68 publications from this institution
The prolonged duration of future manned space missions conceals potential threats associated with microbial contamination. Such closed environments are susceptible to formation of complex biofilm communities, where microorganisms can thrive and further evolve. The objective of this study was to evaluate the impact of surface type, surface treatment and shear stress on biofilm formation in water facilities. To that aim, the ability of Pseudomonas fluorescens SBW25 to adhere on three space applications related materials, including passivated (SS) and both passivated and electropolished (SSEP) stainless steel, as well as Ti-6Al-4V (Ti) alloy was studied under stagnant and shear stress conditions after 24 h of exposure. Results indicated that surface type strongly affects bacterial adhesion under the same conditions. Surface coverage during static experiments was in the following order: SS > Ti > SSEP, while SS exhibited a fourfold surface coverage compared to SSEP highlighting the significance of surface treatment. Moreover, SS and Ti stimulate the formation of several microcolonies and their growth. On the other hand, the application of shear stress diminished bacterial attachment to the studied materials, the degree of which relied on the material type. In this case, bacterial settlement on SS and Ti was dependent on the surface texture, implying that surface roughness may also play an important role in cell adhesion under shear conditions. Furthermore, the metallic surfaces did not hinder bacterial attachment when silver ions were previously deposited on their surface. The deposition that occurs on metallic surfaces when in contact with water disinfected with silver ions, for example, during space missions, highlights its impact on the loss of disinfection capacity of silver ions.
Abstract The objective of this work was the examination of the efficiency of coagulation and ozonation processes for the production of reclaimed wastewater with low toxicity. Municipal secondary effluents were treated by FeCl 3 , Al 2 (SO 4 ) 3 (alum), and a commercial substance at metal ion concentrations of 0.5 and 1 mmol/L. Alternatively, the effluents were treated by ozonation in a semibatch ozone reactor. The feed gas was introduced at a flowrate of 3 L/min containing ozone at various concentrations, ranging between 2.5 and 8 mg/L; ozone residence times were 2, 5, 15, and 30 min. The toxic effects of the advanced treated effluents were examined by a battery of tests using the marine bacteria Vibrio fischeri , the freshwater crustaceans Daphnia magna , Daphnia pulex , and Thamnocephalus platyurus , and the rotifers Brachionus calyciflorus . The addition of alum decreased the toxic effect of reclaimed wastewater on immobilization of D. pulex , from 90 to 60%. Ozonation was also effective for toxicity removal, which decreased to 25% effect on D. pulex after treatment by 2.5 mg O 3 /L for 2 min. However, acute toxic effects after ozonation, were observed on V. fischeri and were related to ozone gas concentration and contact time. At the highest ozone dosage, the toxicity reached almost 100% inhibition of bioluminescence after 15 min. The toxicity of the ozonated effluents to bacteria decreased with sample storage time and was almost negligible after 48 h, indicating that the potential adverse effect of reclaimed wastewaters on receiving waters might be reduced by storage for a certain time. © 2006 Wiley Periodicals, Inc. Environ Toxicol 21: 417–424, 2006.
Online techniques for monitoring biofilm formation and evolution are limited, especially as regards its application in flowing water systems. This is chiefly due to the absence of efficient non-destructive and non-invasive sensing methods. In this study, a sensitive electrical resistance spectroscopy technique is developed to monitor non-invasively and in real time the growth of biofilms over metallic surfaces inside water flow systems. To this aim, Pseudomonas fluorescens strain is used for biofilm development lasting 72 hours in a laboratory-scale test channel of orthogonal cross section. Biofilm development corresponds to a progressively increasing coverage of the metallic surface area up to full coverage and a progressively increasing thickness. Biofilm development is registered by continuous recording of electrical impedance signals (time series). Proper configuration and tuning of the electronics promote the resistive contribution to the signal whereas careful grounding diminishes electrical interferences and yields superb sensing sensitivity. An increase of relative electrical resistance of around 15% is noticed in 72 hours flow experiments which is attributed to both an increase of metallic surface area coverage and an increase of biofilm thickness. An independent estimation of these quantities using imaging tools and microscopy analysis, indicates that full coverage of the metallic surface occurs after only 48 hours of the flow experiment, whereas biofilm thickness increases gradually along the entire 72 hours of the experiment. Cross-examination of electrical signals with biofilm characteristics (metallic surface coverage and biofilm thickness) reveals that, qualitatively speaking, electrical signals are rather more sensitive to metallic surface coverage than biofilm thickness.
