Effect Of Ultrasonic Pretreatment On Hydrolysis And Acidification Of Sludge

Sewage sludge contains rich organic matter, and various nutrients such as nitrogen and phosphorus. In the hydrolysis and acidification of sludge, short chain fatty acids are produced. It is essential substrate for removing nutrients, and it can be used as the additional carbon source for nitrogen and phosphorus removal of sewage treatment plants; meanwhile, released nitrogen and phosphorus can be recovered, so that sludge can be reused effectively. In this study, hydrolysis and acidification of the sludge was promoted by ultrasonic pretreatment, which speeded up the release of nutrients, enhanced reuse of the sludge.The hydrolysis-acidification characteristics of sludge pretreated by different ultrasonic intensities and time were explored; the sludge properties and its influences on subsequent hydrolysis and acidification caused by different ultrasonic treatment conditions were investigated, and the process conditions for the release of organic matter and nutrients were optimized. The following contents were studied: 1. Initial understanding the impact on the process of sludge hydrolysis and acidification caused by ultrasonic pretreatment; 2. Impact on the natures of the sludge itself caused by ultrasonic pretreatment; 3. Influence on products of sludge hydrolysis and acidification exerted by reaction progress; 4. Further study of the influence on the process of sludge hydrolysis and acidification caused by different ultrasonic intensities and time; 5. Optimizing the process conditions of organic mater and nutrients release from sludge in the context of low energy input; 6. The impact on promoting hydrolysis and acidification of sludge by ultrasonic pretreatment under different temperatures.The results indicated that, 1. Sludge respectively pretreated by ultrasonic withф6mm horn of 0.6W/mL and 1.0W/mL with 5min, the sludge with ultrasonic pretreatment at 1.0W/mL, its efficiency of producing VFAs (Volatile Fatty Acids) significantly lower during follow-up process of hydrolysis and acidification; 2. In the first 5d of hydrolysis and acidification, SCOD (Soluble Chemical Oxygen Demand) release of the fastest, and when the first 7d, VFAs, HAc (Acetic Acid) reached maximum; 3. In the ultrasonic intensity 0.127~0.950W/mL, and time 1~9min, with the increase of ultrasonic intensity and time, SCOD, VFAs, HAc, and formic acid in sludge supernatant increased; 4. There was a big influence on hydrolysis and acidification of sludge caused by difference of ultrasonic equipment and ultrasonic horn size; 5. Sludge pretreated by ultrasonic of 0.095, 0.190, 0.380W/mL respectively with 5min, in the process of hydrolysis and acidification, SCOD release rate 0.095W/mL﹥0.380W/mL﹥0.190W/mL, and increase of the ultrasonic intensity could improve VFAs, ThODVFAs (Theoretical Oxygen Demand of VFAs)/SCOD and HAc in the sludge supernatant, on the contrary it had different effect with the sludge pretreated by ultrasonic of 0.570W/mL with 5min; 6. Sludge pretreated by ultrasonic of 0.323W/mL with 0.5, 1.5, 3, 5min, in the first 3d of hydrolysis and acidification, SCOD release rate 3min﹥1.5min﹥0.5min﹥5min, and increase of ultrasonic time, HAc in sludge supernatant was increased; 7. Within range of low power and short time, when sludge moisture content was 94.52%, ultrasonic intensity was 0.342W/mL, ultrasonic pretreatment time was 3min, the optimal hydrolysis and acidification time for SCOD release was 5d, and for VFAs production was 7d; when hydrolysis and acidification time was 7d, sludge moisture content was 95.64%, ultrasonic intensity was 0.342W/mL, the best ultrasonic pretreatment time for HAc production was 3 min, and for phosphorus release was 2 min; when hydrolysis and acidification time was 7d, ultrasonic pretreatment time was 3min, ultrasonic intensity was 0.114W/mL. The optimal sludge moisture content for TN release was 95.64%, and for NH4+-N release was 94.52%; 8. Sludge pretreated by ultrasonic of 0.209W/mL with 5min, increase ambient temperature of hydrolysis and acidification was beneficial to release of SCOD, VFAs, HAc, nitrogen, phosphorus, but there was no obvious promotion to the release of phosphorus when ambient temperature was higher than 25℃.Therefore, using ultrasonic pretreatment could promote the efficiency of hydrolysis- acidification of sludge, increase amount and rate of organic matter and the release of nutrients, but when the ultrasonic energy was over input, instead, it was not conducive to hydrolysis and acidification of sludge and quickly release of nutrients, because microbial activity was impaired by excessive ultrasonic pretreatment.