The industrial divers climb down into the sewage sludge wearing close-fitting, rubberised full-body suits and a 12kg helmet and carrying equipment weighing 65 kilos. Their job: to remove the deposits and solids from the warm (ca. 40 °C), viscous mixture of brown water and digested sludge. Working for their client EURAWASSER, these specialists are able to carry out their work without the facility having to be shut down. At the same time they protect the billions of tiny helpers: the bacteria responsible for breaking down the organic material.
The environmental divers worked in 70-minute shifts using suction equipment to clean the 15-metre high tower at the central sewage treatment plant in Goslar. This length of time was necessary as divers must always ascend very slowly to the surface. Nitrogen bubbles accumulate in divers’ joints when they are under water which cause pain similar to rheumatism. These are broken down when divers move slowly upwards towards the surface.
The divers had direct voice contact with their colleagues on the tower and they were also connected to a hose enabling them to cool themselves down with water if necessary – helping them to keep calm in these completely black surroundings. The consistency of the liquid helped them judge their position, as the sludge-water mixture is less thick in the middle of the digester. The further they moved towards the walls, therefore, the thicker the sludge became. Other resources were used to help them find their bearings such as ladders which were laid across the inside of the tank.
Industrial divers must also make safety stops as they move upwards towards the surface.
“The last time the tower was emptied, cleaned and renovated was 20 years ago,” explained Jörg Hinke, head of water management technology at EURAWASSER, the operator of the sewage treatment plant. The build-up of deposits reduces the capacity of the digester which in turn considerably slows down the digestion process. By deploying environmental divers to clean the facility, there is no need to remove the sludge. Operations in the digester can continue as usual which means the bacteria, which are primarily responsible for breaking down the organic material in the wastewater, are not destroyed.
Video impressions of the cleaning work carried out on the digester.