Filter Clogging Research Articles

Enzymatic analysis in household intermittent slow sand filters as a tool for assessing biological clogging

Intermittent slow sand filters for household use have become an established technology that is efficient, simple, and affordable for water treatment. However, bio-clogging can seriously limit hydraulic efficiency and water quality in this treatment system. Therefore, the use of new techniques for studying clogging in slow sand filters has been proposed. This study aimed to evaluate biological clogging using an enzymatic approach, considering also hydraulic aspects and water quality. Six filtration columns with two different granulometric characteristics (fine sand and medium sand) were operated with a downward flow and intermittent flow regime for 120 days. The bio-clogging of the filter media was evaluated considering the presence of esterase enzymes through the degradation of fluorescein diacetate (FDA). So, daily raw and filtered water analyses were performed for physical and chemical characteristics and hydraulic monitoring. The two granulometric characteristics used did not significantly differ between physical and chemical aspects of water quality within the parameters analyzed. The filters showed an average efficiency of turbidity removal of 79.6 % and 80.5 % for fine and medium sand, respectively. The enzymatic assay revealed the existence of microbiological activity throughout the extent of the filters in both granulometric configurations used. The results indicated a potential risk of contamination of the filtered water. The FDA technique proved to be an exciting tool in evaluating biological clogging in intermittent slow sand filters.

Understanding the Microscopic Mechanism of Clogging of both Fibrous and Mesh Filters in Flooded-bed Wet Scrubbers

Flooded-bed scrubbers are commonly employed in continuous miners to capture and remove dust particles at the cutting face in underground coal mines. To date, the mechanism of filter clogging as well as the evolution of pressure drop has not been well understood. In this work, clogging of filters in a relevant flooded-bed scrubber environment have been investigated in a laboratory setting by spraying a slurry onto a filter assembly while pulling the air through. Two types of filters have been investigated, including a) a multi-layer mesh filter and 2) a fibrous woven filter. Results showed that the differential pressure (or pressure drop) increased with an accumulation of clogged particles within the filter. The timed evolution of the pressure drop varied with both pore size and pore structure of the filter medium. When dust particles were much smaller than the pore size of the filter, dust particles predominantly accumulated inside the filter pack. When dust particles had comparable or larger sizes compared with the pore (or mesh) size of the filter medium, the filter was dominantly clogged at its front layers. Experimental results were compared with a modified model to account for the development of the pressure drop across the filter. The clogging of scrubber filters may be presented in two mechanisms, namely a) internal clogging and b) caking. The present result demonstrates the fundamental mechanism of clogging of dust particles within fibrous and mesh filters during dust capture and removal by flooded-bed wet scrubbers as well as other engineering applications involving in multi-phase interaction within a porous medium.

Development of an in-house bone marrow collection kit: The Catalan bone marrow transplantation group experience.

Bone marrow (BM) harvesting is one of the essential sources of stem cells for haematopoietic stem cell transplantation. In 2019, commercial BM collection kits became unavailable in Europe. Consequently, we created an in-house BM collection kit as an alternative. We compared two groups of BM collections. The first collections were taken using an in-house kit from June 2022 through February 2023 and the second with a commercial kit from February 2021 through May 2022. These all took place at seven collection centres (CC). We analysed the harvest quality (cell blood count, CD34+ cells, viability, potency and sterility), the incidents occurring with each kit and the time to neutrophil and platelet engraftment in recipients. A total of 23 donors underwent BM harvesting with the in-house kit and 23 with the commercial one. Both cohorts were comparable regarding donor characteristics, CC and time to procedure. No statistical differences were found in harvest quality between the in-house and commercial kits. A new transfusion set was required in three BM harvests (13%) with the in-house kit because of filter clogging. The median time to neutrophil and platelet engraftment was 21 days for both cohorts and 29 days (in-house) and 33 days (commercial), p = 0.284, respectively. The in-house BM collection kit offers a real approach to solve the diminished supply of commercial kits. A higher risk of filter clogging was observed compared with commercial kits due to the lack of 850 and 500 μm filters.

