Reduction Of Sewage Sludge Using Ultrasonic Combined With ClO₂ Disintegration In Sewage Treatment Process

Along with the development of social economy and urbanization in our country, the production of residual sludge was also growing. A lot of harmful and unstable organic substances were contained in sludge, which would endanger the environment if improperly handled or disposed. Now the sludge disposal method directly was generally used after dehydration, but the water content and disposal costs of dewatered sludge were high, which is also bulky. Thus, how to dispose residual sludge effectively as well as low cost and reduce the production of sludge without affecting the performance of sludge and quality of effluent have become the problems faced by the wastewater treatment plant.In this paper, on the basis of the analysis of comparing the advantages and disadvantages of different methods of sludge reduction, the reduction of sewage sludge through ultrasonic treatment combined with chlorine dioxide oxidation was proposed, and the small scale and pilot exploratory research were carried out. The major achievements are as follows:High density ultrasonic was used to disintegrate waste activated sludge from SBR system with pilot scale of 2.4 m³/d in this study, which focused on the effect of solid content, ultrasonic density and time on sludge disintegration. As a result, it has been found that the SCOD presented a linear increase with the ultrasonic time when ultrasonic density and solid content were in the range of 0.5³.0W/mL and 1.0%¹.5%, respectively. However, only slightly increase of SCOD with ultrasonic time was observed when ultrasonic density and solid content were in the range of 1.0³.0W/mL and 0.25%⁰.5%, respectively. It could conclude that high density ultrasonic was more suitable for disintegratation of sludge with high solid content, in which the increase of SCOD, NH₄⁺-N, TN and TP were all positively correlated with the ultrasonic density and structure of sludge could be destroyed after 6 min.Comparing two sets of SBR systems, about 2/3 of residual sludge discharged by one of SBR was returned to reactor after 6 min of ultrasonic treatment with ultrasonic density of 1.0 W /mL and response of the SBR system was tested. As a result, it has been found that no significant change was observed for the removal efficiency of SS, COD, TN and NH₄⁺-N in the effluent when compared with the control reactor, but TP was slightly higher than that of the control reactor. The amount of residual sludge decreased about 2.9kg which account for 45% of the total amount of ultimate sludge. The effect of sludge reduction is remarkable.The impact of chemical lysis of chlorine dioxide on microorganism in the excess sludge through single factor tests was studied. The results show that the content of the SCOD, NH₄⁺-N, TN, TP in the mixed liquor increase because of some microorganism of sludge leaching into the water phase after adding chlorine dioxide to the sludge for about one hour. Besides, best dosage of chlorine dioxide was 6mg/g dry sludge, suitable reaction time was 40 min and the best temperature was 35℃.3 factors and 3 levels of orthogonal experiment were investigated. The results showed that the main relation of the factors which had influence on the cell disintegration by ultrasonic coupling with chlorine dioxide was: ultrasonic time> ultrasonic density> dosage of chlorine dioxide. And the conditions of optimum coupling were ultrasonic density of 1.0W/mL, ultrasonic time of 6 min, dose of chlorine dioxide of 6mg/g.