The problem of drinking water access: A review of disinfection technologies with an emphasis on solar treatment methods

Solar Water Disinfection to Produce Safe Drinking Water: A Review of Parameters, Enhancements, and Modelling Approaches to Make SODIS Faster and Safer

Solar water disinfection (SODIS) is one the cheapest and most suitable treatments to produce safe drinking water at the household level in resource-poor settings. This review introduces the main parameters that influence the SODIS process and how new enhancements and modelling approaches can overcome some of the current drawbacks that limit its widespread adoption. Increasing the container volume can decrease the recontamination risk caused by handling several 2 L bottles. Using container materials other than polyethylene terephthalate (PET) significantly increases the efficiency of inactivation of viruses and protozoa. In addition, an overestimation of the solar exposure time is usually recommended since the process success is often influenced by many factors beyond the control of the SODIS-user. The development of accurate kinetic models is crucial for ensuring the production of safe drinking water. This work attempts to review the relevant knowledge about the impact of the SODIS variables and the techniques used to develop kinetic models described in the literature. In addition to the type and concentration of pathogens in the untreated water, an ideal kinetic model should consider all critical factors affecting the efficiency of the process, such as intensity, spectral distribution of the solar radiation, container-wall transmission spectra, ageing of the SODIS reactor material, and chemical composition of the water, since the substances in the water can play a critical role as radiation attenuators and/or sensitisers triggering the inactivation process.

Simultaneous Disinfection and Organic Microcontaminant Removal by UVC-LED-Driven Advanced Oxidation Processes

This work presents the comparison of four advanced oxidation processes driven by UVC-LED radiation (278 nm—2 W/m2) for simultaneous bacteria inactivation (Escherichia coli—106 CFU/mL) and microcontaminant removal (imidacloprid—50 µg/L) in simulated wastewater secondary effluent. To this end, the activation of H2O2 and S2O82− as precursors of HO• and SO4•−, respectively, by UVC-LED and UVC-LED/Fe3+–NTA (ferric nitrilotriacetate at 0.1 mM) has been studied at different oxidant concentrations. For the purpose of comparison, conventional chlorination was used as the baseline along with bacterial regrowth 24 h after treatment. Disinfection was achieved within the first 30 min in all of the processes, mainly due to the bactericidal effect of UVC-LED radiation. UVC-LED/H2O2 did not substantially affect imidacloprid removal due to the low HO• generation by UVC irradiation at 278 nm, while more than 80% imidacloprid removal was achieved by the UVC-LED/S2O82−, UVC-LED/Fe3+–NTA/S2O82−, and UVC-LED/Fe3+–NTA/H2O2 processes. The most efficient concentration of both oxidants for the simultaneous disinfection and microcontaminant removal was 1.47 mM. Chlorination was the most effective treatment for bacterial inactivation without imidacloprid removal. These findings are relevant for scaling up UVC-LED photoreactors for tertiary wastewater treatment aimed at removing bacteria and microcontaminants.

Disinfection characteristics of an advanced rotational hydrodynamic cavitation reactor in pilot scale

Hydrodynamic cavitation is a promising technique for water disinfection. In the present paper, the disinfection characteristics of an advanced hydrodynamic cavitation reactor (ARHCR) in pilot scale were studied. The effects of various flow rates (1.4-2.6 m³/h) and rotational speeds (2600-4200 rpm) on the removal of Escherichia coli (E. coli) were revealed and analyzed. The variation regularities of the log reduction and reaction rate constant at various cavitation numbers were established. A disinfection rate of 100% was achieved in only 4 min for 15 L of simulated effluent under 4200 rpm and 1.4 m³/h, with energy efficiency at 0.0499 kWh/L. A comprehensive comparison with previously introduced HCRs demonstrates the superior performance of the presented ARHCR system. The morphological changes in E. coli were studied by scanning electron microscopy. The results indicate that the ARHCR can lead to serious cleavage and surface damages to E. coli, which cannot be obtained by conventional HCRs. Finally, a possible damage mechanism of the ARHCR, including both the hydrodynamical and sonochemical effects, was proposed. The findings of the present study can provide strong support to the fundamental understanding and applications of ARHCRs for water disinfection.

