| Manganese-oxidizing aerobic granular sludge（Mn-AGS）is a new type of aerobic granular sludge discovered in recent years which not only inherits the typical advantages of traditional aerobic granular sludge（AGS）such as high biomass concentration and strong shock load resistance,but also has high redox potential and catalytic performance duet to biogenic manganese oxides（bio-Mn Ox）.It has the characteristics of strong activity,and has excellent performance in the treatment of wastewater containing heavy metal ions and organic wastewater.However,Mn-AGS needs to be further studied in terms of culture acclimation,running stability,and formation mechanism.In this study,the sludge characteristics,operating efficiency,extracellular polymeric substances（EPS）and 3’,5’-cyclic diguanylic acid（c-di-GMP）changes,combined with characterization methods such as microbial population identification,to deeply analyze the formation mechanism of Mn-AGS,and further explore the application of Mn-AGS in wastewater containing tetracycline（TC）.The following conclusions were drawn:（1）In this experiment,Mn-AGS was successfully harvested after 72 days of continuous cultivation,and the maturation time was 16 days longer than that of AGS.The particle size of Mn-AGS particles is smaller than that of AGS in the same period,and the median particle size is 719.03μm and 1304.12μm respectively on the 75th day.Compared with AGS,Mn-AGS showed excellent removal ability for chemical oxygen demand（COD）,total phosphorus（TP）,and Mn2+,but it was poor in removal of ammonia nitrogen（NH4+-N）.The SEM-EDS results showed that the ability of Mn-AGS to handle TP benefited from the adsorption of bio-Mn Ox on phosphorusl.The results of X-ray photoelectron spectroscopy and X-ray diffraction analysis show that the manganese in Mn-AGS mainly exists in three occurrence forms:Mn（Ⅳ）,Mn（Ⅲ）and Mn（Ⅱ）,with the proportions of 37.87%,44.50%,.and 17.63%,respectively.（2）The detection of c-di-GMP concentration in the granulation process of Mn-AGS and AGS shows that the granulation degree of the two kinds of granular sludge is closely related to the c-di-GMP concentration.c-di-GMP mainly regulates the process of sludge granulation by changing the bacterial movement state and EPS secretion concentration.The content of c-di-GMP in Mn-AGS system is lower than that of AGS in the same period,which directly affects the process of Mn-AGS granulation.（3）Based on the theoretical calculation of XDLVO（Extended Derjaguin-Landau-Verwey-Overbeek）,it was found that the energy barrier of Mn-AGS gradually increased with the degree of granulation,and the aggregation between sludge particles and flocs gradually weakened;however,the energy barrier of AGS gradually decreases with the degree of granulation,and the aggregation potential between flocs,between particles,and between particles and flocs continues to increase.（4）From the perspective of microbial community structure changes,the formation of Mn-AGS is a process of selective enrichment of some functional microorganisms,and the relative abundance of bacteria related to pollutant degradation in mature Mn-AGS is higher than that of AGS.The relative abundance of Proteobacteria in Mn-AGS at the phylum level was 97.39%,which was 6.76%higher than that of AGS（90.62%）in the same period,moreover,the dominant flora at the genus level were mainly Thauera（44.41%）and Paracoccus（42.13%）,whose relative abundances increased by 11.2%and 7.2%,respectively,compared with AGS in the same period.（5）Mn-AGS showed a significant increase in c-di-GMP and extracellular protein content under TC stress,which strengthened the shock resistance of Mn-AGS to TC.The removal rate of TC by Mn-AGS was 90.1±1.49%,and it also showed a good removal effect for conventional pollutants.Microbial community analysis showed that when Mn-AGS was exposed to TC for 50 d,the relative abundance of bacteria with poor TC tolerance significantly decreased,while Flavobacterium,Leptothrix and Thauera had strong TC tolerance,the bacterial groups were gradually enriched. |
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