Blowers for aeration in STP and ETP

In an activated sludge, MBBR, SBR or MBR plant, the blowers are usually the largest energy user, often more than half of the plant power. They supply the oxygen the bacteria need to remove BOD and ammonia. A blower that is too large wastes power, one that is too small leaves the plant short of oxygen, and a wrong type can give years of high running cost. The choice depends on the air required, the discharge pressure, how much the load varies, noise limits and maintenance capacity.

Twin-lobe (roots) blowers

Positive displacement blowers with two rotating lobes. The most common type in STPs and ETPs because they are sturdy, simple and cover small to medium plants. They give nearly constant flow against changing pressure. Noise is high, so an acoustic enclosure is normal. Efficiency is moderate. Flow is varied with a variable frequency drive.

Rotary screw blowers

Positive displacement blowers with intermeshing screws. More efficient than roots blowers, quieter and with lower pulsation, at a higher purchase price. Suit medium plants running continuously where power cost matters.

Centrifugal (turbo) blowers

Dynamic blowers with high-speed impellers, available in single and multistage designs. High efficiency and low noise at large flows. Suited to large plants. They respond to changing pressure and temperature, so they need careful selection and controls to avoid surge.

Regenerative (ring or side-channel) blowers

Small, low-pressure blowers with a single impeller. Used in small packaged plants, diffused aeration in shallow tanks and sludge holding. Simple and compact. Not for deep tanks or high pressure, and not efficient at larger sizes.

Surface aerators and jet aerators (alternatives)

Surface aerators mix and oxygenate from the surface without a blower and diffusers, and suit lagoons and shallow tanks. Jet aerators combine a pump and air to give both mixing and oxygen, and suit equalisation tanks and high-strength effluent.

Fine-bubble membrane diffusers (disc and tube)

Produce small bubbles that transfer oxygen efficiently. The standard for biological tanks. Membranes need care to avoid clogging and have a limited life, so a good pre-treatment and screening matter.

Coarse-bubble diffusers

Produce larger bubbles with lower oxygen transfer but less clogging. Used for equalisation tanks, grit removal and mixing.

Air headers and valves

Distribution piping, valves and flow meters balance the air across the tank and make future adjustment possible.

Air requirement

Calculated from the oxygen demand (BOD and ammonia load) and the oxygen transfer efficiency of the diffusers at your tank depth and water temperature.

Discharge pressure

Set by diffuser submergence (each metre of water is about 0.1 bar), pipe losses, diffuser losses and a margin for clogging. Selecting too much pressure wastes power.

Variation of load

A plant rarely runs at design load from day one. A variable frequency drive, multiple blowers or inlet guide vanes let the air follow the actual load.

Duty and standby

Most plants have a standby blower. In a small plant the standby may be the same size as the duty unit.

Hot climate and altitude

Hot air is less dense, so a blower delivers less oxygen on a hot day. For Gulf, African and hot-inland sites, size for the maximum ambient temperature. High altitude also reduces air density.

Noise

Choose acoustic enclosures, intake and discharge silencers and a blower room when the plant is near housing, hospitals or hotels.

Maintenance

Check belt or direct drive, access for filter and oil changes, and the availability of spares. A simpler blower that your team can service often beats a more efficient one that needs a specialist.

Intake filter

A clean intake filter protects the blower and is a regular maintenance item, especially in dusty sites.

We size the air requirement for your plant, select blowers and diffusers, and supply them as part of a plant or on their own, against your specification and approved make list. We can also review an existing plant where power use is high or oxygen is short. Send your plant details. See also mechanical equipment, pumps and MBBR vs SBR vs MBR.