The development and use of hybrid aeration processes - Discussion

Requirements to improve effluent quality have led to the establishment of b etter design procedures for activated-sludge plants, The recognition that a ctivated-sludge aeration is responsible for a large proportion of the energ y used in sewage treatment has resulted in the specification of energy-effi cient aeration systems as part of such design procedures. Fine-bubble diffu sed-air techniques are potentially more efficient than mechanical surface-a eration systems, but low oxygen-transfer efficiency is often observed in pr actice under conditions of high aeration tank solids loading. Surface-aerat ion systems appear to be able to operate at reasonable aeration efficiencie s under conditions of high loading, but they are not as effective as diffus ed-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 plan ts utilizing hybrid aeration.