Underground sewer pipes are difficult to access, making their condition hard to monitor, while conventional camera inspections are costly and time-consuming. Damaged pipes can leak wastewater and contaminate surrounding water, and severe failures can damage infrastructure above them, including causing sinkholes in city streets. Regular inspections are therefore important for aging sewer networks, but the new study addresses the practical challenge of deciding where inspections should be concentrated when resources and access are limited.

For the field test, the researchers collected wastewater samples from 40 manholes across the residential network. They measured DNA associated with sulfate-reducing bacteria, a group that can contribute to pipe corrosion. Information on pipe slope and the area of upstream buildings was used to estimate where these organisms were more likely to occur across the sewer system. These ecological estimates of bacterial habitat potential were then combined with sewer-network characteristics—pipe age, diameter and slope—and entered into a Random Forest machine-learning model. Among the bacteria studied, Desulfobulbus showed the strongest relationship with pipe deterioration and was the most important microbial predictor. Professor Daisuke Sano said the team was surprised by how useful it was for predicting corrosion and noted that among all the biological factors tested, its predictive importance ranked second only to pipe age.

The model was tested against inspection records for 3,498 pipe sections, and the results showed that adding the wastewater-derived microbial information improved its ability to identify severely corroded pipes. Rather than directly examining the condition of every buried pipe, the method uses biological signals detected in wastewater to create geographic estimates that can be compared with the sewer network. The approach thus converts microbial DNA measurements into a network-scale screening tool. It also reduces the need to treat each manhole sample as an isolated observation: the ecological model estimates potential bacterial habitat between sampling locations, while the machine-learning model relates those estimates to pipe characteristics and known inspection outcomes.

The findings support wastewater monitoring and habitat mapping as tools for directing further inspection toward sections that may warrant closer attention. Municipalities could compare the modeled risk areas with existing infrastructure records to focus camera inspections and other assessments on pipes with a higher likelihood of severe corrosion. The study tested the method in one residential sewer network using samples from 40 manholes and validation against 3,498 pipe-section inspection records, so its reported performance is specific to that setting. The method remains a screening and prioritization strategy rather than a substitute for direct inspection, which is still required to evaluate the condition of individual pipes. As Sano explained, combining wastewater DNA with ecological modeling converted invisible biological signals into geographic maps that may help cities identify high-risk areas and allocate limited inspection resources more efficiently.

Subject of Research: Environmental DNA and ecological modeling for network-scale screening of sewer-pipe corrosion risk.

Article Title: AI and wastewater DNA-based mapping helps identify sewer pipes at risk of corrosion

Article References: AI and wastewater DNA-based mapping helps identify sewer pipes at risk of corrosion. Original publication (Bibliographic details unavailable.)

Image Credits: AI Generated

DOI: Not provided

Keywords: sewer corrosion, wastewater DNA, environmental DNA, sulfate-reducing bacteria, Desulfobulbus, species distribution modeling, machine learning, Random Forest, infrastructure monitoring, pipe inspection, wastewater, DNA-based

Researchers assessed the environmental impact of the discharge from the Samokov Wastewater Treatment Plant, which releases up to 44,100 cubic meters of treated effluent per day into a 10-kilometer stretch of the upper Iskar. The plant handles mixed municipal, industrial and storm wastewater from the town of Samokov using a denitrification-nitrification scheme, yet the team found that its outfall still measurably alters the river’s chemistry, microbial communities and sediment dynamics in ways that standard monitoring programs may be missing.

The study, published in BioRisk, combined chemical analyses, microbiological counts, fluorescent imaging of bacterial activity and macroinvertebrate surveys across four sampling sites positioned above, at, and below the discharge point. Two sampling campaigns in November 2020 and March 2021 captured contrasting seasonal conditions, revealing how the river’s response to effluent shifts with flow, temperature and surrounding land use.

At the discharge site, the chemical fingerprint of urban wastewater was unmistakable. Nitrate concentrations spiked nearly 20-fold compared to the upstream reference site in November and eight-fold in March. Ammonium jumped more than 15-fold during the autumn campaign, and phosphate levels at the outfall reached 0.750 milligrams per liter in March, exceeding Bulgarian regulatory thresholds. Water temperature at the outfall was consistently higher than upstream, conductivity rose, and dissolved oxygen dropped below recommended norms for high ecological status during both seasons.

Yet the picture is not simply one of degradation. The river’s self-purification capacity, driven largely by microbial communities in the sediment, appears to absorb much of the impact within a short distance downstream. By the next sampling site at Dragushinovo village, many parameters had begun to normalize, and the ecological status of the entire river sector was assessed as “good” based on macrozoobenthos indicators, with a biotic index score of 4 at both surveyed sites.

The microbial story is more nuanced. Using a combination of CTC and DAPI fluorescent staining, the researchers distinguished metabolically active bacteria from total bacterial counts in sediment samples. They found that the fraction of live, active cells was roughly three percent at the discharge site in both seasons, compared to less than one percent upstream. Mean fluorescence intensity, a proxy for cellular metabolic activity, was up to 2.3 times higher at the site just below the plant, suggesting that the sediment microbiome downstream remains in a state of heightened biological processing long after the effluent enters the river.

Sediments also act as reservoirs for coliform bacteria, with counts reaching 3,000 to 11,000 colony-forming units per gram in the discharge zone. The researchers warn that this makes the riverbed a potential “natural depot” for opportunistic and pathogenic microorganisms, a dimension that conventional water-column monitoring entirely overlooks. Including sediment analysis in routine monitoring could therefore provide an early warning of accumulating microbial risks that might otherwise go undetected until they surface in downstream water quality.

The study also flagged seasonal spikes in heavy metals. Mercury, a priority pollutant under EU legislation, peaked at 1.42 micrograms per liter at the site below the plant in November, while copper reached 44 micrograms per liter at the outfall. These concentrations, along with elevated zinc, chromium and arsenic levels linked to post-summer anthropogenic activity, pose potential toxic risks that compound the nutrient loading from the treatment plant and surrounding agriculture.

Perhaps most striking is the finding that the current ecological status and water quality have deteriorated compared to earlier studies in the same sub-catchment. The cumulative pressure from the treatment plant, intensive agriculture, livestock breeding and untreated sewage from small villages is creating a background load that self-purification may not indefinitely absorb. Given the Iskar Reservoir’s role as Sofia’s primary drinking water source, the researchers argue that existing monitoring programs must be extended with more detailed assessment of sediment microbial communities, seasonal metal dynamics and the long-term environmental impact of wastewater discharge before the river’s buffering capacity is pushed past its limits.

The concept of self-purification that underpins the study’s findings is one of the oldest ideas in freshwater science, yet it remains difficult to quantify in regulatory terms. When nutrient-rich effluent enters a river, a cascade of physical, chemical and biological processes begins: dilution, settling of particulates, microbial degradation of organic matter, and uptake of nitrogen and phosphorus by periphyton and macrophytes. The upper Iskar’s pebble and sand substratum provides substantial surface area for these biofilms, which explains why the river can partially recover within a few kilometers of the outfall. However, self-purification is not a limitless buffer; it depends on flow regime, temperature, oxygen availability and the structural integrity of the riverbed, all of which can be disrupted by channel modification, water abstraction or climate-driven changes in seasonal discharge.

The choice of macrozoobenthos as the biological quality element reflects the requirements of the European Water Framework Directive, which structures water management across the European Union around the goal of achieving good ecological status for all surface water bodies. Benthic invertebrates are favored indicators because they integrate environmental conditions over weeks and months, respond predictably to organic pollution, and occupy a central position in river food webs. Metrics such as the biotic index assign tolerance scores to families of organisms, with pollution-sensitive taxa like mayflies and stoneflies absent from degraded reaches while tolerant groups persist. A score of 4, recorded in the study sector, sits within the band classified as good for semi-mountain river types, but the local deterioration observed immediately below the outfall illustrates how a reach can mask localized stress when assessed at the broader water-body scale.

The fluorescent techniques employed in the study deserve particular attention because they address a long-standing weakness of conventional microbiology. Standard cultivation methods detect only a small fraction of environmental bacteria, since many viable cells enter dormant or viable-but-not-culturable states that do not form colonies on agar plates. By contrast, CTC staining identifies cells with active electron transport chains, effectively flagging those that are respiring and metabolizing, while DAPI stains all cells with intact DNA regardless of activity. The combination allowed the researchers to show that the proportion of active cells, not merely total abundance, shifted in response to the effluent plume. This distinction matters because metabolically active sediment communities drive the biogeochemical transformations that constitute the biotic half of self-purification, including nitrification, denitrification and the breakdown of organic carbon.

The seasonal dimension of the findings aligns with the hydrological character of the river. The upper Iskar experiences pronounced spring high flows of 15 to 25 cubic meters per second, contrasted with summer and winter low flows of only 1 to 3 cubic meters per second. The sampling campaigns, conducted at moderate autumn and spring flows of 5 to 8 cubic meters per second, captured intermediate conditions. During low-flow periods, the same effluent volume represents a far larger share of total river discharge, so dilution capacity shrinks and concentrations of nutrients, organic matter and micropollutants rise correspondingly. This hydraulic sensitivity means that a discharge which appears tolerable in March may impose substantially greater stress in August, a timing mismatch that annual or infrequent monitoring schedules can easily miss.