Cancer risk assessment from exposure to trihalomethanes in showers by inhalation

In many countries water disinfection for human consumption is still carried out via chlorination which generates by-products such as trihalomethanes (THM). Exposure to THM constitutes a public health risk as such substances are known to be carcinogenic. This study evaluated exposure to THMs by inhalation in showers and assessed the carcinogenic risk for lifetime exposure. The study population involved students at Universidad de los Andes residing in Bogotá, Colombia. The risk assessment was performed stochastically and the exposure parameters were taken as probability distributions. Most variables were measured in relation to the chosen population. The risk was calculated using two different methodologies but no significant variations were obtained. The average risk calculated for men and women was 56 cases in a million (5.6 × 10^-5). A sensitivity analysis was carried out where it was found that the parameters that increase risk the most are the concentration of chloroform in the water, exposure time, and the volume of the shower cubicle.

Ion-Imprinted Polymer Modified with Carbon Quantum Dots as a Highly Sensitive Copper(II) Ion Probe

Fluorescence analysis technology and ion imprinting technology are combined to prepare a copper ion fluorescence sensor. Carbon quantum dots (CQDs), with a quantum yield of 79%, were synthesized by a hydrothermal process using citric acid as the carbon source. The prepared CQDs, acting as the fluorophore, were grafted onto the surface of an SBA-15 mesoporous molecular sieve by an amidation reaction. Then, the fluorescent sensor CQDs@Cu-IIP was prepared using a surface imprinting technique with the modified SBA-15 as the substrate, copper ions as a template, tetraethoxysilane as the crosslinker, and 3-aminopropyl-3-ethoxysilane as the functional monomers. The sensor showed strong fluorescence from CQDs and high selectivity due to the presence of Cu(II)-IIP. After the detection conditions were optimized, the fluorescence intensity of the sensor had good linearity with Cu(II) concentration in a linear range of 0.25-2 mg/L and 3-10 mg/L. This CQDs@Cu-IIP was applied to the determination of traces Cu(II) in real water samples and good recoveries of 99.29-105.42% were obtained. The present study provides a general strategy for fabricating materials based on CQDs for selective fluorescence detection of heavy metals.

Regrowth of bacteria after light-based disinfection - What we know and where we go from here

Regrowth of bacteria after water/wastewater disinfection is a serious risk to public health, particularly when such pathogens carry antibiotic resistance genes. Despite increasing interest in light-based disinfection using ultraviolet or solar radiation, the mechanism of bacterial regrowth and their concentration upon light exposure (i.e., during storage, or after discharge into rivers or lakes) remain poorly understood. Therefore, we present a focused critical review to 1) elucidate regrowth mechanisms, 2) summarize the pros and cons of available experimental designs and detection techniques for regrowth evaluation, and 3) provide an outlook of key research directions for further investigations of post-disinfection bacterial regrowth. Bacterial regrowth can occur through reactivation from a viable but non-culturable state, repair of photo-induced DNA damage, and reproduction of bacteria surviving disinfection. Many studies have underestimated the degree of actual regrowth because of the use of simple experimental designs and plate count methods, which cannot quantify actual abundance of viable bacteria. Further research should investigate the effects of various factors on bacterial regrowth in realistic conditions in regrowth tests and adopt multiplex detection methods that combine culture-based and culture-independent approaches. An accurate understanding of the mechanisms involved in bacterial regrowth following disinfection is critical for safeguarding public health and aquatic environments.

Structuring of ZnTiO3/TiO2 Adsorbents for the Removal of Methylene Blue, Using Zeolite Precursor Clays as Natural Additives

Adsorption is an effective method of removing harmful pollutants from air and water. In the present study, zeolites prepared by sol-gel method from two Ecuadorian clays were combined with precursor clays and the ZnTiO3/TiO2 semiconductor for adsorbing methylene blue (MB) as a water contaminant. The synthesized compounds were characterized using powder X-ray diffraction, X-ray fluorescence, scanning electron microscopy, energy dispersive X-ray, and surface area measurement. These compounds were combined to form cylindrical extrudates of 0.2 cm (diameter) and 1.0 cm (length). The adsorption characteristics of the composites were measured using batch sorption studies as a function of pH, initial concentration, and contact time. The pseudo-second-order model and the Langmuir isotherm model were better suited to the adsorption process. The equilibrium state was achieved around 180 min of adsorption, and a pH of 7 was established as the optimal operating condition. The maximum adsorption values of the dye were obtained with the composites derived from G-Clay, whose average adsorption capacity was 46.36 mg g-1, in contrast with composites derived from R-Clay, whose average adsorption value was 36.24 mg g-1. The results reflect that synthesized composites could be used potentially for the removal of cationic dye from wastewater.

