Wastewater treatment : Strip diffusers guarantee flexibility for enormous load peaks

PI Husum1 Aquaconsult
© Aquaconsult

Wastewater treatment plants have to overcome a wide range of challenges. One of these is the often highly diversified wastewater inputs and the resulting significant variations in wastewater volumes that need to be treated. This often requires enormous flexibility and adaptability from the aeration systems - requirements that innovative technology aim to fulfill. The AEROSTRIP strip diffusers from AQUACONSULT Anlagenbau in Lower Austria are a prime example. They also prove this at the wastewater treatment plant in Husum, which is now a showcase example in Germany in terms of system elasticity.

In principle, the plant is designed for a wastewater volume of around two million cubic metres per year and a population equivalent of 110,000. However, the region's largest slaughterhouse alone, located at the other end of the city, utilises up to 60% of the plant's capacity - especially during the day: "After slaughtering in the morning, the first wastewater volumes arrive at our plant around an hour later," explains Dieter Petersen, Operations Manager at Stadtwerke Husum Abwasserentsorgung. "We usually end up with very high nitrogen loads in the wastewater, which we treat in our plant." The inputs fluctuate throughout the day until the slaughter centre is cleaned in the evening and there is another peak in the input. After that, the wastewater volume and load often drops dramatically and remains well below 50% of the plant's capacity throughout the night, including at weekends and on public holidays. In summer, there are still selective increases due to tourist activity that can occur in the North Sea city. Added to this are the downpours typical of the region, which bring a lot of load with them due to the blocked mixed sewer in the old town area. "All in all, our wastewater treatment plant has to be designed to be highly flexible and cope with enormous differences in its intake," says Petersen. This task is extremely important because the wastewater treatment plant's outlet runs directly into the North Sea via Husum's outer harbour near a bathing beach. This means that wastewater treatment requires a high level of care.

Dealing with enormous load peaks

The AEROSTRIP diffusers from AQUACONSULT Anlagenbau have been proving their efficiency in this challenging situation since January 2024. In a conversion project, over 450 AEROSTRIPs were installed in the plant's two basins in the summer months of last year, switching wastewater treatment from surface to pressurised aeration using strip diffusers. "The aim of Stadtwerke Husum was to use this conversion to absorb the enormous peak loads and thus increase operational safety. In addition, the cleaning performance was to be improved and energy efficiency increased," says Christoph Kormann, project manager at aqua & waste International GmbH from Hanover. "The AEROSTRIP diffusers are ideal for all of these requirements," says the planning engineer.

The innovative diffusers from AQUACONSULT Anlagenbau guarantee optimum flexibility and adaptation to different operating conditions in many different types of wastewater treatment plants. The ultra-fine air bubble diameter results in very efficient oxygen inputs. The large range for the specific pressurisation of the individual diffusers enables good controllability, so that no under- or over-aeration is to be expected in any operating or load condition of a wastewater treatment plant. "The flat design of the strip diffuser - with an installation height of just two centimetres - also results in minimal flow resistance in the tank, which in turn favours high-yield surface aeration, regardless of the tank geometry and size", Gerald Glaninger, Managing Director of AQUACONSULT Anlagenbau explains.

In Husum one of the two basins can also be taken out of operation for inspection purposes, as the entire volume of air required can be fed into the remaining basin.

"Our AEROSTRIPs have been proven to save up to 40 % energy compared to conventional ventilation systems", says Glaninger. "In special settings, even significantly higher savings potentials can be achieved. The essential and special component of the Aerostrips is the perforated polyurethane membrane, which is stretched over a stainless steel or plastic base body. 400,000 pores per square metre of membrane surface form the basis for an ultra-fine bubble pattern. The diameter of the air bubbles is around one millimetre, which gives the entrained air a high specific surface area. In combination with a long residence time of the air bubbles in the tank, this results in high oxygen utilisation and therefore high efficiency of the system."

PI Husum3 Aquaconsult, he flat design of the strip diffuser - with an installation height of just two centimetres - also results in minimal flow resistance in the tank
The flat design of the strip diffuser - with an installation height of just two centimetres - also results in minimal flow resistance in the tank. - © AQUACONSULT

Consistent oxygen zone - high energy savings

"The advantages of our AEROSTRIPs really show their full potential at the Husum wastewater treatment plant," concludes Rüdiger Vrabac, Branch Manager at AQUACONSULT Anlagenbau GmbH in Germany. "Whether it's flexibility, oxygen input, cleaning performance or energy savings - the performance of our diffuser solution really comes into its own in this challenging setting."
Finally, Husum also benefits from another special AEROSTRIP feature: "Thanks to the different sizes of these strip diffusers, we were able to fully adapt the configuration to the pool geometry - even in the bends, where shorter diffusers were installed in order to be able to supply the bend constantly and over the entire surface," explains Operations Manager Dieter Petersen. "We expected a great deal from this continuous occupancy and were not disappointed: after our first tests, we achieved the expected oxygen zone at a consistently high level."

The plant has now been in full-load operation since January and oxygen input tests are already showing impressive values of 6 kg per kWh. In addition, energy savings of up to 30% are forecast in controlled operation. With an increase in efficiency of this magnitude, the wastewater treatment plant in Husum would soon be able to supply itself completely with energy. This is because the wind turbine on the sewage treatment plant site already supplies a large proportion of the electricity required. Until now, around 700,000 kWh of additional electricity had to be drawn from the public grid to run the sewage treatment plant throughout the year. By converting to AEROSTRIP strip diffusers, the plant now hopes to take a big step towards self-sufficiency.

Innovative technology

The innovative strip diffusers from Traiskirchen in Lower Austria are now used in more than 2,500 industrial and municipal wastewater treatment plants around the world. Currently, AQUACONSULT Anlagenbau can also look back on a number of very special references in Germany, such as the "Alte Emscher" sewage treatment plant in Duisburg, one of the largest sewage treatment plants in Germany, or the Zweibrücken sewage treatment plant in Rheinland-Pfalz, which is now regarded as a prime example of economical plant operation. AEROSTRIPs are also used in the three wastewater treatment plants in Copenhagen (Lynetten, Damhusåen and Avedore) and in the Western Treatment Plant in Melbourne (Australia).