The technology, described in Environmental Science and Pollution Research, is called the Advanced Thermal Processor, or ATP, and its defining feature is that it operates continuously rather than in batches. Contaminated cuttings are fed through a sealed hopper and screw conveyor into a slightly inclined rotating drum, where they are heated simultaneously by two different mechanisms. Microwave energy penetrates the material volumetrically, exciting polar molecules such as water throughout the bulk of the waste rather than merely at its surface. Infrared heaters arranged along the drum provide uniform surface heating, filling in the thermal gaps that microwaves alone can leave. The researchers argue that this hybrid approach solves the two problems that have dogged microwave treatment in earlier studies: uneven heating and poor scalability to industrial throughput.

To test the system, the team collected six samples of water-based drill cuttings contaminated with sour crude oil from real Middle Eastern offshore drilling operations, then processed them in two batches through a pilot-scale prototype under inert, low-oxygen conditions maintained by nitrogen purging. The treatment was deliberately gentle: solids left the drum at discharge temperatures of just 60 to 100 degrees Celsius, after residence times of roughly 15 to 30 minutes. Despite these mild conditions, the results were striking. Oil removal efficiencies ranged from 95.0 to 97.8 percent across all six samples, and in every case the residual oil-on-cuttings fell below the 1 percent regulatory threshold. Total Petroleum Hydrocarbons and Total Oil and Grease, the two standard measures of hydrocarbon contamination, were each reduced by more than 96 percent.

The low operating temperature is the headline finding. Conventional thermal desorption and incineration systems typically run at 300 to 500 degrees Celsius or higher, demanding large energy inputs and risking secondary emissions. Thermogravimetric analysis of the treated solids showed why the hybrid process can be so much cooler. In one sample, a major mass loss of about 21.17 percent occurred at around 106 degrees Celsius, corresponding to the release of water and light volatile hydrocarbons. Only minor additional losses appeared at higher temperatures between 275 and 413 degrees, indicating that what remained was mostly thermally stable inorganic rock. In other words, most of the contamination that regulators care about volatilises below 110 degrees when heat is delivered volumetrically, without overheating or degrading the solid matrix.

The physics behind this selectivity is well understood. Water is a highly polar molecule and absorbs microwave radiation far more efficiently than hydrocarbons, so microwave energy preferentially drives off moisture, opening a porous structure in the cuttings that enhances heat and mass transfer. Previous studies have shown that microwave-treated residues are more porous than those dried by conventional electric heating, which relies on thermal conductivity and tends to leave higher residual oil. Microwaves can also promote pyrolysis of petroleum hydrocarbons, making them particularly suited to oil-based contamination. Earlier work demonstrated that microwave radiation could reduce n-paraffin content in cuttings contaminated with non-aqueous fluids below discharge limits, and that the recovered organic phase retains its chemical composition well enough to be reused in fresh drilling fluid.

The Brunel study also mapped the limits of the process. A clear inverse trend emerged between initial water content and oil removal efficiency: the sample with the highest moisture, 24 percent by weight, achieved the lowest removal at roughly 95 percent, while drier samples approached 97.8 percent. The explanation is energetic competition. Because water soaks up microwave energy so readily, wetter feed demands more of the available power for evaporation, leaving less to volatilise oil. Water may also form a transient barrier around oil droplets, impeding heat transfer and delaying volatilisation. A similar, weaker trend appeared with total fluid content: samples above about 23 percent combined oil and water showed marginally lower efficiency, possibly because rapid heating creates insulating vapour layers around droplets, a phenomenon analogous to the Leidenfrost effect. The practical lesson is that feed pre-conditioning, particularly dewatering with a decanting centrifuge, is essential to squeeze maximum performance from the system.

The prototype was designed as a complete process train rather than a laboratory curiosity. After centrifuge dewatering and homogenisation, cuttings pass through an airlock hopper into the rotating drum, where nitrogen purging and a slight positive pressure keep oxygen out, a critical safety measure in the ATEX Zone 2 environment of a drilling platform. Volatilised oil and water vapour are continuously extracted, scrubbed of entrained particles, and condensed; an oil-water separator then recovers oil suitable for reuse and produces water with residual oil content between 0 and 15 parts per million. Non-condensable gases are recirculated as carrier gas, cutting emissions further. The treated solids emerge dry and powder-like through a sealed screw conveyor and rotary airlock, with a water mist suppressing dust. Oxygen levels are monitored continuously, with automatic shutdown protocols and emergency nitrogen purging standing by.

