Figures, data, facts

The amount of wastewater produced depends on the number of residents and the industrial and commercial operations serviced by the wastewater treatment plant. The pollutant load is indicated by the population value (PV), resulting from the number of residents (NR) plus population equivalents (PE).

The population equivalent (PE), a measure for the pollutant load to be degraded, corresponds to the amount of pollutants passed into the wastewater by one resident daily and is indicated as BOD5. 1 PE equates to a BOD5 of 60 g/d. This also allows to compare the pollutant load of commercial and industrial wastewater with that of municipal sewage. The main wastewater treatment plant needs to cope with an average load of 3 million PV60. It has been designed to handle 4 million PV60 and has enough capacity to clean 680,000 m³ of effluents during dry weather periods.

During heavy rainfalls or winter snow melt, the plant is loaded with up to 1.6 million m³ of highly diluted wastewater per day. As a result of plant expansion and controlled retention measures in the sewer system, the wastewater reaches the plant at a maximum flow rate of 18 m³/sec and is cleaned by a fully biological process. The wastewater takes around 20 hours to flow through the plant, which extends over a total area of 42 hectares.

Technical parameters

Population values (PV)
Rated capacity4.0 million PV60
Current average load3.0 million PV60


Minimum cleaning efficiencies
BOD5> 95 %
COD> 85 %
TOC> 85 %
Nitrogen removal> 70 %


Threshold values of outlet concentration
BOD515 mg/l
COD75 mg/l
TOC25 mg/l
NH4-N5 mg/l
Ptotal1 mg/l


Residence time of wastewater inside the plant under dry weather conditions20 Stunden
Average inflow under dry weather conditions7 m³/s
Maximum inflow during rainfallmax. 18 m³/s


Reference load
BOD5240 t
COD455 t
Nitrogen38 t
Phosphorus5,7 t

Plant technology

Mechanical cleaning stage 
Gravel trap2 tanks
Screw pump facility6 screw pumps, capacity: 3 or 4.5 m³/s, head: 5.2 m
Screening plant6 screens, screen width: 3 m resp. 3.25 m, distance between screen bars: 8 resp. 3 mm
Sand trap

6 tanks, total volume: 4,320 m³, depth: 3.6 m

Primary clarifiers

4 tanks, total volume: 27,700 m³, depth: 3 m
Primary sludge is removed by scrapers

First biological cleaning stage 
Aeration tank4 tanks, total volume: 51,000 m³, depth: 6.8 m
Intermediate clarifiers24 tanks, total volume: 123,000 m³, depth: 6.45 m
Sewage sludge is removed by scrapers
Transport of return sludge2 screw pump units with 4.5 m³/sec capacity each
Precipitate stationPhosphate precipitation with iron(III)sulphate
Second biological cleaning stage 
Compressor station5 compressors with 45,000 Nm³/h or 1,250 kW capacity each
Intermediate pumping station8 propeller pumps for wastewater with 2.6 m³/sec each and 6 propeller pumps for return sludge with 2.7 m³/sec each
Distribution chamber15 inductive flow meters with control valves, DN 1200
Aeration tanks15 tanks, length: approx. 79 m, width: approx. 33 m, depth: approx. 5.5 m, total volume: 171,000 m³
Secondary clarifiers15 tanks, inner diameter: 64 m, mean depth: 4.1 m, total volume: 200.000 m³
Outlet structure3 propeller pumps with 8 m³/sec capacity each during high flow conditions in Danube/Danube Canal, 2.5 m head in outlet channel during dry conditions
Sewage sludge treatment 
Sewage sludge thickeners4 sludge thickeners, total volume: 13,500 m³, amount of thickened sludge: 4,000-12,000 m³/d, dry matter content: 3-5%
Sludge dewatering22 centrifuges,
Dry matter content of dewatered sludge: 35-39%,
Calorific value: approx. 16,500 kJ/kg DM
Sludge incineration3 fluidised bed furnaces, dewatered sewage sludge is incinerated at a temperature of 850°C


BOD5 stands for the biochemical oxygen demand after 5 days. It is an indicator for the content of biologically degradable components in the water. The biochemical oxygen demand is the amount of dissolved molecular oxygen needed by microorganisms for the oxidation (or conversion) of organic components (carbon compounds) in the water under defined conditions within a certain period (5 days). The BOD5 is indicated in mgO2/l (water).

COD stands for chemical oxygen demand. The COD is an indicator for the content of oxygen-depleting components in the water. The chemical oxygen demand is the consumption of potassium dichromate calculated during the chemical oxidation of organic water constituents under standardised conditions. It is indicated as oxygen equivalent in mg/l of water.

TOC stands for total organic carbon, which is the entire amount of organically bound carbon. Together with the chemical oxygen demand (COD), the TOC is a key indicator for the organic load of a body of water. It is indicated in mg C/l (water).

NH4-N stands for ammonia nitrogen. Ammonia nitrogen is an inorganic nitrogen compound which is produced during the biological breakdown of organic nitrogen compounds (e.g. protein). Ammonia nitrogen is indicated in mg N/l (wastewater).

Ptotal stands for total phosphorus. Total phosphorus is a sum parameter comprising dissolved inorganic phosphorus (orthophosphate) and dissolved or undissolved organic phosphorus. Total phosphorus is indicated in mg P/l (wastewater).

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