Design and process optimization of an integrated turbidity removal unit in a pilot-scale continuous-flow system using hybrid coagulants for decentralized water treatment

Abstract

This study investigates a compact pilot-scale continuous-flow system for turbidity removal from raw water, integrating chemical and hydrodynamic optimization. A horizontal sedimentation tank was designed and evaluated under varying conditions, including a hybrid inorganic-organic coagulant-flocculant system using polyaluminum chloride (PAC) and polyacrylamide (PAM), coagulant dosages, influent flow rates, aeration, baffle number, and inclination angle. Response surface methodology (RSM) was used to predict and optimize system performance. Optimization indicated that 45 ppm PAC and 2 ppm PAM achieved the highest turbidity removal efficiency of 94.3 % at a low flow rate of 0.5 L/min with aeration at 300 mL/min. At a moderate flow rate of 1.25 L/min, thirteen baffles set at a 75° inclination provided optimal hydraulic performance, yielding 85.3 % removal. Integration of a gravel-sand-anthracite filtration unit further increased removal to 98.3 %. RSM revealed significant interactions between influent flow rate and baffle configuration, enabling prediction and optimization of overall system performance. Mechanistic analysis illustrated floc formation behavior under different PAC and PAM dosages. By combining chemical optimization, hydraulic design, and multiple unit processes in a compact pilot-scale system, this study demonstrates an effective and adaptable approach for decentralized water treatment, suitable for rural, emergency, or resource-limited environments.