OXYGEN CONTROL FOR WASTEWATER TREATMENT

摘要

A method and system for controlling dissolved oxygen levels in a secondary treatment system of a wastewater treatment facility that can employ a membrane bioreactor in which oxygen introduction into mixed liquor is controlled to prevent bulking and minimize generation of extra cellular polymeric substances. The control is exercised by insuring that dissolved oxygen levels within the mixed liquor do not fall below a minimum system level at which microorganism stress would occur. This is done by setting a minimum dissolved oxygen level control point equal to a sum of the minimum system level and an adjustment factor determined on the basis of oxygen uptake rate and time delays inherent in sensing oxygen levels and changes thereof within the mixed liquor. The minimum system dissolved oxygen level can be continually calculated on the basis of an inferred food to mass ratio that would vary with sensed mixed liquor suspended solids.

主权项

1. A method of controlling dissolved oxygen levels in a secondary treatment system of a wastewater treatment facility to prevent bulking and minimize generation of extra cellular polymeric substances, said method comprising:
introducing oxygen into mixed liquor contained in the aeration basin of the secondary treatment system to support bacterial activity within the aeration basin provided in part by return activated sludge; measuring a dissolved oxygen concentration within the mixed liquor with an oxygen sensor having a response time equal to a time delay between measurement of the dissolved oxygen and a change in the oxygen injection rate; multiplying an oxygen uptake rate at which the oxygen is consumed in the mixed liquor by the response time to obtain a dissolved oxygen adjustment factor; calculating a minimum dissolved oxygen set point by adding the dissolved oxygen adjustment factor to a minimum system dissolved oxygen concentration selected to prevent bulking and minimize generation of extra cellular polymeric substances; and controlling the oxygen introduction into the mixed liquor so that the dissolved oxygen concentration is no less than the minimum dissolved oxygen set point and no greater than a maximum dissolved oxygen set point that is less than a solubility limit of the dissolved oxygen within the mixed liquor.