Study On The Cultivation Of Symbiosis Granular Sludge With Different Carbon Sources And Its Salt Tolerance

Salty wastewater is widely used in the production processes of food processing,medical treatment,and industrial industries.Its component is complex,the cost of physical and chemical methods to treat salty wastewater is high,and the high-salt environment has a certain toxic effect on microorganisms,making the treatment efficiency of traditional biological methods greatly reduced.As a new biological technology for water treatment following aerobic granular sludge technology,algae-bacteria granular sludge technology can combine microalgae and bacteria,which greatly saves operating cost.This study mainly compared the culture characteristics of algae-bacteria granular sludge under the conditions of sodium acetate+glucose(1:1)and sodium acetate+starch(1:1)in photo-sequencing batch rector(PSBR),as well as its growth in the high-salt environment after maturity.During the experiment,the physicochemical properties and the hierarchical extract Extracellular Polymeric Substances(EPS)of algae-bacteria granules were regular monitored.Through analyzed the content and component changes of LB-EPS and TB-EPS in algae-bacterial granulation process,revealed the action mechanism of EPS in the process of sludge granulation under different carbon source conditions and the changes of EPS secretion under salt stress.The results are as follows:(1)When the particles were mature,the particle sizes in the two reactors were 335.3and 357.6?m,and the SVI₃₀ were 32.9 and 21.2 m L/g,respectively.The COD and NH₄⁺-N removal rates of the mature algae-bacteria granules reach about 97%and 90%,respectively.In the algae-bacteria granulation process,the concentration of TB-EPS in two reactors was much higher than that of LB-EPS,and it was about 8-10 times that of LB-EPS.The concentration of PN in LB-EPS increased by 2.3 times,while that in TB-EPS increased by 1.5 times.The variation range of extracellular PN was greater than that of PS,indicating that the extracellular PN in LB-EPS played a crucial in the granulation of algae-bacteria granulation,and the performance of algae-bacteria granules cultured by sodium acetate+starch(1:1)was better.(2)According to the results of 3D-EEM,the fluorescent components of EPS in the two reactors were mainly tyrosine,tryptophan,aromatic proteins,and soluble microbial metabolites.The peak position and fluorescent components changed significantly during the granulation process,and the fluorescence intensity of TB-EPS was higher than that of LB-EPS.The infrared spectrum showed that in the Amide compound C=O stretching vibration absorption characteristic peaks,characterization of protein secondary structure Amide?absorption characteristic peaks had volatility in algae-bacteria granulation,indicating that the secondary structure of protein was changed during the process of granulation,in which the polymer chain and?-helical secondary structure were beneficial to the aggregation of microorganisms,while the random coiled structure could reduce the flocculation ability of microorganisms.The XPS test results showed that the main elements in the EPS of the two reactors are C,N,and O.Among them,the chemical groups C=O,C?O and?NH₂ were the basic constituent groups of PN and PS compounds in EPS.In the process of granulation of symbiotic sludge,the proportion of carbon in the two reactors increases,while the proportions of nitrogen and oxygen decrease,and the changes in the reactor with particulate carbon source as COD were more obvious.Correlation analysis was carried out between different EPS components and granular characteristics.The results showed that different EPS components were positively correlated with MLSS and d50 in two reactors,and the EPS components were negatively correlated with the SVI₃₀ of the sludge.Moreover,the correlation between extracellular proteins and granular sludge characteristics was stronger.(3)After the bacteria and algae symbiotic sludge particles matured,when the salt concentration increased to 25 g/L,the particle sizes in the two reactors were maintained at 249.7 and 308.6?m,the SVI₃₀ was 38.5 and 35.5 m L/g,the COD removal rates were92.8%and 93.1%,the NH₄⁺-N removal rates were 62.4%and 91.4%,respectively.It indicated that the algae-bacteria granules cultured with particulate carbon sources in a high-salt environment have a better sewage treatment effect than soluble carbon sources.Two levels of EPS concentration in the high salt environment were fluctuating by salinity.When the salt concentration was 25 g/L,the concentrations of LB-EPS in the two reactors were 5.6 and 3.1 mg/(g-MLSS),the concentrations of TB-EPS were 132.9 and 117.3mg/(g-MLSS),respectively.The content of extracellular PN in EPS was higher than that of extracellular PS,and the effect of salinity on extracellular protein was more obvious.The PN/PS of LB-EPS in the two reactors decreased by 1.0 and 1.6,respectively,and the PN/PS of TB-EPS both decreased by 1.6.(4)It can be seen from the 3D-EEM spectrum that the intensity of fulvic acid in LB-EPS increases significantly,and the rest of the fluorescence peak position and intensity changes were basically consistent with the content of EPS.At the same time,the infrared spectrum of EPS showed that the vibration peaks of the Amide I and the Amide III,which represented the secondary structure of the protein changed.The XPS analysis results of EPS showed that under high salt environment,the changes in the proportions of C?C,C?O,C=O and?NH₂ groups in the two reactors were opposite to the granulation process.The increase of the proportions of C=O and?NH₂ indicated that the stimulation of salinity,was conducive to the synthesis of alcohols,ketones and aldehydes in EPS secreted by algae-bacteria granules,and the macromolecular protein decomposed more?NH₂.The change of C?O was closely related to the extracellular PS.The correlation between EPS and granular sludge characteristics in the salting stage was different from that in the granulation stage.