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How to Calculate MCRT

MCRT stands for Mean Cell Residence Time. It refers to the length of time, typically expressed in days, that solids and bacteria are kept in the activated sludge process during the treatment of wastewater. Calculating MCRT requires a number of separate calculations to determine the values for each variable in the equation.

Things You'll Need

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Instructions

    • 1

      Write down the equation to calculate MCRT. This equation is MCRT = (Manox + Maer)/(Mw + Me).

    • 2

      Calculate Manox. This variable refers to the mass of solids in the anoxic (oxygenless) zone. The calculation to determine Manox is (Vanox)(8.34)(MLSSanox). In this equation, Vanox is the anoxic volume, and MLSSanox refers to the mixed liquor suspended solids in the anoxic zone. (In this terminology, mixed liquor refers to the bacteria in a wastewater aeration tank.) These two variables should be known quantities. The unit of this calculation is pounds.

    • 3

      Calculate Maer. This variable refers to the mass of solids in the aerobic zone. The calculation to determine Maer is (Vaer)(8.34)(MLSSaer). In this equation, Vaer is the aerobic volume, and MLSSaer refers to the mixed liquor suspended solids in the aerobic zone. These two variables should be known quantities. The unit of this calculation is pounds.

    • 4

      Calculate Mw. Mw is the mass of solids that are removed from the system in waste sludge. The calculation to determine Mw is (Qw)(8.34)(TSSw). In this equation, Qw is sludge wasting rate, and TSSw is the waste sludge solids concentration. The unit of this calculation is pounds per day.

    • 5

      Calculate Me. Me refers to the mass of solids removed in the wastewater plant effluent. The calculation to determine Me is (Qe)(8.34)(TSSe). Qe is the clarifier effluent flow, and TSSe is the clarifier effluent total suspended solids concentration. The unit of this calculation is pounds per day.

    • 6

      Once you determine Manox, Maer, Mw and Me, place their values in the equation to calculate MCRT. The resulting value is expressed in days.

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