Impact of wall shear stress on initial bacterial adhesion in rotating annular reactor

Responses of drinking water bulk and biofilm microbiota to elevated water age in bench-scale simulated distribution systems

Reductions in nonresidential water demand during the COVID-19 pandemic highlighted the importance of understanding how water age impacts drinking water quality and microbiota in piped distribution systems. Using benchtop model distribution systems, we aimed to characterize the impacts of elevated water age on microbiota in bulk water and pipe wall biofilms. Five replicate constant-flow reactors were fed with municipal chloraminated tap water for 6 months prior to building closures and 7 months after. After building closures, chloramine levels entering the reactors dropped; in the reactor bulk water and biofilms the mean cell counts and ATP concentrations increased over an order of magnitude while the detection of opportunistic pathogens remained low. Water age, and the corresponding physicochemical changes, strongly influenced microbial abundance and community composition. Differential initial microbial colonization also had a lasting influence on microbial communities in each reactor (i.e., historical contingency).

Effects of flow velocity on biofilm composition and microbial molecular ecological network in reclaimed water distribution systems

The existence of biofilm on the reclaimed water pipeline seriously affects the safety of water distribution. And the flow regimes in the pipeline play a crucial role in the growth of biofilms. In this study, the biofilm composition, surface topography and bacterial community were detected under eight levels of flow velocity in the range of 0.10-1.40 m s-1. The results showed that the dry weight, the concentration of extracellular protein and extracellular polysaccharide in the biofilm reached a dynamic stable period after 640 h. The biofilm composition and surface topography of biofilm were significantly different under the different flow regimes (laminar flow belongs to [0.10, 0.19] m s-1, and turbulent flow belongs to [0.29, 1.40] m s-1). As the flow velocity range increases, the concentration of each component in the biofilm and the parameters of biofilm surface topography increased and then decreased. The flow velocity could be a strong environmental stimulus resulting in the succession of bacterial community in biofilm. As the flow velocity increased from 0.10 m s-1 to 1.40 m s-1, at the phylum level, the average relative abundance of Firmicutes mainly showed a trend of first increasing and then decreasing with the highest abundance value of 71.57% at 0.49 m s-1. The flow velocity increased from 0.10 m s-1 to 0.49 m s-1, a significant increase in microbial diversity could be detected. The increase in flow velocity promoted the proliferation of microorganisms, and the interaction between different microbial components was enhanced. At 0.49 m s-1, the function of the biofilm is complex, and the ability to resist environmental stress is the strongest. This study can effectively improve the cognition depth of biofilms under the influence of flow velocity in the reclaimed water distribution systems, and provide an important theoretical support for the safe distribution of reclaimed water.

Challenges and current advances in in vitro biofilm characterization

Biofilms are structured communities of bacterial cells encased in a self-produced polymeric matrix, which develop over time and exhibit temporal responses to stimuli from internal biological processes or external environmental changes. They can be detrimental, threatening public health and causing economic loss, while they also play beneficial roles in ecosystem health, biotechnology processes, and industrial settings. Biofilms express extreme heterogeneity in their physical properties and structural composition, resulting in critical challenges in understanding them comprehensively. The lack of detailed knowledge of biofilms and their phenotypes has deterred significant progress in developing strategies to control their negative impacts and take advantage of their beneficial applications. A range of in vitro models and characterization tools have been developed and used to study biofilm growth and, specifically, to investigate the impact of environmental and growth factors on their development. This review article discusses the existing knowledge of biofilm properties and explains how external factors, such as flow condition, surface, interface, and host factor, may impact biofilm growth. The limitations of current tools, techniques, and in vitro models that are currently used for biofilms are also presented.

Role of Biofilms in Waste Water Treatment

Biofilm cells have a different physiology than planktonic cells, which has been the focus of most research. Biofilms are complex biostructures that form on any surface that comes into contact with water on a regular basis. They are dynamic, structurally complex systems having characteristics of multicellular animals and multiple ecosystems. The three themes covered in this review are biofilm ecology, biofilm reactor technology and design, and biofilm modeling. Membrane-supported biofilm reactors, moving bed biofilm reactors, granular sludge, and integrated fixed-film activated sludge processes are all examples of biofilm reactors used for water treatment. Biofilm control and/or beneficial application in membrane processes are improving. Biofilm models have become critical tools for biofilm foundational research as well as biofilm reactor architecture and design. At the same time, the differences between biofilm modeling and biofilm reactor modeling methods are acknowledged.

