Synthesis Of Polyhydroxyalkanoates (PHA) By Propylene Oxide Wastewater Activated Sludge Bacterial Consortium From Excess Sludge Fermentation Liquid

It is of great significance to synthesize polyhydroxyalkanoates(PHA) by activated sludge bacterial consortium from the excess sludge fermentation liquid using anaerobic sludge digestion which will result in the sludge difficult to deal with reduction and recycling and greatly lower the cost of PHA production. Accordingly, PHA production by propylene oxidewastewater activated sludge bacterial consortium from excess sludge fermentation liquid is important to solve this problem.The composition and content of hydrolytic acidification liquid generated by the sludge anaerobic digestion was firstly explored in this paper. However, the content of volatile fatty acids was lower. In order to guarantee the stability and reliability of the PO wastewater active sludge in subsequent experiments, a series of studies on PHA production was conducted. It was demonstrated that the PHA production from PO saponification wastewater activated sludge was dependent on the type and consumption of VFAs.Firstly, by using anaerobic digestion method, the kinds, content and proportion of the excess sludge fermentation liquid produced under different temperature and pH conditions were analyzed. It was exhibited the resulting VFAs mainly consisted acetic acid, propionic acid, butyric acid with low content. Under the condition of temperature37°C and pH 5, the maximum yield of acetic acid was about 470 mg/L, and the proportion of three kinds VFAs was 2:1:1.In order to further study the PO saponification wastewater activated sludge for PHA accumulation, four different proportion of VFAs were explored as the substrate, and it was showed that maximum PHA yield and the fastest VFAs consumption were achieved when acetic acid: propionic acid: butyric acid = 2:1:1 was carried out, and the PHA production rate can reach 24.20%.Sequencing batch reactor was then performed for activated sludge bacterial consortium from the simulate excess sludge fermentation liquid(acetic acid: propionic acid: butyric acid = 2:1:1) to produce PHA.The samples was taken outevery 2 hours before 16 hours and 4 hours after 16 hours. Part of the samples were stored in the refrigerator to determine the concentration of PHA and VFAsby chromatographic analysis. The maximum PHA production reached at 16 hour which occupied about 25% of the dry weight of the sludge. From the monomer ratio analysis, it was demonstrated VFAs with even number of carbon atoms were in favour of 3HB synthesis and VFAs with odd number of carbon atoms were conducive to the synthesis of 3HV.Another part of the samples preserved in liquid nitrogen were used to study the molecular mechanism of PHA synthesis. By means of RNA extraction, reverse transcription and real-time fluorescent quantitative PCR, positive correlation was indicated between PHA accumulation and the expression level of phaC gene.This work will lay a solid foundation for large-scale production of PHA by activated sludge bacterial consortium from the excess sludge fermentation liquid, and the exploration of the effect of phaC on the yield of PHA will provide a reference for further research.