Living on water from Mars

Wastewater from the Mars factory in Veghel, the largest chocolate producer in Europe, feeds bacteria in an STW-funded pilot plant, producing bioplastic.

A tiny part (much less than a percent) of the cream-coloured wastewater stream containing sugars and fatty acids is drawn off toward a white container that houses the pilot plant. Operations here are run by Avans Academy student Casper Borsje and TU PhD-student Jelmer Tamis MSc. The process runs in three steps: fermentation, selection and accumulation.

In the first step, wastewater is fermented by microbes that convert all sugars in the solution into a mix of fatty acids. The fatty acid mix is kept in a steel vessel to be fed intermittently to the plastic-producing bacteria.

Earlier research from Prof. Mark van Loosdrecht’s group (faculty Applied Sciences) showed that if you apply a feast-famine regime to a mix of bacteria drawn from a wastewater, you end up with a population that quickly digests fatty acids into a sort of bacterial fat known as polyhydroxy alkanoate or PHA. This substance can be used as a bioplastic that is both biobased and biodegradable.

This population then goes on into the third phase in which they are fattened up into the extreme. In the lab, bacteria grew so obese that 80 to 90 percent of their dry body mass consisted of the PHA polymer. Such values have as yet not been attained in the pilot plant.

The pilot plant, which was built by Paques, has been operational since November 2012 and will probably be in use until the end of 2013. By that time, Tamis hopes to have increased the PHA content of the produced biomass, in order to bring down the production costs of the bioplastic and make sustainability more affordable.

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