Study On Effects Of Static Magnetic Field On Polyhydroxyalkanoate Synthesis By Activated Sludge

Polyhydroxyalkanoates(PHAs) have been considered as the promising substitutes for the petrochemical-derived plastics due to their similar properties to petrochemical-derived plastics and biodegradability.The major barrier to the wide application of PHA is the high cost.In order to reduce the cost,the bioeffect of magnetic field was introduced to the PHA biosynthesis by activated sludge.The study was concentrated on three aspects:1.Devoloped an effective method to acclimatize activated sludge with high PHA storage capacity.Chose significant factors out of seven ones(SRT,C/N,FE/FA,COD₀, pH,load increase rate,C/P) in acclimatization process and optimized.2.Studied the effect of magnetic exposure mode and duration time on PHA synthesis by activated sludge and obtained the optimum magnetic treatment condition.3.Observed the effect of SRT and pH on PHA synthesis by activated sludge under different magnetic intensity and optimized the condition.The main results were as follows:1.Plackett-Burman design was employed to screen parameters.The most significant parameters were SRT,C/N,COD₀ and C/P.The optimum conditions obtained through uniform design was:SRT of 15 d,C/N of 50,C/P of 530,COD₀ of 1050 mgCOD/L.The corresponding maximum PHA yield and acclimatization duration time were 0.73 and 25 d respectvely.The experimental value of 0.71(maximum PHA yield) and 23 d(acclimatization duration time) were well in agreement with those of the predicted ones.2.The promotion effect of magnetic exposure in the famine phase on PHA synthesis was more significant than magnetic exposure in the feast phase or in feast-famine phase.The stronger the magnetic field was,the more significant the promotion effect of magnetic exposure in the famine phase was.There were no obvious differences between the promotion effect of magnetic exposure in the feast phase and in feast-famine phase.The q_HB/q_S reached the maximum of 0.52 at 21 mT magnetic exposure in the famine phase.The q_HV/q_S reached the maximum of 0.23 at 11 mT magnetic exposure in the famine phase.3.During the famine phase,the degradation rate of HB was higher than that of HV, and so the metabolism of activated sludge mainly relied on HB degradation.Magnetic exposure in the famine phase showed the greatest promotion effect on PHA degradation,followed by magnetic exposure in the feast phase,and in feast-famine phase.The k reached the maximum of 0.035 at 11 mT magnetic exposure in the famine phase.4.It was non-linear relationship between magnetic exposure duration time and PHA yield.The promotion effect reached the maximum when the magnetic exposure duration time was less than 3 d and then it decreased with the magnetic exposure prolonged.When the the duration time was more than 8 d,magnetic field inhibited PHA synthesis.The optimum magnetic exposure time was less than 3 d.5.The pH significantly influenced the acid comsuption rate and PHA synthesis rate.q_S,q_HB,and q_HV all increased with the pH from 7 to 8.5,and 9.5.0,11,21 mT,q_S, q_HB and q_HV reached maximum at pH 9.5,9.5,8.5 respectively.The effect of pH on PHA yield was less significant than the effect of pH on PHA synthesis rate.When magnetic field was 0 or 11 mT,Y_PHA at pH 7 and at pH 9.5 reached the maximum. When magnetic field was 21 mT,Y_PHA at pH 9.5 increased 6%compared to Y_PHA at pH 8.5.Controlling pH at higher value was more favorable to enhance PHA synthesis and increase synthesis rate.6.The q_S decreased with the SRT increased.There was strong positive correlation between q_S and F/M(R=0.916,p＜0.01).But there was no correlation between Y_HB and F/M,Y_HV and F/M(p＞0.05 both).11 mT,Y_HB,Y_HV,and Y_PHA reached maxmum of 0.24,0.11,0.35 Cmmol/Cmmol at SRT 10 d.21 mT,Y_PHA of SRT 5,10 d were 0.42,0.43 Cmmol/Cmmol respectively,and there was no obvious difference.