The Brazilian chemical engineering students, Caio and Larissa, are now interns at the Centre of Expertise Biobased Economy for the WOW! project. Their research aims to optimize the production of biodegradable plastic (PHA) from secondary sludge. Caio en Larissa will continue the research of former Brazilian interns Tielly en Thalles.
PHA is a bioplastic that can be produced by PHA accumulating bacteria. Streams that contain volatile fatty acids (VFAs) or carbohydrates (like primary sludge from sewage treatment plants, or high concentrated industrial effluents) can be used as feed for a mixed culture of bacteria (aerobic sludge from a sewage treatment plant).
These bacteria are capable of converting these VFAs or carbohydrates to the bioplastic PHA. PHA is accumulated and stored inside the bacteria in intracellular granules. In order to improve the accumulation potential of PHA in the biomass, there is an enrichment step, which is a selection process of the best bacteria capable of producing PHA.
With this method, the content of PHA inside the biomass can increase from 30% to 50%. They also found out that the enrichment phase is important to modify the color of the biomass, which becomes lighter, and the aspects of the final plastic as well. The extraction of the PHA from the biomass is performed with dimethyl carbonate as a solvent, which is an environmentally friendly solvent, using a reflux process. Afterwards, the rotavap is used to obtain a usable bioplastic.