Aqua-Audit: Treatment Plant Optimisation  
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Getting Better Performance
Diffuser Cleaning and Maintenance: There is another level of aeration system care beyond simple tests and monitoring, and that is to carry out periodic diffuser cleaning operations.

The two benefits to be gained by this level are:

  • Longer diffuser service life between replacement operations; and

  • Reduced blower power consumption through oxygen transfer efficiency gains and reduced backpressures.

One cleaning method involves washing operations with high-pressure water jets. This can be done either by draining and entering the tanks, or by raising removable grids one at a time with lifting equipment. Diffuser washing is effective, but quite labour-intensive, so is usually only undertaken every 2 or 3 years.

Another frequently used method is to clean the diffusers insitu using acid vapour, gas or solution. This is much less costly than pressure washing, so it can be done annually or more frequently if desired. One proprietary cleaning method uses hydrochloric acid gas; another floods the aeration pipework with muriatic acid.

In the method favoured by Aqua-Audit, small quantities of formic acid are pumped into the aeration pipework through fixed or portable injector nozzles. The quantities used are small – typically only 30-60g per diffuser – and an entire plant can usually be treated in one day.

The effectiveness of acid vapour dosing varies from plant to plant, depending mostly on influent conditions. But for many plants, regular acid vapour dosing can remove most of the backpressure increases sustained since the last cleaning operation, and in some plants the effective life of the diffusers can be doubled between replacement operations.

The cost of acid vapour dosing is extremely small in relation to the potential energy cost savings this cleaning operation almost invariably achieves.

The method preferred by Aqua-Audit involves injection of formic acid vapour into the aeration pipework. Formic acid is relatively non-corrosive, can be safely injected into steel pipework, and has a negligible effect on the treatment process.
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