Search Results (162)

Access to safe drinking water remains a global challenge, particularly in decentralized and low-resource settings where conventional treatment technologies may be economically or operationally impractical. Combining low-energy hydraulic flocculation systems with biodegradable natural coagulants represents a promising strategy for sustainable water treatment. This study investigated the influence of hydraulic retention time (HRT) on the clarification performance of aluminum sulfate, Moringa oleifera, and Aloe vera in continuous-flow helically coiled tube flocculators (HCTFs). Four HRTs (1.71–6.84 min) were obtained by varying reactor length while maintaining a constant flow rate of 0.5 L/min. Synthetic water with an initial turbidity of approximately 100 NTU was treated, and clarification performance was evaluated by residual turbidity and turbidity removal efficiency. Two-way ANOVA revealed significant effects of HRT and coagulant type, as well as a significant interaction between these factors (p < 0.001), indicating that the influence of HRT depended on the dominant coagulation mechanism. Aluminum sulfate maintained consistently high turbidity removal efficiencies (96.3–98.1%) regardless of HRT. In contrast, Moringa oleifera achieved the highest clarification efficiency (99.5%) and a final turbidity of 0.49 NTU at the longest HRT, whereas Aloe vera exhibited the greatest hydraulic sensitivity, with turbidity removal increasing from 78.9% to 96.1% as HRT increased. The results demonstrate that HRT should be selected according to the dominant coagulation mechanism of the coagulant rather than adopted as a fixed design parameter. This mechanism-based approach provides a rational basis for designing and optimizing continuous-flow flocculators and supports the development of compact, efficient, and sustainable decentralized water treatment systems. Full article

Implementation of real-scale systems for rainwater harvesting, treatment and reuse of greywater in residential areas is challenging because several factors should be considered for full adoption and satisfaction of decision-makers, urban developers and users. Technological, construction, operational, social (acceptance), impact on water resources, regulatory, and economic factors are involved. This study presents the implementation of a full-scale hybrid system for rainwater harvesting, treatment and reuse of greywater in a residential building located in Monterrey, Nuevo León, Mexico. The study included intervening in the hydraulic infrastructure of an already constructed residential building for collecting greywater, harvesting and collecting rainwater, designing and constructing an 80 m² controlled natural soil treatment system (CNSTS) and a 65 m³ storage tank for treating and storing rain and greywater. Furthermore, the full-scale hybrid system was monitored under real operating conditions for a two-month period to assess its performance. Results showed that the CNSTS has the potential to replace up to 2835 m³ year⁻¹ of potable water, equivalent to 65% of the building’s annual water consumption. The CNSTS achieved removal efficiencies of up to ~90% for Chemical Oxygen Demand, 90% for surfactants, and 50% for total nitrogen. Most of the measured parameters complied with the corresponding limits established by the Mexican standards NOM-003-SEMARNAT-1997 for non-potable water reuse, NOM-001-SEMARNAT-2021 for wastewater discharges, and NOM-127-SSA1-2021 for potable water with the exception of methylene blue active substances (surfactants), which exceeded the permissible limit during the initial monitoring stage, highlighting the need for further optimization of the system’s vegetative cover. Based on these findings, conceptual designs and preliminary evaluations were conducted for additional buildings, resulting in potable water substitution rates above 90% with investment payback periods of 2 to 5 years, depending on the water demand and the water catchment potential. Full article

