Automated ORP Control for Aerobic/Anoxic Cycling in Oxidation Ditch Treatment

by Thomas E. Coleman, (M.ASCE), Gray & Osborne, Inc, Yakima, United States,
H. David Stensel, (M.ASCE), Gray & Osborne, Inc, Yakima, United States,
Darrel Fleischman, Gray & Osborne, Inc, Yakima, United States,
W. Brent Denham, (M.ASCE), Gray & Osborne, Inc, Yakima, United States,

Document Type: Proceeding Paper

Part of: Critical Issues in Water and Wastewater Treatment


The 1140 m3/d (0.3 mgd) Grand Coulee, WA. oxidation ditch was modified to incorporate a computer-control anoxic/aerobic cycle operation to investigate SVI control and nitrogen removal. A directional mixer placed in the ditch is turned on and the aerators are turned off at selected times to create the anoxic cycle. The control system requires continuous ORP measurements in the ditch, with computer logging, data synthesis and decision making. An automated, single anoxic/aerobic control cycle was studied for a 5-month period. Diluted SVI values were maintained in a range of 70-110 mL/g for a 3-month period after chlorination was used to breakup a filamentous floc. Nitrogen removal averaged between 76 and 80 percent.

Subject Headings: Water treatment plants | Aerobic processes | Oxidation | Nutrient pollution | Nitrogen | Control systems | Computing in civil engineering

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