Disinfection of indoor air microorganisms in stack room of university library using gaseous chlorine dioxide

Cleaning technologies integrated in duct flows for the inactivation of pathogenic microorganisms in indoor environments: A critical review of recent innovations and future challenges

Pathogenic microorganisms are a major concern in indoor environments, particularly in sensitive facilities such as hospitals, due to their potential to cause nosocomial infections. This study evaluates the concentration of airborne bacteria and fungi in the University Hospital Complex of Albacete (Spain), comparing the results with recent literature. Staphylococcus is identified as the most prevalent bacterial genus with a percentage distribution of 35%, while Aspergillus represents the dominant fungal genus at 34%. The lack of high Technology Readiness Levels (TRL 6, TRL 7) for effective indoor air purification requires research efforts to bridge this knowledge gap. A screening of disinfection technologies for pathogenic airborne microorganisms such as bacteria and fungi is conducted. The integration of filtration, irradiation or and (electro)chemical gas treatment systems in duct flows is discussed to enhance the design of the air-conditioning systems for indoor air purification. Concerns over microbial growth have led to recent studies on coating commercial fibrous air filters with antimicrobial particles (silver nanoparticles, iron oxide nanowires) and polymeric materials (polyaniline, polyvinylidene fluoride). Promising alternatives to traditional short-wave UV-C energy for disinfection include LED and Far-UVC irradiation systems. Additionally, research explores the use of TiO2 and TiO2 doped with metals (Ag, Cu, Pt) in filters with photocatalytic properties, enabling the utilization of visible or solar light. Hybrid photocatalysis, combining TiO2 with polymers, carbon nanomaterials, or MXene nanomaterials, enhances the photocatalytic process. Chemical treatment systems such as aerosolization of biocidal agents (benzalkonium chloride, hydrogen peroxide, chlorine dioxide or ozone) with their possible combination with other technologies such as adsorption, filtration or photocatalysis, are also tested for gas disinfection. However, the limited number of studies on the use of electrochemical technology poses a challenge for further investigation into gas-phase oxidant generation, without the formation of harmful by-products, to raise its TRL for effectively inactivating airborne microorganisms in indoor environments.

A Titration Method for Standardization of Aqueous Sodium Chlorite Solutions Using Thiourea Dioxide

Accurate and cost-effective methods for the analysis of oxychlorine compounds in water are critical to modern chlorine-based water treatment. With alternatives to elemental chlorine and hypochlorite bleaches growing in popularity, simple quantification methods for the disinfectant chlorine dioxide (ClO2) in water, as well as chlorite (ClO2-) and chlorate (ClO3-), which are commonly used precursors in ClO2 generation, are required. However, currently, regulated standard methods require specialized equipment and do not effectively discriminate between molecular and ionic species. In this contribution, we present a simple titration-based method for chlorite determination in water using commercially available and easy-to-handle reagents. Specifically, chlorite is reduced with a slight excess of thioureadioxide (TUD). The remaining reductant is then back-titrated against a known amount of potassium permanganate, affording calculatable chlorite concentrations through measured consumption of a reductant and a clear visual endpoint upon accumulation of excess KMnO4. Straightforward methods for chlorite standardization with reasonable error and accuracy for field and/or lab application have the potential to greatly enhance quality assurance and therefore assist in resource deployment in water treatment.

Ultra-low concentration of chlorine dioxide regulates stress-caused premature leaf senescence in tobacco by modulating auxin, ethylene, and chlorophyll biosynthesis

