From indus­trial age to green revolution

At Stock­holm Royal Seaport, a new, sustain­able neigh­bor­hood is being built on an indus­trial site. But first, the cont­a­m­i­nated soil is being reme­di­ated with KLOZUR® persul­fates so that future resi­dents can live here in good health.

Viewed from above, the city of Stock­holm seems to shim­mer: Bright archi­tec­ture, green parks, and a network of bridges are densely clus­tered around wide chan­nels of the Baltic Sea.

These water­ways have been inte­gral over the years to Stockholm’s devel­op­ment into one of Europe’s lead­ing cultural and commer­cial centers. Yet the geog­ra­phy is not with­out its drawbacks.

Lack of space is a major contrib­u­tor to the current hous­ing crunch in Sweden’s capi­tal, a coun­try where nearly 90% of the popu­la­tion lives in cities.

A role model for green urban development

That is why the City of Stock­holm has under­taken a massive rede­vel­op­ment of its histor­i­cal Royal Seaport district.

The Stock­holm Royal Seaport was once the site of a sprawl­ing manu­fac­tured gas plant (MGP) and a main harbor for coal trans­port. Now, this area is poised to become an inter­na­tional role model for green urban living. When construc­tion is complete in 2030, at least 12,000 new homes and 35,000 work­places will be powered by renew­able energy and connected by public trans­port and walk­ing or cycling paths.

Circu­lar waste manage­ment and an inte­grated commer­cial and resi­den­tial concept aim to ensure self-suffi­ciency and a mini­mal envi­ron­men­tal foot­print. Desig­nated space for urban garden­ing, an acces­si­ble shore­line, and repur­posed indus­trial build­ings will trans­form the Stock­holm Royal Seaport from an aban­doned remnant of the city’s coal age into an attrac­tive and highly sustain­able new neighborhood.

Start­ing with a clean foundation

But first there is work to be done. Once the main source of power for indus­tri­al­iz­ing commu­ni­ties at the end of the 19th century, MGPs have left consid­er­able organic and inor­ganic cont­a­m­i­nants in the loca­tion where they oper­ated. Over time, these residues release emis­sions through soil vapors that can pose a health threat to people living in the area. Thor­ough soil reme­di­a­tion must take place before any build­ing can begin.

This is where persul­fates come into play. Sodium and potas­sium persul­fates are power­ful oxidants — in other words, they rapidly degrade harm­ful compounds into noth­ing but benign basic compo­nents, like oxygen and carbon. The KLOZUR® SP-brand envi­ron­men­tal grade sodium persul­fate produced by Evonik Active Oxygens has been formu­lated to treat a wide range of cont­a­m­i­nants, includ­ing the coal tar and naph­tha­lene commonly left behind by MGPs.

“One common way to restore cont­a­m­i­nated sites is simply to dig up the impacted soil and trans­port it away. But that just moves the prob­lem some­where else and causes traf­fic from heavy-load trans­port,” points out Josephine Molin, a Stock­holm native and Tech­nol­ogy Appli­ca­tions Manager for soil and ground­wa­ter reme­di­a­tion at Evonik Active Oxygens. “On-site treat­ment is a more respon­si­ble approach. Using prod­ucts like KLOZUR® SP actu­ally elim­i­nates the cont­a­m­i­na­tion right in place — or ‘in situ,’ as we say in the industry.”

For the Stock­holm Royal Seaport, the city decided on a method that combined soil stabi­liza­tion with cement binders and cont­a­m­i­nant destruc­tion using persul­fate. The less-perme­able clay layer will be mixed with persul­fates and binders to essen­tially seal away harm­ful substances through a combi­na­tion of oxida­tion and immo­bi­liza­tion. Mean­while, the more perme­able soil layers will be injected with persul­fate solu­tion in order to completely break down the harm­ful substances.

The full treat­ment with KLOZUR® SP is expected to be completed by 2024.

Ready for the future

Persul­fates are not only effec­tive at clean­ing up the residues of the past; they also have a role to play in build­ing a sustain­able future.

For one thing, persul­fates are produced through elec­trol­y­sis, a process that requires a lot of elec­tric­ity. The elec­tric­ity for Evonik’s persul­fate produc­tion is gener­ated by hydro­elec­tric power — an emis­sion-free power source.

For another, persul­fates enable in-situ reme­di­a­tion that allows for safe reuse of the site while keep­ing it funda­men­tally intact. There is no need to trans­port the cont­a­m­i­nated soil away in heavy trucks, which prevents emis­sions and is less disrup­tive to the surround­ing community.

“This kind of treat­ment harmo­nizes with the reduce-reuse-recy­cle approach of the whole Stock­holm Royal Seaport project,” says Josephine Molin. “The plant was once a major source of power for the city and impor­tant for its devel­op­ment. Today, we have the knowl­edge to move beyond fossil fuel, but this site and its infra­struc­ture will still contribute to power­ing a new, greener development.”

Molin smiles, “I rather like that the big old brick build­ings of the Stock­holm Royal Seaport are being repur­posed into cultural centers. We are setting the stage for the future by build­ing on the past.”