Role of nanocatalyst in the treatment of organochlorine compounds - A review

Since a few centuries ago, organochlorine compounds (OCs) become one of the threatened contaminants in the world. Due to the lipophilic and hydrophobic properties, OCs always discover in fat or lipid layers through bioaccumulation and biomagnification. The OCs are able to retain in soil, sediment and water for long time as it is volatile, OCs will evaporate from soil and condense in water easily and frequently, which pollute the shelter of aquatic life and it affects the function of organs and damage system in human body. Photocatalysis that employs the usage of semiconductor nanophotocatalyst and solar energy can be the possible alternative for current conventional water remediation technologies. With the benefits of utilizing renewable energy, no production of harmful by-products and easy operation, degradation of organic pollutants in rural water bodies can be established. Besides, nanophotocatalyst that is synthesized with nanotechnology outnumbered conventional catalyst with larger surface area to volume ratio, thus higher photocatalytic activity is observed. In contrast, disadvantages particularly no residual effect in water distribution network, requirement of post-treatment and easily affected by various factors accompanied with photocatalysis method cannot be ignored. These various factors constrained the photocatalytic efficiency via nanocatalysts which causes the full capacity of solar photocatalysis has yet to be put into practice. Therefore, further modifications and research are still required in nanophotocatalysts' synthesis to overcome limitations such as large band gaps and photodecontamination.

Electrochemical Disinfection in Water and Wastewater Treatment: Identifying Impacts of Water Quality and Operating Conditions on Performance

Electrochemical disinfection-a method in which chemical oxidants are generated in situ via redox reactions on the surface of an electrode-has attracted increased attention in recent years as an alternative to traditional chemical dosing disinfection methods. Because electrochemical disinfection does not entail the transport and storage of hazardous materials and can be scaled across centralized and distributed treatment contexts, it shows promise for use both in resource limited settings and as a supplement for aging centralized systems. In this Critical Review, we explore the significance of treatment context, oxidant selection, and operating practice on electrochemical disinfection system performance. We analyze the impacts of water composition on oxidant demand and required disinfectant dose across drinking water, centralized wastewater, and distributed wastewater treatment contexts for both free chlorine- and hydroxyl-radical-based systems. Drivers of energy consumption during oxidant generation are identified, and the energetic performance of experimentally reported electrochemical disinfection systems are evaluated against optimal modeled performance. We also highlight promising applications and operational strategies for electrochemical disinfection and propose reporting standards for future work.

The Effect of Environmental Values on German Primary School Students’ Knowledge on Water Supply

Permanent access to safe drinking water is guaranteed in most industrialized countries, while climate change is turning it into a serious global issue. Knowing how to use the valuable resource water consciously and sustainably requires well-informed and ecologically aware citizens. Environmental education approaches should help develop long-term environmental knowledge, pro-environmental attitudes, and behavior with the overall goal of promoting environmental citizenship. The present study, thus, examines the influence of environmental values on students’ environmental knowledge in a German primary school sample (9–10-year-old students) by providing an authentic, out-of-school learning experience on the topic of fresh water supply. Our approach goes beyond mere correlation analyses by using structural equation modeling (SEM) to measure effects between the two variables. Environmental values were monitored using the Two Major Environmental Values Model (2-MEV) with its two dimensions, Preservation and Utilization of nature. Following a quasi-experimental design, we assessed the learners’ knowledge before (T0), directly after (T1), and six weeks after (T2) module participation. Confirmatory factor analysis verified the two-factor-structure of the 2-MEV. Preservation turned out as a direct positive predictor of pre-knowledge (T0) but did not show any significant effect on post-knowledge (T1) and knowledge retention (T2). Utilization displayed a larger albeit negative direct effect on knowledge across all testing times, especially for pre- and post-knowledge. Our findings shed light on the significant impact of anthropocentric attitudes on knowledge acquisition within primary school samples and provided valuable insights into feasible environmental learning approaches.

Occurrence of Human Enteric Viruses in Water Sources and Shellfish: A Focus on Africa

