There is a trend towards decentralized source separation (DSS) for wastewater treatment and resource recovery. An assessment framework is required to assess whether implementing a DSS treatment over a conventional centralized one is advantageous. This framework needs to account for the performance of the wastewater treatment plant (WWTP) and the effect that resource recovery has on closely-linked sectors such as food and energy production. A framework is lacking that covers the economic dimension, the circularity, the nature reciprocity of resource recovery and that can be applied to real-life cases. A novel WFE framework has been developed here to compare a conventional centralized and a DSS-based WWTP. This novel WFE framework contains assessment methods that are reproducible, and applicable to real-life cases. It also accounts for the local climatic conditions that determine irrigation water requirements. The comparison results revealed that the need to construct new DSS infrastructure leads to a lower economic efficiency of water treatment. Further, chemical-intensive treatment reduces the DSS's material resource circularity and efficiency. Using heat pumps increases the energy use of the DSS WWTP, causing a reduction in water treatment energy efficiency. However, the advantages of DSS show up in the freshwater and nutrient efficiency of food production as well as in the energy self-sufficiency of the WWTP. The novel WFE framework contains indicators specific to water treatment and the food production sectors to improve inter-sectoral communication. Also, including the nature reciprocity assessment can help demonstrate the issue with treated wastewater discharge, especially in arid regions with low stream flows. It can potentially help improve the acceptance of treated wastewater-based reuse. To conclude, the novel framework helps to assess real-life case studies in a more integrated and holistic way. It can help make decisions related to decentralization and source separation by simultaneously considering the water treatment, energy production, and food production sectors.

This mini review explores the potential of visible light–driven bismuth vanadate (BiVO₄)-based photoanodes for removing trace organic pollutants from water. It highlights the advantages of using BiVO₄-based photoanodes over conventional UV-driven photoanodes in water treatment. The mechanism of reactive species generation through water oxidation is discussed. The review also highlights the role of sulfate and sulfite radicals in enhancing pollutant degradation. Furthermore, it evaluates how heterojunction formation improves the removal efficiency of BiVO₄-based photoanodes by reducing charge carrier recombination. Limited research on BiVO₄-based photoanodes for the simultaneous removal of multiple organic pollutants at low concentrations (<1 mg L⁻¹) from real wastewater is identified as a key knowledge gap. Addressing this gap could advance the application of BiVO₄-based photoanodes in photoelectrocatalytic-based advanced oxidation processes.

Pharmaceuticals have received extensive scientific and socio-economic attention worldwide due to their acute and chronic toxic effects on plants, animals, and human health. However, the geographical distribution and seasonal variability of pharmaceutical mixtures in aquatic environments remain underexplored, especially in resource-deficient countries. The present review provides an in-depth analysis of the seasonal occurrence of pharmaceuticals, particularly antibiotics detected over the last five years in surface water, groundwater, and drinking water. The effectiveness of the conventional and advanced drinking water treatment processes is discussed with a focus on the adsorption and ozonation processes, commonly employed at drinking water treatment plants (DWTPs). Findings reveal median concentrations of antibiotics and other pharmaceuticals in drinking water worldwide, often exceeding their levels in groundwater. This underscores the urgent need for global-scale, long-term monitoring of antibiotics in aquatic systems, especially in DWTPs. Beyond targeted analysis, non-targeted analysis (NTA) should be integrated into routine water quality monitoring at DWTPs to identify novel contaminants, including fluorinated pharmaceuticals. Finally, this review provides an overview concerning the process-based and data-driven modelling of pharmaceutical occurrence, fate, and transport as a complementary approach to sampling and lab-scaled experiments, especially in resource-limited settings. Strengthening long-term monitoring, expanding treatment solutions, integrating modelling tools, and promoting green chemistry innovations are crucial to mitigating risks and safeguarding water quality.

