Optimization Of Process Conditions For PHA Synthesis From Activated Sludge

Polyhydroxyalkanoate(PHA)is a natural macromolecular polymer that accumulates as a carbon source,energy source and reducing energy storage substance in microbial cells.Because PHA can be completely biodegradable and biocompatible,it has been regarded as a substitute for petrochemical plastics and has attracted the interest of a large number of researchers.At present,the production cost of PHA is still too high to compete with traditional petroleum plastics.In order to make PHA commercially available,volatile fatty acids(VFAs)produced by activated sludge mixed bacteria and waste fermentation are used as substrates to reduce the production cost of PHA.In the research of using activated sludge to synthesize PHA,most of them use the "aerobic feed" method to keep the dissolved oxygen(DO)concentration in the reaction system above 3mg / L,which is not conducive to energy saving.In order to further reduce the production cost of synthetic PHA,this experiment used the anaerobic-oxygen-limited process,using sodium acetate as the carbon source,under the condition of balanced nutrition,to explore the appropriate substrate concentration and anaerobic time.In order to improve the yield of PHA synthesis by activated sludge mixed bacteria,various factors that affect the synthesis of PHA,such as carbon-to-nitrogen ratio,carbon-phosphorus ratio,PH,etc.,were investigated to obtain the optimal nutritional conditions for mixed bacteria to synthesize PHA.In order to reduce the production cost of PHA and facilitate the requirements of waste recycling and industrialized production of PHA,a preliminary study was carried out on the synthesis of PHA from activated sludge using volatile fatty acids produced by fermentation of solid waste as carbon source,and the utilization of activated sludge was obtained.Changes in the content of PHA synthesized by different odd-even carbon VFAs and monomer composition.After testing,the following conclusions were drawn::(1)Within a certain concentration range,the production of PHA increases with the increase of substrate concentration.When the substrate concentration is 800-1000 mg / L,it is the best concentration range for synthetic PHA,and the maximum content of synthetic PHA accounts for 20.52% of the sludge dry weight.(2)Limiting the nitrogen or phosphorus source will help the activated sludge to synthesize PHA.Both ways of limiting nitrogen source and phosphorus source can promote the synthesis of PHA by activated sludge mixed bacteria,and the effect of limiting nitrogen source is more obvious.But too many restrictions will cause sludge expansion and system collapse.When COD: N = 150: 1,the content of PHA synthesized by activated sludge is the largest,which is 50.39% of the dry weight of sludge;when COD: P = 150: 1,the content of PHA synthesized by activated sludge is the largest,which is sludge 36% of dry weight.Investigated the synthesis of PHA by activated sludge under different p H conditions.The experiment showed that the effect of PHA synthesis by activated sludge was the best under the condition of no p H control.Reducing the p H would inhibit the activity of enzymes or change the electronegativity of microorganisms.PHA synthesis is inhibited.(3)The formation of struvite precipitation by adding magnesium salt(MAP method)can remove and recover excess nitrogen and phosphorus in the fermentation broth to increase the carbon-nitrogen ratio in the fermentation broth.VFAs are good substrates for the synthesis of PHA.The type of VFAs determines the proportion of monomer components of PHA.(4)The maximum content of synthetic PHA using even carbon VFAs produced by anaerobic fermentation of peanut residue was 34.87% of the dry weight of sludge,in which PHB accounts for 65% and PHV accounts for 35%.The maximum content of synthetic PHA using odd carbon VFAs produced by swilling waste oil is 25.24% of the dry weight of sludge,of which PHB accounts for 50.58% and PHV accounts for 49.42%.