Enteric viruses are a diverse group of human pathogens which are primarily transmitted by the faecal-oral route and are a major cause of non-bacterial diarrhoeal disease in both developed and developing countries. Because they are shed in high numbers by infected individuals and can persist for a long time in the environment, they pose a serious threat to human health globally. Enteric viruses end up in the environment mainly through discharge or leakage of raw or inadequately treated sewage into water sources such as springs, rivers, dams, or marine estuaries. Human exposure then follows when contaminated water is used for drinking, cooking, or recreation and, importantly, when filter-feeding bivalve shellfish are consumed. The human health hazard posed by enteric viruses is particularly serious in Africa where rapid urbanisation in a relatively short period of time has led to the expansion of informal settlements with poor sanitation and failing or non-existent wastewater treatment infrastructure, and where rural communities with limited or no access to municipal water are dependent on nearby open water sources for their subsistence. The role of sewage-contaminated water and bivalve shellfish as vehicles for transmission of enteric viruses is well documented but, to our knowledge, has not been comprehensively reviewed in the African context. Here we provide an overview of enteric viruses and then review the growing body of research where these viruses have been detected in association with sewage-contaminated water or food in several African countries. These studies highlight the need for more research into the prevalence, molecular epidemiology and circulation of these viruses in Africa, as well as for development and application of innovative wastewater treatment approaches to reduce environmental pollution and its impact on human health on the continent.

Autopsy, thanatopraxy, cemeteries and crematoria as hotspots of toxic organic contaminants in the funeral industry continuum

The occurrence and health risks of toxic organic contaminants (TOCs) in the funeral industry are relatively under-studied compared to other industries. An increasing body of literature reports TOCs including emerging contaminants in the funeral industry, but comprehensive reviews of the evidence are still lacking. Hence, evidence was analysed to address the proposition that, the funeral industry constitutes several hotspot reservoirs of a wide spectrum of TOCs posing ecological and human health risks. TOCs detected include embalming products, persistent organic pollutants, synthetic pesticides, pharmaceuticals, personal care products and illicit drugs. Human cadavers, solid wastes, wastewaters and air-borne particulates from autopsy, thanatopraxy care facilities (mortuaries, funeral homes), cemeteries and crematoria are hotspots of TOCs. Ingestion of contaminated water, and aquatic and marine foods constitutes non-occupational human exposure, while occupational exposure occurs via inhalation and dermal intake. Risk factors promoting exposure to TOCs include unhygienic burial practices, poor solid waste and wastewater disposal, and weak and poorly enforced regulations. The generic health risks of TOCs are quite diverse, and include; (1) genotoxicity, endocrine disruption, teratogenicity and neurodevelopmental disorders, (2) development of antimicrobial resistance, (3) info-disruption via biomimicry, and (4) disruption of ecosystem functions and trophic interactions. Barring formaldehyde and inferential evidence, the epidemiological studies linking TOCs in the funeral industry to specific health outcomes are scarce. The reasons for the lack of evidence, and limitations of current health risk assessment protocols are discussed. A comprehensive framework for hazard identification, risk assessment and mitigation (HIRAM) in the funeral industry is proposed. The HIRAM includes regulatory, surveillance and control systems such as prevention and removal of TOCs. Future directions on the ecotoxicology of mixtures, behaviour, and health risks of TOCs are highlighted. The opportunities presented by emerging tools, including isotopic labelling, genomics, big data analytics (e.g., machine learning), and in silico techniques in toxicokinetic modelling are highlighted.

Photovoltaic and solar disinfection technology meeting the needs of water and electricity of a typical household in developing countries: From a Solar Home System to a full-functional hybrid system

A novel SolWat system designed exclusively as a Solar Home System that also meets the drinking water access in a family of a rural community in a developing country has been designed, manufactured and tested outdoors. The system is composed of 5 photovoltaic modules of monocrystalline silicon solar cells technology, each 20 Wp, parallel-interconnected, adding up to a 100 Wp system. The modules have a water reactor on top with the capacity of providing a minimum of 37.5 L per day for a family of 5 members, guaranteeing the minimum daily needs. Experimental campaign run tests of SODIS of 3 h each, running the system 3 times per day (with a total of 9 h of experimentation per day). Results show that the water treatment of 3 h should be increased at certain periods of the day when the UV dose is not sufficient (late in the afternoon). E. coli and Enterococcus spp achieved total inactivation or almost total disinfection. Regarding electrical production, although energy losses of 5.6-10% were observed in comparison with a single PV module, it was sufficient to fully meet the load demand of the solar home system. The system could be used in a household of a developing country, using only solar energy to meet the electricity and drinking water demand.

