The research, published in Cleaner Engineering and Technology by a team from the Tecnológico Nacional de México led by Bethsabet Jaramillo-Sierra, tackles a contamination problem that spans the globe. Acetaminophen has been detected in wastewater and surface waters on nearly every continent, at concentrations ranging from tens of nanograms per liter in France and Canada to hundreds of micrograms per liter in Colombia and northern Mexico. Although each individual measurement may seem small, the compound’s sheer consumption volume, its availability over the counter, and its resistance to biological degradation mean it accumulates persistently in rivers, drinking water sources, and even treated effluents.

The concern is not merely the presence of the parent molecule. Acetaminophen is poorly biodegradable, so it passes through conventional treatment largely intact, and it has been linked in laboratory studies to genetic damage, oxidative lipid degradation, and liver injury in living organisms. Worse still, during some tertiary treatment steps the compound can transform into by-products that are more dangerous than the original drug, including 1,4-benzoquinone and N-acetyl-p-benzoquinone imine, a hepatotoxic metabolite capable of causing hepatic failure and necrosis. Any credible remediation strategy must therefore do more than hide the molecule; it must destroy it or convert it into harmless end products.

The Mexican team turned to advanced oxidation processes, or AOPs, a family of water treatment methods that operate at ambient temperature and pressure and rely on the generation of highly reactive chemical species, most notably the hydroxyl radical. This radical carries a higher oxidation potential than chlorine and reacts non-selectively with a broad range of organic pollutants, which makes it attractive for treating trace contaminants of many kinds. AOPs also avoid sludge production, do not require adsorbents that need controlled disposal, and can be driven by easily handled reagents such as ozone and hydrogen peroxide, with ozone generated on site from atmospheric air to reduce storage and transport costs.

The experimental apparatus was deliberately simple: a cylindrical stainless-steel reactor with an 11-watt ultraviolet lamp emitting at 200 to 280 nanometers, housed in a quartz tube, coupled to a 12-watt ozone generator and a recirculating reservoir. Synthetic solutions of acetaminophen at 100 milligrams per liter were treated for 60 minutes in 500-milliliter batches, with hydrogen peroxide added at doses of 5, 10, and 15 milligrams per liter. Degradation was tracked by ultraviolet-visible spectrophotometry, chemical oxygen demand was measured colorimetrically, and oxidation by-products were identified using gas chromatography-mass spectrometry following solid-phase extraction.

The results revealed a clear hierarchy of effectiveness. Ultraviolet light alone managed only about 11 percent degradation in an hour, primarily by photolyzing water molecules into hydroxyl radicals and hydrogen atoms, a process that accelerates around the 254-nanometer wavelength. Hydrogen peroxide alone reached roughly 27 percent at the highest dose. Ozone alone, attacking through both direct molecular oxidation and indirect decomposition into hydroxyl radicals, achieved 73 percent. Pairing ozone with ultraviolet light pushed the figure to 84 percent, because photolysis of dissolved ozone generates additional atomic oxygen, hydroxyl radicals, and even hydrogen peroxide in solution, creating multiple parallel destruction pathways.

The real breakthrough came when all three agents were applied simultaneously. The ozone-hydrogen peroxide combination, known as peroxone, promotes hydroxyl radical formation through the mutual reaction of the two oxidants, and adding ultraviolet irradiation on top of this triggered photolysis of both peroxide and dissolved ozone. Under these conditions, with an initial hydrogen peroxide concentration of just 5 milligrams per liter, the team achieved 99 percent acetaminophen degradation in 60 minutes. Notably, the study found an optimal peroxide dose: higher concentrations of 10 and 15 milligrams per liter actually performed worse over time, because excess peroxide and the hydroperoxyl radical it forms act as scavengers, consuming the very hydroxyl radicals that destroy the pollutant.

Chemical analysis confirmed that the combined treatment went beyond mere transformation. Carbon dioxide production rose steadily across the treatment combinations, peaking at 37 milligrams per liter for the triple system, evidence of genuine mineralization rather than simple conversion to other organics. Chemical oxygen demand removal reached 74 percent in the same configuration, compared with just 9 percent for ultraviolet light alone. Color measurements told a parallel story: untreated solutions stayed clear, ultraviolet treatment alone produced a pale carmine tint at 150 platinum-cobalt units as aromatic ring breakdown products accumulated, while the triple system yielded only a faint yellow at 5 units, indicating that even the colored intermediates were being further oxidized. Gas chromatography-mass spectrometry identified by-products dominated by carboxylic acid, ester, and alcohol structures arising from aromatic ring cleavage and recombination, and crucially, the team did not detect hydroquinone or 1,4-benzoquinone, suggesting these hazardous intermediates were themselves degraded during the process.

