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.
Highlights
The global demand for freshwater increases constantly (UNESCO UN-Water, 2020)
An inspection of the spiral wound reverse osmosis (RO) membrane module revealed no macroscopic damage to the outer module components, and there was no telescoping of the membrane
Results of total organic carbon (TOC), adenosine triphosphate (ATP), and cell counts accumulated on the feed spacer and membrane evidenced the presence of organic and biological fouling (Figure 3)
Summary
The global demand for freshwater increases constantly (UNESCO UN-Water, 2020). The natural replenishment of freshwater, in most regions, is not sufficient to meet current human demands. To address this issue, the production of freshwater through desalination can alleviate water scarcity, but the process is energy-intensive (Mazlan et al, 2016). Decreased costs of materials make desalination an attractive alternative for the production of freshwater in arid regions, as well as in regions with a stressed hydrologic cycle due to climate change. The preferred method for desalination is via water filtration through reverse osmosis (RO) membranes. Among the available desalination methods, RO is the most effective in terms of energy requirements and unit water cost (Qasim et al, 2019). Current RO desalination plants produce 65.5 million m3/day, which accounts for 69% of the volume of desalinated water produced worldwide (Jones et al, 2019)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
