The distinction is central to evaluating biochar as a carbon-storage material. Pyrolysis redistributes carbon among solid biochar, bio-oil and gases, including carbon dioxide, carbon monoxide and hydrocarbons. A higher-temperature char can contain a greater fraction of carbon because volatile compounds have been removed, yet the absolute amount of carbon in the recovered solid can be lower when much of the feedstock has decomposed.

In the experiment, material produced at 420 °C had the highest measured carbon concentration, 46.080%, but the 380 °C biochar retained more carbon because it weighed 60.108 g rather than 40.153 g. The study therefore distinguishes carbon concentration, which describes the composition of the recovered solid, from total carbon retention, which depends on both that concentration and the mass of biochar produced. The researchers obtained rice husk from a local agricultural biomass vendor.

Before pyrolysis, the material was visually inspected to remove impurities, gently washed with distilled water, dried in an oven at 110 °C for 24 hours until it reached a consistent weight, and stored in a pre-weighed vacuum desiccator. It was then mechanically ground and sieved to standardize particle size. No chemical activation or compositional modification was applied during pretreatment.

These steps were intended to reduce moisture and contamination and make the thermal comparison reproducible. The baseline sample, designated BM001, consequently represented standardized, pretreated rice husk rather than the material exactly as received from the vendor. Biochar was produced in a laboratory-scale fixed-bed reactor at three temperatures while continuous nitrogen flowed through the system at 1.5 L/min and the pressure remained at 1 bar.

The heating rates were 2.917 °C/min, 3.083 °C/min and 3.250 °C/min for the 380, 400 and 420 °C treatments, respectively, and every treatment had a two-hour residence time. Pyrolysis was performed independently in triplicate at each temperature, allowing biochar yield to be calculated for three runs under each condition. A representative sample from each temperature was then selected for analytical characterization.

Per 100 g of initial dry biomass, mean biochar yield fell from 60.108 g at 380 °C to 43.236 g at 400 °C and 40.153 g at 420 °C. The decline in solid yield was statistically significant. One-way analysis of variance found an effect of pyrolysis temperature on yield, with F(2,6) = 4535.05 and p < 0.001.

Tukey’s honestly significant difference test found that all three pairwise comparisons were significant at p < 0.001: 380 versus 400 °C, 380 versus 420 °C, and 400 versus 420 °C. The measured trend is consistent with greater thermal decomposition at higher temperatures, as dehydration and devolatilization release gases, vapours and condensable products and leave less solid residue. This loss of feedstock mass was the principal reason that the higher-temperature biochars retained less total carbon despite containing a larger carbon fraction. Powder X-ray diffraction revealed major structural changes during thermal conversion.

The cellulose-associated feature visible in the untreated rice husk disappeared from the biochar patterns, consistent with degradation of the native cellulose structure. At the same time, the initially sharper silica-rich diffraction feature became broader and more diffuse, indicating a greater contribution from poorly ordered or amorphous silica together with disordered carbonaceous material. The area-based Crystallinity Index was 67.27% for the biomass, rose to 88.37% for BC380, and then declined to 86.85% for BC400 and 83.18% for BC420.

The authors cautioned that this comparative index is not a direct measurement of cellulose or graphitic crystallinity. Its increase after pyrolysis primarily reflects removal of amorphous cellulose and a change in the relative contributions of ordered and disordered components, not formation of a uniformly crystalline carbon matrix. Elemental analysis documented progressive enrichment and chemical transformation within the surviving solid.

Carbon concentration increased from 39.617% in BM001 to 42.250% in BC380, 43.064% in BC400 and 46.080% in BC420. From the pretreated biomass to the highest-temperature biochar, the hydrogen-to-carbon atomic ratio declined from 0.94 to 0.76, while the oxygen-to-carbon ratio fell from 0.98 to 0.79. The authors interpret these trends as evidence of deoxygenation, loss of hydrogen- and oxygen-rich constituents, and greater aromatic condensation at elevated temperatures.

Declining H/C and O/C ratios are associated with increasing carbon recalcitrance, but the experiment measured chemical and structural indicators rather than directly demonstrating how long the retained carbon would persist under field conditions. Proximate analysis showed substantial removal of unstable material during heating. Moisture decreased from 9.08% in the pretreated biomass to 2.28% in BC380, while volatile matter fell from 61.32% in the biomass to 23.26% in BC380, 17.04% in BC400 and 16.55% in BC420.

Ash increased from 12.68% in BM001 to 50.00%, 55.72% and 56.74% in the three biochars. The authors attributed this increase to concentration of thermally stable, silica-rich minerals as volatile organic constituents were lost, rather than to the generation of new inorganic matter. Fixed carbon rose from 16.92% in the biomass to 24.46% at 380 °C, then measured 22.54% at 400 °C and 22.79% at 420 °C. The authors described the slight reduction between the two higher-temperature samples as an apparent anomaly that might reflect mathematical, instrumental or handling variation.

