Thinking Outside the Treatment Plant: UV for Water Distribution System Disinfection

Advancing Light-Driven Reactions with Surface-Modified Optical Fibers

ConspectusThe challenge of optimizing decentralized water, wastewater, and reuse treatment systems calls for innovative, efficient technologies. One advancement involves surface-modified side-emitting optical fibers (SEOFs), which enhance biochemical and chemical light-driven reactions. SEOFs are thin glass or polymeric optical fibers with functionalized surfaces that can be used individually or bundled together. They can be attached to various light sources, such as light-emitting diodes (LEDs) or lasers, which launch ultraviolet (UV) or visible light into the fibers. This light is then emitted along the fiber's surface, creating irradiance similar to a glow stick. The resulting SEOFs uniquely deliver light energy to complex environments while maximizing photon utilization and minimizing energy loss, addressing long-standing inefficiencies in photolysis and photocatalysis systems. SEOFs generate and leverage refracted light and evanescent waves to achieve continuous irradiation of their cladding, wherein photocatalysts are embedded. This method contrasts with traditional slurry-based systems, where light energy is often scattered or absorbed before reaching the reaction sites. Such scattering typically reduces quantum yields and reaction kinetics. In contrast, SEOFs create a controlled light delivery system that enhances reaction efficiency and adaptability to diverse applications.Important chemical and physical concepts are explored when scaling up SEOFs for three potential engineered applications. The selection of polymer materials and nanoparticle compositions is crucial for optimizing SEOFs as waveguides for visible to UV-C wavelengths and for embedding surface-accessible photocatalysts within porous polymer coatings on SEOF surfaces. Additionally, understanding how light propagates within SEOFs and emits along their exterior surface and length is essential for influencing the quantum yields of chemical products and enhancing biochemical sensitivity to low UV-C exposure. UV-C SEOFs are employed for germicidal disinfection, inactivating biofilms and pathogens in water systems. By overcoming UV light attenuation issues in traditional methods, SEOFs facilitate uniform distribution of UV-C energy, disrupting biofilm formation at early stages. SEOFs enhance UV-A and visible-light photocatalytic degradation of pollutants. Embedding photocatalysts in porous polymer cladding enables simultaneous improvements in reaction kinetics and quantum yields. SEOFs enable decentralized light-driven production of clean energy resources such as hydrogen, hydrogen peroxide, and formic acid, offering sustainable alternatives for off-grid systems.The design principles of SEOFs emphasize scalability, flexibility, and efficiency. Recent innovations in polymer chemistry, nanoparticle coatings, and surface roughness engineering have further optimized light delivery and side-emission. Tailoring the refractive index and nanoparticle distribution on fiber surfaces ensures precise evanescent wave propagation, enhancing photocatalytic performance. These advancements, coupled with scalable fabrication techniques, have positioned SEOFs as promising platforms for broad photochemical applications.By summarizing recent advances and identifying future needs, this Account positions SEOFs as a transformative approach to light-driven reactions, merging cutting-edge materials science with sustainable water treatment and energy production goals. This emerging technology offers immense potential to reshape photochemical processes for decentralized applications. Despite significant progress, challenges remain. Future research should focus on optimizing catalyst loading, improving uniformity in side emissions, and enhancing polymer durability for long-term operational stability. Additionally, scaling SEOF configurations to multifiber bundles and integrating them into decentralized water systems will be critical for broader adoption.

Recent Advances of Sustainable UV Shielding Materials: Mechanisms and Applications

The escalating global threat of ultraviolet (UV) radiation is manifested through multifaceted damage pathways including cutaneous carcinogenesis, photodegradation of organic substrates, marine ecosystem destabilization, and infrastructure weathering. These urgent challenges have catalyzed sustained interdisciplinary efforts toward advanced UV-shielding technologies spanning biomedical, environmental, and industrial domains. Current material arsenals include melanin, lignin, tannin, polydopamine, zinc oxide and titanium dioxide, etc. These materials can be applied to diverse fields such as food packaging, sunscreen fabrics, sunscreen creams, eyeglasses, and sunscreen films through tailored processing techniques and employing distinct photoprotective mechanisms. Notwithstanding significant progress, the development of an integrated selection framework that reconciles efficiency, durability, and environmental compatibility persists as a critical knowledge gap. In this context, the main mechanisms of various types of UV shielding materials and their applications in different fields are described systematically. Subsequently, a comparative analysis of the advantages and shortcomings of different materials is presented, focusing on their UV shielding efficiency and stability impact. Moreover, the review delves into their unique value in specific scenarios. Finally, building on these analyses, current challenges and future development prospects of UV shielding materials are further discussed, with emphasis on scalability, eco-friendly alternatives, and multifunctional integration, providing valuable insights and guidance for advancing research and promoting sustainable and functional innovations in this field.

Innovative microbial water quality management in water distribution systems using in-pipe hydropowered UV disinfection: envisioning futuristic water-energy systems

Hydropower UV disinfection has not been explored as a possible alternative for off-grid disinfection. Hydropowered UV LED technology was developed using off-the-shelf UV-C LEDs and pico - and femto-scale hydro turbine generators and evaluated across point-of-use relevant flow rates. Commercially available UV LED flow through reactors were subjected to microorganism challenge testing with 3 power schemes: wall-plug, hydropower, and hydropower-charged battery. UV LEDs powered by hydropower-charged battery demonstrated similar disinfection as wall-plug powered UV LEDs, achieving 0.5-1.8 MS2 log10 reduction at flow rates 0.5-2.3 L min-1, corresponding to reduction equivalent doses (RED) up to 16 or 30 mJ/cm2 for 254 and 285 nm, respectively. With hydropowered UV LEDs alone, MS2 log10 reduction decreased to <0.3 log10 reduction due to an underperforming and grossly inefficient turbine, with RED of 8 or 18 mJ/cm2 for 254 and 285 nm, respectively. Assessment of existing markets of UV disinfection systems and pico-hydro turbines demonstrated that hydropowered UV systems are already theoretically feasible for scales at point-of-entry (POE) and above. Economic feasibility will improve if turbines and/or UV system efficiencies improve. Prototype hydropower UV LED systems ranged from $145 to 220 depending on the UV LED reactor, and the battery system added $81. This study demonstrates the practicality of sustainable, renewable energy POU UV disinfection technology that can benefit decentralised, off-grid, rural and remote communities. The system may also scale up to provide renewable energy disinfection at larger scales, such as buildings and water distribution systems, for protecting human health in highly populated areas.

Far-UVC (222 nm) irradiation effectively inactivates ssRNA, dsRNA, ssDNA, and dsDNA viruses as compared to germicidal UVC (254 nm)

Ultraviolet-C (UVC) irradiation is being used as an effective approach for the disinfection of pathogenic viruses present in air, surfaces, and water. Recently, far-UVC radiation (222 nm) emitted by KrCl* (krypton-chloride) excimer lamps have been recommended for disinfecting high-risk public spaces to reduce the presence and transmission of infectious viruses owing to limited human health exposure risks as compared to germicidal UVC (254 nm). In this study, the UVC inactivation performances of individual filtered KrCl* excimer lamp (222 nm) and germicidal UVC lamp (254 nm) were determined against four viruses, bacteriophages MS2, Phi6, M13, and T4, having different genome compositions (ssRNA, dsRNA, ssDNA and dsDNA, respectively) and shapes (i.e., spherical (Phi6), linear (M13), and icosahedral (MS2 and T4)). Here, the disinfection efficacies of filtered KrCl* excimer lamp (222 nm) and germicidal UVC lamp (254 nm) were evaluated for highly concentrated virus droplets that mimic the virus-laden droplets released from the infected person and deposited on surfaces as fomites. Filtered KrCl* excimer (222 nm) showed significantly better inactivation against all viruses having different genome compositions and structures compared to germicidal UVC (254 nm). The obtained sensitivity against the filtered KrCl* excimer (222 nm) was found to be in the order, T4 > M13 > Phi6 > MS2 whereas for the germicidal UVC (254 nm) it was T4 > M13 > MS2 > Phi6. These results provide a strong basis to promote the use of filtered KrCl* excimer lamps (222 nm) in disinfecting contagious viruses and to limit the associated disease spread in public places and other high-risk areas.