The analytical rigor of the chemical measurements also strengthens the study’s conclusions. Trace element determination by inductively coupled plasma mass spectrometry offers detection limits low enough to resolve environmentally relevant concentrations of metals such as mercury, which is regulated as a priority hazardous substance under EU environmental quality standards because of its persistence, bioaccumulation potential and neurotoxicity. Validation against certified reference materials from Norway and Canada confirmed the accuracy of the measurements, an essential step when concentrations in the microgram-per-liter range carry regulatory significance. Comparisons against Bulgarian regulations for surface water characterization and for waters intended for drinking-water abstraction provided a national legal benchmark alongside the EU framework.

The downstream implications extend beyond the study reach. Iskar Reservoir, the largest in Bulgaria, functions as the terminal sink for material transported from the upper catchment, and reservoirs are particularly efficient at trapping sediments, phosphorus and associated contaminants. Chronic inputs from the river can therefore accumulate in the reservoir’s sediments over years, where they may fuel internal nutrient loading, alter algal dynamics and complicate drinking-water treatment. Elevated microbial loads arriving from upstream likewise increase the disinfection burden faced by water treatment operators, making catchment management a direct component of public health protection for the capital.

More broadly, the study contributes to a growing body of evidence that wastewater treatment plants, despite their essential role, function as continuous point sources of residual pollution rather than as barriers to it. Effluents consistently carry worse quality than receiving waters, and emerging concerns such as pharmaceutical residues, microplastics and antimicrobial resistance genes are not addressed by conventional nutrient-removal schemes. Integrating sediment microbiology, seasonal trace-element monitoring and sensitive biological indicators into routine surveillance, as the researchers propose, would bring assessment practice closer to the actual complexity of pollution and recovery dynamics in rivers that serve simultaneously as recipients of waste and sources of drinking water.

Subject of Research: Environmental impact assessment of discharge of treated wastewater effluent in Upper Iskar sub-catchment

Article Title: Environmental impact assessment of discharge of treated wastewater effluent in Upper Iskar sub-catchment

Article References: Yordanova, V., Todorova, Y., Belouhova, M., Kenderov, L., Lyubomirova, V., & Topalova, Y. (2022). Environmental impact assessment of discharge of treated wastewater effluent in Upper Iskar sub-catchment. BioRisk, 17, 59-71. https://doi.org/10.3897/biorisk.17.77381

Image Credits: AI Generated

DOI: 10.3897/biorisk.17.77381

Keywords: water quality, microbiology, environmental monitoring, Bulgaria, wastewater treatment, Environmental, impact, assessment, discharge, treated, wastewater, effluent

The review, led by Lovepreet Singh of the Thapar Institute of Engineering and Technology in India alongside colleagues from Delhi Technological University, Maharishi Markandeshwar Deemed to Be University, Gombe State University in Nigeria, and Amity University, introduces and consolidates the concept of “secondary nanowaste”—the nanomaterials and nano-derived residues that are released, transformed, or accumulated during the operation, regeneration, disposal, or reuse stages of nano-enabled water treatment. Drawing on research from the last decade, the authors argue that while most studies focus on removal efficiency and material performance, the post-treatment fate of these materials has received far less attention, leaving a critical blind spot in environmental risk assessment.

The problem is fundamentally one of material recovery. Nanomaterials used in water treatment are often not fully recoverable at the end of their service life. They can break down chemically, leach their constituent elements, accumulate in treatment sludge, or escape directly into the environment. Each of these pathways generates what the researchers call post-treatment pollution—a category of contamination that emerges not from the original wastewater being treated, but from the treatment technology itself. The review identifies several major routes of secondary nanowaste formation: the buildup of nanoparticles in sludge, the aging and degradation of nanocomposite membranes, the loss of catalytic materials during advanced oxidation processes, and the incomplete recovery of magnetic or immobilized nanoparticles after repeated use cycles.

The scale of the challenge becomes clear when considering the diversity of nanomaterials now deployed in water treatment. Nano-adsorbents—including carbon nanotubes, graphene oxide, metal-organic frameworks, layered double hydroxides, and clay-based nanocomposites—are prized for their enormous surface areas and tunable surface chemistry. Photocatalytic systems built on titanium dioxide, zinc oxide, bismuth oxyhalides, and graphitic carbon nitride can degrade organic pollutants under light activation. Magnetic nanomaterials such as iron oxide spinels and ferrites enable rapid separation from treated water. Membranes embedded with silver nanoparticles, MXenes, or metal-organic frameworks offer both filtration and antimicrobial function. Each of these material classes carries its own distinct profile of potential release, transformation, and environmental persistence once the treatment cycle ends.

Once released, secondary nanowaste does not simply vanish. The review traces its environmental fate across water, soil, and sediment systems, where nanomaterials can undergo agglomeration, dissolution, surface transformation, or interaction with natural organic matter—processes that alter their mobility, bioavailability, and toxicity. In aquatic environments, engineered nanoparticles have been shown to affect microbes, algae, invertebrates, and fish, with documented impacts on cellular function, growth, and reproduction. In soil and sediment, accumulated nanomaterials can persist and potentially enter food webs. The authors also highlight concerns for drinking water safety, noting that nanomaterials that leach from treatment systems may themselves become contaminants in the very water they were designed to purify.

The ecotoxicological evidence reviewed by the team is sobering. Studies on silver and zinc oxide nanoparticles, for instance, demonstrate toxic effects across multiple trophic levels in aquatic ecosystems. Research on cerium oxide nanoparticles has revealed impacts on gene expression in aquatic organisms such as Daphnia magna. The interaction of engineered nanoparticles with microplastics and other co-existing pollutants adds another layer of complexity, as sorption and co-transport can amplify exposure in ways that single-substance toxicity tests fail to capture. The review emphasizes that these effects are not merely laboratory curiosities—they represent plausible real-world exposure scenarios as nano-enabled treatment systems scale up globally.

What makes the situation particularly urgent, the authors argue, is the mismatch between the pace of nanomaterial deployment and the pace of environmental monitoring. Long-term toxicity data remain sparse, and exposure assessment methodologies for nanomaterials in real environmental matrices are still immature. Standard analytical techniques struggle to detect and characterize engineered nanoparticles at environmentally relevant concentrations, especially once they have undergone transformation in complex matrices like sludge, sediment, or natural waters. Without robust monitoring frameworks, regulators and operators have limited ability to track secondary nanowaste as it moves through the environment, making it difficult to establish safe operating thresholds or design effective mitigation strategies.

The review does not simply catalogue the problem—it also surveys emerging solutions. The authors discuss safe-by-design approaches that aim to minimize secondary nanowaste generation from the outset, including strategies to immobilize nanomaterials more securely within treatment matrices, improve recovery rates through magnetic or other separation mechanisms, and design materials that degrade into benign end products after their useful life. Regeneration technologies for saturated adsorbents, which allow nanomaterials to be reused rather than discarded, represent another important avenue. The researchers also point to the potential of post-use recovery strategies that capture nanoparticles before they can enter the environment, transforming what would otherwise be waste into a recoverable resource.

Looking forward, the review calls for a fundamental shift in how nano-enabled water treatment is evaluated and regulated. Rather than assessing these technologies solely on their pollutant-removal performance during operation, the authors argue that lifecycle thinking must become standard practice—accounting for what happens to nanomaterials during regeneration, disposal, and environmental release. They advocate for the development of risk-informed monitoring strategies that can detect secondary nanowaste in real time, coupled with sustainable design principles that prioritize both treatment efficacy and environmental safety across the full technology lifecycle. Such an approach, they contend, is essential for the responsible deployment of nanotechnology in water treatment at global scale.

The findings arrive at a moment when water scarcity and pollution are intensifying worldwide, driving rapid investment in advanced treatment technologies. Nano-enabled systems promise to address contaminants that conventional treatment cannot touch—from pharmaceutical residues and per- and polyfluoroalkyl substances to microplastics and antibiotic-resistant genes. But the review serves as a timely reminder that every technological solution carries its own environmental footprint. As the global water treatment sector accelerates its adoption of nanomaterials, understanding and managing the afterlife of these materials may prove just as important as the pollutants they were designed to remove. The researchers hope their synthesis will catalyze the development of comprehensive monitoring protocols, standardized risk assessment frameworks, and design guidelines that ensure nano-enabled water treatment delivers on its promise without creating a new generation of environmental problems in the process.

Subject of Research: Environmental monitoring and risk assessment of secondary nanowaste generated by nano-enabled water and wastewater treatment technologies

Article Title: Environmental monitoring and risk assessment of secondary nanowaste in nano-enabled water treatment systems

Article References: Singh, L., Pathak, J., Arora, J., Shehu, Z., Michael, E., & Jain, H. (2026). Environmental monitoring and risk assessment of secondary nanowaste in nano-enabled water treatment systems. Environmental Monitoring and Assessment, 198(9), Article 1011. https://doi.org/10.1007/s10661-026-15852-7

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15852-7

Keywords: nanotechnology, water treatment, secondary nanowaste, environmental monitoring, ecotoxicity, nanomaterials, wastewater, risk assessment, safe-by-design, environmental fate, sludge, membranes

The material at the heart of the study belongs to a well-known family of compounds with the general formula AB2O4, known as spinels. These mixed metal oxides are stable semiconductors that have repeatedly demonstrated strong photocatalytic efficiency in destroying organic pollutants. In a photocatalytic process, the semiconductor absorbs photons, generating reactive species such as hydroxyl radicals and superoxide radicals that attack pollutant molecules and tear them apart. How well an oxide performs this job depends on several parameters, including its band gap energy, crystallinity, specific surface area and morphology. The Moroccan team set out to tune those parameters by replacing half of the zinc ions in zinc aluminate with magnesium, producing a compound written as Mg0.5Zn0.5Al2O4, and then testing it against tetracycline hydrochloride, a widely used antibiotic chosen as a representative pharmaceutical pollutant.

