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The Use of Automated Oxygen Uptake Rate Measurements to Improve the Reliability of a Nitrification/Denitrification Activated Sludge Treatment Plant

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Solutia Inc. produces acrylic fibers and intermediate organic chemicals at its Decatur, Alabama facility. The process wastewater generated and sanitary sewer wastes are treated in an on-site anoxic-aerobic activated sludge wastewater treatment plant (WWTP) prior to discharge into the Tennessee River. The 3.2 mgd WWTP can treat 700 to 1,800 mg/L TC and 300 to 500 mg/L TKN. Historically the WWTP experienced at least 2 major upsets (nitrifier inhibition) each year, many of which resulted in curtailed production. Upsets typically occurred in the November- December period, although other times were not uncommon. Although Solutia initiated an intense proactive program in early 2000 to produce a more stable and robust nitrification/denitrification treatment system, a major upset occurred in November 2000. Clearly a major improvement in WWTP operation had been made, but a more clear understanding of the system was needed.

The primary goal of this work was to improve the understanding of the WWTP process fundamentals and to improve its reliability by measuring oxygen uptake rates (OUR) of the nitrifiers and heterotrophs at the exit of the denitrification and nitrification basins. These OUR measurements could then be used to determine the health of the biomass as well as detecting excessive loading in the denitrification basin. A second goal was to measure toxicity to nitrifiers of various plant streams or chemicals. The automated OUR system, designed and built by Solutia, features readily available components with all functions of the procedure under LabView® software for control, acquisition of data, and calculation of OUR results.

As a result of implementing the automated OUR measurements on a daily basis in 2001, WWTP operational decisions and early intervention are made to avoid upsets. Routine plant data will be shown to demonstrate the usefulness of the automated OUR system as well as the effects of process changes on the WWTP. The usefulness of the automated OUR instrument is clearly demonstrated by the long-term stability of the system. The last upset in January 2003 happened after approximately 2 years of stable operation and in part was the result of operating the WWTP in a way that the automated OUR system was predicting might be problematic. Routine OUR measurements have been instrumental in identifying root causes of recent nitrification upsets and in managing the process to expedite recovery.

Document Type: Research Article


Publication date: 2004-01-01

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