Converting the retained solid carbon into carbon dioxide equivalent produced the same overall ranking as the absolute carbon measurements. BC380 retained 93.127 g of carbon dioxide equivalent per 100 g of biomass, BC400 retained 68.275 g and BC420 retained 67.846 g, while the original 100 g of BM001 contained a calculated 145.276 g of carbon dioxide equivalent. These values describe carbon remaining in the biochar under a mass-based calculation; they are not verified net removals of carbon dioxide from the atmosphere.

The study did not quantify carbon in bio-oil or gaseous products and did not include process-energy inputs or emissions from feedstock handling and transportation. It also did not directly test the long-term fate of retained carbon under an end-use environment. A complete assessment of net climate benefit would require a whole-system carbon balance covering solid, liquid and gaseous products, process inputs and the persistence of biochar-derived carbon over time.

Within the 380–420 °C range tested, the results reveal a trade-off between the carbon concentration and the total quantity of carbon in the recovered biochar. Pyrolysis at 380 °C yielded more biochar and therefore preserved more carbon in absolute terms, even though its carbon concentration and degree of carbonization were lower. The study does not establish that 380 °C is universally optimal; its evidence applies to the tested feedstock, reactor conditions, heating rates, two-hour residence time and temperature range.

Its central finding is that elemental concentration alone is an incomplete measure of biochar carbon storage: total retention depends on the composition and yield of the solid, while claims of atmospheric carbon removal require additional measurements of coproducts, process emissions and long-term carbon stability.

Subject of Research: Laboratory assessment of how pyrolysis temperature affects rice-husk biochar properties and carbon retention.

Article Title: Pyrolysis temperature-induced changes in physicochemical properties of rice husk-derived biochar: an assessment for CO2 retention potential

Article References: Singh, R. K., Wadhwa, V., & Nayak, N. P. (2026). Pyrolysis temperature-induced changes in physicochemical properties of rice husk-derived biochar: an assessment for CO2 retention potential. Frontiers in Earth Science, 14, Article 1894009. https://doi.org/10.3389/feart.2026.1894009

Image Credits: AI Generated

DOI: 10.3389/feart.2026.1894009

Keywords: rice husk, biochar, pyrolysis, carbon retention, carbon dioxide equivalent, biochar yield, aromatic carbon, rice-husk silica, agricultural waste, temperature-induced, changes, physicochemical

The system itself is elegantly straightforward. Rather than relying on energy-intensive mechanical plants, the team designed a two-stage downflow filtration arrangement in which wastewater cascades through columns of rice husk biochar. Biochar, the charcoal-like material produced by heating biomass in low-oxygen conditions, is prized for its enormous internal surface area and its capacity to adsorb contaminants, buffer pH, and host microbial communities that break down organic pollutants. Because the feedstock in this case came from residues generated within the same agricultural landscape that needs the treated water, the approach embodies a circular economy in miniature: farm waste cleans farm water, which then returns to irrigate crops.

Over the ten-day trial, the filter demonstrated substantial physical and chemical polishing of the incoming wastewater. Turbidity, the cloudiness caused by suspended particles, dropped by 66.92 percent, a critical outcome since suspended solids shield pathogens from disinfection and clog soil pores. Total dissolved solids fell by 38.19 percent, and salinity declined by 22.03 percent. Both of the latter measures matter enormously for irrigation, because accumulated salts can degrade soil structure and damage crops over successive growing seasons. Importantly, the treated water met the irrigation quality limits set by the Food and Agriculture Organization of the United Nations on these parameters, meaning that from a crop and soil protection standpoint, the effluent was fit for purpose.

One counterintuitive finding, however, complicates the picture. Electrical conductivity, a proxy for the total ionic content of water, actually rose by 26.58 percent during treatment. The researchers attribute this increase to the leaching of ash minerals from the biochar itself. When rice husks are pyrolyzed, potassium, calcium, magnesium, and other soluble compounds remain concentrated in the resulting char, and fresh biochar can release these ions into water passing through it. While this mineral release is not necessarily harmful to soils and may even supply plant nutrients, it signals a practical consideration for anyone deploying biochar filters in the field: the material may benefit from pre-washing or conditioning before it enters service, particularly where irrigation water salinity is already a concern.

