Recent advances in measuring and modeling reverse osmosis membrane fouling in seawater desalination : a review

A review of recent literature focuses on the fouling phenomena in membrane systems for desalination, quantification and qualification of parameters related to biological fouling (biofouling), and emerging areas for prevention. In particular, biofouling of seawater reverse osmosis (SWRO) is widely regarded as the most important area for future research on this topic. Reducing membrane fouling is fundamental to seawater treatment but is not well managed. The current state of industry knowledge is evaluated with particular focus on SWRO membrane biofouling, as well as its measurement and mitigation. Specific shortcomings and possible solutions are reviewed regarding the role of assimilable organic carbon, chemical treatment and other components in understanding the fouling process, impacts from pretreatment, level of assimilable nutrients, modeling applications, and real time monitoring. A critical review of recent advances in understanding organic and biological fouling is presented because these are the most difficult to control and least understood. doi: 10.2166/wrd.2013.056 s://iwaponline.com/jwrd/article-pdf/3/2/85/377843/85.pdf Lauren Weinrich (corresponding author) American Water, 213 Carriage Lane, Delran, NJ 08075, USA E-mail: Lauren.Weinrich@amwater.com Charles N. Haas Department of Civil, Architectural and Environmental Engineering, Drexel University, 3141 Chestnut Street, 251 Curtis Hall, Philadelphia, PA 19104, USA Mark W. LeChevallier Innovation and Environmental Stewardship, American Water, 1025 Laurel Oak Road, P.O. Box 1770, Voorhees, NJ 08043, USA

In the USA, two-thirds of the desalination capacity is used for municipal water supply (Carter ). to pose a costly challenge for aspects related to prediction, prevention, and, when possible, removal. The following sections will briefly describe the four types of fouling: inorganic, particulate, organic and biological. A critical review of recent advances in understanding organic and biological fouling is presented because these are the most difficult to control and least understood. Evidence of exacerbated fouling from chemicals used in SWRO pretreatment is examined; investigating the effects of chemical pretreatment is emerging as an important area for the reduction of fouling.
The paper also presents recent advances and current applications for understanding, measuring, and predicting fouling through analytical and microbiological techniques for quantification and qualification. Prediction of fouling through computer modeling also shows promise, and prevention is evaluated based on recent reports during the pretreatment process for SWRO. Traditional approaches for predicting organic fouling potential include DOC, UV absorbance, and color; however, the measured fouling rates for NOM in seawater do not correlate with these parameters (Amy et al. ). Discovering the link between potential and realistic fouling rates is critical and additional understanding of organic matter behavior in high salinity, i.e., seawater, environments will be most useful for successful O&M applications at the full scale.

FOULING
Opportunities exist for either breaking NOM down into smaller fractions that can be removed by biological pretreatment, or some other combination of organic absorption and removal. These approaches will be discussed in more detail in the following sections.

Biological fouling
Biofouling is by far the least understood and most proble- about the oxidation impacts on NOM and chemical impacts in seawater. The ongoing research shows promise for dually estimating the growth rate and the growth potential-induced AOC. The method will be described in more detail later.
Red tides are highly destructive events that can occur when marine algae rapidly increase in concentration, called an algae bloom, and are often recognized by the visible red color and therefore appropriately named. Blooms can severely increase turbidity of seawater; however, the release of organic material, algogenic organic matter (AOM), is also a major concern. Dinoflagellates are generally recognized as most frequently responsible for marine

Conventional pretreatment (coagulation by ferric chloride (FeCl 3 ), sedimentation, and two-stage sand filtration)
showed average turbidity removal of 93% in a pilot system operating for 1.7 years in which average turbidity was 3.6 ± 2.9 NTU, but went as high as 20 NTU during the rainy Qualitative results from a SWRO pilot system employing MF indicated removal of putative biofilm-forming bacteria, decreasing relative abundance from 98 to 10%. However, the conventional system was also shown to reduce γ-proteo- (1) mechanistic or membrane transport model and (2) lumped parameter model (Sobana & Panda ).
Estimating flux in a membrane that has not yet been fouled can be expressed as J w ¼ ΔP-π/(μ × R m ) where J w is the pure water flux estimated from resistance-in-series model, ΔP is the applied pressure, π is the osmotic pressure,

Limitation of nutrients
Nutrient limitation is a practical approach for reducing the quantity of life-sustaining elements, carbon, nitrogen, and phosphorus, in order to minimize unwanted microbial assimilation and growth. Although this is a fairly simple con- Other quantitative and qualitative techniques for monitoring water quality and microbiology of seawater intakes and during pretreatment will aid current and future SWRO applications. Additional SWRO research and development is crucial for the efficiency of this growing industry.