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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., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

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., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Pretreatment of feed water is widely applied to mitigate NOM-induced fouling of low-pressure membranes. This research investigated the effectiveness of two pretreatment modes for NOM removal by heated aluminum oxide particles (HAOPs) and the associated reductions in membrane fouling and trihalomethane (THM) formation potential. One mode, referred to here as pre-adsorption, is the conventional process in which adsorbent particles are added to and thoroughly mixed with the feed, after which the particles are separated from the water either upstream of or by the membrane. By contrast, in the pre-deposition mode, a thin layer of adsorbent particles is deposited on a support media (which could be the membrane) prior to passing feed through the layer and the membrane. Although both pretreatment methods remove similar amounts of DOC at the same adsorbent dose, pre-deposition is superior with respect to mitigating membrane fouling and reducing DBP formation. UV and fluorescence spectroscopy and HPSEC analysis indicate that a pre-deposited adsorbent layer removes more chromophores and low apparent molecular weight (AMW) material than pre-adsorption does. Based on absorbance ratios at selected wavelengths, a pre-deposited HAOPs layer removes more aromatic moieties than aliphatic carboxyls, especially at higher HAOPs doses. In addition, pre-deposition is more effective than pre-adsorption at reducing the THM formation potential. The results provide new insights into the interactions between HAOPs and NOM molecules and shed light on the significantly different effects of different adsorbent contacting modes on the fouling potential of the pretreated water., (Copyright © 2016 Elsevier Ltd. All rights reserved.)