Overlooked Generation of Reactive Oxidative Species from Water and Dioxygen by Far UV Light

Far UV light at 222 nm (UV222) is gaining much attention for efficient water purification in UV222 irradiation and UV222-based advanced oxidation processes (AOPs). The direct photolysis of pollutants is regraded to be their major removal mechanism by a sole UV222 treatment. However, this paper reports the important roles of reactive oxidative species (ROS) generated from dioxygen and water under only UV222 radiation. Multiple ROSs are identified, including hydroxyl radical (HO·), singlet oxygen (1O2), superoxide radical anion (·O2-), and ozone (O3). HO· is the major ROS for the degradation of 18 organic micropollutants under UV222 radiation, with an observed quantum yield of 0.447 and the concentration of 10-13 M at pH 7. Dioxygen is the initial source of ROS, while water mainly serves as a medium to react with the photolytic intermediate of O3 (i.e., O(1D)) to form HO·. Water matrix components of HCO3- and natural organic matter can inhibit the HO· concentration, whereas NO3- significantly enhances it. In drinking water, UV222 alone removes 18 micropollutants more efficiently than the typical UV254/H2O2 AOP (150 μM), with reduced energy consumption. This study discloses a novel mechanism of ROS generation in UV222 irradiation and underscores UV222 as an emerging chemical-free AOP for water purification.

Quantifying the effects of chlorine disinfection on microplastics by time-resolved inductively coupled plasma-mass spectrometry

Using current water treatment systems, significant amounts of microplastics (MPs) are passing through and being released into the aquatic environment. However, we do not clearly know what effects disinfection processes have had on these particles. In this study, we applied inductively coupled plasma-mass spectrometry (ICP-MS) operating in time-resolved analysis (TRA) mode for quantifying changes in the chlorine (Cl) content of MPs under a variety of water treatment scenarios. Our results illustrated that time-resolved ICP-MS offers a potential method for sensitive and direct analysis of Cl content, including Cl mass and chlorine association (%Cl/C), of discrete particles in the MP suspension by the fast sequential measurements of signals from 35Cl1H2 and 12C1H. Our research, across various water treatment scenarios, also showed that polystyrene (PS) MPs exhibited greater reactivity to Cl disinfectant after being pre-disinfected with UV light and in mildly acidic to neutral pH environments. It is noteworthy that about half of the particles in MP suspension exposed to 10 mg Cl2/L, a typical Cl dose applied in water treatment, were chlorinated, and had a Cl content comparable to that of particles subjected to extreme conditions. Of even greater concern is the fact that our cell viability tests revealed that chlorinated MPs induced considerably higher rates of cell death in both human A549 and Caco-2 cells, and that the effects were Cl dose- and polymer type-dependent. Overall, this study demonstrates the potential of time-resolved ICP-MS as a valuable technique for quantifying the Cl content of MP particles, which is crucial to assessing the fate and transformation of MPs in our water supply and treatment systems.

Biofilm inactivation using LED systems emitting germicidal UV and antimicrobial blue light

Biofilms have been widely detected in water distribution and water storage systems posing potential risks to drinking water safety by harboring and shedding pathogens. Light-based disinfection methods, such as germicidal ultraviolet (UV) and antimicrobial blue light (aBL), could serve as non-chemical alternatives for biofilm control. This study investigated the inactivation of pure-culture Pseudomonas aeruginosa biofilms and mixed-culture biofilms using three distinct light-based disinfection methods: a low-pressure (LP) UV lamp emitting at 254 nm, a UV light emitting diode (LED) at 270 nm, and an aBL LED at 405 nm. The biofilms were developed on three commonly used materials including polycarbonate (PC), polytetrafluoroethylene (PTFE), and polyvinyl chloride (PVC), to assess the impact of surface characteristics on light-based biofilm inactivation. Our findings show that all selected devices can effectively inactivate pure-culture and mixed-culture biofilms. While both UV devices (LP UV lamp and UV LED) provided significant inactivation at lower fluences (>1 log reduction at 20 mJ/cm2), aBL LED achieved significant inactivation at higher fluences for pure culture (maximum log reduction of 3.8 ± 0.5 at > 200,000 mJ/cm2). Inactivation performance also varied with surface materials, likely attributed to different surface properties including roughness, hydrophobicity, and surface charge. This study provides important information on using light-based technologies for biofilm control and highlights the effect of surface materials on their inactivation performance.

A critical review of ultra-violet light emitting diodes as a one water disinfection technology

UV light emitting diode (LED) disinfection technologies have advanced over the last decade and expanded the design space for applications in point of use, industrial, and now full-scale water treatment. This literature review examines the progression of UV LED technologies from 2007 to 2023 using key features such as total optical power, price, and wall-plug efficiency. The review found that optical power is increasing while the price per Watt is decreasing; however, the wall plug energy (WPE) is slowly improving over the last decade. These factors govern the feasibility of many UV LEDs applications and establish the current state of the art for these technologies. An analysis of inactivation rate constants for low-pressure, medium-pressure, and UV LED sources was undertaken and provides a comprehensive view of how current UV LED technologies compare to traditional technologies. This comparison found that UV LEDs perform comparably vs conventional UV technologies when disinfecting bacteria and viruses. Furthermore, comparison of reported reduction equivalent fluences for UV LED flow-through reactors at the bench-, pilot-, and full-scale were explored in this review, and it was found that LED treatment is becoming more effective at handling increased flowrates and has been proven to work at full-scale. UV LEDs do however require additional research into the impacts of water matrices at different wavelengths and the impact that each available LED wavelength has on disinfection. Overall, this work provides a broad assessment of UV disinfection technologies and serves as a state-of-the-art reference document for those who are interested in understanding this rapidly developing technology.

UV LED wastewater disinfection: The future is upon us

The world's first full-scale, 280 nm UV LED reactor for wastewater disinfection was tested at flows of 545 and 817 m3 day-1. The system achieved a > 3 average log reduction of total coliform at 545 m3 day-1 and the 817 m3 day-1 flow rate achieved over a > 2.5 average log reduction for all operational conditions. The delivered fluence of the full-scale system ranged from 28 to 148 mJ cm-2 and aligns with a UV auditing study that was conducted prior to the installation of the wastewater reactor. These results benchmark the performance that can be achieved by UV LED disinfection and further connect bench-scale disinfection results with full-scale performance. The approach established in this manuscript provides a novel tool for utilities when considering emerging UV disinfection technologies. In summary, this study establishes that UV LEDs are an effective wastewater disinfectant at-scale and are comparable to conventional low-pressure UV systems. This is the first instance where the efficacy of UV LEDs for municipal wastewater disinfection has been demonstrated using a large-scale installation at a functioning wastewater facility.

Sunlight-triggered prebiotic nanomotors for inhibition and elimination of pathogen and biofilm in aquatic environment

Pathogen contamination in drinking water sources causes waterborne infectious diseases, seriously threatening human health. Nowadays, stimuli-responsive self-propelled nanomotors are appealing therapeutic agents for antibacterial therapy in vivo. However, achieving water disinfection using these nanobots is still a great challenge. Herein, we report on prebiotic galactooligosaccharide-based nanomotors for sunlight-regulated water disinfection. The nanomotors can utilize galactooligosaccharide-based N-nitrosamines as sunlight-responsive fuels for the spontaneous production of antibacterial nitric oxide. Such a solar-to-chemical energy conversion would power the nanomotors for self-diffusiophoresis, which could promote the diffusion of the nanomotors in water and their penetration in the biofilm, significantly enhancing the inhibition and elimination of the pathogens and their biofilms in aquatic environments. After water treatments, the prebiotic-based residual disinfectants can be selectively utilized by beneficial bacteria to effectively relieve safety risks to the environment and human health. The low-energy-cost, green and potent antibacterial nanobots show promising potential in water disinfection.

