Weft-knitted media development for technical application for wastewater post-treatment: Effect of spatial sample shape and porosity

Abstract

The innovative designs come from the authors’ idea to similarity with commercially usable plastic media (AnoxKaldnes), which could be replaced with weft-knitted fabric with loose loops required for water flow during wastewater treatment. By a tailored mass fraction of polypropylene and polyester yarns, the necessary purpose of floating the sample due to the lower density, mimicking water, can be achieved. The textile-based microfiber structure supports bacterial attachment. The bacteria surface covering is examined with image analysis during the first period of the experimental bioreactor post-treatment process with the aim of helping media development. The surface bacteria covering is tracked in the location of media shape (inner, outer, held and transfer loops), and samples with high single jersey porosity improved the cell capture. Regarding initial adhesion and quick-up colonization process (advantage of fiber application), the results concerned yarn count and knitting parameters and recommended structure and patterning elements. Experimental tests did not confirm the necessity of openings in the media structure. A highly porous weft-knitted media of the spatial shape, including the simple pipe shape, could be an alternative to a plastic one, which would benefit while maintaining the existing infrastructure of the wastewater treatment process.

Keywords

bacteria covering weft-knitted fabrics carrier for wastewater treatment filtration media multifilament

Introduction

Solid plastic media (“biocarriers”) are used in biological wastewater treatment processes to allow good microbes attachment.¹ Plastic materials are widely used due to low density and high mechanical resistance.² Many of the carriers resemble a pasta-shaped wheel. They usually mimic the density of wastewater, allowing them to mix throughout the liquid rather than sink or float. Among some advantages of using plastic media are the large surface area for microbial attachment (allows for the growth of robust biofilms), mechanical durability (resistant to wear and tear), resistance to chemicals and corrosion, easy handling, low cost (cost-effective compared to ceramics, metals, and natural materials, now available in the market). The strategies to achieve increasing the specific surface area of novel media (carriers) are: Innovative designs (3D-printed-topology optimization, gyroid-shaped biocarriers); surface modification (increase roughness—promotes biofilm adhesion.); coating, etching, or introducing nanostructures; composite biocarrier—incorporating activated carbon for increasing surface area.^1,2

In wastewater purification, the textile-based structures were applied to increase nitrogen removal (sheets - nonwoven with the mesh³; another nonvowen⁴). Other fiber textiles have been introduced (bio-nest,⁵ imitation-aquatic-grass “spiral” fibers,⁶ fiber thread,⁷ sulfur-based fiber carrier,⁸ three types of fibers—juite, bio-fringe, and siliconised conjugated polyester,⁹ electrospun nanofibers,¹⁰ acryl fiber—biomass carrier,¹¹ fibers packing material,¹² flexible fiber biofilm reactors¹³). The warp-knitted fabrics—spacer fabrics were developed for wastewater treatment and described in the study.¹⁴ The 3D warp-knitted fabric had openings to allow water to flow through.

The authors’ idea was to use weft-knitted fabric without the openings, but with loose loops required for water flow and microfiber structure to increase the surface area for microorganism attachment. Fabric porosity will probably be the factor that influences the attachment of bacteria. The porosity is defined as the proportion of the fiber/fabric unit filled with air.¹⁵ A lot of research on the porosity of knitted fabrics has underscored the complex interplay between fabric structure, yarn characteristics, and porosity, which is vital for applications such as thermal management, comfort, and tissue engineering. Knitted fabrics, characterized by their unique interloped structure, inherently exhibit higher porosity than woven fabrics, making them particularly suitable for applications that require breathability, and moisture management.¹⁶

The type of pattern elements and the stitch parameters in knitted fabrics significantly influence their porosity. For example, the tuck stitch creates a more open structure, increasing the void volume and overall porosity of the fabric.¹⁷ In contrast, tighter stitches, such as those found in rib-knitted fabrics, can decrease porosity due to increased stitch density.¹⁸ Additionally, yarn thickness plays a key role; thicker yarns can diminish overall porosity by occupying more space within the knitted structure.¹⁹

