Suchergebnisse

AbstractRequirements to improve effluent quality have led to the establishment of better design procedures for activated‐sludge plants. The recognition that activated‐sludge aeration is responsible for a large proportion of the energy used in sewage treatment has resulted in the specification of energy‐efficient aeration systems as part of such design procedures. Fine‐bubble diffused‐air techniques are potentially more efficient than mechanical surface‐aeration systems, but low oxygen‐transfer efficiency is often observed in practice under conditions of high aeration tank solids loading. Surface‐aeration systems appear to be able to operate at reasonable aeration efficiencies under conditions of high loading, but they are not as effective as diffused‐air systems in low‐rate processes.There is evidence that a properly designed combination of the two types of aeration system in the same process (hybrid aeration) can result in optimum energy use and good effluent quality. The paper describes the development of this concept, showing the long‐term performance of three full‐scale plants utilizing hybrid aeration.