Evaluation of Previous Experiments, Summer 2009

General Procedure

1. In Process Controller, configure the system so that the aerator air pressure is maintained at roughly 100 kPa.

2. Fill the sand column with 60 cm of Sand 40 and adjust the flow rate on the pump forcing water through the sand filter to establish a bed expansion of 50%. For the first experiment, manual measurements of flow rate were performed by unhooking the influent water tube into the sand filter and allowing the influent to fill a large graduated cylinder over the course of a minute. In order to minimize changes made to the system, flow rate measurements for the second experiment were taken at the system effluent tube. The flow rates were roughly 225 ml/min and 485 ml/min for Sand 40 and Sand 30, respectively.

3. Run the Process Controller method file, given here, on the "On" state.

Note: The "On" state regulates the air pressure in the aerator by releasing small amounts of air through a valve when the system exceeds the maximum aerator air pressure of 102 kPa. The water level in the aerator is controlled in a similar manner; however, the water wasting valve is also subject to a duty cycle in which the valve will open for a set period of time and close for a set period of time. If the "on" condition for the wasting valve is not met (that is, if the water level does not exceed the regulated height), the wasting valve will remain closed.

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