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Energy Efficiency in Wastewater Treatment

It is a known fact that within the wastewater treatment process large amounts of electricity are required for aeration devices, large pumps and agitators and sludge treatment. In the future it will be possible to increase electricity generation from the fermentation gas produced in the plants by up to 90%.

Thus a significant part of the energy required for wastewater treatment plants will be generated within the plants themselves.

We should not, however, ignore the potential for savings possible through the optimisation of the use of energy within wastewater treatment plants. The possible percent improvement is smaller than in the case of in-plant electricity generation, but in terms of savings, cutting electricity consumption by just 20% would be the equivalent of doubling the amount of electricity generated from fermentation gas.

Furthermore, the optimisation of process technology which accompanies electricity-saving measures such as the energy-efficient design and control of aeration systems or the use of high-efficiency pump impellers often has an additional positive effect on the operation of wastewater treatment plants. One interesting alternative with regard to economy in wastewater treatment is the use of pneumatic automation solutions.

The central pumping station of the Sindelfingen wastewater treatment plant in Germany provides a particularly good example of increased energy efficiency. Wastewater from the preclarification stage is pumped into the distribution system for the trickling filters. For this purpose, six rotary pumps are available in the pumpstation – each with a power rating of 90 kW and a delivery rate of up to 500 l/s with a hydraulic height of 8 - 9 m.

Before the modernisation work, the pump system had non-return valves, that must be held open at all times, which leads to a reduction in pump delivery of up to 10 % and also reduces the open flow cross-section. A water-hammer effect occurs when the non-return valve closes and leads to vibration in the piping system.

In order to increase operational reliability, the check valves were completely replaced physically and functionally in the course of modernisation work by a pneumatic automation solution for the existing shut-off knife-gate valves. An additional compressed air reservoir was installed to provide enough reserve air to actuate the shut-off valves even in emergencies.

The same pump delivery as before can now be obtained with significantly less energy. This results in an annual saving of 2% of the total energy consumption of the wastewater treatment plant with a return on investment below one year.

The reason why the plant operator chose a pneumatic solution was the continuous load capacity of this technology, its long service life and the overload tolerance of the pneumatic drives during the opening and closing of the shut-off valves. In practical terms, this means easy operation, few breakdowns and thus high plant availability, combined with a nice cost saving effect.
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