Air Load Research Articles

Assessment of waste workers occupational risk to microbial agents and cytotoxic effects of mixed contaminants present in the air of waste truck cabin and ventilation filters

ABSTRACT Workers in the waste-processing industry are potentially exposed to high concentrations of biological contaminants, leading to respiratory and digestive problems and skin irritations. However, few data on the exposure of waste collection truck (WCT) drivers are available. The goal was to document the microbial risk of the waste collection truck (WCT) workers while in the vehicle cab. Long-period sampling using the truck air filters (CAF) and short time ambient air sampling in the cab were used. The potential release of microbial particles from CAFs was also investigated since it could contribute to the microbial load of the cabin air. A combination of analytical methods also helped assess the complex mixture of the biological agents. Aspergillus sections Fumigati and Flavi, E. coli, Enterobacter spp. and Legionella spp. were detected in the CAF of trucks collecting three types of waste. The highest levels of bacteria and fungi were found in the CAF from organic WCT. The highest endotoxin concentrations in CAF were 300 EU/cm2. Most of the CAF showed cytotoxic effects on both lung cells and hepatocytes. Only one mycotoxin was detected in a CAF. The maximal concentrations in the ambient WCT air varied according to the type of waste collected. The highest proportion (84%) of the air samples without cytotoxic effects on the lungs cells was for the recyclable material WCTs. The results revealed the potential microbial risk to workers from a complex mixture of bio-contaminants in the cabs of vehicles collecting all types of waste. The sustained cytotoxic effect indicates the potential adverse health-related impact of mixed contaminants (biological and non-biological) for the workers. Overall, this study highlights the benefits of using complementary sampling strategy and combined analytical methods for a the assessment of the microbial risk in work environments and the need to implement protective measures for the workers. Implications: Exposure to microbial agents is a well-known occupational hazard in the waste management sector. No previous study had evaluated the cytotoxicity of ambient air and ventilation filters to document worker exposure to a combination of contaminants during waste collection. This research confirms the usefulness of ventilation filters for long-term characterization of exposure to infectious agents, azole-resistant fungi, coliform bacteria and mycotoxin. Overall, this study highlights the importance of using several sampling and analysis methods for a comprehensive assessment of microbial risk in work environments, as well as the need to implement appropriate protective measures for collection workers.

Concentration levels of anthropogenic organic compounds in suspended particulates matter and indoor settled from Algiers, Algeria

Total suspended particles (TSP) and indoor settled dust (ISD) were collected at an annual religious event in November 2019. Fifteen outdoor TSP and forty-one ISD samples (at two hospitals, university laboratories, and research centers) were collected in two Algerian urban areas. Gas chromatography/mass spectrometry (GC/MS) was used to look for solvent-extractable organic chemicals comprising alkanes, polycyclic aromatic hydrocarbons (PAHs), phthalate esters, and other polar organic compounds (OPOC). The origin of pollution was investigated, and source apportionment was performed. Phthalates were predominant in soot (the most abundant, di-2-ethylhexyl phthalate, varying between 11.5 and 106.3 ng m−3), followed by alkanes (with hentriacontane ranging between 3.9 and 6.1 ng m−3 and accounting for 39.5%), OPOCs (the most abundant, caffeine, ranging 2.7–182 ng m−3), and PAHs (the predominant, phenanthrene, ranging 29.8–130.6 ng m−3). Mean concentration of benzo[a]pyrene (BaP) reached ∼5 and ∼21 ng m−3, respectively, on weekends and working days in TSP, exceeding the WHO recommendation range of 1 ng m−3. Meanwhile, BaP ranged from 0.01 to 1.02 ng m−2 in ISD. Nicotine, cotinine and caffeine, were detected in different amounts in TSP (2.1–3.5, 0.0 to 3.3, and 2.7–182 ng m−3, respectively). In ISD, nicotine and caffeine occurred in all samples, while cotinine was present in ∼82% of samples and ranged from 0.0 to 3798 ng m−2. Traces of N, N-diethyl-meta-toluamide DEET (5.2 ng m−3 on average in soot and up to 168 ng m−2 in dust) and methyl dihydrojasmonate MDHJ (up to 124 ng m−2 in dust and ≈0.26 ng m−3 in soot) were found at all sites. This study provided new information about organic contaminants of environmental concern in Algiers, which would be useful in assessing the chemistry of interiors and exposure to toxicants. It also highlighted the impact of special events on environmental quality in terms of increased toxicant loads in ambient air. The findings thoroughly assess Algeria’s atmospheric particulate matter endocrine-disrupting chemicals when combined with earlier studies.