The regulatory context gives the work its urgency. Since 2001, OSPAR has banned offshore discharge of cuttings contaminated with oil-based or synthetic-based fluids unless residual oil is below 1 percent by dry weight, and in 2012 it added stringent sediment monitoring and hydrocarbon reporting requirements to support benthic ecosystem recovery. Other frameworks, including the United States EPA Effluent Guidelines, the Barcelona Convention and the London Protocol, regulate discharge but none are as strict. The stakes extend beyond ecology: returned drilling fluids can carry heavy metals such as nickel, mercury, cadmium, chromium, copper and lead, elements associated with chronic diseases including cancer. Life cycle assessments of conventional management options, from land spraying to solidification and reinjection, show that solidification carries the highest environmental burden because of cement and lime consumption, while reinjection, though comparatively benign, simply relocates contaminants to deeper formations.

What distinguishes the ATP from earlier microwave remediation efforts is continuity. Pilot-scale microwave studies dating back more than a decade proved the chemistry but stalled at the batch scale, unable to match the relentless output of a drilling operation, particularly during top-hole sections where cuttings production peaks. By integrating microwave and infrared heating into a continuously fed rotating drum with automated vapour recovery, the Brunel team has produced a system whose throughput can in principle be scaled with drum size and feed rate rather than being capped by batch cycle times. The ability to remove oil, water and hydrocarbons in a single processing step, rather than the multiple stages conventional methods often require, further improves the operational economics of on-site treatment.

The authors are careful about what remains to be done. The experimental programme analysed here was conducted some years before publication, and the available records did not preserve the individual analytical protocol numbers behind the oil, TPH and TOG determinations, a transparency note that underscores the need for full-scale validation. The team itself flags that future work should focus on full-scale demonstration and detailed energy and economic assessments before the technology can be considered proven at industrial scale. Even so, the combination of results, above 95 percent oil removal on real field samples, compliance with the strictest discharge thresholds, and treatment temperatures below 110 degrees, makes a credible case that hybrid microwave-infrared desorption could turn one of offshore drilling’s most stubborn waste problems into a manageable, and potentially resource-recovering, side stream of production.

Subject of Research: Hybrid microwave-infrared thermal desorption treatment of oil-contaminated offshore drill cuttings

Article Title: Hybrid microwave–infrared thermal desorption for remediation of oil-contaminated offshore drill cuttings: field-sample evaluation and process performance

Article References: Babaei-Mahani, R., Fereidounpour, A., He, Y., & Scholes, P. (2026). Hybrid microwave–infrared thermal desorption for remediation of oil-contaminated offshore drill cuttings: field-sample evaluation and process performance. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38229-2

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38229-2

Keywords: drill cuttings, microwave heating, infrared heating, thermal desorption, offshore drilling, oil contamination, waste treatment, OSPAR Convention, hydrocarbon removal, thermogravimetric analysis, environmental remediation, Brunel University London

The research, led by Lukas Fliri of Aalto University and BOKU University together with colleagues at Aalto and VTT Technical Research Centre of Finland, focused on fibers spun with the Ioncell technology, a process that dissolves pre-hydrolyzed kraft birch pulp in a superbase-derived ionic liquid and dry-jet wet spins it into filaments. Unlike the native cellulose I allomorph found in wood and cotton, these regenerated fibers crystallize in the cellulose II form, the same allomorph that matters for carbon fiber production. Yet, as the authors point out, nearly all of the fundamental mechanistic data on cellulose pyrolysis has been gathered on cellulose I, while studies on cellulose II have mostly reported end-material properties without the underlying physics and chemistry. That gap made it difficult for the team to compare their own carbonization experiments with the literature, so they decided to build the reference dataset themselves.

The experimental design deliberately echoes a classic: the influential 1960s work by Tang and Bacon on the carbonization of Fortisan cellulose II fibers. Fliri and colleagues heated Ioncell fibers from room temperature up to 1100 degrees Celsius under helium in a simultaneous thermal analyzer coupled to a mass spectrometer, using heating rates spanning 2.5 to 40 kelvin per minute. Tiny samples of around 3.5 milligrams minimized heat and mass transfer distortions, and the evolved gases, water, carbon monoxide and carbon dioxide, were quantified through a calibration procedure based on calcium oxalate monohydrate. In parallel, batch carbonizations were carried out in a tubular furnace under nitrogen at nine target temperatures between 300 and 1100 degrees Celsius, with no thermostabilization pretreatment and no tension applied to the fibers, so that the intrinsic behavior of the material could be observed without process tricks that boost yield.

