Economy of space in existing structures – STP St. Oswald in Austria

Room concept: everything on 41 m², installation engineering by FORSTENLECHNER INSTALLATIONSTECHNIK Gesellschaft mbH, supervision of construction by engineering office Eitler & Partner
Room concept: everything on 41 m², installation engineering by FORSTENLECHNER INSTALLATIONSTECHNIK Gesellschaft mbH, supervision of construction by engineering office Eitler & Partner

HUBER ROTAMAT® Rotary Drum Fine Screen Ro 2, COANDA Grit Washer RoSF 4 and Screw Press RoS 3Q installed on 41 m²

The building for wastewater screening equipment on STP St. Oswald near Freistadt, on the northern border of Upper Austria, is 7.5 m long and 5.5 m wide and now houses a HUBER ROTAMAT® Rotary Drum Fine Screen Ro 2, COANDA Grit Washer RoSF 4 and a complete sludge dewatering plant RoS 3Q. Too much crammed into it? No, all machines can still be accessed easily for operation and maintenance!

St. Oswald, a municipality in the Mühlviertel district, counts 2780 residents. The municipality lies on the Böhmerwald Road (B 38), the most northern federal road in Upper Austria which starts near Passau and runs south of the border to the Czech Republic across the Mühlviertel and then through the Waldviertel district in Lower Austria. South-east of St. Oswald, in Echsenholz, there is the famous Sanctuary of Virgin Mary "Maria Bründl" with its medicinical spring that has been a popular destination for pilgrims for more than 350 years.

From 2001 on, St. Oswald's population has grown continuously and soon, when the express highway from Linz to Budweis will be completed, the region will be even better accessible from the Linz region. Work on STP St. Oswald started in 2013 according to the plans and with the supervision from the engineering office Eitler & Parter at Linz. Their concept included the additional use of the screening room for the sludge dewatering plant.

The room houses three systems:

  • COANDA Grit Washer RoSF 4, size 1
  • ROTAMAT® Rotary Drum Fine Screen Ro 2, size 600/3
  • ROTAMAT® Screw Press RoS 3Q 280
COANDA Grit Washer RoSF 4, size 1
COANDA Grit Washer RoSF 4, size 1
ROTAMAT® Rotary Drum Fine Screen Ro 2, size 600/3
ROTAMAT® Rotary Drum Fine Screen Ro 2, size 600/3
ROTAMAT® Screw Press RoS 3Q 280
ROTAMAT® Screw Press RoS 3Q 280

It was possible to arrange the systems in this way as the inlet channel is running parallel with the long side of the screening room. Before the ROTAMAT® Rotary Drum Fine Screen Ro 2 (size 600, 3 mm bar spacing), which is designed for a flow rate of 34 l/s, could be installed the old screen had to be dismounted and the channel width extended. Due to a number of vertical core holes and the installation and backfilling of two stainless steel baffle plates the new screen could be installed along the rear wall. The existing doors right and left of the ROTAMAT® Rotary Drum Fine Screen Ro 2 can still be accessed conveniently with an access width of one metre.

On the outer wall there is a shaft for the grit trap pump behind which the channel leads into the circular grit trap. The COANDA Grit Washer RoSF 4 is located to the right of the pump shaft where the conical grit tank was installed on a column previously. The diagonally arranged grit removal screw allows for sufficient free moving space.

The workshop behind the screening room had to remain there. The place would have been unsuitable as container installation place. There was also no usable space available above for installation of the sludge dewatering plant. A paved floor space and flying roof were therefore built outside the workshop as container installation space. As liquid sludge is easier to transport upwards than dewatered sludge, the RoS 3Q Screw Press was put onto a two metre high pedestal so that the dewatered sludge can be transported directly from the press discharge through the attic above the workshop to the container. It was therefore not necessary two have two different screw conveyors (diagonal and vertical).

Besides, the pedestal of the screw press provides more room for occasional inspection and maintenance. It should be mentioned that all function-relevant components (such as sludge pump, coagulant conditioning plant and coagulant pump, flow meters, mixing device) are well accessible at floor level without having to make use of the pedestal very often.

Concerns that the aggressive milieu in the screening room could affect mechanical or electro-technical equipment proved to be unfounded. Die ROTAMAT® Rotary Drum Fine Screen Ro 2 is a completely encased unit with a screen basket cover. As the channel inside the screening room is completely covered and has pendulum flaps at the entrance and exit, this area is permanently kept under a slight underpressure by an Ex-ventilator so that no moisture or aggressive vapours can enter the screening room.

With its generously dimensioned screening room STP St. Oswald provided good preconditions for the project. The brilliant space-economic concept provided by the planning office could be implemented perfectly due to excellent collaboration between the customer, planning office and executing companies. Many thanks to the plant manager Siegfried Glaser, as well as Dipl.-Ing. Matzinger and Ing. Schmitzberger of ZT-Büro Eitler & Partner in Linz, and Ing. Angerer and Mr. Nenning from the company Forstenlechner in Perg.

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