Exploring novel growth regulators for premature senescence regulation is important for tobacco production. In the present study, chlorine dioxide (ClO2) was explored as a novel plant growth regulator for tobacco growth, particularly its effect on leaf senescence and root development. The results showed that 0.15 μM ClO2 maintained the lushness of detached leaves and whole plants. Also, the leaves of ClO2-treated plants exhibited a chlorophyll content of 58% higher than in CK (control) plants (P < 0.05). Besides, ClO2 treatment increased the biomass of roots and aboveground parts by 54 and 16%, respectively. The ClO2-treated plants also showed enhanced activities of antioxidant enzymes and significantly reduced malondialdehyde contents (P < 0.05). Moreover, ClO2 treatment remarkably alleviated drought-caused premature senescence in the tobacco plants and partly rescued the exogenous ethylene-caused plant dwarfism. The indole-3-acetic acid content in ClO2-treated plants was higher than in non-treated plants (P < 0.05), but ethylene content was significantly lower (P < 0.05). Gene expression analysis showed that ClO2 treatment remarkably suppressed ethylene synthase genes. However, the auxin biosynthesis and transport genes were up-regulated, with NtIAA17 increasing by five folds (P < 0.05). Further, ClO2 remarkably up-regulated the expression of chlorophyll biosynthesis genes, with a >20-fold increase in NtHEMA1 and NtCHLH expressions. These results designate ClO2 as a potential regulator for improving tobacco productivity by retaining higher chlorophyll content and promoting root growth.

Respiratory Safety Evaluation in Mice and Inhibition of Adenoviral Amplification in Human Bronchial Endothelial Cells Using a Novel Type of Chlorine Dioxide Gas Reactor

Since the onset of the COVID-19 pandemic, there has been a growing demand for effective and safe disinfectants. A novel use of chlorine dioxide (ClO2) gas, which can satisfy such demand, has been reported. However, its efficacy and safety remain unclear. For the safe use of this gas, the stable release of specific concentrations is a must. A new type of ClO2 generator called Dr.CLOTM has recently been introduced. This study aimed to investigate: (1) the effects of Dr.CLOTM on inhibiting adenoviral amplification on human bronchial epithelial (HBE) cells; and (2) the acute inhalation safety of using Dr.CLOTM in animal models. After infecting HBE cells with a recombinant adenovirus, the inhibitory power of Dr.CLOTM on the virus was expressed as IFU/mL in comparison with the control group. The safety of ClO2 gas was indirectly predicted using mice by measuring single-dose inhalation toxicity in specially designed chambers. Dr.CLOTM was found to evaporate in a very constant concentration range at 0-0.011 ppm/m3 for 42 days. In addition, 36-100% of adenoviral amplification was suppressed by Dr.CLOTM, depending on the conditions. The LC50 of ClO2 gas to mice was approximately 68 ppm for males and 141 ppm for females. Histopathological evaluation showed that the lungs of female mice were more resistant to the toxicity from higher ClO2 gas concentrations than those of male mice. Taken together, these results indicate that Dr.CLOTM can be used to provide a safe indoor environment due to its technology that maintains the stable concentration and release of ClO2 gas, which could suppress viral amplification and may prevent viral infections.

Investigation and disinfection of bacteria and fungi in sports fitness center

This study investigated the air quality improvement in terms of bacterial and fungal contamination in an exercise room of a fitness center under normal operating conditions. Environmental conditions including air conditioning, ventilation, moisture, CO₂, particulate matters, and total number of users were also recorded. In addition, fungal and bacterial load were assessed and disinfection on sports equipment surface was also examined. Background bacteria and fungi densities in bioaerosols were in the range of 249 ± 65 to 812 ± 111 CFU/m³ and 226 ± 39 to 837 ± 838 CFU/m³ in the exercise room of the fitness center and 370 ± 86 to 953 ± 136 CFU/m³ and 465 ± 108 to 1734 ± 580 CFU/m³ in the outdoor air, respectively. Chlorine dioxide and weak acid hypochlorous water aerosols could remove both bacteria and fungi much better than water scrubbing. Contact time of 15 min was sufficient to control both bacteria and fungi to comply with the official air quality standards. User density and carbon dioxide deteriorated both bacteria and fungi disinfection performance whereas temperature was only statistically significant on fungi disinfection. Other factors including relative humidity, airflow velocity, and particulate matters did not have any statistically significant effect on microbial inactivation. Apart from bioaerosol disinfection, inactivation of microorganisms on surfaces of sports equipment was also conducted using chlorine dioxide, zinc oxide, weak acid hypochlorous water, and commercial disinfectant. The surfaces of bicycle handle, dumbbell, and sit-up bench were found to be contaminated with bacteria. Overall bacterial load was 390 to 3720 CFU/cm² with Escherichia coli specifically 550 to 1080 CFU/cm². Chlorine dioxide and zinc oxide were noticeably better than weak acid hypochlorous water and commercial disinfectant in terms of bacteria inactivation whereas all tested disinfectants had comparable effectiveness on E. coli disinfection. Targeted microorganisms on the sports equipment surface were sufficiently inactivated within 2 min after the application of disinfectant.

