Clinical Autopsy of a Reverse Osmosis Membrane Module

Abstract

The desalination of seawater using reverse osmosis membranes is an attractive solution to global freshwater scarcity. However, membrane performance is reduced by (bio)fouling. Membrane autopsies are essential for identifying the type of fouling material, and applying corrective measures to minimize membrane fouling. Information from full-scale membrane autopsies guiding improved plant operations is scant in the formal literature. In this case-study, a reverse osmosis membrane from a full-scale seawater desalination plant with a feed channel pressure drop increase of about 218% over the pressure vessel was autopsied. The simultaneous determination of microbial cells, ATP, and total organic carbon (TOC) abundances per membrane area allowed estimating the contributions of biofouling and organic fouling. The abundance of microbial cells determined by flow cytometry (up to 7 × 108 cells/cm2), and ATP (up to 21,000 pg/cm2) as well as TOC (up to 98 μg/cm2) were homogeneously distributed on the membrane. Inorganic fouling was also measured, and followed a similar coverage distribution to that of biofouling. Iron (∼150 μg/cm2, estimated by ICP-MS) was the main inorganic foulant. ATR-FTIR spectra supported that membrane fouling was both organic/biological and inorganic. High-resolution SEM-EDS imaging of cross-sectioned membranes allowed assessing the thickness of the fouling layer (up to 20 μm) and its elemental composition. Imaging results further supported the results of homogeneous fouling coverage. Moreover, imaging revealed both zones with and without compression of the polysulfone membrane layer, suggesting that the stress due to operating pressure was heterogeneous. The procedure for this membrane autopsy provided a reasonable overview of the diverse contributors of fouling and might be a starting point to building a consensus autopsy protocol. Next, it would be valuable to build a RO membrane autopsy database, which can be used as a guidance and diagnostic tool to improve the management and operation of RO desalination plants.

Oxide– and Silicate–Water Interfaces and Their Roles in Technology and the Environment

“…Hence, current membrane research focuses on maximizing permeability-selectivity, performing solute-specific separations, and preventing membrane fouling. − Membrane fouling, the precipitation of sparingly soluble phases in solution, at membrane surfaces, and within porous membranes contributes to flux declines, reduces membrane lifespan, and increases energy demands. , Other important scalants (fouling phases) affecting water purification membranes are CaCO 3 and CaSO 4 , followed by Si- and Fe-oxides . Fe-(hydr)oxides were the major inorganic scalants on a full-scale reverse osmosis membrane module taken from a seawater desalination plant performing coagulation pre-treatment with FeCl 3 . Local effects at the interface (e.g., concentration, polarization) can lead to supersaturation with respect to inorganic scalants near membrane surfaces, especially in highly contaminated waters, which are of great interest to future water reuse and resource recovery.…”

“…856 Fe-(hydr)oxides were the major inorganic scalants on a full-scale reverse osmosis membrane module taken from a seawater desalination plant performing coagulation pre-treatment with FeCl 3 . 857 Local effects at the interface (e.g., concentration, polarization) can lead to supersaturation with respect to inorganic scalants near membrane surfaces, especially in highly contaminated waters, which are of great interest to future water reuse and resource recovery. These include seawater, industrial wastewater, and unconventional water resources such as produced waters.…”

Seawater Reverse Osmosis Performance Decline Caused by Short-Term Elevated Feed Water Temperature

“…Several studies focus on how SEC can be decreased by using membranes with a higher permeability [16][17][18][19][20][21]; a higher permeability allows for a lower pressure required to achieve the same permeate flux [22]. Membrane deformation or compaction due to increased hydraulic pressure and changes in feed water temperatures is observed in SWRO [23][24][25], which reduces the permeability of the membrane and requires the need for higher pressures to maintain a constant permeate flux [26]. Compaction is primarily irreversible [27], and membrane deformation has been verified through membrane autopsies after their use [25].…”

“…Membrane deformation or compaction due to increased hydraulic pressure and changes in feed water temperatures is observed in SWRO [23][24][25], which reduces the permeability of the membrane and requires the need for higher pressures to maintain a constant permeate flux [26]. Compaction is primarily irreversible [27], and membrane deformation has been verified through membrane autopsies after their use [25]. The fundamental behavior of compaction and its effect on SWRO performance remains poorly understood.…”