In Q1 2017 Air Technology were engaged by a customer as part of their ongoing acid cleaning scheme, to use their proprietary diffuCLEAR acid cleaning method upon the aeration lanes at a sewerage treatment works in the east of England.  The works consists of an inlet works, primary settlement, secondary treatment in biofilters, followed by tertiary treatment in a three cell BAFF plant. The BAFF plant is filled with bio-bead media, which consists of 3-4mm diameter polymer beads which the bacteria attach to. The aeration is through diffusers which comprise stainless steel pipes with small diameter holes. Before cleaning the cells were suffering with poor pattern and as a result large dead zones.

To perform the acid clean Air Technology used formic acid which is then atomised within the pipework and carried by the air to the diffusers. This acid clings to the inside of the pipework and diffuser heads and dissolves any build-up of minerals or particles that may be blocking the air from entering the effluent efficiently. This is the preferred process as the air supply does not need to be turned off, the Cells do not need to be drained and the disruption to the sites running is minimal.

This has resulted in the blower relief valves not lifting anymore and energy savings of £4,400/annum are expected.

Once distribution of the acid was complete it was noted that there had been an average pressure drop of 88mbarg per blower and an average increase in air supply in excess of 10%. This has resulted in the blower relief valves not lifting anymore and energy savings of £4,400/annum are expected. This gives a payback of 0.6 years.

On top of the energy saving from reducing the pressure on the system this work will help to extend the operating life of the aeration diffusers thereby reducing future maintenance costs and also increase the efficiency of oxygen transfer resulting in additional savings.

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