An autopsy study of a fouled reverse osmosis membrane element used in a brackish water treatment plant

Abstract

The fouling of a spiral wound RO membrane after nearly one year of service in a brackish water treatment plant was investigated using optical and electron microscopic methods, FTIR and ICP-AES. Both the top surface and the cross-section of the fouled membrane were analysed to monitor the development of the fouling layer. It has been found that the extent of fouling was uneven across the membrane surface with regions underneath or in the vicinity of the strands of the feed spacer being more severely affected. The fouling appeared to have developed through different stages. In particular, it consisted of an initial thin fouling layer of an amorphous matrix with embedded particulate matter. The amorphous matrix comprised organic-Al-P complexes and the particulate matter was mostly aluminium silicates.Subsequently, as the fouling layer reached a thickness of about 5 to 7 μm, further amorphous material, which is suggested to include extracellular polymeric substances such as polysaccharides, started to deposit on top of the existing fouling layer. This secondary amorphous material did not seem to contain any particulate matter nor any inorganic elements 1 25 26 27 28 29 within it, but acted as a substrate upon which aluminium silicate crystals grew exclusively in the absence of other foulants, including natural organic matter (NOM).

Analysis of reverse osmosis membrane performance during desalination of simulated brackish surface waters

“…The EDSX spectra in Figure C14 show that the cake formation of run 21 has the carbon range of 77.6% -79.1% and oxygen of 13.8% -14.4%, suggesting that the majority of the fouled material is organic matter. However, the EDSX spectra of Figure C15 exhibit a high range of calcium (25.5% -59.1%), besides the high ranges of the carbon (7.9% - Overall, the results of the SEM images and EDSX spectra of the previously discussed runs revealed that the selected RO membranes have high rejection of organic matter, carbonate, and calcium, as also observed by Antony et al (2011), Koyuncu & Wiesner (2007), Tran et al (2007), and Koyuncu et al (2006). Another observation is that although the feed waters in locations 1 and 6 had high concentrations of sulfate (312-320 mg/L and 681-687.4 mg/L, respectively), sulfur peaks were at very low levels, as shown in some of the spectra of the runs, indicating that some potentially low level of CaSO4 precipitated on the membrane surface.…”

“…High TOC forms complexes that enhance RO membrane fouling when some metals are present, such as Ca +2 (Antony et al, 2011;Tran et al, 2007;Koyuncu & Wiesner, 2007). The high permeate fluxes observed in the runs of locations 1 and 5, compared to those of location 6, are apparently due to a lesser scale formation on the membrane surface from the feed water with lower TOC and TDS concentrations.…”

“…Fouling may occur as a result of microbial growth, scaling, or accumulating of dissolved organic materials, particulate and colloidal matters (Malaeb & Ayoub, 2011;Kucera, 2010;Tran et al, 2007;Speth et al, 2000).…”

“…To obtain more precise information about the fouling layer such as the chemical composition, SEM is coupled with energy dispersive X-ray spectroscope (EDS) (Malaeb and Ayoub, 2011). Other spectroscopic tools, which have been used in RO membrane fouling studies, are confocal laser scanning microscopy (CLSM), inductively coupled plasmaatomic emission spectrometry (ICP-AES), infrared (IR) spectroscopy, and Fourier transform infrared spectroscopy (FTIR) (Karime et al, 2008;Tran et al, 2007;Chu and Li, 2005).…”

The role of cell-surface interactions in bacterial initial adhesion and consequent biofilm formation on nanofiltration/reverse osmosis membranes

“…Furthermore, in most cases, membrane fouling by natural organic matter, polysaccharides and inorganic material will occur, which can change substantially the membrane surface properties such as hydrophobicity [107], roughness [108] and surface charge [109]. Several membrane autopsies carried out on NF and RO membranes have showed the fouling layer to be composed of different materials [110][111][112][113], caused by the different water quality treated. The characteristics of the fouling layer can therefore be expected to influence the nature of subsequent bacterial adhesion and possibly biofilm formation.…”