Effect Of Pretreatment Of Alkali Addition And Ultrasonic Breakage On Sludge Aerobic Digestion

The hydrolysis of sludge solid is the key step for sludge aerobic digestion. While ultrasonic breakage is an effective method to decompose sludge. At present, the most commonly applied method for sludge ultrasonic breakage uses ultrasonic densities ranged from 0.096W/mL to 2W/mL. However, higher ultrasonic density will result in higher energy consumption, which is hard for actual engineering broadly applying. So, in this experiment, ultrasonic with relatively lower ultrasonic density, that is ultrasonic with frequency of 25 kHz and ultrasonic density of 0.05W/mL, was employed to treat sludge that alkali was added in before. And the promoting effect of breakage to sludge aerobic digestion was also studied in this experiment.In the experiment, the adjusting pH values were kept at 8.0,9.0,10.0,11.0,respectively,then, ultrasonic with ultrasonic density of 0.05W/mL was applied to disintegrate the sludge, and the breakage times are 5min,10min,20min,30min and 40min, respectively. After that, the sludge added with seed sludge digested aerobically for 10 days at the temperature of 32±1℃. Meanwhile, the effects of pH value (alkali amount added) and ultrasonic breakage time on sludge breakage and follow-up biogas production, organic matters remove rate and digesting velocity were studied.The experiment results suggested that alkali and ultrasonic breakage could enhance the SCOD leaching rate of sludge and decrease the content of organics. When alkali amount and ultrasonic breakage time increased, the SCOD leaching rate and the VSS decreasing rate raised greatly. During the procedure of aerobic digestion, the stage of hydrolysis acidification was shortened greatly. In the experiment, it is founded that with proper pretreatment the remove rate of COD and organic matters, biogas production and VFA production raised as the increase of pH value and ultrasonic breakage time. In the contrast group, during the 10 days'aerobic digestion 1L sludge could attain to VSS remove rate of 14.4%, final organic matter content (VSS/TSS) of 56.7% and total biogas production of 903mL, while when pH was 11.0 and ultrasonic breakage proceeded for 40min, it could attain to VSS remove rate of 35.5%, final organic matter content (VSS/TSS) of 48.65% and total biogas production of 1606mL. These experimental results demonstrated that ultrasonic breakage after adding alkali can have well promoting effect on sludge digestion.