Study On Biosynthesis Of PHA From Hydrolysate Of Oil Palm Fruit

In order to reduce the production cost of bioplastic polyhydroxyalkanoate（PHA）and realize large-scale application in packaging field,the resource-rich and waste oil palm hydrolyzate was used as the carbon source to synthesize PHA by using activated sludge mixed microbial culture（MMCs）in this paper.Based on the ultrasonic assisted water-enzymatic extraction of palm oil,the effects of liquid-solid ratio,enzyme addition and enzymolysis temperature on the extraction rate of palm oil were investigated.Response surface design was used to optimize the technological parameters and analyze the chemical components of palm oil for analysis and identification.At the same time,collaborative wastewater and palm oil as carbon source,the use of activated sludge MMCs model,through exploring different nitrogen source,C/N ratio and C/P ratio conditions on the PHA synthesis and changes of microbial growth.The molecular structure of synthesized PHA was analyzed by gas chromatography-mass spectrometry,nuclear magnetic analysis and gel chromatography,which explored a new way for the low-cost and efficient transformation of PHA from agricultural and forestry wastes.The main conclusions are as follows:（1）With fruit of palm as raw material,the palm oil was extracted by ultrasound-assisted enzymatic aqueous method.Single factor experiment and Box-Benhnken experiment design and response surface analysis were used.Single factor experiment showed that the extraction rate of palm oil increased first and then decreased with the increase of liquid-solid ratio,enzyme dosage and enzymolysis temperature.The optimum extraction conditions was the ratio of liquid to solid 8.2﹕1,enzyme dosage of 4.2%and enzymolysis temperature 42℃.The extraction rate of oil under this condition was34.62%.（2）PHA was synthesized by aerobic process using enzymatically pretreated palm oil wastewater as carbon source.The factors affecting PHA synthesis in the reactor were investigated,including nitrogen source,phosphorus source,C/N ratio and C/P ratio.The results showed that the best nitrogen source was NH₄Cl and the best phosphorus source was Na₂HPO₄.After 12 cycles of cultivation,a high PHA yield of 805 mg COD/L was obtained under the conditions of C/N ratio of 33 and C/P ratio of 100.The monomers were HB（94%）,HV（2%）and HO（4%）.The bacterial genus showed a highly diverse microbial community for the synthesis of PHA.Microbial species analysis showed that the abundance of phylum did not change significantly under different conditions.（3）Using palm oil synergistic hydrolysate as carbon source to biosynthesize PHA under aerobic conditions.The effects of p H value,different carbon source concentrations and the ratio of mixed carbon sources on the yield and composition of PHA were studied.The microbial diversity analysis was carried out.At the same time,the extracted PHA was analyzed by NMR and GPC.The results showed that the acidic or alkaline environment was more conducive to the accumulation of PHA by microorganisms.The total PHA yield increased with the increase of carbon source concentration,and the PHO content increased with the increase of palm oil concentration.The maximum PHA yield was 1073.13 mg COD/L when the carbon source concentration was 2000mg/L.NMR analysis showed that the synthesized PHA was PHBV and PHO.