The thermal analysis revealed the familiar fingerprint of cellulose pyrolysis: a violent mass loss concentrated in a window of only 70 to 100 degrees, with onset temperatures between 288 and 322 degrees Celsius depending on heating rate. At the peak of this event, cellulose chains depolymerize and expel levoglucosan, the sugar anhydride that dominates the volatile stream, alongside furans, dehydrated sugars, water and carbon oxides. Crucially, the slower the heating, the more char survived. Char yield at 1100 degrees Celsius fell log-linearly as the heating rate rose, and the combined yields of water and carbon dioxide tracked the char yield almost perfectly. This is exactly what the two-competing-pathway model of cellulose pyrolysis predicts: long residence times below 300 degrees favor dehydration reactions that lock carbon into char precursors, while rapid heating funnels the material toward volatilization as levoglucosan instead.

The kinetic analysis added quantitative teeth to this picture. Using Friedman’s isoconversional method, the team found that the apparent activation energy of Ioncell fiber pyrolysis sits in a narrow band of roughly 190 to 220 kilojoules per mole up to about 80 percent conversion, consistent with a single dominant step: the rupture of the beta-O-4 glycosidic bond that links the glucose units of cellulose. Beyond that conversion level, the activation energy climbs sharply, signaling a shift from depolymerization to reactions within the solid carbonaceous residue. A first-order kinetic model, fitted with activation energies of 227 to 231 kilojoules per mole and pre-exponential factors matching literature values for cellulose I, described the mass loss curves well, but the authors caution that this is a phenomenological description of the main mass loss step, not proof of a simple one-step mechanism, and the parameters should not be extrapolated to isothermal treatments or temperatures above about 600 degrees.

One of the more surprising results concerns heat. The apparent heat of pyrolysis, measured by integrating the differential scanning calorimetry signal, came out between roughly 180 and 250 kilojoules per kilogram across all heating rates, in close agreement with decades of measurements on microcrystalline cellulose and filter paper. When the team ran control experiments on pure levoglucosan, the heat of its thermal evaporation matched the apparent heat of cellulose pyrolysis almost exactly. The implication is striking: the endothermic demand of cellulose pyrolysis is largely just the energy needed to evaporate levoglucosan. From a process engineering standpoint, this reaction heat is small compared with the roughly 650 kilojoules per kilogram of sensible heat required simply to bring the fibers up to their degradation temperature, a fact that matters for anyone designing industrial carbonization furnaces.

The batch carbonization experiments then traced how the fibers’ properties evolve with the final heat treatment temperature. Yields dropped steeply between 300 and 500 degrees and then plateaued between 6.8 and 9.4 percent by weight. Elemental analysis showed hydrogen and oxygen draining away as carbon accumulated, and a van Krevelen plot revealed two distinct linear regimes: below about 400 degrees the hydrogen-to-carbon and oxygen-to-carbon ratios follow a slope of roughly two hydrogens per oxygen, the signature of dehydration, while above that temperature decarboxylation and decarbonylation take over. Notably, oxygen loss largely stops above 600 degrees, and X-ray photoelectron spectroscopy confirmed that thermally stable oxygen functionalities remain embedded in the carbon even at 1000 degrees. These trapped oxygen atoms, the authors argue, act like reticulation agents, promoting five- and seven-membered rings that curve and distort the growing aromatic network and prevent the formation of a graphite-like structure, a key reason cellulose-derived carbons are non-graphitizing.

Morphology told a parallel story. The round cross-section of the Ioncell filaments survived carbonization intact, but the diameter shrank by roughly 60 percent by the time the fibers reached 600 degrees, after which further shrinkage was minimal. Fiber diameter correlated linearly with carbon content and log-linearly with carbonization yield, and the team interprets the shrinkage as the surface degradation of oriented cellulose microfibrils followed by their coalescence into denser cross-linked furanic and polyaromatic structures. Raman spectroscopy completed the picture: a polyaromatic network was already detectable at 400 degrees, and the ratio of the disorder-induced D band to the graphitic G band jumped from 0.59 to 0.93 between 600 and 700 degrees, then climbed more slowly toward 1100 degrees. The D-to-G intensity ratio correlated linearly with the hydrogen-to-carbon ratio above 600 degrees, indicating that large aromatic domains grow through dehydrogenation and radical condensation of smaller ring systems. Estimated in-plane aromatic cluster sizes grew from about 1.0 to 1.4 nanometers between 600 and 800 degrees and then stalled.

