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Water quality--Minnesota; Sewage disposal plants


ABSTRACT-The Metropolitan Waste Control Commission and its predecessors have operated the Metropolitan Wastewater Treatment Plant on the Mississippi River at St. Paul, MN, for the past 50 years. Analysis of water quality data collected over the past 60 years shows a general improvement of water quality as the waste treatment process has been upgraded. In 1926, dissolved oxygen ranged from <1 mg/L to 2 mg/L in the river reach from St. Paul to Lock and Dam 3 (August mean values). In 1987, dissolved oxygen values in the same area were 7 mg/L or greater. The drought of 1988 produced severe low flow conditions in the Mississippi River, but dissolved oxygen values continued to meet or exceed the 5 mg/L water quality standard. Biological sampling in 1926 and 1959 showed an absence of clean water organisms. Biological sampling in 1985 showed an abundance of clean water organisms. The most dramatic evidence of this resurgence is the reappearance of the Hexagenia mayfly in St. Paul after a 50 year absence. The water quality improvements in the Mississippi River correlate directly with improved treatment plant processes, particularly the current advanced secondary treatment facility, and with improved waste control throughout the Minneapolis/St. Paul area.

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