Decontamination of common healthcare facility surfaces contaminated with SARS-CoV-2 using peracetic acid dry fogging

BACKGROUND

The SARS-CoV-2 pandemic has highlighted the urgent need for safe and effective surface decontamination methods, particularly in healthcare settings.

AIM

To evaluate the effectiveness of peracetic acid (PAA) dry fogging in decontaminating healthcare facility surfaces experimentally contaminated with SARS-CoV-2.

METHODS

Nine materials (stainless steel, latex painted wood, unsealed hardwood, melamine countertop, vinyl flooring, clear plastic, faux leather, computer keyboard button, and smartphone touch screen) were surface contaminated with >106 median tissue culture infectious dose (TCID50) of SARS-CoV-2, and allowed to dry before exposing to PAA dry fogging.

FINDINGS

When fumigated with PAA dry fog for 1 h, no infectious SARS-CoV-2 virus was recovered from any of the experimentally inoculated surface types. By contrast, high titres of infectious virus were recovered from corresponding untreated drying controls of the same materials.

CONCLUSION

Standard surface decontamination processes, including sprays and wipes, are laborious and frequently cannot completely decontaminate sensitive electronic equipment. The ease of use, low cost, and overall effectiveness of a PAA dry fogging suggest that it should be considered for decontaminating healthcare settings, particularly intensive care units where severely ill SARS-CoV-2 patients are cared for.

Temporal variation of airborne fungi in university library rooms and its relation to environmental parameters and potential confounders

Indoor airborne fungi have been associated with adverse human health effects. Therefore, it is important to understand the causes of underlying variation in airborne fungi in indoor environments. This study consequently aimed to investigate the association between indoor fungi with temporal variation, environmental parameters, and potential confounders over 10 months in four library rooms using Andersen samplers. Indoor fungal concentrations peaked in October and were lowest in March in both stack rooms, whereas the highest concentrations in both reading rooms were observed in September with lowest concentrations in July. Nonparametric analyses revealed higher fungal concentrations in the rooms that were significantly associated with relative humidity ≥ 60%, PM_2.5 ≥ 35 μg/m³, number of people ≥ 16, open windows, working air conditioners, and room area < 400 m². Multiple linear regression modeling for the library building considering only continuous variables revealed that relative humidity, PM_2.5, and the number of people were significant predictors of fungal concentrations. Additionally, the model with continuous and categorical variables suggested that relative humidity, PM_2.5, the number of people, ceiling fan condition, window state, and air conditioner operating status were significant predictor variables of concentrations. Outdoor fungal concentrations were a significant predictor for the two models of indoor fungal concentrations for each room. Ceiling fan or air conditioner operation was associated with altered fungal particle concentrations. These results provide a deeper understanding of indoor air fungal quality.

Disinfection performance of chlorine dioxide gas at ultra-low concentrations and the decay rules under different environmental factors

