Membrane and Desalination Technologies - TCE Moodle Website

470 J. Qin and K.A. Kekre
become one of the most active research fields in the development of membrane and membrane
processes because they reduce operating cost, cleaning frequency, membrane area
required, and energy consumption. Current R&D on membranes and membrane processes for
converting municipal sewage to water resources is focused on the follow aspects (54–81).
8.1. Membrane Development
It is first consideration to use a hydrophilic membrane for the reduction of membrane
fouling. Development of hydrophilic PVDF hollow fiber MF membranes has been very active
due to its high tolerance to chlorine and oxidant. Research on the applications of the PVDF
hollow fiber membranes are intensively focused on MBRs for the treatment of municipal
wastewater (54–56). Investigation on fabrication of hydrophilic membranes from cellulose is
also a trend as cellulose is the most abundant natural organic resource in the world and has
excellent hydrophilicity as well as resistance to acid, alkali, and organic solvents (57–59).
Research on temperature sensitive membranes with the unique characteristic to favorite
the membrane cleaning is increasing (60–61). The membranes are temperature sensitive as
the temperature is higher than the normal operating temperature range but not temperature
sensitive as the temperature is within the normal operating temperature range. Therefore, the
membrane pores can be enlarged for the ease of foulant removal by controlling the temperature.
In addition, the membrane can be cleaned with pure water alone, without chemical
agents.
Development of membranes with long life has been paid much attention due to the
requirement of end-users for low cost of membrane replacement. For example, the period
of warrantee on hollow fiber membranes tends to increase from 1–2 to 3–5 years even up to
5–7 years. The challenge is to develop hollow fiber membranes with high mechanical strength
of >25 kg/fiber. New membrane modules with lower packing density and sludge thickening
membranes are very attractive for the MBR application for municipal wastewater treatment.
A high flux RO membrane with high salt rejection and low fouling tendency for municipal
wastewater treatment is another challenge. The RO membrane can be operated under a low
pressure of 5 bar with the normal designed flux as an operating pressure of 10 bar is required
normally for current RO membrane system. It has potential on energy saving of 50%.
8.2. Membrane Processes
Recent development of new membrane (integrated) processes for the reclamation of
municipal wastewater has been focused on both the reduction of membrane fouling and the
enhancement of effluent quality. It includes (a) hybrid coagulation-UF process; (b) gas
scouring in UF and MF systems; (c) submerged MF/UF membrane systems; (d) direct
nanofiltration; (e) osmotic pressure cleaning technique; (f) ultrasonic technology; and (g)
integrated membrane technology.
Hybrid coagulation-UF process can not only efficiently reduce phosphate contaminant in the
effluent, but also control the membrane fouling. Gas scouring or sparging in UF and MF systems
can significantly reduce fouling and enhance the membrane flux (62, 63). Submerged MF/UF
membrane systems have demonstrated low power consumption and higher water recovery.