Response Of Anammox Process To Different Dosing Strategies Of Spiramycin And Streptomycin

Anaerobic ammonium oxidation?anammox?has attracted public attention in the field of wastewater treatment,due to low energy consumption and sludge production.However,it also has the disadvantages of low cell yield and susceptibility to external adverse environment.Especially,the application of anammox-based process for real wastewater treatment has been limited due to various inhibitors.For instance,a large number of antibiotics could bring lots of antibiotic resistance bacteria?ARB?and antibiotic resistance genes?ARGs?,which bring great risks to the environment.In this study,three lab-scale upflow anaerobic sludge blanket?UASB?reactors?R₁,R₂ and R₃?were established to evaluate the response of the anammox process to typical antibiotics with different exposure strategies,including the operational performance,microbial community,and key genes:The strategy of gradiently increasing the concentration of spiramycin in R₁;the strategy of repeated exposure to high-concentration spiramycin in R₂;the strategy of successive exposure of streptomycin and spiramycin in R₃.The variations in reactor performance,key genes and microbial community under three different strategies were studied.In the process of gradiently increasing the concentration of spiramycin in R₁,It was found that 0.5 mg L^-1 of spiramycin did not significantly affect the nitrogen removal performance,but increased the abundances of spiramycin resistance genes and int I1.Correlation analysis showed that int I1 promoted the horizontal transfer of resistance genes.The abundances of functional genes related to anammox reaction,hzs A and hdh,decreased first and then increased.Anaerobic ammonia-oxidizing bacteria?An AOB?could adapt to low concentrations(<1 mg L^-1)of spiramycin,while high concentrations(?3 mg L^-1)of spiramycin had a negative effect on its activity.With the addition of spiramycin,it took different time for the recovery of reactor performance.Alpha diversity analysis showed that the introduction of spiramycin reduced the microbial diversity of the anammox system.In addition,the introduced spiramycin changed the microbial communities and increased the abundances of spiramycin resistance genes.The process of repeated exposure to high-concentration spiramycin revealed that5 mg L^-1 spiramycin significantly inhibited the reactor performance.The relative abundance of Planctomycetes decreased to 15.41%on Day 105 with the addition of 5mg L^-1 of spiramycin.When R₁ was first exposed to 5 mg L^-1 spiramycin,the reactor performance could recover without any future measures in a short period,while the R₂took a longer time to reach higher levels of nitrogen removal efficiency.R₂ had a greater antibiotic loading rate because of the prolonged spiramycin exposure.Alpha diversity analysis showed that the microbial diversity and richness of R₂ were lower than those of R₁.Meanwhile,int I1 promoted the horizontal transfer of resistance genes in these two reactors.Adding spiramycin changed the microbial communities and decline the diversity of anaerobic ammonia-oxidizing bacteria.The reactor performance of R₂fluctuated greatly,however,the R₁ was relatively stable.The study on the effects of streptomycin and spiramycin exposure on An AOB showed that the exposure of streptomycin did not affect the performance,but reduced the anammox activity and increased the abundances of streptomycin resistance genes in R₃.Furthermore,the subsequent addition of spiramycin increased the abundances of spiramycin resistance genes.Meanwhile,it also promoted an increase of the abundances of streptomycin resistance genes.The pretreatment of streptomycin in R₃exhibited a higher resistance to the gradient increased concentrations of spiramycin.These results suggested that the strategy of gradiently increasing the antibiotic concentration was more effective for the improvement of the tolerance of the anammox process to high-concentration antibiotics.In the sequential dosing strategy of streptomycin and spiramycin,spiramycin promoted the horizontal transfer of streptomycin resistance genes,and the R₃ reactor had a higher resistance to the gradient increase of spiramycin after the streptomycin pre-exposure.This study provided a guidance for the stable operation of the anammox process for the antibiotic-containing wastewater treatment.