Various methodologies have been developed to assess porosity, each with distinct advantages and limitations. Geometric calculations based on the fabric’s structural parameters are a common approach.^20
–24 The pore volume for simple weft-knitted structures was calculated with thickness and other geometrical details of the fabric.²⁵ Based on 3D modeling of stitch overlap, the theoretical porosity of elastic plain fabric is presented in²⁶ using AutoCAD software. Liquid absorption tests measure the amount of liquid absorbed by the fabric to infer porosity.²⁷ Air permeability tests are also frequently employed, as the air permeability of knitted fabrics is directly related to their porosity.^25,28 The air permeability tests are particularly useful for understanding the dynamic behavior of knitted fabrics under varying conditions. Porosity is critical for the filtration capabilities of knitted fabrics, and this relationship is further complicated when the fabric is saturated (mentioned in²⁹), as pore sizes can change. The study³⁰ enabled the development of an apparatus for measuring the amount of light transmitted through knitted fabrics. The stitch length, tightness factor, and porosity affect the light permeability property of knitted fabrics. Moreover, study³¹ introduces a method employing Fourier transformation on microscopic images to extract geometrical data related to loop parameters in knitted fabrics from monofilament, smooth or textured multifilament.

In summary, the porosity of knitted fabrics is a multifaceted property influenced by stitch type, yarn thickness, and structural dynamics. Ongoing research continues to explore these relationships with the aim of optimizing knits for different applications. For example, as a medium for nitrogen removal in biological wastewater post-treatment,^1,32
–34 the shape and design of the media must also be mechanically stable and allow mixing in the bioreactor.

This study mainly focused on tracking the bacteria capture (surface bacteria covering) on the sample surface after the first period of the biological post-treatment process as the wastewater flowed through the porous knitted samples—media (without openings) developed for this application. Different shapes and two yarn counts could cause variable porosity. With the help of image analysis, the investigation of the bacteria capture (attachment) on the loops and their parts, and the research of the media design can be examined. It is assumed that the media’s spatial shape, also caused by the curling of the loose single jersey knitted fabric, further encourages wastewater to flow through the sample (loops), and between its media parts. The 3D structure created with the multifilaments and monofilaments could increase the possible contacts and areas for microorganism capture.

Materials and methods

Material and sample fabrication

For this purpose, the technical application, designed and fabricated media—the weft-knitted samples with loose loops from polypropylene (PP) and polyester (PES) yarns, were manufactured with a flat knitting machine, Shima Seiki NSSG 122, 7.2E. The same machine setting (tensioner, take-down mechanism, cam system, etc.) was used for the production of all samples, which differ in the media’s shape and the yarn assembly. The yarn compositions (PP and PES) were selected for both types of media (see Table 1).

Table 1.

Description of measured yarn characteristics (PP multifilament for twisting and PES monofilaments).

Multifilament
100% PP (textured)	Yarn fineness (dtex)	Diameter (mm)	Number of fibrils (-)	Twist (m⁻¹)/direction twist per inch/direction
Three twisted	330/334.3	0.449	99	100 (93.4)/Z 2.53 (2.37)/Z
Monofilament
100% PES	-	0.1	1	-
100% PES	-	0.2	1	-

All materials and their related characteristics that could be used for evaluation media for wastewater post-treatment process are analyzed. The materials that were investigated³⁵ are potentially applicable and suitable for our research. The verified values of the multifilaments’ fineness and the monofilaments’ diameters correspond to the nominal ones, they are summarized in Table 1.

The small knitted sample (similar to the mainly plastic AnoxKaldnes), named media, was a double-faced fabric with some parts in a single-faced structure. A characteristic feature, that is, horizontal and vertical curling of the single jersey structure, was applied to create a spatial sample. The first media type had one horizontal tube with a single jersey fabric (“pipe”). The second media type (“curl”) consisted of four pieces of single jersey parts Figure 1. The technique of the transport stitches will be used between these single jersey parts, which started on empty needles. To support the curling of the media shape, the bottom edge was a single jersey, too.

Figure 1.

Developed media (tested samples). The figure presents two different weft-knitted fabrics (a) “pipe” and (b) “curl”; progress from the first idea through the technological requirements to real samples for the experiment and their indication.

For reinforced curling and some kind of media rigidity, the monofilament will be incorporated into all parts. From subjective curling experience and to prevent unraveling after casting-off, the top part was carried out with a higher yarn count (PP), small loops and thicker monofilament (PES). The method of media bind-off with knitted technology was not considered due to cost increases. The simplest shape-type of samples was formed as a pipe media with left and right openings for comparison with the curl media, a more complicated form. Figure 1. Two counts of yarns were selected to compare the fabric’s planar porosity and the bacteria capture.

