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Two methods for coating a microporous surface of a membrane support layer with a photocatalyst are comparatively evaluated. Layer-by-layer self-assembly of nanoTiO 2 with a multilayer of poly(diallyldimethylammonium chloride) and poly(acrylic acid) as a binder produces a sub-monolayer of photocatalyst nanoparticles on the grains of the membrane support. In contrast, plasma-enhanced chemical vapor deposition gives a dense uniform coating on the membrane grains. Neither method reduces membrane permeability. The photocatalytic activity of the coated membranes was evaluated in filtration tests with methylene blue as a probe compound. To compare photocatalytic performance of the two coatings, measured values of the reactive flux (, m/s) were normalized by reaction rate constants (′′, m/s) determined in batch tests with the same catalyst. The proposed modeling approach relates coating's reactivity (and ′′) to the reactor's geometry expressed in terms of the length of the reaction zone () and coating density (). Both coating techniques result in a similar coating quality as witnessed by similar values of / ′′ (or, equivalently, similar values of). The proposed analysis offers insights into possible ways for improving each coating technique.

Two different sludge retention times (SRTs) were tested in order to assess the impact on membrane fouling and effluent quality in an anaerobic membrane bioreactor (AnMBR). Two up-flow anaerobic sludge bed (UASB) reactors (1 l volume) coupled to external tubular ultrafiltration membranes (filtration area = 81 cm(2)) were operated at a hydraulic retention time of 3 h and two different SRTs (100 and 60 days). The transmembrane pressure (TMP), flux (J) and relevant parameters to assess water quality were measured. Effluents from UASB reactors were filtered for 500 h without intermediate cleaning. The permeate met Mexican standards for wastewater reclamation in both tested conditions. Abrupt and periodical changes in the TMP and J were noticed during the experimental period. A fouling layer collapse and compression hypothesis was set forth in order to explain these changes. An autopsy performed on biofouled membranes indicated that deposited mass was mainly composed of volatile solids (85%) and the rest related to mineral matter, with the presence of inorganic salts containing Ca, Mg, Fe, P and Si. Biomass in the fouling layer was estimated at 0.27% based on the DNA/biomass ratio for the bacterial biofilm. No clear difference in membrane fouling was detected under the two SRTs applied to the systems. However, when operated over 500 h, repetitive sudden TMP and flux changes occurred later in system A (SRT of 100 days) than in system B (SRT of 60 days) suggesting a stronger fouling layer structure in the former.

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