This study investigated the impact of flow path geometry on Pseudomonas fluorescens SBW25 biofilm structure, on different surface materials. A custom- experimental setup featuring vertically oriented millimeter-scale-flow channels was employed to grow biofilms on test coupons made of stainless steel electropolished (SSEP) and Teflon fluoroethylenepropylene (FEP), at 72 h after flow onset under constant flow conditions. Each flow channel accommodated an upstream and a downstream coupon placed in a row. Two channel types were employed: (i) one with a straight flow path throughout, and (ii) one with an upstream straight section and a downstream square-wave (zig-zag) flow path. Biofilm thickness and structure were quantified using Optical Coherence Tomography (OCT) images analyzed by a novel, in-house Matlab software. Results demonstrated that SSEP consistently supported thicker and more uniform biofilms compared to FEP. In straight channels (type i), biofilms on SSEP reached mean thicknesses of approximately 29 ± 9 μm (upstream) and 46 ± 17 μm (downstream), while FEP showed thinner biofilms (19-20 μm, COV ≈ 47 %). In square-wave channels (type ii), thicker biofilms developed on the upstream surfaces, with thicknesses of 86 ± 14 μm (COV ≈ 17 %) for SSEP and 81 ± 34 μm (COV ≈ 42 %) for FEP, respectively. Furthermore, biofilms on SSEP increased further along the downstream zig-zag path, indicating enhanced accumulation due to flow geometry. This effect was absent on FEP, where detachment occurred in certain zig-zag sections. Overall, the findings emphasize the critical interplay between surface properties and flow dynamics in shaping biofilm structure.
<p>Biofilms prevention and removal are crucial in many industrial and medical applications. Their complex and cohesive structure provides resistance to cleaning even to strong disinfectants. A key factor for their behavior is the wetting properties of their surfaces.</p> <p>The main goal of this work is to study the wetting properties of biofilms produced by bacteria <em>Pseudomonas fluorescens</em>. Biofilms are obtained on glass coupons under well controlled flow conditions, using custom-made flow cell devices. Different nutrient concentration and shear flow conditions are investigated.</p> <p>Biofilm wetting properties are examined under imposed external body forces (forced wetting) through a specialized device, named Kerberos®. Kerberos® is capable of subjecting sessile droplets to varying tilting angles and centrifugal forces while monitoring the variation of the droplet shape in X, Y and Z-directions through three Wi-Fi cameras. Wetting experiments are carried out using water-based solution (dye solution) droplets on biofilm-coated glass coupons. In this work, spreading/sliding behaviour of droplets are investigated only on horizontal substrates (no tilting) under the action of centrifugal forces. Apart from wetting properties, biofilm growth kinetics and surface morphology at different nutrient and shear flow conditions are also assessed.</p> <p>Results show that, according to the different growth conditions, biofilms present different wetting properties. At lower nutrient concentration and shear flow conditions, spreading and sliding behaviour are similar to that observed in glass coupons in the absence of biofilm. At higher nutrient and shear flow conditions, spontaneous wicking of the biofilm occurs the moment of droplet deposition on the biofilm leading to irregular and jagged shapes of droplets, while on the contrary water droplets look like smooth spherical sections on pure glass. The spontaneous wicking affects the droplet initial shape and so the wetting behaviour during the subsequent rotation tests. In each examined condition, biofilms show hydrophilic properties.</p> <p> </p>
Processing of the produced primary and secondary sludge during sewage treatment is demanding and requires considerable resources. Most common practices suggest the cotreatment of primary and secondary sludge starting with thickening and anaerobic digestion. The aim of this study is to investigate the anaerobic digestion of the primary sludge only and estimate its impact on sludge treatment and energy recovery. Within this context, the performance of the anaerobic digestion of primary sludge is explored and focused on practices to further enhance the methane production by using additives, e.g., a cationic polyelectrolyte and attapulgite. The results showed that the overall yield in methane production during anaerobic digestion of primary sludge alone was higher than that obtained by the anaerobic digestion of mixed primary and secondary sludge (up to 40%), while the addition of both organic polyelectrolyte and attapulgite enhanced further the production of methane (up to 170%). Attapulgite increased the hydrolysis rate of biosolids and produced relatively stabilized digestate, though of lower dewaterability. Moreover, the results suggest that single digestion of primary sludge may accomplish higher methane production capacities at lower digestors’ volume increasing their overall efficiency and productivity, while the produced digestates are of adequate quality for further utilization mainly in agricultural or energy sectors.
