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.

Oxidized Polyethylene Wax as a Potential Carbon Source for PHA Production

“…The environmental and health impact of these plastic wastes are severe and have been extensively discussed by previous authors [6]. Polyethylene (PE) is known to be the most manufactured petrochemical polymer making up over 29% of global petrochemical plastic production [7] and with only 10% of plastic waste presently being recycled [8], there is a huge demand for alternative uses of these waste materials to reduce the environmental burden they have on today’s society.…”

“…Oxidation of PE can generate a valuable feedstock in the form of oxidized PE wax rich in hydrocarbons. Some microbes should be able to use this highly complex substrate for synthesis of the added value biodegradable polymers such PHA, therefore, the conversion of PE to a high value product should lead to higher level of PE recycling [7]. This process should also have an impact on the production cost of PHA as the use of waste O-PEW feedstock for microbes accumulating PHAs can lead to their greater economic viability and sustainability.…”

Start a Research on Biopolymer Polyhydroxyalkanoate (PHA): A Review

“…Pseudomonads are also well-known for their bioremediation properties including the biodegradation recalcitrant and/or toxic aromatic carbon substrates [98], and have been successfully applied in the treatment of contaminated effluents, exhaust gas and soils [99][100][101]. Recent studies demonstrated that aromatic-degraders P. putida F1 (DSM 6899), P. putida mt-2 (NCIMB 10432), and P. putida CA-3 (NCIMB 41162) could bioconvert toxic pollutants benzene, toluene, ethylbenzene, xylene (BTEX) and styrene to mcl-PHA [86] [76,77,80], which offers the potential benefit to off-set waste treatment cost through PHA recovery.…”

Synthesis Gas (Syngas)-Derived Medium-Chain-Length Polyhydroxyalkanoate Synthesis in Engineered Rhodospirillum rubrum

“…Alternatively, readily available fatty acids that are metabolized to 3-hydroxyacyl-CoA through ␤-oxidation can be converted to a substrate for the PHA polymerase PhaC. Many recent studies have focused on the efficient production of PHA MCL in wild-type and recombinant microorganisms from abundant and cheap carbon sources, such as carbohydrates (6), fatty acids (7), or even polyethylene and aromatic compounds (8,9).…”

“…Synthesis of poly(3-hydroxybutyrate) [poly(3HB)] is deactivated by the deletion of phaC1 R. rubrum and phaC2 R. rubrum , which code for PHA SCL synthases (6). Additional carboxylases, which might be also involved in assimilating additional CO 2 (16), include a pyruvate synthase (Rru_A2398 [7]), a crotonyl-CoA reductase (Rru_A3063 [8]), a propionylCoA carboxylase (Rru_A1943 [9]), and a 2-oxoglutarate synthase (Rru_A2721 [10]). HS-CoA, coenzyme A thiol; HS-ACP, acyl carrier protein thiol.…”