Polyhydroxyalkanoate (PHA) Synthesis By Glycerol-based Mixed Culture,Modelling And On-line Monitoring

Polyhydroxyalkanoate(PHA) production are high renewable biopolymer materials as an alternative to petrochemical plastics with the advantages of being physical(mechanical), chemical, biocompatible and biodegradable. At present, due to the complex process and high operating costs, the industrial synthesis method including pure cultures and genetic engineering has seriously hampered the commercialization of PHA production.The phenomeon that activated sludge can synthesis PHA has maked the mixed cultures as a alternative method possible.The paper aims to enrich a glycerol-fed PHA-producing mixed cultures under feast and famine remgine,and evaluate the PHA production capability using glycerol and others as substrate. Based on monitoring oxygen uptake rate(OUR), PHA and chemical oxygen demand(COD) profiles, the paper investigated the relation between OUR and PHA in the feast phase.The linear equation based on the model of simultaneous storage and growth can predicte PHA contents, which provided theoretical guidance and technical support for improving PHA yield and PHA measurement for industrial large-scale PHA production.(1) The substrate versatility and polyhydroxyalkanoate(PHA)production capacity of the mixed culture was studied using acetate, propionate, butyric, glucose and lactate respectively. When glycerol and glucose were used as substrate, PHB and PG were found.Only PHB was synthesized when acetate, butyric and lactate were fed.Also PHB and PHV produced when propionate as substrate. The yield of PHA was showed: lactate(0.60)>acetate(0.56)>propionate 0.39)>glucose(0.34)>butyric 0.30)>glycerol(0.26). The lower PHA yield may be due to the lower DO concentration, The lower DO concentration in favor PG synthesis.(2) Three acetate/propionate ratio(1:1, 3:1, 1:3) as mixed substrates to produce PHA. The PHA contents were showed: acetate/propionate 3:1(0.54)> acetate/propionate 3:1(0.51)> acetate/propionate 3:1(0.45). The PHA contents increased with the proportion of acetate.When acetate/propionate ratio was 3:1 and 1:3, The microbial storage rate/growth rate ratio were 1.57and1.33.Therefore, the external substrates were used for storage process.There was linear relationship between OUR and PHA when acetate, propionate, butyric, glucose and lactate were used as substrate.(3) The model of simultaneous storage and growth for OUR simulation results and experimental results are consistent.The simulation results of OUR presented each process' s contribution.The oxygen consumtion rate of growth process was higher than the storage process when propionate was fed.While acetate/propionate ratio was 3:1 and 1:3, the oxygen consumtion rate of storage was higher than the growth process.The external substrates were mainly used for storage process to produce international storage products.(4)When acetate/propionate mixure as substrate, the predicted results based on the linear relationship established online OUR data were essentially consistent with measured ones, and indicate that the method is feasible.