APPLICATION OF ULTRA-VIOLET RADIATION TO CONTROL BACTERIAL GROWTH IN THE RO FEED WATER FROM NANOFILTRATION MEMBRANES 1

SUMMARY The study was carried out to evaluate the effectiveness of UV treatment on bacterial growth in a NF-SWRO Pilot Plant at Al-Jubail. The study was divided into five phases: (i) regular operation stage (without UV), (ii) operation under UV-radiation at raw seawater (RSW) inlet, (iii) plant operation under UV- radiation at RSW inlet and up-stream of NF membrane, at the same time (iv) plant operation under UV-radiation ahead of the NF membrane and (v) the operation phase with the least biofilm potential and higher percentage of biofouling control (Phase #IV) was selected and investigated further. Water samples were collected from five locations: RSW, after UV unit (AUV), after media filter (AMF), after cartridge filter (ACF), nanofiltration permeate (NFP) and nanofiltration brine (NFB). Bacterial count, bacterial aftergrowth, biofilm, TOC, PO4, pH and conductivity were estimated for all these samples. The study showed up to 99.15% reduction in bacterial counts after UV treatment as compared to raw seawater at different study phases suggesting an effective performance of UV sterilization. However, an increase in bacterial count was noticed at AMF and ACF location. Presumably, due to recovery of bacteria these filters and in storage tank ACF. Laboratory studies also showed that, incubation of UV treated samples for 48-h resulted in bacterial recovery or aftergrowth. AUV and NFP also registered reduced TOC, nitrite and phosphate levels in the feed water indicating the presence of nutrient scavengers before the NF membrane. A decline in phosphate, nitrite and TOC levels was also found in 48-h incubated samples indicating nutrient up-take by bacteria. The study suggests that while UV treatment may considerably