Photochemical weathering and eco-corona formation through natural organic matter (NOM) adsorption play vital roles in the aggregation tendencies of nanoplastics (NPs) in aquatic environments. However, it remains unclear how photochemical weathering alters the adsorption patterns of NOM and the conformation of the eco-corona, subsequently affecting the aggregation tendencies of NPs. This study examined the effect of Suwannee River NOM adsorption on the aggregation kinetics of pristine and photoaged polystyrene (PS) NPs in monovalent electrolyte solutions. The results showed that photochemical weathering influenced the conformation of the eco-corona, which, in turn, determined NP stability in the presence of NOM. Hydrophobic components of NOM predominantly bound to pristine NPs through hydrophobic and π-π interactions, and extended hydrophilic segments in water hindered NP aggregation via steric repulsion. Conversely, hydrogen bonding facilitated the binding of these hydrophilic segments to multiple photoaged NPs, thereby destabilizing them through polymer bridging. Additionally, the stabilization and destabilization capacities of NOM increased with its concentration and molecular weight. These findings shed light on the destabilizing role of NOM in weathered NPs, offering new perspectives on environmental colloidal chemistry and the fate of NPs in complex aquatic environments.

Organic micropollutants, such as pharmaceuticals, represent a significant environmental and public health challenge due to their persistence, toxicity, and potential to contribute to antimicrobial resistance. These contaminants often pass through conventional wastewater treatment, entering aquatic environments and posing risks to ecosystems and human health. Advanced oxidation processes (AOPs), particularly photoelectrochemical oxidation (PEC), offer a promising solution for removing trace -level pharmaceuticals from secondary-treated wastewater. However, the photocurrent conversion efficiency, catalytic activity, and stability of BiVO4-based photoanodes, which are key components in PEC systems, are still limited. Surface modifications have shown potential to address these challenges and enhance their performance. This study aims to improve the PEC activity of BiVO4-based photoanodes for the degradation of pharmaceutical mixtures in secondary-treated wastewater through surface modification using quaternary ammonium-based compounds (QACs). The photoanodes were fabricated using ultrasonic spray pyrolysis and characterized using techniques such as scanning electron microscop y (SEM), X-ray diffraction (XRD), and linear sweep voltammetry (LSV). PEC experiments were conducted under simulated solar light to assess the degradation of a mixture of pharmaceuticals at an initial concentration of 10 μg/L.

The results demonstrated that the surface modification of BiVO4 with QACs significantly enhanced the degradation rate of pharmaceuticals compared to unmodified BiVO4 photoanodes. SEM images confirmed the successful deposition of needle-like QAC particles on the BiVO4 surface, leading to improved charge separation. Notably, pharmaceuticals such as diclofenac, sulfamethoxazole, sulfadimethoxine, and acetaminophen showed higher removal rates in the presence of the modified photoanodes. This research highlights the potential of QAC-modified BiVO4 photoanodes as an effective approach for enhancing the degradation of pharmaceuticals in wastewater. The findings contribute to advancing the field of PEC-based wastewater treatment technologies and offer promising implications for upscaling and practical application in treating pharmaceutical-contaminated wastewater.

The publisher regrets that in the original publication, the disclosure statement in the footnote is incorrect. It should read as follows:
“Given the role as a guest editor, Sanjeeb Mohapatra had no involvement in the peer review of the article and has no access to information regarding its peer review. Full responsibility for the editorial process of this article was delegated to Rakesh Kumar”.
The publisher would like to apologise for any inconvenience caused.

Mutual symbiosis of electroactive bacteria (EAB) and denitrifier may be the key for solving the refractory carbon and residual nitrogen in wastewater treatment plant effluent. However, its application is hampered by unclear co-metabolic model and uncertain electron transfer. Here, we achieved 3–5 times increase in refractory carbon degradation, 40 % improvement in denitrification, and 36.0 % decrease in N₂O emission by co-culturing P. aeruginosa strain GWP-1 and G. sulfurreducens. Such an enhancement is obtained by both refractory carbon co-metabolism and interspecies electron transfer (IET) between GWP-1 and G. sulfurreducens. Importantly, IET was quantified via isotopic approach, which revealed that G. sulfureducens supplies more electrons to GWP-1 when the system was fed with cellulose (0.071 mM) than glucose (0.012 mM). This study demonstrates that the residual refractory carbon and nitrogen in treated wastewater could be further converted by mutual symbiosis of EAB and denitrifiers, which paves a synergic way for pollution and carbon reduction.

