The water treatment plant has three large trickling filters - large round bins filled with granite rock. The wastewater trickles over the rocks and the algae growing on them.
The algae take massive amounts of nutrients out of the wastewater and clean it up. It’s a very robust and natural process, accelerated by engineering technology.
The algae attract small snails (about 3 millimetres long), which just love the environment in the trickling filter – it is wet and full of food. The snails grow there by the billions.
Every now and then a few snails are swept out with the wastewater and are filtered out before the water goes to further cleaning.
Those “few snails” however, add up to two to three cubic metres per week. We put them in our snail bin and empty it every week.
However, this is long enough for it to develop one of the worst smells in the wastewater treatment plant.