The authors describe the framework as a decision aid that organizes established engineering and life-cycle methods, not a new life-cycle assessment method or a universal ranking of treatment technologies. The first step is to define the treatment service as one cubic metre of influent treated to a specified discharge or reuse quality. Comparisons must cover the complete final specification rather than a selected analyte, because the same percentage removal from different starting concentrations can produce water that meets very different requirements.

The operating boundary should include pretreatment, pumping, mixing, reaction, separation, cleaning, regeneration, conditioning and residual handling. A life-cycle inventory must additionally include the production and replacement of materials, chemicals and infrastructure, as well as downstream emissions and product use. Total volume treated and the volume of compliant product water should be reported separately, since an average concentration can conceal periods of inadequate treatment and because discharge and reuse may provide different services.

Energy accounting must then follow the physical plant and its metering arrangements. Gross demand includes all equipment needed to deliver the declared service: reaction, pumping, mixing, separation, cleaning, residual handling and energy-recovery equipment. Recovered energy can be credited only after conversion losses and only if it supplies a useful internal load or is delivered to an external user.

Methane qualifies as an electricity credit only after capture and conversion; flared methane and unused heat receive no credit. Electricity should be reported in kilowatt-hours per cubic metre and heat in kilowatt-hours of thermal energy per cubic metre, and the two should not be added without an explicit conversion basis. Recovered work must not be deducted twice, while gross demand should remain visible so that a large prospective recovery credit cannot obscure an inefficient operation.

Ozonation illustrates how a strong removal result can change meaning when the complete process is examined. In a full-scale study at the Neugut wastewater treatment plant, specific ozone doses of 0.35–0.97 grams of ozone per gram of dissolved organic carbon were tested. The site recommendation of 0.55 grams per gram achieved at least 80% average removal of 12 indicators across the plant.

However, seven quantified primary transformation products resisted biological post-treatment, and fresh granular activated carbon removed them less effectively than their parent compounds. The measured result therefore supported effective indicator removal but did not establish complete mineralization or control of final-effluent effects; the relevant treatment chain extended from ozone dose through the contactor and downstream filtration to the final water-quality requirement. An illustrative screening calculation shows how ozone input can be related to energy without pretending to provide a complete plant balance.

Secondary effluent containing 10 milligrams of dissolved organic carbon per litre, equivalent to 10 grams per cubic metre, would require 5.5 grams of ozone per cubic metre at the recommended dose. Applying an air-fed generation inventory of 18.8 kilowatt-hours per kilogram of ozone gives a generation electricity estimate of 0.1034 kilowatt-hours per cubic metre. The authors caution that this calculation combines inputs from different studies and is not a measured Neugut value.

Auxiliary loads, downstream treatment and other excluded demands must be checked before they are added, partly to avoid double counting. A published life-cycle comparison produced a more consequential result: assumed liquid-oxygen-fed generation used 25% less electricity than air-fed generation, but including oxygen production and transport yielded approximately four times the operating climate impact under the study’s Swedish electricity assumptions. Advanced-treatment benefits must also remain distinct from the burdens required to obtain them.

One comparative life-cycle assessment included 65 micropollutants and found that modelled benefits from their removal were outweighed by added energy and resource impacts. That finding did not establish that advanced treatment should be omitted, because uncharacterised toxicity effects and the required discharge quality still matter. A separate assessment found net toxicity benefits when bioassay-based effects were included.

Together, the results support reporting chemical removal, biological effects and life-cycle consequences separately and identifying the method and boundary behind any preference. A sustainability claim should therefore state whether it rests on measured pollutant reduction, modelled toxicity change, resource impacts or a defined combination, rather than presenting a removal percentage as the complete answer. PFAS treatment reveals another important distinction: capture is not destruction.

Activated carbon and ion-exchange media can transfer PFAS from water into a concentrated phase, while electrodes may transform or destroy compounds in that concentrate. Sorption performance leads to a capture process and creates spent media or regenerant, whereas electrochemical performance raises questions about transformation products, remaining fluorine and electricity demand. In landfill leachate treated at a current density of 75 milliamperes per square centimetre, one study reported average removals of 80% for PFOA and 78% for PFOS under its electrochemical conditions, but these were parent-compound endpoints.

A separate laboratory study combining graphite-based adsorption with electrochemical regeneration obtained 99.4% PFOA removal while detecting shorter-chain products. Neither result by itself establishes complete or safe PFAS destruction across other matrices or at plant scale. The framework calls for a staged mass balance using the same source water.