Blue green infrastructure (BGI) is widely implemented as an adaptive stormwater management measure at the household level to reduce flood risk. However, more greenery also raises water demand during droughts due to higher evapotranspiration. This study examines the impact of 14 commonly used BGI types on household water balance under climate projections in the Netherlands. Several scenarios were modeled, from a ‘Grey’ setup with no BGI to a ‘Greenest’ option with an intensive green roof, facade, and orchard. Intermediate configurations were also analyzed, representing more common household configurations. On a typical 100 m2 household plot, the ‘Greenest’ option results in an extra demand of 154.3 L/day. This exceeds the current average daily indoor water use of a typical household of 129 L/day. In contrast, intermediate setups with a native plant garden or fully grassed garden and a gray roof require 8.4 and 9.9 L/day, respectively. To meet 80% of the projected additional external water demand from intensified greenery, intermediate setups need up to 2.3 m3 of rainwater tank. The ‘Greenest’ option requires 14.9 m3 of water storage to achieve the same coverage, underscoring the challenge of balancing space for water harvesting systems and intensified greenery within a limited household plot.

Background: Denitrification in wastewater treatment is severely limited under low-temperature and low-carbon (“dual-low”) conditions, hindering sustainable nitrogen removal. Biofilm systems, though energy-efficient, suffer from reduced efficiency in such environments due to impaired interspecies electron transfer (IET). Granular activated carbon (GAC), a conductive mediator, offers potential to enhance IET between electroactive microorganisms (EAMs) and denitrifiers, yet its role in dual-low systems remains underexplored. This study investigates GAC’s capacity to optimize biofilm functionality and mitigate greenhouse gas (GHG) emissions under these constraints. Results: Under dual-low conditions (4–6°C, C/N = 4), GAC increased denitrification efficiency by 19.4–21.9% and reduced N₂O emissions by 10.6–22.9%. Metatranscriptomes revealed upregulation of denitrifying genes (e.g., nosZ) and electron transport pathways (e.g., omcB in Geobacter). FISH/SEM confirmed GAC-driven coacervates of EAMs and denitrifiers, linked by nanowires, enhancing direct electron transfer. Microbial diversity decreased, but functional redundancy improved, with Pseudomonas fluorescens and Geobacter sulfurreducens dominating. TOC removal rose under low temperatures, indicating enhanced carbon utilization. Conclusions: GAC fosters synergistic EAM-denitrifier partnerships, enabling efficient denitrification and GHG mitigation in cold and carbon-limited (“dual-low”) biofilm systems, advancing sustainable wastewater management.

Optimising rainwater harvesting (RWH) systems’ design involves sizing the storage and catchment areas to enhance cost-effectiveness, self-sufficiency, and water quality indicators. This paper considers the design of RWH systems under long-term uncertainty in precipitation and demands. In this work, we formulate and solve a multi-objective stochastic optimisation problem that allows explicit trade-offs under uncertainty, maximising system efficiency and minimising deployment cost. We use the yield after spillage (YAS) approach to incorporate the physical and operational constraints and the big-M method to reformulate the nonlinear min\max rules of this approach as a mixed-integer linear programming (MILP) problem. By posing a risk averseness measure on efficiency as a conditional value at risk (CVaR) formulation, we guarantee the designer against the highest demand and driest weather conditions. We then exploit the lexicographic method to effectively solve the multi-objective stochastic problem as a sequence of equivalent single-objective problems. A detailed case study of a botanical garden in Amsterdam demonstrates the framework's practical application; we show significant improvements in system efficiency of up to 15.5% and 28.9% in the driest scenarios under risk-neutral and risk-averse conditions, respectively, compared to deterministic approaches. The findings highlight the importance of taking into account multiple objectives and uncertainties when designing RWH systems, allowing designers to optimise efficiency and costs based on their specific requirements without extensive parameterisation.

At present, there is a lack of understanding regarding the extent to which various sources contribute to the total incoming load of microplastics (MPs) into wastewater treatment plants (WWTPs). This study investigated the contribution of an industrial textile laundry facility (ITLF) to the overall influx of MPs and their removal in two WWTPs. MPs were analysed by means of microscopic quantitative analysis in the wash water from a large textile laundry facility, as well as in the influent of the receiving WWTP. Additionally, influent and effluent flows of two WWTPs were analysed. Results demonstrated that a single-point emitter of MPs, i.e. an ITLF, contributed substantially (13%) to the overall influx of MPs in a WWTP. MPs were effectively removed (≥ 99.8% removal, particle size > 50 µm) in two separate WWTPs. As indicated in this study, actions mitigating the emission of MPs from single-point emitters are worthwhile and could be more cost-effective than implementing additional treatment processes in the WWTPs.