Real-Time Assessment of the Size Changes of Individual Sub-Visible Protein Particles under Buffer Variations: A Microfluidic Study.

Protein particles in biological drugs can significantly impact drug efficacy and carry the risk of adverse effects. Despite advancements, the understanding and control of particle formation in biopharmaceutical manufacturing remain incomplete. Therefore, further investigation into protein particles is warranted, especially considering that novel formats of biological drugs may be more susceptible to aggregation and particle formation than conventional monoclonal antibodies. In this study, we introduce a microfluidic approach for the real-time analysis of individual sub-visible protein particles during buffer exchange. We find that the modulation of intermolecular forces, achieved by changing the buffer pH or urea concentration, leads to the reversible swelling and shrinkage of particles by up to 50%, which is a consequence of altered intermolecular distances. Additionally, we identify a discrepancy in the biophysical behavior of protein particles compared to monomeric protein. This finding highlights the limited predictive power of commonly applied biophysical characterization methods for particle formation in early formulation development. Moreover, the observed particle swelling may be associated with manufacturing deviations, such as filter clogging. These results highlight the importance of studying individual particles to gain a comprehensive insight into particle behavior and the impact of formulation variations in the biopharmaceutical industry.

Multi‐species occupancy modeling reveals methodological and environmental effects on eDNA detection of amphibians in temporary ponds

AbstractAquatic environmental DNA is increasingly used for biodiversity monitoring, such as surveying threatened and invasive species. Mainstreaming these methods in practical applications, however, still requires significant standardization and optimisation, namely regarding DNA capture methods. Here we evaluated how filter type (standard disc filters vs high‐capacity capsules), number of sampling sites, volume of water filtered and environmental factors affected amphibian detection in Mediterranean temporary ponds. The study involved water filtering until clogging at one (capsules) and five (discs) sites from 16 small and shallow ponds, where three urodele and seven anuran species were recorded through sweep‐netting and adult observations. Detection probabilities were estimated from site occupancy models based on replicate sampling and from an adaptation of time‐to‐detection models relating detection probability to volume of water filtered. Discs filtered relatively small volumes (15–1250 mL), with detection probabilities of the two abundant species (Pelobates cultripes, Hyla meridionalis) increasing rapidly with sample size and water volume, reaching almost perfect detection (0.95) at four and seven discs, and 420 mL and 1860 mL, respectively. However, reaching high detection probabilities for rare species (Pelodytes atlanticus, Pleurodeles waltl, Triturus pygmaeus) would require larger sampling effort than that used in our study. Despite filtering much larger volumes (600–5300 mL), filtering with capsules at a single site per pond provided lower detection probabilities for abundant species than filtering with discs at five sites. Rarer species showed no difference between methods, which may be due to small sample sizes and reduced statistical power for species with few detections. The effect of conductivity on species detectability was largely negative, while the influence of water clarity varied across species, and pH had no effects. Overall, our results suggest that eDNA amphibian surveys in Mediterranean temporary ponds need to consider filter clogging, heterogeneous DNA distribution, and highly conductive waters.

The effect of silica nanoparticles on the dustiness of industrial powders

Industrial powders are prompt to be airborne during processing. High dustiness levels may cause process complications like cross-contamination, product loss and filter clogging while increasing the risk of inhalation, dust explosion and fire. Thus, dustiness is often associated with occupational exposure. Despite this, powder products are usually composed of multiple ingredients with silica nanoparticles (S-NP) systematically added to ease their handling. Surprisingly, the relationship between dustiness and product formulation has not been commonly studied. This work investigates the influence of S-NP, SIPERNAT D10 (SD10), on the dustiness of four industrial powders–Avicel PH102, wheat flour, joint filler, and glass beads–using two standard methods: the rotating drum (EN 15051–2) and the vortex shaker (EN 17199–5). Our results show that the dustiness of mixtures powder + SD10 are statistically higher than those of the powder alone and can reach the levels of SD10. TEM micrographs from airborne particles collected in the vortex shaker showed that SD10 detached from the surface of the powder during aerosolisation, emitting nanometric dust; adding SD10 increases the potential for inhalation exposure during industrial processing and handling. Surface energy analysis by inverse gas chromatography (IGC) leads us to conclude that stronger powder-to-SD10 interactions result in less dust emission.

