Research On The Effect Of NaCl On The Synthesis Of Polyhydroxyalkanoates(PHA)by Mixed Microbial Culture From Food Waste Fermentation Liquid

It is of great significance to synthesize polyhydroxyalkanoates(PHA)by the mixed microbial culture from the food waste fermentation acid liquid which will greatly lower the cost of PHA production and result in the food waste and sludge reduction and recycling.However,the high intial carbon concentration without limit of nitrogen and high salinity in acid liquid may have the effect on the synthesis of PHA and the practical application of the project.Therefor,it is important to study the effect of salinity on the synthesis of PHA by MMC,which will provide important theoretical and guiding significance for future engineering practice.Firstly,two kinds of non-salt domesticated PHA bacteria were used to synthesize PHA by using organic wastewater added NaCl,and the instantaneous salt concentration impact test was carried out by the domesticated and stable PHA mixed microbial culture using the compound group as the substrate.The results showed that the instantaneous salt concentration shock suppression of the PHA microbial culture without enrichment by salinity acclimation The activity of mixed microbial culture was inhibited and the PHA capacity was inhibited.The hybridization rate of 843 mgCOD / L,1686 mgCOD / L and 6745 mgCOD / L were simulated by ADD mode in the same period.The results showed that 843 mgCOD / L could enrich the mixed microbial culture with the maximum synthesis capacity of 51.24% at 7 days after initiation,and the activated sludge concentration and SVI were the best,and the stability of the system was the best.It was suitable for the subsequent experiment providing PHA mixed microbial culture.Secondly,the main products of volatile acid(VFAs)were used as the substrate,and the influent NaCl concentration was set to 0.0g / L(1#SBR)?5.0g/L(2#SBR)?10.0g/L(3#SBR)?15.0g/L(4#SBR).The physicochemical properties of and laws of PHA accumulation by enrichment MMC of different salinity under low water load of 1350 mgCOD / L in ADF mode was studied.It shows that under feast and famine regime,when the NaCl concentration was lower than 15.0 g / L,the total amount of EPS increased with the increase of salinity and the effect of salinity on PN was higher than that of PS.Activated sludge morphology with the increase in salinity and reunion dense,and sedimentation is proportional to salinity.The sludge conversion rate,PHA ratio,sludge growth rate and substrate absorption rate in the 2 # SBR enrichment MMC have the advantages of 0.1622mgCOD(MMC)?mg-1COD(VFA),0.6800mgCOD(PHA)?(mgX?h)-1,0.1731 mg COD?(mgX?h)-1and 1.0669mgCOD?(mgX?h)-1.The highest PHA synthesis rate was 50.47% in the batch test.In the instantaneous salt concentration impact test,the highest PHA synthesis rate increased to 51.31% when the 2 # SBR domesticated MMC was affected by the instantaneous salt concentration of 10.0 g NaCl / L.The proportion of HB and HV monomers in the PHA products synthesized by the four groups of SBR was almost unaffected by salinity and maintained at 4: 1.Adjusting the influent load to 8433 mgCOD / L,the operation mode of ADF was changed,and the MMC characteristics of different salinity acclimation and enrichment were investigated.The results showed that the highest content of EPS in the soil was 138.53 mg / gVSS in 2#SBR,and the morphology of the bacteria was the most agglomerated.The PHA in the typical cycle was superior to the synthetic rate,the sludge growth rate and the substrate absorption rate: 0.7977mgCOD(PHA)?(mgX?h)-1,0.0861 mg COD(X)?(mg X?h)-1,1.7324 mgCOD?(mg X?h)-1.In the corresponding batch test,the rate of PHA synthesis was 60.95%,46.98%,51.69% and 36.94% respectively in the four groups.In the instantaneous salt concentration impact test,2 # SBR domesticated MMC was treated with 10.0g NaCl / L,the highest PHA synthesis rate increased to 53.22%.For analtsising the microbial community structure,combined with high-throughput sequencing results,in the low-water load,2 # SBR enrichment MMC contains the highest abundance of Thauera,witch was an important factor that lead to its performance in all aspects better than other domesticated MMC.The 4 # SBR-enriched MMC also contained the higher abundance of Thauera,but its synthetic PHA ability was weaker than that of other conditions.The reason was that high concentrations of substrate produced substrate inhibition.Finally,carry out the actual food waste anaerobic fermentation acid production test,then use the actual acid production as the substrate,adding different NaCl salinity(2.5g / L,5.0g / L,10.0g / L).The results showed that the PHA conversion rate,PHA ratio,the sludge conversion rate,and the sludge conversion rate of the MMC with 10.0 g / L NaCl achieved the best: 0.2260 mgCOD PHA?mg-1COD VFA?0.1018 mg COD PHA?(mg X?h)-1?0.1714 mgCOD MMC?mg-1COD VFA and 0.0782 mg COD X?(mg X?h)-1.The lowest substrate yield was 0.4597 mg COD?(mg X?h)-1.The maximum PHA synthesis rate of the three groups was about 30%,indicating that 10.0g / L salinity stimulated the rapid growth rate of bacteria and the rate of PHA synthesis.While the utilization rate of the microbial bacteria in the low salinity was not high,and more carbon sources were consumed in the endogenous respiratory metabolism process.In summary,this paper has proved that the actual fermentation of food waste can be used by activated sludge MMC to synthesize PHA,MMC by 5.0g / L NaCl salinity for a period of domestication,with excellent salt resistance,for the actual water salinity increased to 10.0g / L,still maintain a stable synthesis of PHA capacity.