Micro- and nanoplastics (MNPs) are attracting increasing attention due to their persistence and potential ecological risks. This review critically summarizes the effects of photo-oxidation on the physical, chemical, and biological behaviors of MNPs in aquatic and terrestrial environments. The core of this paper explores how photo-oxidation-induced surface property changes in MNPs affect their adsorption toward contaminants, the stability and mobility of MNPs in water and porous media, as well as the transport of pollutants such as organic pollutants (OPs) and heavy metals (HMs). It then reviews the photochemical processes of MNPs with coexisting constituents, highlighting critical factors affecting the photo-oxidation of MNPs, and the contribution of MNPs to the phototransformation of other contaminants. The distinct biological effects and mechanism of aged MNPs are pointed out, in terms of the toxicity to aquatic organisms, biofilm formation, planktonic microbial growth, and soil and sediment microbial community and function. Furthermore, the research gaps and perspectives are put forward, regarding the underlying interaction mechanisms of MNPs with coexisting natural constituents and pollutants under photo-oxidation conditions, the combined effects of photo-oxidation and natural constituents on the fate of MNPs, and the microbiological effect of photoaged MNPs, especially the biotransformation of pollutants.

Organic micropollutants (OMPs) enter the aquatic environment via municipal wastewater treatment plants (WWTPs). As conventional WWTPs have limited capacity for the removal of OMPs, additional processes are required, like ozone - granular activated carbon (GAC) filtration. A specific lay-out of this process is the O3-STEP® process, in which the removal of suspended solids, OMPs, phosphate and nitrate is combined. However, ozonation may result in formation of bromate, a compound with a strict water quality standard of 1 μg/L for surface waters in The Netherlands. This limits the applicability of ozonation in wastewater treatment. This study examined biological bromate removal associated with denitrification processes in the GAC filter of the O3-STEP® process. In this GAC filter methanol is dosed for nitrate removal by biological denitrification. In column experiments, bromate and nitrate were removed simultaneously under both anoxic and oxic conditions. Depletion of oxygen within the biofilm surrounding the GAC granules most probably is the reason for denitrification under oxic bulk conditions, although aerobic denitrification cannot be excluded. In batch experiments, the presence of nitrate did not affect bromate removal, whereas the presence of dissolved oxygen had a slight inhibitory effect on bromate removal and nitrate removal. Addition of methanol increased both nitrate and bromate removal, which is hypothesized to occur through an increased availability of electron donors in the water. The results show that a denitrifying GAC filter in the ozone - GAC filtration process mitigates the bromate formation, which broadens the applicability of this process for OMP removal from wastewater.

Hoewel de rwzi’s Amsterdam-West en Horstermeer meer dan 99,8% van de microplastics verwijderen, blijft het absolute aantal dat in het milieu terechtkomt aanzienlijk. Tevens bleek dat één industriële textielwasserij verantwoordelijk is voor 13% van het totale aantal microplastics dat de rioolwaterzuivering binnenkomt.

