PDS AP Environmental Science 8th Period 2010-11

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 Mallard 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. This system is comprised of bar screens, which 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 clarifier, the wastewater’s velocity is slowed and the solid components of the water, the “sludge,” settle to the bottom. After the clarifier allows the solids to settle to the bottom and the oils settle on top, giant rotating weirs move circularly around each clarifier, scraping the bottom where the solids have accumulated and the surface of the water, and the resulting somewhat cleaned water moves on to the next step. The removed sludge is transported to an anaerobic digester which heats and spins the wet mixture and is then dried for fertilizer for crop land or a landfill.

The heart of the facility is found in the aeration tank. 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 aerobic 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.) The aeration tank can be thought of as a “zoo of microorganisms,” and the water is oxygenated so that the aerobic microorganisms can effectively break down the bacteria and solids in the water. From the aeration tank, the water is moved on to more 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 dividers with anthracite coal 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 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 is what our indoor lab consisted of... as we worked with the Dichotomous Key, we identified bug larvae and then looked at their adult form...

Images source: Derrick Willard

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 Miriam’s post that details our day.

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

On October 1st, our APES Class took a field trip to Davidson College to participate in an experimental design lab in the field. The day went as follows: we arrived at Davidson College, and attended a lecture by Dr. Mike Dorcas, a leading herpetologist. The lecture was interesting, and frightening, because it was about….giant Burmese pythons! Dr. Dorcas showed us a powerpoint concerning the history of how Burmese pythons were introduced to the Florida Everglades, how the python populations have grown, and what is being done to try and curtail the rapid growth of the python populations. For those of us in AP Stat, many of the statistical tools we learn in class were presented in Dr. Dorcas’ data, and the overall presentation was an excellent example of how precise field work can really make a difference. We also heard a presentation about Barn Swallow nesting habits, another example of a lab designed for the field.

Here is a link to a website talking all about Burmese pythons, and a video in which Dr. Dorcas is interviewed. (it’s the first one) http://www.nps.gov/ever/photosmultimedia/invasives.htm

Second, we actually went out into the ecological preserve. We split into groups, and walked around the forest area, looking for organisms (mainly frogs, snakes, and the occasional spider) in the drift fences on the ground. Drift fences are small tarps that are put up and 5 gallon buckets line the edge of the fence. The aim is to get organisms who walk towards the fence, and can’t get passed it, to walk along the edge of the tarp until they fall into a bucket and can be examined. We found small bullfrogs, spiders, and a dead mouse, but our group found no snakes. Along the drift fence were several traps for larger animals, such as larger snakes, that were lined with bait. Next, we went to a more clear area, and checked under coverboards (large boards made of wood or tin that can serve as resting places for ectothermic animals who need external temperature to regulate their own temperature). Snakes and small critters such as insects use these coverboards, and can be a useful place to look for organisms.

Checking Coverboards

We then went back to the buildings themselves to eat lunch and attend student presentations. (and hold a black snake!) The presentations were helpful in learning how to set up an experimental design. Some things we learned: 1) funding and man power can make a lab tricky. The result is to adapt to get the results you need. One of the students designed a lab to count types of frogs, yet didn’t have the funding to go out and search for hours for frogs. Instead, she listened to frog calls at dusk with other students (cost-friendly) and gathered her research that way. 2) labs that are done outside can take a lot longer than those done inside. We are accustomed to labs that can occur in one class period, or at most over the weekend, whereas some experimental design labs outdoors can last years. One of the student presentations was of a lab that lasted all summer, and will continue next summer. 3) It is important to get good and accurate data for many reasons; to prove your model (or disprove your model), make yourself understood, get published, and get more funding for research.

Finally, we headed back out to the field to start our detritivore lab. We split into boys and girls, and the boys went to the oak dominated forest, girls to the pine dominated forest. We learned how to use transects (measuring tape that is extended a certain number of feet, depending on the size of the area under study), a random number generator (numbers that are chosen off of a piece of paper to decided how far (in ft.) to travel to the left or the right of the transect) and a quadrat (a piece of tubing, square shaped, that can be any size. A quadrat is used to keep a constant amount of ground under research. We used our quadrat to collect the same amount of leaf litter from each area). Transects and quadrats are ways to take control of a situation when doing experiments outdoors: the transect and random number generator ensure that you take samples from all different areas of the space you are examining, and the quadrat helps to ensure you take the same amount of samples from the different areas.

After collecting our samples, and bagging and labeling them, we went to an open field with what looked like corn plants. (I have no idea if that is actually true, probably not.). The purpose of this exercise was to use a transect-like set up, where we used two measuring tapes stretched up and down and side to side. We then used larger quadrats, 1m by 1m I believe, and counted the number of stalks to each side of the transect like device. Our group leader, a spider lover and expert, then used sweep nets (they look like big butterfly nets made of canvas) to swish over the plants 20 times (10 to each side) and collected insects from off of the plants. We put the insects he caught in pharmacy bottles and examined them, looking at the biodiversity in the area of insects (note* they were not all insects, there were some spiders in there as well)

From our Davidson field trip, we learned some techniques of how to take samples in the field for experimental design labs. It was very helpful, and Mr. Willard recommends we discuss actual METHODS of how to collect data in our AP essays, as that is a more clear idea of what you are trying to convey.