Ultraviolet technology application in urban water supply and wastewater treatment in China: Issues, challenges and future directions

This study thoroughly explores the application of Ultraviolet (UV) water treatment technology in urban wastewater treatment and water supply in China, highlighting its crucial role in enhancing water quality safety. UV technology, with its environmentally friendly and low-carbon characteristics, is deemed more in line with the demands of sustainable development compared to traditional chemical disinfection methods. The widespread application of UV technology in urban wastewater treatment in China, particularly in the context of urban sewage treatment, is examined. However, to better promote and apply UV technology, there is a need to deepen the understanding of this technology and its application among a broad base of users and design units. The importance of gaining in-depth knowledge about the performance of UV water treatment equipment, the design calculation basis, and operational considerations, as well as the ongoing development of relevant standards, is underscored to ensure that the equipment used in projects complies with engineering design and production requirements. Furthermore, the positive trend of UV technology in the field of advanced oxidation, indicating a promising trajectory for engineering applications, is pointed out. Regarding the prospects of industrial development, a thorough analysis is conducted in the article, emphasizing the necessity for all stakeholders to collaborate and adopt a multi-level approach to promote the sustainable development and application of UV water treatment technology. This collaborative effort is crucial for providing effective safeguards for China's environment, ecology, and human health.

Reinforcing Feedbacks for Sustainable Implementation of Rural Drinking-Water Treatment Technology

Progress toward universal access to safe drinking water depends on rural water service delivery models that incorporate water safety management. Water supplies of all types have high rates of fecal contamination unless water safety risks are actively managed through water source protection, treatment, distribution, and storage. Recognizing the role of treatment within this broader risk-based framework, this study focuses on the implementation of passive chlorination and ultraviolet (UV) disinfection technologies in rural settings. These technologies can reduce the health risk from microbiological contaminants in drinking water; however, technology-focused treatment interventions have had limited sustainability in rural settings. This study examines the requirements for sustainable implementation of rural water treatment through qualitative content analysis of 26 key informant interviews, representing passive chlorination and UV disinfection projects in rural areas in South America, Africa, and Asia. The analysis is aligned with the RE-AIM framework and delivers insight into 18 principal enablers and barriers to rural water treatment sustainability. Analysis of the interrelationships among these factors identifies leverage points and encourages fit-for-purpose intervention design reinforced by collaboration between facilitating actors through hybrid service delivery models. Further work should prioritize health impact evidence, water quality reporting guidance, and technological capabilities that optimize trade-offs in fit-for-purpose treatment design.

Optimizing radical yield from free chlorine with tailored UV light emitting diode emission spectra

Novel UV sources, which do not contain mercury, provide the opportunity for enhancement of current oxidation technologies through spectral optimization, minimizing inefficiencies that currently limit conventional technology. Wastewater reuse is the primary full-scale application of UV advanced oxidation processes (AOPs) in practice but any background absorbance and the low molar absorption by conventional radical promoters (hydrogen peroxide) have historically limited their system efficiency, resulting in the underutilization of photons in a reactor. This bench-scale research evaluated use of longer wavelength UV light emitting diodes (265, 280, and 300 nm) matched with free chlorine to optimize the utilization of photons for advanced oxidation. Free chlorine possesses large absorption bands in the 280 to 300 nm range in basic pH waters which are common in carbon-based reuse and was used to experimentally verify quantum yields of hydroxyl radical generation across the UV LED peak emission wavelengths. pH- and wavelength-dependent fluence-based rate constants were experimentally derived using Nitrobenzene and Benzoic acid as probe compounds and evaluated to determine the contribution of the hydroxyl and chlorine radical. Reclaimed water taken from various advanced treatment steps was treated with this UV LED AOP to investigate how background absorbance affects radical generation and contaminant transformation kinetics. In addition, alternative performance metrics to evaluate hydroxyl radical production at different incident fluence rates and different rates of photon absorption at unique wavelengths across varying background UV absorbance levels were assessed.

Establishment and inactivation of mono-species biofilm in a semipilot-scale water distribution system using nanocomposite of silver nanoparticles/montmorillonite loaded cationic chitosan

This study presents a novel approach in the synthesis and characterization of nanocomposites comprising cationic chitosan (CCS) blended with varying concentrations of silver nanoparticles/montmorillonite (AgNPs/MMT). AgNPs/MMT was synthesized using soluble starch as a reducing and stabilizing agent. Subsequently, nanocomposites, namely CCS/AgMMT-0, CCS/AgMMT-0.5, CCS/AgMMT-1.5, and CCS/AgMMT-2.5, were developed by blending 2.5 g of CCS with 0, 0.5, 1.5, and 2.5 g of AgNPs/MMT, respectively, and the corresponding nanocomposites were prepared using ball milling technique. Transmission electron microscopy (TEM) analysis revealed the formation of nanocomposites that exhibiting nearly spherical morphologies. Dynamic light scattering (DLS) measurements displayed average particle sizes of 1183 nm, 131 nm, 140 nm, and 188 nm for CCS/AgMMT-0, CCS/AgMMT-0.5, CCS/AgMMT-1.5, and CCS/AgMMT-2.5, respectively. The narrow polydispersity index (~0.5) indicated uniform particle size distributions across the nanocomposites, affirming monodispersity. Moreover, the zeta potential values exceeding 30 mV across all nanocomposites that confirmed their stability against agglomeration. Notably, CCS/AgMMT-2.5 nanocomposite exhibited potent antibacterial and antibiofilm properties against diverse pipeline materials. Findings showed that after 15 days of incubation, the highest populations of biofilm cells, Pseudomonas aeruginosa biofilm, developed over UPVC, MDPE, DCI, and SS, with corresponding HPCs of 4.79, 6.38, 8.81, and 7.24 CFU/cm2. The highest cell densities of Enterococcus faecalis biofilm in the identical situation were 4.19, 5.89, 8.12, and 6.9 CFU/cm2. The nanocomposite CCS/AgMMT-2.5 exhibited the largest measured zone of inhibition (ZOI) against both P. aeruginosa and E. faecalis, with measured ZOI values of 19 ± 0.65 and 17 ± 0.21 mm, respectively. Remarkably, the research indicates that the youngest biofilm exhibited the most notable rate of inactivation when exposed to a dose of 150 mg/L, in comparison to the mature biofilm. These such informative findings could offer valuable insights into the development of effective antibiofilm agents and materials applicable in diverse sectors such as water treatment facilities, medical devices, and industrial pipelines.

Singlet oxygen: Properties, generation, detection, and environmental applications

Singlet oxygen (1O2) is molecular oxygen in the excited state with high energy and electrophilic properties. It is widely found in nature, and its important role is gradually extending from chemical syntheses and medical techniques to environmental remediation. However, there exist ambiguities and controversies regarding detection methods, generation pathways, and reaction mechanisms which have hindered the understanding and applications of 1O2. For example, the inaccurate detection of 1O2 has led to an overestimation of its role in pollutant degradation. The difficulty in detecting multiple intermediate species obscures the mechanism of 1O2 production. The applications of 1O2 in environmental remediation have also not been comprehensively commented on. To fill these knowledge gaps, this paper systematically discussed the properties and generation of 1O2, reviewed the state-of-the-art detection methods for 1O2 and long-standing controversies in the catalytic systems. Future opportunities and challenges were also discussed regarding the applications of 1O2 in the degradation of pollutants dissolved in water and volatilized in the atmosphere, the disinfection of drinking water, the gas/solid sterilization, and the self-cleaning of filter membranes. This review is expected to provide a better understanding of 1O2-based advanced oxidation processes and practical applications in the environmental protection of 1O2.