To overcome the limitations of insufficient driving force in traditional microbial desalination batteries, this paper constructs a microbial anode-membrane capacitive deionization (B-MCDI) coupling system. For the first time, direct coupling between extracellular electron transfer in Shewanella oneidensis and double-layer adsorption at the MCDI cathode is achieved at the circuit and material levels, realizing self-driven, low-energy desalination. High-specific-surface-area carbon felt is used as the anode, and a stable electrogenic biomembrane (output voltage >400 mV) is formed after directional domestication with Shewanella oneidensis MR-1. Activated carbon is used as the cathode to construct the MCDI electrode. In the three-chamber reactor, the desalination chambers are separated by cation and anion exchange membranes. Under the drive of the bioelectric field, Na⁺ and Cl⁻ selectively permeate into the cathode and anode chambers, respectively, effectively suppressing the co-ion effect. Under optimal operating conditions (external resistance 1000 Ω, initial NaCl concentration 2.0 g/L), the system achieved a cumulative desalination rate of 85.1% after 12 h of operation, with a salt adsorption capacity of 162.1 mg/g, an average desalination rate of 13.51 mg/(g·h), and an energy consumption of only 0.58 kWh/m³. This demonstrates that bioelectric energy can effectively provide targeted power to drive capacitive adsorption and desalination. Under initial NaCl concentrations of 1.0 g/L and 3.0 g/L, the highest desalination rates reached 78% and 68%, respectively. The maximum instantaneous desalination rate occurred within 0.5–1.0 h (64 mg/h under 2.0 g/L conditions), exhibiting a three-stage kinetic characteristic of “fast-slow-equilibrium”. The energy consumption in this study was only 0.51 kWh/m³, further demonstrating the high energy efficiency of bioelectrically coupled MCDI in low-salinity treatment areas. Therefore, this B-MCDI can serve as a theoretically feasible proof-of-concept technology for desalination of brackish water that meets the requirements of self-driven, low-energy consumption, and has promising applications in decentralized water supply systems in areas with limited energy supply or no available electricity. Full article

Freeze desalination (FD) is being reconsidered as a low-temperature desalination route because it separates water through ice formation rather than evaporation or membrane pressure. This review examines FD from the perspective of sustainable water–energy systems, with emphasis on applications where conventional desalination may face technical or energy limitations. Unlike general reviews focused mainly on freezing principles, this work connects crystallization mechanisms, experimental performance, energy integration, and scale-up barriers. The literature analyzed, consisting primarily of studies published between 2015 and 2026, was grouped into four areas: modeling and simulation, experimental and pilot-scale validation, technological integration, and energy–economic assessment. Recent progress has been reported in eutectic freeze crystallization, vacuum-assisted ice–brine separation, ice morphology control, LNG cold recovery, solar-assisted FD, and hybrid systems that combine desalination with cooling or energy recovery. Reported performance varies widely. Reported SEC varies by more than an order of magnitude: values near 3 kWh/m³ occur mainly under favorable integration or external-cold assumptions, whereas conventionally refrigerated laboratory and pilot systems can require substantially more energy. This difference shows that FD performance depends strongly on crystallizer design, feedwater composition, separation strategy, and cold-energy recovery. FD should not be viewed as a direct replacement for RO, MED, or MSF. Its strongest potential is in hypersaline brine treatment, LNG terminals, cold regions, off-grid systems, island communities, and decentralized water production coupled with renewable or waste-cold sources. Full article

Access to reliable water quality monitoring remains a significant challenge in rural and underserved regions, where laboratory-based analyses are often constrained by logistical and economic limitations. This study presents the design and functional laboratory-scale implementation of a low-cost IoT-based monitoring platform intended to support the digitalization of decentralized water treatment and water management through remote assessment of pH, temperature, electrical conductivity, dissolved oxygen, and turbidity. The proposed architecture integrates commercial sensors within a valve-controlled hydraulic chamber that performs intermittent fill–retain–measure–drain cycles, a Pycom LoPy 4.0 acquisition unit, LoRaWAN-based data forwarding, and cloud-based visualization. Functional testing demonstrated successful end-to-end integration of the hydraulic, sensing, communication, and visualization subsystems under controlled prototype conditions. The minimum demonstrated operational cycle was approximately 90 s; however, this value corresponded to the shortest functional testing condition rather than the intended routine monitoring interval, which incorporates a configurable inactive period between consecutive measurement cycles. The results demonstrate the feasibility of integrating low-cost sensing technologies, intermittent hydraulic sampling, and LoRaWAN connectivity into a laboratory-scale engineering prototype for decentralized water quality monitoring. The proposed platform should therefore be regarded as a functional proof-of-concept that establishes the technological basis for future metrological validation, long-term field deployment, and integration with decentralized water treatment systems rather than as a fully validated monitoring instrument. Full article