Gaseous chlorine dioxide (ClO₂) is one of the most promising air disinfectants. In this study, an ultra-low concentration of ClO₂ gas (< 1.2 mg/m³) was generated in an office at various levels of humidity and illuminance to investigate the decay law. The disinfection efficiency and metal corrosiveness of ultra-low concentrations of ClO₂ gas were also studied using an experimental chamber. At 48% and 75% humidity, the decay rate constants of ClO₂ gas were 0.0034 min^-1 and 0.0036 min^-1, respectively. The rate of decline of the ClO₂ concentration increased as the humidity of the environment increased. The decay rate constant of ClO₂ gas at an illuminance of 76 lux and 3429 lux was 0.0034 min^-1 and 0.00427 min^-1, respectively; hence, the decay rate increased with increased illumination. At a humidity of 72% and illuminance of 2112 lux, the decay rate constant reached 0.00880 min^-1. The effects of humidity and illuminance on the attenuation of the ClO₂ concentration were strongly synergistic. When the gas concentration was maintained below 0.9 mg/m³, the disinfection rate of ClO₂ on bacteria (P. aeruginosa, V. mimicus and S. aureus) exceeded 99.9%; thus, ClO₂ gas exhibited a high disinfection efficiency. In addition, there was no corrosion to various metals by ClO₂ under the same conditions. Consequently, gaseous ClO₂ at ultra-low concentrations has a high sterilization efficiency and is non-corrosive to metals.

IMPLICATIONS

Humidity and illuminance can influence decay laws of extremely low concentration ClO₂ gas. The gaseous ClO₂ at ultra-low concentrations has a high sterilisation efficiency and is non-corrosive to metals.

Optimization of a Portable Adenosine Triphosphate Bioluminescence Assay Coupled with a Receiver Operating Characteristic Model to Assess Bioaerosol Concentrations on Site

Rapid monitoring of the microbial content in indoor air is an important issue. In this study, we develop a method for applying a Coriolis sampler coupled with a portable ATP luminometer for characterization of the collection efficiency of bioaerosol samplers and then test this approach in field applications. The biological collection efficiencies of the Coriolis sampler and a BioSampler for collecting four different types of bioaerosols, including Escherichia coli, Staphylococcus aureus, Candida famata and endospores of Bacillus subtilis, were compared in a chamber study. The results showed that the ATP assay may indicate the four microbes' viability, and that their defined viabilities were positively correlated with their culturability. In addition, the optimal sampling conditions of the Coriolis sampler were a 200 L/min flow rate and a sampling time of 30 min. Under these conditions, there was no significant difference in sampling performance between the BioSampler and Coriolis sampler. In field applications, the best ATP benchmark that corresponded to culturable levels of < 500 CFU/m³ was 287 RLUs (sensitivity: 100%; specificity: 80%) for bacteria and 370 RLUs (sensitivity: 79%; specificity: 82%) for fungi according to receiver operating characteristic curve analysis. Consequently, an ATP criterion is recommended for indicating whether the corresponding airborne culturable concentrations of microbes meet those of published guidelines.

On-site investigation of the concentration and size distribution characteristics of airborne fungi in a university library

It is important to investigate fungal air quality in libraries because they represent a complex indoor environment. The aim of the study was to quantitatively investigate airborne fungal contamination levels based on field measurements in autumn and winter in four selected library rooms (compact stack, lending room, reading room, study room) in a university library building, as well as the effects of several factors on the culturability of airborne fungi. Airborne fungal levels varied by room, with the highest fungal levels in the reading room (634 ± 275 CFU/m³) and the lowest in the lending room (486 ± 177 CFU/m³). Airborne fungal concentrations were significantly different with seasonal variation (p < 0.05) for all rooms except for the reading room. The size distribution analysis showed that the most airborne fungi were 1.1-3.2 μm in size; based on the schematic diagram of the human respiratory system, more than 80% of airborne fungi could be deposited in the lower respiratory tract (0.65-4.7 μm). Indoor/outdoor airborne fungal concentration ratios were below 1.0 for all four rooms during autumn and winter, showing that outdoor fungi are the main source of indoor fungi. Pearson correlations showed that the fungal concentration was significantly positively correlated with both temperature (r = 0.531, p < 0.05) and relative humidity (r = 0.555, p < 0.05). Indoor temperature, indoor relative humidity and number of open windows significantly positively affected airborne fungal concentration in a multiple linear regression model (p < 0.05). This paper provides fundamental data on fungal contamination that can help experts in indoor air quality to develop guidelines for airborne fungi in libraries and create a safe environment for library patrons and staff.

