•PGM systems effectively removed viruses.•Effective virus removal attributed to biofilm layer.•LRVs for viruses of 4.0+ could be consistently achieved.•Standard PDTs did not reflect improved virus ...removal caused by biofilm layer.•Alternative PDT protocol suggested for PGM systems.
Passive gravity-driven membrane (PGM) filtration is a type of gravity-driven membrane (GDM) filtration operated with passive physical fouling control measures that add limited to no complexity to the system (e.g. permeate flux interruptions, gravity-driven air scouring, system draining), allowing a greater permeate flux to be sustained. A key aspect of PGM/GDM systems is the development of a structurally loose and permeable biofilm layer on the membrane that enables a sustainable flux to be achieved and has also been associated with improved removal of humic acids, polysaccharides, proteins, assimilable organic carbon and microcystins. The present study investigated if the biofilm layer of PGM systems also contributes to virus removal, for both intact and breached PGM systems. Breach sizes considered ranged from 20 to 180 µm. Challenge tests (CTs) identified an increase of 2.0+ in the log removal value (LRV) for viruses in both intact and breached PGM systems when a biofilm layer was present, suggesting that the biofilm layer is capable of bridging the gap over integrity breaches, acting as a secondary barrier to contaminants that would otherwise bypass treatment by flowing through the breach. Pressure decay tests (PDTs), however, did not identify the same increase in LRVs as that of CTs, suggesting that the standard PDT approach cannot consider the contribution of the biofilm layer to the removal of small material such as viruses. An alternative integrity testing protocol for PGM systems was developed using a modified PDT approach that takes into account the additional removal provided by the biofilm layer. This alternative protocol is also simpler and requires less frequent testing, contributing to the simplification of overall operation of PGM systems in small/remote communities and decentralized applications.
To shed light onto the relationship between sparging conditions and fouling control in submerged hollow fiber membranes, the effects of bubble size and frequency on the hydrodynamic conditions ...induced in membrane system were studied. Two general classes of bubbles were considered: coarse (0.75–2.5 mL) and pulse (100–500 mL). The power transferred (Ptrans) onto membranes could be used to characterise the multiple effects induced under different sparging conditions. Ptrans is proportional to root mean square of shear stress (τrms), the area of zone of influence (i.e. the fraction in the system where high velocity and high vorticity (turbulence) are induced by the bubble) and their rise velocity. At a given sparging rate, the power transferred onto membranes was less with coarse bubble sparging than pulse bubble sparging and increased with the size of pulse bubbles. For all cases, the power transfer efficiency was consistently higher for pulse bubble sparging than for coarse bubble sparging. The power transfer efficiency to the system was greatest for the small pulse bubbles considered when a small amount of power is required for fouling control. However, when fouling is extensive, large pulse bubbles may be required to generate the required amount of power for fouling control.
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•Power transferred can be used to quantify the effectiveness of air sparging for fouling control.•Power transferred onto the membranes was affected by sparged bubble size & frequency.•The resulting power transfer efficiencywas affected by sparged bubble size & frequency.•Significantly greater power transfer efficiency for pulse bubble than for coarse bubble sparging.
Biofiltration is a widely used process in drinking water treatment plants to remove natural organic matter (NOM). A novel biofiltration process using ion exchange resins as supporting media (i.e., ...biological ion exchange or BIEX) has been demonstrated to provide a superior performance compared to conventional biological activated carbon (BAC). In order to optimize the performance of BIEX filters, the impact of temperature and empty bed contact time (EBCT) on NOM removal was systematically studied. In the present study, bench-scale BIEX filters were set up in parallel with BAC filters and operated at different temperatures (i.e., 4 °C, 10 °C and 20 °C) and EBCTs (i.e., 7.5 min, 15 min and 30 min). Higher average dissolved organic carbon (DOC) removal was achieved in BIEX filters (73 ± 6%) than BAC filters (22 ± 9%) at the steady state with an EBCT of 30 min. Higher temperatures improved NOM removal in both BAC and BIEX filters, with the impact being greater at lower EBCTs (i.e., 7.5 min and 15 min). Higher EBCTs could also improve NOM removal, with the impact being greater at lower temperatures (i.e., 4 °C and 10 °C). DOC removal for BIEX and BAC filters can be modeled with a first-order kinetic model (R2 = 0.93–0.99). BAC had a higher temperature activity coefficient than BIEX (1.0675 vs. 1.0429), indicating that temperature has a greater impact on BAC filtration than BIEX filtration. Overall, temperature and EBCT must be considered simultaneously for biofilters to efficiently remove NOM.