Bacterial load of the surroundings during rigid diagnostic bronchoscopy under high frequency jet-ventilation

High-frequency jet ventilation (HFJV) is used in pneumological endoscopy for rigid, diagnostic, and therapeutic bronchoscopies. It is unclear to what extent the unobstructed flow of respiratory gas from the patient's lungs causes microbial contamination of the surrounding air. After the start of the HFJV (15 min) in 16 rigid bronchoscopies, airborne pathogen measurements were taken directly at the distal endoscope outlet, at examiner height (40 cm above the endoscope outlet), at a 2 m distance from the endoscope in the room and at the supply air outlet of the examination room using an RCS air sampler. The number and type of pathogens isolated in the air samples were then determined, as well as germs in the bronchoalveolar lavage fluid (BALF) from the patient's lungs. An increased bacterial density (136 and 114 CFU/m3) was detected directly at the distal end of the endoscope and at examiner height at a distance of 40 cm, which decreased significantly with increasing distance from the bronchoscope (98 CFU/m3 at a distance of 2 m and 82 CFU/m3 at the supply air outlet). The most frequently detected bacteria were Staphylococcus spp., Micrococcus spp. and Bacillus spp. In the BALF, pathogens could only be cultivated in four of 16 samples, but the same pathogens were detected in the BALF and the ambient air. When performing a rigid bronchoscopy, in which patients are mechanically ventilated in a controlled manner using an open HFJV system, there is an increased pathogen load in the ambient air and therefore a potential risk for the examiner.

Integrating Latent Load into the Cooling Degree Days Concept for Current and Future Weather Projections

Rising temperatures, increase in population, and dense urban morphology have resulted in increased cooling energy demands. The conventional degree-days method to calculate cooling energy demand considers only the sensible heat load of air and neglects the latent component. This study aims to estimate the cooling degree days based on the heat index (by considering both the sensible and latent loads) for the current and future years (2050 and 2080). Further, the ventilation load index for each of these cities has been established to unlock the impact of ventilation on the building’s total energy consumption for current and future years. The results show that heat index-based degree days have a stronger relationship with the buildings’ cooling energy consumption and, therefore, can predict the cooling energy demand of buildings with 20% higher accuracy than conventional temperature-based degree days. Analysis shows that cooling degree-days and frequency of temperature above the comfort range continue to increase in Pakistan, highlighting increased degree-days in the range from 11.0 to 41.6% by 2050 and from 28.4 to 126.5% by 2080. Prompt actions are essential to enhance the resilience of Pakistan’s national grid to meet these future cooling energy demands.

Mechanical and tribological properties of (AlCoCrNiSi)100−xNx thin films

High entropy thin films of (AlCoCrNiSi)100−xNx were deposited on silicon wafers using a pulsed DC magnetron sputtering technique, with nitrogen gas flow ratios (RN) of 0, 0.33, and 0.50. The structure and properties of these films were analyzed for elemental composition, surface and cross-sectional morphologies, microstructure, roughness, and mechanical properties. The coatings were primarily composed of an amorphous structure with a minor presence of a BCC structure and exhibited periodic variations in chemical composition from the substrate to the free surface. An increase in RN enhances crystallinity of the materials. Nanoindentation results showed that the films deposited at RN = 0.50 displayed the highest hardness (10.7 ± 0.5 GPa) and reduced modulus (176 ± 5 GPa), which were the highest among the films. Microtribology testing was conducted using a 20 μm radius spherical diamond tip under ambient air and normal loads ranging from 0.5 to 9 mN. Worn surfaces were characterized using atomic force microscopy. The coefficient of friction was evaluated to investigate the elastic and plastic behaviors of films using Schiffmann’s model. The coating without nitrogen displayed a predominant plastic behavior during the initial cycles, while the coating deposited at RN = 0.33 demonstrated a more elastic behavior, particularly at lower loads.

