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6. If residual turbidity is not decreasing as coagulant dose increases, the coagulant dose may be too low due to one of the following: 1) inaccurate running rate of coagulant pump; 2) the air inside the coagulant pump tube; 3) water trapped in the coagulant pump tubes; 4) malfunctioning of valves that connect with the coagulant pump; or 5) the loading duration is too short ( not taking into account the wrong set-up on Process Controller). If the pumps were recently calibrated, the first reason can be ruled out. If the residual turbidity does not significantly decrease after a residence time, the second cause can be eliminated. You can check for water trapped in the coagulant pump tubes by opening the tube connection between the coagulant pump and the rapid mix unit. If there is water present, it may be due to high pressure during backwash.
Problems with Process Controller
If you turn on all the switches, and none of the green indicator lights on Process Controller are on, that means you are not connecting with the right server or the server may have crashed. Check the main server to make sure it is functioning properly and check the data server on Process Controller (should be "aguadata.cee.Cornell.edu"). When you're operating from one state, sometimes nothing is shown on the "current state" and the "state list" is not shown at "rules and states" at the next state. When this happens you need to reload the method file and save it in your experiment folder.
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