Abstract
Sludge settling tests using activated sludge from various types of municipal and industrial wastewater treatment plants were carried out to collect the data for zone-settling velocity. The data from 97 separate runs covering 11 different treatment plants were analyzed and the empirical parameters of V0 and k in Vesilind's equation were estimated. The value of maximum settling velocity (V0) was found to be almost constant at 7.8m/hr. On the other hand, value of k was observed to vary and possible to be expressed by a linear function of either Stirred SVI (SSVI) or Diluted SVI (DSVI). These relationships between value of k and SSVI (or DSVI) were observed to be in close agreement to relationships suggested insome earlier reports that were mainly based on data from municipal sludge. These results suggested that suchrelationships could be valid when further extended to activated sludges of industrial nature. Based on Flux theory and the empirical relations obtained in this study, attainable Sludge Loading Rates (SLRmax) in a secondary settling tank were estimated and compared with those predicted through relationships by earlier reports. Based on the comparison studies using SSVI based relationship, a reliable prediction of SIRmax can be expected for activated sludge having SSVI value of more than 80ml/g.
