Multi-Layer Filters: Adsorption and Filtration Mechanisms for Improved Separation

Abstract

Filters made of cellulose fiber and perlite particles were prepared using a wet laying papermaking technique. Polyamide-amine-epichlorohydrin (PAE) was added to provide wet strength. Filters were prepared at two different total basis weights of 200 and 400 grams per square meter (gsm). Single and multi-layered filters were structured for each total basis weights. The effect of total basis weights and multi-layered structure on methylene blue adsorption and silicon dioxide (SiO2) particle filtration was investigated. Methylene blue adsorption was performed in two modes: constant pressure and constant flow rate. In both operation modes, the adsorption capacity of multi-layered filters was significantly higher (16–100%) than for single-layer filters at the same overall weight. The effect of layer separation was also characterized using polypropylene separators and tested under constant flow rate operation. Separators provided more effective methylene blue adsorption by generating a well-distributed flow. Filtration performance was quantified with 0.5 μm silicon dioxide particles under constant pressure conditions; this is to mimic bacteria rejection. Filtration capability of SiO2 particles was reduced slightly (12%) with decreasing individual filter layer thickness regardless of the multi-layered structure. Filtering polyethylene glycol (PEG) molecules with two different molecular weights was performed; however, no rejection was recorded. The filter internal pore structure was visualized by 3D-X ray computed tomography and the void fraction was quantified. 400 gsm single layer presented areas of low fiber density forming pores, while the pore volume decreased for thinner filter layers.

Design of Web-to-Web Spacing for the Reduced Pressure Drop and Effective Depth Filtration

“…The well-distributed dP for the 4L-S gap construction led to the extended service life as shown in Figure 5 and Figure 6. On the other hand, the bulk air gap provides a free space between the MB layers, causing preferential air flow through the gaps, which results in a poor distribution of air flow and the pressure drop [49]. Though the insertion of air gap or S-gap considerably reduced the dP, the penetrations were very similar for the different constructions.…”

“…For the same amount of filter material, a number of split media in multi-layers were preferable to a single-layered, thicker media [48,49]. It was thought that even a slight space between the media could act as an air pathway, and this implies that the space between the layers could be utilized as a design factor to manipulate the performance and resistance.…”

A Review on the Application of Granular Filter Media and the Utilization of Agro-Industrial Wastes for Stormwater Quality Improvement

“…When particles are deposited on media, the resistance for the fluid increases, and media porosity decreases [43]. Dual or multilayered media may provide better adsorption than a single media layer, which performs a better filtration mechanism [54]. Although single, dual and multilayered filters are known, further studies are required to optimize the filter media based on the type of materials and the configuration used.…”

Advanced Design of Fiber-Based Particulate Filters: Materials, Morphology, and Construction of Fibrous Assembly

“…Notably, the electret charges of the produced web were eliminated by isopropanol to account for only the mechanical filtration efficiency of the web. The multi-layered hybrid construction has been suggested as a powerful approach for improving the quality factor and dust holding capacity, enabling the depth filtration with a multi-level capture of various sized particles [ 84 , 85 , 108 , 109 ]. Various morphological variations of filter media that have been investigated in recent studies are illustrated in Figure 6 .…”