Wastewater treatment remains a major challenge in rural and peri-urban areas, where conventional centralized infrastructure is often unavailable or insufficient. In this context, Nature-Based Solutions (NBS) have emerged as cost-effective and energy-efficient alternatives for decentralized wastewater treatment. This review presents a comprehensive and multidimensional assessment of 15 NBS types, evaluating their technical performance, economic viability, environmental sustainability, and social dimensions. The analysis indicates that NBS can achieve pollutant removal efficiencies comparable to those of conventional treatment systems, particularly for organic matter and, in some cases, emerging contaminants. However, their performance is strongly influenced by system design and operational conditions. The main limitations of NBS include relatively low hydraulic and pollutant loading capacities, as well as substantial land requirements, ranging from 0.45 to 840 m²·PE⁻¹. These constraints limit their applicability in densely populated areas while making them particularly well suited for rural and low-density settings. From both economic and environmental perspectives, NBS offer significant advantages, including construction cost reductions of up to 66% and substantially lower energy consumption than conventional technologies. Nevertheless, their successful implementation depends not only on technical performance but also on social acceptance, stakeholder engagement, and the establishment of appropriate governance frameworks. Overall, NBS constitute a flexible and sustainable approach to wastewater treatment, whose effectiveness ultimately depends on site-specific conditions and the integration of complementary treatment components. Full article

Increasing water scarcity and pollution have intensified the need for low-cost wastewater treatment in developing regions. Constructed wetlands (CWs) offer a nature-based solution for pollutant removal but often fail, on their own, to meet discharge and reuse standards. This study evaluated four CW systems planted with Cyperus latifolius, Juncus effusus, Phragmites mauritianus, and Pennisetum purpureum, integrated with banana fibre filtration as a polishing step. The CWs alone achieved ammonium removal of 74–83%, nitrate 78–85%, phosphorus 86–91%, and COD 78–83%. Banana fibre filtration enhanced overall removal efficiencies to 93–96%, 94–96%, 81–88%, and 82–87% for ammonium, phosphorus, nitrate, and COD, respectively. Pennisetum purpureum had the highest aboveground nitrogen accumulation (74.4 g N/m²), with its coupled system achieving the highest nitrate removal, whereas Juncus effusus had the highest phosphorus accumulation (93.1 g P/m²), with its coupled system showing the best overall removal of ammonium, phosphorus, and COD. The integrated system reduced fecal coliforms and Escherichia coli by 6–8 log and eliminated detectable Salmonella and Shigella. Treated effluent met FAO irrigation, Rwanda discharge, and European Union (EU) standards for all evaluated parameters except phosphorus, which remained above the stricter EU limit. Despite bench-scale operation over four months, these findings demonstrate a low-cost, nature-based treatment approach suitable for decentralized wastewater treatment and reuse, with harvested wetland biomass offering additional potential for animal feed, energy, or fibre valorization. Full article

Emulsified oily wastewater from industrial activities remains challenging to treat because kinetically stable oil droplets hinder efficient separation, threatening water resources and ecological environments. To address this issue, this work develops an inclined solar-driven evaporator based on a polypyrrole (PPy)-coated bacterial cellulose (BC) gel (PPy-BC gel), which has enlarged effective evaporation areas and an environmental heat effect. Under one sun (1 kW m⁻² under standard solar illumination), the PPy-BC gel achieves an evaporation rate of 2.14 kg m⁻² h⁻¹, which is 494% higher than that of the uncoated BC gel. In diesel-in-water emulsions with oil concentrations ranging from 0 to 15 vol%, the gel maintains stable evaporation performance, achieving an oil removal efficiency exceeding 99% across all tested concentrations. After 15 consecutive cycles of treating actual oily wastewater, no significant performance degradation is observed. The collected condensate exhibits excellent water quality, with removal efficiencies for total organic carbon (TOC), chemical oxygen demand (COD), and total dissolved solids (TDS), and ionic conductivity (IC) exceeding 94%. This work presents a solar-powered evaporation platform, which demonstrates potential in the stable treatment of complex oily wastewater, and offers a sustainable reference solution for decentralized industrial wastewater management. Full article