Rapid Inactivation of Fungal Spores in Drinking Water by Far-UVC Photolysis of Free Chlorine

Effective and affordable disinfection technology is one key to achieving Sustainable Development Goal 6. In this work, we develop a process by integrating Far-UVC irradiation at 222 nm with free chlorine (UV222/chlorine) for rapid inactivation of the chlorine-resistant and opportunistic Aspergillus niger spores in drinking water. The UV222/chlorine process achieves a 5.0-log inactivation of the A. niger spores at a chlorine dosage of 3.0 mg L-1 and a UV fluence of 30 mJ cm-2 in deionized water, tap water, and surface water. The inactivation rate constant of the spores by the UV222/chlorine process is 0.55 min-1, which is 4.6-fold, 5.5-fold, and 1.8-fold, respectively, higher than those of the UV222 alone, chlorination alone, and the conventional UV254/chlorine process under comparable conditions. The more efficient inactivation by the UV222/chlorine process is mainly attributed to the enhanced generation of reactive chlorine species (e.g., 6.7 × 10-15 M of Cl•) instead of hydroxyl radicals from UV222 photolysis of chlorine, which is verified through both experiments and a kinetic model. We further demonstrate that UV222 photolysis damages the membrane integrity and benefits the penetration of chlorine and radicals into cells for inactivation. The merits of the UV222/chlorine process over the UV254/chlorine process also include the more effective inhibition of the photoreactivation of the spores after disinfection and the lower formation of chlorinated disinfection byproducts and toxicity.

Comparison of Legionella pneumophila and Pseudomonas fluorescens Quantification Methods for Assessing UV LED Disinfection

This study assesses the efficacy of ultraviolet light-emitting diodes (UV LEDs) for deactivating Legionella pneumophila (pure culture) and Pseudomonas fluorescens (pure culture and biofilms) on relevant drinking water distribution system surfaces (cast iron and stainless steel). UV LED treatment at 280 nm demonstrated superior performance compared to that at 365 nm, achieving a 4.8 log reduction value (LRV) for P. fluorescens pure cultures and, for biofilms, 4.02 LRV for stainless steel and 2.96 LRV for cast iron at 280 nm. Conversely, the results were less effective at 365 nm, with suspected photolytic reactions on cast iron. Quantification of L. pneumophila yielded varying results: 4 LRV using standard plate counts, 1.8 LRV with Legiolert, and 1 LRV with quantitative polymerase chain reaction at 280 nm, while the results were less than 1.5 LRV at 365 nm. This study provides insights into managing opportunistic pathogens and biofilms, emphasizing the need for improved quantification tools to better assess treatment efficacy.

Mixed chlorine/chloramines in disinfected water and drinking water distribution systems (DWDSs): A critical review

Mixed chlorine/chloramines are commonly occurring in real drinking water distribution systems (DWDSs) but often overlooked. This review provides a comprehensive overview of the occurrences, characteristics, analysis methods, and control strategies of mixed chlorine/chloramines in DWDSs. The characteristics of mixed chlorine/chloramine species are summarized for treated water in drinking water treatment plants (DWTPs), secondary disinfection facilities, and DWDSs where different disinfectants could be blended. The key to differentiating and quantifying mixed chlorine/chloramine species is to separate organic chloramines (OCs) from di/tri-chloramines and overcome certain interferences. The complex interactions between water matrixes and chlorine/chloramine species could accelerate pipeline corrosions, enhance emerging disinfection by-products risks, lead to off-flavors in drinking water, and induce bio-instability issues (such as nitrification, microorganism regrowth, and promotion of horizontal gene-transfers). Three promising strategies for alleviating mixed chlorine/chloramine species are recommended, which include (i) removing precursors intensively and reconditioning the treated water, (ii) combining UV irradiation to eliminate undesired chlorine/chloramines species, and (iii) strengthening monitoring, operation, and maintenance management of DWDSs. Finally, the challenges for gaining insights into the mechanisms of mixed chlorine/chloramine species conversion are discussed and promising research directions are proposed.

A UV-Resistant Heterogeneous Wettability-Patterned Surface

Preparing UV-resistant heterogeneous wettability patterns is critical for the practical application of surfaces with heterogeneous wettability. However, combining UV-resistant superhydrophobic and superhydrophilic materials on heterogeneous surfaces is challenging. Inspired by the structure of cell membranes, a UV-resistant heterogeneous wettability-patterned surface (UPS) is designed via laser ablation of the coating of multilayer structures. UV-resistant superhydrophobic silica patterns can be created in situ on surfaces covered with superhydrophilic TiO2 nanoparticles. The UV resistance time of the UPS with a TiO2 -based surface is more than two orders of magnitude higher than that obtained with other surface molecular modification methods that require a mask. The cell-membrane-like structure of the UPS regulates the migration of internal siloxane chain segments in the hydrophilic and hydrophobic regions of the surface. The UPS enables efficient patterning of functional materials under UV irradiation, controlling the wetting behavior of liquids in open-air systems. Furthermore, its heterogeneous wettability remains stable even after 50 h of intense UV irradiation (365 nm, 500 mW cm-2 ). These UV-resistant heterogeneous wettability patterned surfaces will likely be applied in microfluidics, cell culture, energy conversion, and water collection in the future.

Field demonstration of UV-LED disinfection at small and decentralized water facilities

Ultraviolet light-emitting diodes (UV-LED) can be a good option for disinfecting water in small and decentralized facilities. A flow-through UV-LED disinfection module was evaluated at three remote locations in Japan. The disinfection efficiency of the module was monitored for over one year, targeting indigenous Escherichia coli, total coliforms, standard plate count, and heterotrophic plate count (HPC) bacteria. The physicochemical parameters of the source water, including UV transmittance (UVT), were also monitored to understand their natural fluctuation and impacts on UV disinfection. Overall, the UV-LED module showed efficient disinfection at all locations, achieving 2.7 log inactivation of E. coli at 30 L/min in a community-based water supply. HPC inactivation did not significantly differ among the three test sites (p > 0.01). One test site experienced a decrease in HPC inactivation after 10 months, whereas the other two sites did not show performance deterioration after one year. HPC inactivation was not correlated with the UVT of source water at any location, implying the difficulty to use UVT as a single parameter to predict disinfection efficiency in practical applications. This study demonstrates the effectiveness of UV-LED technology for water disinfection in small and decentralized water supply systems.

Self-cooling water disinfection reactor with ultraviolet-C light-emitting diodes

The use of ultraviolet-C (UV-C) light-emitting diodes (LEDs) as a water sterilization light source poses a serious challenge in heat dissipation. High junction temperatures reduce the radiant power and lifespan of UV-C LEDs. In this study, a novel self-cooling water disinfection reactor was developed to dissipate Joule heat from UV-C LEDs. The advantage of the self-cooling design is that cooling can be achieved without requiring additional power consumption and cooling liquid. The effects of the water flow rate and driving current of UV-C LEDs on the sterilization of Escherichia coli were investigated for a traditional flow-through reactor and a reactor with self-cooling. The experimental results indicated that an increase in driving current resulted in a considerable increase in the LED temperature of the flow-through reactor but only a marginal increase in the LED temperature of the self-cooling reactor. Under a driving current of 150 mA, the LED temperature of the self-cooling reactor was 55.5°C less than that of the flow-through reactor. The time required by the self-cooling reactor to reach the steady state decreased as the water flow rate increased. Under a flow rate of 100 mL/min, the self-cooling reactor reached the steady state within 62 and 70 s when the driving current was 100 and 150 mA, respectively. Moreover, the average irradiance and inactivation values of the self-cooling reactor were up to 16.5% and 26.0% higher than those of the flow-through reactor, respectively.

