wastewater line Unteres Pustertal

Wastewater treatment process

The sewage treatment plant was dimensioned and engineerized for a 55.000 inhabitants equivalent capacity, in the way to satisfy the needs of population in local areas, of tourism, of industry and artisan shipment, guarantying in the meanwhile higher levels in quality, with the maximum efficiency in organic pollutant load knocking down and phosphoric and nitrogen componentsstrong reduction.

The target of sewage treatment is reached with physical, biological, chemical and biochemical processes.

Legend Function diagram

Water	sludge	Gas

1) inflow	11) Pre-thickener	16) gas accumulator
2) rain relief	12) Digestion chamber	17) gas torch
3) pumping station	13) Post thickeners	18) gas utilisation
4) screening plant	14) sludge press
5) Aerated grit chamber	15) sludge disposal
6) Preliminary clarifier
7) Biological basin
8) Final clarifier:
9) drain
10) Rienz River

Inlet channel and pumping station

The waste water is fed to the sewage treatment plant via the sewer system [1]. There the wastewater must be lifted via two pipe screws [3] so that the water can then pass through the plant in free fall.

Mechanische Reinigung

The mechanical sewage, with a 25% organic load reduction efficiency, is assured by a spire screen [4], by aerated grit chamber [5], bar-screens and primary clarifier [6] which is covered to avoid unpleasant odours.

Biological cleaning

After that, the sewage treated mechanically cross a series of 5 cascade [7]: in the first one, in totally oxygen absence, takes place the bio-chemical process of partial phosphoric compounds deleting, in the second one, the nitrous compounds reduction is realized (denitrification) while in the last three, the biggest ones, atmospheric oxygen is injected to permit la biodegradation of organic compounds and nitrous compounds oxidation (nitrification). The recycle of vented sewage, of actives sludges and the regulation of oxygen concentration, permit the creation of an ambient in which microorganisms and various nature batteries may easily
do the proper work of degradation of pollutant load.
These microorganisms, in bow structures, are the actives sludges that are separated by sedimentation in the big secondary clarifier. The last reduction of phosphoric compounds is obtained by simultaneous precipitation (adding chemicals agents).

final clarification

The water’s superior layer, now purified, flows out on toothed threshold [8], is analyzed by a measurement and metering station [9] (for quality and flow rate), and flows out into Rienza river [10].

The sludge treatment

The sludge coming from the first clarifiers [6] (primary sludge) is thickened mechanically by a pre-thickener. The sludge is now eliminated from secondary clarifiers [8]
and thickened mechanically by disc thickener. The pre-thickened sludges are now reached at a temperature of 38°C approx and digested into an anaerobic digestion
chamber [12]. The sludges, now stabilized and neutrals, are dried with a screw press [14] .

The dewatered sludge [15] is transported to Tobl for incineration.

The sludge treatment — Mechanical sludge thickening

Gas line

During the digestion process [12], the microorganisms transforming the organic compounds on CO² and methane with high energetic content, available for thermal heating
of digestion chambers and for factory heating. To take a solution at the gas over production, in the Mühlbach plant is provided a storage gas tank [16].

The gas line is composed by: gasometer [16], pressurization station, gas flare [17], 2 heaters and 2 cogeneration groups [19].

The gas engines (BHKW) produce heat and electricity for the needs of the plant.

Ventilation system

During Bassa Val Pusteria plant engineer studies, a special importance matter was the particular attention at stinks emissions monitoring. All the stronger sources and ways of stinkness (fine bar screen, aerated grift chamber, clarifier and the entire sewerage treatment plant) are positioned on warehouses with the proper air purification system.

The stink air, until a flow rate of 21.000 m³/h, is purified with scrubber at crossing flows system with, storing the thermal energy produced.

Components and power

For sewerage system and sludges treatment were provided a total amount of 120 units divided into instrumentation, machineries, for a total amount of power
consumption of approx 200 kW; the same items quantity were necessary for heating system, ventilation, air treatment, lightness systems, hydro feed exc.. For power
plant, control and regulation of all these plants and systems, 25 km of bundles and cables were provided.

The energy requirement of the entire plant is about 750,000kWh per year.

Components and power — The control centre of the plant