Study On Hydrolysis And Acidification Of Propylene Oxide Saponification Wastewater Residual Sludge And Synthesis Of Polyhydroxyalkanoates By Using Sludge Bacterial Consortium

Waste activated sludge(WAS)production is still increasing with urbanization and industrialization and it will rise up to 60 million tones(80% moisture content)by 2020.The synthesis of biodegradable plastics,polyhydroxyalkanoates(PHA) is important to reduce cost of PHA production and recycle(and reduce) waste sludge.PHA is synthesized via sludge bacterial consortium,using waste sludge fermentation liquid as substrate.WAS composition and the pretreatment technology of anaerobic digestion process have a great effect on the yield and composition of fermentation liquid,on efficiency of PHA synthesis and the monomer compositions of PHA.Therefore,in this paper,influences of hydrolytic acidification liquid by different sources of sludge interaction and biological pretreatment were studied,and different conditions were used to domesticate WAS and explore the effect on PHA synthesis efficiency and PHA composition.It would lay a foundation for the synthesis of PHA by the actual hydrolysis acidification liquid formed by the sludge anaerobic digestion.WAS of propylene oxide(PO) saponification wastewater was mixed with domestic sludge according to different mass ratios.The results of anaerobic fermentation showed that the anaerobic fermentation of residual sludge from PO saponification wastewater was the optimal one,and the maximum yield of volatile fatty acids(VFAs) on the 20th day of fermentation was about 4295.11 mg/L.It showed that the resulting VFAs mainly consisted of acetic acid and propionic acid,the proportion of the total amount of VFAs was about 40.00%,and the proportion of two kinds VFAs was nearly 1:1.Therefore,the effect of biological pretreatment on the VFAs production of residual sludge from PO saponification wastewater by anaerobic digestion was further studied.A strain of thermophiles(L30) which had protease activities was isolated from WAS of PO saponification wastewater at 60 ?.Through morphological observation and 16S rRNA gene sequencing,the strain L30 was identified as Bacillus tequilensis.WAS was treated with fermented liquid of the Bacillus tequilensis L30,and the maximum concentration of VFAs produced was 5776.65 mg/L,which was 34.66% higher than the maximum concentration of the control group.At the same time,this was achieved under the following conditions:Bacillus tequilensis L30 dosage was 10%(V/V) and the pretreatment time was 6 h.The production of VFAs was improved to 6519.04 mg/L,which was 1.35-fold of the control.The hydrolysis acidification liquid was still mainly consisted of acetic acid and propionic acid,and the ratio was about 1:1.Sodium acetate was used as the sole carbon source and sodium acetate:sodium propionate mixture was used as the 1:1 preparation culture media to acclimate the residual sludge for 35 days to synthesize PHA,respectively.The results showed that after acclimation with sodium acetate as the sole carbon source,the maximal PHA yield could reach 34.37% of cell dry weight,and the monomer in PHA was mainly 3-hydroxybutyrate(3HB),accounting for more than 95%.The maximum PHA accumulation of residual sludge after acclimation with sodium acetate and sodium propionate accounted for 51.23% of cell dry weight,and the proportion of 3-hydroxyvalerate(3HV) increased,accounting for about 30%.The highest proportion of 3HB:3HV was about 2:1.The single-molecule real-time sequencing(SMRT) technique was used to analyze the changes of bacterial communities in the residual sludge before and after domestication.At the level of the phylum,Proteobacteria were the dominant microorganisms in the sludge community before and after acclimation.The sludge acclimated with sodium acetate(AccAS) and the sludge acclimated with sodium acetate and sodium propionate mixture(PrAccAS),Proteobacteria were increased by 52.28% and 55.23%,respectively,compared to original activated sludge(OriAS),and most of the bacteria in this population have been identified as capable of synthesizing PHA.At the genus level,Tessaracoccus was significantly decreased from 31.87% before acclimation to 3.63% and 1.50% in AccAS and PrAccAS,respectively.Pseudomonas was significantly increased to 24.35%,3.22%in AccAS and PrAccAS,respectively,from 0.0025% before acclimation.In addition,Phycisphaera and Azoarcus were also the dominant genus in PrAccAS.Phycisphaera and Azoarcus increased from 0.06% and 0% before acclimation to 9.32% and 47.68%,respectively.These increased genus have the ability to synthesize PHA,while some genus which could not adapt to the domesticated environment were gradually eliminated.This study will provide a useful reference for the anaerobic digestion of PO saponification wastewater residual sludge and the PHA synthesis combination technology,and provide a new way to reduce sludge treatment cost and comprehensive utilization of industrial wastewater sludge.