Disinfection by-products in drinking water: Occurrence, toxicity and abatement

Disinfection means the killing of pathogenic organisms (e.g. bacteria and its spores, viruses, protozoa and their cysts, worms, and larvae) present in water to make it potable for other domestic works. The substances used in the disinfection of water are known as disinfectants. At municipal level, chlorine (Cl₂), chloramines (NH₂Cl, NHCl₂), chlorine dioxide (ClO₂), ozone (O₃) and ultraviolet (UV) radiations, are the most commonly used disinfectants. Chlorination, because of its removal efficiency and cost effectiveness, has been widely used as method of disinfection of water. But, disinfection process may add several kinds of disinfection by-products (DBPs) (∼600-700 in numbers) in the treated water such as Trihalomethanes (THM), Haloacetic acids (HAA) etc. which are detrimental to the human beings in terms of cytotoxicity, mutagenicity, teratogenicity and carcinogenicity. In water, THMs and HAAs were observed in the range from 0.138 to 458 μg/L and 0.16-136 μg/L, respectively. Thus, several regulations have been specified by world authorities like WHO, USEPA and Bureau of Indian Standard to protect human health. Some techniques have also been developed to remove the DBPs as well as their precursors from the water. The popular techniques of DBPs removals are adsorption, advance oxidation process, coagulation, membrane based filtration, combined approaches etc. The efficiency of adsorption technique was found up to 90% for DBP removal from the water.

Decentralized solar-powered drinking water ozonation in Western Kenya: an evaluation of disinfection efficacy

 Background: Decentralized drinking water treatment methods generally apply membrane-based treatment approaches. Ozonation of drinking water, which previously has only been possible at large centralized facilities, can now be accomplished on a small-scale using microplasma technology. The efficacy of decentralized solar-powered drinking water treatment systems has not previously been described.

Methods: We established a 1,000L decentralized solar-powered water treatment system located in Kisumu County, Kenya. Highly contaminated surface water is pumped to the treatment system, which includes flocculation and filtration steps prior to ozonation. Turbidity, total coliform bacteria, and E. coli were measured at various stages of water treatment, and bacterial log reduction values (LRVs) were calculated.

Results: Forty-seven trials were conducted in which1000L of water were flocculated, filtered, and ozonated for 180 minutes. Baseline turbidity and E. coli concentrations were reduced from a median of 238 nephelometric turbidity units (NTU) and 2,419.7 most probable number/100mL, respectively, in surface water to 1.0 NTU and undetectable E. coli after ozonation for 180 minutes. The median E. coli LRV was 3.99.

Conclusions: The solar-powered, decentralized water treatment system that utilizes ozonation for disinfection was founded to reduce E. coli by more than 3 log-orders of magnitude despite the high turbidity of the raw water. Further research is needed to characterize limitations, scalability, economic viability, and community perspectives that could help determine the role for similar systems in other settings.

A review on hydrodynamic cavitation disinfection: The current state of knowledge

Disinfection, which aims to eliminate pathogenic microorganisms, is an essential step of water treatment. Hydrodynamic cavitation (HC) has emerged as a promising technology for large-scale disinfection without introducing new chemicals. HC, which can effectively induce sonochemistry by mechanical means, creates extraordinary conditions of pressures of ~1000 bar, local hotspots with ~5000 K, and high oxidation (hydroxyl radicals) in room environment. These conditions can produce highly destructive effects on microorganisms in water. In addition, the enhancements of chemical reactions and mass transfers by HC produce the synergism between HC and disinfectants or other physical treatment methods. HC is generated by hydrodynamic cavitation reactors (HCRs), therefore, their performance basically determines the effectiveness, economical efficiency, and applicability of HC disinfection. Therefore, developing high-performance HCRs and revealing the corresponding disinfection mechanisms are the most crucial issues today. In this review, we summarize the fundamental principles of HC and HCRs and recent development in HC disinfection. The energy release from cavitation phenomenon and corresponding mechanisms are elaborated. The performance (effectiveness, treatment ratio, and cost) of various HCRs, effects of treatment conditions on performance, and applicability of HC disinfection are evaluated and discussed. Finally, recommendations are provided for the future progress based on the analysis of previous studies.

The occurrence, characteristics, transformation and control of aromatic disinfection by-products: A review

With the development of analytical technology, more emerging disinfection by-products (DBPs) have been identified and detected. Among them, aromatic DBPs, especially heterocyclic DBPs, possess relatively high toxicity compared with regulated DBPs, which has been proved by bioassays. Thus, the occurrence of aromatic DBPs is of great concern. This article provides a comprehensive review and summary of the characteristics, occurrence, transformation pathways and control of aromatic DBPs. Aromatic DBPs are frequently detected in drinking water, wastewater and swimming pool water, among which swimming pool water illustrates highest concentration. Considering the relatively high concentration and toxicity, halophenylacetonitriles (HPANs) and halonitrophenols (HNPs) are more likely to be toxicity driver among frequently detected phenyl DBPs. Aromatic DBPs can be viewed as important intermediate products of dissolved organic matter (DOM) during chlor(am)ination. High molecular weight DOM could convert to aromatic DBPs via direct or indirect pathways, and they can further decompose into regulated aliphatic DBPs such as trihalomethanes (THMs) and haloacetic acids (HAAs) by ring opening and side chain cleavage. Even though no single DBPs control strategy is efficient to all aromatic DBPs, the decrease of overall toxicity may be achieved by several methods including absorption, solar radiation and boiling. By systematically considering aromatic DBPs and aliphatic DBPs, a better trade-off can be made to reduce health risk induced by DBPs.