The preparation method is one of the most appealing aspects of the work, because it is deliberately simple and inexpensive. The researchers dissolved analytical grade zinc nitrate, aluminium nitrate and magnesium nitrate in water at a metal ion concentration of 0.2 molar, keeping the stoichiometric molar ratio of trivalent to divalent cations at 0.5. Urea was added in excess to act simultaneously as a chelating agent and as a fuel. The solution was evaporated at 80 degrees Celsius until a viscous gel formed, then dried at 120 degrees Celsius for 24 hours to yield a xerogel. That xerogel was pre-calcined at 300 degrees Celsius for 12 hours in air to burn off the organic matter through pyrolysis, and the resulting precursor was finally heat-treated at 700 degrees Celsius for 5 hours. This soft chemistry route avoids the high temperatures and elaborate equipment often required to make high-quality spinel ceramics.

Characterisation of the powders followed established analytical protocols. Thermogravimetry and differential thermal analysis tracked the crystallisation of the xerogel, revealing a total mass loss of about 78 percent between 30 and 550 degrees Celsius. Those mass losses appeared as thermal effects attributable to dehydration, the elimination of ammonium nitrate species, decomposition of the complexing agent and the eventual crystallisation of the oxide phase. X-ray diffraction, performed with a Bruker D8 Advance diffractometer using copper K-alpha radiation, then mapped the crystalline structure of samples taken before and after the high-temperature treatment. The pre-calcined sample showed broad, weak diffraction peaks signalling the very beginning of crystallisation, while the sample annealed at 700 degrees Celsius displayed sharper, more intense reflections, a clear sign of improved crystallinity.

The diffraction pattern of the annealed powder told a satisfying story. Peaks appeared at 2-theta values of 31.2, 36.8, 44.8, 49.1, 55.8, 59.4, 65.3, 74.1 and 77.5 degrees, and these could be indexed to the (220), (311), (400), (331), (422), (511), (440), (620) and (533) crystallographic planes of a cubic spinel structure belonging to the Fd-3m space group. Crucially, no additional diffraction peaks were detected, indicating that a single-phase spinel had formed rather than a mixture of unwanted secondary phases. Scanning electron microscopy with a JEOL JSM-6400 instrument showed that the calcined powder consists of submicron-sized agglomerates, a morphology typical of powders produced by gel-based combustion and chelation routes. The authors note that the study was limited to a single magnesium-to-zinc ratio of x equal to 0.5, and that a systematic survey of different ratios would be needed to fully map how composition controls phase formation, crystallinity, optical behaviour and catalytic performance.

Optical measurements provided the key numbers that connect the material to its photocatalytic role. Ultraviolet-visible absorption spectroscopy revealed a broad absorption band extending into the visible region. Using Tauc analysis, in which the absorption coefficient raised to an exponent appropriate for direct transitions is plotted against photon energy, the team identified two quasi-linear regions corresponding to apparent transition energies of approximately 3.14 and 4.65 electronvolts. The authors are careful to point out that these values should not necessarily be read as two independent fundamental band gaps. The lower energy of 3.14 electronvolts is treated as the more relevant optical absorption edge for discussing photocatalytic behaviour under ultraviolet irradiation, while the higher-energy feature is regarded as an apparent transition whose precise origin cannot be pinned down from the available diffraction and spectroscopy data alone.

With the catalyst characterised, the team turned to the practical test: degrading tetracycline hydrochloride in water. The experiments took place in a cylindrical reactor built around a 250-millilitre double-walled Pyrex beaker held at room temperature. The light source combined two UVA lamps and two UVB lamps, each rated at 10 watts and positioned roughly 12 centimetres from the beaker, plus a 15-watt submersible UVC lamp placed directly in the reaction solution. The whole apparatus sat inside an opaque box to exclude ambient sunlight, and no optical filters were used. The pollutant solution started at a concentration of 30 milligrams per litre, and its absorbance maximum at 357 nanometres allowed concentration to be tracked with a linear calibration curve obeying the Beer-Lambert law.

The results unfolded in two stages. First, 50 milligrams of the Mg0.5Zn0.5Al2O4 powder were dispersed in 200 millilitres of the antibiotic solution and stirred in the dark. Adsorption-desorption equilibrium was reached within 30 minutes, during which 17 percent of the tetracycline disappeared from solution, an initial removal attributed mainly to adsorption onto the catalyst surface. Then the lamps were switched on. Samples collected every 30 minutes showed a steady decline in absorbance, and by the end of two hours of ultraviolet irradiation a total of 76 percent of the pollutant had been eliminated. The removal process followed pseudo-first-order kinetics, with an apparent rate constant of 0.020 per minute. As a benchmark, the authors cite a recent study reporting 66.9 percent tetracycline degradation with the spinel ZnFe2O4 alone, although they caution that differences in catalyst composition, pollutant concentration, catalyst dosage and irradiation conditions make direct comparisons between spinel materials imperfect.

The authors are equally candid about what the experiments cannot yet prove. Because no light-only photolysis control and no radical-scavenger tests were performed, the specific contributions of direct photolysis and of reactive oxygen species such as hydroxyl and superoxide radicals cannot be experimentally separated; their involvement is discussed only on the basis of the generally accepted photocatalytic mechanism. The team also notes that further control experiments using undoped ZnAl2O4 would be needed to quantify exactly how much the magnesium substitution enhances performance. Even with those caveats, the study demonstrates that a light-induced process makes a significant contribution to tetracycline removal and that a cheap, urea-assisted gel route carried out at just 700 degrees Celsius can deliver a phase-pure, crystalline spinel photocatalyst capable of attacking one of the most worrying classes of aquatic micropollutants. For an environmental challenge in which pharmaceutical effluents, particularly wash water from mixing tanks in drug and cosmetics manufacturing, can be highly concentrated and variable throughout the year, robust and adaptable treatment technologies are urgently needed, especially in developing countries where resources and advanced infrastructure remain limited. Alongside established approaches such as dense-membrane filtration, activated carbon adsorption and other advanced oxidation processes, this magnesium-substituted spinel now offers a low-cost candidate worth refining, one whose next iterations will need to probe different magnesium-to-zinc ratios, sunlight-driven operation and recyclability if it is to move from the laboratory beaker to real treatment trains.

Subject of Research: Magnesium-substituted zinc aluminate spinel photocatalysts for degrading tetracycline antibiotics in wastewater

Article Title: Facile preparation, characterization and photocatalytic activity of magnesium-substituted zinc aluminate

Article References: El Jabbar, Y., Lakhlifi, H., Talhajt, S. A., & El Ouatib, R. (2026). Facile preparation, characterization and photocatalytic activity of magnesium-substituted zinc aluminate. Results in Chemistry, 31, Article 103980. https://doi.org/10.1016/j.rechem.2026.103980

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103980

Keywords: photocatalysis, zinc aluminate, spinel, tetracycline, water treatment, pharmaceutical pollution, magnesium substitution, urea-assisted gel route, semiconductor, antibiotics, UV irradiation, wastewater

The physicochemical analysis revealed a complex mixture of micronutrients, inorganic salts, and heavy metals in the rubber wastewater. Iron was present at 0.5 milligrams per litre and nitrate at 25 milligrams per litre, while total hardness reached 625 plus or minus 3.60 milligrams per litre. More alarming were the biochemical oxygen demand of 547.10 plus or minus 10 milligrams per litre and the chemical oxygen demand of 866 plus or minus 11 milligrams per litre, both indicators of a heavy load of organic pollutants that consume dissolved oxygen as they break down. Heavy metals such as zinc, measured at 5297.50 plus or minus 167.50 parts per billion, and nickel at 56.00 plus or minus 2.12 parts per billion, were also detected. Every one of these parameters exceeded the permissible limits set for drinking water or for the general discharge of environmental pollutants under Indian standards.

Those numbers matter because rubber processing is fundamentally a colloidal chemistry operation. Liquid latex is a stable suspension of rubber particles that must be destabilised, typically by adding acid, to coagulate into solid slabs. The acid coagulation tanks where this happens generate waste streams loaded with dissolved salts, organic matter from the latex itself, and whatever metals and additives the raw material carried. When that waste is released untreated, it enters streams, soils, and groundwater with its chemical signature intact. The high BOD and COD values in the Dakshina Kannada samples point to exactly this kind of untreated or poorly treated discharge, one that can strip oxygen from receiving waters and suffocate aquatic life before plants and animals ever feel the direct toxic effects of the dissolved contaminants.

