It seems that use of the design of Direct coupling of UF with RO facilitates the intermediate feed tanks , pumps and cartridge filter are eliminated, simplifying the process and layout with reduced maintenance on frequent replacement of cartridge filters and servicing of associated infrastructure.
There are Desal plants using this Design especially in Adelaide (628mld) /2002 and Perth(300mld) and recently commissioned in SIngapore Keppel Marina East Desalination plant(137mld). MEMCOR CS Membranes of EVOQUA used for pretreatment and claims to have achieved the specific power consumption of 2.10 kWh/cu. m of water produced. There are modular containerised plants also. Really this is great . In such case , why this is not widely adopted.?
Besides, it is learnt that many of the marine micro algae which grow excessively when there is Algal Bloom can not withstand pressure more than 0.5 bars and hence algal the cells would break down under pressure or vacuum and release easily biodegradable organic compounds. This would facilitate growth and formation of Biofim on the SWRO membranes .This film would foul the membranes and thus resulting in reduction of plant production within weeks from the beginning of algal Bloom.
How this problem is addressed In the absence of Cartridge filters which would otherwise protect the SWRO membranes from the damaged particles,
(Retired . Chief Engineer,i/c;/Chennai Metropolitan Water Supply& Sewerage Board,Chennai,.India