Energetically, the triple treatment also proved competitive. The researchers calculated the electrical energy per order, a standard metric describing the kilowatt-hours needed to reduce pollutant concentration by one order of magnitude per cubic meter, and obtained 23.00 kilowatt-hours per cubic meter for the peroxide-ozone-UV system, well below the 537 kilowatt-hours per cubic meter required for ultraviolet treatment alone and below several values reported in comparable literature. The estimated operating cost of the best configuration came to 5.04 US dollars per cubic meter, with ultraviolet irradiation dominating the energy bill, ozone generation second, and hydrogen peroxide contributing least. The degradation kinetics followed a pseudo first-order model, with rate constants rising as processes were combined, consistent with the theory that degradation depends primarily on pollutant concentration while oxidant doses remain effectively constant.

Finally, the team assessed whether the treated water was actually safer, using the germination of lettuce seeds as a biological toxicity screen. Untreated and lightly treated samples showed moderate toxicity, with ozone alone inhibiting germination by 40 percent, a sign that oxidative intermediates can be more harmful than the parent drug. But the full triple treatment reduced inhibition to 15 percent, close to the control level, demonstrating that synergistic oxidation both destroys the pollutant and neutralizes its residual toxic footprint. Taken together, the findings position the combined peroxide-ozone-UV process as an operationally simple, reproducible, and relatively inexpensive route to eliminating one of the world’s most ubiquitous pharmaceutical pollutants, though the authors note that complete mineralization would likely require longer treatment times or more intensified oxidative conditions to drive the remaining low-complexity organic by-products all the way to inorganic carbon.

Subject of Research: Degradation of the pharmaceutical pollutant acetaminophen in water using combined advanced oxidation processes involving ozone, hydrogen peroxide, and ultraviolet radiation.

Article Title: Acetaminophen degradation process applying a combination of oxidizing agents and ultraviolet radiation

Article References: Jaramillo-Sierra, B., Mercado-Cabrera, A., Ibañez-Olvera, M., Peña-Eguíluz, R., Rodríguez-Méndez, B. G., & López-Callejas, R. (2026). Acetaminophen degradation process applying a combination of oxidizing agents and ultraviolet radiation. Cleaner Engineering and Technology, 34, Article 101301. https://doi.org/10.1016/j.clet.2026.101301

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101301

Keywords: acetaminophen, paracetamol, advanced oxidation processes, ozone, hydrogen peroxide, ultraviolet radiation, hydroxyl radicals, wastewater treatment, pharmaceutical pollution, water purification, mineralization, chemical oxygen demand

The core of the innovation lies in combining two well-known but notoriously difficult-to-pair processes. The first is anammox, short for anaerobic ammonium oxidation, in which specialized bacteria convert ammonium and nitrite directly into inert nitrogen gas without oxygen or organic carbon. The second is sulfide-dependent autotrophic denitrification, or S-SADN, in which sulfur-oxidizing bacteria use sulfide as an electron donor to reduce nitrate and nitrite. Each process alone has limitations: anammox bacteria are slow-growing and sensitive to sulfide toxicity, while conventional autotrophic denitrification with sulfide generates excessive sulfate and competes with anammox for nitrite. The new work shows that a carefully tuned mixotrophic design, in which the denitrifying partner also consumes a small amount of organic carbon, resolves these conflicts.

Lead author Yifan Zhang and colleagues integrated an anammox-enriched culture designated KAS1 with Thauera sp. AutoDN2, a sulfide-oxidizing denitrifying bacterium previously identified by the same group. Crucially, AutoDN2 is not a strict autotroph; it can use both sulfide and acetate, allowing the researchers to maintain a very low carbon-to-nitrogen ratio of just 0.8. Under these conditions, the coupled system removed 98.1 percent of ammonium and 99.4 percent of total nitrogen, performance figures that rival or exceed the best reported values for similar coupled systems while requiring far less external carbon than heterotrophic denitrification would demand.

Long-term operation in fed-batch mode revealed how the workload was divided between the two guilds. Anammox accounted for 71.2 to 77.1 percent of the total nitrogen removed, confirming that it remained the dominant pathway throughout extended operation. The mixotrophic S-SADN component provided a complementary route, polishing nitrate produced by anammox and handling sulfide oxidation. This division of labor proved stable over repeated feeding cycles, a critical finding because many attempted couplings of anammox with sulfur-driven denitrification have collapsed under sulfide inhibition or nitrite starvation of the anammox population.

One of the most striking outcomes concerns sulfate, the typical end product of sulfide oxidation. In conventional sulfide-based autotrophic denitrification systems, sulfide is fully oxidized to sulfate, which accumulates in the effluent, corrodes infrastructure, and raises salinity in receiving waters. In the mixotrophic system, sulfate yields were 63 to 68 percent lower than in purely autotrophic counterparts. The mechanism appears to be stoichiometric: when acetate is available, the denitrifiers require less sulfide per unit of nitrate reduced, and the reduced sulfide oxidation load shifts the sulfur balance away from complete oxidation. In effect, the organic co-substrate absorbs part of the electron-donation burden that sulfide would otherwise carry alone.

