Effect of chlorine and acid injection on hollow fiber RO for SWRO

Bio-fouling results in deterioration of permeate quality and flux in reverse osmosis (RO) process. Cellulose triacetate hollow fiber membrane used for RO in SWRO has anti-chlorine property that makes technical sense compared to polyamide spiral-wound RO for overcoming bio-fouling. Mode of chlorine injection is the controlling factor of sterilization in SWRO system. This work evaluated the effects of five different modes of chlorine injecting system as well as HCl injection on the performance of HF RO system. In addition, effects of HCl and anti-scalants on anti-scale performance of HF RO system were also investigated, respectively. A brief list of chemical costs under different abovementioned operating conditions was covered in a cost analysis. The results indicated that the injecting mode that employed continuous chlorine with a relatively low concentration of 0.3-0.4 mg/L at pH 5.8-6.2 was preferable in the aspects of total bacterial count (TBC) removal, permeate flow rate, differential pressure, permeability (P_p), performance factor (η) and chemical costs. HCl injection could improve the sterilization and prevent scaling on the membrane surface efficiently. The expense of anti-scalant (MDC220) was higher than HCl.