The concept of circular economy, aiming at increasing the sustainability of products and services in the water and other sectors, is gaining momentum worldwide. Driven by this concept, novel bio-composite materials produced by recovering resources from different parts of the water cycle are now manufactured in The Netherlands. The new materials are used for different products such as canal bank protection elements, as an alternative to similar elements made of hardwood. As much as these new materials are appealing from the sustainability point of view, they may leach toxic substances into the aquatic environment given some of their ingredients, e.g., cellulose recovered from wastewater treatment. Therefore, a methodology for the assessment of related environmental risks is needed and it does not exist currently. This paper addresses this knowledge gap by presenting a framework for this. The framework is based on European environmental risk assessment guidelines, and it includes four key steps: (i) hazard identification, (ii) dose–response modelling, (iii) exposure assessment and (iv) risk characterisation (i.e. assessment). As part of the first step, laboratory leaching tests were carried out to evaluate the potential release of specific chemical substances such as heavy metals and resin compounds into the aquatic environment. Laboratory test results were then used as input data to evaluate the risk of potential leaching from canal bank protection elements into surface water. A deterministic model was used first to identify the chemicals exceeding the guideline threshold. Subsequently, a stochastic model was applied to evaluate the environmental risks across a range of leachate concentrations and water velocities in the canal, thereby simulating a broader spectrum of possible situations. The risk analyses were conducted for four alternative bio-composite materials made of different ingredients, two different flow conditions (stagnant water and advective flow) in two types of canals (wide ditch and primary watercourse) and for two different water levels based on season conditions (summer and winter conditions). The results obtained from leaching tests identified Cu, Mn, Zn, styrene and furfuryl alcohol as potentially troublesome chemicals. In the case of stagnant water, the absence of a flow rate increases the residence time of the chemicals in the surface water, resulting in a higher PEC/PNEC (i.e. risk) value. However, under stagnant case conditions, environmental risks for all chemicals considered turned out to be below the safety threshold. In the advective case, the existence of a flow rate, even at low velocities simulating the conditions of ‘almost no flow,’ contributes to increased dilution, resulting in lower PEC/PNEC ratio values. The results presented here, even though representing real-case scenarios, are only indicative as these are based on laboratory leaching tests and a number of assumptions made. Additional field tests involving collecting and analysing water and sediment samples from the canal where the canal bank protection elements are located, over a prolonged period, are required to come up with more conclusive findings.

Photodegradation of microplastics (MPs) induced by sunlight plays a crucial role in determining their transport, fate, and impacts in aquatic environments. Dissolved black carbon (DBC), originating from pyrolyzed carbon, can potentially mediate the photodegradation of MPs owing to its potent photosensitization capacity. This study examined the impact of pyrolyzed wood derived DBC (5 mg C/L) on the photodegradation of polystyrene (PS) MPs in aquatic solutions under UV radiation. It revealed that the photodegradation of PS MPs primarily occurred at the benzene ring rather than the aliphatic segments due to the fast attack of hydroxyl radical (•OH) and singlet oxygen (¹O₂) on the benzene ring. The photosensitivity of DBC accelerated the degradation of PS MPs, primarily attributed to the increased production of •OH, ¹O₂, and triplet-excited state DBC (³DBC*). Notably, DBC-mediated photodegradation was related to its molecular weight (MW) and chemical properties. Low MW DBC (<3 kDa) containing more carbonyl groups generated more •OH and ¹O₂, accelerating the photodegradation of MPs. Nevertheless, higher aromatic phenols in high MW DBC (>30 kDa) scavenged •OH and generated more O₂•^-, inhibiting the photodegradation of MPs. Overall, this study offered valuable insights into UV-induced photodegradation of MPs and highlighted potential impacts of DBC on the transformation of MPs.

The fate and toxicity of nanoplastics (NPs) in the environment is largely determined by their stability. We explored how water composition, nanoplastic size, and surface carboxyl group density influenced the aggregation of polystyrene (PS) NPs in fresh water. Unfunctionalized 200, 300, 500, and 1000 nm PS NPs and 310 nm carboxylated PS NPs with carboxyl group densities of 0.35 and 0.6 mmol g⁻¹ were used to simulate pristine and aged NPs. Natural water matrices tested in this study include synthetic surface water (SSW), water from the Schie canal (Netherlands) and tap water. Suwannee River Natural Organic Matter (SRNOM) was included to mimic organic matter concentrations. In CaCl₂, we found PS NPs are more stable as their size increases with the increase of the critical coagulation concentration (CCC) from 44 mM to 59 mM and 77 mM for NP sizes of 200 nm, 300 nm and 500 nm. Conversely, 1000 nm PS NPs remained stable even at 100 mM CaCl₂. Increasing the carboxyl group density decreased the stability of NPs as a result of the interaction between Ca²⁺ and the carboxyl group. These results were consistent with the mass of Ca²⁺ adsorbed per mass of NPs. The presence of SRNOM decreased the stability of PS NPs via particle bridging facilitated by SRNOM. However, in SSW, Schie water and tap water with low divalent cation concentrations, the hydrodynamic size of PS NPs did not change, even at prolonged durations up to one week. We concluded that PS NPs are unlikely to aggregate in water with low divalent cation concentrations, like natural freshwater bodies. Ecotoxicologists and water treatment engineers will have to consider treating PS NPs as colloidally stable particles as the lack of aggregation in fresh surface water bodies will affect their ecotoxicity and may pose challenges to their removal in water treatment.