To verify that both processes were genuinely active rather than merely coexisting, the researchers tracked transcript levels of key functional genes. Stable expression of hzsA and hzsB, which encode hydrazine synthase subunits essential to the anammox metabolism, demonstrated that the anammox bacteria maintained their central catabolic machinery. Simultaneously, steady transcription of narG and napA, genes encoding nitrate reductases in the denitrification pathway, confirmed that AutoDN2 was actively respiring nitrogen oxides. The synchronized activity of these gene sets provides molecular evidence of metabolic synergy rather than competitive exclusion, and it suggests the partnership could be monitored in real time at full-scale plants through transcriptomic or genomic surveillance of activated sludge.

Equally notable is what the system did not emit. Across the experimental campaign, the researchers detected no nitrous oxide, a greenhouse gas roughly 265 times more potent than carbon dioxide over a century and a notorious byproduct of conventional nitrification-denitrification. The authors attribute this to the high nitrite affinity of anammox bacteria, which scavenge nitrite so efficiently that denitrifiers are rarely pushed toward the nitric oxide reductase steps that leak nitrous oxide. For utilities facing tightening greenhouse gas accounting rules, an ammonium treatment train that emits essentially no nitrous oxide represents a significant compliance advantage alongside its energy savings.

The practical implications extend to several wastewater streams where sulfide and ammonium co-occur with little biodegradable carbon. Anaerobic digester liquors, landfill leachate, tannery effluents, petrochemical wastewater, and sidestream returns from sludge treatment all fit this profile. In such streams, sulfide is usually treated as a nuisance to be stripped or precipitated before biological nitrogen removal, adding cost and complexity. The coupled platform instead treats sulfide as a free electron donor, converting a pollutant into a process resource. Because anammox does not require aeration and the denitrifying partner needs only a whisper of organic carbon, the system avoids the aeration and carbon-dosing costs that dominate conventional treatment economics.

The authors caution that translating a fed-batch laboratory model to continuous full-scale operation will require attention to process control, particularly maintaining the delicate nitrite balance that both guilds depend upon and managing sulfide loading to keep concentrations below anammox inhibition thresholds. Nevertheless, the demonstration that strategic mixotrophy can simultaneously mitigate sulfide toxicity, suppress sulfate overproduction, stabilize integrated carbon-nitrogen-sulfur cycling, and deliver near-complete nitrogen removal marks a substantial advance. As water utilities worldwide seek low-carbon pathways to meet stricter nitrogen discharge limits, this anammox-mixotrophic denitrification partnership offers a compelling blueprint: two microbial metabolisms, each compensating for the other’s weaknesses, working in concert to turn some of wastewater’s most stubborn pollutants into harmless nitrogen gas.

Subject of Research: Coupling anammox with mixotrophic sulfide-driven autotrophic denitrification for extensive biological nitrogen removal from sulfide-rich, carbon-limited wastewater

Article Title: Synergistic coupling of anammox and mixotrophic sulfide-driven denitrification for extensive nitrogen removal

Article References: Synergistic coupling of anammox and mixotrophic sulfide-driven denitrification for extensive nitrogen removal. (n.d.). https://doi.org/10.1007/s11783-026-2281-y

Image Credits: AI Generated

DOI: 10.1007/s11783-026-2281-y

Keywords: anammox, autotrophic denitrification, sulfide oxidation, wastewater treatment, nitrogen removal, Thauera, mixotrophic metabolism, nitrous oxide, sulfate reduction, carbon-nitrogen-sulfur cycling, environmental biotechnology, low-carbon sanitation

Sewage sludge, the residual semi-solid material generated during treatment, traditionally undergoes various handling and disposal strategies. However, to valorize this byproduct and reduce ecological footprints, thermal transformation methods such as pyrolysis have garnered considerable attention. Pyrolysis decomposes organic sludge constituents under oxygen-deprived high-temperature conditions, yielding biochar — a carbon-rich, stable material with extensive utility in agriculture, soil remediation, and carbon sequestration. The properties and environmental safety of biochar depend intricately on both the origin of the sludge and the pyrolysis parameters. Notably, biochar derived from CEPT sludge (CS) has shown divergent characteristics compared to that from biologically treated sludge (BS), particularly concerning heavy metal retention and stability.