Natural coagulants have emerged as potential alternatives to synthetic chemicals in water treatment, especially for decentralized and low-resource applications. However, many previously reported Aloe vera-based coagulant preparation methods rely on drying, powder production, distilled water extraction, refrigeration, or other laboratory-dependent procedures that increase operational complexity and limit practical implementation. This study presents a simplified and rapid protocol for producing an Aloe vera-based natural coagulant using accessible materials and simplified preparation steps. The proposed methodology consists of extracting Aloe vera g13el, homogenizing 2 g of fresh gel with 50 mL of tap water using a household blender, and applying simple paper filtration to obtain the liquid coagulant. The protocol can be completed in less than 10 min without specialized laboratory infrastructure, energy-intensive processing, or laboratory-grade reagents. Coagulation performance was evaluated using synthetic turbid water with initial turbidity levels of 100, 200, and 300 NTU. Significant turbidity reduction was observed under all tested conditions, with several samples reaching residual turbidity values close to or equal to 0 NTU after 50–60 min of sedimentation. The results demonstrate the potential of the proposed protocol as a rapid, reproducible, and accessible approach for future investigation in point-of-use and decentralized water treatment applications. Full article

Water scarcity is an increasingly urgent global challenge, prompting the development of new water purification technologies that surpass conventional solutions. Decentralized greywater treatment is emerging as a viable option for enhancing water reuse in multifunctional systems that contribute to microclimate regulation, cooling, and urban climate adaptation. In this context, water-storage mats have been identified as a form of decentralized, roof-based biofilter for greywater treatment. The aim of this study was to assess the performance of newly developed, innovative, bio-based textile mats and assess their effectiveness in treating pre-treated greywater from a canteen (CGW) with a high organic content, in both laboratory- and pilot-scale experiments. The findings from the lab-scale testing revealed that the mats made from polyethylene terephthalate (PET) nonwoven fabric materials had the highest water storage capacity and dried out more slowly in outdoor conditions than mats made from polylactide (PLA) spunbonded fabric and polyhydroxyalkanoate (PHA) spunbonded nonwoven fabric. The PET hydroentangled nonwoven fabric mat (PET-WS) performed better than the other sample mats in the lab-scale experiment, and also outperformed the PHA mat consistently in the pilot-scale experiment when treating CGW. Apparent reductions in the concentration of the macro-pollutant parameters were observed at the outflow of the PET-WS mat compared to the inflow (p < 0.05) at the pilot-scale. Mean concentration reductions were comparatively higher for the five-day biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), total nitrogen (TN), and total suspended solids (TSS), with mean reductions of 64%, 54%, 39% and 60%, respectively. This indicated the superior treatment performance of the PET-WS mat compared to the PHA mat, with mean reductions of only 36%, 25%, 6%, and 32%, respectively. However, the lower E. coli counts of 1.1 and 0.5 log reduction for the PET-WS and PHA mats, respectively, indicated that an additional disinfection unit was necessary. The findings of this study may help to determine the performance, stability and reliability of using lightweight, nonwoven fabric mats to treat high-strength GW, which is currently considered as an intermediate treatment step. The study also provides recommendations for process optimization. Additional post-treatment steps are required to produce high-quality treated effluent for non-potable reuse, particularly in urban areas facing high water scarcity, provided that the relevant reuse regulations or discharge criteria are met. Full article

