The main source of potable water in high water-stress areas is commonly produced in brackish and seawater desalination plants. Owing to the presence of high concentration of suspended solids, organic matter and colloidal particles in raw water, pretreatment processes are needed for a stable operation of desalination plants. A submerged membrane ultrafiltration pilot plant has been operated as pretreatment of complex brackish surface water to study the filtration performance. The results show the membrane performance, chemical reagent requirements, water quality and cleaning procedures efficiency of an ultrafiltration pilot plant used as pretreatment for a reverse osmosis system. Alternative chemical cleaning procedures have been satisfactorily implemented, which maximize permeability recovery and allow a stable operation.

@en

Controlling fouling in seawater reverse osmosis and ultrafiltration systems is a major challenge during algal blooms. This study investigates UF fouling potential of four marine algae and their algal organic matter (AOM): Chaetoceros affinis (Ch), Rhodomonas balthica (Rh), Tetraselmis suecica (Te), and Phaeocystis globulosa (Ph). Batch culture monitoring of the four different marine algal species showed remarkable differences in their production of biopolymers, transparent exopolymer particles (TEP) and their membrane fouling potential (MFI-UF_{10 kDa}). MFI-UF_{10 kDa} was linearly related to biopolymer concentration, and TEP during the growth and stationary/death phase of all four algal species. But the linear relation of MFI-UF_{10 kDa} with algal cell density and chlorophyll-a concentration did not continue during the stationary/death phase. In experiments with capillary UF membranes, non-backwashable fouling of UF membranes varied strongly for the four different AOM solutions tested, and was linked to the presence of polysaccharides (stretching-OH) and sugar ester (stretching S˭O) groups in the AOM. The non-backwashable fouling coincided with MFI-UF_{150 kDa} and TEP concentration. Therefore, determination of these parameters (MFI and TEP) and correlating with MODIS satellite data may generate useful information about the fouling potential of seawater at different locations during an algal bloom.

@en

This research is structured on two hypotheses in which the first one is that pre-coating method using iron hydroxide particles in combination with ultrafiltration (UF) is able to control the non-backwashable (nBW) fouling in outside-inside UF membrane system caused by transparent exopolymer particles produced by marine algae species, Chaetoceros affinis. The initial assumption is that the success of the pre-coating method strongly depends on the uniform coverage of pre-coat material along the membrane surface that forms a protective layer. The second hypothesis is based on the presumption that a sequestering agent can avoid the growth of the iron hydroxide nanoparticles over time. Pre-coating experiments were performed with 6, 1, and 0.15 mg Fe3+/L coagulant equivalent dose to synthetic seawater spiked with algal organic matter to assess its effect to membrane backwashability, especially the nBW fouling development. The results showed that all of the applied dosages for pre-coating were able to reduce the nBW fouling rate. Based on the observations, coating with 1 mg Fe3+/L equivalent dose was the optimum dose to control the nBW fouling. It immediately stabilizes the fouling resistance from the first filtration cycle onwards. When a lower dose was applied, the stabilization occurred at lower rate. However, the success of pre-coating did not seem to be only attributed to a physical mechanism, (protective layer) but there is another mechanism that helps to control the nBW fouling. Results from SEM images supported this hypothesis by showing that the membrane surface was not fully covered by the iron hydroxide particles. It was an indication that there must be another mechanisms occurring in the pre-coating process.@en