How the Biocoil Works



The Students: Kirsten Adams and Sarah Tucker

The Teacher: Clinton A. Kennedy




The Biocoil Operations Manual

(The Trip From the Algae's Point of View)


The Biocoil is a tertiary sewage treatment system which utilizes light and algae to remove phosphates and nitrates from secondary effluent. The Biocoil is a round unit eight feet tall and six of those feet are surrounded by 1600 feet of clear one inch inside diameter food grade tubing. This tubing is exposed to light 24 hours a day, either by natural sunlight or artificial light. The inside of the Biocoil is composed of three tanks, the contact, holding, and settling tank. The manifold which distributes water from the tanks to the tubes is also located inside the Biocoil.

The algae, Chlorella, is basically run through two cycles, the light and dark cycle. The light cycle is obviously the time the algae is spent in the tubing and the dark cycle is the time spent in the tanks. The operation of the Biocoil is fairly simple and starts when water is pumped from a submerged pump in the sewer pond into the mixing tank. The pump itself is held in a five gallon bucket with small holes in the sides, to keep out the large chunks that may clog the pump. The bucket is connected to a large Styrofoam block to keep the bucket from sinking. A tube is attached to the pump and it runs to the Biocoil to the mixing tank. This tube has been insulated to avoid freezing. When the water is pumped into the mixing tank, it is pumped for a variable amount of time which can be programed by a timer. If the timer malfunctions, we have float valves installed in the tanks, which is a safety measure we used to prevent overflowing. Located at the bottom of the mixing tank is a circulating pump which mixes the algae so it cannot settle and separate from the water.

When the Biocoil is fully functional and ready to run, all three tanks are full and have been in this state for either 24 or 48 hours. A pump, connected to and ran by a programmable timer, turns on automatically in the settling tank and the water which has been treated is pumped off the top of the settled algae. Next, a pump in the holding tank turns on and starts to fill the settling tank with algae water that has been running through the tubing and the holding tank for the last 24 or 48 hours. Then a pump in the mixing tank automatically starts and fills the holding tank with the same amount of water that was pumped out. Next, the submergible pump starts and pumps water from the sewage pond into the mixing tank until the tank is filled to its original level. The final step in the process is when the starved algae that was settled out in the settling tank is dosed back into the mixing tank so the algae can "gobble" up the nutrients in the sewage water. After this process is completed the water will sití for 24 or 48 hours and then the treatment starts all over again.

We are now about to embark on a journey that is usually reserved for algae, however, with to power of imagination, we can become one with the algae and travel through the mysterious Biocoil to discover for ourselves its hidden secrets. Close your eyes and take a deep breath and imagine you are small, very small, and green, very green.

We will begin our journey in the mixing tank, actually we have just been injected into the mixing tank from the settling tank. We had been in the settling tank for a while now, at least 24 hours, without any food or light. We are very hungry, and now in the mixing tank we are surrounded by delicious nitrates and phosphates from the water in the sewage pond. So like any normal life form we eat, and eat, and eat. We eat so much we have no room for anything else, kind of like the feeling one has after Thanksgiving dinner. We begin to realize now that we have to do something with all this food we have eaten. So before we know it we are violently pumped from this giant feast into yet another tank, the holding tank. However, this tank is different from any other we had been in before. After we sit in the tank for awhile, we are pumped into clear tubing and exposed to light, which is a pleasant surprise as we haven't seen light for a long time. So naturally we utilize this light source and start to photosynthesize. During photosynthesis we are able to use up all of that food so we can reproduce and grow into big, strong, sticky algae. Sticky? Yes sticky, this is very important for the next step of our journey. After being exposed to light for a while we are able to utilize all of our food from the mixing tank and are ready for the next leg of our trip, this time to a conical shaped tank named the settling tan or for animal feed. Aren't you glad you got to see the Biocoil from the algae's point of view?

The Biocoil is currently a research project, so the Advanced Biology class has been doing our share of research in order to improve the design of the Biocoil and in the long run making it much more efficient. One of the major changes we have made from the original design is to do away with the mixing tank. We have started pumping water from the sewage pond directly into the holding tank and are currently converting the mixing tank into a sand filter. The sand filter will hopefully remove all traces of algae from the treated water. We are also experimenting with the time it will take to treat the water. We are able to do this with our programmable timers; we can vary the time the water spends in the tanks. The two main things that influence how long it takes for the water to be treated is the rate at which the algae can use the nutrients in photosynthesis, and the rate at which the algae settles in the settling tank. We are hoping we can cut the time at which water is treated down to around six hours.


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