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•BIEX achieves higher DOC removal than BAC at all tested temperatures and EBCTs.•High temperature increases the DOC removal in biofilters, especially at low EBCTs.•High EBCT increases the DOC removal in biofilters, especially at low temperatures.•Temperature has a greater impact on BAC filters than BIEX filters for NOM removal.
The present study investigated the impact of different loading approaches and microbial activity on the Natural Organic Matter (NOM) removal efficiency and capacity of ion exchange resins. Gaining ...further knowledge on the impact of loading approaches is of relevance because laboratory-scale multiple loading tests (MLTs) have been introduced as a simpler and faster alternative to column tests for predicting the performance of IEX, but only anecdotal evidence exists to support their ability to forecast contaminant removal and runtime until breakthrough of IEX systems. The overall trends observed for the removal and the time to breakthrough of organic material estimated using MLTs differed from those estimated using column tests. The results nonetheless suggest that MLTs could best be used as an effective tool to screen different ion exchange resins in terms of their ability to remove various contaminants of interest from different raw waters.
The microbial activity was also observed to impact the removal and time to breakthrough. In the absence of regeneration, a microbial community rapidly established itself in ion exchange columns and contributed to the removal of organic material. Biological ion exchange (BIEX) removed more organic material and enabled operation beyond the point when the resin capacity would have otherwise been exhausted using conventional (i.e. in the absence of a microbial community) ion exchange. Furthermore, significantly greater removal of organic matter could be achieved with BIEX than biological activated carbon (BAC) (i.e. 56 ± 7% vs. 15 ± 5%, respectively) when operated at similar loading rates. The results suggest that for some raw waters, BIEX could replace BAC as the technology of choice for the removal of organic material.
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•Mass transfer conditions are critical when interpreting multiple loading tests.•Biological ion exchange (BIEX) achieved stable NOM removal for ∼1yr.•The long-term stability of BIEX is affected by the raw water characteristics.•If required, BIEX can be regenerated using standard regeneration approaches.•BIEX could replace BAC as the technology of choice for NOM removal.
•Adsorption destabilization is optimal for reducing UF fouling.•Sweep maximizes NOM removal while minimizing increases in UF fouling.•Coagulation + flocculation reduces UF fouling when compared to ...coagulation alone.•Increased floc size and concentration decreases the resistance of accumulated foulants.
Despite widespread application of coagulation/flocculation prior to ultrafiltration (UF), a lack of knowledge remains regarding the appropriate selection of conditions to reduce fouling and/or improve the removal of natural organic matter (NOM). The present study investigates the impact of conditions (alum dosage, pH) associated with specific coagulation mechanisms along with two different coagulation/flocculation configurations, on UF performance in terms of fouling and NOM removal. In-line coagulation/flocculation configurations were provided at bench-scale under continuous-flow conditions, which enabled quantification of hydraulically reversible/irreversible fouling over multiple permeation cycles. When compared to raw water without the addition of coagulant, utilization of coagulation/flocculation generally increased hydraulically irreversible fouling resistance. Conditions that promote adsorption destabilization (2.5 mg/L alum, pH 5.5) substantially reduced or eliminated the hydraulically irreversible accumulation of NOM, likely by minimizing interactions between certain NOM components (e.g. biopolymers and humic substances) and the membrane surface. When considering conditions that promote combined (8 mg/L alum, pH 7.5) and sweep (15 mg/L alum, pH 7) mechanisms, inclusion of flocculation increased TOC removal while reducing total/hydraulically irreversible fouling resistance (when compared to coagulation alone), despite greater amounts of NOM being retained by the membrane. The reduced fouling resistance was likely due to the formation of larger floc which formed a more permeable foulant layer. Results from the present study suggest that if only fouling control is required, conditions that promote adsorption destabilization are optimal, whereas if NOM removal is required, conditions that promote sweep are optimal. Inclusion of flocculation provided an optimal trade-off between fouling reduction and NOM removal for both adsorption destabilization and sweep, which should be considered during the design of coagulation/flocculation-UF systems to reduce operating costs despite potentially higher construction costs when compared to coagulation alone.
