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.
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.
<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>
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.
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.
The physicochemical and toxic properties of fly ash samples obtained from various coal combustion power plants were evaluated in this work using an integrated approach including chemical analyses and bioassays. Physicochemical analyses showed that Al, Ca, Fe, Mg and Si were the elements presented in high concentrations in all solid samples. The results of the chemical analysis of eluates deduced by the application of standard leaching tests according to EN 12457-2 and TCLP methods indicated that the compounds contained in the fly ash samples presented a potential to be transferred to the liquid phase depending upon the leaching method used. The pH values of the EN eluates were in most cases in the high alkaline range, ranging from 9.5 up to 12.7, while the pH value of TCLP eluates varied between 3.9 and 7.5. The leachability of the compounds was higher in TCLP leaching test, indicating that the initial pH value of the leaching medium affected significantly the transfer of these elements to the liquid phase. The photobacterium Vibrio fischeri (Microtox test), the crustaceans Daphnia magna and the rotifers Brachionus calysiflorus were used for the toxicity measurement of the eluates obtained by the EN leaching test, suggesting that the toxicity of the eluate samples depended on the test organism used. The toxicity of the fly ash samples and the corresponding solid filter residuals that were remained after the EN and TCLP leaching tests was also measured using the Microtox Basic Solid Phase Test.
Epidemic spread models are useful tools to study the spread and the effectiveness of the interventions at a population level, to an epidemic. The workhorse of spatially homogeneous class models is the SIR-type ones comprising ordinary differential equations for the unknown state variables. The transition between different states is expressed through rate functions. Inspired by -but not restricted to- features of the COVID-19 pandemic, a new framework for modeling a disease spread is proposed. The main concept refers to the assignment of properties to each individual person as regards his response to the disease. A multidimensional distribution of these properties represents the whole population. The temporal evolution of this distribution is the only dependent variable of the problem. All other variables can be extracted by post-processing of this distribution. It is noteworthy that the new concept allows an improved consideration of vaccination modeling because it recognizes vaccination as a modifier of individuals response to the disease and not as a means for individuals to totally defeat the disease. At the heart of the new approach is an infection age model engaging a sharp cut-off. This model is analyzed in detail, and it is shown to admit self-similar solutions. A hierarchy of models based on the new approach, from a generalized one to a specific one with three dominant properties, is derived. The latter is implemented as an example and indicative results are presented and discussed. It appears that the new framework is general and versatile enough to simulate disease spread processes and to predict the evolution of several variables of the population during this spread.
The complex nature and behavior of Engineered Nanomaterials (ENMs) has led to adoption of customized experimental ecotoxicity practices that are prone to possible artefacts in the inherent toxic properties of ENMs. In addition, the lack of standardized handling procedures for the ecotoxicity testing of ENMs prevents the development of experimental protocols for regulatory purposes. In this study, a suite of techniques for dispersion of ENMs was adopted and tested for two types of surface-modified alumina nanoparticles-one hydrophobic and one hydrophilic-towards the bacteria, Vibrio fischeri. The effect of certain handling practices on the observed ecotoxic effects on V. fischeri was examined. The overall goal was to evaluate by what means the handling practices of ENMs may affect the obtained toxicity results. It was realized that the toxicity of the hydrophilic and hydrophobic ENMs was mainly affected by the centrifugation and the salinity of the tested dispersions, respectively. It is more likely that both aluminium and coating substance contributed to the overall toxicity. Toxicity results are discussed with regard to generic physicochemical characteristics of the dispersions.