To test whether the wastewater actually harms living organisms, and not just looks bad on a lab report, the researchers grew onion bulbs and mung bean seeds in the effluent at different concentrations. The results were dose-dependent and unambiguous. As the concentration of wastewater increased, root and shoot lengths shrank, biomass declined, and the antioxidant capacity of the plants dropped. Protein and sugar contents were altered as well, suggesting that the plants’ basic metabolism was being disrupted. In mung bean, a staple legume widely cultivated across Asia, the effects on germination and seedling growth point to real agricultural risk if such effluent reaches irrigated fields. In onion, a classic bioassay organism used for decades in environmental monitoring, the changes provided a measurable readout of physiological stress.

The most striking findings came from the onion root tips, where the team looked directly at cell division. At higher concentrations of wastewater, the mitotic index, a measure of how many cells are actively dividing, decreased significantly. At the same time, chromosomal aberrations increased. These are the hallmarks of genotoxicity, damage to the genetic material itself. Chromosomal aberrations can include breaks, fragments, and other structural anomalies that arise when dividing cells are exposed to mutagenic agents. A decreased mitotic index means the effluent is suppressing cell proliferation, either by poisoning the division machinery directly or by halting cells before they enter mitosis. Together, these cytogenetic effects confirm that rubber wastewater is not merely a growth inhibitor but a genuine mutagenic hazard to plant cells.

Heavy metals are the leading suspects behind these cytogenetic effects. Zinc at nearly 5300 parts per billion is orders of magnitude above what plants would normally encounter in uncontaminated water, and nickel, even at 56 parts per billion, is a known genotoxic agent in many bioassay systems. Both metals can interfere with DNA replication and repair, generate oxidative stress, and disrupt the spindle apparatus that segregates chromosomes during cell division. The high organic load, indicated by the elevated BOD and COD, may compound the problem by adding additional dissolved contaminants that the physicochemical analysis did not fully characterise. The researchers suggest that these pollutants, acting individually or in combination, are what drove the observed changes in the plants.

The study’s implications reach beyond the laboratory and into the rubber-producing economy of Dakshina Kannada, a district where rubber plantations and processing industries have expanded substantially in recent decades. Small-scale rubber industries are numerous in the region, and their effluent often flows into local water bodies with little oversight. The new data show that this effluent carries a pollutant load capable of damaging crop plants at the cellular level, which raises concerns about food safety, soil health, and the long-term sustainability of agriculture near rubber processing operations. The findings also add to a growing international literature on the genotoxicity of industrial wastewaters, from pharmaceutical effluents to municipal waste, all pointing to the same conclusion: what we discharge matters, and bioassays can detect harm that chemical analysis alone might miss.

The researchers argue that pre-treatment of rubber wastewater before its release into the environment is essential. Various treatment approaches have been explored in the literature, including constructed wetlands, chemical precipitation, flocculation, and membrane filtration, each with its own advantages and limitations. The high organic load and heavy metal content identified in this study suggest that a multi-stage treatment system would be needed to bring the effluent within permissible discharge limits. The authors also note that the presence of micronutrients such as iron and nitrate, while beneficial in small quantities, becomes problematic when combined with the toxic load of heavy metals and organic pollutants, making simple dilution or land application risky strategies.

What makes this study particularly compelling is its integration of chemical analysis with biological testing. Chemical parameters tell us what is in the water, but bioassays tell us what that water does to living organisms. The onion and mung bean models used here are inexpensive, reproducible, and sensitive, which is why they remain standard tools in environmental toxicology decades after their introduction. By combining physicochemical characterisation with phytotoxicity and genotoxicity screening, the researchers built a case that is hard to dismiss: rubber wastewater in Dakshina Kannada is chemically out of compliance and biologically harmful, and the two findings reinforce each other. This kind of convergent evidence is what regulators need to justify stricter enforcement of discharge standards.

The study, published in Environmental Science and Pollution Research, was supported by Yenepoya (Deemed to be University) through a seed grant and a Junior Research Fellowship. The authors declare no competing interests. As rubber production continues to expand across southern India and beyond, the message from this research is clear: the water that rubber factories leave behind is not benign, and treating it before release is not optional. The chromosomes of the plants growing downstream are already telling us what happens when we forget that.

Subject of Research: Evaluation of physicochemical parameters of rubber industry wastewater and screening for its phytotoxicity and genotoxicity from Dakshina Kannada district, Karnataka, India

Article Title: Evaluation of physicochemical parameters of rubber industry wastewater and screening for its phytotoxicity and genotoxicity from Dakshina Kannada district, Karnataka, India

Article References: Neelakantappa, C. A., Govinda, P., & Nekrakalaya, B. (2026). Evaluation of physicochemical parameters of rubber industry wastewater and screening for its phytotoxicity and genotoxicity from Dakshina Kannada district, Karnataka, India. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38320-8

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38320-8

Keywords: Evaluation, physicochemical, parameters, rubber, industry, wastewater, screening, phytotoxicity, genotoxicity, Dakshina, Kannada, district

The cradle-to-grave system boundary adopted in the study deserves closer examination, because it shapes how the findings should be interpreted. The assessment covered raw material extraction, energy inputs, production infrastructure, and transportation of both fertilizers to the point of application, but it deliberately excluded field-phase emissions. This exclusion matters most for the synthetic fertilizer, since nitrogen applied to soils is a well-documented source of nitrous oxide, a greenhouse gas with a global warming potential roughly 265 to 298 times that of carbon dioxide over a century-long horizon depending on the assessment convention used. Synthetic nitrogen fertilization is responsible for a substantial share of the emissions that Brazil attributes to soil management within its agricultural sector. Had field emissions been included, the gap between the two products would likely have widened further, since organic and microbial fertilizers tend to release nitrogen more slowly and can reduce nitrous oxide losses. At the same time, excluding the field phase keeps the comparison conservative and focused on the emissions that differ most clearly between the two supply chains, namely manufacturing and logistics.

The emissions figures reported for the two products place them in a recognizable range within the broader literature on fertilizer carbon footprints. Conventional NPK fertilizers commonly carry cradle-to-gate footprints on the order of one to several tonnes of carbon dioxide equivalent per tonne of product, depending on the nutrient ratio, the nitrogen source, and the energy mix of the producing country. The figure of roughly 1,313 kilograms of carbon dioxide equivalent per tonne for the NPK 5-20-20 formulation sits comfortably within this range. A large share of such emissions typically traces back to nitrogen components, since industrial nitrogen fixation through the Haber-Bosch process relies on natural gas both as a hydrogen source and as an energy source, and ammonia synthesis alone can account for the majority of a blended fertilizer’s footprint. Phosphorus and potassium components add emissions through mining, beneficiation, and granulation, but these are generally smaller contributors per unit of product.

The biofertilizer footprint of roughly 486 kilograms of carbon dioxide equivalent per tonne reflects a fundamentally different production logic. Instead of extracting finite mineral reserves or fixing atmospheric nitrogen at high temperature and pressure, the system cultivates Limnospira sp., a filamentous cyanobacterium capable of fixing atmospheric nitrogen biologically while assimilating nutrients already dissolved in brewery effluent. This dual function is central to the environmental profile of the product. The cyanobacterial cultivation acts simultaneously as a bioremediation step, removing nitrate, ammonia, and sulfate from the wastewater, and as a biomass production step, converting those nutrients and ambient carbon dioxide into a nutrient-rich substrate. Because the effluent would otherwise require conventional treatment before discharge, some life cycle practitioners would argue that a portion of the cultivation burden could even be credited against wastewater treatment that would have occurred anyway, which would further improve the biofertilizer’s apparent footprint. The study’s decision not to claim such credits keeps its accounting conservative.

The sensitivity analysis exploring substitution scenarios of fifty and seventy-five percent adds a practical dimension that pure headline comparisons often lack. Complete replacement of synthetic fertilizers by novel biofertilizers is rarely feasible in the short term, both because production volumes of microbial biomass remain modest relative to national fertilizer demand and because farmers typically transition gradually. The finding that partial substitution yields emission reductions of 1.46-fold at fifty percent substitution and 1.89-fold at seventy-five percent substitution indicates that the environmental benefit scales in a broadly proportional manner, without obvious thresholds or diminishing returns within the tested range. For policymakers, this proportionality is encouraging, because it means that even incremental adoption delivers measurable climate benefits, and that the biofertilizer can be deployed as a complement to conventional inputs rather than requiring an all-or-nothing shift.

Brazil’s structural dependence on imported fertilizers gives these findings an additional strategic significance beyond emissions accounting. With roughly eighty-five percent of the fertilizers consumed nationally being imported as of 2022, the country is exposed to international price volatility, supply chain disruptions, and geopolitical risk in fertilizer markets. The emissions associated with long-distance maritime transport of fertilizers are embedded in the cradle-to-grave boundary of the assessment, meaning that the comparison implicitly captures part of the logistical penalty of import dependence. A domestically produced biofertilizer derived from an industrial byproduct shortens the supply chain considerably, and the transportation stage of the biofertilizer’s life cycle is correspondingly simpler. The Brazilian National Fertilizer Plan explicitly encourages the development of domestic and recycled nutrient sources, and cyanobacterial biofertilizers produced from agro-industrial effluents fit squarely within that policy direction.

