Pilot study for reclamation of secondary treated sewage effluent

A pilot study for reclamation of secondary treated sewage effluent in Singapore was conducted using a MF/RO system with the capacity of 20 m3/d. A 0.1 µm MF membrane from Asahi and RE-4040-FL RO membrane from Saehan were used in this study. The pilot plant consists of six spiral-wound RO elements. The RO train was configured in single stage. The pilot plant was designed with automatic control system and it was operated continuously (24 h) during the study. Trial runs on various flux rates of the RO membrane at different operating pressures were conducted over 3 months. The pilot results showed that the optimal operation flux rate of the RO membrane ranged from 10 to 15 gal/f2/d (GFD) for this application. The normalized flux after CIP was 97% of the initial one. At a flux rate of 10 GFD and water recovery of 50%, the average operating pressure of 57 psi was noted corresponding to a high normalized flux of 38 L m!2 h!1 MPa!1 at 25°C. Rejections of the RO membrane in terms of conductivity, TOC, ammonium and nitrate were higher than 96%, 97%, 90% and 85%, respectively. It was concluded that the RO permeate quality in terms of conductivity, turbidity, TOC, ammonium, nitrate, hardness, total bacteria and total coliform matched the quality of high-grade water (NEWater) for use in the electronics industry.

Table 6 shows the permeate quality of the RO membrane during the study and the target quality The conclusions from the pilot study are summarized as follows. Parameter RO permeate quality Target quality pH Conductivity (µS/cm) Ammonium-N (mg/L) Nitrate (mg/L) Hardness as CaCO3 (mg/L) TOC (mg/L) Total bacteria HPC (cfu/mL) Total coliform (cfu/100mL) Turbidity (NTU) 5.7–6.1 18.4–46.4 0.01–0.47 1.8–7.1 0.03–0.38 0.06–0.37 <3 <1 <0.1 7–8.5 <200 <0.5 <15 <20 <0.5 <300 <1 <5 as NEWater [9]. It can be seen that quality of the RO permeate meets the target quality as NEWater in terms of the parameters measured, except for pH, which could be easily raised by adding NaOH. The analytical results also indicated that the average rejections of the RO membrane for TOC, ammonium and nitrate were >97%, 90% and 85%, respectively, which matched the RO membrane performance used at the demonstration plant [7].