Shrimp Shell Chitosan Extracted With Green Solvent Pulls Microplastics From Water

Microplastics have become one of the most stubborn pollution problems of the modern era, drifting through rivers, oceans, soil and even the air we breathe. Among the many proposed clean-up strategies, coagulation and flocculation remain among the most practical: they are relatively cheap, well understood by water treatment engineers and scalable to the enormous volumes handled by municipal plants. Yet the chemicals most commonly used to clump tiny plastic particles together, such as aluminium and iron salts, carry their own environmental baggage, generating sludge and raising concerns about secondary impacts on ecosystems. A new study published in Environmental Science and Pollution Research offers a greener twist on this familiar technology, showing that a bio-based coagulant made from shrimp shell waste, extracted with an unusual class of solvents, can strip polyethylene microplastics from water with impressive efficiency.

The research, led by Nor Jumanah Said Mohamed of Universiti Kebangsaan Malaysia together with colleagues including Ahmad Razi Othman, Siti Rozaimah Sheikh Abdullah and Nur ‘Izzati Ismail, with Clara Manno of the British Antarctic Survey and Mohd Yunus Abd Shukor of Universiti Putra Malaysia, focuses on chitosan, a biopolymer derived from chitin. Chitin is the structural material that gives crustacean shells their strength, and it is abundantly available as waste from the seafood industry. When chitin is deacetylated, meaning that acetyl groups are chemically removed from its long molecular chains, it becomes chitosan, a positively charged polymer that can bind negatively charged particles suspended in water and draw them into settleable clumps. That charge behaviour is precisely what makes chitosan attractive as a coagulant for microplastics, which tend to carry surface charges that keep them dispersed.

The catch lies in how chitosan is produced. Conventional extraction relies on strong acids and alkalis, processes that consume chemicals and energy and can themselves create environmental burdens that offset the benefits of using a bio-based coagulant. The Malaysian team therefore turned to deep eutectic solvents, or DESs, a family of designer solvents formed by mixing a hydrogen bond donor and a hydrogen bond acceptor, in this case all based on choline chloride. The resulting liquids have unusual solvation properties, low volatility and a reputation for being far gentler on the environment than traditional industrial solvents. Because their composition can be tuned by choosing different donor molecules, DESs offer chemists a kind of molecular dial for controlling extraction outcomes.

The researchers tested four choline chloride-based deep eutectic solvents, pairing the choline chloride with glycerol, malonic acid, glucose or urea. Each combination interacts differently with the mineral and protein components of shrimp shells, and the team wanted to know which would best liberate chitin and convert it toward chitosan. The winner was choline chloride combined with malonic acid, abbreviated CCMA. Shells of the whiteleg shrimp Litopenaeus vannamei, one of the most farmed shrimp species in the world and therefore a plentiful waste stream, treated with this solvent yielded 19.09 percent chitosan with a solubility of 90.68 percent, the best figures among the four solvents examined.

Characterisation confirmed that the extracted material was genuine chitosan with useful structural properties. Fourier transform infrared spectroscopy, which probes the chemical bonds in a sample, verified the functional groups expected of deacetylated chitin. X-ray diffraction revealed a semicrystalline structure, a balance of ordered and disordered regions that is typical of chitosan and relevant to how the polymer behaves in solution. Scanning electron microscopy added a striking visual detail: the DES-extracted chitosan displayed a porous, honeycomb-like morphology. Such an open architecture increases the surface area available for contact with suspended particles, a feature that plausibly supports the material’s performance as a coagulant.

Getting the most out of the extraction required careful optimisation. The team first used a one-variable-at-a-time approach, adjusting temperature, reaction time and the ratio of shrimp shell material to solvent individually, and then refined the process with response surface methodology, a statistical technique that maps how several variables interact simultaneously and locates the true optimum rather than a series of local improvements. The optimal conditions emerged as a temperature of 93.91 degrees Celsius, a reaction time of 8.15 hours and a shell-to-solvent ratio of 0.042 grams per millilitre, corresponding to 21 grams of shell per 500 millilitres of solvent. Under these conditions the chitosan reached a degree of deacetylation of 89.05 percent, and the statistical model describing the process showed a strong fit with an R-squared value of 0.9521, indicating that the chosen variables explain most of the variation in the outcome.

The degree of deacetylation matters enormously for coagulation. The more acetyl groups removed, the more free amino groups the polymer carries, and at acidic to neutral pH these amino groups become protonated, giving the chain its positive charge. A chitosan with nearly 90 percent deacetylation is therefore a highly charged molecule, well suited to neutralising the negative surface charges that keep microplastic particles suspended. Charge neutralisation and the subsequent bridging of particles by long polymer chains are the two principal mechanisms by which coagulants turn a cloudy suspension into settleable flocs.

With the optimised chitosan in hand, the team put it to the test against polyethylene, one of the most common plastics in the waste stream and a frequent component of microplastic pollution. In a controlled suspension of polyethylene microparticles in deionised water, the CCMA-derived chitosan achieved a maximum reduction of 58.10 percent in turbidity and 63.55 percent in total suspended solids at a dose of 50 milligrams per litre. Importantly, these figures were corrected against a no-coagulant control, ensuring that the measured removal reflected genuine coagulation rather than simple settling. The performance was comparable to that of commercial chitosan under the same conditions, a significant result for a material produced through a greener extraction route.

The authors are careful about the limits of their findings. The coagulation experiments were conducted in deionised water, a clean and simplified matrix that lacks the organic matter, salts and competing particles found in real wastewater. Natural waters can dramatically alter coagulation behaviour, since dissolved organic carbon competes for the polymer’s binding sites and ionic strength changes the electrostatic interactions at play. The study itself notes that further validation under representative wastewater conditions is required before the approach can be considered ready for practical deployment. That caveat is standard for laboratory-scale coagulation research, but it is an essential one for readers hoping to gauge how quickly this technology might reach treatment plants.

Even with those caveats, the study contributes a meaningful piece to the puzzle of sustainable microplastic remediation. It links two waste streams in a single solution: shrimp shells that would otherwise be discarded become a high-performance coagulant, and the solvent used to extract it is designed to be environmentally benign and potentially recoverable. It also demonstrates a rigorous workflow, from solvent screening through statistical optimisation to materials characterisation and application testing, that other groups can adapt to different feedstocks and different pollutant targets. As regulators and utilities worldwide grapple with how to remove microplastics from effluents and drinking water, approaches that avoid swapping one pollution problem for another will be increasingly valuable. This work suggests that the answer to a plastic problem might, in part, come from the seafood counter, provided the chemistry behind it stays as green as the ambition.

Subject of Research: Green extraction of chitosan from shrimp shell waste with deep eutectic solvents for microplastic coagulation

Article Title: Deep eutectic solvent-assisted extraction of chitosan for polyethylene microplastic coagulation

Article References: Mohamed, N. J. S., Othman, A. R., Manno, C., Shukor, M. Y. A., Abdullah, S. R. S., & Ismail, N. I. (2026). Deep eutectic solvent-assisted extraction of chitosan for polyethylene microplastic coagulation. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38253-2

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38253-2

Keywords: chitosan, deep eutectic solvents, microplastics, polyethylene, coagulation-flocculation, shrimp shell waste, chitin, degree of deacetylation, response surface methodology, water treatment, green chemistry, Litopenaeus vannamei