Port of Oskarshamn, Sweden
Historic pollution addressed
Oskarshamn is a Swedish port town with a rich industrial history. A copper production site and battery factory discharged polluted wastewater into the sea since the mid-19th century. This resulted in heavy metals, PCBs – in full polychlorinated biphenyls – and dioxins infiltrating the seabed. As ships sailed in and out, the contaminated sediments also spread across the Baltic Sea.
The aim of the whole operation was to clean the contaminated seabed in the port basin. This covers an area of 500,000 m2 with 400,000 m3 of contaminated sludge. In March 2016, we started the remediation works by building facilities in the port that dewater the sediments and treat the released water. The project was completed in 2018.
Sofie Herman, Project Manager
There was nothing at all here, just the port and a large asphalt area that we were allowed to occupy. We brought all the components here to build the plant on site. From filter presses and thickeners to all pipes, scaffolding and steel structures.
Olivier De Lange, Offshore Superintendent
It is an atypical project for the dredging department. Because the dewatering plant can process only 1,000 m³ of sediment per day, we can dredge about one out of twelve working hours. Completely different from dredging projects where we dredge around the clock.
Port of Oskarshamn in numbers
Did you know?
- Until 2018, Oskarshamn harbour basin was one of the most polluted basins in Sweden.
- The design of the dewatering and treatment plants we built in the port was done entirely in house.
- For this project, we converted the cutter suction dredger Petrus Plancius into an environmental dredger. The head of the vessel was fitted with valves to remove contaminated sediment layers.
Port of Oskarshamn in detail
Cutter dredger Petrus Plancius carried out the rough work. For the areas with a lot of debris on the bottom – including stones – the trailing suction hopper dredger Pinta was used, which has a larger loading capacity and pump.
The Pinta pumps the dredged sediments to the plant built in the port. There, they immediately enter a sieve to separate the coarser material. The sediments then proceed to the thickeners. Through sedimentation, these provide the first major separation of the water and sediments. The water is pumped away to the water treatment plant. The sediments go to a silo for treatment and further dewatering. In the silo, we add milk of lime to accelerate dehydration. The final step in the dewatering process happens in the filter presses. There, the last water is pressed out of the sediments, leaving a hard cake. We dispose of this in a licensed landfill. The water coming out of the filter presses is purified. Part of it is reused as process water in the plant, while another part is released back into the sea after quality control.
