Conversion of post consumer polyethylene to the biodegradable polymer polyhydroxyalkanoate

Abstract

A process for the conversion of post consumer (agricultural) polyethylene (PE) waste to the biodegradable polymer medium chain length polyhydroxyalkanoate (mcl-PHA) is reported here. The thermal treatment of PE in the absence of air (pyrolysis) generated a complex mixture of low molecular weight paraffins with carbon chain lengths from C8 to C32 (PE pyrolysis wax). Several bacterial strains were able to grow and produce PHA from this PE pyrolysis wax. The addition of biosurfactant (rhamnolipids) allowed for greater bacterial growth and PHA accumulation of the tested strains. Some strains were only capable of growth and PHA accumulation in the presence of the biosurfactant. Pseudomonas aeruginosa PAO-1 accumulated the highest level of PHA with almost 25 % of the cell dry weight as PHA when supplied with the PE pyrolysis wax in the presence of rhamnolipids. The change of nitrogen source from ammonium chloride to ammonium nitrate resulted in faster bacterial growth and the earlier onset of PHA accumulation. To our knowledge, this is the first report where PE is used as a starting material for production of a biodegradable polymer.