Cyclic Impact Test with the Hopkinson Bar: Application to Granite

A laboratory scale cyclic impact loading test was developed by modifying a Hopkinson Bar test setup. The modifications involve placing a special shank piece between the striker and the rest of the setup. The shank transmits the impact loading and enables the use of compressed air for rapid reloading of the striker. The short shank is in direct contact with the specimen, i.e., there is no long input bar. With this configuration residual wave motion and reloading of the specimen is avoided. Behind the striker an output bar and momentum trap bar are placed for specimen loading measurement and removal of the wave motion in the system, respectively. The trap bar is stopped by a pneumatic actuator, which also resets the bars and the specimen before the next impact loading. The compressed air flow driving the striker is controlled by high-speed electropneumatic valves connected to a control unit and operated in simple open-loop control. Numerical simulations of both the striker motion by compressed air and dynamic loading wave propagation during impact were used in the design phase as well as setting up the test parameters. The test setup is able to produce stable cyclic impact loading at a frequency of up to 10 impacts per second with striker velocity up to 9 m/s. The feasibility of the test method is demonstrated by providing data from cyclic Brazilian disc experiments on Balmoral Red granite at both impact and quasi-static cyclic loading.

Bactericidal efficacy of mobile ultraviolet-C disinfection devices in reducing contamination in biosafety laboratories.

Biosafety research requires a wide range of microorganisms and thorough disinfection to prevent laboratory infection is often required. Ultraviolet-C (UV-C) exposure reduces bacterial and viral concentrations. Therefore, in this study, we aimed to evaluate the efficacy of a mobile UV-C device as a non-contact disinfection strategy. The bactericidal efficacy of the UV-C device was determined based on log10 decreases in the relative abundances of bacterial indicators, including Escherichia coli, Staphylococcus aureus, Staphylococcus albus, and Pseudomonas aeruginosa at 0.5 and 1.0 m after irradiation for 30, 60, and 90 min. Next, the reduction of natural bacteria in air and on surface as a result of the UV-C device exposure in the laboratory were determined. Exposure to the UV-C disinfection device resulted in mean log10 decreases in microbial contamination of 3.55 and 5.85 following irradiation for 30 and 90 min, respectively, at a distance of 0.5 m. Further, P. aeruginosa and E. coli were the most and least sensitive to UV-C exposure, respectively. The bacterial load in air decreased by 65.53% after 60 min of irradiation, while those on surfaces decreased by 44.19% and 78.23% after 30 and 60 min of irradiation, respectively. The UV-C device effectively reduced bacterial load after irradiation for over 60 min. Further studies are encouraged to determine the effectiveness of the UV-C disinfection device in frequently occupied institutions, such as primary medical, health, and nursery, and its efficiency in infection control.

The reliability of models for converting formaldehyde emissions from wood-based materials to different environmental conditions

The monitoring of the formaldehyde emission potential of wood-based materials by means of test chamber investigations has been established by national and international standards and has made an important contribution to significantly reducing the formaldehyde concentrations indoors. The procedures used are mostly methodologically different, so that the results cannot be directly compared. The first empirical models for converting formaldehyde steady-state concentrations as a function of temperature, air humidity, air change rate and loading were derived in the 1970s. However, the development of lower-emitting materials made it necessary to modify and adapt these models. Formaldehyde emissions from wood-based materials are complex from both a reaction-kinetic and dynamic perspective. There is an exponential dependence of the steady-state concentration on temperature and humidity and an inverse proportionality to the air change rate. The mathematical analysis requires multiple non-linear regression tools. A large data set with reliable results obtained under different conditions is available from previous investigations. With a total of 128 measurement data, there was very good agreement between theory and experiment for a wide range of chamber settings from a statistical point of view. However, the model is not suitable for predicting the emission behavior of individual products. Some uncertainty also exists due to the allowed tolerance limits of the chamber parameters. Since the formaldehyde emission rate depends on the air change rate, a simple linear conversion of steady-state chamber concentrations into room air concentrations for indoor exposure assessments is not possible even at constant temperature and humidity.