The circular economy framing of the study is more than rhetorical. Breweries generate large volumes of nutrient-laden wastewater that must be treated before discharge, and conventional treatment converts those nutrients into forms that are lost to the atmosphere or to sludge. By routing the effluent through cyanobacterial cultivation instead, the nutrients are recovered in a usable biological form and the treated water can potentially be reused within the brewery. This closes a nutrient loop that would otherwise remain open, and it does so using a photosynthetic organism that requires only light, carbon dioxide, and the nutrients already present in the wastewater. The approach also avoids the synthetic culture media that are typically used to grow Spirulina for food and supplement markets, which are a major cost and environmental burden in conventional microalgal production. Growing Limnospira sp. on effluent therefore addresses two cost drivers at once, the culture medium and the waste treatment obligation.

It is worth noting that the earlier agronomic work underpinning this assessment reported that barley plants treated with the Limnospira-based biofertilizer grew the aerial portion of the plant sixty percent faster than plants receiving commercial fertilizer. Faster early growth can translate into shorter cropping cycles, better weed competition, and in some cases improved final yields, although yield effects would need to be confirmed across seasons and sites before being generalized. The present life cycle assessment deliberately stops short of claiming yield benefits, since its functional unit is defined on mass of fertilizer rather than on mass of harvested grain. A future assessment normalized to a tonne of barley produced would be the natural next step, and it would allow the emissions intensity of the crop, rather than of the input, to be compared directly between fertilization regimes.

The choice of OpenLCA software with the Ecoinvent 3.8 cutoff database reflects standard practice in Brazilian and international life cycle assessment work. The cutoff system model assigns the environmental burdens of recycling and byproduct flows to the primary product that generates them, which means that the brewery effluent enters the biofertilizer’s inventory with minimal embedded burden. This convention is favorable to byproduct-based products and is widely used, though practitioners should be aware that alternative allocation approaches, such as economic allocation, could shift some burden onto the effluent and modestly increase the biofertilizer’s footprint. The combination of firsthand process data for the biofertilizer production stages with secondary database data for background processes, such as electricity and transport, is a common and defensible hybrid inventory strategy, and the authors’ note that they documented where inputs and losses could affect biomass measurements suggests attention to inventory quality.

From the perspective of national emissions accounting, the potential scale of impact is nontrivial. Synthetic nitrogen fertilizer use was reported to account for 36.6 million tonnes of carbon dioxide equivalent within Brazil’s agricultural soil management emissions in 2024, which itself represented about twenty percent of the soil management sub-sector. If biofertilizers of the type assessed here were to substitute even a modest fraction of synthetic nitrogen inputs, the avoided emissions would accrue both from the displaced manufacturing and import logistics and, potentially, from altered soil nitrogen dynamics that were outside the study boundary. The agricultural sector’s dominant share of Brazil’s national emissions, roughly twenty-nine percent of a gross total of 2.2 billion tonnes of carbon dioxide equivalent in 2024, means that fertilizer-related interventions sit within one of the most consequential levers available to the country’s climate policy.

Several caveats should temper extrapolation of the results. The assessment reflects a specific production configuration, a specific brewery effluent composition, and a specific destination farm in Passo Fundo, and footprints for both products would vary with energy sources, transport distances, and cultivation productivity. Cyanobacterial biomass productivity is sensitive to light, temperature, and contamination, and large-scale open or closed cultivation systems may perform differently from the pilot-scale conditions reflected in the inventory. The global warming impact category, while central to climate policy, is only one of several environmental dimensions that a fuller assessment would address, including water use, eutrophication potential, land occupation, and ecotoxicity. Nevertheless, within its stated scope, the study provides a quantified, standards-based comparison indicating that a circular biofertilizer produced from brewery effluent carries a substantially lower carbon footprint than the imported synthetic fertilizer it could partially replace, and that the benefit scales predictably across partial substitution scenarios relevant to real-world adoption.

Subject of Research: Life cycle assessment of a cyanobacterium-based biofertilizer produced from brewery wastewater: a low-carbon alternative to NPK fertilizers for barley (Hordeum vulgare) production in Passo Fundo, Brazil

Article Title: Life cycle assessment of a cyanobacterium-based biofertilizer produced from brewery wastewater: a low-carbon alternative to NPK fertilizers for barley (Hordeum vulgare) production in Passo Fundo, Brazil

Article References: Silva, P. A. D., Lima e Silva, A., Kurpan, D., Monteiro, B. B., Freitas, T. O. P. D., Novo, B. D. L., Ribeiro, R. D. O., Sher, A. A., Hoffmann, B. S., Freire, D. M. G., & Valle, A. F. D. (2026). Life cycle assessment of a cyanobacterium-based biofertilizer produced from brewery wastewater: a low-carbon alternative to NPK fertilizers for barley (Hordeum vulgare) production in Passo Fundo, Brazil. Frontiers in Sustainability, 7, Article 1960505. https://doi.org/10.3389/frsus.2026.1960505

Image Credits: AI Generated

DOI: 10.3389/frsus.2026.1960505

Keywords: Life, cycle, assessment, cyanobacterium-based, biofertilizer, produced, brewery, wastewater, low-carbon, alternative, fertilizers, barley

The research team, led by scientists at the Southern Nevada Water Authority, mounted one of the most comprehensive PFAS source investigations ever attempted for an arid, water-stressed system. They sampled Lake Mead itself at three locations, including the Boulder Basin and the effluent just below Hoover Dam, drawing on monthly monitoring records stretching from July 2021 through May 2025. They collected rainwater on the southeast side of the Las Vegas Valley and snowmelt from Vasquez Creek, 45 miles west-northwest of Denver in the Upper Colorado River watershed. They sampled the Las Vegas Wash during both dry weather—after more than 200 days without significant rain—and during a first-flush storm event. And they went deep into the sewersheds of two wastewater treatment plants, sampling manholes serving residential neighborhoods, the Las Vegas Strip, Nellis Air Force Base, and Harry Reid International Airport, along with commercial laundries, car washes, truck washes, a paper factory, and an electroplating facility.

Nineteen PFAS were quantified using isotope dilution liquid chromatography tandem mass spectrometry following automated solid phase extraction. But the team went further. Some samples were analyzed by non-targeted high resolution mass spectrometry, allowing tentative identification of PFAS compounds absent from the targeted analyte list. Others were processed using the total oxidizable precursor assay, a technique that subjects samples to strong oxidizing conditions—80 millimolar potassium persulfate and 200 millimolar sodium hydroxide at 85 degrees Celsius for six hours—transforming precursor compounds into the more persistent perfluoroalkyl acids they would eventually become in the environment. This matters because a significant portion of PFAS mass entering treatment plants typically exists as precursors that conventional targeted methods miss entirely.

The headline finding is counterintuitive. Total PFAS in the Boulder Basin of Lake Mead measured just 3.84 nanograms per liter, dominated by short-chain perfluorocarboxylic and perfluorosulfonic acids such as perfluoropentanoic acid at 1.1 nanograms per liter and perfluorobutane sulfonic acid at 0.747 nanograms per liter. Despite the Las Vegas Valley’s reputation as a wastewater-dominated system, the Colorado River—which supplies 97 percent of the lake’s flow—turned out to be the primary PFAS source, contributing 65 percent of total loading. The Las Vegas Wash, despite conveying the city’s treated effluent, accounted for only 27 percent. The PFAS fingerprint at Boulder Basin closely resembled that at the Colorado River confluence, confirming that most of the chemistry in the lake arrives from upstream rather than from local discharge.

Precipitation, often theorized as a growing PFAS pathway now that scientists argue the planetary boundary for these chemicals has been exceeded, played a surprisingly minor role. Four rainwater samples contained total PFAS between 0.329 and 1.51 nanograms per liter—low compared with recent measurements in Wyoming rainfall, where total PFAS reached 39 nanograms per liter, or Arizona rainfall at 92 nanograms per liter. Las Vegas rainwater was dominated by long-chain perfluoroalkyl acids, with PFOA and PFOS as recurring detections, while snowmelt from the Upper Colorado River watershed contained only perfluorobutane sulfonic acid at 0.329 nanograms per liter. Given the valley’s meager 4.18 inches of annual rainfall, precipitation is not expected to be a major PFAS loading pathway to the lake, though the researchers note that sampling rainfall in the Upper Colorado River watershed would provide further insight into atmospheric contributions to the river system itself.

Within the Las Vegas Wash, the picture sharpened considerably. During dry weather, effluent from the four wastewater reclamation facilities discharging to the wash accounted for 105 percent of the flow at the Rainbow Gardens sampling location and 56 percent of the PFAS mass flow. When concentrations below method reporting limits were conservatively assumed at half those limits, the facilities plus a stormwater channel near the airport explained 83 percent of the mass flow. The wash was an important secondary source to the lake for specific compounds, alone accounting for 42 percent of PFHxS loading, 37 percent of PFHxA, 20 percent of PFOA, 18 percent of PFOS, and 13 percent of PFBS. Shallow groundwater near Harry Reid International Airport—contaminated by historic use of PFAS-containing aqueous film forming foam in firefighting and training activities—registered extraordinarily high concentrations, up to 4,768 nanograms per liter total PFAS in the Rawhide Channel, but low flows limited its dry-weather contribution.

