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Microgranular adsorptive filtration (μGAF) is a water treatment technique in which adsorption and granular media filtration operate simultaneously as water passes through a thin layer of adsorbent pre-deposited on a woven mesh or membrane. Our previous work showed that when heated aluminum oxide particles (HAOPs) are the adsorbent in such systems, substantial natural organic matter (NOM) removal and fouling reduction can be achieved. The present study investigated the effects of feed water chemistry and operational conditions on μGAF performance. Parameters investigated include the pH, ionic strength, and concentration of divalent cations in the feed, the flux through the adsorbent layer, and the pressure drop across both the adsorbent layer and the membrane. In the range from pH 3 to 9, lower pH promoted removal of NOM in general, and transparent exopolymer particles (TEP) in particular, by HAOPs. These enhanced removals led to increased fouling of the HAOPs layer and reduced fouling of a downstream membrane. Higher ionic strength exacerbated fouling of the bare membrane but had little effect on the ability of HAOPs to collect foulants from the feed. Increased concentrations of divalent cations reduced membrane fouling slightly, possibly due to the agglomeration of polysaccharides caused by divalent cations. Increasing the flux through the HAOPs layer had essentially the same effect as lowering the pH of the feed – it enhanced removal of NOM and TEP by, and increased fouling of, the HAOPs layer, thereby reducing fouling of the downstream membrane. The HAOPs layer was incompressible, even when some NOM had accumulated on or in it, suggesting that NOM molecules adsorb on the HAOPs throughout the layer and do not form a continuous gel layer on top of the HAOPs layer. Particulate and colloidal matter were inferred to be the dominant foulants in μGAF units, whereas soluble NOM (including soluble TEP) was the key foulant in the downstream membrane units. [ABSTRACT FROM AUTHOR]

Fouling of an ultrafiltration membrane by raw lake water, the same water after passage through a layer of heated aluminum oxide particles (HAOPs), and the fractionated natural organic matter (NOM) (based on hydrophobicity) of each of those waters was investigated. When each fraction of the raw water was fed to the membrane at the same DOC concentration, the hydrophobic (HPO) fraction was the least well retained by the membrane, but it caused the most fouling, whereas the hydrophilic (HPI) fraction was the most efficiently retained fraction and caused the least fouling. Furthermore, whenever the feed contained mixtures of different fractions, fouling was worse than would be predicted by a simple mixing model, indicating that interactions among the fractions are important factors in the fouling process. Treatment of the raw water by HAOPs substantially removed fulvics from all five feed solutions (raw water, the HPO, TPI [transphilic], and HPI fractions, and the reconstituted water) and humics from all except the HPI fraction (which contained very little humic material in the first place). In contrast, HAOPs treatment removed aromatic proteins only from the HPI fraction. HAOPs also selectively removed higher-MW NOM. The treatment significantly mitigated membrane fouling by all the fractions to a greater extent than would be expected based on DOC removal. The fouling of membranes fed either raw water or HAOPs-pretreated water was largely reversed by alkaline cleaning. The NOM that was released by the cleaning step was enriched in aromatic proteins and non-fluorescent fractions, but it contained much less humic and fulvic matter and overall fluorescence than raw water. The results suggest that a non-fluorescent HPO fraction of the NOM accumulated on the membrane and is responsible for substantial fouling, and that interactions among different fractions are important contributors to fouling. [ABSTRACT FROM AUTHOR]

Fouling by natural organic matter (NOM) is a major obstacle when water from natural sources is treated using low-pressure membranes. Prior research by our group has demonstrated that passing natural water through a thin, pre-deposited layer of heated aluminum oxide particles (HAOPs) can remove substantial amounts of NOM from the feed and thereby reduce the fouling rate of downstream membranes. The work reported here explored the technical efficacy of such a pretreatment process under more challenging (and therefore realistic) conditions than reported earlier. Several analytical techniques were applied to the feed and permeate in an attempt to identify the key fouling components. The results demonstrate that a HAOPs layer can be pre-deposited on a stainless steel mesh and then be readily washed off at the end of a filtration cycle with very little irreversible fouling due to residual NOM or HAOPs left on the mesh. In addition, the pretreatment step removes enough foulant to allow a downstream UF membrane to operate at significantly higher fluxes than when conventional pretreatment is applied. HAOPs pretreatment also reduced the formation of chlorinated and brominated trihalomethanes (THM4) by more than 67% and of haloacetic acids (HAA9) by 64%–88% in simulated distribution system (SDS) tests. [ABSTRACT FROM AUTHOR]

Fouling by natural organic matter (NOM) is a major obstacle when water from natural sources is treated using low-pressure membranes. Prior research by our group has demonstrated that pre-deposition of a thin layer of heated aluminum oxide particles (HAOPs) on pristine microfiltration and ultrafiltration membranes can remove substantial amounts of NOM from the feed before the water reaches the membrane and thereby reduces the membrane fouling rate. The work reported here demonstrates that the pre-deposited layer can be readily washed off the membrane, and a new layer deposited, with very little evidence of irreversible fouling due to residual NOM or HAOPs left on the membrane. Furthermore, in direct comparisons of systems receiving equal doses of Al (i.e., mg Al per liter of water treated), the system in which the HAOPs were pre-deposited removed more NOM and mitigated fouling more effectively than systems where either alum or HAOPs were added to the bulk feed, even though the system with pre-deposition was backwashed only one-tenth as frequently as the other systems. The benefits of passing the feed through pre-deposited HAOPs are even greater if that step is separated from and upstream of the membrane filtration step. When this operating mode is used and the upstream unit with HAOPs is backwashed at a frequency of ~1/d, downstream microfiltration and ultrafiltration membranes can be operated at aggressive fluxes for long periods (two weeks or more in our experiments) without any hydraulic or chemical cleaning whatsoever. The process is effective not only with high quality source water, but also with water that is high in TOC and/or turbidity. [ABSTRACT FROM AUTHOR]

Abstract: Fouling by natural organic matter (NOM) is a major impediment to cost-effective operation of membrane processes in water treatment. This research investigated the removal of NOM by three adsorbents: heated iron or aluminum oxide particles (HIOPs and HAOPs, respectively) and powdered activated carbon (PAC). Although PAC removed a larger fraction of the DOC than did either HAOPs or HIOPs, it adsorbed non-fouling molecules preferentially over foulants, whereas the opposite was true for the metal oxide particles. In addition, when the oxide adsorbents were pre-deposited on a microfiltration membrane, foulants that were not adsorbed in batch tests were effectively removed from the solution before it reached the membrane, leading to excellent performance with respect to both NOM removal and fouling. SEM images showed that membranes under a layer of HAOPs and HIOPs were virtually as clean as a pristine membrane. [Copyright &y& Elsevier]