Direct Membrane Filtration of Municipal Wastewater: Studying the Most Suitable Conditions for Minimizing Fouling Rate in Commercial Porous Membranes at Demonstration Scale

Abstract

This study aimed to evaluate the feasibility of applying a commercial porous membrane to direct filtration of municipal wastewater. The effects of membrane pore size (MF and UF), treated influent (raw wastewater and the primary settler effluent of a municipal wastewater treatment plant) and operating solids concentration (about 1 and 2.6 g L−1) were evaluated on a demonstration plant. Filtration periods of 2–8 h were achieved when using the MF membrane, while these increased to 34–69 days with the UF membrane. This wide difference was due to severe fouling when operating the MF membrane, which was dramatically reduced by the UF membrane. Use of raw wastewater and higher solids concentration showed a significant benefit in the filtration performance when using the UF module. The physical fouling control strategies tested (air sparging and backwashing) proved to be ineffective in controlling UF membrane fouling, although these strategies had a significant impact on MF membrane fouling, extending the operating period from some hours to 5–6 days. The fouling evaluation showed that a cake layer seemed to be the predominant reversible fouling mechanism during each independent filtration cycle. However, as continuous filtration advanced, a large accumulation of irreversible fouling appeared, which could have been related to intermediate/complete pore blocking in the case of the MF membrane, while it could have been produced by standard pore blocking in the case of the UF membrane. Organic matter represented more than 70% of this irreversible fouling in all the experimental conditions evaluated.

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“…These values correlate well with those expected for the state-of-the-art PVDF-based microfiltration membranes. [61][62][63] The increment in the initial flux followed by a flow reduction in the long term, especially for pH 2 (see the extrapolation to 1 month, considered long-term operation conditions for commercial microfiltration membranes, 64 in Fig. S1 and Table S1 in the ESI †), corresponds to a synergistic effect between their improved hydrophilicity/oleophobicity and pore size reduction.…”

Versatile Silver-Nanoparticle-Impregnated Membranes for Water Treatment: A Review

“…Therefore, these processes can theoretically achieve perfect exclusion of particles regardless of operational parameters such as influent concentration, pressure, or the skills of the operator. The separation is based on the membrane pore size and the quality of product is determined by the membrane [9][10][11]. The major mechanisms of separation in MF and UF include: (a) straining, which occurs when particles are physically retained because they are larger than the pores (Figure 1a).…”

“…This cake acts as a pre-coat filtration medium, often called a dynamic membrane since its filtering capability varies with time, growing in thickness during filtration but being partially or wholly removed by cleaning [9]; and (c) adsorption, which results when material small enough to enter pores adsorbs to the walls of the pores. If the particles and the membrane are oppositely charged, or if their zeta potentials are appropriate, the particles adhere to the membrane matrix, resulting in removal of the particles smaller than the pores of the membrane [8,11]. This means that soluble materials may be rejected even though their physical dimensions are much smaller than the membrane retention rating (Figure 1c).…”

Estudio de la eliminación/recuperación de nitrógeno en el permeado de la ultrafiltración de la línea de aguas de una EDAR mediante eliminación por nitrificación parcial y recuperación con zeolitas

“…Aunque las membranas de MF presentan una menor resistencia a la filtración debido a su mayor tamaño de poro, este mayor tamaño de poro las hace susceptibles a que las partículas penetren en los poros y los bloqueen, provocando un ensuciamiento irreversible. Por el contrario, la UF conlleva un mayor resistencia a la filtración porque su tamaño de poro es menor, pero esto le protege en mayor medida de la obstrución interna de sus poros por la penetración de partículas (Sanchis-Perucho et al, 2023) Membranas dinámicas…”