Quality change mechanism and drinking safety of repeatedly-boiled water and prolonged-boil water: a comparative study

Quality, safety and potability of repeatedly-boiled water (RBW) and prolonged-boil water (PBW) lead to concern and even misgivings in the public from time to time, especially in China, and other societies have a habit of drinking boiled water, with improvements of living standards and owing to increasing concerns for human health. This phenomenon is mainly attributed to the fact that the conclusions drawn from existing scientific experiments could not respond well to the concerns. In order to make up for this deficiency, tap water was selected to carry out RBW and PBW experiments independently. The quality changes of RBW and PBW show very similar trends that are not as great as might be imagined, and both are impacted by the tap water quality and the physiochemical effects. The dominating physiochemical effects are the water evaporation and the resulting concentration of unreactive components (most dissolved components), which can be easily explained by the existing evaporation-concentration theory. The results show that tap water will be still safe and potable after being frequently boiled or after having undergone prolonged boiling, as long as it satisfies the sanitary standards of drinking water prior to heating. Therefore, there is no need to worry about drinking RBW or PBW in daily life.

Portable point-of-use photoelectrocatalytic device provides rapid water disinfection

Portable water purification devices are needed to provide safe drinking water in rural communities, developing communities with low quality centralized water distribution, and military or recreational applications. Filtration, ultraviolet light, or chemical additives provide a spectrum of alternatives to remove pathogens from water. For the first time, we design, fabricate and demonstrate the performance of a small portable photoelectric point-of-use device, and document its performance on pathogen inactivation. The device utilizes a commercial teacup from which TiO₂ nanotube photoanodes were produced in-situ and, with a small rechargeable battery powered 365 nm light emitting diode, was able to achieve 5-log inactivation of Escherichia coli in 10 s and 2.6-log of Legionella in 60 s of treatment in model water samples. Treatment of natural water achieved a 1-log bacteria inactivation after 30 s due to matrix effects. The electro-photocatalytic disinfection reactor in a kup (e-DRINK) can provide a feasible and affordable solution to ensure access to clean water. More broadly, this work demonstrates the potential for illumination to improve the efficiency of electrocatalytic surfaces.

Evidence for decontamination of single-use filtering facepiece respirators

Single-use filtering face respirators (FFRs) are critical pieces of personal protective equipment for healthcare workers treating patients with suspected upper respiratory tract pathogens. Experiences during pandemics in the 2000s, as well as the ongoing COVID-19 pandemic caused by the SARS-2-CoV-2, have highlighted concerns over the pressures that sustained respiratory virus pandemics may have on supplies of FFRs globally. Decontamination of FFRs has been posited as one solution to support the re-use of FFRs with a growing body of literature over the last 10+ years beginning to examine both the efficacy of disinfection of contaminated FFRs but also the impact of the decontamination process on the FFR's performance. Physical and chemical methods of decontamination have been tested for treatment of FFRs with ultraviolet germicidal irradiation, sterilization by steam, ethylene oxide and vaporous hydrogen peroxide, demonstrating the most promising results thus far. Many of these methods utilize existing equipment that may already be available in hospitals and could be re-purposed for FFR decontamination. Importantly, some methods may also be replicated on household equipment, broadening the utility of FFR decontamination across a range of healthcare settings. Utilizing techniques to experimentally contaminate FFRs with a range of microorganisms, most decontamination methods appear to reduce the risk of the mask as a source of infection to the wearer and others to negligible levels. The performance of the filter, especially the efficiency of particle penetration following treatment, varied greatly depending on the processing method as well as the model of the filter itself, however. Urgent regulatory body-supported research is required to endorse the routine decontamination of FFRs. In emergency settings, these methods should nevertheless be carefully considered as one strategy to address potential shortfalls in supplies of FFRs for healthcare workers.