Application of poly (vinyl alcohol)-cryogels to immobilizing nitrifiers: Enhanced tolerance to shear stress-induced destruction and viability control

The hardness of poly (vinyl alcohol)-cryogels (PVA-CGs) was improved under three parameter conditions: 7.5 %-12.5 % PVA, 1-5 freezing-thawing cycles (FTCs), and the addition of 0 %-10 % glycerol as a cryoprotectant. This study investigated the effects of shear stress-induced destruction (SSID) on mechanical strength by inducing rapid erosion with a high frictional force. Tolerance to SSID (Tol-SSID) exhibited different sensitivities and trends depending on the above three fabrication parameters. The measured Tol-SSID exhibited consistent and inconsistent trends with tensile strength and swelling, respectively. Tol-SSID evaluation provides new insights into the practically meaningful mechanical strength of PVA-CGs against strong friction, which simulates extreme shear stress in a bioreactor. A PVA-CG with a PVA concentration of 10 % and in two FTCs resulted in Tol-SSID and tensile strength of 88.3 % and 0.59 kPa, respectively. Here, 5 % glycerol was added to maintain the bacterial respiration activity of immobilized nitrifiers of 0.097 mg-O₂/g-VSS·min and survival of 88.6 %. The continuous mode of nitrification using the optimized PVA-CG for 10 days resulted in an ammonia removal rate of 0.2173 kg-N/m³·d, which is an improvement over cases without glycerol addition: 0.1426 and 0.1472 kg-N/m³·d for PVA-CGs in two and three FTCs, respectively.

Insight into dead space effects in granular anammox process with organic stress

In this study, the dead space was demonstrated to enhance the robustness of anammox nitrogen (N)-removal under organic stress. Different from the "yellow aggregates" that inhabit in mixing space were assembled by anammox and heterotrophic micro-colonies, the "red granules" that inhabit in dead space were formed by initial anammox aggregates that growing outward with higher anammox-activity, settleability and sludge stability, which endowed the dead space the role of "anammox-stabilizer" with prominent anammox N-removal contribution (63.8%) especially under high organic stress. The extracellular polymeric substances (EPS) dynamic balance test revealed that the high and stable EPS contents in dead space were attributed to the low EPS degradation rate and low proportion of heterotrophic bacteria (HB)-produced EPS, respectively. The weak hydrodynamic forces were the key to less HB-colonization and high granular stability in dead space. Retaining a certain dead space is necessary to prevent anammox bacteria (AnAOB) loss under organic stress.

Emerging nanotechnologies for targeting antimicrobial resistance

Antimicrobial resistance is a leading cause of mortality worldwide. Without newly approved antibiotics and antifungals being brought to the market, resistance is being developed to the ones currently available to clinicians. The reason is the applied evolutionary pressure to bacterial and fungal species due to the wide overuse of common antibiotics and antifungals in clinical practice and agriculture. Biofilms harbour antimicrobial-resistant subpopulations, which make their antimicrobial treatment even more challenging. Nanoparticle-based technologies have recently been shown to successfully overcome antimicrobial resistance in both planktonic and biofilms phenotypes. This results from the combination of novel nanomaterial research and classic antimicrobial therapies which promise to deliver a whole new generation of high-performance active nanocarrier systems. This review discusses the latest developments of promising nanotechnologies with applications against resistant pathogens and evaluates their potential and feasibility for use in novel antimicrobial therapies.

Biofilm formation under high shear stress increases resilience to chemical and mechanical challenges

The effect that the hydrodynamic conditions under which biofilms are formed has on their persistence is still unknown. This study assessed the behaviour of Pseudomonas fluorescens biofilms, formed on stainless steel under different shear stress (τw) conditions (1, 2 and 4 Pa), to chemical (benzalkonium chloride - BAC, glutaraldehyde - GLUT and sodium hypochlorite - SHC) and mechanical (20 Pa) treatments (alone and combined). The biofilms formed under different τw  showed different structural characteristics. Those formed under a higher τw were invariably more tolerant to chemical and mechanical stresses. SHC was the biocide which caused the highest biofilm killing and removal, followed by BAC. The sequential exposure to biocides and mechanical stress was found to be insufficient for effective biofilm control. A basal layer containing biofilm cells mostly in a viable state remained on the surface of the cylinders, particularly for the 2 and 4 Pa-generated biofilms.

