Ultrafiltration as direct pre-treatment of seawater – a case study

Reverse osmosis (RO) and nanofiltration (NF) processes gain more and more interest in the desalination market. Recently, seawater reverse osmosis (SWRO) has become more widespread, using relatively large plants, whilst NF is being applied before thermal desalination, as an advanced treatment for increased efficiency of thermal processes. A proper and reliable seawater treatment before RO and NF, capable to retain suspended solids that cause fast fouling and plugging of sensitive spiral wound membrane modules, is a key to success of desalination processes. Reliability, high and constant quality of permeate, regardless of changes in seawater characteristics, are major advantages of microfiltration/ultrafiltration (MF/UF) over conventional pre-treatment, allowing a stable and high performance of RO and NF processes. This experimental work evaluates performance of two different UF, hollowfibre membrane modules, when fed directly with raw seawater taken from the industrial harbour of Genoa. The study reports the performance of nanofiltration process fed with UF permeate versus the performance of NF fed with raw seawater.

Acknowledgment Investigated ultrafiltration modules proved to be perfectly applicable to seawater pre-treatment prior to RO/NF processes. Both tested membrane modules were capable to deliver low turbidity permeate, regardless of changes in seawater turbidity. Nanofiltration process exhibited a stable performance when fed with permeates produced with both ultrafiltration modules. During field experiments, module A was characterised by a higher stability of TMP and a lower permeate turbidity than module B. TMP increased slower for module A, although for module B stronger and longer backwashing was used. Though slightly higher starting permeability of module B, module A showed better features The authors would like to acknowledge FISIA ITALIMPIANTI for the financial support.