Project Background & Challenges

The Austrian Energy Efficiency Act (Energieeffizienzgesetz EEffG) from August 11^th, 2014, obligates local energy providers to reduce their energy sales by 0.6% per year up to 2020. Wastewater treatment plants (WWTPs) are a significant energy consumer and make up approximately 20% of total municipal energy consumption. The biggest portion of the energy consumption is used by biological processes, mainly aeration, followed by pumps.

The Neusiedlersee Westufer (NW) WWTP is located in Schützen am Gebirge, a municipality about 40 km southeast of Vienna with an abundant culture of viticulture and tourism, in a close-knit community of about 1,450 inhabitants. NW’s WWTP treats the wastewater from nine municipalities on the west side of the Neusiedlersee Lake. Starting its operations in 2000, it is designed for 66,500 Population Equivalent (PE) with a peak load of 200,000 PE because of summer tourism and local wineries.

The biological unit consists of two aerated selector tanks, two oxidation ditches with simultaneous nitrification / denitrification and two post-aeration tanks, including aerobic sludge stabilization and phosphorus removal.

The proximity to a bathing hotspot and national park waters requires low discharge values of 0.5 mg/l total P, NH₄-N and NO₂-N, as well as a minimum of 85% N reduction. Annual energy consumption before the upgrade was ~1 GWh.

Each oxidation ditch had 240 flat panel diffusers installed directly onto the basin floor. Sedimentation in certain areas increase the energy consumption and require the basins to be emptied and cleaned annually.

The EDI Solution

The optimization of the biological unit was done by the consultants at New Water Technology (NWT OG).  With financing from Verbund Solutions GmbH, the Reinhaltungs-verband Region’s Neusiedlersee-Westufer Wastewater Treatment plant chose EDI for their aeration system and Wilo Pumpen Österreich GmbH for their pump system.

The complete biological unit was optimized including a CFD simulation. With a total of 300 FlexAir^® Pro MiniPanel diffusers (including 30 of the 3 Duplex and 270 of the 4 Duplex varieties), the new aeration system totals an area of 191.3 m^² polyurethane actively installed.

Purpose of Technology Used

Replacing the existing flat panel diffusers—which were installed directly onto the basin floor—with EDI’s FlexAir^® Pro MiniPanel diffusers caused the membranes to rise ~25cm above the basin floor. This allows those diffusers to be less vulnerable to sedimentation, the membranes to be replaced in-situ rather than sending the diffusers back to the manufacturer for membrane replacement, and it reduces the operational pressure of the aeration system. It also provides for an easy installation, levelling of the diffusers on the PVC laterals and simpler cleaning of the basin floor.

Site Construction

The new EDI aeration system was connected to the existing SS drop pipes with factory prefabricated uPVC subheaders and laterals. After installing and levelling those pipes with a limited number of SS pipe supports, the EDI FlexAir Pro diffusers were quickly clamped onto the laterals by using EDI’s SDM saddle mounted connections.

Upgraded System Performance

The reduced hydrostatic pressure from the little lower aeration depth and lower diffuser / membrane losses reduced the system pressure from an average of 568 millibar to an average of 471 millibar, resulting in an approximately 17% pressure reduction.

During the first two years of operation, the total energy consumption of the biological unit was reduced by about 50% compared to the baseline annual energy consumption of 2013 and 2014. Approximately 65% of this reduction was achieved from the new aeration system, while the other 35% from the new pump system.

As the energy consumption of the aeration system is a function of the wastewater flow and loadings, too, the energy consumption is evaluated on a load-adjusted basis. The energy savings of the aeration system was achieved with having 58.9% of the membrane area of the original flat panel aeration system only and without any need for the annual cleaning that was necessary with the old system.

As with any fine bubble membrane aeration system in such applications, the efficiency of the aeration system reduced due to scaling, fouling, organic and/or inorganic growth into the perforation slits etc. at this plant over time, especially as no cleaning was performed. Fe₂⁺ dosing at this plant results in ferrous oxide scaling on the membranes, which increases the pressure loss additionally. Nevertheless, the load-adjusted energy consumption of the aeration system remains lower than the baseline, which was based on the performance of the previously installed panel diffuser system. A cleaning of the diffuser membranes in May 2021 led to significant improvement, especially reducing the peaks from September and October 2020.