Non-targeted analysis revealed distinct chemical fingerprints separating dry from wet weather samples. The AFFF-impacted dry weather locations—the airport well, the Paradise Vista Park well, and the Rawhide Channel—showed large peaks for seven perfluorosulfonate and perfluorosulfonamide compounds not on the targeted list, including perfluoropropane sulfonate and perfluorobutane sulfonamide, classes commonly associated with aqueous film forming foam formulations. These samples also carried high PFOS to PFOA ratios and elevated branched-to-linear PFOS isomer ratios, hallmarks of electrochemical fluorination-derived foam plumes. Wet weather samples, by contrast, were dominated by short-chain polyfluorinated compounds, with two substances—4H-perfluoro-1-butene and heptafluoropentanoic acid—tentatively identified in all wet weather runoff samples and also present in rainwater collected from the same storm, suggesting rain itself may be an important source of these short-chain PFAS.

The sewershed investigation produced perhaps the most striking results. Las Vegas is unusual among major cities: its primary industry is hospitality, and it lacks the industrial PFAS sources—fluorotelomer manufacturers, semiconductor plants, carpet cleaning facilities, landfill leachate—that dominate PFAS loading elsewhere. Consequently, domestic wastewater emerged as the primary PFAS contributor to both treatment plants, accounting for 63 to 94 percent of flow and roughly 86 percent of the mass flow to the largest facility’s influent. Residential wastewater samples showed the highest contributions from TOP-quantified precursors, reflecting activities like showering and laundry that peak in the evenings and on weekends. Even the Las Vegas Strip line, conveying flow from casinos and hotels, carried a total PFAS concentration of 0.312 nanomoles per liter, similar to the treatment plant influent at 0.291 nanomoles per liter.

The everyday sources within that domestic wastewater proved remarkably specific. A sample from a household laundry machine washing synthetic sports clothing contained perfluorobutanoic acid at 115 nanograms per liter—83 percent of its total PFAS—along with measurable PFOS. Control samples from an empty machine and from detergent alone showed almost nothing, implicating the synthetic fabrics themselves. If every household in the valley ran six such loads per week, laundry would contribute approximately 11 percent of total influent PFAS loading to the treatment plants. Estimated mass flow contributions from PFAS-containing personal care products added further granularity: shampoo at 9.3 percent and cosmetic foundation at 2.2 percent, while toilet paper and human excretion each contributed less than 1 percent. Commercial laundries, though low-flow, registered total PFAS concentrations as high as 3.24 nanomoles per liter, almost entirely perfluorobutanoic acid, making them significant intermittent sources.

These findings arrive at a regulatory inflection point. In 2024, the United States Environmental Protection Agency established maximum contaminant levels for six PFAS, including 4 nanograms per liter for PFOS and PFOA. Historical monitoring shows a slowly increasing trend for total PFAS in Lake Mead since mid-2021, particularly at the Hoover Dam intake, where average total PFAS reached 8.46 nanograms per liter compared with 6.58 nanograms per liter at Boulder Basin—consistent with the greater recycled water contribution there, as confirmed by the wastewater tracer sucralose. As drought continues to lower the reservoir and the proportional influence of the Las Vegas Wash grows, understanding that the city’s own domestic wastewater—its laundries, shampoos, and foundations—is the dominant local PFAS source gives water managers a concrete target. The chemistry of a desert metropolis’s tap water, it turns out, is written as much in its washing machines and bathrooms as in the river that feeds it.

Subject of Research: New research maps PFAS sources to Lake Mead, finding the Colorado River is the primary contributor while household laundry and personal care products dominate local wastewater loading.

Article Title: Identifying sources of per- and polyfluoroalkyl substances (PFAS) in an arid environment with de facto reuse

Article References: Steigerwald, J., Trenholm, R., Quiñones, O., Vanderford, B. J., & Dickenson, E. (2026). Identifying sources of per- and polyfluoroalkyl substances (PFAS) in an arid environment with de facto reuse. Frontiers in Environmental Chemistry, 7, Article 1694851. https://doi.org/10.3389/fenvc.2026.1694851

Image Credits: AI Generated

DOI: 10.3389/fenvc.2026.1694851

Keywords: PFAS, Lake Mead, Colorado River, Las Vegas Wash, drinking water, wastewater, TOP assay, non-targeted analysis, AFFF, de facto reuse, arid environment, water quality

The multi-soil-layering approach, known as MSL, is a decentralized filtration concept in which wastewater percolates through alternating permeable layers and compacted soil mixed blocks, or SMBs. The permeable layers, made here of porous volcanic pozzolan, distribute the flow evenly and keep oxygen moving through the system. The SMBs act as the reactive heart of the filter: each block is a mixture of 70 percent local soil, 10 percent charcoal, 10 percent Phoenix dactylifera—date palm residue—and 10 percent iron debris. As the effluent winds through this sandwich of reactive and permeable materials, nutrients bind to mineral surfaces, phenolic compounds adsorb onto carbon and iron sites, and microbial communities break down organic matter along the way.

What makes this particular configuration new is the combination of amendments. Traditional MSL designs have relied on conventional carbon sources and metal adsorbents that were tested separately, but the Moroccan team blended locally sourced agro-industrial residues with iron-based adsorbents in a single block composition—a combination never before evaluated for OMW treatment. The researchers fed the system a 50 percent diluted OMW, a realistic pretreatment step for small mills, and varied the hydraulic load rate across three levels: 200, 400, and 500 liters per day per square meter. This parameter, abbreviated HLR, determines how fast wastewater moves through the filter and therefore how long the liquid remains in contact with the reactive surfaces.

The results at the lowest loading rate were striking. At 200 liters per day per square meter, the MSL system removed 93.42 percent of ammonium, 99.67 percent of orthophosphates, 96.8 percent of phenolic compounds, and 97.41 percent of chemical oxygen demand, or COD. These removal rates exceed those reported for MSL systems using conventional carbon and iron amendments, suggesting that the unusual SMB recipe—part soil, part charcoal, part date palm, part iron scrap—creates a geochemical environment unusually well suited to capturing OMW pollutants. Orthophosphate removal above 99 percent is particularly notable, since phosphorus is notoriously difficult to strip from wastewater without chemical dosing or specialized adsorbents.

The geochemistry behind these numbers is worth unpacking. Ammonium, a positively charged ion, binds readily to negatively charged clay and soil surfaces through cation exchange. Orthophosphates, by contrast, are captured primarily by iron oxides and hydroxides that form on the iron debris surfaces, where phosphate ions precipitate or adsorb onto ferric sites. Phenolic compounds—the signature pollutants of OMW, responsible for its dark color, antibacterial activity, and ecotoxicity—adsorb onto the charcoal and date palm carbon surfaces, and can also complex with iron. The pozzolan layers, rich in silica and alumina, contribute additional silanol and exchange sites while maintaining the hydraulic conductivity that keeps the system from clogging under high organic loads.

Crucially, the team did not simply report removal percentages. They applied an inferential statistical framework—analysis of variance, Tukey HSD post-hoc testing, and effect-size calculation—that had never before been used to validate MSL-OMW treatment performance. This approach confirmed the robustness of the removal rates and revealed something quantitative and design-relevant: COD was the only parameter significantly sensitive to hydraulic load rate. In other words, ammonium, phosphate, and phenol removal held steady across the tested loading range, but organic matter removal degraded as flow rate increased, providing clear guidance for scale-up. Engineers designing full-scale systems now know that if COD compliance is the binding constraint, the hydraulic load rate must be kept near the 200-liter threshold.

The implications for Mediterranean olive-growing regions are substantial. OMW volumes are enormous—each mill can generate several cubic meters of effluent per ton of olives processed—and the liquid is typically stored in open ponds or spread on land, where it can leach into groundwater, kill soil microorganisms, and contaminate wells. Untreated OMW disposal carries documented human health and ecotoxicological risks, from phenol contamination of drinking water sources to the collapse of aquatic ecosystems downstream. The study’s authors argue that the SMB acts as an efficient barrier controlling these risks, and that the system’s reliance on local, low-cost materials makes it viable for the small, decentralized mills that dominate olive production in Morocco, Tunisia, Greece, and southern Spain.

The choice of date palm residue as a carbon amendment is also a story of circular economy logic. Phoenix dactylifera waste is abundant across North Africa and the Middle East, where millions of tons of palm fronds, seeds, and fibers are discarded annually. Previous research has shown that date palm-derived biochar can adsorb heavy metals, inorganics, and organic pollutants from water. By incorporating raw date palm residue directly into the SMB mixture, the Moroccan team avoided the energy cost of pyrolysis while still providing a carbon surface for phenol adsorption. Iron debris, similarly, is a scrap material that would otherwise require disposal, yet it supplies the reactive ferric sites responsible for phosphate capture. The system thus converts two waste streams into treatment infrastructure.

Compared with alternative OMW treatment approaches—constructed wetlands, sequencing batch reactors, nanofiltration, straw filtration, or land spreading—the MSL system offers a distinctive combination of low energy demand, no chemical dosing, and modular construction. Constructed wetlands require land area and plant management; biological reactors require aeration and skilled operators; membrane systems require electricity and fouling control. The MSL approach, by contrast, is essentially a passive filter that can be built from local soil and scrap materials, operated by mill workers, and maintained by replacing SMBs when they saturate. For rural mills without access to skilled labor or reliable electricity, this simplicity is not a compromise but a design feature.