The samples were manufactured separately, but they could be produced in a narrow stripe, and the sample cutting could be solved later.

Samples description: Samples 1 and 3 were produced from PP multifilaments 2 × 334 dtex, samples 2 and 4 from PP multifilaments 3 × 334 dtex. Gray (main) part—reinforced with PES monofilaments 2 × 0.1 mm, violet part—reinforced with PES monofilament 0.2 mm*.

Twisting textured PP yarn is an option to prevent full-filling of the structure and to support the holes between the yarns. The effect of clogging is described in³⁶ a well-known occurrence in wastewater treatment. For textile-based media, a similar phenomenon could also occur.

After fabricating the samples from PES monofilament (0.1 mm) and two or three assembled PP multifilament (334 dtex), the five pieces of each variant were analyzed and separated to obtain the basic structural characteristics (shown in Table 2).

Table 2.

Characteristics of weft-knitted media (experimentally analyzed untreated samples).

Characteristic properties	Sample 1	Sample 2	Sample 3	Sample 4
Number of twisted PP (334 dtex)	2	3	2	3
Media composition PP/PES (%)	76.6/23.4	80.6/19.4	83.7/16.3	84.2/15.8
Total weight (g)	1.17 ± 0.02	1.43 ± 0.02	1.80 ± 0.03	2.37 ± 0.05
Wale spacing (mm)	3.54 ± 0.05	3.48 ± 0.07	3.61 ± 0.05	3.19 ± 0.04
Course spacing (mm)	1.72 ± 0.03	1.73 ± 0.03	1.68 ± 0.02	1.76 ± 0.02
Loop length (mm)	10.13 ± 0.03	10.13 ± 0.03	10.02 ± 0.10	10.08 ± 0.13

The “pipe” samples (1 and 2) are characterized by the smallest weight value, and the benefit is due to the knitting technique without transfer loops. The smaller stitch amount is through the small dimensions of the 3D form (Figure 1), and the ratio of the PP/PES was experimentally evaluated. The loop length values of the media Table 2 were supposed not to differ from each other, owing to the same machine setting, although a different PP yarn count was used. However, it was supposed that the weight and porosity would be various and sufficient for the bacteria attachment, thanks to different shapes and the microfiber porous structure in the initial period of the testing in a bioreactor.^11,13,14

Measurement methods

The measurement principle of the multifilament yarn diameter using Uster Tester 4-SX apparatus is based on the illumination of the passing yarn with infrared rays and the simultaneous two-dimensional scanning of this yarn using the cross-wise arrangement of the sensors at angles of 0° and 90°. The shaded area by the yarn is recorded on the receivers, the measurement result is the average two-dimensional yarn diameter (yarn diameter in 2D). The measurement conditions were a speed of 50 m/min for 2.5 min.

Due to the spatial form of the samples and small size of the samples, the properties were not characterized according to the related standards for mass per unit area, fabric thickness, and structure parameters of the knitted fabrics. The loop lengths and weights were obtained based on experimental measurements. The wale and course spacing were measured by the software NIS Elements (8.16 × µm/px, and 2880 × 2048 px, length of 5 wales and 7 courses; 2 values from 1 image) and statistically evaluated from 30 measurements of all samples Table 1. Mean values of the experimental data, together with the 95% confidence intervals, were displayed in each graph.

The structural properties of all knitted fabric—samples were evaluated in the untreated and after 4 weeks in a laboratory moving bed biofilm reactor (MBBR) with a continuous aeration system and a 13 L total volume was filled with 100 pcs. The reactor inlet contained tap water, ammonium ions (NH₄ +-N 10 ± 2 mg/L), phosphate buffer (PO₄ 3 -P approximately 820 mg/L; composition of the stock solution 8.5 g/L KH₂PO₄, 21.75 g/L K₂HPO₄, 33.4 g/L Na₂HPO₄ 7H₂O), and NaHCO₃ (according to the current reactor’s pH) /14/. A laboratory room was tempered to 20°C, and the bioreactor was checked once a week using chemical analysis of the reactor medium. The bioreactor was described in more detail in.¹⁴ The untreated samples were conditioned for at least 24 h, examined at the standard atmosphere of 21°C and 52% RH, and weighed (analytical balance, Denver, readability 0.1 mg, ISO 9001:2015).

