Well, today I finished my final course requirement for my graduate work. Yep, one crappy presentation half-assed a couple hours before it was due, and I'm that much closer to having a Master's degree! They'll give those things to anyone these days, I hear.
What is my research on, you ask? Well, here's the short version. I'm looking at the role of dissolved oxygen and microorganisms in the removal of MtBE from drinking water by granular activated carbon (GAC). Huh? Here's the slightly expanded version: MtBE is part of gasoline in urban areas here in the US. It's used as an oxygenate to help gas burn cleaner, therefore reducing air pollution. That's great - if there's never a leak or spill of gas. MtBE is very soluble in water (unlike most of the rest of the components of gasoline) so once it gets into the groundwater it travels quite far. It also isn't easily degraded, so it sticks around for quite a while. Top it all off with MtBE's status as a potential carcinogen and Houston, we have a problem.
I looked specifically at small treatment units in people's basements here in NH. The treatment units use activated carbon - essentially the leftover 'popcorn-like' residual from extreme heating of things like coal and coconut shells. It's the same stuff that you find inside your Brita filter. Basically what it does is absorb things out of the water - when contaminants float by in the water, they stick to the surface of the carbon and are 'removed' from the water. So this carbon has a certain amount of surface area - like a velcro tennis ball. You can only stick so much stuff to it before you run out of room to stick any more. Same idea with the carbon - it has only so much surface (capacity) to absorb MtBE from the water. Thing is, other stuff sticks to carbon, too. It would be great if it would only absorb the bad stuff, but it's such sticky stuff that almost everything sticks to it including any oxygen dissolved in the water and some of the microorganisms that naturally occur in groundwater. (If you're a sterilization freak I hate to break this to you, but there are about 1,000,000,000,000+ microorganisms in every ounce of water that comes out of your tap)
So what I was looking at is this: What happens when you have oxygen, MtBE, and microorganisms in the water? There are a couple possibilities.
- The oxygen and/or microbes stick to the carbon, meaning that there's not as much capacity for MtBE.
- The oxygen and/or microbes don't make a difference, and MtBE gets removed the same no matter what's in the water.
- The microbes eat the MtBE, and more MtBE gets removed than the carbon could otherwise hold.
Bored yet? Hope not, cause there's more...
So we grabbed some carbon from someone's existing treatment system to test in the lab. It was assumed that this carbon had existing microbes stuck to it, since it had been in operation for about a year. It was also thought that these microbes might be adapted to MtBE (and thus able to eat it) since they were in a system treating MtBE contamination in the source groundwater. We also got some fresh (no microbes on it) carbon from the manufacturer to compare to the above mentioned 'fouled' carbon. We then split the virgin and fouled carbons up into 4 columns - 2 of each - and supplied two with oxygenated water, and two with anoxic (without oxygen) water. We ended up with one column containing fouled carbon and oxic water, one containing fouled carbon and anoxic water, one containing virgin carbon and oxic water, and one containing virgin carbon and anoxic water. We then pumped water with MtBE through each for a couple months.
What did we find? Well, a couple of things. First, if your microbes are lazy and don't degrade MtBE, then you're better off having no oxygen in your water. Otherwise, the oxygen competes with the MtBE for carbon space, meaning there's less room to adsorb the MtBE. However, if your microbes are hungry (or able to use MtBE for food), then it's better to have oxygen in your water. Why is that? When you eat, you need to breathe. Same deal with the microbes. If oxygen is there, they can then eat the MtBE fast enough to make a difference. If the oxygen isn't there, they breathe other stuff (like sulfate, iron, or nitrate) that still works, but much slower. They may still be eating MtBE, but not nearly fast enough to make a difference.
So what's the best solution to our problem? Stop driving your damn car so much! There's nothing in gasoline that's particularly healthy whether you burn it, breath it, or drink it. Make a statement that you care about your health by supporting alternative fuels and alternative transportation methods. Purchase fuel efficient vehicles - vote with your wallet and let them know you care about our health! There will be no change in the market until consumers demand it, and that starts right here with you and me.
May compassion be always in your heart, and peace be always on your tongue.
- J