Transitioning from conventional wastewater treatment to circular wastewater management requires novel technologies that enable resource recovery, energy efficiency, and resilience under variable conditions. Within the NAMOR project, hybrid microalgae–bacteria Membrane PhotoBioReactors (MPBRs) are assessed as a sustainable solution for decentralized wastewater treatment and reuse. This study focuses on screening and optimizing mixed microalgae–bacterial consortia to treat municipal wastewater streams in the Mediterranean region, with an emphasis on achieving high nutrient removal, biomass productivity and robustness. A diverse set of strains will be evaluated under controlled temperature, light and nutrient regimes to enhance the symbiotic synergy between photosynthetic microalgae and heterotrophic bacteria, while minimizing aeration demand. Based on these results, a pilot demo in Lagadas, Greece, will integrate the optimized consortia into a moving-bed PBR equipped with polymeric carriers and membrane filtration for advanced effluent polishing, intended to produce reclaimed water for irrigation and biomass for valorisation into fertilizers or biogas. Full article

Solar-driven interfacial evaporation (SIE) has emerged as a transformative, off-grid technology that confines heat at the air–liquid interface, enabling high-efficiency vapor generation for decentralized water purification. Here, we present a comprehensive and critical review of the field, tracing its evolution from fundamental photothermal principles to integrated multifunctional systems. We first elucidate the thermodynamics of interfacial heat localization and the resultant enhancement in evaporation efficiency. We then systematically analyze material innovation strategies—including broadband-absorbing photothermal agents and tailored evaporator architectures—designed to overcome persistent challenges such as salt crystallization, fouling, and thermal losses. Moving beyond freshwater production, we highlight emerging pathways for extending SIE platforms toward water–energy cogeneration, selective resource recovery, and zero-liquid-discharge wastewater treatment. We further identify and objectively assess the key bottlenecks that currently hinder the transition from laboratory-scale prototypes to real-world deployment, with a focus on long-term material robustness under harsh environments, adaptability to fluctuating water chemistries, and techno-economic viability. Finally, we outline forward-looking research directions, including stimulus-responsive smart evaporators, elucidation of multi-field coupling mechanisms, and the establishment of standardized performance evaluation protocols. This review aims to provide both a tutorial for newcomers and a critical assessment for experienced researchers, offering a balanced perspective on the current state-of-the-art and a roadmap for translating SIE from academic research into sustainable, impactful technologies. Full article

For the removal of hexavalent chromium [Cr(VI)] from drinking water, a hybrid biosorbent designated chitosan–natural diatomaceous earth (CNDE) was developed and thoroughly characterized. The material couples the ion-exchange and chelating capacity of chitosan—applied at an 85% degree of deacetylation—with the high-surface-area mineral framework of natural diatomaceous earth, onto which the polymer was deposited as a conformal coating. Surface morphology and internal microstructure were examined by scanning and transmission electron microscopy (SEM/TEM), while elemental composition across the hybrid matrix was resolved by energy-dispersive X-ray spectroscopy (EDX). Fourier transform infrared (FTIR) spectroscopy was employed to identify the surface functional groups responsible for chromate binding, and streaming current measurements established the pH of zero charge (pH_pzc), which governs the electrostatic environment at the sorbent–solution interface. Specific surface area was quantified by the Brunauer–Emmett–Teller (BET) method, and the balance of surface acidic and basic sites was determined through titrimetric analysis of total acidity and alkalinity. Thermogravimetric analysis (TGA) was conducted to assess thermal stability. Batch equilibrium isotherm experiments were performed to evaluate Cr(VI) uptake from model drinking water prepared using dilute potassium dichromate solutions adjusted to target pH levels. The effects of solution pH and competing anions (chloride and sulfate) were also investigated. Kinetic studies were conducted to determine the rate of Cr(VI) adsorption, and residual metal concentrations were measured using inductively coupled plasma mass spectrometry (ICP-MS). Results indicated that CNDE containing 30% chitosan (CNDE30) achieved effective Cr(VI) removal at pH 5. Adsorption was strongly pH-dependent, decreasing as pH increased from 5 to 8. Equilibrium data were well described by both Langmuir and Freundlich isotherm models, while kinetic data followed a pseudo-second-order model. The presence of chloride ions (15 mg/L) reduced adsorption capacity by approximately one-third, whereas sulfate at the same concentration significantly inhibited Cr(VI) removal. Overall, the isotherm results suggest that CNDE30 is a promising material for Cr(VI) removal from drinking water. Its cost-effectiveness, ease of synthesis, and potential for reuse make it particularly attractive for small-scale and decentralized water treatment applications. Full article

