When Hydria Water’s new step screen, Step Screen Delta (SSD), was tested at the Hjultorp Wastewater Treatment Plant in Vårgårda, a separation efficiency of over 90% was achieved – a result that significantly exceeds previously documented levels for both conventional and progressive step screens.
“This is a fantastic result and proof that we actually deliver even more than we promise,” says Andreas Riedel, Technical Director at Hydria Water.
The test was carried out together with the plant’s own staff and validated by Envidan, one of the Nordic region’s leading specialists in water and water treatment.
In 2005, a study was conducted at Chalmers University of Technology to examine the separation efficiency of different types of step screens. The results showed that progressive screens could achieve a separation efficiency of up to 81% under optimized conditions with pulse mode and a 200 mm pressure drop, while conventional step screens reached 52% when operated in step mode.
To examine the screenings separation efficiency of a further developed step screen – Step Screen Delta SSD from Hydria Water – a capture rate test was conducted in 2025 at the Hjultorp Wastewater Treatment Plant in Vårgårda. The test setup was based on the methodology described in the study carried out at Chalmers University of Technology (Larsson & Andersson, 2005).
The test result showed a separation efficiency of over 90%.
“The test was conducted to obtain third-party validation that the machine delivers as promised. Now we can confidently say it performs even better,” says Andreas Riedel.
“These types of tests, and the results we are now seeing, align fully with both our heritage and our vision for the future: to develop world-class technical engineering solutions. It’s a testament to the shared technical and innovative capabilities throughout our entire organization. And this is just the beginning – we have much more in the pipeline,” says Tobias Barrstrand, CEO of Hydria Water.
“With SSD, we’ve found the key to truly high separation efficiency”
Traditional step screens have a design where all steps are identical, creating a constant geometry along the entire length of the screen (linear design). This allows the screenings to be transported while maintaining the structure of the screenings mat. The tested screen, Step Screen Delta SSD 1100-600-2, is a further developed model of Hydria Water’s XS step screen. The tested machine has a 2 mm slot width but can be configured within a range of 1–6 mm and is designed to operate in both step and pulse modes. The bottom construction of the SSD differs from previously tested models in that the bottom step is movable and follows the screen’s movement, while the screen bars and steps have the same dimensions across the entire transport surface.
This prevents larger openings from forming in the lower part of the screen during operation and is the key to achieving truly high separation efficiency. The SSD retains the robustness and reliability of our earlier machines, but we have also carefully refined every detail to create a machine ready for autonomous applications and digital diagnostics. “The devil is in the details,” says Andreas Riedel.
A total of five tests were conducted with varying test durations, flow rates, and screen sizes. The separation efficiency (SCR, Screen Capture Rate) was calculated based on both wet weight and dry solids content. The highest SCR values – over 90% based on wet weight – were achieved with longer test durations (40–45 minutes) and a 2 mm slot width, which indicates and confirms that the buildup of a screenings mat significantly impacts the separation efficiency. The two test occasions that resulted in an SCR below 90% were conducted with shorter test durations due to the outlet screen’s limited capacity, caused by an initial load of fat-saturated fibers, which may have prevented the screenings mat from forming sufficiently during the test period.
“The results from this study show that Hydria Water’s step screen model SSD, with a movable bottom step and operation in pulse mode, can achieve a separation efficiency above 90%. That is a higher separation than the progressive screens tested in the Chalmers study,” states Petter Lind, Process Specialist at Envidan, who participated in the study as an independent party responsible for documentation and quality control of the tests.
A new market standard
Based on the study by Hydria Water and Envidan, it can be concluded that this type of machine, with such high separation efficiency, delivers what perforated screens promise – but without the costly operational parameters such as brushes and rinse water.
“This sets a new standard for separation efficiency in the market. With an SCR as high as 90%, both money and equipment in downstream process stages can be saved. We look forward to speaking further with both existing and new customers about how SSD and mechanical water treatment can handle large flow variations without compromising performance,” says Johan Fritz, Sales Manager at Hydria Water.
Questions and more information
Below you can find the full study. You are also welcome to contact any of us if you have questions regarding the implementation or the results.
Evaluation of the separation efficiency of step screens from Hydria Water
Andreas Riedel, Technical Director, Hydria Water
+46 33 23 67 17
andreas.riedel@hydriawater.com
Johan Fritz, Sales Manager, Hydria Water
+46 73 681 57 20
johan.fritz@hydriawater.com