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A reactor system was designed and fabricated to facilitate treatment of municipal wastewater. Carbon oxidation and nitrification was accomplished in an aerated, completely mixed vessel simulating the activated sludge process. This system was enhanced with an external clarifier to achieve waste activated sludge recycle, providing more efficient treatment and sludge age control. Four reactors were operated in parallel at varying solids retention times (SRTs). The four SRTs were maintained at 2, 5, 10 and 20 days by wasting a calculated volume of the reactor contents each day. Various parameters were measured during start-up and operation of this system to define treatment efficiency. Initial MLSS concentrations were 3000, 2200, 1300, and 900 mg/L for the 20, 10, 5 and 2 day SRTs, respectively. Influent total COD levels ranged from 175 to 275 mg/L. The SVI values were below 80 mL/g for the first 6 days of operation but increased to values as high as 1500 mL/g denoting poor settling. A subsequent increase in the effluent suspended solids accompanied the poor settling. The influent wastewater strength then increased significantly resulting in a drastic increase in solids concentration for all four reactors. A corresponding decrease in SVI and effluent suspended solids was noted. The additional substrate supported growth of more bacteria, enhanced bioflocculation, improved settlability, and subsequently decreased effluent suspended solids. Ultimately, steady state was achieved in all reactors.
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Document Type: Research Article

Publication date: 2000-01-01

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