This study reports the development of a hierarchically porous material based on natural diatomite, thermally treated diatomite (450 °C), and an activated carbon-modified diatomite composite for saline groundwater treatment in West Kazakhstan, addressing the need for efficient desalination solutions under real environmental conditions. The material was synthesized via sequential thermal activation at 450 °C followed by incorporation of activated carbon, with bentonite used as a binder to improve mechanical stability. Comprehensive physicochemical characterization (SEM, XRD, XRF, BET, DTA, and FTIR) confirmed significant structural and compositional transformations, including silica enrichment, removal of impurities, and the development of a well-defined hierarchical porous network. The specific surface area increased from 8 to 10 m²/g for natural diatomite to 35–40 m²/g for thermally treated diatomite and further to 55–60 m²/g for the activated carbon-modified diatomite composite, accompanied by enhanced pore volume and mesoporosity. Performance evaluation using real groundwater samples demonstrated that thermally treated diatomite (450 °C) improved removal efficiency by approximately 19%, while the activated carbon-modified diatomite composite achieved 35–37% removal of chloride, sulfate, and total dissolved solids under multi-ion competitive conditions. The enhanced adsorption performance is attributed to the synergistic effect of increased surface area, improved pore accessibility, and additional active sites introduced by activated carbon. The adsorption process is governed by ion bridging mediated by multivalent cations, pore filling within the hierarchical pore structure, and surface complexation on silanol and metal–hydroxyl functional groups. Leaching tests confirmed the structural stability of the composite and indicated no significant release of environmentally relevant elements under aqueous conditions. Compared with natural diatomite, the thermally treated and activated carbon-modified materials demonstrate improved adsorption efficiency and stable performance under realistic groundwater conditions. These results highlight their applicability for decentralized water treatment systems in regions affected by saline groundwater contamination. Full article

This study presents a short-term, IoT-enabled sensor-based assessment of treated municipal water and decentralized groundwater in Bragança, northeastern Portugal. Two drinking-water supply contexts were compared: treated surface-water-derived municipal water from the public supply system and groundwater from a decentralized supply system serving part of a higher education campus. Five sampling points were monitored during three campaigns between January and March 2026. At each point, pH, electrical conductivity, temperature, oxidation–reduction potential, and total dissolved solids were recorded at 10 s intervals over approximately 10 min monitoring windows using a multiparameter probe integrated into an IoT-enabled data acquisition workflow. Microbiological analyses were performed on groundwater samples as complementary information. Treated municipal water showed lower mineralization, narrower parameter ranges, and higher oxidation–reduction potential, reflecting source-water characteristics, treatment, and operational control. Groundwater showed higher mineralization, lower oxidation–reduction potential, and greater variability among sampling points and campaigns, consistent with stronger local hydrogeochemical and operational influences. The repeated short-interval readings provided more detailed physicochemical profiles than isolated spot measurements, although the short monitoring windows do not represent continuous long-term high-frequency monitoring. Overall, the results support standardized IoT-enabled sensor-based monitoring as a complementary tool for short-term water-quality assessment and indicate the need for longer seasonal datasets and laboratory confirmation. Full article