Aeration blowers: looking after the most expensive equipment in a wastewater plant

In an activated sludge plant, the aeration blowers are the equipment everyone notices quickly when it stops. Dissolved oxygen in the aeration basin drops, the biological process slows, and if it goes on, effluent quality falls. A large share of the plant’s electricity usually goes to these same blowers.

Even so, in many plants blower maintenance is reactive: as long as they run, nobody touches them.

The standby blower is a maintenance opportunity

Most blower buildings have a standby blower. It is not only there for the day of a failure; it is the chance to take the other blowers out of service in turn for PM without reducing aeration.

To use that chance, the planner needs to know how much each blower has run and when it was last serviced. Rotating the blowers regularly spreads the wear between them, and makes sure the standby blower actually works on the day it is needed.

A standby blower that hasn’t been started for six months isn’t a standby; it’s a question mark.

What to keep an eye on

Depending on the type of blower, a few points always matter:

• Bearing temperature. The most common sign before a failure. A gradual rise over a few weeks usually points to insufficient lubrication or wear.
• Vibration. Rising vibration can come from imbalance, loose foundation bolts or a failing bearing.
• The inlet air filter. A clogged filter lowers suction pressure and makes the blower work harder.
• Belts on belt-driven blowers: wrong tension damages both the bearings and the belt.
• The check valve and pressure relief valve on the discharge.

These can be read and recorded on the shift round or at the monthly PM. If the readings are recorded as numbers, their trend gives a warning before the failure.

See the repeat failures

One of the most useful things a failure history can do is show recurrence. Say aeration blower 2 has failed four times in the last 18 months:

If each failure is just a separate work order, nobody may notice that three times out of four the failure mode was the same. But when a cause is recorded for each failure, for example “insufficient bearing lubrication”, and failures with a similar cause are linked, the pattern becomes clear.

Then you can ask: why is lubrication insufficient? Perhaps the lubrication interval in the monthly PM is too long for this blower, which runs more than the others. Perhaps the grease isn’t right. Perhaps lubrication is done but not recorded, and sometimes gets missed. Whatever the answer, it costs less than the fourth bearing replacement.

Record mode, cause and effect separately

For recurrence analysis to be possible, three things have to be recorded separately:

1. Failure mode: what happened? “High bearing temperature.”
2. Cause: why? “Insufficient lubrication.”
3. Effect: what did it do to the process? “Reduced aeration capacity on line 2; blower 3 brought into service.”

If all three are written in one free-text sentence, failures cannot be compared later.

A temporary fix is not a full fix

Sometimes a blower is brought back with a temporary repair: for example by limiting its load until a bearing arrives. That state should be recorded separately. “Temporary fix; maximum load 70% until the bearing is replaced; owner: maintenance supervisor.” Until the permanent work is done, the failure is still open and should not appear as “resolved” in reports.

Blower spare parts

A blower’s fast-moving parts are usually predictable: inlet air filters, belts, bearings and grease. Set minimum stock levels for them and reserve them for planned PM. If a blower’s monthly PM is due this week and the inlet air filter is not in stock, the planner should see it today, not on the day of the job.

A week in the blower building

To make this more concrete, picture an ordinary week. On Saturday, on the morning shift round, the operator reads blower 2’s bearing temperature at 78 degrees; the week before it was 72. The number is still within the allowed range and the blower is running, so usually nobody does anything.

If that reading is only written in the round logbook, next week when the temperature reaches 85 nobody sees the two numbers side by side. But if the reading is recorded on the bearing temperature measurement point of that blower, the rising trend is visible on the chart. The operations supervisor can record a process condition with a “high” attention level, and the maintenance supervisor can plan an inspection, before the blower trips on high temperature in the middle of the night.

On Monday, the planner sees that blower 2’s monthly PM is also due this week. They combine it with the bearing inspection, reserve an inlet air filter and grease, and plan for blower 3 to cover during the service. On Wednesday the job is done, and in the completion report the technician writes that the grease in the drive-end bearing was almost dry.

That is the sentence that, three months later, when someone asks why blower 2 fails more often than the others, brings them close to the answer.

One last point about electricity: a blower running with a clogged inlet filter or a worn bearing usually uses more power to deliver the same air. Regular blower maintenance helps it run more efficiently as well as preventing failures; but that should be measured with the plant’s own readings, not with a general figure.

In short

• Use the standby blower for rotation and regular PM.
• Record bearing temperature, vibration and inlet filter pressure drop as numbers.
• Record mode, cause and effect separately for every failure, so recurrence becomes visible.
• Record a temporary fix with its limit and owner, not as a full fix.
• Have fast-moving parts in stock and reserved before the PM is due.