Heavy metals inherent to sewage sludge, including copper, lead, cadmium, and zinc, pose significant environmental challenges due to their toxicity and potential bioaccumulation. Their behavior during pyrolysis determines the environmental risks of biochar usage, especially when intended as soil amendments. Despite its importance, the scientific community has yet to fully unravel how CEPT influences heavy metal dynamics during biochar formation. This knowledge gap is critical as improper thermal treatment might inadvertently mobilize these metals, leading to secondary pollution through leaching and atmospheric dispersion.

A breakthrough study conducted by Professor Kitae Baek and his research team at Jeonbuk National University endeavors to demystify these aspects by directly comparing the heavy metal characteristics and stabilities in biochars originating from CEPT and conventional sludge. Using experimental setups involving optimized pyrolysis at distinct temperature regimes, the team meticulously assessed metal speciation, retention rates, and leaching potentials, aiming to identify thermal treatment parameters that maximize safety and sustainability.

The research unveiled stark contrasts in biochar yields and heavy metal retention between the two sludge types. CEPT sludge biochar production displayed substantially lower yields—ranging from 32.1% to 40.9%—relative to biologically treated sludge, which achieved yields up to 75.2%. This decrease in yield suggests more substantial organic degradation or volatilization during CEPT sludge pyrolysis. Moreover, heavy metals presented lower retention within CS-derived biochars across the pyrolysis temperature spectrum, indicating a heightened propensity for these metals to escape into the environment under thermal treatment.

Further investigations into thermal stability revealed that at elevated pyrolysis temperatures exceeding 800 °C, CS biochars exhibited markedly increased heavy metal mobility, rendering these metals susceptible to leaching when in contact with water or soil. Such findings herald significant environmental concerns, as mobile heavy metals can infiltrate groundwater and enter food chains, undermining ecological and human health. Contrarily, when pyrolysis was conducted at an optimized temperature of approximately 550 °C, both CEPT and conventional sludge biochars demonstrated commendable heavy metal stability, with metals effectively immobilized within the biochar matrix.

These insights underscore the necessity of carefully calibrating pyrolysis parameters to harness the benefits of CEPT sludge without exacerbating environmental hazards. The study advocates for employing lower-temperature pyrolysis regimes when treating CEPT sludge, balancing effective pollutant degradation with retention of heavy metals. This strategy aligns with sustainable waste management principles, facilitating the reclamation of biochar for beneficial uses such as soil enhancement and carbon sequestration, thereby closing the loop in urban resource recycling.

Professor Baek emphasizes the broader implications of their findings: “While CEPT offers tangible advantages in reducing energy consumption for sewage treatment, our work articulates the critical importance of integrating environmental risk assessments into the entire treatment chain. Appropriate thermal management of CEPT sludge is vital to mitigating potential secondary pollution and ensuring that biochar applications do not inadvertently compromise soil and water quality.”

Methodically, the study employed an array of analytical techniques including sequential chemical extraction, leaching tests, and advanced spectroscopic methods to quantify heavy metal speciation and mobility. This rigorous approach ensured a multifaceted understanding of how thermal processes influence metal transformations, providing robust evidence to shape future guidelines and regulatory frameworks.

The ramifications of this research extend beyond local sewage treatment facilities, offering a template for urban centers worldwide contending with burgeoning wastewater challenges. By highlighting the nuanced interplay between treatment chemistry and thermal processing, the study bridges critical knowledge gaps, inspiring innovation in resource recovery and sustainable infrastructure design.

Moreover, these findings resonate within the broader context of global environmental conservation and climate action. Wastewater treatment plants are significant energy consumers and contributors to greenhouse gas emissions. Adopting CEPT alongside optimized biochar production methods promises to curtail these impacts, augmenting the resilience and environmental stewardship of urban systems. This research thus aligns with the growing paradigm shift towards circular economy practices in environmental engineering.

In conclusion, the pioneering work led by Professor Baek delineates a sophisticated framework to exploit CEPT-derived sewage sludge via pyrolysis, emphasizing thermal regimes that safeguard against heavy metal dispersion while maximizing biochar utility. This comprehensive assessment not only addresses current environmental concerns but also propels the field towards integrated, eco-efficient wastewater management solutions, fostering a sustainable future for urban ecosystems worldwide.

Subject of Research: Environmental Engineering, Sewage Sludge Management, Heavy Metal Stability in Biochar

Article Title: Stability assessment of heavy metals in sewage sludge pyrolysis biochar based on the chemical-enhanced primary treatment (CEPT) process

News Publication Date: 15 January 2026

References: DOI: 10.1016/j.psep.2025.108338

Image Credits: Professor Kitae Baek, Jeonbuk National University, Republic of Korea

Keywords

Chemical-enhanced primary treatment, CEPT, Sewage sludge, Pyrolysis, Biochar, Heavy metals, Heavy metal stability, Environmental risk, Thermal treatment, Wastewater treatment, Soil amendment, Sustainable wastewater management