The microbial results tell a more dramatic story. The biochar filter achieved log-scale reductions in the indicator organisms that public health engineers use to track fecal contamination. Escherichia coli concentrations fell by 90.42 percent, fecal coliforms by 98.39 percent, and total coliforms by 99.99 percent. These are remarkable figures for a passive, unpowered filter built from agricultural waste. The removal likely reflects a combination of mechanisms: physical straining of bacteria within the biochar’s porous matrix, adsorption of cells onto charged surfaces, and possibly the antimicrobial properties that some biochars exhibit due to residual phenolic compounds and reactive mineral phases.

Yet here lies the study’s most important caveat. Despite reductions approaching or exceeding 99 percent, the final effluent concentrations of these indicator bacteria still exceeded the thresholds established by the World Health Organization and Ghana’s Environmental Protection Agency for unrestricted irrigation, meaning water that can safely be applied to any crop, including those eaten raw. The arithmetic of pathogen removal is unforgiving: when raw municipal wastewater carries bacterial loads in the millions per 100 milliliters, even a three-log reduction can leave behind counts in the thousands. The authors conclude that the rice husk biochar filter is best understood as an efficient pre-treatment component within a treatment train, one that would still require a secondary disinfection step, such as chlorination, solar exposure, or slow sand filtration, to eliminate residual public health risk.

This framing is not a weakness of the research but arguably its greatest strength. Too often, discussions of water reuse in low-resource settings swing between two unhelpful extremes: either expensive centralized plants that never get built, or unregulated direct reuse that exposes farmers and consumers to genuine hazards. The Obuasi study charts a middle path, demonstrating that locally produced biochar can shoulder a large share of the treatment burden affordably, while honestly documenting the gap that remains. That gap, bridged by an appropriate post-treatment technology, defines a scalable engineering blueprint rather than a dead end.

The choice of Obuasi as a study site adds another layer of significance. The town is historically Ghana’s gold mining heartland, a landscape where water resources face pressure from both mining legacy contamination and untreated municipal discharge. Smallholder farmers in such peri-urban areas frequently irrigate with polluted streams out of necessity, a practice the WHO acknowledges is widespread and better managed than prohibited. Technologies like the biochar filter tested here directly address that reality, offering farmers a way to reduce the pathogen and solids load in the water they already use, rather than demanding they abandon irrigation altogether.

Rice husk availability makes the model particularly attractive for scale-up. Ghana’s rice production generates substantial quantities of husk as a milling byproduct, and similar residues are abundant across West Africa. Converting them into biochar requires only simple pyrolysis kilns that can be fabricated locally, and the spent char, after its filtration service ends, retains value as a soil amendment that can improve water retention and carbon sequestration on the very fields it serves. Few treatment technologies can claim such a complete lifecycle: grown on the farm, deployed on the farm, and returned to the farm.

The broader implications extend well beyond one Ghanaian community. As climate variability intensifies and urban populations grow across sub-Saharan Africa, the pressure to reuse wastewater in agriculture will only increase, and the FAO estimates that vast volumes of urban wastewater are already used for irrigation worldwide, most of it untreated. Studies like this one provide the evidence base needed to make that practice safer through incremental, affordable engineering rather than aspirational infrastructure. The Obuasi biochar filter may not yet deliver water clean enough for unrestricted use on its own, but as a rigorously tested building block in a circular, community-scale treatment system, it points toward a future in which the solution to water pollution grows in the same fields it protects.

Subject of Research: On-farm wastewater treatment using rice husk biochar filtration for agricultural irrigation reuse in Ghana

Article Title: On-farm wastewater treatment for irrigation using biochar from local agro-residues in Obuasi, Ghana

Article References: Amponsah, L. O., Obemah, D. N., Quayson, B. L., Banunle, A., Asamoah, D. K. O., & Mwema, M. F. (2026). On-farm wastewater treatment for irrigation using biochar from local agro-residues in Obuasi, Ghana. PLOS Water, 5(9), e0000612. https://doi.org/10.1371/journal.pwat.0000612

Image Credits: AI Generated

DOI: 10.1371/journal.pwat.0000612

Keywords: biochar, wastewater treatment, rice husk, irrigation, Ghana, water reuse, E. coli, coliforms, circular economy, decentralized treatment, PLOS Water, agro-residues

The research, led by Daniel Dzepe of the International Institute of Tropical Agriculture in Benin together with colleagues from AfricaRice, Wageningen University and Research, and the Swedish University of Agricultural Sciences, focused on the larvae of the black soldier fly, Hermetia illucens. These larvae have become the darlings of the circular economy movement because of their remarkable ability to consume organic waste and convert it into protein-rich biomass suitable for animal feed, while leaving behind frass, a nutrient-dense residue that works as an organic fertilizer. The problem is that black soldier fly larvae struggle with lignocellulosic materials. Lignin acts as a physical barrier that shields cellulose and hemicellulose from degradation, making fibrous substrates like rice husk nearly indigestible for the insects and resulting in poor bioconversion efficiency when the husk is offered untreated.