Perhaps the most consequential conclusion is what the study did not find. Older carbon fiber literature, still frequently cited, holds that the cellulose II crystal structure follows a special carbonization mechanism tied to the recondensation of four-carbon intermediates. The new data show no evidence of such a peculiarity: the pyrolysis behavior of Ioncell fibers matched the classic two-pathway models, and the high-temperature evolution agreed with general models for non-graphitizable carbons. The authors also observed an unexplained systematic mass loss above 800 degrees, but only at the slowest heating rate of 2.5 kelvin per minute, a phenomenon not previously reported that they flag for further confirmation. By identifying the temperature windows where dehydration, volatilization, dehydrogenation and aromatization each dominate, the dataset gives carbon fiber researchers a practical map for optimizing thermostabilization and carbonization schedules, and a common reference point for comparing cellulose II precursors of every kind. For a field trying to make carbon fiber cheap, renewable and strong enough for the mass market, that map may prove as valuable as the fibers themselves.

Subject of Research: Pyrolysis dynamics and physicochemical property development during the carbonization of Ioncell regenerated cellulose II fibers for carbon fiber production

Article Title: Tracking carbonization in Ioncell cellulose II fibers: pyrolysis dynamics and development of the physicochemical properties

Article References: Fliri, L., Yildirim, Z., Meinander, K., Guizani, C., & Hummel, M. (2026). Tracking carbonization in Ioncell cellulose II fibers: pyrolysis dynamics and development of the physicochemical properties. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13716-6

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13716-6

Keywords: carbon fibers, cellulose II, Ioncell, pyrolysis, carbonization, levoglucosan, char yield, Raman spectroscopy, thermogravimetric analysis, biobased materials, turbostratic carbon, kinetic modeling

The research team, led by Désiré Ndahirwa of UniLaSalle with colleagues including Hélène Lenormand, Hafida Zmamou and Nathalie Leblanc, focused on a question that has dogged the field for years. Wood ash contains reactive silica, alumina and calcium-bearing phases that can, in principle, behave like cement itself, reacting with water through hydraulic and pozzolanic pathways. In practice, however, pastes made from pure wood ash are weak and porous. Previous studies had shown that replacing moderate amounts of cement with wood ash often reduces compressive and flexural strength, and most work had examined substitution levels below 50 percent. Almost nothing was known about what happens at very high replacement levels, where wood ash dominates the mixture, and the stiffness of such materials, measured as Young’s modulus, had rarely been quantified despite its importance for structural design.

To close that gap, the researchers gathered four locally sourced wood ashes from the Normandy region of France. Two of them, designated WFA3 and WBA, came from the combustion of wood pellets and were delivered as wet sludge, requiring oven drying and crushing before use. The other two, WFA8 and WFA9, arrived as dry fine powders from a local heating plant operated by Coriance in Mont-Saint-Aignan, where boilers with power inputs of 6 and 8 megawatts burn forestry wood chips, bocage wood chips and pallet residues at temperatures between 900 and 1100 degrees Celsius. The team prepared seventeen paste formulations in total: four containing only wood ash, twelve blending 80 to 95 percent wood ash with 5 to 20 percent ordinary Portland cement, and a reference paste of pure cement, all compacted with a mini-Proctor device to boost density and cured for up to 28 days.

The chemical analysis alone revealed why wood ash is such a tricky raw material. The four ashes were dominated by calcium oxide, silica, potassium oxide and sulfur trioxide, but in wildly varying proportions. Sulfate contents reached 15.4 percent in WFA8 and 14 percent in WFA9, far above the 4 to 5 percent limit set by ASTM standards for pozzolans, and their combined pozzolanic oxides fell well below the required thresholds. In plain terms, these ashes do not qualify as conventional pozzolans, yet X-ray diffraction showed they carry crystalline phases such as portlandite, calcite, albite, alite, dolomite and sylvite that can still participate in binding reactions. The variability is a direct consequence of differing feedstocks, boiler designs and combustion temperatures, and it means each ash must be evaluated on its own terms rather than lumped into a single category.