Capture followed by the proposed destruction step should be compared with a feasible capture-and-residual-management alternative, with the capture medium followed through breakthrough and regeneration, treated and concentrated volumes recorded, and PFAS mass assigned to each outlet. Three destruction endpoints must remain separate: loss of the target PFAS, reduction in measured organic fluorine, and recovery of fluorine as inorganic fluoride. Flow-weighted sampling should cover liquid, solids and any relevant gas outlet, while analytical recovery, detection limits and the unclosed fraction must be disclosed.

Missing mass is not evidence of mineralization. Where those measurements are unavailable, the claim should be restricted to disappearance of the compounds actually measured, and the PFAS-rich residual must still have a documented management route. Anaerobic membrane bioreactors show why estimated recovery is not yet a delivered energy benefit.

The membrane is the engineered treatment material, and its permeability, selectivity and fouling behaviour influence solids retention, permeate production, cleaning and fouling-control energy. At 15 degrees Celsius, one study measured permeate chemical oxygen demand of 76 ± 10 milligrams per litre and five-day biochemical oxygen demand of 24 ± 3 milligrams per litre. Dissolved methane represented 40%–50% of total methane production, representing both an unrealised recovery opportunity and a potential emission.

Effective carbon removal alone therefore cannot establish energy neutrality or a low-carbon outcome, because dissolved and fugitive methane, downstream polishing and residual nutrient management remain part of the system. A pilot assessment estimated an energy surplus of 0.55–0.74 kilowatt-hours per cubic metre for an anaerobic membrane bioreactor used as an initial anaerobic treatment stage. The estimate relied on a carbon balance for methane production, critical-flux tests, calculated fouling-control energy and assumptions about methane recovery and conversion.

Membrane reciprocation required an estimated 0.59 kilowatt-hours per cubic metre at a flux of 7 litres per square metre per hour, compared with 1.56 kilowatt-hours per cubic metre for biogas sparging at 6 litres per square metre per hour; because the fluxes differed, these were not measurements at identical operating conditions. The surplus was not metered electricity exported by a complete reuse facility. Deployment would require metering of recovery equipment and useful output, measurement of dissolved methane before and after recovery, and inclusion of polishing, leakage and nutrient management.

Across the three applications, the decisive question is whether a promising material or reactor result survives the checks for final-water quality, a complete process inventory, a credible destination for residuals and useful outputs, and transparent environmental and cost comparisons.

Subject of Research: A decision framework for assessing system-level sustainability in water treatment through treatment performance, energy accounting, resource recovery and residual fate.

Article Title: Beyond pollutant removal: a material–process–resource perspective on sustainable water treatment

Article References: Ogwu, M. C., Izah, S. C., Aseibai, E. R., & Promise, V. I. (2026). Beyond pollutant removal: a material–process–resource perspective on sustainable water treatment. Frontiers in Chemical Engineering, 8, Article 1957125. https://doi.org/10.3389/fceng.2026.1957125

Image Credits: AI Generated

DOI: 10.3389/fceng.2026.1957125

Keywords: water treatment, sustainability, ozonation, PFAS capture, PFAS destruction, anaerobic membrane bioreactor, life-cycle assessment, energy accounting, resource recovery, transformation products, Beyond, pollutant

The study, published on 27 July 2026 in the journal Energy & Environment Nexus by Mei Ma’s team at the Chinese Academy of Sciences, is notable for its unusually comprehensive scope. Rather than measuring a handful of known chemicals, the team assessed the total biological activity of wastewater samples using effect-based tools that capture the combined action of entire chemical mixtures. This matters because oxidation and photochemical reactions during advanced treatment can generate transformation products whose biological properties differ sharply from those of their parent compounds. Some of these byproducts may be cytotoxic, genotoxic, or endocrine-disrupting, yet routine chemical analysis—built to detect known target compounds—can miss their combined effects entirely.

The researchers worked at a typical wastewater treatment plant in Tianjin, China, supplemented by two pilot-scale treatment systems. Samples were collected from 11 locations spanning the full treatment train: the plant inlet, preliminary sedimentation, anaerobic-anoxic-oxic (A2O) biological treatment, secondary sedimentation, ultraviolet disinfection, ozonation, coagulation, and biological activated carbon filtration. Organic compounds were isolated from each sample using solid-phase extraction, concentrating the dissolved chemistry so that even trace activity could be measured.

