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Diffuser (sewage)

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An Air Diffuser or Membrane Diffuser is an aeration device typically in the shape of a disc, tube or plate, which is used to transfer air and with that oxygen into sewage or industrial wastewater. Oxygen is required by bacteria resident in the water to break down the pollutants. Diffusers use either rubber membranes or ceramic elements typically and produce either fine or coarse bubbles. These are referred to as fine bubble diffusers or coarse bubble diffusers. They are typically connected to a piping system which is supplied with pressurized air by a blower.

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Other technologies: - mechanical aerators (low or high speed mixers, submersible and surface aerators), - jet aerators (Venturi) - paddle aerators

Typical efficiency of a full floor coverage diffused aeration system in clean water is 2%/ft or 6.6%/m. When converted to mass transfer into process or dirty water, it is typically closer to about half of those figures.

Both retrievable and fixed grid type diffused aeration systems are made and serve different purposes. In case a plant has a single tank, a retrievable system is desirable, in order to avoid stopping operation of the plant when maintenance is required on the aeration system. Fixed systems, on the other hand, are typically less costly, and are often more efficient because it is easier to make full use of the floor.

A developments in recent years has been surface coatings of PTFE on EPDM membranes. This provides a buffer between the EPDM substrate and wastewater, hence reducing the likelihood of chemical attack and oxidation, and also providing better resistance to biological fouling and calcium scaling.

Automated software is available on the web to assist with drafting of aeration systems in CAD, as well as calculation software to help determine diffuser requirements for a given wastewater.