Assessing the impact of particulate fouling on the long-term performance of energy recovery ventilators

Energy recovery ventilators (ERVs), which integrate fresh air supply, air purification, and energy recovery, are prominently employed in buildings. Particulate fouling and dynamic climate conditions in real-time scenarios could cause the deviation of operating parameters from the designed values, impacting the long-term performance of ERVs. In this study, a non-linear regression model of energy exchanger involving imbalanced airflow rate conditions was derived based on experimental data, considering the decreased supply air volume caused by dust-loading of fresh air filter. Model validation presented errors within ±10 %. Furthermore, an ERV model was established by integrating the energy exchanger, filter, and fan. Simulation results indicate that particulate fouling could decrease the instant supply airflow rate and recovered energy to maximums of 15 % and 12 % respectively, compared to the ideal performance in the clean state. Analysis throughout the heating season concludes that, the reduced recovered energy together with the unorganized air infiltration consequent on the imbalanced airflow rates could increase the seasonal fresh air load by 10.9 %, 13.1 %, and 24.1 % in three typical cities, Shanghai, Beijing, and Harbin, respectively. The proposed model provides a reliable platform for evaluating the performance and analyzing the maintenance strategies of ERVs, contributing to improving their practical effects.

Airborne Culturable Fungi in Primary Schools

The aim of this current research was to investigate airborne fungi in indoor environments at primary schools. The study also examined the correlation between these fungi and building characteristics, as well as some geographical and meteorological parameters. To achieve this aim, a passive sampling method was used. In this study, 148 samples were collected from the indoor environments of 24 schools located in Qom, Iran. To collect the samples, passive sampling was performed using Petri plates containing Sabouraud dextrose agar (SDA). The characteristics of school buildings were evaluated by checklist. The mean ± SD fungal load of indoor air in selected schools was found to be 10.1 ± 14.0 colonies (CFU/dm2/ h). According to the IMA standard, the majority of the classes (71.7%) were in very good condition. The dominant species were as follows: Aspergillus niger, Aspergillus candidus, and Aspergillus flavus. Furthermore, the fungal load of girls’ schools was significantly higher than that of the boys' schools (p < .05). The correlation analysis using the Pearson test showed that there was a direct correlation between the mean fungal load of classrooms and the number of students (p < .01). The highest concentration of fungi was found on the ground floor and in poor ventilation conditions (p < .05). During the study, it was found that schools located in the western part of Qom, Iran, had a higher concentration of fungi. This can be attributed to their exposure to the prevailing winds and the penetration of outdoor dusty air into indoor environments. The large number of students in each class and the inappropriate ventilation, which are the causes of airborne culturable fungi of these classes, call for the need for proper operation of school buildings.

Mobile measurements for distribution and attribution of particulate matter in urban environments

Particulate matter (PM) sources differ in urban environments and may show spatiotemporal distinct patterns for varying particle aerodynamic diameters (DP). We here assess such patterns using high-resolution PM ≤10 μm data recorded with a cargo bike along a 14 km route through urban, suburban, and rural areas in Mainz (Germany). The measurements conducted twice a day between May and August 2021 reveal decreasing particle number concentration (PNC) with increasing DP including ∼6000 times higher particle numbers at DP 0.22–0.25 μm compared to DP 4–5 μm. Total mass concentration is bi-modally distributed and dominated by particles <0.3 μm and from 3 to 5 μm representing 36 and 22% of the entire air load, respectively. PM concentrations in Mainz are significantly higher in the morning than in the afternoon, and PM1 and PM10 are 13 and 31% higher in urban compared to surrounding suburban and rural areas. The high-resolution measurements also revealed 30% higher PM concentrations at DP 3–5 μm in the urban compared to the rural sectors, which is indicative for road dust, brake and tyre abrasion as the main source. DP distribution in rural hotspots is generally shifted toward larger particles >3 μm, most likely related to natural dust from agricultural fields. These findings show that high-resolution PM profiles can skillfully be recorded using bikes as mobile platform to identify spatial pollution patterns and attribute DP spectra to particular emission sources.