Water systems are highly vulnerable to biofilm formation, which can compromise water quality, operational efficiency, and public health. Factors such as surface material properties and gravitational orientation of the surface play critical roles in the early stages of microbial attachment and biofilm development. This study examines the impact of gravity and surface composition on the initial adhesion of Pseudomonas fluorescens AR11—a model organism for biofilm research. Focusing on stainless steel (SS) and polycarbonate (PC), two materials commonly used in water and wastewater infrastructure, bacterial adhesion was evaluated at surface inclinations of 0°, 45°, 90°, and 180° to assess gravitational impact. After three hours of contact, fluorescence microscopy and image analysis were used to quantify surface coverage and cluster size distribution. The results showed that both material type and orientation significantly affected early biofilm formation. PC surfaces consistently exhibited higher bacterial adhesion at all angles, with modest variations, suggesting that material properties are a dominant factor in initial colonization. In contrast, SS showed angle-dependent variation, indicating a combined effect of gravitational convection and surface characteristics. These insights contribute to a deeper understanding of biofilm dynamics under realistic environmental conditions, including those encountered in space systems, and support the development of targeted strategies for biofilm control in water systems and spaceflight-related infrastructure.
ABSTRACT During the COVID-19 pandemic, wastewater-based epidemiology (WBE) has been engaged to complement medical surveillance and in some cases to also act as an early diagnosis indicator of viral spreading in the community. Most efforts worldwide by the scientific community and commercial companies focus on the formulation of protocols for SARS CoV-2 analysis in wastewater and approaches addressing the quantitative relationship between WBE and medical surveillance are lacking. In the present study, a mathematical model is developed which uses as input the number of daily positive medical tests together with the highly non-linear shedding rate curve of individuals to estimate the evolution of virus shedding rate in wastewater along calendar days. A comprehensive parametric study by the model using as input actual medical surveillance and WBE data for the city of Thessaloniki (∼700,000 inhabitants, North Greece) during the outbreak of November 2020 reveals the conditions under which WBE can be used as an early warning tool for predicting pandemic outbreaks. It is shown that early warning capacity is different along the days of an outbreak and depends strongly on the number of days apart between the day of maximum shedding rate of infected individuals in their disease cycle and the day of their medical testing. The present data indicate for Thessaloniki an average early warning capacity of around 2 days. Moreover, the data imply that there exists a proportion between unreported cases (asymptomatic persons with mild symptoms that do not seek medical advice) and reported cases. The proportion increases with the number of reported cases. The early detection capacity of WBE improves substantially in the presence of an increasing number of unreported cases. For Thessaloniki at the peak of the pandemic in mid-November 2020, the number of unreported cases reached a maximum around 4 times the number of reported cases. HIGHLIGHTS Model estimates viral load evolution in wastewater from infected people dynamics Identifying actual conditions for which WBE can be used as an early warning tool Early warning capacity increases with an increasing number of unreported cases In Thessaloniki Nov20 outbreak, the early warning capacity of WBE was about 2 days In Thessaloniki Nov20 outbreak, unreported cases were up to 4 times reported cases
Microbial adhesion and spreading on surfaces are crucial aspects in environmental and industrial settings being also the early stage of complex surface-attached microbial communities known as biofilms. In this work, Pseudomonas fluorescens-laden droplets on hydrophilic substrates (glass coupons) are allowed to partially evaporate before running wetting measurements, to study the effect of evaporation on their interfacial behavior during spillover or splashing. Forced wetting is investigated by imposing controlled centrifugal forces, using a novel rotatory device (Kerberos). At a defined evaporation time, results for the critical tangential force required for the inception of sliding are presented. Microbe-laden droplets exhibit different wetting/spreading properties as a function of the imposed evaporation times. It is found that evaporation is slowed down in bacterial droplets with respect to nutrient medium ones. After sufficient drying times, bacteria accumulate at droplet edges, affecting the droplet shape and thus depinning during forced wetting tests. Droplet rear part does not pin during the rotation test, while only the front part advances and spreads along the force direction. Quantitative results obtained from the well-known Furmidge's equation reveal that force for sliding inception increases as evaporation time increases. This study can be of support for control of biofilm contamination and removal and possible design of antimicrobial/antibiofouling surfaces.