To crack this barrier, the team designed four pretreatment strategies and tested them in triplicate against untreated controls. The first involved adding enzymes directly to ground, hydrated rice husk: one percent cellulase, one percent pectinase, or a one-to-one combination of both totaling one percent. The second added a 24-hour fermentation step at room temperature, around 30 degrees Celsius, after enzyme application, with the mixture held in covered, perforated containers to maintain aerobic conditions. The third began by heating the husk to 100 degrees Celsius for one hour in a pressure cooker monitored with a probe thermometer before enzymes were introduced. The fourth combined all three steps: heating, enzyme addition, and fermentation. The researchers are careful to note that their fermentation involved no added microorganisms, though naturally occurring microbes in the husk and environment likely contributed to the hydrolysis process.

The choice of enzymes was grounded in the biochemistry of plant cell walls. Cellulase is actually a cocktail of three cooperating enzymes: endo-1,4-beta-D-glucanase attacks internal sites along cellulose chains, exo-1,4-beta-D-glucanase hydrolyzes the nonreducing ends of crystalline cellulose to release cellobiose and glucose, and beta-glucosidase finishes the job by cleaving cellobiose and cellodextrins into simple glucose units. Together they depolymerize cellulose by breaking its glycosidic bonds, converting an indigestible polymer into sugars the larvae can absorb. Pectinase, by contrast, targets pectin, the structural glue that binds cellulose fibers together, loosening the husk matrix and theoretically improving nutrient access. The experiment used 300 grams of each pretreated substrate fed in a single batch to 200 six-day-old larvae in small plastic containers, a feeding load of 1.5 grams per larva and a density of 0.8 larvae per square centimeter, with composting running for 15 days at ambient temperature.

The results were striking, and highly dependent on the exact treatment recipe. The winning combination was heating followed by cellulase addition and fermentation, which achieved a bioconversion efficiency of 34.8 percent on a total solids basis, meaning more than a third of the digestible solid material in the husk ended up as larval biomass. Heated husk treated with cellulase alone reached 28 percent bioconversion with a material reduction rate of 92.5 percent, while direct cellulase addition without heating still outperformed the untreated control, lifting bioconversion from below 5 percent to 7.9 percent and substrate reduction from 61 to 71.2 percent. Larval yields told a similar story: the heated, enzyme-treated and fermented husk produced an average of 39.0 grams of larvae per unit, compared with just 14 grams on untreated husk, and final larval masses in the best treatments reached 220 to 240 milligrams.

Not every pretreatment helped, however, and some proved lethal. The fermented treatments that had not been heated first were catastrophic for the insects: mortality exceeded 96 percent in the fermented husk with cellulase, with pectinase, and with the enzyme combination, and in one treatment all larvae died before day five of composting. The researchers suggest that fermentation of the raw husk may have generated inhibitory compounds such as biogenic amines, which arise during microbial degradation of amino acids. Intriguingly, when the husk was heated before enzyme treatment and fermentation, mortality dropped dramatically, to under 10 percent in the best case, possibly because more complete degradation of the organic material prevented the formation of those toxic byproducts. Pectinase generally underperformed, and combinations involving it sometimes harmed survival, underscoring that enzyme selection matters as much as enzyme use.

The study’s context makes these numbers meaningful. When wheat straw was pretreated by steam explosion at 185 degrees Celsius followed by enzymatic hydrolysis in earlier work, bioconversion efficiency rose from roughly 5 to 16 percent, less than half of what the milder Benin protocol achieved with rice husk. Other research has shown that heat treatment can backfire: pressurized heating of banana peels at 120 degrees Celsius lowered black soldier fly conversion efficiency, apparently by releasing phenolic compounds. The Benin team’s heating at 100 degrees Celsius without pressure appears to avoid that trap for husk. The findings also echo work showing that alkaline pretreatment of rice straw increased harvested larval biomass by 32 percent, and that enzyme cocktails added to vegetable waste improved efficiency by 22 percent, though the less fibrous vegetable waste did not require pretreatment at all. Substrate composition, particularly protein and fiber content, remains a critical determinant of larval performance.