Experimental Study on the Impact of Hydrogen Injection Strategy on Combustion Performance in Internal Combustion Engines.

Hydrogen is an ideal alternative fuel for internal combustion engines due to its fast combustion rate and near-zero carbon emissions. To further investigate the impact of the injection strategy on combustion performance under various excess air coefficients and loads, experimental methods were employed to systematically study injection timing, injection pressure, and dual injection. The results demonstrate that appropriately delaying hydrogen injection timing can improve the thermal efficiency by up to 2.6% and reduce NOx emissions of equivalent combustion by nearly 88%. While increasing the hydrogen pressure to 8 MPa does not directly enhance the thermal efficiency and emissions, it can reduce the injection pulse width by approximately 75%, allowing for more flexibility in delaying the injection timing. Delaying the secondary end of injection (SEOI) leads to a reduction of over 47% in NOx emissions for λ (excess air coefficient) values of 1.5 and 1.0. The combustion duration and ignition delay initially increase and then decrease with the delay in SEOI, depending on the movement state of the fuel jet. With the increase in secondary injection proportion (SIP), brake thermal efficiency increases by no more than 1%, but NOx is reduced by more than 43% for λ values of 1.5 and 1.0. In the case of ultralean conditions (λ = 2.3), increasing the SIP from 0 to 30% results in a nearly 14% increase in the peak heat release rate (HRR) and a 19% reduction in combustion duration.

Data-Driven Modeling of HVAC Systems for Operation of Virtual Power Plants Using a Digital Twin

Confronted with the climate crisis, the world is making tremendous efforts in energy transition, such as expanding renewable energy that does not emit carbon. The importance of virtual power plant (VPP) operation technology has emerged to secure grid flexibility in response to the expanding renewable energy implemented due to these efforts. Accordingly, VPPs, which include photovoltaics, wind turbines, heating, ventilation, and air conditioning (HVAC), load, and EV, have been constructed. HVAC, one of the component resources, is a system that controls and regulates temperature, humidity, and airflow. Since it responds sensitively to the building’s heat capacity and changes in the external environment, it requires continuous and stable control. In this paper, we used data-based modeling to implement the HVAC required for the optimal operation of VPP. Since accurately creating an equation-based HVAC model was difficult considering building information modeling and external environment variables, we used historical HVAC operation data to perform data-based modeling. The model was implemented using nonlinear regression and machine learning, such as a support vector machine and artificial neural network. Then, the data-based HVAC and the actual HVAC operation results were comparatively analyzed based on a case study, and the model’s goodness-of-fit was evaluated based on performance metrics. Model performance indicators confirmed that the ANN-based HVAC model was most similar to the actual HVAC system.

Mechanical Ventilation Heat Recovery Modelling for AccuRate Home—A Benchmark Tool for Whole House Energy Rating in Australia

To manage energy-efficient indoor air quality, mechanical ventilation with a heat recovery system provides an effective measure to remove extra moisture and air contaminants, especially in bathrooms. Previous studies reveal that heat recovery technology can reduce energy consumption, and its calculation needs detailed information on the thermal performance of exhaust air. However, there are few studies on the thermal performance of bathroom exhaust air during and after showers. This study proposed a detailed thermal performance prediction model for bathroom exhaust air based on the coupled heat and mass transfer theory. The proposed model was implemented into the AccuRate Home engine to estimate the thermal performance of residential buildings with heat recovery systems. The time variation of the water film temperature and thickness on the bathroom floor can be estimated by the proposed model, which is helpful in determining whether the water has completely evaporated. Simulation results show that changing the airflow rate in the bathroom has little effect on drying the wet floor without additional heating. The additional air heater installed in the bathroom can improve floor water evaporation efficiency by 24.7% under an airflow rate of 507.6 m3/h. It also demonstrates that heat recovery can significantly decrease the building energy demand with the fresh air load increasing and contribute about 0.6 stars improvement for the houses in Hobart (heating-dominated region). It may be reduced by around 3.3 MJ/(m2·year) for the houses in other regions. With this study, guidelines for optimizing the control strategy of the dehumidification process are put forward.