Decentralized solar-powered drinking water ozonation in Western Kenya: an evaluation of disinfection efficacy

Background: Decentralized drinking water treatment methods generally apply membrane-based treatment approaches. Ozonation of drinking water, which previously has only been possible at large centralized facilities, can now be accomplished on a small-scale using microplasma technology. The efficacy of decentralized solar-powered ozonation for drinking water treatment is not known. Methods: We established a 1,000L decentralized solar-powered water treatment system located in Kisumu County, Kenya. Highly contaminated surface water is pumped to the treatment system, which includes flocculation and filtration steps prior to ozonation. Turbidity, total coliform bacteria, and E. coli were measured at various stages of water treatment, and bacterial log reduction values (LRVs) were calculated. Results: Nine trials were conducted treating 1000L of water in three hours. Baseline turbidity and E. coli concentrations were reduced from a median of 238 nephelometric turbidity units (NTU) and 2,752 most probable number/100mL, respectively, in surface water to 1.0 NTU and undetectable E. coli per100mL in finished drinking water. The nine trials yielded a mean E. coli LRV of 3.36 (2.71-4.00, 95% CI). Conclusions: Based on the observed reduction of E. coli, the solar-powered system shows promise as a means for producing safe drinking water. Further research is needed to characterize limitations, scalability, economic viability, and community perspectives that could help determine the role for similar systems in other settings.

Agglomeration of Viruses by Cationic Lignin Particles for Facilitated Water Purification

Virus contamination of water is a threat to human health in many countries. Current solutions for inactivation of viruses mainly rely on environmentally burdensome chemical oxidation or energy-intensive ultraviolet irradiation, which may create toxic secondary products. Here, we show that renewable plant biomass-sourced colloidal lignin particles (CLPs) can be used as agglomeration agents to facilitate removal of viruses from water. We used dynamic light scattering (DLS), electrophoretic mobility shift assay (EMSA), atomic force microscopy and transmission electron microscopy (AFM, TEM), and UV spectrophotometry to quantify and visualize adherence of cowpea chlorotic mottle viruses (CCMVs) on CLPs. Our results show that CCMVs form agglomerated complexes with CLPs that, unlike pristine virus particles, can be easily removed from water either by filtration or centrifugation. Additionally, cationic particles formed by adsorption of quaternary amine-modified softwood kraft lignin on the CLPs were also evaluated to improve the binding interactions with these anionic viruses. We foresee that due to their moderate production cost, and high availability of lignin as a side-stream from biorefineries, CLPs could be an alternative water pretreatment material in a large variety of systems such as filters, packed columns, or flocculants.

Solar Powered Microplasma-Generated Ozone: Assessment of a Novel Point-of-Use Drinking Water Treatment Method

Ozonation is widely used in high-income countries for water disinfection in centralized treatment facilities. New microplasma technology has reduced the energy requirements for ozone generation dramatically, such that a 15-watt solar panel is sufficient to produce small quantities of ozone. This technology has not been used previously for point-of-use drinking water treatment. We conducted a series of assessments of this technology, both in the laboratory and in homes of residents of a village in western Kenya, to estimate system efficacy and to determine if the solar-powered point-of-use water ozonation system appears safe and acceptable to end-users. In the laboratory, two hours of point-of-use ozonation reduced E. coli in 120 L of wastewater by a mean (standard deviation) of 2.3 (0.84) log-orders of magnitude and F+ coliphage by 1.54 (0.72). Based on laboratory efficacy, 10 families in Western Kenya used the system to treat 20 L of household stored water for two hours on a daily basis for eight weeks. Household stored water E. coli concentrations of >1000 most probable number (MPN)/100 mL were reduced by 1.56 (0.96) log removal value (LRV). No participants experienced symptoms of respiratory or mucous membrane irritation. Focus group research indicated that families who used the system for eight weeks had very favorable perceptions of the system, in part because it allowed them to charge mobile phones. Drinking water ozonation using microplasma technology may be a sustainable point-of-use treatment method, although system optimization and evaluations in other settings would be needed.