Monoclonal Antibody Purification with Reduced Turbidity by using High-salt Elution Buffer During Protein a Chromatography

During purification of monoclonal antibodies, viral inactivation/removal step is a mandatory step to comply with the regulatory guidelines which commonly performs at low pH about 3.5 and further neutralizes it to a pH about 7.0. Neutralization of monoclonal antibodies results formation of high turbidity which is troublesome for further processing such as filtration and other chromatography processes and it eventually leads to filter clogging and increases column back pressure. In this work, we propose a new optimized process of affinity chromatography (Protein A) by using a high salt elution buffer which reduces turbidity more than 80%. A systematic study of different concentration of salts were analysed and it reveals that salt concentration greater than 100mM in Protein A elution buffer reduces turbidity during neutralization of monoclonal antibodies when compared to low salt concentration of elution buffer. We also found that elution of monoclonal antibodies during Protein A chromatography at pH 3.5 results higher reduction of turbidity compared to pH 3.0. These findings provide both cost and time effective for large scale production of monoclonal antibodies as it eliminates the use of multiple filters throughout the purification process.

RENAL3: Hybrid Concentration Method of Ascites Filtration and Concentration Equipment for Cell-free and Concentrated Ascites Reinfusion Therapy

Study: As a safe and effective treatment for refractory ascites, more than 30,000 cases of Cell-free and concentrated ascites reinfusion therapy (CART) are performed annually in Japan. In ascites processing, concentration has been performed at a fixed concentration ratio (constant ratio concentration) with a standard value of 10-fold concentration. However, as the main target disease for CART has shifted from cirrhosis to cancerous peritonitis, it has become necessary to deal with the clogging of the concentration filter when processing large amounts of cancerous ascites with high protein concentrations. Our technology for self-regulation function of the concentration ratio has been introduced into M-CART and other CART specialized equipment, enabling safe automatic concentration within set pressure range (constant pressure concentration). However, when treating ascites with low protein concentration, constant pressure concentration at a high concentration ratio may enhance protein leakage into the waste fluid and reduce protein recovery rate. Therefore, we devised a hybrid concentration method that combines constant pressure and constant ratio concentration, and investigated its usefulness in improving protein recovery by using simulated ascites and analyzing multicenter clinical evaluations. Methods: In the experiment, simulated ascites using substitute plasma agent (hydroxyethylated starch, HSE) was used to simulate cancerous ascites. In the clinical evaluation, 129 sessions of CART performed using M-CART were examined. Results: In the experiment, as the control pressure was increased, the waste fluid volume and HSE concentration in the waste fluid increased and the recovery rate decreased. In the analysis of clinical cases, protein recovery rate was lower in cases where constant pressure concentration was performed. These results indicate that constant-pressure concentration at a high concentration ratio in ascites with a low protein concentration risks decreasing the protein recovery rate, and that the hybrid concentration method enables concentration with a high recovery rate according to the condition of the ascites fluid.

THE MOST COMMON TYPES OF HEMODIALYSIS MACHINE DAMAGE AND THE FACTORS THAT INFLUENCE THEM

Hemodialysis, or kidney replacement therapy, has been introduced in our country since 1975. Research ways to maintain the hemodialysis machine in good condition, minimizing damage to the apparatus. The study included a total of 52 medical devices from hospitals such as The First Central Hospital, Second State Central Hospital, and State Central Third Hospital named after P.N.ShastinandThe National Center for Maternal and Child Health of Mongolia.Chlorine test liquid, chlorine testing strip, Neo2 analyzer at The First State Central Hospital, chlorine testing liquid at the Second State Central Hospital, chlorine testing liquid at the State Central Third Hospital named after P.N.Shastin, analyzers and chlorine test strips in hospitals, chlorine testing liquid at the National Center for Maternal and Child Health, flow setting damage, filter clogging, pressure loss, filtration loss, and damage to a heparin pump are all common issues. Influencing factors include load, cleaning, operating conditions, and electricity fluctuations. The load and cleaning were the elements that influenced the hemodialysis equipment of the majority of previously named hospitals according to the study. Cleaning is responsible for the majority of the damage to the hemodialysis machine, accounting for 40 percent or more of it.