The study does leave open questions. The researchers tested a 50 percent diluted OMW, so full-strength effluent performance remains to be demonstrated. Long-term saturation of the SMBs, the fate of adsorbed phenols and phosphates over years of operation, and the regeneration or disposal of spent blocks are all areas for future work. The team also notes that the system’s reliance on local materials means performance may vary with soil composition and pozzolan availability in different regions. Nevertheless, the combination of high removal rates, statistical validation, and quantitative design guidance marks this study as a significant step forward for decentralized OMW treatment. If the approach scales successfully, the dark liquid that has plagued Mediterranean mills for generations might finally have an affordable, passive, and locally built solution.

Subject of Research: Multi-soil-layering wastewater treatment

Article Title: A performance evaluation of a multi-soil-layering for the treatment of an olive mill wastewater

Article References: Zine, M., Asli, H., Bamaarouf, M., Touach, N., Tajounte, L., Kara, K., & Lotfi, E. M. (2026). A performance evaluation of a multi-soil-layering for the treatment of an olive mill wastewater. Environmental Geochemistry and Health, 48(16), Article 641. https://doi.org/10.1007/s10653-026-03532-x

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03532-x

Keywords: olive mill wastewater, multi-soil-layering, wastewater treatment, MSL technology, phenolic compounds, Morocco, performance, evaluation, treatment, olive, mill, wastewater

Citrobacter species are facultative anaerobic, Gram-negative bacteria of the order Enterobacterales, common in water, soil, food, and the intestines of humans and animals. Although they are not generally regarded as frequent pathogens, certain species cause urinary tract and bloodstream infections that can be acquired in hospitals or in the community. Immunocompromised patients and neonates are particularly vulnerable. Reported cases include a bloodstream infection caused by C. braakii in an immunocompromised allogeneic stem cell transplant patient, and an analysis of nine newborns with C. freundii sepsis in which one infant died within seven hours and three developed meningitis, with multidrug resistance present in every isolate. Against this backdrop, hospitals act as ecological niches that select for resistant bacteria, making hospital sewage a predictable reservoir of multidrug-resistant organisms.

The Greifswald strain was actually discovered by accident. It appeared within the inhibition zone of an imipenem-sensitive C. portucalensis isolate during routine testing, a hint that something in the sample could survive the antibiotic. Imipenem belongs to the carbapenems, β-lactam antibiotics with broad-spectrum activity against pathogens including Pseudomonas, streptococci, Neisseria, and Haemophilus. Carbapenems resist hydrolysis by most β-lactamases and are typically reserved for severe nosocomial infections caused by extended-spectrum β-lactamase-producing Enterobacteriaceae and Pseudomonas aeruginosa. The World Health Organization now lists carbapenem-resistant Enterobacterales among the bacteria most threatening to human health, which makes any new isolate carrying such resistance worth dissecting at the molecular level.

Resistance to carbapenems can arise through several mechanisms. Some Enterobacterales carry carbapenemases, β-lactamases capable of directly cleaving the drugs. Others combine porin loss or dysfunction with ESBL or AmpC β-lactamase production, modify their penicillin-binding proteins so the antibiotics bind poorly, reduce drug uptake through altered outer membrane proteins, pump drugs out via systems such as AcrAB-TolC, or remodel their biofilms. To determine which of these strategies GW-Imi-1b1 employs, the researchers subjected it to antimicrobial susceptibility testing using the Kirby-Bauer disc diffusion method and E-tests, following EUCAST guidelines, alongside microscopy, motility assays, and comprehensive proteomic analysis.

The results revealed a broad resistance spectrum. GW-Imi-1b1 proved resistant to tobramycin, ceftazidime, chloramphenicol, the fluoroquinolones ciprofloxacin, levofloxacin, and ofloxacin, and ertapenem, with an average ertapenem minimum inhibitory concentration of 12 µg/mL. It remained susceptible only at increased exposure to imipenem and meropenem, and fully susceptible to amikacin and trimethoprim/sulfamethoxazole. Proteomic analysis identified a striking culprit: a plasmid-encoded GES-5 β-lactamase, a carbapenem-hydrolyzing class A enzyme, ranked among the ten most abundant proteins in the whole-cell proteome even when no antibiotic was present. When the team grew the strain in meropenem concentrations of 0.064, 0.125, or 20 µg/mL, the abundance of this enzyme did not change significantly, indicating constitutive rather than inducible expression. A carbapenem-sensitive C. portucalensis strain used as a control lacked the enzyme and was readily inhibited by low meropenem concentrations, supporting the link between GES-5 and the resistance phenotype.

The plasmid location of the bla_GES-5 gene raises particular concern. The researchers confirmed the gene’s position on plasmid CP115731 by plasmid isolation and PCR. Because plasmids can move between bacteria through conjugation or transformation, this resistance mechanism may be transferable within the wastewater microbiota. Case reports have already documented plasmid-encoded GES-5 spreading among different species, including E. coli, Klebsiella oxytoca, and Enterobacter cloacae, across patients and hospital settings, and conjugation experiments with a GES-5-bearing plasmid in Pseudomonas knackmussii increased resistance to several carbapenems. The proteome also revealed all subunits of the AcrAB-TolC efflux pump, which exports multiple antibiotics and likely contributes additional resistance capacity beyond the β-lactamase alone.

Beyond resistance, the characterization uncovered features relevant to virulence. Scanning electron microscopy showed rod-shaped cells roughly 2 µm long and 0.5 µm wide that produce outer membrane vesicles, or OMVs, spherical blebs shed from the bacterial surface. OMVs in other Gram-negative pathogens such as Helicobacter pylori, P. aeruginosa, and Citrobacter rodentium carry lipopolysaccharides, peptidoglycans, enzymes, and toxins that can trigger inflammatory responses. They may also ferry antibiotic resistance genes to susceptible cells, and in some bacteria they act as decoys that bind phage particles and shield the cell from infection. Whether GW-Imi-1b1’s OMVs serve these roles remains unresolved; the authors note that sequencing the vesicle cargo and comparing it with the bacterial genome would be needed to identify potentially transferred genes. Motility assays, meanwhile, showed the strain is completely non-motile in swimming, swarming, and twitching tests, and electron microscopy confirmed the absence of flagella, despite the genome containing 92 putative motility-related domains. No protease secretion was detected either, in contrast to some other Citrobacter species.

The solution half of the story came from the same wastewater. In November 2023, the team collected water from the inflow to the Greifswald sewage treatment plant, treated it with chloroform to eliminate bacteria, and incubated it with GW-Imi-1b1. Plaques on a double agar layer lawn yielded a pure phage after three rounds of isolation. Sequencing revealed a circular double-stranded DNA genome of 39,389 base pairs with a GC content of 50.04 percent, closely matching its host’s 51.81 percent, a similarity consistent with close co-evolution. The genome encodes 57 potential proteins, 26 of unknown function, and contains no tRNAs, CRISPRs, or integration and excision modules, marking it as exclusively lytic. Electron microscopy showed an icosahedral capsid about 54 nm in diameter with a short, non-contractile tail of roughly 12 nm, podovirus morphology that places the phage in the class Caudoviricetes and the genus Kayfunavirus.

Functional testing showed the phage is a specialist with a fast lifestyle. Its lytic host spectrum was restricted to GW-Imi-1b1 itself; none of the other tested Citrobacter, Klebsiella, or E. coli strains, whether ESBL-producing or carbapenem-resistant, were lysed. Adsorption was nearly complete within five minutes, the latent period lasted about five minutes, and complete phage release occurred within the following ten, giving an infection cycle of roughly 20 minutes and a burst size of 12 plaque-forming units per cell. That burst size is small compared with the 35 to 55 PFU per cell typical of other Kayfunavirus phages, but small bursts are often paired with short lysis times, allowing rapid reinfection of new host cells. The phage also proved environmentally robust, retaining infectivity from 4 to 40 °C and across pH values from 6 to 10, though it lost infectivity at 50 and 60 °C and at acidic pH, with no infectious particles remaining at pH 2.

The narrow host range cuts both ways. It spares the rest of a microbiome, an advantage over broad-spectrum antibiotics, but it also means monophage therapy would fail against polymicrobial infections or mismatched strains, a limitation that phage cocktails can partially overcome. The authors caution that all assays were performed in vitro, and that preclinical trials testing ex vivo and in vivo lytic activity and potential cytotoxicity toward eukaryotic cells are required before vB_CbrP_HGW_001 could be considered a treatment option. Still, the study demonstrates a practical workflow: sewage, the very environment that breeds resistant bacteria, can be mined for phages that attack them, and global proteomics can expose the actively expressed resistance and virulence factors of problematic pathogens. Combining such phages with antibiotics, an approach that has reduced hospitalizations in enterococcal infections, may further extend the toolkit against multidrug-resistant organisms. For now, the Greifswald pair stands as a model system showing that for every resistance problem emerging in wastewater, a solution may be waiting in the same water.

