Sludge aeration air in sewage plants

Measuring sludge aeration air in sewage plants


Process data

Measuring task:
To increase the plant’s energy efficiency flow velocity should be measured in order to calculate (mass) flow rate.

Measuring point:
Supply pipe leading to the aeration basins or in every ventilation pipe towards the basins

Measuring range:
Low m³/h up to higher than 10,000 m³/h depending on the measuring point and pipeline
Pipelines from DN 32 and smaller up to DN 1000 and larger

Process pressure
Usually 0.4 – 0.6 bar overpressure

Process environment:
Normally in non explosive areas as outdoor installations or in the plant’s engineering room


Many municipal sewage plants apply the activated sludge process where sludge aeration air is being pumped into aeration basins, speeding up the degradation process.

Large compressors ensure sufficient sludge aeration air in the basins which requires a lot of energy. Generating sludge aeration air makes up the majority of the sewage plant‘s electricity requirement causing a significant power requirement in the municipality and therefore it has the greatest potential for energy saving.

The demand for sludge areation air depends on the level of pollution and the amount of water in the aeration basins. Said demand can be regulated by measuring the actual flow rate. The measurement increases the plant’s energy efficiency in combination with a corresponding compressor control.

Your advantage

Safe, fast measurement under all weather conditions

Installation via ½“ bushing optionally with a ball valve

Data transmission:
Two analog outputs 4-20 mA for flow rate/mass flow/flow velocity and temperature as well as a digital output as the limit value or counter

Recommended products

Thermal flow sensor TA10

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Thermal flow sensor TADi

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Increasing the plant’s energy efficiency by measuring sludge aeration air

Depending on the sewage plant the costs for generating sludge aeration air and scavenging air for filters can take up to 45 % - 75 % of the entire electricity costs. The average in Baden-Württemberg is at 39 kWh/a per citizen. About 12 – 19 kWh/a per citizen are used for ventilation alone, making it a major factor in the municipalities‘ overall balance and providing great potential for savings.

The guideline for the energy efficiency in sewage plants in Baden-Württemberg recommends: „Effective ventilation, carefully regulated air supply and a conscientious maintenance of the entire ventilation system provides the greatest potential for saving electricity in municipal sewage plants. Minimizing air supply while maintaining the best possible drainage quality and high process stability is the goal.“

Solution: flow measurement of sludge aeration air in sewage plants
Höntzsch thermal flow sensors TA 10 can monitor and regulate even air distribution in the supply pipes and all outgoing lines while also determining overall consumption of sludge aeration air and regulating fluctuations. This reduces the consumption of compressed air and increases the energy efficiency of the sewage plants. Changes in air supply and increasing pessure can often help detect contamination in the aeration plates and to then take counteracting measures. One option is the injection of formic acid downwards the flow after the point of flow measurement. Pressure control alone might not detect fluctuating air flow reliably.

The calometric flow sensor TA10 can easily be installed with a ½“ bushing and ball valve. The use of a ball valve allows you to remove the sensor from the installation for maintenance or cleaning without interruptions. For smaller diameters there are measuring tubes available with different nominal diemeters. Thanks to the robust aluminium die-cast housing, sensors can be installed permanently outdoors. The sensor‘s positioning place and installation position is variable. There’s also a display available to adjust parameters.

Not only can our TA10 sensors measure in sludge aeration air pipes, they can also measure scavenging air of filters etc.

Another robust, easy and effective solution by Höntzsch.