Constructing year-round energy-efficient fresh air handling unit with exhaust air heat recovery using multi-condition design

Traditional fresh air handling units with exhaust air heat recovery insufficiently utilize exhaust air waste energy, and are designed under the design-load condition, which are unable to efficiently adapt to the varying fresh air conditions for both the energy consumptions of compressors and fans. To promote energy efficiency, a fresh air handling unit with exhaust air heat recovery is constructed in this study by grade matching of loads and waste and natural energies under different typical fresh air parameter conditions, and the improved year-round efficient system configuration is determined by combining the configurations obtained under each typical condition. In addition, numerical models are adopted to calculate the energy and economic performances of the system in an office building in Nanjing, China, and a traditional system is also analyzed for performance comparison. The main conclusions are as follows: 1) The improved system configuration is determined to be a heat-recovery device plus a two-stage heat pump that can operate close to a separately designed configuration under various cases, thereby ensuring efficient operation throughout the year; 2) Compared with a traditional fresh air handling unit for fresh air load treatment with a variable refrigerant flow system in Nanjing, China, the annual saving rate of the proposed system is 14.4 %; 3) Compared with the traditional system, the static payback period is 1.1 years.

Flame Propagation in Blends of R-152a, R-134a, and R-1234yf with Air

ABSTRACT Some new, low-global warming potential refrigerants will be flammable, and the laminar burning velocity is a useful parameter for quantifying fire risk. Laminar burning velocity measurements have been made using a constant volume experiment with dry air and the refrigerant R-152a (CH3CHF2), pure and blended with R-134a (CH2FCF3), or R-1234yf (CF3CFCH2). The resulting burning velocity data deduced from the pressure rise in the chamber are presented for a range of fuel air equivalence ratio and loading of the less flammable refrigerant, for unburned gases at 298 K and 101 kPa as well as at 375 K and 253 kPa. For comparison, the 1-D, planar laminar burning velocity was numerically simulated using a recently developed kinetic mechanism that includes a wide range of refrigerants with air. The predicted burning velocities agree reasonably well with the experimental values, and the numerical results are used to understand the kinetic mechanism of the reaction of the refrigerants. Uncertainties in the experimental data from radiation heat losses as well as extrapolation to ambient conditions are explored.

Energy-efficient fresh air system with pressure-independent dampers for nearly zero energy buildings

Fresh air volume control is of great significance in reducing energy consumption in nearly zero energy buildings. Previous studies have shown that the operating fresh air volume often deviates significantly from the design value, resulting in unnecessary energy consumption. To overcome this problem, this study proposes an energy efficiency fresh air system for NEBs by using pressure-independent dampers to balance system resistance and control the operating fresh air volume accurately. A typical fresh air system used in a typical NZEB was tested both in laboratory and on site for a whole heating season. Based on the test data, the energy consumption model of the proposed fresh air system was established and validated. The energy performance of the proposed system was analyzed comprehensively. Results show that using the pressure-independent damper in the fresh air system to control the fresh air flow rate can significantly reduce the fresh air load by 39.2%, 49.4%, 52.3% and 45.5% in Harbin, Beijing, Shanghai and Guangzhou, respectively; The annual energy saving rates in these cities are approximately 29.3%, 28.7%, 27.0% and 19.1%, respectively. These energy saving rates are smaller than the corresponding fresh air load reductions due to the additional energy consumption caused by the pressure-independent damper; Furthermore, replacing the pressure-independent damper with an ideal variable speed ventilator for fresh air flow rate control can further increase the energy saving rate by 12%∼16%. This study identifies the energy saving potential of fresh air systems and contributes to achieving sustainable development in nearly zero energy buildings.

