| 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 combined ultrasonic treatment and alkaline adjustment, which speeded up the release of nutrients, enhanced reuse of the sludge.The following contents were studied:(1) the combined modes and conditions of combined ultrasonic treatment and alkaline adjustment were investigated. (2) Impact on the natures of the sludge itself and it's subsequent hydrolysis and acidification caused by the pH's variation in enhancement by combined ultrasonic treatment and alkaline adjustment; (3) Impact on the natures of the sludge itself and it's subsequent hydrolysis and acidification caused by different ultrasonic intensities in enhancement by combined ultrasonic treatment and alkaline adjustment; (4) Impact on the natures of the sludge itself and it's subsequent hydrolysis and acidification caused by different ultrasonic time in enhancement by combined ultrasonic treatment and alkaline adjustment; (5) Study of the start-up of the sludge hydrolysis-acidification reactor by combined ultrasonic treatment and alkaline adjustment; (6) The impact on effect of hydrolysis and acidification of sludge in the condition of hydrolysis-acidification reactor running with continuous feeding.The results indicated that, (1) Sludge respectively pretreated by ultrasonic treatment and alkaline adjustment, the hydrolysis and acidification process of sludge were enhanced, and the condition that pH was adjusted at 9.5 just after ultrasonic treatment was more helpful for the conversion of organic matter; (2) Sludge was adjusted by NaOH contraled pH at 8.5,9.0,9.5,10.0 with the ultrasonic intensity 0.095 W/mL, and time 3 min,, we get the best effect on the forth day at pH 8.5; The conversion rate SCOD and VFAs could reach 45.10% and 9.17% and about 13.55% of VSS of sludge could be reduced; (3) Sludge treated by ultrasonic of 0.095W/mL,0.209W/mL,0.323W/mL respectively with 3min and at pH 9.0, in the process of hydrolysis and acidification, with the increase of ultrasonic intensity, the consistency of SCOD,VFAs and HAc in sludge supernatant increased, the conversion rate of SCOD and VFAs could reach 16.10% and 5.86% and about 20.13% of VSS of sludge could be reduced at ultrasonic intensity was 0.323W/mL; (4) In the ultrasonic intensity 0.209W/mL and time lmin,3min and 5min treated sludge, which pH was controlled at 8.5, with the increase of ultrasonic time, the consistency of SCOD,VFAs and HAc in sludge supernatant increased, When ultrasonic treatment time was 5min, the maximum value of SCOD conversion rate and ThODVFAs/SCOD could reach 16.05% and 28.83%, respectively, and about 12.87% of VSS of sludge could be reduced; (5) In the start-up process of hydrolysis-acidification reactor, the starts-up could be completed after the 11-day hydrolysis-acidification, the consistency of SCOD in ultrasonic treatment reactor could reach 5274.2mg/L, and in alkaline adjustment reactor reached 8256.1mg/L; (6) In the running stage of continuous feeding of the hydrolysis-acidification reactor, at the sludge raw ratio of 10%, ultrasonic intensity and time were 0.209W/mL and 3min, pH was 9.0, the production of SCOD in combined ultrasonic treatment and alkaline adjustment reactor were about 11701.9mg/L, and about 29.98% of VSS of sludge could be reduced, and combine enhancement is useful the accumulation of HAc;(7) The effects of combined ehancement is more significant at higher sludge raw ratio and lower alkaline adjustment, and it had no vantage at lower sludge raw ratio as the alkaline adjustment played a dominant role;(8) With the increase of raw ratio, production of organic matter,VFAs and so on in hydrolysis-acidification reactors supernatant reduce slightly, and had no apparent influences on the releases of phosphorus, the effect of combined enhancement appear at the ratio of 20%, especially it had better effectiveness for the accumulate of HAc; (9) With ultrasonic intensity increase from 0.209W/mL to 0.323W/mL, the conversion of organic matter and VFAs have a little increase in combined enhancement reactor, meanwhile the effect of combined enhancement more appear; The consistency of SCOD,VFAs,HAc and NH3-N began to lower in combined enhancement reactor, but phosphorus consistency increased while the pH from 9.0 become 8.5; (10) SCOD consistency increased rapidly, when the mode of pH adjusted become twice a day, but VFAs,HAc and NH3-N have a slightly reduced, and phosphorus consistency declined speedily; Stopping to adjust the pH of hydrolysis and acidification reactor, the conversion of SCOD and the release of nitrogen had a large scale decline, and phosphorus consistency increased.Therefore, using ultrasonic treatment and alkaline adjustment could promote the efficiency of hydrolysis-acidification of sludge, increase amount and rate of organic matter and the release of nutrients, and in the condition of hydrolysis-acidification reactor running with continue feeding, which by combined ultrasonic treatment and alkaline adjustment, the hydrolysis-acidification can reach ideal result with high-raw ratio. |
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