Research On New Process Of PHA Production Using Activated Sludge Based On Dynamic Pulse Discharge-aerobic Dynamic Feeding Mode

Polyhydroxyalkanoates(PHAs) is a kind of inner energy storage material that can be produced by PHA accumulating bacteria under unbalanced growth conditions. Because PHAs can be completely biodegraded and can be made from wasted carbon source, they are expected to become a substitute for the traditional plastics. The biosynthesis of commercial PHAs is mainly from pure bacteria fermentation, however, the high cost of raw material, disin fection and purification of microbes limits its large-scale application. The use of mixed culture, such as activated sludge, to synthesize PHA with the selection process of ADF(Aerobic Dynamic Feeding) mode has become a hotspot in the field of biosynthesis of PHAs. However, the overall PHA synthesis ability is quite low and the selection and enrichment period of PHA producing mixed culture is very long under ADF process. An dynamic pulse discharge-aerobic dynamic feeding mode(Abbreviation:Aerobic Dynamic Discharge, ADD) mode was proposed in this study based on the ADF mode. The ADD process was used for selection the efficient PHA production culture from activated sludge system. The main influencing factors of the process were analylized and optimizated, a fast and stable synthesis of PHA was realized by activated sludge under the new operating mode.Considered that both PHA producing bacteria and aerobic granular sludge settled quickly, aerobic granular sludge was produced and used to synthesis PHA in this research. Selection and enrichment of PHA producing culture was conducted under the ADF mode when sludge settleability screening was imposed. A PHA content of 58.3% was achieved under the operation condition with aerobic granular sludge after 30 days operation. A comparison was conducted between the ADF mode and sludge settleability screening plus ADF mode, the results showed that the introduction of the sludge settleability screening improved the number of PHA producing bacteria in the mixed culture significantly, and the impose of sludge settleability screening also improved the PHA content of the mixed culture.ADD mode was proposed and used for the selection and enrichment of efficient PHA producing mixed culture based on sludge settleability screening. The operating parameters were optimized, an initial selective pressure strength of 0.8-0.9 was found to be the best value for ADD operating mode. ADD mode was proved to be able to promote PHA synthesis efficiency of the mixed culture and save the time required for the enrichment phase.Research based on BP artificial neural network model, the parameters of the coupling for the operation mode of the ADD under the action of various parameters on the content of the PHA in SBR reactor effect(used to describe the improve the effect of PHA synthesis of bacteria concentration in the mixed bacteria) sensitivity is analyzed. Using neural network model, the parameters of iterative calculation, optimizing the best operation parameter combination and experimental verification, get activated sludge mixed bacteria within 30 days of PHA production is 74.2wt%. Based on the experimental data, the lack of carbon source filling(feast) mechanism of microbial cell metabolism model, based on the proposed model is applicable to the ADD operation mode of metabolism.The multi-parameter sensitivity analysis of the influence on the PHA content(to describe the effect of PHA enrichment by the MMCs) was conducted based on BP Artificial Neural Network under the ADD operating mode. The optimized parameters got through the parameter iteration calculation ANN model were verified by the followed experiment involved the optimized parameters. The maximum PHA content of 74.2wt% was achieved after 30 days operation. A metabolic model applied to ADD mode was proposed on the basis of the feast-famine regime.PHA producing performance with mixed carbon source under ADD mode with optimized operating parameters was conducted. The simulated fermentation liquid of kitchen waste was used as the mixed carbon source. The content of the even and odd carbon source were 77.4%(mol%) and 18.7%(mol%), respectively, in VFAs of the simulated fermentation liquid of kitchen waste. The consequent monomer component HB and HV accounted for 78.5% and 21.5% of the total PHAs. 52.8% of the PHA content was achieved when the simulation mixed carbon source was added. Under an optimized process of the third phase(PHA accumulation), the PHA content of 58.4% of the dry cell weight was achieved. A metabolic model was developed for the ADD mode with mixed carbon source and the ANN model were used to predict the PHA content. The simulation results showed that the selection process operated under the ADD mode could maintain the stability after 30 days accumulation.