Knitted fabric’s porosity measurement

The approach of the planar proportion of the areas was chosen from the three basic techniques for the characterization of the idealized - simplified fabric porosity: volumetric filling-based porosity, the density-based porosity and the area filling-based porosity (planar). For our application purpose of the loose structure and for the bacteria surface capture (covering) research and the design of the media were determined the planar porosity.

The planar porosity εA (%) that is, two-dimensional interpretation of porosity, is defined as the ratio of the areas of the multifilament yarn and the knitted fabric^21,23,24:

ε_{A} = 1 - A_{m} / A_{k},

(1)

where Am (m²) is the area of multifilament projection of repeat loop unit (Figure 2) and Ak (m²) is the area of repeat loop unit in the knitted structure.

Figure 2.

Porosity measurement: (a) schema of the procedure of porosity determination by image analysis (8.16 × µm/px), (b) cross-section of PP multifilaments and PES monofilaments (PP 3 × 334 + PES, and 2 × 0.1 mm), (c) repeat loop unit.

This area Am covered by a multifilament yarn (yarn projection) can be calculated as the multiplication of its length and diameter, subtracting the overlapping areas of the yarns in a repeat loop unit, and Ak (m²) is the area of the repeat loop unit in the knitted structure Figure 2, which is obtained by multiplying the course and wale spacing of the loop, that is,

A_{m} = d l - 4 d^{2},

(2)

A_{k} = c w .

(3)

where d is the diameter of yarn (mm); l is the length of yarn in repeat loop unit (mm); c is the course spacing (mm); w is the wale spacing (mm) shown in repeat loop unit in Figure 2.

The resulting equation for planar porosity is obtained by substituting the equations (2) and (3) into the equation (1):

ε_{A} = 1 - ((d l - 4 d^{2}) / (c w))

(4)

The diameters of multifilament assembled yarns were not measured, but calculated based on the relation,³⁷ that equation will be:

d = \sqrt ((4 T a) 10^{6} / π μ ρ))

(5)

where d is the diameter of multifilament yarn (mm); T is the yarn fineness (tex); a is the number of assembled yarn (-); $μ$ is packing density of the multifilament yarns (-); and $ρ$ is the fiber density (kg/m³).

According to the simplification and idealization of the cross-section, the packing density of the assembled and twisted yarns is the same. With the experimental parameters (the fineness and yarn diameter) and material characteristics (fiber density) of the twisted yarns, the packing density will be determined:

μ = \sqrt ((4 T a) 10^{6} / (π D ρ))

(6)

where T is the twisted yarn fineness (tex); a is the number of assembled yarn (-); D is the diameter of twisted yarn (mm); and $ρ$ is the fiber density (kg/m³).

The calculated results of the planar porosity of the media samples are shown in Figure 3, and using the formula equation (6) the packing densities are found for the diameters of the assembled multifilament yarns (equation (5)). The porosity of the weft-knitted media is influenced by these diameters and geometrical parameters of loops (w, c, and l) given in the equation (4).

Figure 3.

The values of the untreated structure porosity (weft-knitted media).

The procedure of porosity determination is briefly presented in Figure 2 in separate steps.

The experimental expression of the planar porosity (and bacteria covering area) is related to the ratio of the number of pixels in the image. The surface bacteria covering is defined as the area of the surface of the knitted fabric covered by the biofilm (bacteria) and expressed as a percentage.

The bacteria area (projection) as morphological parameters was calculated from the extracted binary layer, which was obtained in RGB mode. To threshold an image of a bacteria’s surface, all pixels with similar intensity values were highlighted and detected as a binary layer by selecting the cross-hair tool. Two optional operations can be performed on this binary layer (clean, smooth—multiply times). The image of the knitted fabric (planar porosity) was determined as Intensity mode, which fills the second binary layer with threshold limits (the intensity values range from 48 to 255). Images of untreated samples and samples with bacterial biofilm were captured with a macroscope connected to a digital camera (JENOPTIK ProgRes CT3) and a computer with the image analysis system NIS-Elements. All images had the same resolution of 8.16 μm/px.

