PDS AP Environmental Science 5th Period 2010-11

Note: A guest post by CarolineJ in the other class-good recap of lessons learned:

On any given day, each one of goes to the bathroom at least a few times, and most likely without any thoughts of where our waste is going or what it will become. After venturing to the Mallard Creek Wastewater Treatment Facility; however, what happens when we flush, at least for me, is a much more prevalent thought. When we got to the treatment facility and stepped off of the bus, I think almost every single one of us had something to say about the smell, but little did we know that the worst was still to come. My group began our tour in the office building looking at an aerial view of the entire facility.

aerial view of Sugar Creek Wastewater Treatment Facility

As you can see, it’s pretty big and pretty spread out. It is designed this way so that each process is separate. One important feature to note that may not be apparent from the above image is that the facility is located on a long, gradual hill. Rather than pumping the water between processes, the water is pumped only one time from its initial incoming from the sewage to the top of the hill. For the remaining processes, the water flows down hill so that less energy is used and the process is more efficient in general.

The treatment process begins when we flush the toilet, and our sewage waste travels through a series of piping systems to one of Charlotte’s multiple wastewater treatment plants. As the wastewater reaches the end of the piping system, it flows into somewhat of a temporary holding tank with screen systems attached. These bar screens reach into the water and anything solid such as toilet paper, condoms, tampons, dead goldfish, etc. get trapped on the screens, which pull these objects out of the water and dispose of them in a dumpster along with any “grit” like undigested corn, gum, etc.–all of which most likely ends up in a landfill. Next, a cyclone type machine spins the still heavy water down a tube and it is moved into a system of clarifiers.

heaps of gross gunk from our sewage...toilet paper, condoms, tampons...and it smelled HORRIBLE

this machine sorted through the "grit" which consists of corn, sand, gum, etc

In each cone-shaped primary clarifier, the wastewater’s velocity is slowed and the solid components of the water settle to the bottom. Giant rotating weirs move circularly around each clarifier, scraping the bottom where the solids have accumulated and draining them out. The surface of the water is also scraped of remaining fats, oil, greases, and the resulting somewhat cleaned water moves on to the next step.  At least 60% of suspended solids are removed at this point in the process.

The heart of the facility is found in the aeration tank (also called activated sludge). The aeration process is a biological process that takes 6-8 hours as organisms are used to break down the excessive ammonia and nitrite found in the water. As a product of these anaerobic organisms at work, the water in the tank is coated with a thick layer of light, brown bubbling foam. (We were all surprised to learn that this foam was not floating poop.) From the aeration tank, the water is moved on to secondary clarifiers and as the solid, heavy water once again settles to the bottom, it is scraped and drained out and back into the aeration tank to feed microorganisms. At this point, the water is (believe it or not) 99.9% cleaned.

This is a photo of the products of the aeration process. Note the brown foam on top.

(Fun fact: As Emily and I reflected upon the horrible idea of jumping into this foamy tank, our tour guide noted that legend has it that because of the way the tank works with suction and because SO much oxygen is produced, there is no surface tension to this water and so if you jumped it, you would immediately sink 20 feet to the bottom and basically drown in poop. We decided this would be the worst possible way to die.)

After the water moves from clarifier > aeration tank > more clarifiers, the water must be filtered one more time before it can be disinfected and released back into the environment. The water is moved from the last clarifiers to another large tank where mixers churn the water so that it does not become septic. In these tanks, traveling bridge filters use charcoal and dividers with anthracites and sand to filter the water. The traveling bridge works by forcing the water through the sand so that the particles collect in the sand and charcoal leaving the water cleaner and without solids.

Next, the water is moved from the filtering system to the disinfection stage. Originally, chlorine was used to disinfect the water; however, the problem with the chlorine treatment was that even though it killed every single microorganism in the water, as the water was then released into the environment, the chlorine continued to kill everything in its path which proved destructive to the stream or creeks the water was released into. Recently, more and more wastewater facilities have begun to use UV rays to disinfect the water. This process works by using the damaging properties of UV rays to basically microwave the microorganisms in the water, scrambling their DNA so that they can’t reproduce. This means that when these organisms reach the environment once again they will decrease and die out in population.

The result of this entire process is a relatively clean water that is suitable and safe for the environment, but not for direct contact with people. After all steps have been completed, sewage > clarifier > aeration > more clarifiers > filters > disinfection, the water is either released into a nearby water source, in this case Mallard Creek, or it is put in some sort of a holding tank. At the facility we visited, some of the water was mixed with hyperchloride which is not safe water for humans but can be used to water golf courses, for example, for free. The remaining solid waste from this entire process is heated for about 45 days, the resulting products being a small amount of water, gases, etc. which are spun into a black material which is used for fertilizers which can’t be used to grow crops but instead are used for growing grass which farmers can turn over to increase an areas fertility, etc. We all wondered what happened when there was a big rain and all of the rainwater filled up the open clarifiers, aeration tank, etc. The facility is built to contain about 20 million gallons of water, so rain is not a problem. There is also a rain retention basin in the middle of the facility as well which can hold up to 50 million gallons of water and stores rain water and other excess raw sewage.