Simulation study on clogging of suspended particles in in-situ leaching of uranium at different concentrations and flow velocity

Clogging problem has become one of the key problems restricting the mining efficiency of in-situ leaching of uranium, and the related research on the law and mechanism of physical clogging has not been reported. In order to identify and understand the complicated law and mechanism, experimental device is established to simulate the physical clogging caused by suspended particles in the uranium process, the physical clogging law and mechanism under different concentrations and velocity of flow are studied. The experimental results show that with the concentration of suspended particles increasing from 100, 200, 300 to 400 mg/L, the permeability of porous media gradually decreases, and the clogging phenomenon becomes more and more obvious. When the size of suspended particles is small and the velocity is 15 mL/min, the porous medium will not appear clogging, while the velocity is 25mL/min, the whole porous medium will slowly appear internal deposition clogging. When the size of suspended solids is larger and the flow rate is 9, 12, 15mL/min, the higher the velocity, the faster the clogging will be, and backwash can alleviate the surface clogging but cannot change the final clogging result. According to the experiment and actual situation, the physical clogging in in-situ leaching of uranium is mainly surface clogging and filter clogging.

Effects of wastewater pre-treatment on clogging of an intermittent sand filter

Intermittent sand filters (ISFs) are widely used in rural areas to treat domestic and dilute agricultural wastewater due to their simplicity, efficacy and relative low cost. However, filter clogging reduces their operational lifetime and sustainability. To reduce the potential of filter clogging, this study examined pre-treatment of dairy wastewater (DWW) by coagulation with ferric chloride (FeCl3) prior to treatment in replicated, pilot-scale ISFs. Over the study duration and at the end of the study, the extent of clogging across hybrid coagulation-ISFs was quantified, and the results were compared to ISFs treating raw DWW without a coagulation pre-treatment, but otherwise operated under the same conditions. During operation, ISFs receiving raw DWW recorded higher volumetric moisture content (θv) than ISFs treating pre-treated DWW, which indicated that biomass growth and clogging rate was higher in ISFs treating raw DWW, which were fully clogged after 280 days of operation. The hybrid coagulation-ISFs remained fully operational until the end of the study. Examination of the field-saturated hydraulic conductivity (Kfs) showed that ISFs treating raw DWW lost approximately 85 % of their infiltration capacity in the uppermost layer due to biomass build-up versus 40 % loss for hybrid coagulation-ISFs. Furthermore, loss on ignition (LOI) results indicated that conventional ISFs developed five times the organic matter (OM) in the uppermost layer compared to ISFs treating pre-treated DWW. Similar trends were observed for phosphorus, nitrogen and sulphur, where proportionally higher values were observed for raw DWW ISFs than pre-treated DWW ISFs, with values decreasing with depth. Scanning electron microscopy (SEM) showed a clogging biofilm layer on the surface of raw DWW ISFs, while pre-treated ISFs maintained distinguishable sand grains on the surface. Overall, hybrid coagulation-ISFs are likely to sustain infiltration capacity for a longer period than filters treating raw wastewater; therefore, requiring smaller surface area for treatment and minimal maintenance.