Analysis of Ureteral Tumour Stents for Malignant Ureteral Obstruction: Towards Reshaping an Optimal Stent

Introduction

Ureteral obstruction hinders the management of malignant diseases. Adequate stent placement does not necessarily guarantee renal decompression. The stent stiffness may play a major role to maintain patency. We carried out the present study in order to evaluate drainage efficiency by using stents with distinctive degrees of stiffness and to identify the physical factors that could prevent obstruction of the stent in patients with malignant ureteral obstruction (MUO).

Materials and Methods

We performed an analysis of 150 patients with MUO drainage at a single institution from June 2009 to June 2019. A progressive choice of stents was shaped to overcome each failure by focusing on the criterion of increasingly stiff stents.

Results

During the study period, 556 ureteral stent procedures (USP) were analysed separately. The stent failure with obstruction occurred in 23.0% (128/556) of USP at a mean of 4.4±3.6 months and depended on the type of stent. Stent failure occurred in 34.2% (70/205) of Vortek^® stents, in 42.9% (15/35) of Urosoft stents, in 15.4% (39/254) of Superglide or ureteral catheters and in 6.5% (4/62) of tandem stents. No significant differences were found between Vortek^® and Urosoft stents regarding stent failures, but there were significant differences between Superglide or Tandem stents and Vortek^® or Urosoft stents (p<10⁻⁷). The study demonstrated that ureteral stent obstruction significantly decreased with a larger lumen or a stiffer stent (p<10⁻⁷).

Conclusion

In the present study, Superglide and tandem stents were the best stents against stent failure, and the lumen and the stiffness of the stent have been shown to be critical factors in controlling patency. The results suggest that the lumen seems more important than the stiffness, and the stiffness would be the only means of keeping the lumen intact. Future stents for MUO should integrate the importance of the lumen of the stent.

Surface Sensing and Adaptation in Bacteria

Bacteria thrive both in liquids and attached to surfaces. The concentration of bacteria on surfaces is generally much higher than in the surrounding environment, offering bacteria ample opportunity for mutualistic, symbiotic, and pathogenic interactions. To efficiently populate surfaces, they have evolved mechanisms to sense mechanical or chemical cues upon contact with solid substrata. This is of particular importance for pathogens that interact with host tissue surfaces. In this review we discuss how bacteria are able to sense surfaces and how they use this information to adapt their physiology and behavior to this new environment. We first survey mechanosensing and chemosensing mechanisms and outline how specific macromolecular structures can inform bacteria about surfaces. We then discuss how mechanical cues are converted to biochemical signals to activate specific cellular processes in a defined chronological order and describe the role of two key second messengers, c-di-GMP and cAMP, in this process.

Effects of turbulence fluctuation intensity in bioreactor of sewage treatment on physical and chemical properties of biofilms

The flow velocity plays an important role in the growth and characteristics of biofilm in the bioreactor as well as its treatment efficiency, which has been a hot research topic. In a sewage treatment bioreactor, the type of flow is usually turbulence. According to the methods of Reynolds decomposition, the flow velocity of turbulence consists of the time-mean velocity and fluctuation velocity, which usually exist simultaneously in real flow. However, the current research on the influence of turbulence flow velocity mainly focuses on the time-mean velocity, while the fluctuation velocity has not been reported because of very difficult to control. To this end, in this paper, a laboratory oscillating-grid turbulence (OGT) bioreactor with zero time-mean velocity and only fluctuation velocity was designed. In this bioreactor, the fluctuation velocity could be easily manipulated by varying the operational parameters of the grid. Based on the numerical simulation of Gas-liquid two-phase flow, the distributions of fluctuation velocity and corresponding turbulence fluctuation intensity, gas holdup, and Reynolds stress were obtained. After that, the effects of the turbulent fluctuation intensity on the biofilm thickness, density, and composition of extracellular polymeric substances (EPS) were studied experimentally. The results showed that turbulent fluctuation had a significant effect on the physical and chemical properties of biofilms, and the fluctuation velocity promoted the increase in the biofilm density and the content of protein and carbohydrates in EPS. This study was intended to provide theoretical support for the design and operation optimization of bioreactors.

