Study On The Efficiency And Regulation Of Completely Autotrophic Nitrogen Removal Granular Sludge In The Treatment Of Low Ammonia Nitrogen Wastewater Under Low Temperatures

Partial nitritation-anammox process（PN-ANAMMOX,PN/A）as an energy self-sufficient process is the urgent research direction of sewage treatment.Based on this,A single-stage PN-ANAMMOX（PN/A）granular sludge cultured at room temperature was used as the object to study the completely autotrophic nitrogen removal efficiency and microbial community structure of low-strength wastewater based on the completely autotrophic nitrogen removal over nitrite based on granular sludge at low temperature.The results showed that under the condition of low temperature（15±1）℃,the ammonia nitrogen load was maintained at 1.29 kg·（m³·d）^-1,and the ammonia nitrogen concentration in the injection was gradually reduced from 70 mg·L^-1to 40 mg·L^-1.DO/TAN was controlled at 0.22～0.25,the total nitrogen removal rate could be maintained at（85±4）%,the average TN concentration in the effluent was about 8.9mg·L^-1,and there was no significant proliferation of NOB during the operation period,and the Nitrospira abundance is less than 1%.Elutriation of floc sludge and control of low DO/TAN values could be used as effective control strategies to inhibit NOB（nitrite-oxidizing bacteria）proliferation.Completely autotrophic nitrogen removal over nitrite granular sludge operated under low temperature and low substrate conditions,the particle size became smaller,and the colour changed from brown red to brown yellow.The total amount of PS decreased slightly,and the ratio of PN/PS stabilized at 2.5～3.Planctomycetes and Proteobacteria dominated in the community.Candidatus＿Kuenenia and Candidatus＿Brocadia are two AMX bacteria in the sludge.A continuous flow reactor was used to study the changes in the denitrification performance of PN/A granular sludge under temperature shock.The effect of a short-term temperature drop on the denitrification effect was studied.The results of the reactor operation test showed that when the temperature dropped from 30℃to 7℃,the average total nitrogen removal load decreased from 1.194±0.0455 to 0.655±0.130 kg·（m³·d）^-1.The SGompertz model was used to simulate the average total nitrogen removal rate at different temperatures to analyze the effect of low temperature on the efficiency of nitrogen removal.Under low temperature conditions,the accumulation rate of nitrous acid increases,and the activity of AMX is inhibited by low temperature,thereby weakening the denitrification effect.The content of EPS increased rapidly（73.03%）under low temperature stimulation,especially TB-EPS secreted a large amount of tryptophan-like protein under low temperature environment to maintain the stable denitrification efficiency of the system.Cold acclimation is an effective approach to improve the nitrogen removal performance and operational stability of partial nitritation/ANAMMOX（PN/A）combined processes at low temperatures.In order to explore the specific effects of cold acclimation on the characteristics of sludge,the differentiations of the temperature sensitivity,granular morphology,the composition of extracellular polymer substance（EPS）and bacterial community structure between PN/A granular sludges cultivated at medium-high temperature（30℃）and acclimated to low temperature（15℃）were investigated in this study.The results of reaction thermodynamics showed that the nitrogen removal performance of the granules acclimated to low temperature（G_L）was significantly higher than that of the ones cultivated at medium-high temperature（G_H）under the low temperature（10～20℃）,and the apparent activation energy（E_a）of total inorganic nitrogen removal for the former was decreased by 28.4%.Compared with G_H,G_Lhad a smaller average particle size of 25.8%and higher EPS contents of 16.6%,resulting in a significant lower settling property.Based on the high-throughput sequencing results,G_Lexhibited a higher diversity of bacterial community,and a lower relative abundance ratio（0.04）of aerobic ammonium-oxidizing bacteria（Nitrosomonas）and anaerobic ammonium-oxidizing bacteria（Candidatus＿Kuenenia）than 0.34 for G_H.It indicated that the PN/A granules held a strong ability to retain slow-growing autotrophic bacteria in the system,even under the low temperature.These findings could provide the meaningful reference for analyzing self-adaption mechanisms of PN/A sludge to low temperature conditions,and promote the industrial application of combined processes.