A combined study of filterability and soaking strength of fuel filter and effect of injection timing on CI engine characteristics using Ceiba pentandra biodiesel

Biodiesel is currently utilised as an alternative to conventional fuels. However, blends only up to a particular ratio improve the engine performance and fuel filterability. Higher biodiesel concentrations may cause diesel fuel filter clogging. The influence of blends of Ceiba pentandra (kapok) biodiesel (B0–B100 in 20% increments) on fuel filter blocking tendency, pressure drop, and soaking strength was investigated through filter media analysis. Fuel filter performance was similar to diesel up to B20, but higher blends had a detrimental effect. As per the filterability results, B20 was selected for further evaluation. Injection timing (IT) of fuel was the most influential parameter on the performance, combustion, and emission behaviour of diesel engines. This work aims to improve engine performance and emissions by altering IT from 21° before top dead centre (BTDC) to 27° BTDC with Ceiba pentandra biodiesel (B20), and results are compared with diesel at IT of 23° BTDC. Advanced IT (27° BTDC) caused lower brake specific fuel consumption (20%) and higher brake thermal efficiency (13%), and we observed low HC and smoke emissions at all advanced ITs. A reduction by 23.5% and 7.5% in hydrocarbon and smoke, respectively, was seen at 27° BTDC.

Investigation of conductive printed thermoplastic polyurethane nanofibers to detect the clogging of air filters

Recently, air pollution attracted many worries because of its high number of deaths per year. To solve the problem, the industries are trying to fabricate the giant air filtration system for public areas. However, the clogging of air filters should be detected in real-time to change or clean them. E-textile is a very fascinating field, which is often used in medical, safety, military and clogging detection applications. These components are integrated into soft textile materials according to their usage requirements. One of the most attractive textile structures is the nanofibers due to their advantageous properties such as porosity, lightweight, and high surface area. To have conductive nanofiber-based membrane sensors, two in situ electrical conductivity principles using conductive particles and surface conductivity, such as immersion and printing methods are recommended. In this research, the thermoplastic polyurethane (TPU) nanofibers’ membranes are produced using an electrospinning system and the carbon ink was printed on the surface of nanofibers to apply in textile sensors applications. SEM images showed the uniform structure of the nanofibers and the porosity of the system even after printing. The electromechanical properties of printed membranes demonstrated the change of electrical resistance under stretch. Conclusively, these conductive membranes could be employed as strain sensors to detect the small changes in the output airflow indicated the possible clogging of air filters.

The effect of filtration and electrolysis on ballast water treatment

Ballast water is required to be treated to reach D-2 standard according to the International Maritime Organization (IMO). Filtration and electrolysis are important technologies for ballast water management systems (BWMS). However, the clogging of filters during the operation of BWMS leads to significant system trips and downtime. In this paper, a mesoscale experiment system was set up and the effects of filtration on ballast water treatment using electrolysis were investigated. The results showed pore size of filter had significant effect on filtration efficiency, total residual oxidant (TRO) decay and inactivation efficacy. The filtration efficiency of filter with 50 μm pore size was over 80% for ≥50 μm organisms. For 200–2000 μm pore sizes (200 μm, 500 μm, 1000 μm and 2000 μm), the filtration efficiency was less than 10%. The effect of filtration on TRO depended on pore size and holding time. Our results indicated that increasing pore size of electrolysis may not a good way for new BWMS design. If electrolysis was applied alone to treat ballast water, higher initial TRO concentration was needed. In our investigation, the initial TRO was more than 12 mg/L.

Characterization of precipitates susceptible to clogging of sump filters after a Loss-of-Coolant-Accident in PWRs

During a Loss Of Coolant Accident involving a primary circuit failure in a nuclear power plant, debris, generated by the impact of the steam jet, is transported to the hot liquid phase formed at the bottom of the nuclear containment. Water is recirculated after passing through filters. Chemicals are released and may precipitate on the filters, increasing the pressure drop. This paper investigates the characterization of precipitate formation in a soda/borate buffer, due to the presence of calcium, silicon, and zinc, released from mineral fibers, concrete particles, or the corrosion of metal surfaces. Experiments run at various temperatures and chemical compositions are presented, with the objective of identifying the precipitates and determining the critical thresholds of concentration and temperature beyond which the risk of chemical clogging disappears. The experimental results are compared to those calculated with the CHESS software, intended to calculate the speciation at thermodynamic equilibrium. The results show the formation of amorphous precipitates: silica, calcium borates, borosilicates and zinc silicate. Precipitation is temperature dependent, with the highest masses obtained between 50 and 60 °C. The comparison of experimental and calculated results indicates a good overall consistency. This work demonstrates the importance of considering chemical clogging in this context.