The occurrence and removal of microplastics (MPs) in drinking water treatment plants (DWTPs) have been evaluated based on particle number, while the mass concentration and removal characteristics based on the mass of MPs, and especially nanoplastics (NPs), remain unknown. This study employed pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) to determine the mass concentration of MPs and NPs with different size ranges (0.01-1, 1-50, and 50-1000 μm) across the entire treatment process in a DWTP. The total polymers were measured at 9.63 ± 1.52 μg/L in raw water and 0.77 ± 0.05 μg/L in treated water, with the dominant polymers being polypropylene and polyethylene terephthalate. NPs (0.01-1 μm) accounted for only 3.2-5.3% of the total polymers, with an average concentration of 0.38 μg/L in raw water and 0.04 μg/L in treated water. Notably, NPs and sub-MPs (1-50 μm) demonstrated relatively low efficiency in the DWTP at 88.9 ± 3.2 and 88.0 ± 2.5%, respectively, compared with that of the large MPs (50-1000 μm) at 92.9 ± 0.3%. Overall, this study examined the occurrence of MPs and NPs, in a DWTP, emphasizing the significance of considering the mass concentration of MPs and NPs when assessing their pollution levels and removal characteristics.

Slow sand filters (SSFs) are widely used in drinking water production to improve microbial safety and biological stability of water. Full-scale SSFs are maintained by scraping the biomass-rich top layers of sand. The period of downtime required for filter recovery after scraping is a major challenge due to limited knowledge of the re-stabilisation of purification processes. This study examined the recovery of microbial biomass, and removal of dissolved organic carbon (DOC) and ammonium (NH4+) in water phase and/or on sand along the depth of a scraped full-scale SSF. Scraping reduced microbial biomass on sand in the top layers, while the main prokaryotic taxa remained unaltered. Cellular ATP (cATP) and intact cell counts (ICC) in water sampled from the top layers increased, indicating a temporary disruption in functionality for 37 days. However, stable concentrations of cATP and ICC and similar microbial community composition in the effluent after scraping revealed that deeper layer biofilms offset any scraping effect. Consistent DOC and NH4+ removal after scraping showed that deeper layers effectively performed the role of the top layer. These findings highlight the resilience and robustness of microbial communities in mature full-scale SSFs and their contribution to water treatment efficiency after disturbances caused by scraping.

Nitrate concentrations exceed standards in many drinking water sources. Solid carbon source (SCS) is usually used to increase the biological denitrification in waters with a low carbon‑nitrogen ratio. However, there is a lack of research on the enhanced denitrification in drinking water sources with nitrate exceeding limits by the introduction of SCS. In this study, a SCS composite was prepared using agricultural waste corncob and polybutylene succinate and the SCS carbon release performance, denitrification effect and potential chemical and biological risks were investigated via a series of batch and column experiments. The SCS composite presented a long-term, stable carbon release performance and good microbial utilization capability for denitrification: SCS composite has a sustained release capacity for over 28 days in dynamic waters. Short-chain fatty acids accounted for over 60 % of the released carbon, and predominant fluorescence compounds were protein organic compounds and soluble microbial metabolites. The introduction of SCS composite evidently improved bio-rope biomass and its denitrification effect. The removal percentage of NO₃⁻ by SCS reactor pretreatment reached 90.9 %, remaining stable within 28 days. The SCS pretreatment increased formation potentials of trihalomethanes, but formation potentials of haloacetonitriles with higher toxicity were effectively reduced, so the comprehensive toxicity risk of disinfection by-products was reduced. The SCS pretreatment has slight negative impact on drinking water biological stability only during the first 10 days, which needs attention. This study demonstrated that the prepared SCS composite has excellent carbon release performance and denitrification effect, and its chemical and biological risks were controllable.