EEGQ 4222Notes 4 Design to procure water

Advantages exhibit high o xygen transfer efficiency

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and sizes, such as discs, tubes, domes, and plates. Advantages • Exhibit high O xygen Transfer Efficiency • Exhibit high aeration efficiencies (mass oxygen transferred per unit power per unit time) • Can satisfy high oxygen demands • Are easily adaptable to existing basins for plant upgrades • Result in lower volatile organic compound emissions than nonporous diffusers or mechanical aeration devices Disadvantages • Fine pore diffusers are susceptible to chemical or biological fouling that may impair transfer efficiency and generate high head loss; as a result they require routine cleaning. • Fine pore diffusers may be susceptible to chemical attack (especially perforated membranes); therefore, care must be exercised in the proper selection of materials for a given wastewater.
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• Because of the high efficiencies of fine pore diffusers at low airflow rates, airflow distribution is critical to their performance and selection of proper airflow control orifices is important. • Because of the high efficiencies of fine pore diffusers, required airflow in an aeration basin (normally at the effluent end) may be dictated by mixing not oxygen transfer. • Aeration basin design must incorporate a means of dewatering the tank for cleaning. The performance of diffused aeration systems under normal operating conditions is directly related to the following parameters: • fouling; • wastewater ch aracteristics; • process type and flow regime Large bubble diffuser These units employ large orifice or hydraulic devices. Large bubble units have lower oxygen-transfer efficiency than fine bubble units, since the interfacial area for oxygen-transfer is considerably less. The a dvantage is that they do not require air filters and generally require less maintenance. Coarse bubble diffusers produce bubbles which rise rapidly from the floor of a wastewater treatment plant or sewage treatment plant tank. They are typically used in grit chambers , equalization basins , chlorine contact tanks , and aerobic digesters , and aeration tanks . Generally they are better at vertically "pumping" water than at mass transfer of oxygen. Coarse bubble diffusers typically provide half the mass transfer of oxygen as compared to fine bubble diffusers, given the same air volume Turbine aeration units These units entrained atmospheric oxygen by surface aeration and dispersed compressed air by a shearing action employing a rotating turbine or agitator. Air bubbles discharged from a pipe below the agitator are broken down by a shearing action of the high speed rotating blades of the agitator. For systems of low oxygen utilization rates, oxygen is supplied by the flow of air self-induced from a negative head produced by the rotor (suction effect). For systems of higher oxygen utilization rate a blower or compressor is needed.
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  • Fall '15
  • Drinking water, Sewage treatment, Water supply network

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