Enhancement Of Partial Nitrification Kinetics And Mechanism By Low-intensity Ultrasound

Partial nitrification（PN）can save aeration and reduce excess sludge,which is of positive significance for promoting energy saving and waste reduction in sewage treatment and efficient biological nitrogen removal.However,the problems of slowly start-up and instability in the PN process limit its further application.In recent years,it has been found that low-intensity ultrasound has the propeties of promoting microbial activity and bacterium screening,which can quickly start-up the PN process and improve system stability,while the enhancement of mechanism still needs to be further explored.Therefore,in order to reveal the mechanism of low-intensity ultrasound to enhance the PN process,the effect of low-intensity ultrasound on the PN process characteristics of kinetics,start-up,stability,microbial and reactor operation.In order to investigate the PN process start-up performance,the start-up time,nitrogen conversion,sludge performance,variation of the bioactivity and kinetic parameters were investigated by using different ultrasonic density treatment in SBR.The results showed that the ultrasound group（0.10,0.15,0.20,0.25,0.30 W/mL）shortened the start-up time of PN process,and the nitrite accumulation capacity was significantly improved.Ultrasound treatment promoted the activity of ammonia oxidizing bacteria（AOB）while reducing the activity of nitrite oxidizing bacteria（NOB）.In addition,the half saturation constant(K_SN)of AOB in the experimental reactor matrix was significantly smaller than the control group,and the NOB K_SNN increased to varying degrees.Therefore,ultrasonic treatment allows AOB to preferentially obtain the substrate and achieve proliferate,and eventually rapidly realized the PN process.In order to further study the effect of low-intensity ultrasound on the rapid start-up the PN process and its stability,the effect of low-intensity ultrasound on the rapid start-up PN process and the resistance to temperature shock load was investigated.The results show that under low temperature conditions（18℃）,the ultrasonic group（density was 0.25 W/mL,irradiation time was 10 min）quickly start-up the PN process（18 days）with NAR exceeding 80%.When the temperature increased to 28℃,the PN process of the control group disappeared,and the NAR of the ultrasonic group remained above 80%,realised a stable PN process.Periodic ultrasound irradiation increases the number of Brevibacterium and Cocci of the sludge,effectively inhibiting the activity of NOB.The results show that the low-intensity ultrasound achieves the rapid start-up the PN process under low temperature conditions,changes the microbial community structure of the system,improves its impact load resistance,and improves the stability.On the basis of the above,the effect of low-intensity ultrasound on the NAR and microbial characteristics of the PN process was further studied.The results show that the ultrasound group（density was 0.25 W/mL,irradiation time was 10 min）steadily operated with NAR remained above 85%for 73 days under ambient temperature conditions.Ultrasonic treatment promotes the activity of AOB and aerobic denitrifying bacteria,improves its oxygen utilization rate,and a low dissolved oxygen（DO）environment was generated that are conducive to the realization of the PN process.Additionally,the application of long-term ultrasonic treatment led to the enhancement of the dominant position of Nitrosomonas in AOB,while Nitrospira in NOB is suppressed.Meanwhile,the relative abundance of the aerobic denitrifying bacteria Thauera,Terrimonas,Defluviimonas,and Thermomonas were enhanced.Therefore,the results show that low-intensity ultrasound could change the characteristics of microorganisms,thereby affecting the operating characteristics of the reactor,which was beneficial to achieve the PN process.Therefore,the mechanism of low-intensity ultrasound to enhance PN process was explored,which was the theoretical foundation for the application of ultrasound technology in the PN process,and have a significance for enhancing the biological nitrogen removal efficiency of sewage treatment.