Novel hole-pillar spacer design for improved hydrodynamics and biofouling mitigation in membrane filtration

Feed spacers are the critical components of any spiral-wound filtration module, dictating the filtration performance. Three spacer designs, namely a non-woven commercial spacer (varying filament cross-section), a symmetric pillar spacer, and a novel hole-pillar spacer (constant filament diameter) were studied using Direct Numerical Simulations (DNS), 3-D printed and subsequently experimentally tested in a lab-scale ultrafiltration set-up with high biofouling potential feed water at various feed pressures. Independent of the applied pressure, the novel hole-pillar spacer showed initially the lowest feed channel pressure drop, the lowest shear stress, and the highest permeate flux compared to the commercial and pillar spacers. Furthermore, less biofilm thickness development on membrane surface was visualized by Optical Coherent Tomography (OCT) imaging for the proposed hole-pillar spacer. At higher feed pressure, a thicker biofilm developed on membrane surface for all spacer designs explaining the stronger decrease in permeate flux at high pressure. The findings systematically demonstrated the role of various spacer designs and applied pressure on the performance of pre-treatment process, while identifying specific shear stress distribution guidelines for engineering a new spacer design in different filtration techniques.

Hydrodynamics and surface properties influence biofilm proliferation

A biofilm is an interface-associated colloidal dispersion of bacterial cells and excreted polymers in which microorganisms find protection from their environment. Successful colonization of a surface by a bacterial community is typically a detriment to human health and property. Insight into the biofilm life-cycle provides clues on how their proliferation can be suppressed. In this review, we follow a cell through the cycle of attachment, growth, and departure from a colony. Among the abundance of factors that guide the three phases, we focus on hydrodynamics and stratum properties due to the synergistic effect such properties have on bacteria rejection and removal. Cell motion, whether facilitated by the environment via medium flow or self-actuated by use of an appendage, drastically improves the survivability of a bacterium. Once in the vicinity of a stratum, a single cell is exposed to near-surface interactions, such as van der Waals, electrostatic and specific interactions, similarly to any other colloidal particle. The success of the attachment and the potential for detachment is heavily influenced by surface properties such as material type and topography. The growth of the colony is similarly guided by mainstream flow and the convective transport throughout the biofilm. Beyond the growth phase, hydrodynamic traction forces on a biofilm can elicit strongly non-linear viscoelastic responses from the biofilm soft matter. As the colony exhausts the means of survival at a particular location, a set of trigger signals activates mechanisms of bacterial release, a life-cycle phase also facilitated by fluid flow. A review of biofilm-relevant hydrodynamics and startum properties provides insight into future research avenues.

A new hydrophilic biodegradable ureteral stent restrain encrustation both in vitro and in vivo

Ureteral stents have been widely used as biomedical devices to treat some urological diseases for several decades. However, the encrustation complications hamper the long-time clinical use of the ureteral stents. In this work, a new type of biodegradable material for the ureteral stents, methoxypoly(ethylene glycol)-block-poly(L-lactide-ran-Ɛ-caprolactone) (mPEG-PLACL), is evaluated to overcome this problem. The results show that the hydrophilicity and degradation rate in artificial urine of mPEG-PLACL are both significantly increased. It is worth noting that the mPEG-PLACL shows a lower amount of encrustation after immersing the stents in the dynamic urinary extracorporeal circulation (DUEC) model for 7 days. In addition, 71% Ca and 92% Mg are inhibited in vivo by quantitative analysis. Pathological analysis exhibit that the mPEG-PLACL cause less diffuse mucosal hyperplasia after 7 weeks of implantation. All the results indicate that this new type of biodegradable material had an excellent potential for the ureteral stents in the future.

Effect of localized hydrodynamics on biofilm attachment and growth in a cross-flow filtration channel

Biofilm attachment and growth in membrane filtration systems are considerably influenced by the localized flow inside the feed channel. The present work aims to map the biofilm attachment/growth mechanism under varying flow conditions. Effect of varying clearance region (space between the spacer filament and membrane surface) on biofouling pattern is investigated by using three 3D-printed pillar spacers having different filament diameters of 340, 500, and 1000 µm while maintaining the same pillar orientation, diameter and height. Direct Numerical Simulations (DNS) and Optical Coherence Tomography (OCT) were carried out to accurately predict the local hydrodynamics behavior and in-situ monitor the biofilm formation. On spacer filaments, biofouling attachment is primarily observed in the regions where low and non-fluctuating shear stresses are present. Conversely, on membrane surface, highest biofouling attachment was observed under spacer filaments where high shear stresses are prevalent along with low clearance height. Furthermore, as filtration time progresses, the biofilm grows faster on the membrane in the center of spacer cells where low shear stress with steady hydrodynamics conditions are prevalent. The proposed hydrodynamics approach envisages a full spectrum of spacer design constraints that can lead to intrinsic biofilm mitigation while improving filtration performance of membranes based water treatment.

