Research On Characteristics And Microbial Community Of Aerobic Granular Sludge Under Alternate Aeration Strategy

Aerobic granular sludge is a microbial aggregate formed by microorganisms under specific conditions,and due to its unique structure of aerobic nitrification in the outer layer and anaerobic or anoxic denitrification in the inner layer,small footprint,high sludge concentration,and excellent settling performance,it is considered the most promising wastewater biological treatment technology in the 21st century.It has the potential to replace the activated sludge process,which has been in operation for a century.However,the high energy demand for aeration due to long aeration operations to promote sludge granulation has also limited the promotion and application of this technology.This thesis proposes an alternating aeration strategy for aerobic granular sludge technology to reduce the aeration energy demand by reducing the aeration time.The changes in sludge characteristics were analyzed in comparison with the conventional continuous aeration operation for aerobic granular sludge cultivation,the effect of different aeration intensities on the denitrification efficiency of aerobic granular sludge under the alternate aeration operation strategy was investigated,and the changes in microbial community under different aeration strategies were explored and the effect of some key functional bacteria on sludge granulation and denitrification efficiency was revealed.The main research contents and findings are as follows.（1）Compared to the continuous aeration operation for aerobic granular sludge reactor R1,the alternate aeration operation strategy apply to reactor R2 also to cultivate compact and regular aerobic granular sludge with an average particle size of 1.0-2.0mm.Alternating aeration operation strategy does not affect the stability of the reactor operation,but significantly reduces the sludge granulation time.The cultivated aerobic granular sludge has a larger particle size,higher sludge concentration,and better settling performance.The two reactors exhibited high performance in the removal of pollutants,and the results indicating that R1 had an average removal efficiency of 90.24%,92.69%,61.65%and 80.16%for COD,NH₄⁺-N,TN and PO₄^3--P,respectively,while R2 had an overall average removal efficiency of 91.3%,92.95%,71.32%and 82.21%for COD,NH₄⁺-N,TN and PO₄^3--P,respectively.The difference between the both two reactors was not significant for COD,NH₄⁺-N,and PO₄^3--P,but for TN removal efficiency R2 was approximately 9.7%higher than R1.This indicates that the R2 alternating aeration operation strategy can enhance the aerobic granular sludge denitrification performance.（2）The performance of the aerobic granular sludge bioreactor was monitored using different aeration intensities under an alternating aeration strategy.The results indicated that different aeration intensities under alternating aeration strategy did not affect the removal of COD,NH₄⁺-N and PO₄^3--P by aerobic granular sludge,but had a greater effect on the removal of TN,and reducing the aeration intensity significantly improved the nitrogen removal efficiency of aerobic granular sludge.In addition,higher aeration intensities may lead to the accumulation of higher effluent NO₃^--N concentrations.Based on the microelectrode dissolved oxygen system,the measured dissolved oxygen profile distribution indicated that the alternating aeration operation strategy created an alternating aerobic-anoxic operating environment in the reactor.（3）Through the analysis of the diversity and structure of microbial communities during the sludge granulation process under two different aeration operation strategies.The results indicated that the abundance and diversity of the microorganisms decreased after the completion of granulation in both the reactors.Whereas,the sludge in the reactor operated under an alternate aeration strategy had higher microbial diversity and richness compared to the reactor operated under continuous aeration.Different aeration strategies have an important impact on the structure of the microbial community.Alternating aeration strategies enriched a higher abundance of Zoogloea and Thauera in the sludge granulation process compared to continuous aeration,two bacterial genera that not only promote the secretion of large amounts of extracellular polymeric substances that facilitate the completion of sludge granulation,but also increase the efficiency of nitrogen removal by aerobic granular sludge.Other relatively abundant genera such as Dechloromonas,Flavobacterium,Tetrasphaera and Thiothrix are able to secrete extracellular polymeric substances which play an important role in promoting sludge granulation and contribute to system stabilization and nutrient removal.Figure[28]Table[7]Reference[121]...