi and run through a filter which would remove items larger than 40 microns (human hair being 60 microns). Students had fun peering through the mesh and seeing if anything could go through.
Having removed large impurities, the first step of advanced treatment began - microfiltration. In this step, water is pumped through pipes containing strands of fibers. These fiber strands have small pores of 0.1 microns so that as water runs through, anything larger than 0.1 microns will be caught in them (Q: What would get caught at 0.1 microns? A: Solids, protozoa, bacteria and even some viruses!).
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| Cross-section of microfiltration pipe |
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| Arrays of microfiltration pipes |
The next step of advanced purification is reverse osmosis. In this step, the water is pumped to extremely high pressure to force it across a reverse osmosis membrane. The membrane has pores that are so small that only molecules the size of water can go through - salts, pesticides and even viruses are left behind.
With this treatment, the water is almost as pure as distilled water - this also means it doesn't contain the minerals found in freshwater so treated water is usually mixed with ground water for a drinking supply.
The final step in advanced water treatment is UV disinfection. Sunlight contains UV rays which can kill bacteria and viruses (specifically, UV-C rays can break down their DNA). Running the water under UV lights replicates this process and kills any living organism still in the water.
The water is safe to drink after this treatment though to bring it up to state standards, advanced oxidation will be required. Since the Silicon Valley plant does not currently supply the drinking water system, it does not do this step at scale though there was a machine labeled. The reason for this step is to add another safeguard against chemicals that might still be present.
Finally, the guide showed us flasks with the water from various stages of treatment - we could see the color shift from slight yellow to colorless, and water become clear/transparent by the end stage. As a challenge, we were asked if there were any volunteers to try the treated water. All the students jumped to their feet to volunteer!
We would like to thank the Center for offering free tours to the community. As specified on the tour reservation page, students need to be 4th grade (preferably 5th grade and up) so parents with younger siblings should plan on alternate activities while their older students go along with the tour; happily, there are fun activities nearby such as Legoland Discovery Center in Milpitas's Great Mall.
The tour is also suitable for high school students who can find out about careers in the water industry, e.g. while we could expect civil or environmental engineering, we were surprised to hear about job openings for biologists. The facility is sophisticated - one aspect of the facility which amazed us was its quiet since everything has been automated including checking of various components for failure. High school students in Santa Clara county can also apply to be part of Valley Water's Youth Commission.
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