Paddle-wheel Type Research Articles

Denitrifying bioreactors are systems that need close monitoring and control. Data concerning several system parameters is updated secondly on a computer, using LabView software and a Lab-PC+ I/O card from National Instruments. The flow rate through a denitrifying bioreactor is possibly the most important variable to monitor and control. The flow sensor used is a low inertia paddle wheel type that generates a digital pulse output whose frequency is proportional to the flow rate. This digital pulse wave is read by the computer, which converts the frequency directly to the flow rate. The computer is capable of operating in either open loop or closed loop settings. The second most important variable in a denitrifying bioreactor is the concentration of dissolved oxygen in the influent water stream. Using standard on/off controls, nitrogen gas, and a turbulator, the oxygen concentration can be maintained at levels below 1.8 mg O2/liter. The dissolved oxygen concentration is monitored with a probe that generates a millivolt signal proportional to the amount of oxygen present in the water. The millivolt signal is read by the computer 1000 times per second, generating a graph of the dissolved oxygen over time. Another signal the computer could use to decide the flow rate is the influent nitrate concentration. The lower concentrations do not require as much residence time to remove all the nitrates. The influent nitrate concentration would also allow the computer to control the flow of substrate into the system.