| In order to investigate the mechanisms of ultrasonic promotion for sludge anaerobic/aerobic digestibility, the index of EPS（polysaccharide, protein, DNA and total content）and dissolved substances were measured by using biochemistrical methods. The optimal conditions of ultrasonic treatment were decided from the uniform design. The uniform design results showed that at the optimal ultrasonic conditions of 15 min ultrasonic time, 0.1 W/mL density and 12 h ultrasonic interval time, the performances of anaerobic/aerobic digestion were greatly improved, the removal rate of VSS reached 42.45% after 10d digestion. The results of sludge anaerobic/aerobic digestion promoted by ultrasonic treatment showed that the variational trend of EPS index in sludge increased firstly and then fell off during 10 d digestion, the maximum of protein, DNA and total content were appeared in the 2 d, while the maximum of polysaccharides was came out in the 4 d. The total content of EPS in ultrasonic sludge was more than the control sludge during 0-6 d digestion, and then less than control in 6-10 d because of a large amount of EPS and cellular substances had been released out. The variational trend of dissolved substances in the supernatant was similar with that in sludge, the dissolved substances concentrations were highly increased after ultrasonic treatment. The maximum of total concentrations in ultrasonic sludge was 34.61 mg·L-1 higher than the beginning, it was about 3.5 multiple of the increased concentrations of control’s maximum, indicated that ultrasonic treatment could release EPS and cellular substances into the supernatant. The greatly release of soluble organics enhanced the consumed proportion of organics, resulted in the removal rate of VSS in ultrasonic sludge was markedly improved. The infrared spectrum analysis of EPS showed that polysaccharide, protein and DNA were the major components of EPS in anaerobic/aerobic sludge, ultrasonic treatment wouldn’t change the organic structure of them. |
