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 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...