A bio-based membrane from seafood waste delivers high water flux and pollutant removal, offering a scalable, low-impact alternative to conventional nanofiltration.
(Nanowerk Spotlight) Advanced water purification technologies are facing an urgent test. As pollutants become more elusive—shrinking to sizes measured in nanometers and resisting chemical breakdown—existing membranes struggle to intercept them. Nanoplastics, synthetic dyes, and metal-based particles are now routinely detected in drinking water, yet most conventional filtration systems fail to fully remove these contaminants. Many rely on dense polymer barriers or chemically modified synthetic materials, which are costly to produce, slow to scale, and often energy-intensive to operate.
Efforts to replace these with filters based on natural materials have met with only partial success. Cellulose nanofibrils, spider silk, and bio-derived hydrogels have all shown promise in controlled experiments, but each suffers critical limitations. Some degrade too quickly, others require harmful solvents, and nearly all fall short when asked to block ultrafine particles below 10 nanometers.
Attempts to improve performance usually trade one constraint for another—higher rejection rates mean lower permeability, more complex fabrication, or poor durability.
But one waste product, largely overlooked, may offer a different path. Squid bones—discarded by the seafood industry in tens of thousands of tons each year—contain a structurally unique form of chitin. This biopolymer, known as β-chitin, has a molecular configuration that invites chemical modification while maintaining mechanical integrity. Embedded within a thin, protein-rich shell, the chitin forms nanofibers that are naturally aligned and easily separated.
For material scientists, this architecture offers an unusual starting point: a biologically optimized structure that can be refined into a porous, high-surface-area network suitable for ultrafiltration.
Building on these properties, researchers at Qingdao University of Science and Technology have developed a method to extract nanofibers from squid bone waste and assemble them into ultra-permeable membranes (Advanced Materials, “Harnessing Squid Bone for Ultra‐Permeable Water Purification Membranes”).
These filters remove contaminants as small as 1.5 nanometers while achieving water flux rates above 46,000 liters per square meter per hour per bar of pressure. The process requires no toxic solvents, uses only milligram quantities of waste material, and can be integrated into simple, low-cost filtration systems. Together, these results point to a viable route for scalable water purification using a source material that would otherwise be discarded.
The route from squid bones biowaste to filtration system. A) Global annual catch weight of squids. B) Photographs of L-squid and O-squid with their corresponding bones. C) Schematic of relationship between 𝛽-phase chitin nanofiber (𝛽-ChNF) and bone. D) Chemical structure of 𝛽-ChNF. E) Schematic and photograph of the biowaste-derived ultra-permeable filter (BUF) with the corresponding syringe device (scale bars, 1 cm). F) The performance of BUM with different ChNF loading mass (scale bars, 1 cm). (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
To produce the nanofibers, the researchers applied an ammonium persulfate oxidation process that stripped away the bone’s protein shell and introduced carboxyl groups along the chitin surface. These chemical groups increase the nanofibers’ surface charge, improving their dispersion and generating electrostatic repulsion between fibers. This repulsion prevents tight packing during membrane formation, leading to a porous structure that facilitates water flow. The team created membranes of varying thicknesses by changing the amount of ChNF deposited on a cellulose support using vacuum filtration.
The membrane’s performance was tested using a range of contaminants. At a thickness of 124 nanometers, the membrane achieved a water flux of 46,207 L·m⁻²·h⁻¹·bar⁻¹ while completely rejecting 100-nanometer polystyrene nanoplastics. Thicker membranes—such as those at 1.8 micrometers—rejected dye molecules like Rhodamine B, which are about 1.5 nanometers in size, at rates exceeding 99%. Even at that greater thickness, water flux remained at 1,350 L·m⁻²·h⁻¹·bar⁻¹, significantly above most existing nanofiltration membranes tested under similar conditions.
The team also investigated the role of squid species on fiber characteristics. They extracted ChNFs from two major groups: Loliginidae and Ommastrephidae. Nanofibers from Loliginidae (L-ChNFs) were found to be smaller and more uniformly dispersed, with average thickness of 1.2 nanometers and width of 2.2 nanometers. These fibers carried a higher density of carboxyl groups than their Ommastrephidae-derived counterparts, resulting in a more stable suspension and lower aggregation. As a result, membranes made from L-ChNFs exhibited higher porosity, which translated into better filtration performance.
To understand the relationship between membrane structure and filtration behavior, the authors used a model combining the Hagen–Poiseuille equation and empirical porosity measurements. This analysis confirmed that water flux increases with porosity and pore size and decreases with membrane thickness.
Importantly, the data revealed that thinner membranes tended to have higher porosity, amplifying water flux beyond what would be predicted from thickness alone. This structural effect was especially pronounced below 200 nanometers, where the combination of small fiber size and strong electrostatic repulsion maximized pore space.
Further experiments demonstrated the membrane’s ability to handle smaller particles and sustain filtration over extended periods. Using magnesium oxide nanoparticles at 10 nanometers in diameter, the researchers tested the membrane under continuous operation. After an initial decline in water flux—common due to fouling—the membrane maintained stable flow and complete contaminant rejection for over two days. This suggests it can operate effectively under prolonged use, a key requirement for practical deployment.
The team also built simple filtration devices using syringe-based setups to evaluate usability in portable or low-resource contexts. These devices successfully filtered nanoplastics, dyes, and metal oxide particles, with high removal efficiency and measurable differences in retained contaminants visible on the membranes. Notably, even under fouling conditions with complex feed solutions, the membranes outperformed commercial alternatives in water flux.
To assess sustainability, the researchers conducted a life cycle assessment (LCA) and techno-economic analysis (TEA). The environmental evaluation showed that producing one membrane required just 6.12 × 10⁻⁴ kilograms of CO₂ equivalents and consumed 6.04 × 10⁻³ megajoules of energy.
Because only milligram-scale amounts of squid bone are needed, and no organic solvents are used, the environmental footprint is low. Vacuum filtration accounted for the majority of energy use, suggesting opportunities for further reduction through improved batch processing.
On the economic side, the production model assumes lab-scale conditions. Despite this, the projected cost per membrane is $0.18—less than many commercial nanofiltration products. Annual operating costs were estimated at $52,000, with a return on investment over 100% and a payback time under one year. The biggest contributor to cost was labor, mainly due to manual filtering steps. However, automating the membrane deposition process could significantly improve efficiency in scaled-up systems.
This study presents a membrane that combines performance, sustainability, and cost-effectiveness in a way that few materials currently do. By upcycling a biological waste stream into a high-efficiency membrane and avoiding complex or hazardous inputs, the work bridges material science with practical, scalable application.
The findings show that the structure and chemistry of β-chitin nanofibers can be controlled to produce a porous network capable of blocking a broad spectrum of contaminants while allowing high water throughput. With the added support of lifecycle and economic analysis, the membrane system stands as a promising candidate for future water purification platforms, particularly in settings where affordability and simplicity are essential.
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