Quorum Induction Effect And Succession Rule Of Microbial Community During The Formation Of Algal-bacterial Granular Sludge

In recent years,the combination of microalgae technology and aerobic granular sludge technology for wastewater treatment has attracted much attention.Algal-bacterial granular sludge has become a new process of wastewater treatment due to its compact structure and excellent settlement.At present,the researches were mainly centered on the formation of algal-bacterial granular sludge,while the influence of different types of carbon sources on the sludge granulation process has not been paid attention to.In view of this situation,this paper compared the formation characteristics,the removal efficiency of nutrients,the quorum sensing effect and the microbial community succession rule of algal-bacterial consortia under the conditions of two mixed carbon sources（glucose and sodium acetate;starch and sodium acetate.COD ratio is 1:1）.The influence of completely dissolved carbon source,mixed carbon source composed of dissolved carbon source and granular carbon source on the formation of algal-bacterial symbiotic granular sludge was clarified.The results were as follows:（1）Algal-bacterial granular sludge was successfully cultivated from both dissolved carbon source and mixed carbon source.The average particle size of the mature granular sludge increased to 335.3 and 357.6μm,respectively.The sludge volume index(SVI₃₀)stabilized at 33 and 21 m L/g,respectively,and the mixed liquid suspended solid concentration（MLSS）increased to 4.70 g/L.The SVI₃₀/SVI₅ ratio showed that starch was conducive to the earlier completion of the granulation process,but SOUR showed that the algal-bacterial granular sludge cultivated by dissolved carbon source had stronger metabolic activity of organic matter in the maturation stage.It was found that LB-EPS played a major role in the granulation of sludge,and the effect of protein was more obvious than that of polysaccharide.（2）By comparison,it was found that the removal efficiencies of COD in two reactors were stable above 96%,and the removal efficiencies of ammonia nitrogen were higher than 85%.Therefore,both the dissolved carobon source and the mixed carbon source could effectively remove organic matter and ammonia nitrogen.However,the removal efficiencies of total nitrogen in two reactors fluctuated at 87%and 61%,respectively.The removal efficiencies of total phosphorus were 90%and 33.91%,respectively.Therefore,the dissolved carbon source may be more conducive to the denitrification and dephosphorization of algal-bacterial granular sludge than the mixed carbon source.（3）It was found that the key AHLs signal molecules in the sludge phase of two reactors included 3-oxo-C8-HSL,C8-HSL,C6-HSL,C10-HSL,3-oxo-C14-HSL and 3-oxo-C12-HSL.Correlation analysis showed that C8-HSL and C6-HSL could promote microbial metabolism,and 3-oxo-C14-HSL was conducive to the secretion of protein and had a stronger effect under the condition of dissolved carbon source.The key AHLs signal molecules in the aqueous phase included 3-oxo-C8-HSL,C8-HSL,C10-HSL,C4-HSL,C6-HSL and 3-oxo-C14-HSL.Statistical analysis showed that C8-HSL and 3-oxo-C14-HSL had more significant coupling relationship with sludge characteristics under dissolved carbon source environment,and C10-HSL,C4-HSL,C6-HSL had more significant correlation with protein（LB-EPS）,particle size and SS under mixed carbon source environment.（4）Through the analysis of the microbial community succession rule in the initial sludge,formative and mature algal-bacterial granular sludge,it was found that the bacterial community succession rule of two reacors were similar but there were significant differences in microalgae.The dominant phylum of sludge in two reactors was Proteobacteria,and the dominant class was Gammaproteobacteria.The dominant genus of sludge transformed from Acinetobacter in the initial sludge to Thauera in the formation stage,and the dominant genus of sludge at maturity was Plasticicumulans.In the environment of dissolved carbon souece,the dominant classes of microalgae changed from Coscinodiscophyceae and Synurophyceae in the formation stage to Bacillariophyceae and Chrysophyceae in the mature stage.The dominant genus of microalgae changed from Ochromonas to Nitzschia and Ochromonas.In the mixed carobon source environment,the dominant classes of microalgal changed from Chlorophyceae and Bacillariophyceae to Chlorophyceae,and the dominant genus of microalgal changed from Nitzschia to Chlamydomonas.（5）In the process of cultivating algal-bacterial granular sludge,the correlation characteristics of microbial population succession with granulation and quorum sensing were analyzed at class and genus levels.The results showed that Gammaproteobacteria,Bacteroidia,Chrysophyceae,Ulvophyceae,Plasticicumulans and Nitzschia can promote sludge granulation under dissolved carbon source environment.Gammaproteobacteria,Bacillariophyceae and Plasticicumulans were beneficial to the secretion of 3-oxo-C8-HSL in the sludge phase.Thauera and Chlamydomonas contributed to the increase of C10-HSL and 3-oxo-C14-HSL in the sludge phase,respectively.Bacteroidia,Deltaproteobacteria,OM190,Chlorophyceae,Coscinodiscophyceae,Zoogloea and Chlamydomonas contributed to the secretion of key signal molecules in the aqueous phase.In a mixed carbon source environment,Alphaproteobacteria,Chlorophyceae and Chlamydomonas may improve the sludge properties.Bacteroidia,Deltaproteobacteria,OM190,Bacillariophyceae,Coscinodiscophyceae,Thauera,Nitzschia and Cholrella significantly contributed to the increase of key signal molecules in the sludge phase and the contents of C8-HSL,C10-HSL,C4-HSL,C6-HSL,3-oxo-C14-HSL in the aqueous phase.