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Before environmental awareness became the norm, it was not uncommon for sea and river beds to become contaminated with pollutants. In Gothenburg, the clay at the bed of the Göta Älv River contains a range of substances, including TBT (tributyltin), an environmental toxin that was previously used in antifouling paints on the hulls of vessels.
When the Port of Gothenburg set about planning a new freight terminal, it decided to build it using clay spoils from Göta Älv. However, due to the presence of contaminants in the mud, including TBT (tributyltin), significant volumes of residual water need to be pH-neutralised and purified before being released back into the sea.
“The material we’re working with is alkaline and the high pH level creates a greater risk of the TBT being freed and released into the environment,” explains Kristina Bernstén, environmental project manager at the Port of Gothenburg.
When it comes to pH, a level of seven is neutral. Anything below six is acidic, while anything above eight is alkaline. Both extremes are potentially harmful to people, animals and the environment. Due to the stricter environmental regulations in place these days, wastewater can only be discharged into outlet channels if it is within a narrow pH range around the neutral point.
At the Port of Gothenburg, the displaced water is pH neutralised using a technology from Linde known as SOLVOCARB, which uses carbon dioxide (CO2) gas to neutralise the alkaline waters. Linde has provided a SOLVOCARB mobile unit – the first of its kind to be installed in the Nordic Region – through which the contaminated water is processed. When dissolved in water, carbon dioxide forms carbonic acid, which reduces the pH value of the water.
“By maintaining the pH of the displaced water at a neutral level and by purifying the water through subsequent sedimentation and filters, we ensure that the TBT remains safely bound up, thereby making it inaccessible to the aquatic organisms in the water,” she continues.
Whereas most pH-neutralisation solutions use mineral acids to reduce alkalinity, Kristina Bernstén says CO2 is a safer, more sustainable option.
“Using CO2 for pH adjustment comes with two major advantages: Firstly we can avoid potentially reducing the pH in the water so much that it becomes too acidic. Secondly, it is far safer from a working environment perspective, since handling acids can always be a risky business,” she explains.
Johan Magnusson is the CEO of Clean Water Engineering, the company responsible for water treatment at the Port of Gothenburg.
“The SOLVOCARB unit is able to dissolve a large amount of CO2, even with its small footprint. This is a great advantage when it comes to dealing with high flows and large volumes of water with a high pH,” says Magnusson.
Eva Ålander, water treatment technology expert at Linde Europe North, says the SOLVOCARB mobile unit provides robust, safe pH-control solution, adding: “Using CO2 also eliminates the harmful, toxic environmental risks associated with use of corrosive mineral acids.”
Tomas Nordås, application engineer and project manager of the Arendal installation, agrees: “Earning trust and living up to customer expectations is of huge importance to us at Linde,” he concludes.
Carbon dioxide can be used for pH control across a variety of industries from food to textile, pulp and paper, chemical and petroleum. In addition to wastewater treatment, it can be used to pH control process water and for increasing the alkalinity and remineralisation of drinking water.
The Port of Gothenburg is strategically located on the west coast of Sweden. Approximately 70% of Sweden’s total population and industrial capability is located within a 500-km radius of the port, which currently manages close to 30 per cent of Swedish foreign trade and operates 130 direct services to destinations in Europe, Asia, the Middle East, Africa and North America.