Effect Of Low-intensity Ultrasound On Anammox Granular Sludge In High Ammonia-nitrogen Inorganic Wastewater

Anammox process is not only low in energy consumption,but also saves the addition of organic carbon sources,greatly reducing treatment costs and achieving efficient and low-energy wastewater treatment for high ammonia nitrogen inorganic wastewater.Rare earth wastewater contains high concentration of ammonia nitrogen and lacks organic carbon sources.The use of anammox process can achieve good results.However,the long start-up time of the reactor,substrate inhibition,and particle flotation issues limit its application.To solve these problems,low-intensity ultrasound technology is combined with anammox process to improve the activity of anammox granular sludge,enhancing the denitrification performance and stability of the reactor.The main content and results are as follows:Firstly,the effects of low-intensity ultrasound treatment with different ultrasound power densities and treatment times on the activity and granule sludge structure of anammox sludge were studied.The results showed that appropriate ultrasound parameters（ultrasound power density of 0.2 W/m L and treatment time of 2 minutes）increased the activity of anammox granule sludge by 20.81%.Under the optimal ultrasound parameters,the activities of three key enzymes involved in anammox（Nar,Nir S,HZO）increased by 43.98%,17.92%,and 16.49%,respectively.The ultrasound action caused the detachment of extracellular polymers and cell clusters from the sludge surface,resulting in a rough and porous structure of the sludge sludge,which improved the mass transfer performance of the sludge.However,when the ultrasound power density or treatment time further increased,the activity of anammox granule sludge was inhibited.Excessive ultrasound energy input（≥7.2 k J/g VSS）resulted in the damage or even rupture of anammox bacterial cell membranes,which was the main reason for their inactivation.Response surface methodology analysis revealed that an increase in ultrasound power density had a greater destructive effect on anammox bacterial cells compared to an extension of the treatment time.Secondly,the effects of low-intensity ultrasound on the treatment of high-ammonia nitrogen inorganic wastewater using an anaerobic ammonia oxidation expanded granular sludge bed reactor（ANAMMOX-EGSB）were investigated.The changes in denitrification performance,sludge characteristics,and microbial community structure of the ANAMMOX-EGSB reactor were examined.The results showed that low-intensity ultrasound could improve the denitrification efficiency of the anammox reactor.At an influent nitrogen load of 6.03 kg N/m3/d,the total nitrogen removal rate in the ultrasound group reactor increased by 11.40%,and its resistance to nitrogen load shocks was also enhanced.After long-term periodic ultrasound treatment,the granule sludge size was maintained at 1.0～1.5 mm,which was beneficial for maintaining good mass transfer efficiency,enhancing the activity of anammox granule sludge,and reducing sludge flotation.The total amount of sludge extracellular polymeric substances（EPS）significantly increased,with a more pronounced increase in TB-EPS,which contributed to the structural stability of the granule sludge.The specific anammox activity of the granule sludge increased by 33.2%,and the simplified Gompertz equation model indicated that the anammox bacterial growth rate in the ultrasound group(0.0127 d^-1)was higher than that in the control group(0.0107 d^-1).High-throughput analysis revealed that low-intensity ultrasound irradiation led to a decrease in microbial community richness and diversity,exerting a selective effect on microorganisms.At the phylum level,the relative abundances of Planctomycetes,Chloroflexi,Nitrospirae,and Acidobacteria increased by 22.18%,0.38%,1.01%,and 1.75%,respectively,indicating the enrichment of anammox bacteria and their symbiotic bacteria,thereby maintaining a favorable ecological balance within the reactor,promoting the rapid proliferation of functional bacteria,and improving the denitrification performance of the reactor.At the genus level,low-intensity ultrasound increased the relative abundances of three anammox bacterial genera,with Candidatus Brocadia showing a 22.03%increase compared to the control group.However,the relative abundance of denitrifying bacteria decreased significantly,reducing their utilization of substrates and living space,and promoting the enrichment of anammox bacterial communities.