Research On Influence Factors And Optimized Strategies Of Mixed Cultures PHA Production Process

As an optimal alternative to the conventional petrochemical plastics,polyhydroxyalkanoates (PHAs), which have the similar characteristics with traditionalplastics and good biodegradability, are always the hot topic of researches in recentdecades. Microbial organisms will uptake the external carbon sources and translate theminto the intracellular polymer in the form of PHA when the electron donor/acceptor(anaerobic-aerobic process) or substrate (aerobic dynamic feeding process) existsdiscontinuously in the surrounding environment. The large scale applications of PHAconcentrate in the pure bacterium fermentation processes, however, the raw material andstrict sterilization environment have increased the cost of production, so the furtherextension is restricted. The production costs have been largely reduced since the mixedcultures PHA production process was put forward, then the activated sludge with largeamounts of microbial organisms and organic wastewater rich in carbon sources attachedthe attention of researchers, hence the mixed cultures PHA production process are ofsignificant environment benefits.In the mixed cultures PHA production processes, the three-stage process, whichcomprises the acidification of organic wastewater, the enrichment of PHA storingorganisms and the PHA batch production, has been studied mostly. The second stageholds the core part of the whole process. Finding the way to enhance the select pressureand to promote the PHA storing ability of mixed cultures is a key problem. Otherwise, astable as well as efficient batch PHA production mode is needed to realize the fullstorage potential of the enrichments.In this study, the impact of sludge retention time (SRT) and initial seed sludgeconcentration on the enrichment of PHA storing organisms, which contains theoperational stability, the enrichment effects and the maximum storing ability of theenrichments, was evaluated using the three-stage process as platform and sugarwastewater as substrate. The T-RFLP was used to realize the primary analysis of mixedmicrobial organisms in the selectors. The feed regime and reactor type of the batchessays were improved, and the utilization of different VFA components was identifiedand discussed.When compared with the selector with SRT of10d, the selector with lower SRT(5d) showed a more stable state under the influent concentration of2520mgCOD/L,from which healthier sludge property and better enrichment results were obtained. Theenrichments from the selector with the SRT of5d could accumulate maximum up to61.26%PHA of cell dry weight in the batch essays. The results of T-RFLP analysis showed a more sample microbial organisms structure in the reactor with SRT of5d,which indicates that mixed cultures in the reactor were under a stronger selectivepressure. The selector with higher initial seed sludge concentration showed a pooroperational stability, in which two deteriorations of sludge property were foundsuccessively. However, the PHA storing ability of the selector with higher initial seedsludge concentration was not significantly inhibited and the maximum PHA contentcould reach to57.84%of cell dry weight in the batch experiment. The impactmechanism of SRT on the PHA storing-organisms enrichment process was reconsideredbased on the experimental results. The EPS of microbial organisms in selector underADF (Aerobic Dynamic Feeding) mode showed some regular variation along theenrichment cycle. The batch reactor under the continuous feeding mode kept the PHAproduction rate at a high level. The specific influent mode could avoid the substrateinhibit action properly, and the problem caused by poor sludge settleability could besolved effectively. The microbial organisms would form a specific community structureby feeding the substrate with a specific component during the long enrichment cycle,which showed a corresponding uptake regularity of VFA.