Process Optimization For Polyhydroxyalkanoate Production By Activated Sludge

A new kind of biodegradable polymer—polyhydroxyalkanoate(PHA) is researched as a potential solution to the environmental problem of plastics pollution, but the expensive price restrict the large-scale commercial exploitation. For decreasing the cost, many researchers use the inexpensive mixed culture biomass, such as activated sludge, to replace the pure culture. The study showed that activated sludge could synthesize PHA from organic wastewater, but the content of PHA in biomass is lower than pure culture, which increase the cost of extraction.The synthesis of PHA by activated sludge was influenced by the factors such as operational process, experimental condition. For improving the utilize rate of substrate and the content of PHA in biomass, this study optimized the operational process and experimental condition of the PHA synthesized by activated sludge.(1) Study the different magnetic field intensity and C: N ratio by changing the intensity of magnetic and the ratio of C: N. Optimized the operational process and experimental condition of the PHA synthesized and decided the favored magnetic field intensity and C: N ratio.(2) Utilized the response surface methodology (RSM) to optimize the operational process and find out the interactive effects of four variables, i.e. static magnetic field intensity, concentration of NH3-N and initial pH on PHA production by activated sludge.(3) Changed the compositional ratio of acetate and propionate in substrate under different magnetic field intensity. The relation between the compositional ratio of acetate and propionate and the ratio of hydroxybutyrate(HB) and hydroxyvalerate (HV) in copolymer has been studied for explorering a new approaches to optimize the composition of copolymer.The main results were as follows:(1) When the synthesis were operated by the magnetic field with 0mT, 3mT, 7mT, 11mT, 16mT, 21mT, 25mT, 30mT, we found that HB content in biomass reached the maximum at 7mT; HV content in biomass reached the maximum at 21mT; magnetic field restricted the biomass growth.(2) When we changed the C: N ratio, the biomass growth was decreased by the increased C: N ratio, and the PHA content increased for the more substrate converting to PHA synthesis. At 0mT PHA content in biomass reached the maximum of 43.09% under the C:N ratio of 200:1; at 7mT PHA content in biomass reached the maximum of 43.90%with no nitrogen added; at 21mT PHA content in biomass reached the maximum of 44.47% under the C:N ratio of 100:1.(3) The contour plots in response depicted the variation in PHA yield, as a function of interaction of variables. It is concluded that decreasing magnetic field and NH3-N and increasing pH resulted into rise in PHA content. The optimum conditions for maximum PHA yield as follows: magnetic field 11mT, C: N ratio of 100:1, initial pH 9.0 and the corresponding PHA yield of 39.8% (dew). The experimental value of 39.6% (dcw) is well in agreement with that of the predicted one.(4) The substrate uptake rate reached the maximum under the acetate: propionate of 60:40(COD: COD). Magnetic field would accelerate the uptake rate of substrate and influenced the PHA synthesis. Compared with 0mT, at 7mT more substrate converted to HB; at 21mT more substrate converted to HV; the effect of 11mT on PHA synthesis between the 7mT and 21mT.