Zeolite Cotton in Tube: A Simple Robust Household Water Treatment Filter for Heavy Metal Removal

It is challenging to develop a low-cost household water treatment (HWT) that simultaneously deliver an effective and robust way for safe and reliable water supply. Here, we report a simple flow-through filter made by zeolite-cotton packing in a tube (ZCT) as low-cost HWT device to remove heavy metal ions from contaminated water. The zeolite-cotton is fabricated by an on-site template-free growth route that tightly binds mesoporous single-crystal chabazite zeolite onto the surface of cotton fibers. As a result, the ZCT set-up with optimized diameter achieves both high adsorption efficiency, proper flow rate, reliable supply and strong stability at the same time. After flowed through the set up packed with 10 g of zeolite-cotton, 65 mL 1000 ppm Cu²⁺ solution was purified down to its safety limit (<1 ppm). Notably, their efficiency remains unaltered when filtering several ions simultaneously. In a simulated purification process, 8 L of water contaminated by Cu²⁺, Cd²⁺ and Pb²⁺ could be transformed into drinking water and it enables the removal of heavy metals to concentrations of below 5 ppb (μg L⁻¹). We also show that the ZCT can be used for disinfection by introducing Ag-exchanged zeolite-cotton without contaminating the water with Ag ions (<0.05 ppm).

Anti-algal activity of Fe2O3-TiO2 photocatalyst on Chlorella vulgaris species under visible light irradiation

Many industries located in coastal areas use a large amount of seawater. Algal biofouling can be a major problem that hinders the efficiency of these industrial facilities. In most cases, seawater requires algal removal pre-treatment to avoid or mitigate biofilm formation. To remediate green microalgae, Fe₂O₃-TiO₂ nanoparticles with 2.5% w/w Fe₂O₃ were applied as a visible light driven photocatalyst. The anti-algal activity of the photocatalytic pre-treatment using green microalgae, Chlorella vulgaris was tested. The experiments were carried out in freshwater, artificial seawater, and real seawater. Effect of photocatalyst dosage, visible light intensity, and water salinity on the removal of microalgae was investigated. The highest inactivation efficiency of Chlorella vulgaris was achieved under 55 W/m² visible light irradiation when 0.25 g/L of Fe₂O₃-TiO₂ photocatalyst was used. The photocatalytic removal kinetics of Chlorella vulgaris followed the pseudo first order Langmuir-Hinshelwood model. The results revealed that the efficiency of photocatalytic removal of algae decreased with increasing of seawater salinity. The anti-algal activity of Fe₂O₃-TiO₂ nanoparticles was attributed to the generation of reactive oxygen species (ROS) through the photocatalytic process. H⁺ radical was shown to be the most important ROS that nanoparticles produced in the aqueous media. Using Fe₂O₃-TiO₂ nanoparticles in photocatalytic pre-treatment could be an efficient environmental-friendly method for micro-algal remediation in seawater under visible light.

Adsorption of Salmonella in Clay Minerals and Clay-Based Materials

A series of clay minerals and clay-based materials have been tested to eliminate one of the most dangerous bacteria we can find in the water: Salmonella. It has been proven that the use of clays and their PCH materials can be a suitable method for removing Salmonella from water. The results of this initial study show that all the materials analyzed have great salmonella adsorption capacities ranging from the lowest value observed in the mont-PCH sample (0.29 × 1010 CFU g−1) to the highest value observed in the natural palygorskite sample (1.52 × 1010 CFU g−1). Macroporosity, accessible external surface area, and the presence of silanol groups in the external surface of the particles appears to be the controlling factors for Salmonella adsorption capacity while it seems that the structural characteristics of the clay minerals and their respective PCH does not affect the adsorption capacity.

Cost-effective reduction of micro pollutants in the water cycle - Case study on iodinated contrast media

Surface waters, especially in densely populated areas, are facing multiple anthropogenic pressures. Micro pollutants are of growing concern. Improved analytical methods are used to focus on substances like ICM with a (high) potential of hazardous effects against water organisms or the water quality in general ICM are essential for instance in computer tomographic examinations in medical facilities. Discharge of ICM to the sewer system occurs via human urine excretions. Common waste water treatment plants do not eliminate these substances completely. Therefore, increasing concentrations are found in the rivers worldwide. The project MERK'MAL explored a potentially cost-effective measure to reduce ICM in the River Ruhr, located in Germany, North Rhine-Westphalia. The results from this pilot study show that urine bags are an effective measure to reduce ICM concentrations. During the urine collection with bags measurements of ICM concentrations have shown a reduction, compared to the baseline concentration that was measured at the same sampling point in the effluent of the corresponding waste water treatment plant. The ICM reduction ranged between 20 and 34% for the mean values and between 7 and 33% for the median value. Additional payment equivalent costs per examination with ICM are approx. 3.36 €, full costs including imputed costs are expected in a cost range of 5.38 € to 6.09 € per examination. The extension of the study is envisioned, helping to sustainably enhance water quality in the River Ruhr in terms of ICM concentrations.