Use of a small-scale, portable test chamber for determining the bactericidal efficacy of aerosolized glycol formulations

This study aimed to understand the efficacy and mechanisms of action of an aerosolized glycol-ethanol formulations against bacteria. We validated a small-scale in-house test chamber to determine the microbicidal efficacy of four aerosolized formulations combining dipropylene glycol and ethanol against Staphylococcus aureus and Escherichia coli embedded in alginate. The aerosolized glycol/ethanol formulation decreased bacterial viability by 3 log₁₀ and was more efficacious than an ethanol only control formulation. Electron microscopic examination indicated extensive structural damage in both bacteria, and membrane damage was confirmed with potassium release in S. aureus and DNA release in E. coli. The development of a small test chamber facilitated the measurement of the microbicidal efficacy and experiments to understand the mechanism of action of an aerosolized microbicidal formulation. SIGNIFICANCE AND IMPACT OF THE STUDY: There is an increased interest in developing effective microbicidal-aerosolized formulations. The development of a small in-house test chamber allowed the measurement of the microbicidal efficacy of an aerosolized glycol/ethanol formulation at a low cost. We showed that a glycol/ethanol aerosolized formulation caused extensive structural damage in Gram-negative and -positive bacteria resulting in a 3 log₁₀ reduction in viability.

Use of chlorine dioxide to sterilize medium for tissue culture of potato

In vitro cultured seedlings or microtubers are the major starting materials for the production of potato. Currently, seedlings are cultured in media sterilized by autoclaving, which, however, consumes more electricity and takes longer for sterilization, and also requires high temperature-tolerant vessel materials. In order to identify alternative methods of sterilizing culture conditions, the disinfection effects of chlorine dioxide (CD) at 88.0, 29.3, 17.6, 12.6 and 8.8 μM were evaluated in potato medium and vessels. The ≥12.6 μM gaseous CD effectively disinfected vessel through a 30-min fumigation process, and its aqueous solution disinfected potato medium efficiently as well. In presence of 12.6 μM CD in the medium, the potato seedlings had similar morphological features as those grown on autoclaved medium, with some exceptions. The use of 12.6-29.3 μM aqueous CD to sterilize the medium increased antioxidant enzyme activities in potato seedlings, while the use of higher concentration decreased antioxidant enzyme activity levels. SSR analysis did not reveal significant molecular differences in potato seedlings cultured between autoclaved and CD-sterilized medium. In addition to this, CD-sterilized medium induced potato microtuber formation at a similar rate as autoclaved medium. In summary, using CD to sterilize potato medium and vessels did not compromise the growth of seedlings and microtuber induction. This study provides an economical and simplified sterilization method for media used to culture potato plantlets, and this can improve energy use of the large-scale tissue culture industry.

Improvement of indoor air quality in pet shop using gaseous chlorine dioxide

Many studies have shown that pet shops have a high concentration of bioaerosols. Thus, effective disinfection protocols are essential to protect the pet shop staff and visitors to the store. The present study examines the effectiveness of gaseous chlorine dioxide (ClO₂) fogging in minimizing the residual bacteria and fungi levels in a typical pet shop in Taiwan consisting of a commodity area, a lodging area, and a grooming area. This investigation uses three disinfection modes (DMs) according to different disinfection periods, namely once every hour (1DM), once every 2 h (2DM), and once every 3 h (3DM). The bacteria and fungi concentrations are measured before and after disinfection treatment, and the effectiveness of each disinfection mode is evaluated using standard statistical techniques. To assess the effect of the environmental factors on the disinfection efficiency, measurements are taken of temperature, relative humidity, airflow velocity, the carbon dioxide concentration, the PM₁, PM_2.5, PM₇, PM₁₀, and TSP level at each sampling locations. The results reveal that the effectiveness of the three disinfection modes depends on both the environmental parameters and the use of the three areas (e.g., commodity, lodging, or grooming). Hence, the choice of disinfection method should be adjusted accordingly. For all three disinfection modes, a faster air velocity is beneficial in spreading the disinfectant throughout the indoor space and improving the disinfection performance. Overall, the results presented in this study confirm that gaseous chlorine dioxide disinfection improves the air quality in the pet shop interior, and thus beneficial in safeguarding the health of the pet shop staff and visitors.