| Over the past years, the nondegradable petrochemical plastics accumulating in the environmenthas exacerbated the problem of disposal of solid waste. In response to the problem and harmfuleffects of the plastic wastes on the environment, there is considerable interest in the developmentof biodegradable plastics. In the latest decades, polyhydroxyalkanoates (PHAs) have attractedincreasing interest as an alternative to petroleum-derived plastics for it having similar mechanicalproperties to those of polypropylene, meanwhile, with the additional advantage of beingcompletely biodegradable, biocompatible, and produced from renewable resources.Among the methods, for industrial production of PHAs, the aerobic dynamic feeding (ADF)approach by activated sludge is the most promising because of high PHA accumulation,meanwhile, this method could substantially decreasing the cost of PHA and increasing theirmarket potential for using activated sludge and renewable sources obtained from waste organiccarbon. A number of studies have been carried out on PHA production with activated sludge underADF conditions, but it is still few study on the cultivation of microorganism with high PHAstorage ability by activated sludge from municipal wastewate treatment plant under ADFconditions. There is also no studies reported about the effect of magnetic field on the synthesis ofpolyhydroxyalkanoates by activated sludge under ADF condition.Our work aimed at these two problems and the effect of permanent magnetic field on theproduction of polyhydroxyalkanoates(PHAs) by activated sludge under ADF conditions and thecultivation of microorganism with high PHA storage ability by activated sludge from municipalwastewate treatment plant under aerobic dynamic feeding conditions was evaluated.The results were as follows:1) It was effective of acclimating activated sludge by gradually increasing organic load underADF conditions. The effect was depend on the the start-up organic load as well as its increasingrate and the "feast"/"famine" ratio. The content of PHA in biomass increased from 1.24ï¼…to40.62ï¼…when the organic load increased gradually to 6.48gCOD/l in 30 days with the start-uporganic load was 1.096gCOD/l and the "feast"/"famine" ratio was 1: 1,but the system was unstable. Whereas, the content of PHA in biomass increased from 8.74ï¼…to 50.24ï¼…when theorganic load increased gradually to 6.48gOOD/l in 35 days with the start-up organic load was0.36gCOD/l and the "feast"/"famhae" ratio was 1: 3, meanwhile, the system was stable. Thelower organic load during start-up will benefit to drivie the system toward one "steady-state"where storing biomass will be dominating the microbial consortium. In order to avoid selecting formicroorganisms with a growth response, after the selection at the lower organic load occurred, theorganic load must be further increased step by step and the "feast" phase could last too long.2) The static magnetic exposure had definitely infuenced the biosynthesis of PHAs and theeffect varies with field strength and substrate. It is different polyester synthases that engaged in theproduction of polymers varied with different substrates. The effect of static magnetic on differentpolyester synthases was dissimilarly. It was demonstrated that, under the same operationconditions, hydroxybutyrate(HB) content in biomass and storage yield reached the maximum at6.7mT, the minimum at 42mT. Whereas, hydroxyvalerate(HV) content in biomass and storageyield reached the maximum at 21mT, the minimum when without magnetic field.
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