Effects of surface skewness on local shear stresses, biofilm activity, and microbial communities for wastewater treatment

This study's objective was to assess attachment surface skewness (asymmetric surface height variation) effects on biofilm development. 3D printed molds were used to create surfaces with 300 μm features to provide opposite skewness but identical roughness values. Surfaces with negative skewness had consistently greater nitrite oxidation and biomass growth than other surfaces during biofilm development when studied in annular bioreactor systems. CFD modelling predicted local shear stress differences that could explain experimental results. 16 s rRNA gene amplicon sequencing revealed population differences, including relatively high Acinetobacter and Terrimonas fractions on the negative skew surfaces, and PCoA analyses indicated the flat surface populations diverged from the skew surfaces by the study's end. The results suggest skewness is particularly important in systems where biofilms have not overgrown surface features, as in system startup, thin biofilms, and shorter time frame studies, which includes much previous microbial attachment research.

Stiffness Analysis of Reinforced Ureteral Stents Against Radial Compression: In vitro Study

Introduction

Malignant ureteral obstruction caused by cancer diseases may induce renal failure. Indwelling stent is a popular method to release renal obstruction. But adequate stent placement across an obstructed ureter does not necessarily guarantee renal decompression. The aim of the study was to compare, in vitro, the physical characteristics and stiffness of several commercially available reinforced ureteral stents and identify the physical factors that could lead to the obstruction of the stent.

Material and Methods

The test apparatus used for measurements allowed applying a radial compression force on a segment of the stent to stop a water flow through the lumen of the stent. Some reinforced double-pigtail stents Teleflex Medical, Bard, and Coloplast were evaluated.

Results

The best physical-stiffness characteristic was obtained with the Teleflex 8F stent (5.4 N mm⁻²). The best result against the radial compression was obtained with tandem stents. The radial compressive stresses of the Teleflex stents (4.4 to 5.4 N mm⁻²) were higher than with the other stents used in the study (1.0 to 2.9 N mm⁻²). Among the reinforced stents selected in the present study, a wider inner diameter helped increase volumetric flow rate but did not affect the stiffness of the stent. The measurement of inner diameter showed heterogeneity along the tube of some stents.

Conclusion

The stiffness of the stent appeared to be an important factor to maintain patency with respect to radial compression forces but the inner diameter of the stent and its preservation may be essential parameters to increase the volumetric flow rate. Some reinforced stents tested in the present study confirmed that it is possible to combine stiffness and wide lumen. The use of tandem stents provided the best stiffness against radial compression and the greatest lumen.

Hydrodynamic effect on biofouling of milli-labyrinth channel and bacterial communities in drip irrigation systems fed with reclaimed wastewater

The clogging of drippers due to the development of biofilms reduces the benefits and is an obstacle to the implementation of drip irrigation technology in a reclaimed water context. The narrow section and labyrinth geometry of the dripper channel results the development of a heterogeneous flow behaviours with the vortex zones which it enhance the fouling mechanisms. The objective of this study was to analyse the influence of the three dripper types, defined by their geometric and hydraulic parameters, fed with reclaimed wastewater, on the biofouling kinetics and the bacterial communities. Using optical coherence tomography, we demonstrated that the inlet of the drippers (mainly the first baffle) and vortex zones are the most sensitive area for biofouling. Drippers with the lowest Reynolds number and average cross-section velocity v (1 l·h^-1) were the most sensible to biofouling, even if detachment events seemed more frequent in this dripper type. Therefore, dripper flow path with larger v should be consider to improve the anti-clogging performance. In addition, the dripper type and the geometry of the flow path influenced the structure of the bacterial communities from dripper biofilms. Relative abundancy of filamentous bacteria belonging to Chloroflexi phylum was higher in 1 l·h^-1 drippers, which presented a higher level of biofouling. However, further research on the role of this phylum in dripper biofouling is required.

Staphylococcus aureus Aggregates on Orthopedic Materials under Varying Levels of Shear Stress

