Research On Polyhydroxyalkanote Production Performance By Mixed Cultures From Activated Sludge

Polyhydroxyalkanoate(PHA)is a bio-polyester that stores the extra energy of microorganisms.When the external grow th conditions of microorganisms are unbalanced,the microorganisms will convert the excess carbon source into PHA storage.PHA has similar physical properties with traditional petroleum-based plastic polyvinyl chloride,and it has good biodegradability,bi ocompatibility as a green alternative to traditional plastics.The high price of industrial large-scale production of PHA,which is 4-9 times higher than ordinary industrial synthetic plastics,is due to expensive substrate,sterile environment requirement.With VFAs-rich sludge fermentation liquid as an alternative to pure substrate and domesticated activated sludge as functional microorganism instead of pure bacteria fermentation,the PHA cost will be significantly reduced.Meanwhile,the process can also to bring economic benefits to the sewage treatment plant,indirectly reduce the sludge disposal costs,achieve both environmental benefits and market efficiency.This study compared the PHA production performance of three typical enrichment reactor by using different C/N ratio substrates.The experimental results show that the biomass from SBR #3 enrichment reactor(high organic load rate(OLR),short cycle length(CL),short SRT)has a wider ability to adapt substrates with different nutrient levels,comp ared to that of SBR # 1(low OLR,long CL,long SRT)and SBR # 2(high OLR,long CL,short SRT).In the presence of nitrogen and phosphorus in PHA production phase,cell growth and PHA synthesis can occur simultaneously,which significantly improved PHA production yield.The highest PHA productivity was 1.64 g PHA/ g X 0 under nitrogen and phosphorus limitation conditions.In SBR # 3 mode,the ability and stability of accumulator subject to different substrate types were analyzed.For biomass accumulated by the mainly butyrate substrate(butyrate-type),the highest PHA content could reach 67.87wt% and 69.25wt%,respectively,under nutrient limitation and excess conditions,which is much larger than propionate-type SBR.The PHA content of biomass from butyric-type SBR was only 0.35wt% when the substrate type was shifted to propionate type,while the PHA content of biomass from propionate-type SBR decreased by 12.47 wt% after substrate conversion.In this study,T_RFLP and high-throughput detection methods were used to monitor the changes in population structure during the operation of each reactor and in PHA production batches.The experimental results show that the different operating strategies lead to different dominant populations in the reactor,and the community structure is dynamic during the operation.The composition of the substrate had little effect on the type of microbial species,but had a significant effect on the relative abundance of the population.PHA batches of experiments showed that the presence of ammonia nitrogen promoted the synthesis of PHA,that is,the simultaneous growth of bacteria and PHA synthesis.This effect is likely to be related with high Thauera sp.population abundance.The higher abundance of Paracoccus sp.may be the reason w hy the higher proportion of HV is achieved under a lower C/N ratio.In the batch experiment,the abundance of Acinetobacter sp.increased significantly at the late stage of reaction with nitrogen and phosphorus.In this study,when the actual sludge fermentation liquid was used as the substrate of accumulator,the mixed cultures did not succeed to achieve the "feast-famine" mode in the SBR reactor,resulting in the transformation of the metabolic flux under the long-term acclimation.Thus,batches of PHA production can not realize its potential,where the final PHA content is only 14.66wt%.