Turning Pest into Concrete: Swiss Cantons Test Mussel Cement

When nature disrupts regional commerce, public authorities usually reach for expensive heavy machinery. In the High Rhine between Diessenhofen and Stein am Rhein, the biological offender is the Quagga mussel. Widespread across Lake Constance and the Rhine, with females laying up to a million eggs a year, dead mussels accumulate on the riverbed. During low water periods, this sediment halts navigation entirely—forcing the local shipping company, Schifffahrtsgesellschaft Untersee und Rhein, to suspend operations for roughly a month last year.

The traditional bureaucratic remedy of dredging and dumping immediately ran into financial realities. As Martin Eugster, head of the Thurgau Environmental Office, pointed out, large-scale dredging was suspended because costs were high and disposal avenues unclear. An interim attempt this summer to simply stir up the riverbed with excavators in the hope that currents would wash the shells away yielded only brief relief.

Now, Thurgau and Schaffhausen are turning to a pragmatic alternative: transforming environmental waste into an industrial resource. Investing tens of thousands of Swiss francs, the cantons have initiated a pilot scheme to supply a local cement factory with approximately 100 cubic meters of excavated mussel sediment.

The economic logic hinges on chemistry. The mussel shells consist of ninety percent limestone, theoretically making them a suitable substitute for mined natural limestone. The key question is whether replacing raw stone with biological lime compromises manufacturing stability. Dino Giuliani, the cantonal engineer for Schaffhausen, noted that industrial trials should show whether the process remains stable even with shell lime.

Alongside cement production, the cantons are evaluating whether the crushed shells can serve the fertilizer industry, with results from both assessments expected by the end of the year. A similar recycling experiment is already underway in Western Switzerland. Whether commercial processing can offset the relentless reproduction of the species remains an open question, but monetizing a biological nuisance beats throwing taxpayer money down a river.

Written by Martina Kirchner martina.kirchner@alpineweekly.com