Farm Waste Turned Water Filters Could Scrub Aspirin Pollution From Wastewater

Every year, humanity swallows roughly 35,000 metric tons of aspirin, and much of it does not simply vanish after doing its job. A sweeping new review published in Advances in Industrial and Engineering Chemistry argues that one of the world’s oldest and most heavily consumed medicines has become one of its most pervasive aquatic pollutants, and that an unlikely class of materials, agricultural wastes such as rice husks, spent tea leaves, coffee grounds, banana stalks and peanut shells, could offer a cheap, renewable and remarkably effective line of defense. The review, led by Bukola Taiwo Atunwa of Curtin University Malaysia, synthesizes more than a decade of research, spanning 2012 to 2024, on how farm-derived adsorbents capture aspirin and its metabolites from contaminated water, and what happens to those materials once their work is done.

The scale of the problem is staggering. More than 650 active pharmaceutical ingredients and their metabolites have now been detected in the environments of over seventy countries, according to studies cited in the review. Pharmaceuticals reach rivers, lakes and groundwater through a web of pathways: human excretion via urine, sweat and saliva, improper disposal of unused medications down sinks and toilets, hospital effluent, veterinary drug residues in manure spread on fields, and even airborne diffusion of medicated dust from livestock facilities. Conventional wastewater treatment plants, designed to strip out organic matter and pathogens rather than trace drug molecules, routinely fail to eliminate these compounds, so they pass through facilities largely intact and re-enter the environment.

Aspirin, or acetylsalicylic acid, occupies a special place in this contamination story. Roughly 23 percent of the United States population, about 28 to 29 million people, takes it as a preventive measure against cardiovascular disease, and millions more use it for pain, fever and inflammation. Because the human body metabolizes only part of each dose, the remainder, along with the drug’s primary metabolite salicylic acid, flows into sewage systems. The review notes that aspirin’s persistence in water is compounded by its chemistry: in aqueous environments it readily hydrolyzes into salicylic acid and acetic acid, and its ionization state shifts with pH, producing a heterogeneous mixture of species with different affinities for any given treatment material.

The ecological consequences are subtle but serious. Chronic exposure to low concentrations of aspirin and its metabolites has been linked in laboratory studies to disrupted growth, reproduction and behavior in algae, invertebrates and fish, along with enzyme inhibition and oxidative stress. Salicylic acid released into waterways may interfere with photosynthesis in aquatic plants, weakening ecosystem dynamics from the base of the food web upward. The review also flags a less obvious casualty: microbial communities. Aspirin residues can alter microbial diversity and activity in natural waters and in the treatment plants themselves, potentially undermining sensitive processes such as nitrification and contributing to the broader crisis of antimicrobial resistance, since sub-therapeutic drug levels can promote horizontal transfer of resistance genes among bacteria.

Against this backdrop, the authors make the case for adsorption using agro-waste-derived materials as a treatment strategy that is simultaneously effective, economical and aligned with circular economy principles. Agricultural residues are abundant, essentially free at the point of generation, and rich in the lignocellulosic building blocks, cellulose, hemicellulose and lignin, that give them their capture power. Their surfaces carry hydroxyl, carboxyl and phenolic functional groups that bind pharmaceutical molecules through hydrogen bonding, electrostatic attraction, van der Waals forces and pi-pi stacking interactions between aromatic rings. Their hierarchical pore networks, ranging from micropores to macropores, provide both the surface area and the diffusion pathways needed to trap molecules of varying size and polarity.

The performance data compiled in the review are striking. Rice husk, characterized by Boehm titration, Fourier-transform infrared spectroscopy and point-of-zero-charge measurements, achieved a maximum Langmuir adsorption capacity of 47.03 milligrams of aspirin per gram at pH 2, while rice hull activated carbon removed 85.79 percent of the drug from contaminated water at pH 3.97 after 90 minutes. Spent tea leaf activated carbon, regenerated chemically with ethanol washing, retained 81.6 percent removal efficiency after six consecutive adsorption-regeneration cycles, down only marginally from 85.5 percent in the first cycle. Beyond aspirin, the review catalogs agro-waste successes against a pharmacopeia of contaminants: walnut shells capturing ibuprofen, pistachio nutshells outperforming carbon nanotubes for the antibiotic sarafloxacin, lotus leaves stripping norfloxacin, and functionalized banana stalks removing ciprofloxacin from solution.

