Modeling of Seepage Losses in Sewage Sludge Drying Bed

Abstract

This research was carried out to develop a model governing seepage losses in sewage sludge drying bed. The model will assist in the design of sludge drying beds for effective management of wastes derived from households’ septic systems. In the experiment conducted this study, 125kg of sewage sludge, 90.7% moisture content was thoroughly mixed and intermittently into a sand drying bed of dimensions 1.0m length, 0.3m width, 0.8m depth including overboard and having a 50mm diameter drain pipe. Seepage were measured at 24 hours intervals for 15 days, after which seepage model was derived from first principles based on the concept that seepage is inversely proportional to time. The model is in the form and for this model, two cases exist, cases I and II respectively. For case I, as time, tends to infinity (i.e. t →∞) at which point seepage has completely stopped (i.e q s =0) and the seepage curve intercepts the x-axis so that the intercept a = 0, data generated was modeled first by calibration using odd number values of seepage corresponding to 1 to 15 days. Coefficient of correlation after calibration was found to be r=-0.8474, and after verification using even number values of seepage corresponding to 2 to 14days, r =0.8474 was the coefficient of correlation between measured and calculated quantities of seepage which validates the model. For seepage model case II, this was at the initial stage of application of sludge into the drying bed at which point seepage was still taking place so that the intercept , then ‘a’ was determined by trial and error. Again, calibration and verification was done as in case I and correlation of measured and calculated seepage gave r=0.972, this high value of ‘r’ validates the model. http://dx.doi.org/10.4314/njt.v34i1.8