THE PROBLEM: Sludge formation, silting, blue algae growth — Located in Bavaria, the Quellitzsee is a natural body of water measuring 6 hectares (14.82 acres), and a popular destination for swimmers and anglers. In the past, these leisure activities were occasionally hampered by strong blue algae blooms and in 2013, the authorities of the city of Döhlau discovered another problem: So much sludge had formed in the lake that immediate action was needed. SchlixX Plus was chosen as the appropriate treatment and it resulted in 75 percent of organic materials broken down, allowing for their Regatta to take place.

Project Overview:

Treatment and Solutions:
Located southeast of Hof in the Tauperlitz region of Bavaria, Germany, the Quellitzsee is a natural body of water measuring 6 hectares (14.82 acres) and a popular destination for swimmers and anglers. In the past, these leisure activities were occasionally hampered by strong blue algae blooms and in 2013, the authorities of the city of Döhlau discovered another problem: So much sludge had formed in the lake that immediate action was needed.

Plan A: An island made of sludge
The conventional approach – dredging the lake – and especially the subsequent disposal of the organic sludge, turned out to be too expensive. Instead, a different plan was decided on: The lake would be drained, the sludge would be dried out and then heaped to create an island in the lake. However, this approach had two major drawbacks: Firstly, the organic material would have remained in the water and continued to have a damaging effect in the future. Secondly, this would have meant cancelling a sporting event that is incredibly important to the region: the annual Hof Regatta, a prestigious highlight of the international canoeing season in which over 1000 people participate.

Plan B: The “mayoral” solution
The mayor of the city of Döhlau wanted to find a way around this. When looking for alternatives, he came across OASE’s procedure. After just one meeting, during which our experts explained the environmentally friendly way in which the SchlixX Plus microorganisms work, he was convinced that this was the solution that would save the lake and the regatta for the city and its residents. He brought together all the relevant decision-makers and together with councilors, officials and OASE experts, it was decided that an initial test run would take place during the quiet winter season, when there would be no fish or bathing: The lake would be drained of half its water, then SchlixX Plus would be applied to part of the lake.

By April 2014 everything was ready: The authorities had carried out preliminary tests to determine the sludge height and the special OASE boat set off to spread the necessary 1.5 tonnes (1.65 US tons) of SchlixX Plus over half of the Quellitzsee. Everything went perfectly – except the weather conditions. When checks were carried out, it was discovered that, due to the low temperatures, the sludge had formed a solid, impermeable surface. As a result, the applied material was not able to penetrate the sludge to take effect. However, the OASE specialists also found a solution to this challenge: They developed an injection procedure that enabled SchlixX Plus to penetrate even the lower layers of sludge.

The Successes:
To record the effects of applying SchlixX Plus, the authorities arranged for the sludge height to be regularly measured by divers – in secret locations to rule out any tampering. The results brought to light by the divers could not have been clearer: By June, the sludge height had already decreased by 10 to 15 cm (3.94 to 5.9 in). And by July 2014, an incredible sludge reduction of 50–75% of the original amount was announced.

The water authority, the health authority, OASE itself and the members of the fishing association drew a clear conclusion from their tests: Applying the product did not affect the quality of the water – but it did break down considerable amounts of sludge. There were other positive effects as well: The reduction in organic material removed a food source for the algae, making it more difficult for them to propagate. And all this cost significantly less than the conventional dredging procedure.

At the end of the treatment period, the original enormous sludge height in the lake had decreased to a layer of just 5 to 25 cm (1.97 to 9.84 in). This result pleased nature lovers, bathing visitors, anglers and of course the regatta participants and organizers alike.