Magic Trees for the sewers
Fighting odour in the Vienna sewerage system
Vienna's sewers have a sophisticated ventilation system. The exchange of air is based on the simple physical principle of the "chimney effect": fresh air enters the system through the street-level storm drains, and exhaust air is blown out through ventilation pipes ending on the roofs of buildings. Odour from the sewerage system occurs only in very few places, where it is neutralised with simple and efficient measures: addition of calcium nitrate to the wastewater stream or "Magic Trees" fixed in manholes to provide a "pleasant smell".
The Vienna Waste Water Management (Wien Kanal) is responsible for running Vienna's 2,400 kilometres sewerage system which transports wastewater from all over the city to the main wastewater treatment plant. The sewers are regularly cleaned and necessary repairs carried out to prevent any odour problems. However, if foul smells do occur, Wien Kanal has to investigate the causes and take effective counter-action.
Vienna's sewerage system is naturally ventilated thanks to the "chimney effect": fresh air continuously enters the system through the street-level storm drains, and exhaust air is blown out of the system through vents which rise from building drains and end at roof level. As a result of this natural ventilation, no harmful concentration of gases can build up, and odour problems are also largely avoided.
Odours may occur, however, in areas where wastewater remains within the sewer pipes for a long time. This may be the case with sewage from the flat city areas east of the Danube,
which is transported rather slowly and over long distances to the treatment plant. In the course of this journey, anaerobic degradation may set in, giving off foul smells under unfavourable conditions. High-pressure flushing is used to clean out the affected sewer portions and eliminate odours swiftly. Persistent problems are treated with calcium nitrate. Dosing units are used to continuously inject precise amounts of this chemical, which effectively blocks anaerobic degradation, into the wastewater stream. Another, simple and cost-effective way to combat odour problems is to use Gelactiv® SHK plates. These are polymer plates which are loaded with natural odour-neutralising substances and are simply placed into manholes, attached to the gully grating. The technology gives quick and effective results at a low cost.
Wien Kanal maintains a central complaints register to identify problematic spots and take economical and effective action wherever odour becomes a problem.
Facts & Figures
- Use of Gelactiv® SHK plates in app. 50 manholes
- Cost per plate: approx. 52 Euro
- Useful life of each plate: 3-6 months
- Total annual wastewater volume in Vienna: approx. 220 million m³
- Cleaning and maintenance of sewerage system: approx. 300 employees
DI (FH) Volker Schaffler
Tel. +43 1 4000 84269
Fax +43 1 4000 7997