Results and discussion

The planar porosity εA (%) of all samples was calculated according to the formula equation (4) for only the single jersey part of the media. To compare the calculated value of all samples with each other, it is visible Figure 3 that porosity is similar for the samples with the same yarn count, that is, sample 1 and 3; sample 2 and 4. The calculated values Figure 3 depend on the diameter of the assembled yarns (texturized multifilaments), which is complicated to find or measure, especially when formed into loops. To obtain the value of the assembled yarn diameter, it was necessary to simplify and assume that the packing density of twisted and assembled yarn in the loops is similar. As the yarn count increases, the planar porosity decreases (comparing samples 1 and 2; samples 3 and 4).

For experimental evaluation, all samples had to be lightly and gently straightened, and after that, the samples were imaged and analyzed. The data were reported as mean and 95% confidence interval determined from 15 measurements from 15 images of each part of all samples. A graph in Figure 3 show the experimental results of the porosity of the media samples. Since the loops is designed to be larger, wastewater will be allowed to flow through it. The porosity of a single jersey structure (samples 1–4) fabricated with the same machine setting, yarn composition and count differs according to the knitted technique. With samples 3 and 4, the single jersey structure started on the empty needles, and the take-down mechanism (comb) does not operate on that part; only sinkers cause the hold-down function. That is why there are different experimental porosity values between samples 1 and 3, respectively, and samples 2 and 4. The other reason for the smaller experimental porosity of pipe samples (1 and 2) is that the back needles held the loops while the front needles knit, and only the stitch presser caught the formed fabric, not the comb. Afterward, a short period and then a long period in the bioreactor will show whether the porosity of samples 3 and 4 is sufficient and effective for cell capture.

The visual appearance of a knitted single jersey structure from 2 or 3 assembled PP yarns is presented in Figure 4. The two PES monofilaments (0.1 mm) were hidden in the structure (marked in the photograph), causing sufficient rigidity and reinforcing the required media shape for that special technical application. The stiffness of the samples with PES monofilament (0.2 mm) was unsuitable for testing in a bioreactor. Maybe because of the rigidity and stiffness of the samples and the non-smooth surface with the “sharp ends,” problematic media movements, collisions, and clusters appeared.

Figure 4.

Weft-knitted fabrics from PES monofilaments 2 mm × 0.1 mm and (a) PP 2 × 334 dtex, (b) PP 3 × 334 dtex.

The role of using the monofilaments can be summarized as follows: They can influence the floating in the bioreactor (mimicking the density of wastewater), open the loops (holes) of the single jersey structure, support the edge curling of the samples, and stabilize and rigidify the media needed to keep their shapes during mixing in the bioreactor. That information comes from the practical testing and initial experiment during the process of the weft-knitted media development.

The fabricated media are stable, 3D-formed fabrics; unraveling is solved by the single jersey curling of the cast-off part. In the laboratory post-treatment bioreactor, no problem appeared with the media’s mixing.

Testing in a post-treatment bioreactor belongs to the long-term tests, and tracking the surface porosity of initial colonization according to the type of patterning elements and material and setting the knitting parameters or different shapes is a good tool for effective media development. The laboratory apparatus, method, and bioreactor conditions were the same.¹⁴ The number of media in the bioreactor from each of the variants was 10; the O₂ rate and surface bacteria covering results are after 4 weeks, Figure 5.

Figure 5.

Laboratory verification of weft knitted media efficiency: (a) laboratory test of weft knitted samples (100 pcs per 13 L); (b) O₂ consumption rates after 4 weeks in the bioreactor post-treatment process for all tested media (1–4).

The effective surface area is the portion of the media inside the media on which the biofilm grows and directly affects the efficiency of the process.² Compared to the plastic media, textile-based media are suitable due to the increased area for attachment of bacteria. With Image analysis, quick step analyses of supporting parts for bacteria could be found. The advantage of textile-based media is that 3D bacteria grow, which can be seen in (Figure 7). Thus, the development of fiber media is in its early stages, and the effect of clogging described in,³⁶ has not been investigated.

The graph in Figure 5(b)) shows the respirometric values after 4 weeks, which indicate oxygen consumption. The change in gas concentration can specify the biofilm activity on the individual media, with higher O₂ consumption indicating greater required biofilm activity.^38
–41 The results are also surprising given the previous tests with microfiber media made by warp-knitting technology.¹⁴

Samples 1 and 2 (respective samples 3 and 4) have the same number of stitches in the whole piece, a higher and lower porosity (different yarn count), and cause a similar biofilm activity in this first part of the experiment. It is necessary to take into consideration the media weight (whole yarn consumption of sample 1, except the cast-off part, is 45% less than that of sample 3), which brings the potential area for bacteria colonization. A simple solution for mutual comparison, that is, increasing the area of samples 1 and 2, will totally change the dimensions of the media, and also compare to the commercially used plastic carriers. So the shape modifications of these samples are now shown in Figure 9.

