Abstract
Tests by Standard Oil Co. (Indiana) over 15 mo showed greatly improved performance by operating the activated sludge process (ASP) at high sludge age (more than 100 days) and by adding powdered activated carbon (PAC) to further reduce residual soluble organics in the wastewater. When high sludge age was maintained by good filtration to eliminate influent solids, a 5000 mg/l. equilibrium mixed-liquor PAC concentration was maintained in a municipal plant with <5 mg/l. PAC makeup rate. This occurs because at high sludge age, bacteria in the sludge utilize organic wastes only for metabolism; growth is kept low enough to merely balance the inevitable sludge losses in the effluent so that there is no production of waste sludge. Maintenance of 45 day sludge age with 2400 mg/l. total suspended sludge solids in the aerator resulted in effluent solids of 4.2 mg/l. or 12.7 lb/day, of which 53% was PAC. A detailed description is given of the biological oxidation processes operative in the ASP.
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