SECONDARY SETTLING-TANK MODELING AND DESIGN .2. LINKING SLUDGE SETTLEABILITY MEASURES

In order to bring theoretical and practical developments in secondary settling tank (SST) design closer together, a number of tasks have bee n identified by the authors in Part1 of this series. The first of thes e tasks is to establish relationships that link conventional sludge se ttleability measures to the flux theory constants, V-0 and n, and is p resented in this paper. Previous work in establishing relationships be tween various sludge settleability parameters (SSPs) is reviewed. Gene ral forms for the V-0-SSP and n-SSP relationships are proposed and two different approaches to fitting the data to the selected functions ar e evaluated: firstly, a one-step direct correlation of zone settling v elocity (ZSV, V-5) on SSP and sludge concentration (X(1)) and secondly , a two-step correlation in which first V-5 is correlated with X(1) to get V-0 and n and then V-0 and n are correlated to the SSP. Statistic al tests were conducted to check which of the different data sets obta ined from the literature could be pooled and treated as one set. One- and two-step linear least squares regression analyses were conducted o n the largest family data for each of the three SSPs to determine the constants in the selected relationships. It was concluded that the rea ltionships based on the stirred specific volume indeax at 3.5 g TSS//( SSVL(15)) are the most reliable. The relationships must be applied wit h caution because the pooling statistical analysis indicates that the results appear to be influenced by activated sludge plant type.