Study On The Ratio Of Cell Lysis Of Disposed Sewage Sludge Under Alkaline Thermal Condition And Short-Chain Fatty Acids Accumulation In The Mesothermal Anaerobic Digestion

With the development of economy and waste activated sludge treatment technology, the amount of waste activated sludge increased very rapidly. The development of effective and environmental friendly disposal techonology of excess sludge had become one of the most complex problems. It was known that anaerobic fermentation can make waste activated stabilized and reduction and produces the methane. However, it took a long time to derupt the cell wall. Recently, to accelerate the hydrolysis of sludge, various sludge pretreatment technologies have been developed, such as chemical, physical, biological and other methods. As an effective method, the thermal–alkaline pretreatment of sludge can not only fruitful to break the cell, but also strengthen the follow-up of sludge treatment results. With respect of anaerobic fermentation, most of these studies in the literature were conducted for direct methane generation,it has few studies aiming at the production of volatile fatty acids which were important intermediates in the metabolic pathway of anaerobic digestion. As the high value-added biochemical products, it was not only the main substace of methane, but also the raw materials of other chemicals.This study applied response surface methodology to optimize the operating parameters of thermal–alkaline pretreatment method. The pretreated waste activated sludge under the optimum conditions was performed to analyze the relationship between VFAs and organic matter in the mesophilic anaerobic fermentation.Based on the analysis of the response surface plots and their corresponding contour plots, the effects of temperature, pH and treatment time were explored. Response surface method was used to study the effect and the significance of each factor and interaction on three factors and three levels. Results showed that the optimal hydrolysisi conditions of lysis rate were temperature89 1°C, pH 12 and time 74 1 min. In this case, the optimal hydrolysisi condition of lysis rate was 48.05%.Based on the optimization results of respose surface methodology, waste activated sludge was pretreated under the optimized operation parameters of thermal–alkaline pretreatment method to investigate the acidification effect under anaerobic fermentation. Results showed that soluble protein, soluble carbohydrate,ratio of cell lysis,acetic acid,propionic acid,isobutyric acid,n-butyric acid,isovaleric acid,and valeric acid in the thermal–alkaline pretreated sludge were much higher than that of the unpretreated sludge,Especially,the acetic acid is more than 8 10~3mgCOD/L,the accumulation of VFAs is more than 2 10~3mgCOD/L.Further investigation showed that the acetic acid concentration was highest in both groups, but thermal–alkaline pretreatment can change the VFAs distribution. The unpretreated test achieved maximum of total VFAs and acetic acid in 8 d and 5 d, respectively, but the thermal–alkaline pretreated test was in 3 d and 4 d, which were 5 d and 1 d earlier than the unpretreated one.