Study On The Start-up And Operation Stability Of ABR By Low Intensity Ultrasound

At present,Chinese urban sewage treatment mainly uses aerobic biological treatment technology,and the problems of high energy consumption and high sludge yield make people turn their attention to the anaerobic biological treatment technology with low energy consumption,low sludge yield and clean.However,the stability of the reactor and the effect of wastewater treatment are seriously affected by the anaerobic bacteria’s long life cycle and harsh living conditions.Therefore,it is very important to maintain the stability of anaerobic biological wastewater treatment process.It has been proved that low-intensity ultrasound can improve cell enzyme activity,promote mass transfer and accelerate cell metabolism.In this paper,the effect of low intensity ultrasound on the start-up stability of anaerobic baffled reactor（ABR）and the change of sludge characteristics enhanced by low intensity ultrasound were studied,the effect of low intensity ultrasound on the performance of ABR under different influent organic substrate concentration,temperature and impact of heavy metal ions was investigated,to reveal the enhancement mechanism of low intensity ultrasound on anaerobic biological treatment of wastewater.The major findings are as follows:During the start-up of ABR,ultrasonic parameters such as frequency 20 k Hz,acoustic energy density 0.1 w/m L,irradiation time 10 minutes,irradiation period 24 h,irradiation sludge ratio 10%were used to irradiate the sludge in ABR compartments.The experimental results showed that the Chemical oxygen demand concentration（COD）of ABR effluent remained stable after the 40th day,and the COD removal rate was about 91%.In the control group,the COD concentration remained stable after the 46th day,and the COD removal rate was about 86%.ABR of ultrasound group shortened the start-up time of 6 days successfully,and the COD removal rate was 5%higher than that of control group.Volatile fatty acids（VFA）were mainly acetic acid and propionic acid,and the concentration of VFA decreased gradually with the passage of compartments.low-intensity ultrasound during domestication promoted more acetic acid production in compartments 1 and 2,and more propionic acid production in compartments 3 and 4,the VFA concentrations in four compartments were139.71,62.49,25.66 and 6.49 mg/L,respectively,and in the control group were 60.44,31.49,8.79 and 4.72 mg/L,respectively,low intensity ultrasound could increase the content of VFA and provide more substrate for subsequent methanogens.1～4（-214.26,-225.61,-232.11,-248.66 m V）of reduction potential compartment in stable phase ultrasound group were lower than those in control group（-209.53,-215.36,-224.21,-234.87 m V）,low intensity ultrasound can promote the consumption of oxidation state in ABR compartments,reduce ORP,and provide a better living environment for methanogens.Therefore,low intensity ultrasound can enhance the start-up and operation stability of ABR.Secondly,the characteristics of ABR sludge were studied during the start-up of ABR,in order to explore the mechanism of low-intensity ultrasound to promote the stable operation of ABR.During the start-up,the total EPS of ABR compartments increased,and the 1～4contents of PN compartments in control group were 34.16,22.96,21.06 and 18.26 mg/g·VSS,respectively,in the ultrasound group,46.24,29.87,28.92,22.74 mg/g·VSS and PN increased respectively.In the control group,the contents of polysaccharide（PS）in compartment 1-4were 54.38,43.68,42.72 and 35.89 mg/g·VSS,respectively,in ultrasound group,47.66,39.26,36.84,32.46 mg/g·VSS,PS content decreased.Compared with the control group,the activity of DHA and coenzyme F₄₂₀were increased by 42.47%,28.13%,27.42%and 31.7%,respectively in stable phase,while coenzyme F₄₂₀was increased by 23.91%,19.74%,14.81%and 6.12%,respectively.It was found that low intensity ultrasonic could make the floc more dispersed and the specific surface area increased,which was beneficial to enhance the mass transfer between sludge and substrate.Finally,after ABR was stable,the influence of low-intensity ultrasound on the stability of ABR under the impact load of temperature,heavy metal ions and organic substrate concentration is analyzed.The results showed that when the temperature decreased from 34℃to 15℃,the removal rate of COD increased by 9.06%,which was better than that of low intensity ultrasound at 34℃.After the substrate concentration was increased from 900 mg/L to 1800 mg/L,the COD removal rate of ultrasound group was reduced to the lowest 81.48%on the 10th day of operation,which was higher than that of Control Group 76.32%.It was found that the Cu（Ⅱ）semi-inhibitory concentration(IC₅₀)was 94.62 mg/L in the ultrasound group and 88.85 mg/L in the control group,and the Cu（Ⅱ）semi-inhibitory concentration(IC₅₀)was increased by low intensity ultrasound,enhanced the tolerance of sludge to Cu（Ⅱ）.It was found that the ultrasound group excreted more PN and reduced the toxicity of Cu（Ⅱ）.