Filtration and Backwashing Studies: Obafemi Awolowo University Waterworks as A Case Study

Abstract

This research centres on the study of the filtration and backwashing operations of the filtration unit of the Opa Waterworks and a  detailed laboratory study of the filtration and backwashing characteristics of the filter medium being used at the treatment plant. A  detailed study of the filtration unit of Opa Waterworks was undertaken with particular emphasis placed on the estimation of the volume  of water used during backwashing, the backwashing procedure and the average backwashing time. Specific properties of the filter  medium used in the gravity filter such as porosity, density, equivalent density, specific gravity and unhindered settling velocity were  investigated in the laboratory. The backwashing properties of the filter medium was also studied using the DSF (Dynamic Shape Factor)  and Sphericity models and the predicted results obtained were compared to the actual laboratory results. Based on works carried out,  the volume of wash-water required for the gravity filters was estimated as 14,200 litres (14.2 m³) which is about 3.12% of the total volume  of the clear water tank, with an outflow rate of 0.01 m³/s. The accuracy of the Blake – Kozeny equation in predicting head loss across a  filter bed using clean water runs was investigated and found to be reasonably accurate, and the prediction errors.