Breathing freely in a UNESCO World Heritage region

The Inner Salzkammergut region in the heart of Austria is breathtakingly beautiful and thoroughly steeped in history. As far back as the Bronze Age, salt mining allowed a historical high culture to flourish here. Today, Hallstatt enjoys a worldwide reputation as a tourist destination. In such extraordinary surroundings, bad smells from the sewer would go together like the proverbial chalk and cheese. ‘And yet in several places, we were indeed confronted with this problem’, recalls Franz Gamsjäger, plant manager at the treatment plant run by the Hallstättersee clean water preservation association. After all, more than 25 km of pressure pipelines – including several lake pipelines – and no fewer than 57 pumping stations are needed to transport the wastewater from the four member municipalities of Bad Goisern, Gosau, Hallstatt and Obertraun to the treatment plant.

Stench even in winter

Wastewater with extended retention times in the absence of oxygen – the ‘best’ conditions for the formation of hydrogen sulphide (H2S) and other odorous substances. And not only during the warmer seasons. Time and again, even during the ski season in the popular family skiing region of Dachstein-West, there was a noticeable stench from the sewer, marring the leisure activities of visitors and the quality of life of the locals, especially in good weather when the hydraulic volume is low.

Not to mention the damage from concrete corrosion that H2S threatened to cause to the wastewater infrastructure. But that’s all in the past now, since VTA Calcoferrit^® has been in use by the Hallstättersee clean water preservation association. ‘This biological double whammy for bad odours prevents the development of anaerobic conditions, inhibiting the formation of H2S and other odorous or toxic substances, which can only be formed in the absence of oxygen’, explains case VTA expert Christian Baier. VTA Calcoferrit^® also binds and neutralises odorous substances that are already present.

Sophisticated control technology

The highly effective system product is introduced at the plant run by the Hallstättersee clean water preservation association with the help of the VTA H2S Reducer, which collects hydrogen sulphide data using a network of online probes and controls the dosing systems accordingly. At the same time, the system also provides objective and complete documentation – not an insignificant matter in the case of odour problems, which of course often have a subjective component.

Franz Gamsjäger has further optimised parts of the sophisticated control technology himself. For example, the increase in dosage for rising inlet volumes is not simply linear, but also takes the proportion of infiltration water into account: ‘That means that the more water there is, the less VTA Calcoferrit^® is dosed in percentage terms’, explains the plant manager, who programmed this mode using characteristic curves.

The staff at the Hallstättersee clean water preservation association also built their own simple but very effective level indicators for the VTA Calcoferrit^® storage tanks using commercially available components. Speaking of storage: VTA also supplies specially adapted container solutions for every space situation that ensure optimum product storage.

Sensible, reliable, economical

‘The use of VTA Calcoferrit^® has worked out well for us and the vast majority of our problems with odours have been eliminated. We are confident that this will continue to be the case, even with temperatures that are now rising. For us, this is a sensible, reliable and indeed an economically impressive solution’, says Franz Gamsjäger in summary.

VTA Calcoferrit^® ...

...ensures odour-free conditions on a biological basis with two different mechanisms of action – safely and reliably. It is based on a highly concentrated nitrate solution with special iron components. This combination system prevents the development of anaerobic conditions, without which hydrogen sulphide and other odorous, and often toxic, substances cannot form in the first place. VTA Calcoferrit^® also binds and neutralises odorous substances that are already present, including amines and mercaptans. It inhibits the formation of aggressive, biogenic sulphuric acid, considerably reducing costs for maintenance and repairs in the sewer system. Last but not least, VTA Calcoferrit^® optimises the quality of the wastewater. It stabilises the floc, supports the biological processes at the treatment plant and improves the sludge properties.

Field report from the VTA Group’s scientific journal “Laubfrosch”, issue  76