RNA sequencing using next-generation sequencing technologies (NGS) is currently the standard approach for gene expression profiling, particularly for large-scale high-throughput studies. NGS ...technologies comprise high throughput, cost efficient short-read RNA-Seq, while emerging single molecule, long-read RNA-Seq technologies have enabled new approaches to study the transcriptome and its function. The emerging single molecule, long-read technologies are currently commercially available by Pacific Biosciences (PacBio) and Oxford Nanopore Technologies (ONT), while new methodologies based on short-read sequencing approaches are also being developed in order to provide long range single molecule level information-for example, the ones represented by the 10x Genomics linked read methodology. The shift toward long-read sequencing technologies for transcriptome characterization is based on current increases in throughput and decreases in cost, making these attractive for de novo transcriptome assembly, isoform expression quantification, and in-depth RNA species analysis. These types of analyses were challenging with standard short sequencing approaches, due to the complex nature of the transcriptome, which consists of variable lengths of transcripts and multiple alternatively spliced isoforms for most genes, as well as the high sequence similarity of highly abundant species of RNA, such as rRNAs. Here we aim to focus on single molecule level sequencing technologies and single-cell technologies that, combined with perturbation tools, allow the analysis of complete RNA species, whether short or long, at high resolution. In parallel, these tools have opened new ways in understanding gene functions at the tissue, network, and pathway levels, as well as their detailed functional characterization. Analysis of the epi-transcriptome, including RNA methylation and modification and the effects of such modifications on biological systems is now enabled through direct RNA sequencing instead of classical indirect approaches. However, many difficulties and challenges remain, such as methodologies to generate full-length RNA or cDNA libraries from all different species of RNAs, not only poly-A containing transcripts, and the identification of allele-specific transcripts due to current error rates of single molecule technologies, while the bioinformatics analysis on long-read data for accurate identification of 5' and 3' UTRs is still in development.
•Continuous-flow coagulation enables evaluation of UF over several permeation cycles.•An extended HRT increases particle size/concentration and reduces UF fouling.•Full-scale HRT values must be ...utilized at bench-scale to produce relevant results.•A kinetic model was derived to predict steady-state particle properties.
Although bench-scale coagulation-ultrafiltration (UF) studies are typically conducted using batch systems, continuous-flow systems allow operational parameters to be more readily evaluated and optimized over consecutive permeation cycles. When simulating coagulation-UF at bench-scale using continuous-flow systems, relevant reactor volumes require flowrates ≥1 L/min in order to achieve hydraulic retention times (HRTs) typical of full-scale rapid mixing (30 s to several minutes). In the present study, HRTs of 2 and 20 min were evaluated to determine their impact on particle properties (size, structure, and concentration) as well as UF performance (fouling resistance, reduction of natural organic matter) over a range of alum dosages. While not practical at full-scale, a 20 min HRT has been previously applied at bench-scale to reduce the overall volume of water required to conduct continuous-flow coagulation-UF studies. However, potential impacts on steady-state particle properties and subsequent UF performance not been clearly elucidated. Results from this study suggest that increasing HRT significantly increases steady-state particle size and concentration, as well as reduces total/hydraulically irreversible UF fouling resistance and improves hydraulic cleaning efficiency. Despite reduced fouling when considering a longer HRT, significant differences in particle properties and UF performance suggest that HRT values equivalent to those typically applied during full-scale rapid mixing (30 s to several minutes) must be considered in order to produce results relevant to full-scale.