The chemistry of why these materials work is now reasonably well understood. Oxygen-containing functional groups on the adsorbent surface form hydrogen bonds with aspirin and its metabolites, while graphitic carbon domains created during pyrolysis accommodate pi-pi electron donor-acceptor interactions with the drug’s aromatic ring. Solution pH governs everything: it determines the ionization state of aspirin, which has a pKa near 3.5, and the surface charge of the adsorbent relative to its point of zero charge, dictating whether electrostatic interactions are attractive or repulsive. Activation with chemicals such as phosphoric acid or potassium hydroxide, or physical treatments like steam and carbon dioxide activation, dramatically expands pore volume and surface area, while techniques such as grafting amine or carboxyl groups onto the biomass surface can tune selectivity toward specific pharmaceutical classes.

Crucially, the review does not stop at adsorption performance; it confronts the lifecycle question that often undermines green technologies. Spent adsorbents loaded with captured pharmaceuticals become hazardous waste in their own right, and improper disposal can simply re-release the contaminants, shifting pollution from the aqueous phase to the solid phase rather than eliminating it. The authors evaluate regeneration strategies in detail: chemical regeneration with acid, base or solvent washing restores capacity with minimal carbon loss; thermal regeneration breaks adsorbate bonds but consumes energy, emits carbon dioxide and degrades mechanical strength; microwave-assisted regeneration heats the carbon matrix internally, recovering more capacity with less energy and shorter process times; and emerging bio-regeneration uses microbial cultures to desorb and biodegrade captured pollutants, though it remains slow and dependent on the biodegradability of the adsorbed compound.

The review is equally candid about the risks embedded in competing recovery technologies. Chemical precipitation generates sludge and can leave residual reagents in treated effluent; membrane filtration suffers from fouling and high energy demands, particularly for reverse osmosis; advanced oxidation processes can produce toxic, stable transformation products and require specialized equipment; and ion exchange produces concentrated regenerant streams that must be carefully managed. Adsorption, by contrast, is simple to operate, inexpensive and generates fewer toxic byproducts, which is precisely why the authors argue it deserves priority for pharmaceutical remediation, provided the full chain from adsorbent preparation through regeneration to final disposal is managed responsibly.

What emerges is both a technical roadmap and a policy challenge. The authors call for life-cycle assessments to verify that agro-waste adsorbents genuinely outperform commercial activated carbon once preparation energy and chemical inputs are counted, for pilot-scale demonstrations of microwave-assisted regeneration at industrial scale, and for unified regulatory standards governing bio-based adsorbents and pharmaceutical discharge limits. They also emphasize prevention: drug take-back programs, greener pharmaceutical design, better hospital waste management and public education about proper medication disposal. If those pieces come together, the humble byproducts of rice milling, tea drinking and coffee brewing could become a cornerstone of sustainable water treatment, advancing clean water and sanitation goals while converting one waste stream into the solution for another.

Subject of Research: Use of agro-waste-based adsorbents for the removal, recovery and regeneration of aspirin pharmaceutical contamination in wastewater

Article Title: Agro-based wastes as sustainable alternatives for the removal of aspirin pharmaceutical: recovery, regeneration and risk assessments

Article References: Atunwa, B. T., Chan, S. Y. S., Tan, I. S., Lee, V. S., Tan, Y. H., & Lin, C.-W. (2026). Agro-based wastes as sustainable alternatives for the removal of aspirin pharmaceutical: recovery, regeneration and risk assessments. Advances in Industrial and Engineering Chemistry, 2(1), Article 2. https://doi.org/10.1007/s44405-026-00042-3

Image Credits: AI Generated

DOI: 10.1007/s44405-026-00042-3

Keywords: aspirin, agro-waste, adsorption, wastewater treatment, pharmaceutical pollution, activated carbon, rice husk, spent tea leaves, adsorbent regeneration, water remediation, emerging contaminants, circular economy