Development of an integrating coagulation and reverse osmosis system to treat highly turbid water using synthesized coagulants

Abstract

In the present study a coagulation process was used as a pretreatment for a reverse osmosis (RO) membrane with turbid raw water collected from Bisalpur dam, Rajasthan, India. To optimize the coagulation performance, three kinds of coagulant, namely, alum (commercially available), synthesized inorganic polymeric coagulant-medium basicity (IPC-M), and inorganic polymeric coagulant-ultrahigh basicity (IPC-UH) were examined for turbidity removal with varying operating parameters. It was observed that in the optimum pH range of 6-7, the IPC-UH was the best performing coagulant with a 0.99 mg/L equivalent Al2O3dose, revealing 2 NTU residual turbidity and residual aluminium of 0.001 mg/L. Moreover, the Langelier saturation index and Ryznar stability index values were evaluated at optimum conditions for all the three coagulants providing negligible scaling potential. Furthermore, the coagulant-treated water (100 L) was fed to the RO membrane, and the performance was noted in terms of flux, pressure, and total dissolved solids. It was observed that IPC-UH had the lowest reduction in permeate flux of 0.78 L/min/m2compared with the commercially available coagulant alum (0.90 L/min/m2). Also, an increased feed pressure was observed for all the coagulant-treated waters with the lowest value of 2.3 kg/cm2for IPC-UH, which was 2.5 kg/cm2for alum (commercially available coagulant). Therefore, integration of coagulation before the RO system resulted in effective pretreatment of turbid water with very minute scaling.