Periprosthetic joint infection (PJI) occurring after artificial joint replacement is a major clinical issue requiring multiple surgeries and antibiotic interventions. Staphylococcus aureus is the bacterium most commonly responsible for PJI. Recent in vitro research has shown that staphylococcal strains rapidly form aggregates in the presence of synovial fluid (SF). We hypothesize that these aggregates provide early protection to bacteria entering the wound site, allowing them time to attach to the implant surface, leading to biofilm formation. Thus, understanding the attachment kinetics of these aggregates is critical in understanding their adhesion to various biomaterial surfaces. In this study, the number, size, and surface area coverage of aggregates as well as of single cells of S. aureus were quantified under various conditions on different orthopedic materials relevant to orthopedic surgery: stainless steel (316L), titanium (Ti), hydroxyapatite (HA), and polyethylene (PE). It was observed that, regardless of the material type, SF-induced aggregation resulted in reduced aggregate surface attachment and greater aggregate size than the single-cell populations under various shear stresses. Additionally, the surface area coverage of bacterial aggregates on PE was relatively high compared to that on other materials, which could potentially be due to the rougher surface of PE. Furthermore, increasing shear stress to 78 mPa decreased aggregate attachment to Ti and HA while increasing the aggregates' average size. Therefore, this study demonstrates that SF induced inhibition of aggregate attachment to all materials, suggesting that biofilm formation is initiated by lodging of aggregates on the surface features of implants and host tissues.IMPORTANCE Periprosthetic joint infection occurring after artificial joint replacement is a major clinical issue that require repeated surgeries and antibiotic interventions. Unfortunately, 26% of patients die within 5 years of developing these infections. Staphylococcus aureus is the bacterium most commonly responsible for this problem and can form biofilms to provide protection from antibiotics as well as the immune system. Although biofilms are evident on the infected implants, it is unclear how these are attached to the surface in the first place. Recent in vitro investigations have shown that staphylococcal strains rapidly form aggregates in the presence of synovial fluid and provide protection to bacteria, thus allowing them time to attach to the implant surface, leading to biofilm formation. In this study, we investigated the attachment kinetics of Staphylococcus aureus aggregates on different orthopedic materials. The information presented in this article will be useful in surgical management and implant design.

Accumulation mechanism of biofilm under different water shear forces along the networked pipelines in a drip irrigation system

The behavior of clogging has a close relationship with the biofilm attached on inner surface of the pipeline in a drip irrigation system using reclaimed water. Therefore, inhibiting biofilm growth is the key to completely addressing the clogging problem. Water shear forces play a vital role in the formation, development and detachment of biofilm. In order to find out the accumulation mechanism of biofilm under different water shear forces, this paper considered 8 different shear forces with a range of [0, 0.7]Pa on the inner surface of pipelines in drip irrigation systems using three kinds of reclaimed water. The results indicate that dry weight (DW), phospholipid fatty acids (PLFAs) and extracellular polymeric substance (EPS) of biofilms show a S-type trend, the maximum contents were observed when τ was 0.2 Pa or 0. 35 Pa. Besides, the influence of water shear forces on biofilms is dual. The formation of biofilm is a dynamic stabilization process. When there is a relatively large shear force, it is favorable to the transport and renewal of microorganisms and nutrients. Meantime, the renewal speed of biofilms is also relatively fast. It is easy to form the biofilms with large surface and small thickness due to relatively high possibility of detachment. When the shear force is small, the transport speed of microorganisms and nutrients are limited, and the ability of microorganisms to secrete polysaccharides is reduced, which makes the nutrients needed for microbial growth insufficient and the adhesion between particles is also reduced, resulting in loose, unstable and an easily removed biofilm structure. After a comprehensive consideration of the dual influence, the critical controlling threshold of internal water shear force was obtained as [0, 0.20] ∪ [0.35, +∞] Pa. In addition, the growth model established in this paper can well describe the growth kinetics of attached biofilms, and provide theoretical reference for monitoring the occurrence of bio-clogging process in drip irrigation systems.

A Microfluidic-Based Investigation of Bacterial Attachment in Ureteral Stents

Obstructions of the ureter lumen can originate from intrinsic or extrinsic factors, such as kidney stones, tumours, or strictures. These can affect the physiological flow of urine from the kidneys to the bladder, potentially causing infection, pain, and kidney failure. To overcome these complications, ureteral stents are often deployed clinically in order to temporarily re-establish urinary flow. Despite their clinical benefits, stents are prone to encrustation and biofilm formation that lead to reduced quality of life for patients; however, the mechanisms underlying the formation of crystalline biofilms in stents are not yet fully understood. In this study, we developed microfluidic-based devices replicating the urodynamic field within different configurations of an occluded and stented ureter. We employed computational fluid dynamic simulations to characterise the flow dynamic field within these models and investigated bacterial attachment (Pseudomonas fluorescens) by means of crystal violet staining and fluorescence microscopy. We identified the presence of hydrodynamic cavities in the vicinity of a ureteric occlusion, which were characterised by low levels of wall shear stress (WSS < 40 mPa), and observed that initiation of bacterial attachment occurred in these specific regions of the stented ureter. Notably, the bacterial coverage area was directly proportional to the number of cavities present in the model. Fluorescence microscopy confirmed that the number density of bacteria was greater within cavities (3 bacteria·mm^-2) when compared to side-holes of the stent (1 bacterium·mm^-2) or its luminal surface (0.12·bacteria mm^-2). These findings informed the design of a novel technological solution against bacterial attachment, which reduces the extent of cavity flow and increases wall shear stress over the stent's surface.

