'New life' for reverse osmosis

Membranes specialist Memcor claims to have provided reverse osmosis with a 'new lease of life' by combining it with a 15-year-old process called continuous microfiltration. The combined process, which stops the reverse osmosis membrane from fouling, is capable of treating raw waters whose quality is not consistent, according to the company.

Reverse osmosis is a highly efficient method for purifying water, but it cannot cope with raw water because RO membranes are particularly susceptible to fouling. The problem is most acute when the inlet water quality is variable; in this case, fouling can be irreversible, which leads to critical system failure. RO therefore needs a pre-treatment step, explains Memcor, to ensure that the water flowing into the system will not foul the membranes.

Memcor's continuous microfiltration (CMF) system uses membranes with a 2 m pore size, arranged as hollow fibres with a 0.3mm internal diameter. These are loaded into 'sub-modules', each containing some 20,000m of fibre. Several of these sub-modules are used. The system also incorporates a compressed air backwashing facility, which Memcor claims is much better than liquid backwashing at removing contaminants, as well as inhibiting 'grow-through' and obviating the need for chlorination of backwash liquor.

This system provides a stable filtrate from even the most difficult raw water sources, claims Memcor, including seawater, brackish and eutrophic waters, sewage and process water. It consumes little energy typically just 0.15-0.3kWh/m3 of treated water, claims Memcor and the filtrate flowrate and quality remains steady, even when the feed water quality changes. Coupled with RO, it can render even the filthiest water drinkable, the company claims and with water shortages spreading around the globe, it adds, the demand is high and rising rapidly.