Up-Cycling of PET (Polyethylene Terephthalate) to the Biodegradable Plastic PHA (Polyhydroxyalkanoate)

Abstract

The conversion of the petrochemical polymer polyethylene terephthalate (PET) to a biodegradable plastic polyhydroxyal-kanoate (PHA) is described here. PET was pyrolised at 450 degrees C resulting in the production of a solid, liquid, and gaseous fraction. The liquid and gaseous fractions were burnt for energy recovery, whereas the solid fraction terephthalic acid (TA) was used as the feedstock for bacterial production of PHA. Strains previously reported to grow on TA were unable to accumulate PHA. We therefore isolated bacteria from soil exposed to PET granules at a PET bottle processing plant From the 32 strains isolated, three strains capable of accumulation of medium chain length PHA (mclPHA) from TA as a sole source of carbon and energy were selected for further study. These isolates were identified using 16S rDNA techniques as P. putida (GO16), P. putida (GO19), and P. frederiksbergensis (GO23). P. putida GO16 and GO19 accumulate PHA composed predominantly of a 3-hydroxydecanoic acid monomer while P. frederiksbergensis GO23 accumulates 3-hydroxydecanoic acid as the predominant monomer with increased amounts of 3-hydroxydodecanoic acid and 3-hydroxydodecenoic acid compared to the other two strains. PHA was detected in all three strains when nitrogen depleted below detectable levels in the growth medium. Strains GO16 and GO19 accumulate PHA at a maximal rate of approximately 8.4 mg PHA/l/h for 12 h before the rate of PHA accumulation decreased dramatically. Strain GO23 accumulates PHA at a lower maximal rate of 4.4 mg PHA/l/h but there was no slow down in the rate of PHA accumulation over time. Each of the PHA polymers is a thermoplastic with the onset of thermal degradation occurring around 308 degrees C with the complete degradation occurring by 370 degrees C. The molecular weight ranged from 74 to 123 kDa. X-ray diffraction indicated crystallinity of the order of 18-31%. Thermal analysis shows a low glass transition (-53 degrees C) with a broad melting endotherm between 0 and 45 degrees C.

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.…”

Plant Oils and Products of Their Hydrolysis as Substrates for Polyhydroxyalkanoate Synthesis

“…Pseudomonas putida GO16 was grown on MSM medium supplemented with sodium terephthalate (TA) (1.95 g carbon L -1 ) and solidified with 15 g L -1 agar as it grew poorly on PIA. TA was used as a selective carbon source, to lower the risk or contamination by other bacterial strains, as P. putida GO16 was originally isolated using this carbon source 54 Growth conditions for PHA accumulation in shaken flask cultures Growth experiments were carried out in 250 mL Erlenmeyer flasks containing 50 mL of nitrogen-limited MSM medium supplemented with the appropriate carbon source at a concentration of 3 g L -1 . Ammonium chloride in this medium was limited to 0.25 g L -1…”

“…Sample concentration of 1 % (w/v) and injection volumes of 500 µL were used. A molecular weight calibration curve was generated with polystyrene standards with low polydispersity 31 . Differential scanning calorimetry (DSC).…”

“…These oils are among the nine major vegetable oils produced globally 31 . The EU is the world's leading producer and consumer of olive oil and rapeseed oil, and a major producer of sunflower oil.…”

On the brink of a recycling revolution?

“…The microbes in O'Connor's study (8), which the scientists isolated from soil exposed to PET granules, use the TA, composed of carbon, hydrogen, and oxygen, to string together monomers of 3-hydroxydecanoic acid into PHA. That technology has been spun out into a company called Bioplastech Ltd., in Dublin, which has taken on the major challenges of scaling up the technology and making it economically competitive.…”