Then comes the economic reality check. The team ran a cost-benefit analysis for the best-performing process, per kilogram of wet rice husk, using experimental yields of 0.35 kilograms of larvae and 0.42 kilograms of frass per kilogram of husk, with larvae priced at $1.50 per kilogram and frass at $0.20 per kilogram. Total processing costs came to $0.85 per kilogram, driven primarily by enzyme and labor expenses, while revenues reached only $0.61 per kilogram, leaving a net loss of $0.24 per kilogram processed. The sensitivity analysis, however, identified plausible paths to profitability. Raising the larval market price to $2.50 per kilogram would push revenue to $0.96 and flip the balance to an $0.11 profit. Halving labor costs through automation or scale-up would cut costs by roughly $0.25 per kilogram, and bulk purchasing or local production of cellulase could substantially reduce the enzyme burden. Economies of scale, the authors note, are likely to further erode per-unit costs.

The study stops short of declaring the technology ready for the market, and its authors are explicit about the limits of their pilot-scale assessment, which rests on several assumptions and local Beninese market prices. They call for mechanistic follow-up work using instrumental techniques such as Fourier-transform infrared spectroscopy and high-performance liquid chromatography to directly track the chemical and structural changes that pretreatment imposes on the husk, and for larger-scale trials with detailed market studies to refine the economics. Still, the core message is compelling: a waste stream that is currently burned, polluting air and endangering communities, can be converted at nearly 35 percent efficiency into animal feed and fertilizer by pairing an ordinary insect with a low-temperature heating step, a common industrial enzyme, and a day of fermentation. For rice-producing regions searching for sustainable waste management, the black soldier fly, given the right chemical assistance, may finally have found a way to stomach the husk.

Subject of Research: Enzymatic pretreatment of rice husk to improve bioconversion by black soldier fly larvae

Article Title: Enzymatic pretreatment optimizes rice husk decomposition by black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae) larvae

Article References: Dzepe, D., Ndindeng, S. A., Ogbon, E. A., Riggi, L., Lalander, C., & Djouaka, R. (2025). Enzymatic pretreatment optimizes rice husk decomposition by black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae) larvae. BMC Environmental Science, 2(1), Article 10. https://doi.org/10.1186/s44329-025-00025-7

Image Credits: AI Generated

DOI: 10.1186/s44329-025-00025-7

Keywords: black soldier fly, rice husk, cellulase, pectinase, bioconversion, lignocellulose, waste management, insect protein, fermentation, pretreatment, circular economy, agricultural waste

The technology addresses a persistent and underappreciated problem in livestock production. Rice husk, an abundant by-product of rice milling, is widely used as poultry bedding because it is cheap, lightweight, and absorbs moisture well. But during storage and use, bedding accumulates organic matter, fecal residues, and moisture that support microbial growth. Contaminated bedding can act as a long-term environmental reservoir for foodborne pathogens, facilitating transmission between production cycles and throughout the poultry supply chain. Conventional sanitation relies on chemical disinfectants such as quaternary ammonium compounds, aldehyde-based treatments, and oxidizing agents, yet these often penetrate bulk biomass poorly, work unevenly in porous substrates, and lose effectiveness under high organic loading, while raising concerns about residues, worker exposure, and environmental impact.

The new system, described in the journal Cleaner Engineering and Technology, is a trailer-mounted, mobile processing platform designed for continuous on-site operation. Its core components include an insulated sanitization chamber, a screw-assisted biomass transport mechanism that lifts and cascades rice husk particles through the treatment zone, an LPG-fueled gas burner generating hot air at 350 to 400 degrees Celsius, a hot-air mixing chamber, forced-air and recirculation blowers, and a cyclone dust separation unit. The screw-assisted cascading design is central to the system’s performance: by continuously lifting and redistributing particles, it repeatedly exposes fresh surfaces to the heated airflow, minimizing localized cold spots and thermal dead zones within the porous biomass bed.

A key engineering innovation is the airflow recirculation architecture. Rather than exhausting heated air after a single pass, the system captures hot air exiting the chamber, passes it through cyclone separators to remove suspended dust, and redirects it back into the heating circuit. This recirculation loop achieved an efficiency of approximately 86.7 percent, substantially improving thermal retention, stabilizing chamber temperature under transient loading, and reducing fuel consumption. Under steady-state conditions, the sanitization chamber held temperatures of roughly 115 to 125 degrees Celsius while rice husk exited at 95 to 100 degrees Celsius, with chamber temperature variation held to about plus or minus 2.1 degrees Celsius.

Residence time proved to be a critical operating variable. By tuning screw rotational frequency between 50 and 60 hertz, the researchers achieved residence times of 15 to 17 minutes, which they identified as the optimal window balancing microbial inactivation against throughput. At these settings the system processed 2.0 to 2.5 tonnes of rice husk per hour with thermal utilization efficiency peaking near 87.6 percent. Shorter residence times below 10 minutes risked ineffective sanitization, while longer exposures reduced productivity without meaningful gains. Statistical analysis confirmed that both temperature and residence time significantly influenced microbial reduction, with their interaction significant at p less than 0.01.