Subject of Research: Characterization of a carbapenem-resistant Citrobacter braakii strain and its lytic bacteriophage isolated from hospital sewage water

Article Title: Problems bring along their solutions: characterization of a carbapenem-resistant Citrobacter braakii strain and its lytic phage both isolated from sewage water

Article References: Pukall, J., Rode, W., Albrecht, J., Oerters, S., Ganbarzade, A., Krombholz, J., Schaufler, K., Eger, E., Schlüter, R., Hinzke, T., Zühlke, D., & Sievers, S. (2026). Problems bring along their solutions: characterization of a carbapenem-resistant Citrobacter braakii strain and its lytic phage both isolated from sewage water. Frontiers in Bacteriology, 5, Article 1864514. https://doi.org/10.3389/fbrio.2026.1864514

Image Credits: AI Generated

DOI: 10.3389/fbrio.2026.1864514

Keywords: Citrobacter braakii, carbapenem resistance, GES-5 beta-lactamase, bacteriophage, phage therapy, wastewater, Kayfunavirus, antimicrobial resistance, outer membrane vesicles, proteomics, Enterobacterales, hospital sewage

The phage was recovered from sewage water collected in Karabük, Türkiye, using the standard laboratory strain E. coli ATCC 25922 as the indicator and propagation host. After enrichment and four consecutive rounds of single-plaque purification, the researchers obtained a homogeneous phage preparation producing circular, clear plaques with well-defined edges. Transmission electron microscopy of negatively stained particles revealed a polyhedral head roughly 45 nanometers in diameter and a long, flexible, non-contractile tail of about 176 nanometers, giving a total particle length of approximately 220 nanometers. The absence of a contractile sheath places KBU_SV1 firmly in the siphovirus morphotype within the class Caudoviricetes, the broad group of tailed double-stranded DNA phages that dominates the bacterial virosphere.

Host-range testing against a panel of 106 bacterial strains revealed a pattern of selective rather than broad lytic activity. Spot assays produced visible clearance on 16 strains, corresponding to a host range index of 0.15. Notably, clearance was detected on 7 of 20 carbapenem-resistant E. coli clinical isolates and 4 of 20 carbapenem-susceptible E. coli isolates, meaning that lysis was actually more frequent among the resistant strains. Four of 40 carbapenem-resistant Klebsiella pneumoniae isolates also showed spot clearance, while none of the 20 Enterococcus faecalis clinical isolates or the other reference strains tested were affected. The researchers caution that spot clearance alone does not prove productive infection, since clearing can arise through mechanisms that do not generate progeny phages, such as lysis from without, and efficiency-of-plating measurements will be needed to confirm true susceptibility, particularly for K. pneumoniae.

In liquid culture, KBU_SV1 suppressed the growth of E. coli ATCC 25922 across the entire range of multiplicities of infection tested, from 100 down to 0.01. During the first 14 hours of incubation, optical density in all phage-treated cultures remained below 0.10, a reduction of at least 93 percent relative to the untreated control, which reached an optical density of 1.70 by 24 hours. Regrowth was eventually observed under all conditions, a common feature of phage-bacterium systems that is often attributed to the emergence of phage-resistant subpopulations. Interestingly, the late growth response showed an apparent non-monotonic relationship with the initial phage dose: cultures treated at multiplicities of 0.1 and 0.01 ended up with lower optical densities at 24 hours than those treated at 10 and 1. The authors emphasize that the mechanism behind this pattern remains unresolved and that it should not be taken as evidence that lower doses are generally superior.

Physicochemical stability is a key practical consideration for any phage envisaged as a therapeutic candidate, and here KBU_SV1 performed well. The phage retained infectivity after one hour of incubation across a pH range from 4 to 12, with only modest declines of roughly 0.25 log units at the extremes of that interval compared with the neutral pH reference. No infectivity was detected at pH 2, however, a point worth noting given the acidic environment of the stomach. Temperature testing showed stable titers at 4, 23 and 37 degrees Celsius, but exposure to 65 degrees Celsius eliminated detectable infectivity. Taken together, these results suggest that KBU_SV1 is robust under moderate conditions relevant to storage, formulation and physiological temperature, although long-term storage stability was not evaluated.

Biofilms, structured bacterial communities embedded in an extracellular polymeric matrix, are a major driver of treatment failure because they dramatically reduce susceptibility to both antibiotics and immune defenses. KBU_SV1 demonstrated meaningful antibiofilm activity in crystal violet assays. Treatment of established biofilms of E. coli ATCC 25922 reduced biomass by 84.5 to 86.0 percent across all tested multiplicities of infection, while inhibition of biofilm formation reached 78.0 to 83.7 percent. Against the carbapenem-resistant clinical isolate Ec59, the effects were smaller but still substantial, with biomass reductions of 22.3 to 54.2 percent and inhibition of formation ranging from 24.6 to 57.5 percent, with the strongest effects at the highest multiplicity. The authors note that crystal violet staining measures total attached biomass rather than viable cells, so these findings reflect reductions in biofilm mass rather than proof of bacterial killing or complete eradication.

The in vivo experiments used the greater wax moth Galleria mellonella, a widely used invertebrate infection model. Larvae infected with a lethal dose of E. coli ATCC 25922 died rapidly, with 40 percent mortality at 12 hours and complete mortality by 18 hours. Larvae that received phage treatment one hour after infection survived significantly longer: mortality was distributed across the 48-hour observation period, and 40 percent of treated larvae were still alive at 24 hours. Kaplan-Meier survival analysis confirmed a statistically significant delay in mortality compared with the infection control, with a log-rank test yielding a p-value of 1.2 × 10⁻⁷. Importantly, no deaths occurred in larvae receiving phage alone or mock injections, indicating no detectable toxicity of the preparation under the tested conditions. The authors stress, however, that the phage delayed rather than prevented death, and that G. mellonella does not fully reproduce mammalian physiology, so these results should be viewed as preliminary evidence supporting further investigation rather than demonstration of therapeutic efficacy.

Genomic sequencing provided the most reassuring safety-relevant findings. The KBU_SV1 genome is a 45,190-base-pair double-stranded DNA molecule with a G plus C content of 53.56 percent, confirmed as complete by CheckV with 100 percent estimated completeness, zero contamination and a high-confidence 272-base-pair direct terminal repeat at both ends. Sequencing depth averaged nearly 24,000-fold with complete positional coverage. The genome encodes 71 putative open reading frames organized into five functional modules covering DNA and RNA replication, DNA metabolism, structural proteins, assembly and lysis, and contains no tRNA genes. Critically, screening with ResFinder, VirulenceFinder, the Comprehensive Antibiotic Resistance Database and the Virulence Factor Database detected no known antimicrobial resistance genes, no virulence determinants and no lysogeny-associated genes such as integrases, excisionases or phage repressors. Machine-learning-based lifestyle prediction tools PhageAI and PhageLeads both classified the phage as virulent, meaning strictly lytic, a property generally considered desirable for therapeutic candidates because it rules out the temperate lifestyle that could mediate horizontal gene transfer.

Comparative genomics clarified where KBU_SV1 fits in the phage taxonomy. BLASTn searches revealed 99.12 percent nucleotide identity with Escherichia phage EPIMAM03, and VIRIDIC intergenomic similarity calculations showed values above the 95 percent species-level threshold with several related genomes, including Dhillonvirus LM40P1 at 98.7 percent. Independent taxonomic analysis with taxMyPhage assigned KBU_SV1 to the genus Dhillonvirus within the class Caudoviricetes, and phylogenetic trees based on the large terminase subunit and whole-proteome comparisons were congruent with this placement. The complete genome has been deposited in GenBank under accession number PZ050807.1. Rather than representing an entirely new species, KBU_SV1 belongs to an existing species-level genomic cluster, which the authors note is consistent with contemporary genome-based approaches to phage classification.

The study has limitations that the authors themselves enumerate candidly. Efficiency-of-plating measurements were not performed on the spot-test-positive isolates, one-step growth experiments to determine adsorption kinetics, latent period and burst size were not carried out, the mechanism of bacterial regrowth was not investigated, and the DNA packaging mechanism implied by the direct terminal repeat was not experimentally resolved. The growth-reduction and in vivo experiments used the reference strain rather than carbapenem-resistant clinical isolates, and endotoxin levels in the phage preparation were not quantified. Nevertheless, the overall profile of KBU_SV1, combining lytic activity against carbapenem-resistant E. coli, broad pH and temperature stability, antibiofilm effects, delayed mortality in an infection model and a genome apparently free of resistance, virulence and lysogeny genes, marks it as a promising candidate for further development, whether deployed alone or as a component of phage cocktails. Before any clinical application, the authors conclude, future work must address productive host range, replication parameters, resistance development, optimized dosing and efficacy in mammalian infection models.

Subject of Research: Isolation and genomic characterization of the bacteriophage KBU_SV1 as a candidate therapeutic against carbapenem-resistant Escherichia coli

Article Title: Biological and genomic characterization of Escherichia phage KBU_SV1 active against carbapenem-resistant Escherichia coli

Article References: Öztaş, S., Karaynir, A., Ozkan, R. G., Bozdogan, B., & Dündar, D. (2026). Biological and genomic characterization of Escherichia phage KBU_SV1 active against carbapenem-resistant Escherichia coli. Frontiers in Microbiology, 17, Article 1927801. https://doi.org/10.3389/fmicb.2026.1927801

Image Credits: AI Generated

DOI: 10.3389/fmicb.2026.1927801

Keywords: bacteriophage, phage therapy, carbapenem-resistant E. coli, antimicrobial resistance, Dhillonvirus, biofilm, Galleria mellonella, Caudoviricetes, siphovirus, phage genome, antibiofilm activity, wastewater