In the Gastein Valley, VTA’s new high-performance product for sludge conditioning is demonstrating its capabilities in daily operation impressively.
‘This is what sewage sludge should look like’, says treatment plant manager, Simon Rieder, taking a shovel full of a dark, crumbly mass from a pile onto which fresh supplies constantly trickle down from above. Above the pile is where the screw press works in the Gastein Valley clean water preservation association treatment plant that is responsible for wastewater disposal in the communities of Bad Gastein, Bad Hofgastein and Dorfgastein. These are familiar names in winter tourism and the seasonal peak loads for the plant are correspondingly high.
However, in the middle of the high season, in January this year, the sewage sludge did not look quite so ideal. The dry residue of the sludge from the two digesters remained below 20% during dewatering and could not be increased even by adding huge amounts of polymer. Reason enough to call on the specialists at VTA.
Following analyses on site and in the laboratory, their eventual recommendation was: VTA Biocitran® FORTE. Based on citric acid, this innovation improves floc structure, binds dissolved organic substances and provides a clearer filtrate. This optimisation of dewatering results in a higher dry residue, lower polymer consumption and less backcharge for the plant.
Plus 5% in the case of dry residue
In practice, these advantages have been confirmed almost to perfection in the Gastein Valley. Huge positive effects were measurable immediately after dosing with VTA Biocitran® FORTE started. The dry residue increased by more than 5% (to over 25%) and polymer consumption was down over 30% per tonne of dry residue.
The fact that these effects are due to VTA Biocitran® FORTE was clearly demonstrated when the product was temporarily unavailable at the plant: immediately, the dry residue dropped to 18.9%. When dosing of the VTA high-performance product was resumed, the parameters improved significantly on the very same day (dry residue 24.4%, see graphic). ‘And this was the case even though we made absolutely no other changes to the plant. This shows just what VTA Biocitran® FORTE does’, reiterates Simon Rieder.
For the Gastein Valley clean water preservation association, the increase in dry residue of more than 5% means significant savings in the disposal of sewage sludge, which has been thermally recycled since last year: ‘We are already paying more than 65 euros per tonne and the trend is still rising. Better dewatering means we can save hard cash’, says Association Director Peter Müllner. Then there is the considerably lower polymer consumption, in this case a reduction of around a third. This also adds up to a considerable saving.
Tried and tested cooperation
Peter Müllner has known and held VTA in high regard for many years. When he took over the management of the Gastein Valley clean water preservation association in 1999, plans were already on the table to extend the treatment plant. It dates back to 1981 and was originally expanded to 37,000 PE – a figure that was regularly exceeded by a considerable margin during the ski season.
However, together with VTA, it was possible to optimise operations so that purification capacity always met the specifications in full despite this disparity. ‘Together, we exploited the plant’s full potential. Experts were amazed at what you can get out of an activated sludge process’, Müllner recalls.
This meant that the million-euro expansion could be postponed for several years before an additional activated sludge tank with a capacity of 1,500 m3 and other measures were finally implemented in 2019 based on a simulation by the Technical University of Vienna; the treatment plant has now been expanded to 60,000 PE. In the meantime, the 200-kilometre-long sewer network was completely renovated and the inflow of external water reduced by more than half – from over six to less than three million m3 per year. When engineer Peter Müllner goes into well-earned retirement this summer, he will hand over to his successor Lukas Leitner MSc a state-of-the-art plant that reliably meets requirements thanks to the long-standing cooperation with VTA.