Embedded Electronic Sensor for Monitoring of Breathing Activity, Fitting and Filter Clogging in Reusable Industrial Respirators.

Millions of workers are required to wear reusable respirators in several industries worldwide. Reusable respirators include filters that protect workers against harmful dust, smoke, gases, and vapors. These hazards may cause cancer, lung impairment, and diseases. Respiratory protection is prone to failure or misuse, such as wearing respirators with filters out of service life and employees wearing respirators loosely. Currently, there are no commercial systems capable of reliably alerting of misuse of respiratory protective equipment during the workday shifts or provide early information about dangerous clogging levels of filters. This paper proposes a low energy and non-obtrusive functional building block with embedded electronics that enable breathing monitoring inside an industrial reusable respirator. The embedded electronic device collects multidimensional data from an integrated pressure, temperature, and relative humidity sensor inside a reusable industrial respirator in real time and sends it wirelessly to an external platform for further processing. Here, the calculation of instantaneous breathing rate and estimation of the filter's respirator fitting and clogging level is performed. The device was tested with ten healthy subjects in laboratory trials. The subjects were asked to wear industrial reusable respirator with the embedded electronic device attached inside. The signals measured with the system were compared with airflow signals measured with calibrated transducers for validation purposes. The correlation between the estimated breathing rates using pressure, temperature, and relative humidity with the reference signal (airflow) is 0.987, 0.988 and 0.989 respectively, showing that instantaneous breathing rate can be calculated accurately using the information from the embedded device. Moreover, respirator fitting (well-fitted or loose condition) and filter's clogging levels (≤60%, 80% and 100% clogging) also can be estimated using features extracted from absolute pressure measurements combined to statistical analysis ANOVA models. These experimental outputs represent promising results for further development of data-driven prediction models using machine learning techniques to determine filters end-of-service life. Furthermore, the proposed system would collect relevant data for real-time monitoring of workers' breathing conditions and respirator usage, helping to improve occupational safety and health in the workplace.

Modelling of Fuel Filter Clogging of B20 Fuel Based on the Precipitate Measurement and Filter Blocking Test

The amount of precipitate and residue affects the timing of fuel filter blockage. This study develops a model for fuel filter blocking based on the Precipitate Measurement. Firstly, a modification of ASTM D 7501 for the Cold Soak Filtration Test (CSFT) measured the amount of precipitate in B20 fuel with variations of soaking temperatures and monoglyceride content in biodiesel. Then, a modified ASTM D 2068 for a filter blocking test (FBT) was conducted to correlate the impurities in the B20 fuel and the clogging limit effects represented by the change of pressure difference and time to reach a pressure drop of 30 kPa. Biodiesel B20 samples were prepared by adding monopalmitin so that each had a monoglyceride value of 0.2%, 0.4%, 0.6%, and 0.8% before blending with petroleum diesel. The modified CSFT showed that the amount of B0 impurity was almost zero. However, the amount of the B20 sample precipitate retained on the filter was higher when a lower soaking temperature and higher monoglyceride content was used in the biodiesel. Similar results in the modified FBT showed that the more impurities, the faster the pressure drop achieved a level of 30 kPa. A much shorter time was needed to reach the pressure drop of 30 kPa for B20 fuel samples with the impurities present in both test powders and precipitate compared to those for the B20 fuel samples with a single type of impurity (either test powders or precipitate). The fuel filter clogging time could also be predicted using the graph of fuel filter clogging time vs. the precipitate weight of B20 fuel derived from the FBT test if the precipitate weight had already been determined by the precipitation test (modified CSFT). The simulation model using Ergun’s equation for the FBT of the B20 fuel could also show similar results to that of the FBT experiment, with the difference (averaged errors) ranging from 4.15% to 5.79%.

