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The VCU Environmental Science Department had in its possession 24 500 gal tanks they had implemented to study the plankton and bacteria activity of the James River. Water was pumped up from the James River a quarter mile to the tanks and studied over week long periods to analyze the growth and survival of plankton and bacteria as it exists in the river. Over time it was found that the bacteria in the mesocosms would growth at an increased rate as sediments and inorganic matter fell out of suspensions. For this reason, it was necessary to develop an agitator that could allow the tank to imitate the turbidity of the river. Said agitator would have to be non-invasive as it couldn’t affect the pumping system beneath the tanks. There could also be no addition to the wall of the tanks or exposed metal inside the tank at all, as it would negatively affect the water conditions. The final design of the agitator was a pitch blade impellor suspended into the tank from above and powered by a 1hp electric motor. The impellor was fixed to a steel frame extending over the tank and fixed to a wooden post next to the tank. Initial testing of the impellor showed an increased turbidity at the onset, but, overtime, inorganic matter fell out of suspension to the same degree as a non-agitated tank. This was found to be due to a lack of torque from the impellor, and a gear reducer has since been added to remedy this. Currently, continued testing has shown a consistent maintaining of sediments in suspension in the stirred tank.
Dr. Stephen Fong
VCU Capstone Design Expo Posters
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