Dose-Response Behavior of Pathogens and Surrogate Microorganisms across the Ultraviolet-C Spectrum: Inactivation Efficiencies, Action Spectra, and Mechanisms

The dose-response behavior of pathogens and inactivation mechanisms by UV-LEDs and excimer lamps remains unclear. This study used low-pressure (LP) UV lamps, UV-LEDs with different peak wavelengths, and a 222 nm krypton chlorine (KrCl) excimer lamp to inactivate six microorganisms and to investigate their UV sensitivities and electrical energy efficiencies. The 265 nm UV-LED had the highest inactivation rates (0.47-0.61 cm2/mJ) for all tested bacteria. The bacterial sensitivity strongly fitted the absorption curve of nucleic acids at wavelengths of 200-300 nm; however, indirect damage induced by reactive oxygen species (ROS) was the leading cause of bacterial inactivation under 222 nm UV irradiation. In addition, the guanine and cytosine (GC) content and cell wall constituents of bacteria affect inactivation efficiency. The inactivation rate constant of Phi6 (0.13 ± 0.002 cm2/mJ) at 222 nm due to lipid envelope damage was significantly higher than other UVC (0.006-0.035 cm2/mJ). To achieve 2log reduction, the LP UV lamp had the best electrical energy efficiency (required less energy, average 0.02 kWh/m3) followed by 222 nm KrCl excimer lamp (0.14 kWh/m3) and 285 nm UV-LED (0.49 kWh/m3).

Improved disinfection performance for 280 nm LEDs over 254 nm low-pressure UV lamps in community wastewater

Ultraviolet (UV) disinfection has been incorporated into both drinking water and wastewater treatment processes for several decades; however, it comes with negative environmental consequences such as high energy demands and the use of mercury. Understanding how to scale and build climate responsive technologies is key in fulfilling the intersection of UN Sustainable Development Goals 6 and 13. One technology that addresses the drawbacks of conventional wastewater UV disinfection systems, while providing a climate responsive solution, is UV light emitting diodes (LEDs). The objective of this study was to compare performance of bench-scale 280 nm UV LEDs to bench-scale low pressure (LP) lamps and full-scale UV treated wastewater samples. Results from the study demonstrated that the UV LED system provides a robust treatment that outperformed LP systems at the bench-scale. A comparison of relative energy consumptions of the UV LED system at 20 mJ cm^-2 and LP system at 30 and 40 mJ cm^-2 was completed. Based on current projections for wall plug efficiencies (WPE) of UV LED it is expected that the energy consumption of LED reactors will be on par or lower compared to the LP systems by 2025. This study determined that, at a WPE of 20%, the equivalent UV LED system would lead to a 24.6% and 43.4% reduction in power consumption for the 30 and 40 mJ cm^-2 scenarios, respectively.

The Minus Approach Can Redefine the Standard of Practice of Drinking Water Treatment

Chlorine-based disinfection for drinking water treatment (DWT) was one of the 20th century's great public health achievements, as it substantially reduced the risk of acute microbial waterborne disease. However, today's chlorinated drinking water is not unambiguously safe; trace levels of regulated and unregulated disinfection byproducts (DBPs), and other known, unknown, and emerging contaminants (KUECs), present chronic risks that make them essential removal targets. Because conventional chemical-based DWT processes do little to remove DBPs or KUECs, alternative approaches are needed to minimize risks by removing DBP precursors and KUECs that are ubiquitous in water supplies. We present the "Minus Approach" as a toolbox of practices and technologies to mitigate KUECs and DBPs without compromising microbiological safety. The Minus Approach reduces problem-causing chemical addition treatment (i.e., the conventional "Plus Approach") by producing biologically stable water containing pathogens at levels having negligible human health risk and substantially lower concentrations of KUECs and DBPs. Aside from ozonation, the Minus Approach avoids primary chemical-based coagulants, disinfectants, and advanced oxidation processes. The Minus Approach focuses on bank filtration, biofiltration, adsorption, and membranes to biologically and physically remove DBP precursors, KUECs, and pathogens; consequently, water purveyors can use ultraviolet light at key locations in conjunction with smaller dosages of secondary chemical disinfectants to minimize microbial regrowth in distribution systems. We describe how the Minus Approach contrasts with the conventional Plus Approach, integrates with artificial intelligence, and can ultimately improve the sustainability performance of water treatment. Finally, we consider barriers to adoption of the Minus Approach.

The effects of racism, social exclusion, and discrimination on achieving universal safe water and sanitation in high-income countries

Drinking water and sanitation services in high-income countries typically bring widespread health and other benefits to their populations. Yet gaps in this essential public health infrastructure persist, driven by structural inequalities, racism, poverty, housing instability, migration, climate change, insufficient continued investment, and poor planning. Although the burden of disease attributable to these gaps is mostly uncharacterised in high-income settings, case studies from marginalised communities and data from targeted studies of microbial and chemical contaminants underscore the need for continued investment to realise the human rights to water and sanitation. Delivering on these rights requires: applying a systems approach to the problems; accessible, disaggregated data; new approaches to service provision that centre communities and groups without consistent access; and actionable policies that recognise safe water and sanitation provision as an obligation of government, regardless of factors such as race, ethnicity, gender, ability to pay, citizenship status, disability, land tenure, or property rights.

A review of long-term change in surface water natural organic matter concentration in the northern hemisphere and the implications for drinking water treatment

Reduced atmospheric acid deposition has given rise to recovery from acidification - defined as increasing pH, acid neutralization capacity (ANC), or alkalinity in surface waters. Strong evidence of recovery has been reported across North America and Europe, driving chemical responses. The primary chemical responses identified in this review were increasing concentration and changing character of natural organic matter (NOM) towards predominantly hydrophobic nature. The concentration of NOM also influenced trace metal cycling as many browning surface waters also reported increases in Fe and Al. Further, climate change and other factors (e.g., changing land use) act in concert with reductions in atmospheric deposition to contribute to widespread browning and will have a more pronounced effect as deposition stabilizes. The observed water quality trends have presented challenges for drinking water treatment (e.g., increased chemical dosing, poor filter operations, formation of disinfection by-products) and many facilities may be under designed as a result. This comprehensive review has identified key research areas to be addressed, including 1) a need for comprehensive monitoring programs (e.g., larger timescales; consistency in measurements) to assess climate change impacts on recovery responses and NOM dynamics, and 2) a better understanding of drinking water treatment vulnerabilities and the transition towards robust treatment technologies and solutions that can adapt to climate change and other drivers of changing water quality.

Deactivating environmental strains of Escherichia coli, Enterococcus faecalis and Clostridium perfringens from a real wastewater effluent using UV-LEDs

Environmental bacteria strains are known to be more resistant but studies on UV-LEDs are scarce, especially for Clostridium perfringens and Enterococcus faecalis. UV-LEDs of different wavelengths (268 nm, 279 nm and 307 nm) have been used for treating real wastewater from the effluent of the municipal plant in Linares (Spain), with real organic matter content, for E. coli, Enterococcus faecalis and Clostridium perfringens disinfection. Experimental results demonstrate that 268 nm was the most effective wavelength for inactivation of the three different bacteria strains: E. coli showed an inactivation rate of 0.561 at 268 nm vs. 0.245 at 279 nm and 0.0029 for 307 nm; E. faecalis inactivation rate was 0.313 at 268 nm, 0.231 at 279 nm and 0.0023 at 307 nm; and C. perfringens inactivation rate was 0.084 at 268 nm, 0.033 at 279 nm and 6.9e-4 at 307 nm. In general, 307 nm wavelength showed a significantly lower inactivation rate so it would not be recommended for practical applications. C. Perfringens required higher UV doses and longer times to achieve complete inactivation.

Recent advances in sterilization and disinfection technology: A review

Sterilization and disinfection of pollutants and microorganisms have been extensively studied in order to address the problem of environmental contamination, which is a crucial issue for public health and economics. Various form of hazardous materials/pollutants including microorganisms and harmful gases are released into the environment that enter into the human body either through inhalation, adsorption or ingestion. The human death rate rises due to various respiratory ailments, strokes, lung cancer, and heart disorders related with these pollutants. Hence, it is essential to control the environmental pollution by applying economical and effective sterilization and disinfections techniques to save life. In general, numerous forms of traditional physical and chemical sterilization and disinfection treatments, such as dry and moist heat, radiation, filtration, ethylene oxide, ozone, hydrogen peroxide, etc. are known along with advanced techniques. In this review we summarized both advanced and conventional techniques of sterilization and disinfection along with their uses and mode of action. This review gives the knowledge about the advantages, disadvantages of both the methods comparatively. Despite, the effective solution given by the advanced sterilization and disinfection technology, joint technologies of sterilization and disinfection has proven to be more effective innovation to protect the indoor and outdoor environments.

