Study on viscosity of high-concentration of excess activated sludge

摘要

Compared to anaerobic digestion technology of low concentration of sludge which has been extensively used currently, anaerobic digestion of high concentration of sludge has some advantages such as high biogas yield, smaller volume anaerobic reactors, low investment and operation cost. Meanwhile, there are some new problems such as the change of flow pattern and the increase of viscosity, etc. In order to investigate the change of stirring power and the apparent viscosity in the process of anaerobic digestion of high concentrations of excess activated sludge with the DNJ-1 rotating viscometer, the relationship among sludge apparent viscosity, sludge concentration, stirring speed, stirring time and stirring power were studied in this paper. The results show that: under specific conditions (constant temperature and stirring speed, etc), sludge apparent viscosity will rise with the increase of sludge concentration. It is positively linearly correlated with stirring power. Apparent viscosity of different concentrations (4%-ll%TS) of sludge will decrease when temperature rises, and the higher the concentration of sludge is, the higher the temperature impact on apparent viscosity will be. But, once it is over 55 °C, temperature impact on the apparent viscosity of sludge becomes very small. Furthermore, the apparent viscosity of sludge can be reduced by increasing stirring speed or extending stirring time in some scope. After stirring for 2-3 hours at the speed of 60 rpm, the apparent viscosity of sludge showed a trend of obvious decrease and then become stable. The results provide important data for proper design of high concentration sludge anaerobic reactor.