In two lakes near the Swedish city of Hultsfred, unacceptable amounts of mercury were encountered.
In the first phase of the three-year project, the mercury contaminated sediments were removed using environmental dredging techniques. A system of geotubes® was used to dewater the sediments. With a diameter of several meters and at 50 to 100 m long, these geotubes® can be compared to geotextile socks. In this way, the sediments were encapsulated and the surrounding soils were protected. The water originating from the dewatering process was purified before discharge.
The process water was collected in a buffer basin from where it was pumped into a biological water treatment unit. Due to the sensitivity of the biological treatment to pH fluctuations, the water was brought to a neutral pH value. The water was then purified in batches: initially there is an aeration phase to feed the activated sludge system, then this is followed by an anoxic phase and finally a settlement phase. Prior to discharge, the residual sludge particles were filtered in a sand filter. The purified water was then ready for discharge.