When it came to mechanical performance, the effect of the small cement additions was unmistakable. Pure wood ash pastes managed compressive strengths of only 0.13 to 1.65 megapascals at 28 days, but raising the cement content to 20 percent lifted those values substantially. The best performer was the WFA8-based blend, which reached 5.49 megapascals, while WFA9 and WFA3 pastes achieved 4.01 and 3.87 megapascals respectively at the same dosage. The researchers attribute the gains to a richer supply of hydration products, including calcium silicate hydrate gel, portlandite and ettringite, formed as the cement’s tricalcium silicate reacts with water and progressively densifies the paste matrix. Stiffness told the same story: the modulus of elasticity, estimated from the linear portion of stress-strain curves, climbed with cement content, curing time and bulk density in three of the four ash families, with the highest values consistently recorded in mixtures containing 20 percent cement.

One ash refused to follow the script. The wood bottom ash, WBA, behaved atypically across every measurement. Its pastes lost compressive strength between 7 and 28 days at certain dosages, its modulus of elasticity peaked at 7 days and then declined, and thermogravimetric analysis found no detectable portlandite whatsoever. X-ray diffraction offered an explanation: the WBA pastes contained no alite, the calcium silicate phase that drives strength development in hydrating cement, and their dominant crystalline phases were calcite and quartz. Adding 20 percent cement pushed the estimated calcite content up from about 47 to 63.5 percent while quartz fell, a signature of carbonation of calcium silicate hydrate or the formation of complex, less efficient hydrate phases, both of which are associated with increased porosity and weaker binding.

Scanning electron microscopy added a visual dimension to the story. Under the microscope, pure cement paste appeared dense and well packed, bristling with the products of hydration, while pastes made from 100 percent wood ash showed loosely arranged particles riddled with interparticle voids, along with unreacted ash grains and dark fragments of unburnt wood. With 20 percent cement added, the microstructure tightened, porosity dropped and hydration products proliferated, with needle-like ettringite crystals, gel-like calcium silicate hydrates, plate-shaped portlandite and rhombohedral calcite all visible. The ashes from the heating plant, WFA8 and WFA9, consistently produced more compact matrices than the pellet-derived WFA3 and the bottom ash WBA, underlining how much origin and processing shape a material’s destiny.

The mineralogical detective work also turned up some genuinely unexpected chemistry. In the WFA8 blends, introducing cement promoted the formation of alunite, a potassium aluminum sulfate hydroxide phase not present in the unblended paste, alongside an array of compounds including syngenite, arcanite, serandite and harmotome. Thermogravimetric analysis at 7 and 28 days complemented the diffraction data, identifying calcium silicate hydrates and ettringite dehydrating between 50 and 200 degrees Celsius, AFm phases such as calcium monocarboaluminate and hemicarboaluminate decomposing between 200 and 300 degrees, portlandite dehydroxylating between 400 and 500 degrees, and carbonates releasing carbon dioxide from 500 to 800 degrees. The two techniques agreed closely, with the single discrepancy being ettringite in the bottom ash pastes, which thermal analysis detected but diffraction did not, likely because its concentration fell below the instrument’s detection limit.

What emerges from the study is a nuanced but practical message. Low doses of ordinary Portland cement, between 5 and 20 percent, can meaningfully upgrade pastes in which wood ash makes up as much as 95 percent of the solid content, provided the ash is fine and reasonably reactive. The improvements in stiffness, strength and microstructure are real, even if the resulting materials remain suited to low-strength applications such as lightweight binders rather than load-bearing concrete. The decisive variable, the authors conclude, is the variability of the ash itself: its origin, chemistry and mineralogy govern everything from phase development to porosity. That insight carries weight well beyond Normandy. With millions of tons of biomass ash generated annually and cement production responsible for a major share of global carbon dioxide emissions, even modest cement dosages that transform a landfill-bound waste into a functional building material represent a meaningful step toward circular, lower-carbon construction. The next challenge will be standardizing how ashes are characterized and selected, so that builders can trust what is in the bag before it ever reaches the site.

Subject of Research: The effect of low ordinary Portland cement content on the stiffness, microstructure and mineralogical composition of wood ash-based pastes

Article Title: Effect of low ordinary Portland cement content on stiffness, microstructure and mineralogical composition of wood ash pastes

Article References: Ndahirwa, D., Lenormand, H., Zmamou, H., Chenot, E., Potel, S., & Leblanc, N. (2026). Effect of low ordinary Portland cement content on stiffness, microstructure and mineralogical composition of wood ash pastes. Cleaner Engineering and Technology, 34, Article 101303. https://doi.org/10.1016/j.clet.2026.101303

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101303

Keywords: wood ash, ordinary Portland cement, Young's modulus, compressive strength, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, calcium silicate hydrate, ettringite, porosity, biomass ash, sustainable construction