| Due to the advantage of compact structure,high biomass,excellent settling ability and greater ability to withstand inhibitory and toxic compounds,aerobic granules are applying to the full-scale industrial and municipal wastewater treatment plant.However,aerobic granules haven't been applied on large scale in the world,mainly due to there are three disadvantages impeding the application:(1)different start-up time under different operation condition;(2)instability during prolonged operation;(3)decrease of microbial activity during storage process.In this study,the whole life cycle of aerobic granules,including granulation process,disintegration process and storage process,were systematically studied.Main contents and results were as follow:(1)This study combined XDLVO theory,physicochemical properties,extracellular polymeric substance(EPS)and acyl-homoserine lactone(AHLs)signals,to qualitatively and quantitatively study the exact aerobic granulation process.Results showed the whole process of aerobic granulation process can be divided into three phases:acclimation phase,granulation phase and maturation phase.In acclimation phase,hydrophobicity of sludge and EPS increased,while electronegativity of zeta potential decreased,aggregation ability of sludge increased,nuclei began to form at the end of acclimation phase.In granulation phase,as nuclei appeared,aggregation ability and EPS secretion decreased,while zeta potential and hydrophobicity kept relatively stable.Meanwhile,potential barrier of flocs and granules decreased,which caused decrease of aggregation ability.However,hydrophobicity of flocs decreased and electronegativity of zeta potential increased,whereas hydrophobicity of granules increased electronegativity of zeta potential decreased.Floes weren't likely to aggregate,while small aerobic granules tended to self-grow rather than aggregate after nuclei appeared.In mature phase,particle size of aerobic granules increased,and flocs washed out from the reactor.During the whole process,the ratio of PN and PS decreased,and AHLs signals increased.(2)Physicochemical properties,microstructure characteristics,EPS,AHLs signals and microbial communities of granules from different life stages were systematically investigated and compared to better understand the disintegration process of aerobic granules.During 460 days' operation,intact young granules(IGY)grew into larger intact aged granules(IGA),then crannied granules(CG),and finally broken granules(BG).Compacter young granules with obvious calcium precipitation in the core grew into cavern-like structure aged granules with Ca precipitation mainly on the outer and middle zone during prolonged operation.With the growth of aerobic granules,microaerophilic TM7,fermentative acidogenic class proteins hydrolysis bacteria Cytophagia Saprospiraceae increased while Microbial communities which can resist shear force decreased and related to AHLs production decreased.All changes concerning disintegration of aerobic granules were closely related to the increase of granule size,and maintaining a steady and proper size is beneficial to the prolonged operation of aerobic granules.(3)This study investigated the physicochemical properties of aerobic granules,such as granular density,integrity coefficient(IC),relative hydrophobicity,EPS and specific oxygen uptake rate,combined with the change of AHLs signals,to further study on the effect of AHLs signals during the storage process.Results showed that granular density,IC,hydrophobicity and specific oxygen utilization rate(SOUR)of aerobic granules decreased during this process.TB-EPS contributed to RH of aerobic granules,rather than LB-EPS.Except C10-HSL and 3OC10-HSL signals,C6-HSL,C8-HSL,C12-HSL,C14-HSL and 30C12-HSL all decreased.During the storage process lack of substrate,C10-HSL and 3OC10-HSL may be the regulation molecules.Live cells decreased,dead cells increased,as well as the SOUR and connection of bacteria decreased during the whole process,which may lead to the decrease of AHLs signals secretion. |
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