Inactivation methods for human coronavirus 229E on various food-contact surfaces and foods

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the cause of the COVID-19 outbreaks, is transmitted by respiratory droplets and has become a life-threatening viral pandemic worldwide. The aim of this study was to evaluate the effects of different chemical (chlorine dioxide [ClO2] and peroxyacetic acid [PAA]) and physical (ultraviolet [UV]-C irradiation) inactivation methods on various food-contact surfaces (stainless steel [SS] and polypropylene [PP]) and foods (lettuce, chicken breast, and salmon) contaminated with human coronavirus 229E (HCoV-229E). Treatments with the maximum concentration of ClO2 (500 ppm) and PAA (200 ppm) for 5 min achieved >99.9% inactivation on SS and PP. At 200 ppm ClO2 for 1 min on lettuce, chicken breast, and salmon, the HCoV-229E titers were 1.19, 3.54, and 3.97 log10 TCID50/mL, respectively. Exposure (5 min) to 80 ppm PAA achieved 1.68 log10 reduction on lettuce, and 2.03 and 1.43 log10 reductions on chicken breast and salmon, respectively, treated with 1500 ppm PAA. In the carrier tests, HCoV-229E titers on food-contact surfaces were significantly decreased (p < 0.05) with increased doses of UV-C (0-60 mJ/cm2) and not detected at the maximum UV-C dose (Detection limit: 1.0 log10 TCID50/coupon). The UV-C dose of 900 mJ/cm2 proved more effective on chicken breast (>2 log10 reduction) than on lettuce and salmon (>1 log10 reduction). However, there were no quality changes (p > 0.05) in food samples after inactivation treatments except the maximum PAA concentration (5 min) and the UV-C dose (1800 mJ/cm2).

Inhibition of biofouling on reverse osmosis membrane surfaces by germicidal ultraviolet light side-emitting optical fibers

Biofouling of membrane surfaces poses significant operational challenges and costs for desalination and wastewater reuse applications. Ultraviolet (UV) light can control biofilms while reducing chemical usage and disinfection by-products, but light deliveries to membrane surfaces in spiral wound geometries has been a daunting challenge. Thin and flexible nano-enabled side-emitting optical fibers (SEOFs) are novel light delivery devices that enable disinfection or photocatalytic oxidation by radiating UV light from light-emitting diodes (LEDs). We envision SEOFs as an active membrane spacer to mitigate biofilm formation on reverse osmosis (RO) membranes. A lab-scale RO membrane apparatus equipped with SEOFs allowed comparison of UV-A (photocatalysis-enabled) versus UV-C (direct photolysis disinfection). Compared against systems without any light exposure, systems with UV-C light formed thinner-but denser-biofilms, prevented permeate flux declines due to biofouling, and maintained the highest salt rejection. Results were corroborated by in-situ optical coherence tomography and ex-situ measurements of biofilm growth on the membranes. Transcriptomic analysis showed that UV-C SEOFs down-regulated quorum sensing and surface attachment genes. In contrast, UV-A SEOFs upregulated quorum sensing, surface attachment, and oxidative stress genes, resulting in higher extracellular polymeric substances (EPS) accumulation on membrane surfaces. Overall, SEOFs that deliver a low fluence of UV-C light onto membrane surfaces are a promising non-chemical approach for mitigating biofouling formation on RO membranes.

Passive In-Line Chlorination for Drinking Water Disinfection: A Critical Review

The world is not on track to meet Sustainable Development Goal 6.1 to provide universal access to safely managed drinking water by 2030. Removal of priority microbial contaminants by disinfection is one aspect of ensuring water is safely managed. Passive chlorination (also called in-line chlorination) represents one approach to disinfecting drinking water before or at the point of collection (POC), without requiring daily user input or electricity. In contrast to manual household chlorination methods typically implemented at the point of use (POU), passive chlorinators can reduce the user burden for chlorine dosing and enable treatment at scales ranging from communities to small municipalities. In this review, we synthesized evidence from 27 evaluations of passive chlorinators (in 19 articles, 3 NGO reports, and 5 theses) conducted across 16 countries in communities, schools, health care facilities, and refugee camps. Of the 27 passive chlorinators we identified, the majority (22/27) were solid tablet or granular chlorine dosers, and the remaining devices were liquid chlorine dosers. We identified the following research priorities to address existing barriers to scaled deployment of passive chlorinators: (i) strengthening local chlorine supply chains through decentralized liquid chlorine production, (ii) validating context-specific business models and financial sustainability, (iii) leveraging remote monitoring and sensing tools to monitor real-time chlorine levels and potential system failures, and (iv) designing handpump-compatible passive chlorinators to serve the many communities reliant on handpumps as a primary drinking water source. We also propose a set of reporting indicators for future studies to facilitate standardized evaluations of the technical performance and financial sustainability of passive chlorinators. In addition, we discuss the limitations of chlorine-based disinfection and recognize the importance of addressing chemical contamination in drinking water supplies. Passive chlorinators deployed and managed at-scale have the potential to elevate the quality of existing accessible and available water services to meet "safely managed" requirements.

Inactivation of biofilm-bound bacterial cells using irradiation across UVC wavelengths

Opportunistic pathogens (OPs), such as Pseudomonas spp., Legionella spp., and mycobacteria, have been detected in biofilms in drinking water distribution systems and water storage tanks and pose potential risks to finished drinking water quality and safety. Emerging UV technologies, such as UV light emitting diodes (LEDs) and krypton chloride (KrCl*) excimers, could provide an alternative to chemical-based secondary disinfection (i.e., chlorine or chloramines) for controlling biofilm-bound OPs. UV systems offer long lifetimes, ability to select wavelength, small size with high power density, and limited-to-no disinfection by-product formation. In this study, inactivation of biofilm-bound Pseudomonas aeruginosa cells across different maturities was investigated using five UVC devices with different peak emission wavelengths, including a KrCl* excimer (222 nm), a low pressure mercury vapor lamp (254 nm), and three UV LEDs (260 nm, 270 nm, and 282 nm). The UV transmittance and absorbance through the biofilm structure was also documented for the first time using a unique approach. Our results show all UVC devices can inactivate biofilm-bound P. aeruginosa cells up to a point, among which the UV LED with peak emission at 270 nm provided the best disinfection performance. UV sensitivities of biofilm-bound cells decreased with biofilm maturity and while initial rates of inactivation were high, no more than 1.5-2.5 log reduction was possible. Re-suspended biofilm bacteria in aqueous solution were highly sensitive to UV, reaching greater than 6 log reduction. UV shielding by biofilm constituents was observed and was likely one of the reasons for UV resistance but did not fully explain the difference in UV sensitivity between biofilm-bound cells versus planktonic cells. This study improves upon fundamental knowledge and provides guidance for innovative designs using emerging UV technologies for biofilm and pathogen control in water distribution systems.

Waterborne protozoan outbreaks: An update on the global, regional, and national prevalence from 2017 to 2020 and sources of contamination

The aim of this review is to identify the worldwide trend of waterborne protozoan outbreaks and how it varies between geographic regions during the period from 2017 to 2020. Data about waterborne protozoan outbreaks were gathered and stratified by continent, country, water source, and protozoan species associated with the outbreak. The highest prevalence of waterborne protozoan outbreaks was reported in developed countries. Out of 251 outbreaks reported worldwide during the studied period, 141, 51 and 24 outbreaks were recorded in the USA, UK, and New Zealand, respectively. These outbreaks were mainly associated with Cryptosporidium (192 outbreaks) and Giardia (48 outbreaks). Cyclospora cayetanensis, Dientamoebafragilis and Toxoplasma gondii were associated with 7 outbreaks. One outbreak was associated with each of Blastocystis hominis, Entamoeba histolytica, Microsporidia or Naegleria fowleri. This data suggests large discrepancies in the number of outbreaks reported between geographic regions, with most outbreaks recorded in developed countries. Differences in the prevalence of outbreaks between countries are likely attributed to the availability of diagnostic capabilities and surveillance programs to monitor water contamination with pathogenic protozoa. More attention and concerted efforts are required to improve water safety and to alleviate the impact of waterborne protozoan infections. Appropriate surveillance of water contamination with protozoa can enable public health officials to identify source of contamination and implement the necessary measures to limit transmission and prevent outbreaks.

