Research On PHAs Production From Activated Sludge Under The Co-effect Of "Feast"/"Famine" Condition And Magnetic Field

Polyhydroxyalkanoates (PHAs) have attracted increasing interest as an alternativeto petroleum-derived plastics for its similar mechanical properties to those ofpolypropylene, meanwhile, with the additional advantage of being completelybiodegradable, biocompatible, and produced from renewable resources. But the costof PHAs production is the major obstacle for large-scale commercial exploitation.Among the methods of industrial PHAs production, the aerobic dynamic feeding(ADF, feast" /"famine condition) approach is the most promising because of highPHAs accumulation, meanwhile, this method could substantially decreasing the costof PHAs and increasing their market potential for using activated sludge andrenewable sources obtained from waste organic carbon. The objective of this study isto accumulate activated sludge from municipal wastewater treatment plant to themicroorganism with high PHAs storage ability under the co-effect of aerobic dynamicfeeding (ADF, feast" /"famine condition) conditions and magnetic field. Acetate,butyrate and propionate, the common product of acidification, are used as thesubstrate. The impact factors such as magnetic field intensity, composition ofsubstrate and C:N are testified during the experiments. The possible mechanism isexplaned by the morden analytical techniques.The results show the substrate concentration of start-up and "feast" /"famine" ratioare the important factor for the activated sludge accumulation. The content of PHAsin biomass increased from 8.74% to 50.24% when the concentration increasedgradually to 6.48gCOD/l with the start-up concentration of 0.36gCOD/l and the"famine" /"feast" ratio was 3: 1, meanwhile, the system is stable. The lower substrateconcentration during start-up are benefit to the system with "steady-state" where thestorage microbial consortium will be the dominated one. The co-effect of magneticfield and ADF will enhance the content of PHAs far more. to be 66.2%.The static magnetic exposure definitely influenced the biosynthesis of PHAs andthe effect depended on the field intensity as following: under intensity of 11mT, themaximum PHAs synthesis occurred; under intensity of 21mT. the maximum HVsynthesis occurred: under intensity of 7mT. the maximum HB synthesis occurred, andunder intensity of 42mT, the minimum HB, HV, PHAs synthesis occurred. PHAs content increase with the ratio of C:N, and reach the maximum at the ratio of 100:1.But the active biomass decreased with the increase of C: N ratio. With the magneticexposure, PHAs content have an enhancement under differ ratio of C: N. According tothe results of orthogonal experiment, the influence order of each factor on PHAsproduction is magnetic field, C:N, intial pH. The best condition for PHAs synthesis ismagnetic intensity 12mT, NH₃-N concentration 3.5mg/L (C: N,160:1 ), initial pHvalue 7.0The polymer produced from either acetate or butyrate is the homopolymer of PHB.whereas the copolymer P(HB/HV) is formed when propionate is fed only or alongwith either acetate or butyrate. When acetate is fed solely, almost 55% of substrate isfor energy storage, 20% of substrate is for oxidation for energy production and theother is for growth. When propionate or butyrate is fed, almost 25% of substrate is forenergy storage. 50% of substrate is for growth and the other is for oxidation forenergy production. Obviously, acetate rather than butyrate and propionate is thesuitable substrate for energy storage.The static magnetic exposure and ADF has definitely infuenced the energydistrubition of substrate in microorganism. The PHAs production yield of acetate orbutyrate reach the maximum value of 0.7(mgCOD/mgCOD) or 0.28(mgCOD/mgCOD) under magnetic intensity of 7mT. And the PHAs production yieldof propionate reach the maximum value of 0.31(mgCOD/mgCOD) under themagnetic intensity of 21 mT.The ratio of acetate/propionate has a linear relationship with the ratio of HV/HB.The magnetic field change the slope of line and it sounds the magnetic field provide anew optimized way to PHV/PHB and the characteristics of PHAs.Based on PCR-DGGE and 16S rDNA analysis, there have a change of microbialcommunity under different magnetic field. The microbial community are dominatedby Leadbetterella byssophila under no magnetic intensity, dominated by Unidentifiedbacterium, (AY34413 ) under magnetic intensity of 7mT, dominated by Clostridium,Alkaliphilus under magnetic intensity of 21mT. dominated by Flavobacterium undermagnetic intensity of 42mT. Based on metabolic flux analysis, we conclude that thereason of PHAs content in biomass improved by magnetic field is that the carbonsource (acetate) is in a state of flux during the metabolic process. There is 2.7times ofacetyl-CoA into PHB synthesis compared to TCA cycle under magnetic intensity of 7mT, and 0.9 times of acetyl-CoA into PHB synthesis compared to TCA cycle undermagnetic intensity of 42mT, and 1.4 times of acetyl-CoA into PHB synthesiscompared to TCA cycle under magnetic intensity of 0mT. The co-effect of staticmagnetic and "famine" /"feast" condition provide us a new method to improve thePHAs synthesis by activated sludge.