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The experimental setup, including equipment, chemicals, and computer software, remained nearly identical to what has been used in past semesters (Figure 1). The main features of the flocculator setup include one 11 gallon bucket containing an alum concentration of 1.5 g/L (originally at 3g/L, but was diluted because flow rates were too low) and another 11 gallon bucket containing a kaolin clay-water mixture of 750 NTU (according to our clay- NTU study found in the first team report of fall 2007), or roughly 2.02 g/L of clay per liter of water. The alum stock bucket was connected to a Masterflex L/S peristaltic pump manufactured by Cole-Parmer Instrument Company by a size 13 flexible rubber tube, whereas the clay stock bucket was connected to a peristaltic pump by a size 14 flexible rubber tube. Raw water from a temperature controlled constant head tank connects to a peristaltic pump with two pump heads by two size 17 flexible rubber tubes. All three pump rates are controlled independently based on the experiment and controlled by the computer program Process Controller. The clay solution and raw water streams are joined and the two mix before entering the influent turbidimeter. One MicroTol 2 Turbidimeter manufactured by HF Scientific, Inc. is connected to the tube leading into and one out of the tube flocculator. The alum solution connects with the rest of the influent solution after the influent turbidimeter, as alum should not be figured into the influent turbidimeter reading, as it is added for the purpose of cleaning the water. A short length of tubing coiled with a 3 inch diameter and a tubing size of a ¼ inch inner diameter - smaller than the flocculator tubing - is placed in between the influent turbidimeter and the start of the tube flocculator, acting as a rapid mix unit. After rapid mix, the solution flows through a clear plastic tube of 6mm inner diameter of varying length (depending on the specifications of a particular experimental run) wrapped around a large, hollow plastic cylinder. This part is the tube flocculator, where particles will have a chance to react with the alum to form flocs. After flocculation, the flocs will flow through the effluent turbidimeter, which consists of a long, clear plastic tube placed through the center of the turbidimeter sensor in order to allow better flow of flocculated material through the sensor and to facilitate clarification once the flow is stopped. The effluent turbidimeter also provides visual confirmation that flocs have formed and settle out at differing rates depending on the size of the floc.
Over the Fall 2007 semester, we have found better ways to manage our experimental setup. Changes have been made only as regular maintenance or if the change increased flexibility in the experiment. We regularly replaced older pumping tubes with new tubes to prevent leaks due to wearing from the constant pump moving over the tube. The lab setup now includes flocculator tubing lengths of 10 feet, 25 feet, and 50 feet. These lengths are used individually during an experiment and can simply be connected by the user. The different lengths of the flocculator tube dictate various flocculator volumes, which ultimately changes the residence time of the flocculator when coupled with certain flow rates. Floc formation and density partly depend on the flocculator residence time. With more time spent in the flocculator, the flocs have more interactions with other flocs and the floc size increases. At shorter flocculator tube lengths, particles have less time to interact, therefore, flocs are smaller.
In the third set of experimentsAdditionally, the team replaced the old flocculator tubes with a set of clear plastic tubes that are more flexible and transparent than the former. Since the new tubes would be crushed under pressure because of the flexibility of the material, it required the flocculator to be balanced on a PVC pipe platform. This platform helps prevent the soft flocculator tubing located on the bottom of the flocculator cylinder to lose shape under the weight of the cylinder.
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A LABVIEW based program called Process Controller (Figure 2), a computer program which controls the experimental setup by managing alum, clay, and raw water flows, also dictates the different cycles of the experiment. Different Process Controller programs can be created to run different experiments, changing parameters such as flow rate, flocculator volume, or the clay stock concentration. The clay stock concentration, the desired alum, and the clay dose, which is equivalent to the desired influent turbidity, are user defined inputs in the Process Controller program. Both the alum and clay flow rates are functions of the flocculator flow rate, the user defined stock concentration and the desired dose. A pump control function then translates the calculated flow rate into a scaled value recognizable by the pump. One of the major challenges of working on this research project is learning about how to control Process Controller to have it compute and run a specific experiment. During this semester, we developed several programs for various experiments, including an increment function to vary the turbidity of the influent water, and a second increment function to vary the G, or flow rate of the flocculator.
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