The microbiological validation was unusually rigorous for an industrial study. Throughout three years of routine monitoring, approximately 67 samples per month were collected from production lots of about 15 tonnes each, and formal annual validations compared 50 samples before treatment with 50 after. All analyses were performed at an ISO/IEC 17025-accredited laboratory, using selective enrichment, culture on Xylose Lysine Deoxycholate agar, and confirmatory identification by MALDI-TOF mass spectrometry. Under optimized conditions, contamination frequency fell from 16 percent to 4 percent, an estimated 75 percent reduction in positive detections. In controlled laboratory experiments, log reductions of total bacterial count reached 6.2 to 6.4 log CFU per gram at 120 to 125 degrees Celsius, corresponding to inactivation efficiencies above 99.999 percent, and Salmonella was not detected under any tested condition.

Perhaps the most instructive finding concerned moisture. Feedstock water content emerged as a dominant constraint on performance, contributing an estimated 18.6 percent of the relative influence on lethality. At moisture levels of 8 to 11 percent, the system achieved log reductions of about 6.3, but at 18 to 20 percent moisture the reduction fell to roughly 2.7 log, a level the authors classified as ineffective. The explanation is thermodynamic: water evaporation consumes latent heat, diverting thermal energy away from microbial destruction and buffering the biomass temperature. Field validation during rainy conditions confirmed the pattern, with positive detections rising to 9 percent at high moisture and 14 percent when high moisture was combined with shortened residence time. The researchers argue that industrial thermal sanitization must therefore be governed by integrated heat-and-moisture frameworks rather than temperature-only criteria, and they recommend real-time moisture sensing and adaptive residence-time control as future upgrades.

The economics are compelling. Total treatment cost was estimated at 0.0083 US dollars per kilogram of rice husk, compared with 0.014 to 0.021 dollars for conventional centralized chemical sterilization, an operating cost reduction of roughly 40 to 60 percent and a benefit-cost ratio of 4.6. LPG consumption averaged 8.3 kilograms per tonne of treated biomass, translating to a fuel cost of about 0.0052 dollars per kilogram. The savings arose from multiple vectors: complete elimination of disinfectant procurement, which alone accounted for 38.4 percent of total savings; removal of dedicated chemical storage warehouses; simplified single-stage logistics replacing multi-stage transport to centralized facilities; and reduced transportation emissions from on-site processing. Over three years, cumulative savings exceeded 0.30 million US dollars, averaging about 100,000 dollars annually.

From a sustainability standpoint, the system embodies cleaner production and circular economy principles. By using thermal energy as the sole sanitizing agent, it removes chemical residues from bedding that might otherwise accumulate in soils when spent litter is applied as fertilizer, and it eliminates occupational exposure to formaldehyde and related compounds. The life-cycle analysis, conducted through a life-cycle thinking approach rather than a formal ISO 14040/14044 assessment, attributed 34.8 percent of sustainability benefits to chemical elimination, 26.5 percent to biomass reuse and valorization, and 11.6 percent to avoided transportation. The technology effectively upcycles a low-value agricultural residue into a standardized sanitary product, closing a resource loop that links rice milling, poultry farming, and eventual nutrient recycling through spent bedding.

The authors are careful to note limitations. The microbiological outcomes reflect the tested operating conditions and should not be read as evidence of complete pathogen elimination under all field scenarios, and the sustainability percentages are relative indicators rather than quantified greenhouse gas reductions. Future work will pursue a full cradle-to-grave life cycle assessment, quantitative microbial inactivation modeling using D-value and z-value kinetics, computational fluid dynamics optimization of the reactor, and predictive process control. Still, the demonstrated combination of scale, reliability, and economics marks a significant step. A system that processes nearly 8,000 tonnes of abrasive, silica-rich biomass over three years with greater than 95 percent availability shows that continuous thermal sanitization has moved beyond the pilot stage, offering poultry producers a practical blueprint for biosecurity that is simultaneously cleaner, cheaper, and more circular than the chemical status quo.