The heart of the method lay in a panel of recombinant yeast assays. Each assay carried a human hormone receptor—estrogen receptor alpha, androgen receptor, or thyroid receptor beta—wired to a reporter system, allowing the team to quantify both receptor-agonistic effects, in which chemicals mimic a hormone, and receptor-antagonistic effects, in which chemicals block a hormone from acting. Bioactivity was expressed as equivalent concentrations of reference chemicals, giving the results a tangible toxicological meaning. Crucially, the team also derived an effect-based trigger value of 7.97 micrograms of flutamide equivalents per liter for androgen receptor-antagonistic activity, providing a benchmark against which treated effluents could be judged.

For estrogenic activity, the treatment train performed largely as intended. Estrogen receptor-agonistic activity was prominent in untreated and preliminarily treated wastewater but declined progressively through the plant, falling below the detection limit after secondary sedimentation. Estrogen receptor-antagonistic activity followed a similar trajectory, dropping from 58.4 micrograms per liter in the influent to roughly 7.8 to 9.2 micrograms per liter after treatment. These results confirm that conventional biological treatment, particularly the A2O process, removes most detectable estrogen-linked endocrine activity before water ever reaches the advanced polishing stages.

Thyroid-related activity told a similar, though slightly more complicated, story. Thyroid receptor-antagonistic activity fell dramatically from 0.56 milligrams per liter to 0.0085 milligrams per liter through the main plant. In the pilot systems, ozonation—and ozonation followed by biological activated carbon filtration—further suppressed this activity, demonstrating that oxidative processes can genuinely help control certain endocrine endpoints. Yet coagulation, a standard physicochemical step, produced a slight rebound in thyroid receptor antagonism. The researchers suggest this may occur because residual endocrine-disrupting chemicals compete with other organic matter during removal, escaping the coagulation process while bulk organic material is stripped away.

The most alarming findings concerned the androgen receptor. No androgen receptor-agonistic activity was detected anywhere in the treatment train—good news in itself—but antagonistic activity, which can interfere with male hormone signaling, was present throughout. The A2O biological process reduced it markedly, from 156.6 to 12.4 micrograms of flutamide equivalents per liter, a roughly twelvefold decrease that brought the effluent comfortably below the trigger value. What happened next undermined that progress. Both ultraviolet irradiation and ozonation increased anti-androgenic activity, pushing the treated effluents above the newly established threshold of 7.97 micrograms per liter. Even biological activated carbon filtration applied after ozonation did not fully reverse the increase.

The researchers propose a chemical explanation for this counterintuitive result. Advanced oxidation and UV-driven photochemistry rarely mineralize organic contaminants completely; instead, they transform parent compounds into partially degraded products through reactions such as hydroxylation, dealkylation, decarboxylation, and deamination. These transformation products may retain or acquire the ability to bind and block the androgen receptor, even as the original pollutants disappear from chemical inventories. In other words, a treatment plant can appear to be succeeding by every conventional metric—removing parent pollutants, reducing chemical oxygen demand, eliminating pathogens—while its effluent grows biologically more hazardous along a specific endocrine pathway.

The broader implication is that treatment performance cannot be judged solely by pollutant removal or by measuring a single biological endpoint. UV irradiation and ozonation remain valuable technologies for pathogen control and contaminant degradation, and the study does not argue for abandoning them. Instead, it calls for optimizing their operating conditions and downstream treatment configurations to prevent the formation or persistence of hazardous transformation products. It also argues for embedding multi-endpoint, effect-based monitoring into routine wastewater management, so that risks invisible to chemical analysis—such as mixture effects that simultaneously activate or inhibit different hormone receptors—can be detected before reclaimed water is discharged or reused.

As water reuse expands from arid regions into mainstream urban planning, the study offers a timely reminder that purification is not the same as safety. Effect-based trigger values like the one derived for anti-androgenic activity could become a template for regulators seeking to balance purification efficiency against ecological and human health protection. For now, the message for engineers and water utilities is clear: the cleanest-looking effluent is not necessarily the safest, and the next generation of wastewater reclamation systems must be designed with the full spectrum of hormone receptor activity in view.

Subject of Research: Endocrine-disrupting effects of transformation products formed during advanced wastewater treatment

Article Title: Advanced wastewater treatments may intensify hidden endocrine risks

Article References: Advanced wastewater treatments may intensify hidden endocrine risks. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: wastewater treatment, endocrine disruption, ozonation, ultraviolet irradiation, androgen receptor, estrogen receptor, thyroid receptor, water reclamation, transformation products, effect-based monitoring, A2O treatment, flutamide equivalents