| Compared with ordinary activated sludge,aerobic granular sludge has excellent sedimentation performance,compact structure,high biomass,and strong adsorption capacity for harmful substances,and has received widespread attention from researchers at home and abroad.However,the long start-up time and poor operational stability have become an important issue in the current development of aerobic granular sludge technology.However,it is more difficult to cultivate granular sludge under low-strength wastewater,and the granulation process is also slower.For this reason,the researchers did a lot of research and found that dosing the carriers is an important way to promote the granulation of sludge.However,most of the studies were carried out in environments with high organic loads.There was a lack of attention to the mechanism of action in the sludge granulation for dosing the carriers with low organic load.Based on the difficult situation of granulation of activated sludge in low-strength wastewater,and in order to promote the formation of granular sludge the polymeric ferric sulfate,aluminum sulfate and diatomite were dosed respectively into different SBR reactors during the logarithmic phase of microorganisms.Studying the effects of polymeric ferric sulfate,aluminum sulfate and diatomite on sludge characteristics,EPS secretion and microbial population structure to reveal the mechanism of different carriers in the process of strengthening granulation and to explore the possibility of enhancing the granulation of aerobic sludge in domestic sewage by feeding carriers.The results of the study are as follows:(1)With a dose of ferrous sulphate,diatomite,and aluminum sulfate in the 16 th to 20 th days,the characteristics of sludge have been significantly improved.Also,the required time of sludge granulation was decreased by 11 d,7d,and 4d respectively.Compared with the control group broking up due to the presence of filamentous bacteria,the structure ofgranules cultivated with carriers was more compact,have more biomass,better sedimentation,larger average particle size,and all have excellent stability.However,compared with the high organic load,the influence of mass transfer resistance under low organic load leads to a smaller particle size of the formed granular sludge.(2)The results of the analysis of EPS showed that,unlike polyferric sulfate and diatomaceous earth,the EPS content of the sludge was significantly increased after adding aluminum sulfate.And PN/PS up to 10 or more,which means that accelerating microbial aggregation by stimulating the secretion of EPS from sludge is one of the ways that aluminum sulfate strengthens the formation of granular sludge,and the protein is more important under low-strength wastewater in the granulation process.The results of fluorescence spectrophotometer showed that the fluorescence intensity of peak B and peak D in R2,R3 and R4 was higher than that of R1,indicating that the dosing of carriers increased the content of aromatic proteins and soluble microbial metabolites in EPS.In addition,the addition of the carrier can affect the structure of the sludge EPS,which may also promote the granulation process of the sludge in some extent.(3)Analyze the removal effect of pollutants in the four groups of reactors.After the operating conditions are stable,the removal rate of COD in the four reactors is stable at more than 90%,and the impact of COD removal by the loading bodies is not significantly affected.Adding carrier has a certain effect on the removal of nitrogen.Compared with diatomite,the addition of polyferric sulfate is beneficial to the nitrification process,and the removal rate of NH4+ is up to 82%.(4)High-throughput sequencing technology was used to compare and analyze the microbial population character of the initial sludge and the mature granular sludge in the four reactors.The ACE index and the Chaol index indicated that the microbial population in the mature granular sludge is more abundant than the initial sludge.In addition,the addition of different carriers had a certain impact on the microbial population richness,and the highest microbial richness was found in mature granular sludge fed with diatomaceous earth,and the microbial richness in mature granular sludge formed by adding polymeric iron sulfate lowest.From the Rank-Abundance curve,it can be seen that the population diversity of microorganisms in the mature granular sludge is lower than that of the initial sludge,and theaddition of different carriers has no significant effect on the microbial population diversity.The above shows that in the initial sludge,the microbial population has the highest degree of homogeneity,which increases the diversity index;and the microbial population formed after the addition of diatomaceous earth has the lowest homogeneity of the microbial population,resulting in a decrease in the diversity index.With the development of granular sludge,important functional bacterial populations can accumulate,microbial population diversity decreases,and the abundance of important functional bacterial groups increases.(5)Analyze the composition of microbial communities in the initial sludge and the four groups of mature granular sludge.The results show that: the dominant bacteria in phylum in the five groups of samples are Proteobacteria and Bacteroidetes.The predominant strains in class level were Betaproteobacteria and Alphaproteobacteria.Compared with the initial sludge,the percentage of Betaproteobacteria and Alphaproteobacteria in the matured granular sludge increased,while the proportion of Sphingobacteriia belonging to the genus Bacteroidetes decreased.This shows the screening effect of Proteobacteria and Bacteroidetes in the process of sludge acclimation.The dominant genus is Unclassified and Zoogloea.Compared with the initial sludge,the ratio of Zoogloea and some nitrogen-removing functional genus increased,making the mature granule sludge more stable structure and higher denitrification capacity.Comparing four groups of mature granular sludge,Thiothrix accounted for the largest proportion in R1 and the least in R2,corresponding to the loosest sludge structure,while R2 had the most compact sludge structure. |
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