Edition 01/2020

Depending on the time of day, the season, and the amount of precipitation in the atmosphere, the volume of wastewater and the degree of pollution will change. The consequence of this is that the air requirement in the aeration tanks varies constantly. If this is not optimally controlled, this will result in extreme energy consumption and an unnecessary waste of resources. The key to maximum efficiency therefore lies in the precise operation of the load changes. AERZEN has developed the most efficient, powerful and flexible blower solution for oxygen supply thanks to Perfomance³ - a customised machine configuration based on advanced technologies. The objective: operate base loads in an energy-saving manner and intercept supply peaks with pinpoint accuracy. 

Whether we’re talking about positive displacement blowers, rotary lobe compressors or turbo blowers, each technology has its strengths, but also its physical limits. The high art is the precise design of the assemblies to meet actual requirements. A precise analysis of the load profiles that occur and the creation of a daily hydrograph is essential. “It turned out that although our plant has an expansion size of 30,000 population equivalents (PE), the current capacity utilisation is only 15,000 PE,” says Anton Mayer, Head of the Oberschleißheim wastewater treatment plant. “Further analysis of the results shows that our wastewater volume has high fluctuations during the course of the day and is characterised by low volumes with relatively high concentrations of load.

Since 1994, AERZEN assemblies have been in operation in the wastewater treatment plant which was built in 1960 (wastewater production approx. 650,000 m³ per year) – these were two positive displacement blowers of type Delta Blower (1x GM 15L, 1x GM 50L). Anton Mayer: “We have always been very satisfied with AERZEN. The blowers have run without any problems and have performed reliably with minimum maintenance. The spare parts procurement and the cooperation with the customer service have always worked out very well.” Since the beginning of this year, an AERZEN Performance³ technology mix, consisting of positive displacement blower Delta Blower GM 15L (max. 1,038 m³/h, 700 mbar pressure difference), rotary piston compressor Delta Hybrid D 36S (max. 2,150 m³/h, 700 mbar pressure difference) as well as turbo blower AT 50 G5plus (max. 1,900 m³/h, 700 mbar pressure difference), has provided the oxygen supply in the aeration tanks. 

“The turbo blower is the most compact and at the same time the most efficient machine,” explains Markus Leidinger, Wastewater Manager at AERZEN. “At the same time, the control range of turbo machines is limited to between 40% and 100%, and the efficiency decreases under partial-load operation.“ The Delta Blower therefore works at low load. It was already there before the retrofitting and optimally covers the low volumes during the night. This way the load peaks in joint operation are served. Completing the trio is the Delta Hybrid. It helps out when the turbo blower is operating at full capacity. The latest assembly generation made by AERZEN combines the advantages of blower and compressor technology in one system and is by far the most efficient machine in the wide control range between 25% and 100%. Should the turbo blower fail, the Delta Hybrid, together with the positive displacement blower, can maintain operation at full load. 

The AERZEN blowers not only work extremely efficiently, they are also oil and absorbent free. This guarantees 100% reliability. “Discharge silencers that are lined with absorption material are subject to natural wear. This is caused by the hot air and the high flow velocity as well as the vibrations of the machines,” says Markus Leidinger. “As a result, particles are released which constrict the piping and clog the finely perforated diaphragms of the aerators.” The reactive silencers by AERZEN work entirely without absorbent and thus maintain the prescribed sound pressure level over the entire life cycle. 

But how do the AERZEN blowers actually know how high the air demand in the aeration tanks is? The aeration system and the blower technology are optimally matched to the requirement profile of the Oberschleißheim sewage treatment plant. As a holistic approach is essential for maximum energy efficiency. “In addition, AERZEN is the only manufacturer that really combines all technologies - blower, hybrid and turbo with air bearings - under one roof,” says the manager.

The control system of the wastewater treatment plant measures the concentrations of oxygen, ammonium and nitrate and thus determines the oxygen and air demand. The innovative machine control system AERsmart from AERZEN then distributes the required volume flows to the machinery in such a way that the blowers operate at very close to the theoretically highest level of efficiency. But there’s more to it than that: the continuous recording of operating parameters and real-time visualisation allows the early detection of drift of individual values. The user can thus react in time and process failures are avoided. 

The intensive cooperation of all actors and the comprehensive optimisation measures have paid off - in the truest sense of the word. As a result of these measures, the electricity consumption for the biological treatment stage has been reduced from 495,600 kWh to 191,720 kWh per annum. This represents a saving of 55%, which corresponds to €40,000 per year. “We definitely hadn’t expected such a good result,” says Anton Mayer, happily. By switching to the new technologies, the basin volume could also be reduced: instead of four, only two aeration tanks are now in operation.

“That was definitely the right step for the future,” says the wastewater treatment plant manager. “We now have pioneering technology that will deliver optimum performance and savings for years to come.” This also benefits wastewater quality: previously, the discharge values showed relatively high fluctuations, but with the new control technology, the values are uniform and in a very low range.

And there is another reason for satisfaction: today, the Oberschleißheim wastewater treatment plant is one of the most modern of its kind in Germany and serves the industry network, German Water Partnership e.V. (GWP), as an international reference plant.