| Conversion of seawater into drinking water using reverse osmosis (RO) membranes is attracting much interest as an alternative water source for water deficiency in coastal areas around the world such as Southern California, Florida, and Texas in the US as well as various locations in Australia, the Caribbean, Singapore, China, South Korea, Southern Europe, North Africa and the Middle East. Membrane fouling remains an important factor for seawater RO plant design and operation, requiring extensive pretreatment while increasing energy and chemical consumption and accelerating membrane replacement. Biofouling is among the most problematic issues for the seawater RO plants because continuous chlorination of polyamide composite RO membranes is not possible and also algal blooms periodically upset feed water quality---introducing higher loads of biomass and assimilable organic matter into the RO system.;A new high-pressure optical membrane module was developed. This novel laboratory tool allows real-time visualization of bacteria cell deposition onto seawater reverse osmosis (RO) membranes running under realistic crossflow and permeate hydrodynamics, which require applied hydraulic pressures up to ∼8.3 MPa. Using this novel tool, fundamental mechanisms governing bacterial deposition onto seawater RO membranes have been studied.;Marine strain Halomonas pacifica (GFP) was employed as model bacterium. Two commercial seawater RO membranes with different surface roughness and hydrophilicity were used as model membranes. Data were produced to compare the influence of module hydrodynamics and membrane properties on the initial bacterial attachment to seawater RO membranes. Permeate flux directly correlated with the initial deposition rate of bacteria, while the deposition rate was not influenced by cross flow velocity. No strong correlation was demonstrated between the interfacial free energy and deposition rate, rather microscopic 'specific interaction' between the membrane and foulant interfaces governed deposition and adhesion.;Finally, commercial, hand-cast, and surface-modified seawater RO membranes were tested in this high-pressure direct microscopic observation system. The direct observation technique proved very efficient for evaluation initial bacterial adhesion and removal. Mechanisms responsible for reversibility of bacterial attachment on anti-adhesion and anti-microbial membranes were proposed based on the fouling and cleaning results. |