The last part of our day consisted of testing the water in Dragonfly pond at Reedy Creek Nature Preserve for turbidity, pH, temperature, phosphate, nitrate, and dissolved oxygen/%DO saturation. (We assumed coliform bacteria to be present)

this is my group conducting our lab tests next to Dragonfly Pond.

1 of 7 tests we conducted, turbidity is measured in jackson turbidity units by chart to the right of water container.

After conducting these physical/chemical tests, we moved to the lab where we focused on bioindex which is basically how clean a body of water, such as a stream, is based on what organisms it can support. All organisms have a different toleration for pollution, an example of an animal that can live in very clean water being a mayfly or a stonefly, while the dirtiest waters are home to organisms like leeches. We used a Dichotomus Key to look at and identify several insects, the process necessary for determining the bioindex of any body of water.

This 18-minute video was made by me a few years ago. While it is a bit grainy, it covers the major field research techniques I try to show students at Davidson each year. It’s mandatory viewing if you did not go, and a good review if you did:

You can also check out Jason’s post that reviews our day.

*Note: The Internet filter at school will not let you view YouTube videos, so you have to watch it at home.

On Friday October 1st, the Environmental Science classes took the day off from school and traveled down to Davidson College for a hands on experience in creating controlled experiments and data gathering in the field. We started off with a presentation on Bernese pythons and how they are ravaging the southern parts of Florida. Although we do not know the source of the problem, we do know that these foreign species of giant snakes (adults can get more than 9 feet long) are procreating very readily and consuming native wildlife with seemingly no natural predators in the area, possibly toppling over an otherwise delicately balanced ecosystem. Although the topic of the presentation was interesting, the main points that we left with (or should have left with) were, field research makes a huge difference in understanding the ecological systems around us, and designing controlled experiments, regardless of the seemingly uncontrollable nature of nature, is completely possible.

From there, we went into the ecological preserve to look into methods for sampling nature. The first that we looked at was a technique called drift fencing. This approach primarily targets small creatures, but has been adapted for slightly larger animals with varying degrees of success. The underlying idea behind this approach is as follows: An animal encounters a large fence, large enough such that it cannot burrow under nor fly over it. In order to get past the obstacle, it must traverse the perimeter of the fence, which while doing so, may fall into a 5 gallon bucket ‘trap’ or larger animals might get stuck in boxes with one way doors. Using this method, we can get an idea of what creatures inhabit the immediate surroundings.

Another method was much simpler: Coverboards were placed in open areas, providing shade to cold blooded animals to help regulate their metabolism. By lifting these coverboards during sunny times, we might be able to observe and document critters who might be taking refuge underneath and, again, get an idea of what animals are around us.

Finally, we tried our hands at acquiring a representative sample of an ecosystem for controlled experiments. Our lab required samples from both pine and oak forests, but acquiring these samples raises two questions: where do we get our samples from, and how much do we get? The inherent laziness of people might cause us to only sample the outer edge of the forest; what lives there might not be the same as what lives slightly deeper. also, we had no method of regulating the sizes of each sample collected. To solve this, we have a device called a quadrat, and transect. A quadrat is merely a rigid square that is placed on the floor of the area in study such that we can analyze what is inside it. It sets boundaries and keeps our sample size constant. A transect is a method to randomly sample parts of the area in question such that we get a representative sample. there are two measuring tapes; one going down the middle of the area, and another placed perpendicular to the first, essentially creating a coordinate-grid system. using a random two digit number generator, or a phone book, we can randomly pick ‘coordinates’ and sample them. the first digit tells us how far down the first tape measure to go, and the second digit indicates how far left or right we move from the first tape measure. We alternate sides (left/right) each sample. For example, if the number was 45, we would travel out 4 meteres and then to the right 5 meteres, place our quadrat at that location and sample whatever was contained within.

The small white frame is a quadrat. We sample only what is contained within its boundaries and take it back to the lab

Drift Fencing is merely a fence that critters must travel around the perimeter to get across, hopefully falling in a trap such that we can count them

Finally, we also looked into how to sample rapidly moving insects that might be on long stemmed plants. Using a large net called a sweep net, we can ‘sweep’ the tops of the stems and catch whatever might be living on them at the moment. By controlling the number of ‘sweeps’ done by the net and sweep area, we can keep the sample size constant and acquire a representative sample size.