Biological ion exchange (BIEX) refers to operating ion exchange (IX) filters with infrequent regeneration to favor the microbial growth on resin surface and thereby contribute to the removal of ...organic matter through biodegradation. However, the extent of biodegradation on BIEX resins is still debatable due to the difficulty in discriminating between biodegradation and IX. The objective of the present study was to evaluate the performance of BIEX resins for the removal of organic micropollutants and thereby validate the occurrence of biodegradation. The removals of biodegradable micropollutants (neutral: caffeine and estradiol; negative: ibuprofen and naproxen) and nonbiodegradable micropollutants with different charges (neutral: atrazine and thiamethoxam; negative: PFOA and PFOS) were respectively monitored during batch tests with biotic and abiotic BIEX resins. Results demonstrated that biodegradation contributed to the removal of caffeine, estradiol, and ibuprofen, confirming that biodegradation occurred on the BIEX resins. Furthermore, biodegradation contributed to a lower extent to the removal of naproxen probably due to the absence of an adapted bacterial community (Biotic: 49% vs Abiotic: 38% after 24 h batch test). The removal of naproxen, PFOS, and PFOA were attributable to ion exchange with previously retained natural organic matter on BIEX resins. Nonbiodegradable and neutral micropollutants (atrazine and thiamethoxam) were minimally (6%–10%) removed during the batch tests. Overall, the present study corroborates that biomass found on BIEX resins contribute to the removal of micropollutants through biodegradation and ion exchange resins can be used as biomass support for biofiltration.
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•BIEX resins were evaluated for micropollutant removal in batch tests.•Both biodegradation and ion exchange contributed to micropollutant removal.•Biodegradation contributes to the removal of caffeine, estradiol, and ibuprofen.•Ion exchange contributes to the removal of naproxen, PFOA, and PFOS.•Ion exchange resins can be used as biomass support in biofiltration.
•Power transferred was delineated to quantify the effect of different sparging scenarios on fouling.•Power transfer efficiency is significantly greater for pulse bubble sparging than for coarse ...bubble sparging.•Lower fouling rates were observed in the zone of influence of the bubbles.•Spacing between spargers could be optimized knowing the width of zone of influence.
The extent of fouling control in air sparged submerged membrane systems is dependent on the hydrodynamic conditions generated by sparging and the resulting shear stress induced onto membranes. Although the optimal sparging conditions (i.e. bubble size and frequency) that promote fouling control remain unclear, recent studies suggest that pulse bubble sparging is more efficient for fouling control than coarse bubble sparging. The present study demonstrated that pulse bubble sparging was substantially more effective at transferring power to the membranes than coarse bubble sparging. Pulse bubble sparging required approximately 50% less power for fouling control than coarse bubble sparging. The spatial distribution of fouling was not homogenous in the system; lower fouling rates were observed in the zone of influence of bubbles. The width of the zone of influence induced by gas sparging increased with bubble size and frequency, indicating that the size and frequency of bubbles can be optimized to minimize the required number of spargers in a system and therefore the total volume of gas required for fouling control.
A three-dimensional Computational Fluid Dynamics (CFD) model was developed to study shear stress induced by spherical cap bubbles in hollow fibre (HF) membrane modules configured with a packing ...density of 38 m2/m3, to predict the shear profile in a commercial hollow fibre membrane module of 265 m2/m3. The CFD model's computational effort was minimised by simulating the formation of bubble structures and their rising velocities in modules with packing densities of 1.8 and 38 m2/m3 and validated with experimental calibration of shear profiles via electro-diffusion methods (EDM). Pulse bubbles (300 mL) generated from a single sparger at 0.5 Hz produced more satellite bubbles in the wake zone of the leading bubble in high packing density (38 m2/m3) than in low packing density modules (1.8 m2/m3). The bubble rise velocity was approximately 8% lower in the 38 m2/m3 than in the 1.8 m2/m3 module. Increasing packing density reduced the shear profile from a single sparger and the dispersion of the satellite bubbles in the horizontal plane, especially in the upper part of the membrane module. For systems with multiple spargers, the interaction between pulses generated more shear than the pulses from a single sparger, and produced a more uniform shear profile in the module through asynchronous bubble release from adjacent spargers than synchronous release. A 33% increase in the “Zone of Influence”, the flow region where the upward velocity >0.2 m/s, was achieved by moving from a synchronous to an asynchronous form of aeration.
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•CFD model of pulse bubbles in commercial MBRs was developed and validated.•Simplification applied and calibrated for high-packed membrane module.•Pulse bubbles induced membrane surface shear was investigated.•Asynchronous bubble release induced more evenly distributed shear.
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