Reconstruction and expansion of the Unteres Pustertal WWTP

Changed wastewater loads at the Lower Puster Valley WWTP

In recent years, the inflow load of the Lower Puster Valley WWTP has risen sharply. The increase in the number of guest beds and new industry has also led to an increase in the loads in the inlet of the Lower Pustertal WWTP. The high concentration of nitrate-nitrogen (NO3-N) in particular has caused problems (20 mg/l annual average).

At these NO3-N values, some of the nitrate is already broken down into molecular nitrogen (N) by special microorganisms (denitrifiers) in the pre-treatment stage. This nitrogen outgasses and prevents the actual function of the pre-treatment. This is where the heavier substances should actually settle and be removed from the wastewater. However, the resulting nitrogen gas bubbles settle in the sludge and this sludge then floats instead of settling. The result is a higher load and energy consumption in the biology and less gas yield.

Changed wastewater loads at the Lower Puster Valley WWTP — ARA UP input load in population equivalent and NO3-N input

The solution

To solve these problems, it was necessary to rebuild the pre-treatment system. However, our primary clarifier had always been too large for the actual volume of wastewater. We were now able to take advantage of this fact by installing a partition wall to create two basins.
The inner tank was used as a primary clarifier, which was equipped with a floating sludge screw that removes the floating sludge.
The outer basin serves as a denitrification basin for the additional nitrate.
Another smaller tank was added, which can be used for both nitrification and denitrification.

With this conversion, we have thus gained 657m³ of aeration volume and can therefore treat a larger wastewater load, increasing the expansion capacity from 55,000EW to 60,000EW.

The solution — The finished new primary settling tank with external anaerobic tank

Project U04_21 with many details

Our managing director, engineer Konrad Engl, included further conversions and improvements in this project in the U04_21 project that has now been launched, and the conversions therefore amounted to the following sections:

Replacement of the gas detection control panel
Replacement of the fire alarm control panel
Installation of new additional ventilated sand and grease trap (previously there was no grease trap)
Replacement of the precipitant station and precipitant tank (now with a capacity of 31.8m³)
Reduction of the VKB volume from 844m³ to 370m³
Installation of new floating sludge scraper in VKB
New VKB cover
Volume freed up in the VKB is now used for denitrification (additional 338m³)
New aerobic tank added (319m³ with 84 plate aerators)
Installation of 264 aerator plates in two former deni zones, which can now be used for nitrification
Replacement of the old aerator plates in one line
Purchase of new aeration compressor 37kW, air volume 9.84m³/min
Residual heat utilization Installation of hot water feed FM station ÜSS thickener
Residual heat utilization Installation of hot water feed FM station sludge press
Residual heat utilization Installation of heat exchanger Inlet VKB
Discharge of the surface water at the unloading station into the wastewater treatment system

The completion

The project was carried out in three construction lots, with the total cost of this project amounting to around 2.24 million euros.

The construction period is also noteworthy: the problems mentioned were identified in the course of 2020, suitable solutions were sought and planning began.
The application to the Office for Water Protection was submitted by ARA Pustertal AG on 22.03.2021.
The Office for Water Protection issued file no. No. A/074A1021/8 of 22.04.2021 issued the positive technical report.
Construction work began at the end of 2022 and lasted until the end of 2023. The site inspection for the building acceptance will take place on 25.01.2024.

With this conversion, ARA Pustertal has adapted to the changed circumstances in accordance with its internal action agreement and has provided solutions to the problems,
to improve the quality of our waters and protect the environment.

The completion — The floating sludge screw in operation

Reconstruction and expansion of the Unteres Pustertal WWTP

Changed wastewater loads at the Lower Puster Valley WWTP

The solution

Project U04_21 with many details

The completion

The floating sludge screw in operation