A common scenario for industrial customers is that their operations often take place over large areas, and this project was no exception. Stena Recycling’s facility in Halmstad covers 100,000 m² of paved surfaces where rain and meltwater are collected and directed to the stormwater system. To manage the water before treatment, it is directed to a pond with a volume of approximately 8,800 m³. The pond functions both as a buffer reservoir and contributes to some purification through pre-sedimentation.

Feasibility studies to find the best solution

Preparations for the project began as early as September 2023 and included an initial overview of the pond’s sizing from Stena, as well as evaluation criteria for the process solution. Swedish Hydro Solutions also conducted site visits to Stena Recycling. At this stage, an initial sketch of the treatment process was developed, but to identify the most effective treatment products for the project, bench tests were also carried out. A total of six tests were conducted, three of which were sent to a laboratory to assess the treatment efficiency.

Finally, after receiving the analysis results, an evaluation was made of which technology was best suited for the facility, from both an economic and performance perspective. The decision was made to use a technology that involves chemical precipitation and flocculation with specifically formulated chemicals, followed by sedimentation in a lamella clarifier.

After treatment, the water is collected in a container where pH, conductivity, and turbidity are measured and logged in real time. Alarms can also be linked to these parameters, which are received by both Stena and us.

The installation area for the facility ended up being 16 x 7 meters in total.

Analyses are submitted monthly, and sampling is done using an automatic sampler. The County Administrative Board's new requirements are strict—Stena Recycling is allowed a maximum of two samples per year that exceed the emission limits by up to 50%.

– We conducted a very intensive testing period over the summer to ensure that Stena Recycling felt confident and well-prepared for the implementation of the new requirements in the fall. All samples have shown very positive results, and we have remained well below the guideline values, says Andreas Pettersson, Project Manager at Swedish Hydro Solutions.

One example is that Stena Recycling previously had a limit of 0.05 mg/L for chromium. After the water has been treated at the facility, the chromium levels have ranged between <0.00050 mg/L and 0.00086 mg/L.

The new requirements from the County Administrative Board are based on updates made to the EU Industrial Emissions Directive (IED) in August 2024. You can read more about the updates and their significance for industries here: https://swehydro.com/news/updates-IED

The facility currently installed at Stena Recycling has a capacity to treat up to 40 cubic meters of water per hour.

– We started by treating about 20 m³/h and gradually optimized the dosage of flocculation and precipitation chemicals. Recently, we've reached a capacity of 35 m³/h, but the facility is designed to handle up to 40 m³/h, says Andreas.

– The facility has been in operation since its launch and has treated large volumes of water, resulting in a low water level in the pond. This has meant that, on certain days, Stena hasn’t needed to pump water to the facility. The sunny days in September have naturally helped, but the facility is also capable of handling the larger volumes expected when the autumn rainstorms arrive, he adds.

The facility is also prepared for stricter future requirements and can easily be scaled up if necessary, including by adding our BioMedia® and physical filter. These are two filtration methods that are particularly effective against metals and suspended solids.

Dewatering bags for sludge

The bench tests conducted in the initial phase of the project indicated relatively low amounts of sludge. However, if the sludge levels were to increase in the future, the facility will be supplemented with sludge dewatering, specifically using our dewatering bags. This is a passive method where water passes through a special textile that captures sediment, sludge, and other particles. It is a cost-effective solution for handling and removing sludge, as it results in drier, more compact sludge and reduces handling costs.