Investigation Of The Effect Of Organic Loading On Aerobic Granular Sludge Performance And Microbial Interactions

Based on the current situation of severe water resources and ecological environment problems,many more efficient sewage treatment technologies have been developed and applied,and aerobic granular sludge technology has become one of the research hotspots because of its advantages of high biomass,good sedimentation performance,small footprint and low operating cost.However,it also has some disadvantages such as long start-up time and poor stability after maturity.This study aims to explore the influence of organic load changes on the performance of aerobic granular sludge and microbial interactions from the perspective of microbial ecology,and relevant studies on the start-up stage of granular sludge are also conducted.The main results are as follows:（1）In the start-up stage,the effect of Ca²⁺on the start-up and performance of aerobic granular sludge was mainly studied.The results showed that the addition of Ca²⁺could promote the maturation of granular sludge,and the aerobic granular sludge was fully mature after 35 days.Ca²⁺has no obvious effect on the removal rate of COD and TN,but TP has a higher removal rate after addition.The average particle size of AGS was 2.30 mm,SVI30 was 41.34m L/g MLSS,and sludge concentration was 2321mg/L when Ca²⁺was added.Ca²⁺promotes the production of extracellular polymers,making the organic matter they contain more complex and more concentrated.（2）The influence of organic load on the system was studied by reducing the organic load,the organic loads of the three stages were 1.6,0.8 and 0.4kg COD/（m³·d）,respectively.The results showed that the reduction of organic load would decrease the removal performance of granular sludge,and the removal rates of COD,TN and TP decreased from 98%,97%and 90%to 80%,54%and 50%,respectively.Sludge concentration and settling capacity decreased first and then increased,and finally MLSS and SVI₃₀ were 1473mg/L and 61.1m L/g MLSS,respectively.The average particle size of AGS decreased to 1.87mm,and the concentration and types of organic compounds in EPS decreased,while only the concentration of key proteins increased to maintain the stability of the particles.（3）Microbial community of aerobic granular sludge at three stages were analyzed in order to study the impact of organic load on the biological community,and molecular ecological network was constructed to study the change of microbial interaction relationship.The results showed that the composition and structure of microbial community changed,and the number of ASV in three stages were 188,294 and 322,respectively.Proteobacteria is the absolute dominant species,decreasing first and then increasing.The abundance of Cyanobacteria increased first and then decreased,and the increasing was related to the deterioration of water quality.The relative abundance of denitrifying bacteria was low,and the abundance of phosphorus-accumulating bacteria decreased,which led to the deterioration of effluent water quality.With the decrease of organic load,the molecular ecological network becomes more complex and the microbial interaction becomes closer.Proteobacteria have the most connections and occupy the dominant position.In the later stage,this phylum is mainly internal connections,and the competition is more intense.However,Bacteroidota was greatly influenced by other bacteria,and in the later stage,it mainly connected with other bacteria phyla and cooperated more closely.At the same time,the number of central nodes of the module is reduced,and there are more connecting nodes of Proteobacteria between modules,proving that the bacteria can adapt to the environment of low organic load.