Enhanced Granulation And Perfo Rmance Of Aerobic Granular Sludge At Low Temperature

Affected by low temperature in winter,the normal operation of wastewater plants due to the low temperature of the influent water,which leads to a decrease in the efficiency of pollutant removal by ordinary activated sludge in biochemical ponds,and in serious cases,triggers sludge expansion,affecting the effluent quality of wastewater plants.Aerobic granular sludge（AGS）has the advantages of good settling performance,high sludge concentration per unit volume,and high resistance to shock loading,but the start-up time of aerobic granular sludge reactor is long at room temperature,and the required start-up time becomes longer under low temperature conditions due to the weakened cellular respiration.Therefore,it is important to study the rapid cultivation of aerobic granular sludge at low temperature and maintain good treatment effect.Based on this,the experiments were conducted in autumn and winter under low water temperature conditions,and will be maintained at low temperature for a long period of time.By using two different culture methods:one is to add coagulant to the reactor,and the other is to add artificial crystal nuclei,the effects of the two culture methods at low temperature on the rate of sludge granulation,the structure of the mature granular sludge microbial community,the efficiency of removing major pollutants and the ability to resist shock loading were investigated.The effect of both culture methods on the rate of sludge granulation,structure of mature granular sludge microbial community,efficiency of removal of major pollutants and ability to withstand shock loading was investigated.For enhanced granulation culture,coagulant（polymeric aluminum chloride,R1reactor）and artificial crystal nuclei（Fe（OH）₃,R2 reactor）were added to the reactor to cultivate and observe aerobic granular sludge formation,respectively.In the R1reactor,it takes 32 days for the granular sludge to mature with an average particle size of 1.25 mm.At this time,the sludge concentration in the reactor is about 8 g/L.The formation process is based on the initial biomass nuclei formed by the flocculation of coagulants and then the formation of other microorganisms attached to the mycelium with filamentous bacteria as the skeleton;while in the R2 reactor,the granulated sludge takes 24 days to mature with an average particle size of 1.75 mm,and the sludge concentration in the reactor is about 10.24 g/L at this time.The formation process is formed by using colloidal particles of iron hydroxide as the core to which other microorganisms attach and grow.In terms of biodiversity,the groups were ranked from highest to lowest in terms of diversity index:inoculated sludge>group with artificial crystalline nuclei>group with coagulant>group without artificial enhancement.As for the microbial community structure,the population and relative abundance of microorganisms in each group were not nearly the same due to the different culture methods.The dominant phyla in all groups at the phylum level were Proteobacteria,Bacteroidota,and Actinobacteriota,with differences in the relative abundance of each phylum in each group.Candidatus＿Micothrix was the dominant genus in both the non-artificially enhanced group and the R1 reactor,but in the non-artificially enhanced group it caused sludge swelling,while in the R1 reactor it participated as a skeleton in the formation of aerobic granular sludge.In the R2 reactor,the genus Sphaerotilus＿natans,which has a stronger affinity for iron,emerged and gradually became the dominant species.In terms of pollutant removal effect,the R1 reactor caused sludge instability when the external environmental conditions changed,resulting in deterioration of effluent quality and longer time to restore the removal efficiency,which proved that the granular sludge in this group was less resistant to shock loading.It has higher pollutant removal efficiency and stronger shock load resistance.The removal rates of major pollutants such as COD,NH₄⁺-N and TP are 98.75%,97.51%and 99.64%respectively,which are far better than the Class A emission standard.