Advances in application of ultraviolet irradiation for biofilm control in water and wastewater infrastructure

Biofilms are ubiquitous in aquatic environment. While so far, most of the ultraviolet (UV) disinfection studies focus on planktonic bacteria, and only limited attention has been given to UV irradiation on biofilms. To enrich this knowledge, the present paper reviews the up-to-date studies about applying UV to control biofilms in water and wastewater infrastructure. The development of UV light sources from the conventional mercury lamp to the light emitting diode (LED), and the resistance mechanisms of biofilms to UV are summarized, respectively. Then the feasibility to control biofilms with UV is discussed in terms of three technical routes: causing biofilm slough, inhibiting biofilm formation, and inactivating bacteria in the established biofilm. A comprehensive evaluation of the biofilm-targeted UV technologies currently used or potentially useful in water industry is provided as well, after comparative analyses on single/combined wavelengths, continuous/pulsed irradiation, and instant/chronic disinfection effects. UV LEDs are emerging as competitive light sources because of advantages such as possible selection of wavelengths, adjustable emitting mode and the designable configuration. They still, however, face challenges arising from the low wall plug efficiency and power output. At last, the implementation of the UV-based advanced oxidation processes in controlling biofilms on artificial surfaces is overviewed and their synergistic mechanisms are proposed, which further enlightens the prospective of UV in dealing with the biofilm issue in water infrastructure.

An electrochemical advanced oxidation process for the treatment of urban stormwater

Recharge of urban stormwater has often been limited by the high cost of land and concerns about contamination of groundwater. To provide a possible solution, we developed an electrochemical advanced oxidation system (UV/H₂O₂) that is compatible with high-capacity stormwater recharge systems (e.g., drywells). The system employed an air-diffusion cathode to generate a H₂O₂ stock solution (i.e., typically around 600 mM) prior to the storm event. The H₂O₂ stock solution was then metered into stormwater and converted into hydroxyl radical (•OH) by an ultraviolet lamp. The energy consumption for H₂O₂ generation was optimized by adjusting the applied current density and adding an inert salt (e.g., Na₂SO₄) to stormwater. H₂O₂ in the stock solution was unstable. By mixing the basic H₂O₂ containing catholyte and the acidic anolyte, the stability increased, enabling generation of the H₂O₂ stock solution up to three days prior the storm event with loss of less than 20% of the H₂O₂. Lab-scale experiments and a kinetic model were used to assess the feasibility of the full-scale advanced oxidation system. System performance decreased at elevated concentrations of dissolved organic carbon in stormwater, due to enhanced light reflection and backscattering at the water-air interface in the UV reactor, competition for UV light absorption with H₂O₂ and the tendency of organic matter to act as a •OH scavenger. The proposed system can be incorporated into drywells to remove greater than 90% of trace organic contaminants under typical operating conditions. The electrical energy per order of the system is estimated to range from 0.5 to 2 kWh/m³, depending on the dissolved organic carbon concentration.

Biofilm growth under continuous UVC irradiation: Quantitative effects of growth conditions and growth time on intensity response parameters

Biofilms can harbor a wide range of microorganisms, including opportunistic respiratory pathogens, and their establishment on engineered surfaces poses a risk to public health and industry. The emergence of compact germicidal ultraviolet light-emitting diodes (UV LEDs) may enable their incorporation into confined spaces to inhibit bacterial surface colonization on inaccessible surfaces, such as those in premise plumbing. Such applications necessitate knowledge of the quantitative response of biofilm growth rates to UV exposure on continuously irradiated surfaces. Herein, we performed experiments at varying flow cell temperatures in order to control baseline biofilm growth rates in the absence of UV; then, biofilm growth was compared under the same conditions but with simultaneous UVC irradiation. The inhibiting effect of UV irradiation on biofilm growth kinetics was diminished by more favorable growth conditions (higher temperature). Increasing the temperature by 10 °C resulted in an increase in biovolume by 193% under a UVC (254 nm) intensity of ∼60 µW/cm². We further fitted an existing intensity response model to the biofilm growth data and analyzed the effects of temperature on model parameters, which were consistent with a hypothesized shielding effect arising from the deposition of extracellular colloidal materials. The shielding effect was found to result in breakthrough behavior of irradiated biofilms after 48 h, wherein accumulation of shielding substances eventually enabled biofilm establishment at even relatively high irradiation intensities (102.3 µW/cm²). With respect to applications of UVC irradiation for biofilm prevention, these results imply that surfaces more prone to bacterial colonization require disproportionately higher-intensity UVC irradiation for prevention of biofilm establishment, and continuous surface irradiation may be inadequate as a sole intervention for biofilm prevention in many scenarios.

UV Inactivation of SARS-CoV-2 across the UVC Spectrum: KrCl* Excimer, Mercury-Vapor, and Light-Emitting-Diode (LED) Sources

Effective disinfection technology to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can help reduce viral transmission during the ongoing COVID-19 global pandemic and in the future. UV devices emitting UVC irradiation (200 to 280 nm) have proven to be effective for virus disinfection, but limited information is available for SARS-CoV-2 due to the safety requirements of testing, which is limited to biosafety level 3 (BSL3) laboratories. In this study, inactivation of SARS-CoV-2 in thin-film buffered aqueous solution (pH 7.4) was determined across UVC irradiation wavelengths of 222 to 282 nm from krypton chloride (KrCl*) excimers, a low-pressure mercury-vapor lamp, and two UVC light-emitting diodes. Our results show that all tested UVC devices can effectively inactivate SARS-CoV-2, among which the KrCl* excimer had the best disinfection performance (i.e., highest inactivation rate). The inactivation rate constants of SARS-CoV-2 across wavelengths are similar to those for murine hepatitis virus (MHV) from our previous investigation, suggesting that MHV can serve as a reliable surrogate of SARS-CoV-2 with a lower BSL requirement (BSL2) during UV disinfection tests. This study provides fundamental information on UVC's action on SARS-CoV-2 and guidance for achieving reliable disinfection performance with UVC devices. IMPORTANCE UV light is an effective tool to help stem the spread of respiratory viruses and protect public health in commercial, public, transportation, and health care settings. For effective use of UV, there is a need to determine the efficiency of different UV wavelengths in killing pathogens, specifically SARS-CoV-2, to support efforts to control the ongoing COVID-19 global pandemic and future coronavirus-caused respiratory virus pandemics. We found that SARS-CoV-2 can be inactivated effectively using a broad range of UVC wavelengths, and 222 nm provided the best disinfection performance. Interestingly, 222-nm irradiation has been found to be safe for human exposure up to thresholds that are beyond those effective for inactivating viruses. Therefore, applying UV light from KrCl* excimers in public spaces can effectively help reduce viral aerosol or surface-based transmissions.

Roles and Knowledge Gaps of Point-of-Use Technologies for Mitigating Health Risks from Disinfection Byproducts in Tap Water: A Critical Review

Due to rising concerns about water pollution and affordability, there is a rapidly-growing public acceptance and global market for a variety of point-of-use (POU) devices for domestic uses. However, the efficiencies and mechanisms of POU technologies for removing regulated and emerging disinfection byproducts (DBPs) are still not systematically known. To facilitate the development of this field, we summarized performance trends of four common technologies (i.e., boiling, adsorption, membrane filtration, and advanced oxidation) on mitigating preformed DBPs and identified knowledge gaps. The following highest priority knowledge gaps include: 1) data on DBP levels at the tap or cup in domestic applications; 2) certainty regarding the controls of DBPs by heating processes as DBPs may form and transform simultaneously; 3) standards to evaluate the performance of carbon-based materials on varying types of DBPs; 4) long-term information on the membrane performance in removing DBPs; 5) knowledge of DBPs' susceptibility toward advanced redox processes; 6) tools to monitor/predict the toxicity and diversity of DBPs formed in waters with varying precursors and when implementing different treatment technologies; and 7) social acceptance and regulatory frameworks of incorporating POU as a potential supplement to current centralized-treatment focused DBP control strategies. We conclude by identifying research needs necessary to assure POU systems protect the public against regulated and emerging DBPs.

