One of the most exciting tools the DOM team has at the Crary Lab is designed and built by one of our very own team members, Chip Kilduff. Chip built a reverse osmosis (RO) instrument that separates out all the dissolved material in our water samples that is smaller than 0.45 micrometers (µm), or 0.00000045 meters (m). The goal of our RO is to remove the excess water down to a point where the dissolved organic matter that is smaller than 0.45µm is concentrated enough to measure. Filtering out everything larger than 0.45µm removes all the "big" stuff like bacteria from the water samples, leaving only the truly dissolved material like dissolved organic matter. This DOM concentrated water is run through a variety of tests to help the DOM team determine the chemical composition of the DOM. I took a field trip today to see another RO system at work- the one that provides freshwater to the great people who live McMurdo Station. Paul Jones, one of the people who keeps McMurdo supplied with freshwater is a former high school teacher and participated in the TEA program, a precursor program to PolarTREC. The scale of the McMurdo Station RO system is much grander than ours. In addition, the purpose of their RO is slightly different. The purpose of the McMurdo RO unit is to turn saltwater into freshwater for drinking, cooking, cleaning, and every other fresh water need of my Antarctic town. Click here for a video from the How Stuff Works website describing a RO system on Catalina Island, California that converts seawater from the Pacific Ocean to freshwater for the Island's inhabitants and is very similar to the one used at McMurdo.
Showing some of the filters of the McMurdo RO unit.
Take a look at this chart comparing the RO units of McMurdo Station and that of the DOM team. What really stands out for you at first? For me it is the large difference in numbers. The McMurdo RO has 74 gallons pumped into the system from McMurdo Sound every minute, whereas the DOM team pumps 4 gallons into our system- almost the same amount of time. Notice how much of that water actually gets through the RO systems every minute- for the DOM team we have as much flow through the system as we pump in, but the McMurdo RO only gets 28 gallons filtered out for every 74 pumped in over a minute, while we get most of it back. The reason for this variability has to do with the source of the water. The DOM water is freshwater collected from glacial streams, while the McMurdo RO is pulling seawater that comes laden with bits of marine life, lots of dissolved salts, and other impurities. It takes a lot longer and a lot more pressure to push the water through the McMurdo RO system.
The McMurdo water treatment facility has the capacity to hold 200,000 gallons of freshwater, enough to provide plenty of water to a town of 1000 people! Granted, we are encouraged to remain conscious of our water use- by taking showers only every other day, washing clothes just once a week and turning off the faucet when not needed. Pretty common sense steps to keep the water system working. The amount of water the DOM team keeps after completing the RO process is the opposite of what the McMurdo facility keeps- we actually do not keep the now ultra-pure water, but the "dirty" water chock-a-block full of dissolved organic matter, distilled down to a measurable concentration.
The large white pipe in the background carries the saltwater to the holding tank.
Compare the RO systems of the McMurdo unit to the DOM unit in these following photos. I find it so incredibly amazing that this type of system even exists and am even more amazed at the capabilities of reverse osmosis.
Just a bit of the equipment that provides McMurdo with freshwater.
Chip built this system primarily out of materials purchased at the hardware store!
Holds 30,000 gallons of McMurdo Sound saltwater.
Holds 52 gallons of water from Antarctic glacial streams.
There are a number of filters the water is pushed through to remove minerals.
Our filters remove all matter larger than 0.45um.
Controls one of the two RO units available to the Town.
A flip of the switch is all we need to control our remarkable RO unit.
50,000 gallons of freshly filtered water!
Compact, efficient and amazing- thanks Chip!