Sustainable Aeration Design: Right-Sizing Blowers and Aeration Systems
- J. Rohrbacher, S. Phipps, E. Stanley - Hazen and Sawyer
Energy efficient aeration is key to moving wastewater treatment facilities (WWTFs) from net energy consumers to producers. Recent focus has been on new aeration technologies including high efficiency blowers and diffusers and controls to reduce aeration energy costs. These technologies provide limited efficiency improvement if not appropriately applied to match specific site conditions.
Aeration systems are often sized based on maximum flow and load conditions at worst case site conditions whereas actual facility operational conditions are typically far below design conditions. The tendency to design aeration systems based on static conditions often results in aeration systems that are unable to efficiently meet process air demands under the majority of conditions over the service life of the equipment. Aeration blowers are often oversized and provide poor turndown and/or overlap to efficiently operate under low loading conditions. Aeration basins are often oversized with excessive diffusers installed, and aeration system operation can be driven by mixing requirements rather than process aeration demands under these conditions. Not only does this result in excessive energy consumption, excess aeration can adversely impact biological nutrient removal processes by returning dissolved oxygen to unaerated zones.
Sustainable aeration system design requires that the full range of flow, load and ambient temperature conditions be accounted for when designing aeration systems and blowers. Changes in aeration efficiency over time due to diffuser fouling and wear also need to be accounted for. Key elements of sustainable aeration system design include providing flexible aeration basin designs to match volumetric capacity to influent flows and loads throughout the life of the system, providing multiple sizes of blowers to ensure turndown requirements can be efficiently met and avoid operational gaps in the blower operating rage, and an effective control system to match blower operation to process aeration and mixing requirements.
Case studies will be presented to illustrate common pitfalls in aeration system design that limit efficient operation and provide solutions to overcoming these obstacles to facilitate more sustainable operations. The impacts of flow equalization, solids recycle flows, diffuser fouling and aeration basin sizing will also be presented to demonstrate how blower selection and design is impacted by variable conditions.
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