Subject of Research: Industrial-scale continuous thermal sanitization of rice husk bedding for chemical-free poultry biosecurity

Article Title: Industrial-scale continuous thermal sanitization of rice husk bedding for cleaner poultry production: Resource valorization, biosecurity improvement, and sustainability assessment

Article References: Sangpradit, K., Thoetrattanakiat, S., Sookyoo, W., Intarasuk, A., & Samseemoung, G. (2026). Industrial-scale continuous thermal sanitization of rice husk bedding for cleaner poultry production: Resource valorization, biosecurity improvement, and sustainability assessment. Cleaner Engineering and Technology, 34, Article 101304. https://doi.org/10.1016/j.clet.2026.101304

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101304

Keywords: rice husk, poultry bedding, thermal sanitization, biosecurity, cleaner production, circular economy, pathogen inactivation, agricultural waste valorization, hot-air heating, Salmonella, LPG energy efficiency, sustainable livestock production

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

The study, published in Case Studies in Construction Materials by Xuanru Wu and Jeong Gook Jang, tackled a deceptively simple question: what happens when you modify the surface of biochar before blending it into cement that has been spiked with cesium chloride? The answer, revealed through a battery of mechanical, spectroscopic, and leaching tests, is that the answer depends critically on dose. At 4 percent by weight of cement, biochar treated with nitric acid cut the 90-day cumulative fraction of leached cesium from 81.97 percent in the control to 77.01 percent, the lowest value measured in the entire study. At half that dose, the same acid treatment actually made cesium release worse, underscoring that surface chemistry alone does not tell the whole story.

Cesium poses a particular headache for cementitious waste forms because of its fundamental chemistry. As a monovalent cation with a large ionic radius and low charge density, cesium carries weak affinity for the calcium silicate hydrate gel—the principal binding phase that normally anchors contaminants in hardened cement. Its already limited sorption is further crowded out by abundant sodium, potassium, and calcium ions in the highly alkaline pore solution. To make matters worse, the chloride ions that arrive packaged with cesium chloride bind into Friedel’s salt within the cement, chemically decoupling the ion pair and leaving the cesium essentially free to diffuse through the pore network.

Biochar, produced by pyrolyzing biomass under oxygen-limited conditions, offers a chemically distinct complement to cement hydrates. Rice husk biochar pyrolyzed at 600 degrees Celsius is riddled with channel-like pores and carries hydroxyl, carboxyl, and carbonyl groups on its surface, all capable of interacting with metal cations. The researchers ground the biochar to particles smaller than 150 micrometers and bathed it in a 1 molar nitric acid solution at 60 degrees Celsius for 24 hours. This oxidation step served two purposes: it dissolved pore-blocking ash and acid-soluble mineral impurities, and it grafted additional oxygen-containing functional groups onto the carbon surface, boosting its capacity to capture positively charged ions.

Characterization revealed that the acid treatment worked its magic on surface chemistry rather than bulk structure. X-ray diffraction patterns of untreated and acid-treated biochar were nearly identical, both dominated by a broad amorphous peak associated with disordered turbostratic carbon and silica, confirming that the crystalline framework survived the acid bath intact. Fourier transform infrared spectra showed changes in the O–H and Si–O bands, consistent with the removal of surface impurities and rearrangement of functional groups. Most tellingly, the zeta potential shifted from minus 22.3 millivolts for the untreated biochar to minus 30.1 millivolts after treatment, a clear indication of a more strongly negatively charged surface ready to attract cations like cesium.

When these materials were blended into ordinary Portland cement paste at a water-to-cement ratio of 0.5, with 2 percent cesium chloride by weight of cement dissolved in the mixing water, the effects rippled through every property the team measured. After 28 days of air curing, the reference paste reached a compressive strength of 42.02 megapascals, while the paste containing 4 percent untreated biochar climbed to 52.22 megapascals, a gain of roughly 24 percent. The porous biochar particles appear to act as internal nucleation surfaces and internal curing reservoirs, releasing absorbed water gradually to sustain hydration and refine the microstructure.

Mercury intrusion porosimetry confirmed this pore refinement. Cumulative mercury intrusion dropped steadily as biochar content rose, and the acid-treated 4 percent mix showed the lowest intrusion of all. The pore-size distribution shifted toward gel-scale pores below 10 nanometers, at the expense of large capillary pores and macropores above 1000 nanometers. Fewer and finer transport pathways mean fewer escape routes for dissolved cesium, which is precisely why the leaching results and the porosity data reinforce each other in the higher-dosage mixes.

The most striking evidence of cesium capture came from scanning electron microscopy paired with energy-dispersive spectroscopy. In pastes containing acid-treated biochar, cesium was clearly detected at carbon-rich regions and at the biochar–cement interface—remarkable, given that the cesium chloride had been dissolved in the mixing water rather than pre-loaded onto the biochar. Quantitatively, the cesium-to-carbon atomic ratio in the carbon-rich regions of the acid-treated paste was 0.0276, compared with just 0.00365 in the untreated counterpart, an approximately 7.6-fold increase. This localized enrichment indicates that cesium preferentially migrated from the pore solution toward the electronegative biochar surfaces during hydration and was retained there.

