Microbial Community Analysis Of Propylene Oxide Saponification Wastewater Activated Sludge And Biosynthesis Of Polyhydroxyalkanoates(PHA) By Using Residual Sludge

Biosynthesis of a kind of biodegradable plastics-polyhydroxyalkanoates(PHAs)by bacterial consortium from the acclimated residual sludge will greatly reduce the cost of PHAs production and result in the sludge reduction and recycling.Firstly,Illumina MiSeq high-throughput sequencing was used to analyse the diversity of bacterial community and eukaryotic algae in propylene oxide(PO)saponification wastewater activated sludge.The core of genus in the aeration tank activated sludge were Marinobacter,Mesorhizobium,Paracoccus,KSA1,Devosia,Methylophaga,while the core of genus in the contact oxidation tank activated sludge were Thalassospira,Marinobacter,Owenweeksia,Novispirillum,Mesorhizobium,Sporotomaculum,Pseudidiomarina and KSA1.These bacteria in the activated sludge probably played essential role to remove organic chlorides in PO saponification wastewater.The diversity of eukaryotic algae in the activated sludge was also carried out,and the eukaryotic algae in PO saponification wastewater activated sludge could be divided into two different groups which have not been identified.Then 18 S rDNA clones library was constructed basing on 18 S rDNA hypervariable region sequences.One of the group was identified as Desmodesmus intermedius,which had the potential ability to produce oil.Desmodesmus intermedius might be explored as an oil producing algae in the future.Secondly,two 50 L Sequencing Batch Reactors(SBRs)were assembled and used in the following experiments.Volatile fatty acids(VFAs)can be generated from activated sludge by anaerobic hydrolysis acidification.Tap water and effluent from secondary sedimentation tank containing Ca2+were used to prepare culture media in the domestication of PO saponification wastewater activated sludge to synthesize PHAs,respectively.The results showed that tap water was more suitable to prepare medium in the progress of sludge acclimination and PHAs accumulation.The contents of PHAs and their monomer components in two SBRs were detected,respectively.PHAs were constitued of two kind of monomers which were3-hydroxybutyric(3HB)and 3-hydroxyvaleric(3HV).When tap water was applied,the maximum amount of PHA reached 20.33% of the dry weight of sludge,and the content of3 HB was significantly higher than 3HV and the highest proportion reached 10: 1.While when effluent from secondary sedimentation tank was used,the maximum accumulation of PHA was only 3.4% of dry weight of sludge.3HB monomer content was higher than 3HV and the highest proportion was 1.68: 1.Thirdly,on the basis of pre-experimentation,it was determined that tap water was used to preparae mediums and a final concentration of 0.75 g/L Rhodobacter sp.XR212 was added to the activated sludge before the acclimation.The activated sludge was acclimated using microaerobic-aerobic model for 21 days.The consumption of acetate was detected among the acclimination.It was found that acetate was significantly consumed by activated sludge microbial flora on the tenth day.The maximal PHA contents could reach 25.52% of dry weight of sludge.And the percentage of volatile suspended solids(VSS)and suspended solids concentration(MLSS)were 52.45%,so the maximal PHA yield could reach 48.66% of cell dry weight.The monomer in PHAs was mainly 3HB,which was significantly higher than that before the acclimation,and the proportion of 3HB: 3HV was about 11.5: 1.Finally,to further investigate the changes of bacterial communities in the activated sludge after acclimation using acetate,Illumina Mi Seq high-throughput sequencing was used to analyze bacterial communities in the activated sludge before and after acclimation.We performed a significant difference in the level of the genus and found that the difference between the two bacterial flora before and after acclimation was mainly concentrated on Proteobacteria and Bacteroidetes.In Proteobacteria,Rhodobacter,Hyphomonas and Agrobacterium which belonged to Alphaproteobacteria increased from almost undetected before acclimation to 12.79%,7.28% and 4.13%,respectively.In Betaproteobacteria,Rhodocyclaceae unclassified and Hydrogenophaga increased from almost undetected before acclimation to 13.50% and 3.87%,respectively.Methyloversatilis increased to 1.87% from0.001%.In Gammaproteobacteria,Alishewanella increased from almost undetected before acclimation to 10.69%.Pseudomonas increased to 4.50% from 0.004% while Marinobacter decreased from 6.89% to not detected.In Bacteroidetes,Flavobacterium increased to 12.34%from 0.001%.Leadbetterella increased to 7.02% from almost undetected before acclimation.Saprospirales and KSA1 decreased to not detected from 14.07% and 2.32%,respectively.These bacteria,which are significantly increased the content of PHA in acclimated activated sludge,can synthesize PHA with acetate.However,some genus were eliminated which were not suitable to the acclimation condition.This study will provide a useful reference for the large-scale utilization of PO saponification wastewater residual sludge to accumulate PHA.