Graz wastewater treatment plant
The wastewater treatment plant of the city of Graz is located in the market town of Gössendorf south of the provincial capital Graz in the Austrian state of Styria . The system, which is currently designed for a population equivalent of 500,000 , has been purifying the wastewater of Graz and several surrounding communities using fully biological methods since 1979 . Operation and maintenance are the responsibility of Holding Graz .
Location and surroundings
The approximately 14 hectare area is 326 m above sea level. A. directly on the left bank of the Mur in the central Grazer Feld . The facility is located just under 2 km south of the Graz city limits and 8 km outside of the city center in the Dörfla district of the market town of Gössendorf. Due to the hydrologically sensitive location on the border streamline to the Graz- Feldkirchen water conservation area and in the Murauen landscape protection area ( LS 31 ), all structural interventions must be monitored. Many house wells in the nearby settlements are part of the groundwater influence area of the system, the structures of which reach up to 7 m below the groundwater level . The Gössendorf Mur power plant was completed in the immediate vicinity in 2012 .
history
Emergence
The first canalization plan for Graz was drawn up in 1925 and implemented three years later with the construction of a new canal of 22 km. In 1928 4,000 buildings were connected to the sewer network. In 1960 more than twice as many houses were connected to the 208 km network. The construction of a sewage treatment plant was initially rejected by the Gössendorfer municipal council in 1961 , but it was decided later. Construction work began in 1971, before the mechanical sewage treatment plant and sludge digestion went into operation three years later. In 1979 the project called the “building of the century for environmental protection ” was completed with the commissioning of the biological purification stage. In this way, the water quality of the Mur downstream from Graz could be improved considerably in the following years. In 1980 407 km of sewer network and 17,000 buildings were connected to the system.
First expansion
In 1991, new purification requirements for sewage treatment plants were passed through the Emissions Ordinance, which made the first remedial measures necessary. Due to the intensive sewer expansion and the connection of more and more residents, there was also the need for a procedural changeover and structural extensions. In 1995, the sewage treatment plant consisted of a computer with two coarse and fine screens, a sand trap , two primary clarification basins of 5000 m³, six activation tanks with a total volume of 14,400 m³, four secondary clarifiers of 5000 m³, two pre-thickeners of 450 m³, three digestion towers of 4000 m³ , two re- thickeners à 900 m³ and four belt filter presses for sludge dewatering. Some of these components were refurbished by 1998 and their capacity increased.
In September 1999 a project was started to adapt to the state of the art . The baseline study revealed a pollution of 470,000 population equivalents (PE) and up to 20% higher pollution on individual days. The low expectation of new connections as well as stagnating industrial freight led to a rated load of 500,000 PE and a hydraulic load of 90,000 m³ per day. In four construction phases up to 2007, mixed water overflow basins and larger secondary clarifiers were built and the aeration basins enlarged. A key objective was to further reduce the ammonium nitrogen input into the Mur. The additional pollution of 0.6 mg / l (with low water flow) could be reduced by the modernization measures to 0.01 mg / l, the daily emission from 2 to 0.1 t. Overall, the expansion cost 50 million euros more than planned. As of 2008, the length of the Graz sewer network was 842 km with 34,900 connected buildings.
Second expansion
In addition to the wastewater from the urban population of Graz , the sewage treatment plant also cleans that of the surrounding communities of Hart bei Graz , Hitzendorf , Kainbach , Raaba-Grambach , Stattegg , Thal and Weinitzen as well as numerous companies. In order to do justice to the growth of the metropolitan area - the city of Graz alone is growing by around 4,000 inhabitants annually - a further expansion was necessary, which provides for the replacement and general renovation of plant components that are now 20 years old and a capacity increase of 61% to 815,000 inhabitants. In addition, the safety equipment is to be modernized.
Construction work on the project, which is estimated at 40.5 million euros, is expected to start in spring 2020 and completion is planned for autumn 2023. In addition to the Mur power plant in Graz and the central storage channel , the expansion is one of the city's three major projects.
function
Every day, an average of 70,000 to 75,000 m³, with precipitation up to 140,000 m³ of treated wastewater flows into the Mur. In the course of the cleaning process, around 700 m³ of sewage sludge are produced . In 2008 the sewage treatment plant had 27 employees.
Wastewater treatment typically takes place in three stages . In addition to the mechanical and biological cleaning stages as well as the sludge treatment, a microplastic particle filter will be included as a fourth stage in the plans for expansion from 2020 . The addition of precipitants is necessary for the phosphate degradation , otherwise the cleaning is biological.
A large part of the sewage sludge produced annually is used to generate energy. The raw sludge is pumped into the digestion towers, where it remains at around 37 ° C in the absence of air for at least 25 days. In the anaerobic environment , methane gas is produced , which, when converted into electricity via three combined heat and power units, covers 75 to 80% of the plant's energy requirements. Part of the sludge is used as a substitute fuel in the Mellach district heating power station . The thermal energy obtained from this flows back to Graz as district heating , saving 2500 t of hard coal and 6000 t of carbon dioxide per year .
Web links
Individual evidence
- ↑ a b c d e H. Kainz, G. Maurer & E. Tschaussnig: Planning and expansion of the Graz sewage treatment plant. In: Österreichische Wasser- und Abfallwirtschaft , 57th volume, issue 5/6 (May / June 2005), pp. 63–70, doi: 10.1007 / BF03169026 .
- ↑ a b c d Holding Graz quoted in: Josef Riegler: Chronik der Marktgemeinde Gössendorf . 2nd, updated and expanded edition, Marktgemeinde Gössendorf 2017, pp. 163–165.
- ↑ a b Gerald Winter-Pölsler: 41 million euros for the sewage treatment plant. In: Kleine Zeitung , issue of May 16, 2018, pp. 26–27.
- ↑ a b Graz-Gössendorf sewage treatment plant - follow-up review. Court of Auditors , April 2009, accessed June 2, 2018 .
- ↑ a b c d Karin Hirschmugl: All right with the Graz wastewater. In: BIG - The official pages of the City of Graz , April 2018 edition, pp. 8–9.
- ↑ We get the best out of wastewater. In: derGrazer , edition of April 8, 2018, p. 13.
- ↑ Daniel Windisch: New sewage treatment plant should stop microplastics. In: derGrazer , edition of May 20, 2018, p. 6. Online , accessed on June 2, 2018.
- ^ Warmth for Graz from Graz wastewater. Holding Graz , accessed on June 2, 2018 .
Coordinates: 46 ° 59 ′ 47.7 " N , 15 ° 28 ′ 22.3" E