Woven-Fiber Microfiltration (WFMF) and Ultraviolet Light Emitting Diodes (UV LEDs) for Treating Wastewater and Septic Tank Effluent

Decentralized wastewater treatment systems enable wastewater to be treated at the source for cleaner discharge into the environment, protecting public health while allowing for reuse for agricultural and other purposes. This study, conducted in Thailand, investigated a decentralized wastewater treatment system incorporating a physical and photochemical process. Domestic wastewater from a university campus and conventional septic tank effluent from a small community were filtered through a woven-fiber microfiltration (WFMF) membrane as pretreatment for ultraviolet (UV) disinfection. In domestic wastewater, WFMF reduced TSS (by 79.8%), turbidity (76.5%), COD (38.5%), and NO3 (41.4%), meeting Thailand irrigation standards for every parameter except BOD. In septic tank effluent, it did not meet Thailand irrigation standards, but reduced TSS (by 77.9%), COD (37.6%), and TKN (13.5%). Bacteria (total coliform and Escherichia coli) and viruses (MS2 bacteriophage) passing through the membrane were disinfected by flow-through UV reactors containing either a low-pressure mercury lamp or light-emitting diodes (LEDs) emitting an average peak wavelength of 276 nm. Despite challenging and variable water quality conditions (2% < UVT < 88%), disinfection was predictable across water types and flow rates for both UV sources using combined variable modeling, which enabled us to estimate log inactivation of other microorganisms. Following UV disinfection, wastewater quality met the WHO standards for unrestricted irrigation.

Inactivation of Coronaviruses and Phage Phi6 from Irradiation across UVC Wavelengths

Ultraviolet (UV) devices emitting UVC irradiation (200-280 nm) have proven to be effective for virus disinfection, especially on surfaces and in air, due to their rapid effectiveness and limited to no material corrosion. Numerous studies of UV-induced inactivation focused on nonenveloped viruses. Little is known about UVC action on enveloped viruses across UVC wavelengths. In this study, we determined inactivation efficiencies of two coronaviruses (ssRNA) and an enveloped dsRNA bacteriophage surrogate in buffered aqueous solution (pH 7.4) using five commonly available UVC devices that uniquely emit light at different wavelengths spanning 222 nm emitting krypton chloride (KrCl*) excimers to 282 nm emitting UVC LEDs. Our results show that enveloped viruses can be effectively inactivated using UVC devices, among which the KrCl* excimer had the best disinfection performance (i.e., highest inactivation rate) for all three enveloped viruses. The coronaviruses exhibited similar sensitivities to UV irradiation across the UVC range, whereas the bacteriophage surrogate was much more resistant and exhibited significantly higher sensitivity to the Far UVC (<230 nm) irradiation. This study provides necessary information and guidance for using UVC devices for enveloped virus disinfection, which may help control virus transmission in public spaces during the ongoing COVID-19 pandemic and beyond.

Mechanism and efficacy of virus inactivation by a microplasma UV lamp generating monochromatic UV irradiation at 222 nm

This study evaluated the potential of a microplasma UV lamp as an alternative UV source to the current mercury-based (Hg-based) UV lamp for water disinfection. We developed a set of PCR-based molecular assays (long-range qPCR, DNase, and binding assay) to quantify the adenovirus genome, capsid, and fiber damage with a wide detection range (10^0.5-10^6.5 PFU/mL). We used these molecular assays to characterize adenovirus (AdV) inactivation kinetics by microplasma UV that produced monochromatic UV at 222 nm. We found that the inactivation rate constant (0.142 cm²/mJ) due to microplasma UV was 4.4 times higher than that of low-pressure Hg UV (0.032 cm²/mJ). This high efficacy was attributed to monochromatic UV wavelength at 222 nm damaging the AdV capsid protein. The results of these molecular assays also proved that microplasma UV and medium-pressure Hg UV with a bandpass filter at 223 nm (MPUV_223nm) have a similar influence on AdV (p>0.05). We then estimated the relative energy efficiency of MPUV and microplasma UV to LPUV for 4 log reduction of the viruses. We found that the microplasma UV resulted in higher inactivation rate constants for viruses than the current Hg-based UV. Consequently, microplasma UV could be more energy efficient than low-pressure Hg UV for water disinfection if the wall-plug efficiency of the microplasma UV lamp improved to 8.4% (currently 1.5%). Therefore, the microplasma UV lamp is a promising option for water disinfection.

Distributed treatment systems

This section presents a review of the scientific literature published in 2019 on topics relating to distributed treatment systems. This review is divided into the following sections: constituent removal, treatment technologies, planning and treatment management, and other topics. PRACTITIONER POINTS: Highlights changes and innovation in removal techniques and technologies in water treatment. Reviews management systems of distributed treatment systems. Discusses point-of-use treatment systems.

Quick assessment of influenza a virus infectivity with a long-range reverse-transcription quantitative polymerase chain reaction assay

BACKGROUND

The polymerase chain reaction (PCR) is commonly used to detect viral pathogens because of its high sensitivity and specificity. However, conventional PCR methods cannot determine virus infectivity. Virus infectivity is conventionally examined with methods such as the plaque assay, even though such assays require several days. Long-range reverse-transcription quantitative PCR (RT-qPCR) has previously been suggested for the rapid assessment of RNA virus infectivity where the loss of infectivity is attributable to genomic fragmentation.

METHODS

IAV was irradiated with 253.7 nm ultraviolet (UV) rays to induce genomic strand breaks that were confirmed by a full-length RT-PCR assay. The IAV was then subjected to plaque assay, conventional RT-qPCR and long-range RT-qPCR to examine the relationship between infectious titer and copy number. A simple linear regression analysis was performed to examine the correlation between the results of these assays.

RESULTS

A long-range RT-qPCR assay was developed and validated for influenza A virus (IAV). Although only a few minutes of UV irradiation was required to completely inactivate IAV, genomic RNA remained detectable by the conventional RT-qPCR and the full-length RT-PCR for NS of viral genome following inactivation. A long-range RT-qPCR assay was then designed using RT-priming at the 3' termini of each genomic segment and subsequent qPCR of the 5' regions. UV-mediated IAV inactivation was successfully analyzed by the long-range RT-qPCR assay especially when targeting PA of the viral genome. This was also supported by the regression analysis that the long-range RT-qPCR is highly correlated with plaque assay (Adjusted R² = 0.931, P = 0.000066).

CONCLUSIONS

This study suggests that IAV infectivity can be predicted without the infectivity assays. The rapid detection of pathogenic IAV has, therefore, been achieved with this sensing technology.

Can incorporation of UVC LEDs into showerheads prevent opportunistic respiratory pathogens? - Microbial behavior and device design considerations

Respiratory infections from opportunistic bacterial pathogens (OBPs) have heightened research interests in drinking water distribution systems, premise plumbing, and point-of-use technologies. In particular, biofilm growth in showerheads increases OBP content, and inhalation of shower aerosols is a major exposure route for Legionellae and Mycobacteria infections. Incorporation of UVC LEDs into showerheads has thus been proposed as a point-of-use option for healthcare facilities. Herein we have examined incongruities between the nature of OBP contamination in shower water and the hypothetical application of conventional UV disinfection engineering concepts. Effective UV dosing within showerheads must overcome significant shielding effects imparted by the biological matrices in which common OBPs reside, including biofilm particles and protozoan hosts. Furthermore, prevention of biofilm growth in showerhead interiors requires a different UV irradiation approach and is lacking in established design parameters. Development of showerhead devices is also likely to face a trade-off between bathing functionality and simpler form factors that are more conducive to internal UV irradiation.