The tons of salt that are sprayed on the roads every year are harmful to the environment. But there is no good alternative to de-ice roads when temperatures drop below zero degrees Celcius. Not yet, at least. Wageningen UR Food & Biobased Research works with a number of regional partners on the production of de-icing salt which is made from biomass: roadside grass or kitchen waste. In 2020 it should be possible to produce this "green salt" on a large scale, predicts initiator Pieternel Claassen of Wageningen UR Food & Biobased Research.

Acetate and hydrogen

The "green salt" is an organic salt: Calcium Magnesium Acetate (CMA). CMA can be produced from fossil raw materials, but some bacteria can also produce acetate (the basis of CMA) from biomass. Laboratory tests have proven that bacteria can convert sugars into acetate and hydrogen. The hydrogen can be used for the production of energy or chemicals; acetate can be used for de-icer. Researchers are currently working on scaling up the fermentation process. Claassen, researcher at Wageningen UR: "Green raw materials, such as roadside grass and swill, contain many sugars. They can therefore be used to make hydrogen and acetate. But recovery of the products is not easy."

Faeces of bacteria

In 2020 it should be possible to produce "green road salt" on a large scale, predicts initiator Pieternel Claassen of Wageningen UR Food & Biobased Research. Photo Credit: Wageningen UR

The main disruption of the fermentation process is caused by the very products the bacteria produce. Acetate and hydrogen are basically the faeces of the bacteria. If the microorganisms keep swimming around in their own faeces, they suffocate. Therefore, Wageningen scientists, together with technology firms, are examining ways to harvest the acetate and hydrogen while the fermentation process continues. "We are involved in a project proposal that is aimed at designing new methods to extract the acetate and hydrogen, separately, from the reactor vessels," says Claassen.

Partners

Because it is possible to get more value from waste streams, a wide variety of parties have joint forces in this TOPAAS project (Technical Development for the Production of Acetate Salts as Alternative De-icing Agent). For instance, there is Heijmans, a company responsible for mowing roadside grass, Van Gansewinkel, which collects organic waste from restaurants, HYET for efficient hydrogen processing and Nijhuis Water Technology as a specialist in bioprocess reactors. The government institution responsible for road maintenance, Rijkswaterstaat, is also involved and the Province of Gelderland subsidizes a large part of the research.

Wageningen UR Food & Biobased Research also coordinates the European project HyTime, in which the same bacteria are used to produce hydrogen. A by-product of this process is acetate. A possible application has now been found for this by-product, making hydrogen production from biomass also more economically viable.

Less rust

It remains to be seen whether CMA will be used widely on Dutch motorways, because CMA produced from biomass is not expected to be cheaper than petrochemical CMA, which is about ten times as expensive as ordinary salt. But CMA is sometimes used at airports, because it is less corrosive than sodium chloride. And in areas with unique nature, the choice for the more environmentally friendly CMA could also prevail over the use of ordinary road salt.