The Optimization And Mechanism Study Of SCFAs Releasing By The Combination Of Sonication And Hydrolysis

Short chain fatty acids (SCFAs) is one of the most easily microorganisms using organic matter. If SCFAs in sludges can release by ultrasonic hydrolysis combination, on one hand, the discharge of waste sludge in wastewater treatment plant can reduce, on the other hand, released SCFAs can recycle to the sewage treatment plant biochemical section to solve problem of the poor condition of running with low carbon and high nitrogen and phosphorus, MWPTs can achieve a win-win of both better running and recycling of sludges.This paper first directly broke sludges by ultrasonic to release SCFAs by changing the sludge density, ultrasonic time, ultrasonis density. The result showed that the amount of released SCFAs increased over ultrasonic time and ultrasonic intensity, but when the input energy was too high sonnication had little effect and the released SCFAs decreased; at the same energy consumption, the situations of longer ultrasonic time and lower ultrasonic intensity resulted in more effective SCFAs release compared to that of relatively shorter ultrasonic time and higher ultrasonic intensity; acetic acid and propanoic acid are the mine parts of SCFAs released from sludge. The optimal parameters were ultrasonic time 80min, sludge density 10g·L-1, ultrasonic density 0.5W·mL-1, highest released SCFAs concentration was 197.0mg·L-1,near 10% of the released COD.In order to get higher SCFAs, this paper combined ultrasonic technology and hydrolytic acidification technology, and changed the sonication parameters to get higher easy-hydrolysis components (EHCs). The result showed that after the treatment of sonication the amount of EHCs released increased over ultrasonic time and ultrasonic intensity when the ultrasonic intensity was lower than 0.6W·mL-1and ultrasonic time was the most effective factor; at the same ultrasonic energy level, the situations of longer ultrasonic time and lower ultrasonic intensity resulted in more effective EHCs release compared to that of relatively shorter ultrasonic time and greater ultrasonic intensity. The optimal parameters were ultrasonic time 100min, sludge density Sg·L-1, ultrasonic density 0.6W·mL-1, highest released EHCs concentration was 5112mgCOD·L-1, carbohydrate was the most important component in released EHCs. Machinery effect was the most important other than free radical effect and thermal effect in the release of SCFAs from WAS by sonication.Hydrolysis results to the ultrasonic treated sludge showed that the sludge inoculation condition, temperature, waving speed have impacts on sludge hydrolysis,5% inoculated anaerobic sludge, hydrolysis temperature 25 ℃, waving speed 100 rpm was best for SCFAs generating, the best hydrolysis time of 16h. Highest generated SCFAs concentration was 1523.0mg·L-1, equivalent COD 1979.4 mg·L-1. Sugar, total sugar and amino acids changes to SCFAs by hydrosis, but SCFAs reduce by microbial utilization after long time hydrolysis.The research results showed that the using of ultrasonic technology and the hydrolytic acidification technology can effectively release and generate SCFAs, which is useful to the reduction and recycle of excess activated sludge.