Performance Assessment of fast Sand Filter for Water Pollution Removal: Head Loss Consideration

Abstract

This study provides a short-term pilot-scale assessment of a rapid sand filter using locally available sand as a tertiary treatment process to improve the quality of treated wastewater in response to the limited implementation of advanced tertiary treatment systems in many wastewater treatment plants, particularly in water-stressed regions such as Algeria. The objective is to reduce water pollution to the recommended standard limits for potential reuse in agriculture and industrial processes, using a simple, low-cost, and locally available filter medium. Particular attention is also given to the critical role of filter media characteristics in filtration efficiency. Through granular analysis of particle size distribution, the effective diameter of the sand was 0.5 mm. The filter performance and removal efficiency of water quality parameters were evaluated using secondary treated wastewater collected from the wastewater treatment plant (WWTP) of Beni Merad. The initial physical and chemical characteristics of the wastewater were: total suspended solids (TSS) 132 mg/L, turbidity 10.2 NTU, chemical oxygen demand (COD) 128 mg O₂/L, and biochemical oxygen demand (BOD₅) 95 mg O₂/L. The sand filter column was operated for six days, corresponding to 22 cumulative operating hours, at a constant filtration rate of 36 L.h-1, corresponding to a filtration velocity of 4.58 m·h⁻¹. Treatment performance was evaluated through the removal of TSS, turbidity, COD, and BOD₅, with filter achieved maximum removal efficiencies of 88.89%, 78.57%, 61.5%, and 47.83%, respectively. These findings show that local sand filtration can significantly improve the physicochemical quality of secondary treated wastewater, especially by reducing suspended solids, turbidity, and organic pollution. Hydraulic performance was monitored by continuously measuring head loss along the filter column. After 16 h of operation, head loss reached its maximum value of 0.61 m, indicating substantial hydraulic resistance and the onset of a backwashing requirement under the operating conditions used in this study and the filter was restarted for an additional 6 h. The main mechanisms governing sand filtration were sedimentation, mechanical trapping, particle accumulation within the filter bed, and adsorption onto sand grains. Overall, the results demonstrate the initial treatment and hydraulic response of the tested sand medium under real secondary wastewater conditions. local sand proved to be an effective, low-cost, and technically simple filter medium for tertiary wastewater treatment in short-term pilot-scale applications.