Membrane and Desalination Technologies - TCE Moodle Website

Membrane Processes for Reclamation of Municipal Wastewater 445
3.4. Conclusions
The conclusions from the study may be summarized as follows:
1. A stable operation of the plant in dead-end flow has been achieved by optimizing the operating
conditions.
2. Alum dosing concentration was critical and the optimum concentration was determined at 2.5 mg/
L as Al.
3. The pilot plant was operated stably for 4 weeks under the optimum conditions that TMP was
between 0.22 and 0.26 bar and normalized flux of UF membrane was 200 250 10 5 L/m 2 hPa
at 20 C.
4. Product water with average SDI of 1.6 and turbidity of 0.13 NTU was produced from the plant at a
water recovery of over 90%. Particle (1–15 mm) in the UF permeate was 2 counts/mL. Total
coliform was not detectable. Total bacteria were 69 cfu/mL.
5. The total power consumption was 0.194 kW-h/m 3 (of which, 0.100 kW-h/m 3 was for the operation
of UF unit and 0.094 kW-h/m 3 was for the submersible pump and the air compressor), and the
chemical cost was 1.3 cents (US)/m 3 product water at the capacity of 5 m 3 /h.
6. The UF membrane used could be attractive as a pretreatment prior to RO for the reclamation of the
secondary treated sewage effluent.
4. MF-RO FOR RECLAMATION OF THE SECONDARY DOMESTIC
EFFLUENT
4.1. Background
A dual membrane MF (or UF)-RO process has become increasingly attractive as a
promising technology for the reclamation of municipal wastewater (8, 11–16, 19–20,
27–29) since it was demonstrated at Water Factory 21 (8, 27). In this process, an MF or an
UF is used as a pretreatment step prior to RO to remove suspended solids and colloidal
materials. RO membranes remove dissolved solids and organics.
Pino and Durham introduced pilot studies of treating an effluent from municipal wastewater
treatment plant for irrigation using an MF/RO process. They reported that rejections of the
RO membrane in terms of conductivity, total organic carbon (TOC), ammonium and nitrate
were 95, 91, 91, and 82% in average, respectively (27). Abdel-Jawad et al. treated a tertiarylevel
effluent of municipal wastewater using an RO unit at operating pressure of 9 bars and
showed that rejections of the RO membrane in terms of conductivity and ammonium were
97.5 and 92%, respectively (29). A demonstration plant of a dual membrane MF/RO process
with the capacity of 10,000 m 3 /day for the production of NEWater from the secondary treated
domestic sewage effluent has been successfully operated since May 2000 in Singapore (19). It
was reported that rejections of the RO unit in terms of conductivity, TOC, ammonium and
nitrate were >97, 97, 90, and 80%, respectively (19). However, attempts are still being made
to optimize the RO process in this application because the process effectiveness depends on
many factors, including the type of the RO membrane, feed concentration, and operating
conditions, etc. (30–31).
This study presents an MF-RO dual membrane process for the reclamation of the secondary
effluent in Singapore. The study focused on the performance of the RO membrane under