Slow sand filtration of secondary effluent

This pilot-scale study comprises a one-year field evaluation of slow sand filtration as a tertiary treatment of secondary wastewater effluents using two different effective sizes of local sand, i.e. 0.31 and 0.56 mm. to find a simple advanced wastewater treatment method. The filter was operated at sand depths of 135, 105, and 55 cm, respectively, for each size of the sand, to determine the operational range of the sand depth. Secondary effluent from North Aramco Wastewater Treatment Plant (NAWTP) was applied at a hydraulic loading of 0.16 m/h. The filter consistently gave over 90% removal of turbidity for both sizes of the sand at various depths of the filter bed along with over 93% removal of total coliform bacteria. It was observed that the use of coarse sand resulted in longer duration of filter operation as compared to the fine sand for similar removal of turbidity and coliform, i.e., 84 days in the case of coarse sand compared to a maximum of 26 days for the finer sand. The development of the head loss in the sand media was extremely small during the initial period of the operation, which later increased exponentially with most of the head loss occurring in the top dirty surface of the filter, known as Schumtzdecke in German.