The trade-offs, however, are real. At 4 percent dosage, the acid-treated paste actually showed lower compressive strength than its untreated counterpart, likely because the more negatively charged surface coordinates calcium ions at the biochar–pore solution interface, subtly altering the local availability of calcium needed for calcium silicate hydrate growth. Spectroscopic data echoed this: acid-treated specimens showed a slight reduction in the Si–O band near 970 wavenumbers, hinting at modified silicate hydrate development around the particles. Notably, after 90 days of leaching, the 4 percent biochar pastes—both untreated and acid-treated—retained higher compressive strength than the 2 percent versions, suggesting that durability benefits persist even as cesium slowly diffuses out.

The authors are candid about the limits of the achievement. Even the best-performing mix lost 77 percent of its cesium over 90 days, a reminder that the diffusion barriers of ordinary Portland cement at a 0.5 water-to-cement ratio are modest compared with optimized high-pH belite-rich systems, where comparable tests have reported cumulative leached fractions of 19 to 38 percent. Still, the result falls within the range seen for challenging carbonated low-pH matrices, and the clear dosage-dependent benefit of acid-treated biochar points a way forward. By pairing engineered carbonaceous adsorbents with conventional cement chemistry, waste-form designers may gain a second, independent line of defense against one of nuclear waste’s most mobile radionuclides—one that works even when the cement’s own binding phases fall short.

The experimental design behind these findings deserves closer attention, because it reflects a deliberate departure from how biochar is usually deployed in construction materials. Rather than substituting biochar for cement, the researchers added it on top of a fixed cement mass, keeping both the water-to-cement ratio and the cement content constant across all eleven specimen sets. This choice matters: replacement strategies confound the effect of the adsorbent with dilution of the binding phases, whereas mass-based addition allows untreated and acid-treated biochars to be compared at identical dosages under otherwise identical chemistry. Any differences in strength, porosity, or leaching can therefore be attributed to the biochar itself and its surface condition, though changes in solid volume and water demand must still be weighed when interpreting dosage effects.

The selection of nitric acid over alkali activation was likewise a considered decision rather than a matter of convenience. Alkaline treatments such as potassium hydroxide activation are known to carve out highly porous, defect-rich biochar surfaces that can accelerate cement hydration and improve long-term strength. However, such treatments leave residual potassium behind, and introducing extra alkali ions into a system already saturated with sodium, potassium, and calcium would muddy the competitive adsorption environment that governs cesium behavior in alkaline pore solution. Acid treatment, by contrast, strips away ash, carbonates, and other mineral impurities while oxidizing reactive carbon sites to form carboxyl and carbonyl groups—modifications aimed squarely at cation binding rather than at hydration kinetics.

The leaching methodology also shapes how the results should be read. The team employed a semi-dynamic leaching test extending to 90 days, in which cylindrical specimens are repeatedly exposed to successive batches of purified leachant with carefully controlled conductivity and organic carbon content to minimize ionic interference. Because the leachant is periodically refreshed, concentration gradients at the specimen surface are maintained, and the test approximates worst-case diffusion conditions rather than equilibrium-limited release. Cesium chloride dissolved directly in the mixing water served as a non-radioactive surrogate, a standard practice that preserves the ionic chemistry of the radionuclide without the handling burdens of active sources.

The cement itself was a Type I ordinary Portland cement produced domestically in South Korea and compliant with ASTM C150, with a mineral composition dominated by alite at roughly 69 percent and a Blaine fineness of 3300 square centimeters per gram. These conventional parameters anchor the study in everyday practice: the findings apply to the same class of cement already used at scale for waste solidification, not to exotic formulations. The rice husk feedstock is equally pragmatic, being an abundant agricultural residue whose pyrolysis at 600 degrees Celsius under oxygen-limited conditions yields a lightweight carbon material of roughly 55 percent carbon content.

What emerges is a framework in which biochar functions simultaneously as microstructural modifier and as an independent sink for cesium, complementing the calcium silicate hydrate mechanism that cement technologists have relied upon for decades. The dosage dependence observed here suggests that future optimization will need to balance adsorption capacity against the calcium-coordination effects that accompany stronger surface charge.

Subject of Research: Nitric acid-modified rice husk biochar as a cesium-retention additive in cement-based radioactive waste solidification

Article Title: Impact of biochar surface modification on hydration, pore structure, and cesium retention in cement matrices

Article References: Wu, X., & Jang, J. G. (2026). Impact of biochar surface modification on hydration, pore structure, and cesium retention in cement matrices. Case Studies in Construction Materials, 25, Article e06497. https://doi.org/10.1016/j.cscm.2026.e06497

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06497

Keywords: biochar, cesium immobilization, radioactive waste, cement, surface modification, nitric acid treatment, leaching, calcium silicate hydrate, Friedel's salt, pore structure, compressive strength, rice husk