Effect of low-intensity ultrasound on controlling the limit concentration of heavy metal Cu(Ⅱ) in anaerobic sludge

With the changes of sludge matrix degradation rate (v_COD), extracellular polymeric substances (EPS) and enzyme activity (DHA) as the evaluation indexes, the effects of low-intensity ultrasound on the tolerance of heavy metal Cu(Ⅱ) in anaerobic sludge were investigated under different influent Cu(Ⅱ) concentrations. The results show that low-intensity ultrasound can improve the tolerance of sludge microorganisms to Cu(Ⅱ). With the increase of the concentration of Cu(Ⅱ) in the influent, the v_COD decreases in both the ultrasound group and the control group, but v_COD in the ultrasound group decreases more slowly. The fit of the relationship between the influent Cu(Ⅱ) concentration and the percentage inhibition rate of sludge matrix degradation in the ultrasonic group and the control group yieldes IC₅₀ of 94.62 mg/L and 88.85 mg/L, respectively, indicating that low-intensity ultrasonic waves can improve the inhibition threshold of Cu(Ⅱ) by anaerobic sludge. The EPS content in the ultrasound group and the control group increase slightly when the concentration of Cu(Ⅱ) is 1 mg/L in the influent, and then decrease gradually with further increasing concentration of Cu(Ⅱ). However, the EPS content in the ultrasound group is higher than that in the control group, which may be that low-intensity ultrasound reduces the biotoxicity of Cu(Ⅱ) by promoting more EPS secretion from sludge. In addition, compared to the control group, the DHA activity of the ultrasound group is increased by 3.95%‒36.31%. Therefore, the tolerance of anaerobic sludge to the heavy metal Cu(Ⅱ) can be improved through low-intensity ultrasound, to maintain the stable operation of the anaerobic biological treatment of sewage.