Effect of portable HEPA filters on COVID-19 period prevalence: an observational quasi-interventional study in German kindergartens

ObjectivesThe aim of the study was to evaluate the effect of high-efficiency particulate air (HEPA) filters on COVID-19 period prevalence in kindergartens.DesignThe observational study follows an intervention design with the...

Monitoring of Air and Water Bacterial Load in the Operation Theatres and Intensive Care Units of Selected Hospitals in Dhaka city: A Cross-Sectional Study

Background: Hospital milieu monitoring is an essential component for controlling healthcare associated infections (HCAIs) as it serves as the reservoir for pathogenic microbes. Aim of this study was to identify the bacterial load in Intensive care units (ICU) and Operation theaters (OT) air and water sources of selected tertiary care hospitals. Material &amp; Methods: The study was organized in Microbiology department, BIRDEM General Hospital. A sum total 28 air samples &amp; 6 water samples were collected from three selected hospitals and those were processed according to the set of protocols. Results: From air sampling, highest load of bacteria was found 480 CFU/dm²/hr in Hospital C ICU, 38.40 ± 9.99 CFU/dm²/hr in pre-OT samples &amp; 218.2±43.35 CFU/dm²/hr in intra OT samples of Hospital C. From water sampling, unacceptable level of coliforms was found in all three hospitals. Among the non-pathogens, 24% – 37% Micrococcus spp. (normal flora) and 2% -18% Bacillus spp. (contaminants) were found in the OTs. Whereas pathogens found were Acinetobacter spp. (20.7%) followed by Pseudomonas spp. (19.4%), Klebsiella spp. (12.1%) &amp; S. aureus (9.2%) in the ICUs. Conclusion: It could be deduced from the study that environmental sources such as air and water contaminations with multidrug resistant pathogens are an ultimate risk factor for all related to the healthcare settings, specially the indoor patients.

Comparison of fine bubble scouring, backwash, and mass air load supply for dynamic membrane maintenance and steady operation in SFD MBR for wastewater treatment

The self-forming dynamic membrane bioreactor (SFD MBR) is an evolution of the conventional ultrafiltration-based MBR where filtration occurs through a cake layer (dynamic membrane, DM) supported by a filtration net. The effluent quality levels that may be achieved through this technology are comparable to those of conventional MBR and suitable for effluent reuse, as shown in previous research. In addition, SFD MBR are more sustainable, both in terms of investment costs (filtration net materials are cheaper than UF membranes), and operation. Indeed, the typical operating pressure of these systems is below 100 mbar, thus compatible with gravity-driven operation. Nevertheless, as all membrane-based processes, also SFD MBR require periodic maintenance cleaning of the supports holding the filtering layers, in order to ensure high and constant effluent quality and steady operation. In this paper, different strategies for continuous or temporized cyclic DM maintenance aimed at limiting the frequency of on-site manual cleaning interventions are compared. In particular, five tests were performed at the bench scale adopting the same process conditions except for the type of DM maintenance strategy. Continuous fine-bubble air scouring of the membrane surface was compared with two intermittent cyclic procedures based on backwash with permeate (with and without simultaneous air scouring) and mass air load supply (with two cycles of different durations), respectively. The results have confirmed the overall high performance of this technology under all the tested conditions, with COD removal efficiencies always exceeding 86 %, effluent turbidity values normally well below 5 NTU (and often much lower), complete nitrification and partial nitrogen removal. Furthermore, the comparison among the different DM maintenance strategies has shown that the mass air load supply is the most efficient approach towards sustainable operation. In particular, shorter mass air load cycles provided the best performance in limiting the manual cleaning needs, which under this condition were as low as once every 3 weeks. The key finding of this study is the demonstration of cyclic air mass load as an effective preventive cleaning strategy allowing good performance of a bench-scale SFD MBR, strongly reducing the manual maintenance requirements. More experiments are required to confirm these results in larger scale installations.