Variations in the microbial community of biofilms under different near-wall hydraulic shear stresses in agricultural irrigation systems

The hydraulic characteristics along agricultural irrigation pipelines directly affect the local near-wall hydraulic shear stress and biofilm accumulation. However, the variations in the microbial community during the process remain unknown. Based on the Couette-Taylor reactor, a device was developed to accurately control the hydraulic shear stress. The results indicated that the near-wall hydraulic shear stresses showed quadratic correlations with microbial contents (represented by phospholipid fatty acids r > 0.77, p < 0.05), and the maximum values were obtained under the shear stresses of 0.20-0.35 Pa. For two types of treated wastewater, the mutual operational taxonomic units among different shear stress treatments showed good consistency (>185). Their corresponding response in the microbial community was represented by the quantitative correlations between the near-wall hydraulic shear stresses and the polymorphism indices (r > 0.82, p < 0.05). Among the microorganisms, Firmicutes at the phylum level were significantly affected by the shear stress and significantly influenced the biofilm accumulation process.

Energy efficient 3D printed column type feed spacer for membrane filtration

Modification of the feed spacer design significantly influences the energy consumption of membrane filtration processes. This study developed a novel column type feed spacer with the aim to reduce the specific energy consumption (SEC) of the membrane based water filtration system. The proposed spacer increases the clearance between the filament and the membrane (reducing the spacer filament diameter) while keeping the same flow channel thickness as compared to a standard non-woven symmetric spacer. Since the higher clearance reduces the flow unsteadiness, column type nodes were added in the spacer structure as additional vortex shading bodies. Fluid flow behaviour in the channel for this spacer was numerically simulated by 3D CFD studies and then compared with the standard spacer. The numerical results showed that the proposed spacer substantially reduced the pressure drop, shear stress at the constriction region and shortened the dead zone. Finally, these findings were confirmed experimentally by investigating the filtration performances using the 3D printed prototypes of these spacers in a lab-scale filtration module. It is observed that the column spacer reduced the pressure drop by three times and doubled the specific water flux. 2D OCT (Optical Coherence Tomography) scans of the membrane surface acquired after the filtration revealed much lower biomass accumulation using the proposed spacer. Consequently, the SEC for the column spacer was found about two folds lower than the standard spacer.

Formation of odorant haloanisoles and variation of microorganisms during microbial O-methylation in annular reactors equipped with different coupon materials

Taste and odor (T & O) issues in drinking water have become serious problems which cannot be ignored by customers. Several studies have confirmed that microbes in water can biotransform halophenols (HPs) to haloanisoles (HAs) with earthy and musty flavors via microbial O-methylation. In this paper, the formation of 2-chloroanisole (2-CA), 2,4-dichloroanisole (2,4-DCA), 2,4,6-trichloroanisole (2,4,6-TCA), 2,3,6-trichloroanisole (2,3,6-TCA) and 2,4,6-tribromoanisole (2,4,6-TBA), and the microbial variation during the microbial O-methylation were investigated in annular reactors (ARs) with three coupon materials. For precursors, 42.5% of 2-CP and 68.9% of 2,4-DCP decayed during the reaction. Among the five HAs, the formation rate constant followed an order of 2,4,6-TCA > 2-CA > 2,4,6-TBA > 2,4-DCA ~ 2,3,6-TCA, while [HA]_max followed a totally opposite one. The simulated flow velocity had no significant effect (p > 0.05) on HA formation. Ductile iron (DI) AR could produce more HAs than stainless steel (SS) and polyvinyl chloride (PVC) ARs. The final HA molar concentration followed an order of 2,3,6-TCA > 2,4-DCA > 2,4,6-TBA ~ 2,4,6-TCA > 2-CA, which might be explained by multiple factors including HP's dissociation degree, halogen atom's steric hindrance and specificity of HP O-methyltransferases. During the reaction, the microbial biomass dramatically increased 6.8-9.0 times in bulk water but dropped significantly on coupon biofilms. The effect of HPs significantly changed the bacterial communities on coupon in terms of composition and diversity, and declined the relative abundance of HA-producing bacteria, while fungi and their HA-producing genus showed better resistance ability towards HPs. By using Pearson correlation analysis, a significant correlation (p = 0.0003) was found between [HA]_max and initial coupon biofilm biomass. Finally, a linear relationship was established between initial total biomass and HA formation potential.

