Seawater pretreatment by dead-end micro and ultrafiltration in pressure-driven inside feed

Abstract

Low pressure microfiltration (MF) and ultrafiltration (UF) is used as seawater pretreatment before reverse osmosis membranes for capacity that ranged from 6,700 to 140,000 m³ per day at Colakoglu Steel Mill (Turkey), Yu-Han (China), Kindasa (Saudi Arabia), Fukuoka (Japan), and Ad Dur (Bahrain). Among all modes of porous membrane filtration, pressure-driven inside feed configuration accounts for about 30% of all membrane configurations used for water and wastewater treatment. The present study deals with the MF and UF with hollow fiber membranes (polyacrylonitrile [PAN] 50 kDa, polyethersulfone [PES] 100 kDa, and polyvinylidene fluoride [PVDF] 0.1 μm) of seawater in pressure-driven inside feed configuration. Several cycles of filtration have been carried out at 100 L h⁻¹ m⁻² during 30 min for each followed by 30 s of permeate backwash at 250 L h⁻¹ m⁻². Microalgae-rich seawater has been prepared at laboratory which contained 30 g of salt, 1.2 × 10⁸ (+/−0.25 × 10⁸) of cells (Nannochloropsis oculata and Skeletonema costatum) per liter. The highest fouling resistance ranging from 1.57 to 3.25 × 10¹¹m⁻¹ has been found for the PES membrane with an increase of the resistance value along filtration cycles. Whatever the used membrane, all microalgae have been retained and the backwash efficiencies to microalgae removal from membrane increased along filtration cycles. On the basis of these results, the 0.1 μm PVDF membrane seems to be more suitable to seawater membrane pretreatment.

Keywords:

• Seawater
• Ultrafiltration
• Microfiltration
• Microalgae
• Natural organic matter

Notes

Presented at the International Conference on Desalination for the Environment, Clean Water and Energy, European Desalination Society, 23–26 April 2012, Barcelona, Spain