Seepage Performance of Fibre Bundle Drainage Pipes: Particle Flow Simulation and Laboratory Testing

Mining coal, oil and other energy will form much slope engineering, such as open-pit mine slope and oil depot slope. The groundwater seepage seriously affects the stability of these slope engineering projects. Drainage pipes are commonly used in slope engineering projects to reduce the risk of moisture decreasing soil stability. Such pipes are prone to blockage by soil accumulation after a period of operation, resulting in decreased drainage or complete failure. By installing fibre bundles in drainage pipes, drainage can be maintained under soil ingress. This paper conducted particle flow simulations of the influences of soil particles on the clogging of geotextile filters and drainage pipes under various influences and estimated their seepage rates. Higher water pressure, smaller flower hole intervals in the pipe, greater soil friction angles and smaller pipe inclination angles are less conducive to drainage. Under silting conditions, the seepage and drainage performance of a drainage pipe can be improved by installing a fibre bundle. Five types of fibre bundles were tested with plastic rope providing the best drainage effect. With plastic rope and cotton rope, the best drainage is achieved using uneven arrangements of fibre bundles. In contrast, nylon rope, hemp rope and polyester rope perform best when uniformly arranged. The greater the number of fibre bundles per unit cross-sectional area of pipe, the better the seepage conductivity. Seepage is also greater when the soil in the pipe has a higher sand content. These results provide a reference for the design and construction of more reliable drainage systems for slope engineering in wet areas.

Underwater Remote Skimming of Slow Sand Filters for Sustainable Water Production

Slow sand filters (SSF) are a simple water treatment technology providing an important alternative to conventional drinking water treatment. SSF are extensive in terms of carbon cost and chemical use but require a large land area and are complex to operate, as periodic cleaning is required to prevent filter clogging. Therefore, redundant SSF beds are required to enable water production to occur during long cleaning downtimes. Underwater skimming (UWS) is a cleaning innovation where the foulant layer (containing sand and particles) is removed using a skimmer consisting of a shrouded blade mounted on a vehicle platform. Sand, particles, and biofilm are skimmed prior to ex situ washing of the recovered sand. In this Viewpoint, we posit that the introduction of an in situ underwater skimmer operated remotely can substantially help to offset the aforementioned challenge of downtime, with its associated loss of production, enabling the technology to operate more efficiently and remain a pertinent and advantageous process option within modern water treatment facilities or possibly resource constrained settings. Otherwise, this resilient biotechnological process could be replaced by chemical and energy-intensive processes which increase the entropy of water treatment more than SSF. The anticipated benefits and challenges of UWS of SSF are discussed.

Coulombic force contribution to nano scale aerosol capture by a wire grid: Quantitative comparison of experiments and simulations

Fibers of filter media and aerosol particles both typically have some distributions of electric charge. Attractive coulombic interactions between charged particles and fibers enhance aerosol filtration efficiency; however, these coulombic interactions are difficult to characterize due to the complex, nonuniform fiber charge, diameter and spacing of typical filter media. We develop an experimental filter assembly to control these coulombic interactions. The filter assembly consists of three sequential electrically isolated metallic grids—high voltage is applied to the middle grid and the adjacent outer grids are electrically grounded such that the electric potential distribution in the filter assembly is well-defined. We test this filter assembly with aerosols of controlled diameter (ranging between ∼70 and 500 nm) and electric charge (1e−), and systematically increase the applied voltage to the middle grid to enhance coulombic interactions and consequently the filter efficiency. We develop particle trajectory simulations to model our experimental filter assembly such that all parameters in the simulation have direct basis from the experimental system. We find excellent quantitative agreement between the filter efficiency measured in experiments and predicted from simulations without any fitting parameters. The precise control and accurate simulation of coulombic interactions demonstrated in this study indicate that the experimental and simulation methodologies developed here may be applied to uncover fundamental insights into the role of coulombic forces in more complex phenomena such as filter clogging.