The impact of medicinal brines on microbial biofilm formation on inhalation equipment surfaces

Materials such as polyvinyl chloride, polypropylene, and polyethylene are used for the construction of medical equipment, including inhalation equipment. Inhalation equipment, because of the wet conditions and good oxygenation, constitutes a perfect environment for microbial biofilm formation. Biofilms may affect microbiological cleanliness of inhalation facilities and installations and promote the development of pathogenic bacteria. Microbial biofilms can form even in saline environments. Therefore, the aim of this study was to evaluate the effect of medicinal brines on microbial biofilm formation on the surfaces of inhalation equipment. The study confirmed the high risk of biofilm formation on surfaces used in inhalation equipment. Isolated microorganisms belonged to potential pathogens of the respiratory system, which can pose a health threat to hospital patients. The introduction of additional contaminants increased the amount of bacterial biofilm. On the other hand, the presence of brines significantly limited the amount of biofilm, thus eliminating the risk of infections.

Fouling resilient perforated feed spacers for membrane filtration

The improvement of feed spacers with optimal geometry remains a key challenge for spiral-wound membrane systems in water treatment due to their impact on the hydrodynamic performance and fouling development. In this work, novel spacer designs are proposed by intrinsically modifying cylindrical filaments through perforations. Three symmetric perforated spacers (1-Hole, 2-Hole, and 3-Hole) were in-house 3D-printed and experimentally evaluated in terms of permeate flux, feed channel pressure drop and membrane fouling. Spacer performance is characterized and compared with standard no perforated (0-Hole) design under constant feed pressure and constant feed flow rate. Perforations in the spacer filaments resulted in significantly lowering the net pressure drop across the spacer filled channel. The 3-Hole spacer was found to have the lowest pressure drop (50%-61%) compared to 0-Hole spacer for various average flow velocities. Regarding permeate flux production, the 0-Hole spacer produced 5.7 L m^-2.h^-1 and 6.6 L m^-2.h^-1 steady state flux for constant pressure and constant feed flow rate, respectively. The 1-Hole spacer was found to be the most efficient among the perforated spacers with 75% and 23% increase in permeate production at constant pressure and constant feed flow, respectively. Furthermore, membrane surface of 1-Hole spacer was found to be cleanest in terms of fouling, contributing to maintain higher permeate flux production. Hydrodynamic understanding of these perforated spacers is also quantified by performing Direct Numerical Simulation (DNS). The performance enhancement of these perforated spacers is attributed to the formation of micro-jets in the spacer cell that aided in producing enough unsteadiness/turbulence to clean the membrane surface and mitigate fouling phenomena. In the case of 1-Hole spacer, the unsteadiness intensity at the outlet of micro-jets and the shear stress fluctuations created inside the cells are higher than those observed with other perforated spacers, resulting in the cleanest membrane surface.

Turbulence accelerates the growth of drinking water biofilms

Biofilms are found at the inner surfaces of drinking water pipes and, therefore, it is essential to understand biofilm processes to control their formation. Hydrodynamics play a crucial role in shaping biofilms. Thus, knowing how biofilms form, develop and disperse under different flow conditions is critical in the successful management of these systems. Here, the development of biofilms after 4 weeks, the initial formation of biofilms within 10 h and finally, the response of already established biofilms within 24-h intervals in which the flow regime was changed, were studied using a rotating annular reactor under three different flow regimes: turbulent, transition and laminar. Using fluorescence microscopy, information about the number of microcolonies on the reactor slides, the surface area of biofilms and of extracellular polymeric substances and the biofilm structures was acquired. Gravimetric measurements were conducted to characterise the thickness and density of biofilms, and spatial statistics were used to characterise the heterogeneity and spatial correlation of biofilm structures. Contrary to the prevailing view, it was shown that turbulent flow did not correlate with a reduction in biofilms; turbulence was found to enhance both the initial formation and the development of biofilms on the accessible surfaces. Additionally, after 24-h changes of the flow regime it was indicated that biofilms responded to the quick changes of the flow regime. Overall, this work suggests that different flow conditions can cause substantial changes in biofilm morphology and growth and specifically that turbulent flow can accelerate biofilm growth in drinking water.