Sustainability in Membrane Technology: Membrane Recycling and Fabrication Using Recycled Waste

Abstract

Membrane technology has shown a promising role in combating water scarcity, a globally faced challenge. However, the disposal of end-of-life membrane modules is problematic as the current practices include incineration and landfills as their final fate. In addition, the increase in population and lifestyle advancement have significantly enhanced waste generation, thus overwhelming landfills and exacerbating environmental repercussions and resource scarcity. These practices are neither economically nor environmentally sustainable. Recycling membranes and utilizing recycled material for their manufacturing is seen as a potential approach to address the aforementioned challenges. Depending on physiochemical conditions, the end-of-life membrane could be reutilized for similar, upgraded, and downgraded operations, thus extending the membrane lifespan while mitigating the environmental impact that occurred due to their disposal and new membrane preparation for similar purposes. Likewise, using recycled waste such as polystyrene, polyethylene terephthalate, polyvinyl chloride, tire rubber, keratin, and cellulose and their derivates for fabricating the membranes can significantly enhance environmental sustainability. This study advocates for and supports the integration of sustainability concepts into membrane technology by presenting the research carried out in this area and rigorously assessing the achieved progress. The membranes' recycling and their fabrication utilizing recycled waste materials are of special interest in this work. Furthermore, this study offers guidance for future research endeavors aimed at promoting environmental sustainability.

Keywords: membrane recycling; sustainable membranes; waste recycling; waste-derived membranes.

Figure 1

End-of-life membrane regeneration using green solvent: (a) schematics of MDMO cleaning mechanism; (b,c) SEM images and performance of the pristine, end-of-life, conventionally cleaned, and green-solvent-cleaned membrane [47]. Reprinted with copyright permission.

Figure 2

Polymeric membrane upcycling: (a) schematic mechanism; (b) upcycled membrane permeance/rejection performance [54]. Reprinted with copyright permission.

Figure 3

Membrane downcycling: (a) schematic illustration of RO membrane downcycling to NF and UF [71]; (b) PA layer chlorination mechanism [72]. Reprinted with copyright permission.

Figure 4

Membrane re-preparation: (A,B) membrane morphology and its fabrication schematics; (C–F) membrane characterizations [79]. Reprinted with copyright permission.

Figure 5

Waste expanded-polystyrene-derived membrane fabrication [88]. Reprinted with copyright permission.

Figure 6

Recycled PET-derived membrane: (a) schematic illustration; (b) water flux (blue line) and rejection (pink line) at different heat pressing temperatures (10 s duration), time (at 130 °C, ΔT = 40 °C, velocity = 0.4 L min⁻¹), temperature difference (feed velocity = 0.4 L min⁻¹), and feed flow velocity (ΔT = 40 °C) [112]; (c) flux and diltiazem rejection of PAT/XA membrane [114]; (d) flux and humic acid rejection of recycled PET/polyvinylpyrrolidone membranes [101]. Reprinted with copyright permission.

Figure 7

Recycled PVC membranes performance: (a) flux recovery ratio; (b) humic acid rejection (MG0, MG1, MG3, and MG5 refers to the membranes fabricated with different gum Arabic concentrations ranging from 0–5%, respectively) [120]; (c) prototype device used for experiments (where F = feed solution; S = strip solution; M = membrane; P = pump; C = controller; B = feedback of feed and strip solution; (d) percent arsenic transport [121]. Reprinted with copyright permission.

Figure 8

Performance of recycled tire-derived membranes: (a) permeance vs. filtration time; (b) permeate permeance and dye rejection as a function of the internal coating; (c) permeance vs. filtration time; (d) permeate permeance and dye rejection as a function of precursor concentration; (e) schematic representation of the separation mechanism by hydration layer [125]. Reprinted with copyright permission. (R₁ refers to reclaimed rubber with devulcanization from a waste tire; C₃, C₆, and C₁₂ refer to %R₁ concentration used; and L₁ and L₃ refer to the number of internal coating cycles ranging from 1–3, respectively).

Figure 9

Recycled keratin-derived membranes: (a) morphology and diameter distribution of keratin/polyethylene oxide nanocomposite membrane ((a₁–a₃) refers to SEM images of 100/0 WK-PEO, 90/10 WK-PEO, and 70/30 WK-PEO nanofibrous membrane while of the inset figures depict diameter distribution of the respective membrane) [129]; (b) schematic illustration of electrospun membrane fabricated using chicken feather (d refers to the distance between the syringe needle and the collector) [130]; (c) stepwise illustration of wool fabric derived membranes [124]. Reprinted with copyright permission.

Figure 10

Membranes fabricated via cellulose and their derivates: (a) morphology of kapok fiber derived membrane ((a₁–a₃) refers to raw kapok fiber, cellulose microfiber after NaOH treatment, and cellulose microfiber after NaClO₂ treatment, respectively. While (a₄–a₉) refer to their SEM morphologies at different resolutions); (b) digital photo of methylene blue before and after adsorption; (c) digital photos of the fabricated membrane showing [135]; (d) schematic illustration of CA (derived from cigarette) membrane fabrication and its performance evaluation [138]. Reprinted with copyright permission.