The curling effect of the single jersey part enhances the spatial shape, and the inner (hidden from water flow) part of the media is more colonized (samples 1 and 2—back, inside of the tubular part, suitable with larger porosity; samples 3 and 4—front, inner curling parts, suitable with larger porosity). See results from wet samples given in graph (Figure 6).

Figure 6.

Surface bacteria covering of media after 4 weeks in bioreactor.

It was necessary to separately evaluate the technical front and back of the structure (indicated—Front, Back). In the first period of bacteria capture (4 weeks), the differences between the front and back (outer and inner) parts of samples 1 and 2 are not negligible (the confidence intervals do not overlap). The similar surprising bacteria covering for samples 1 and 2 causes a positive effect on O₂ consumption due to the low total media weight. The surface bacteria covering was more uniform for both surfaces with the developed samples 3 and 4. Owing to the media construction and shape (samples 3 and 4), the held loops (gray columns) appeared to be a suitable area for bacteria capture—it was unexpected.

Apparently, microorganisms penetrated the structure where they were involved in O₂ consumption, but the surface bacteria covering determined with the help of image analysis did not quite match this. It remains to be seen what this method of assessing bacteria content will show for biofilm development over the longer time period of the experiment. However, what turned out to be a very positive factor was the finding of high cell area at the locations where the held loops were and, moreover, when they were not only placed inside but also in a not-so-protected location (Figure 6; gray column) and structure Figure 7).

Figure 7.

Bacteria covering on the surface of knitted samples: pictures show differences between samples produced from different yarn counts, differences between bacteria covering on front and back sides, and SEM analysis confirmed bacteria (biofilm) presence.

Furthermore, the innovative knitted fabric media are less tight, allow the free flow of wastewater, and provide very good support for trapping microorganisms. As mentioned,² the media with small openings and large effective surface areas benefit the slow-growing microbial biofilm.

Around the media in the bioreactor has elevated turbulent flow and influences cell attachment to the surface. The role of biofilm is of almost significance as without a functional biofilm the bioreactor system would fail. Biofilm development may be defined as the difference between attachment and detachment of the total biofilm growth in the system. This process of biofilm development is based on a phenomenon that depends on microorganisms’ ability to adsorb and desorption on the solid surface along with biofilm thickness, attachment and detachment of the biofilm from the biofilm carrier.⁴², pp. 195–231

In both sample shapes, when the structure porosity increased (yarn count decreased), the bacteria surface covering increased too. Although the front side of the single jersey structure is subjectively smoother, the curling principles cause this side to be inner, and bacteria covering reaches the higher values on the front side of the single jersey (sample 3—two assembled yarn). In the case of pipe media (sample 1), the back side of the single jersey fabric with sinker arcs is more convenient for cell attachment. A special case occurred in the creation of the more complicated shape sample 3 (sample 4), where the purpose was not to create held stitches but was a consequence of the shape design. The bacteria surface covering of rib structure (held loops) is shown for zero value of the porosity (in the graph Figure 8). At this stage of initial colonization by bacteria, this part of the structure (see Figure 7) proved to be the most well-accepted.

Figure 8.

Influence of porosity on the surface bacteria covering (all media samples).

Based on experience and promising results with the pipe shape, future research will also be focused on the additional possible media shape (Figure 9).

Figure 9.

New shape proposal for the media suggested for the wastewater post-treatment process.

Conclusion

According to the authors’ knowledge, this is the first media innovation for nitrogen removal during the wastewater post-treatment process that is weft-knitted to the spatial form. The innovative media are composed of microfiber and tailored to the mass fraction to allow float due to their lower density compared to water. The specifically developed shape and setting parameters of knitting are suitable for the porosity necessary for microorganism attachment and, afterward, colonization and biofilm growth (confirmed with O₂ consumption rate).

The loose loops and used yarn counts allow the free flow of wastewater through the media. It was confirmed that single jersey samples are sufficient for bacteria attachment in bioreactor. The 3D weft-knitted structure increases the number of possible contacts between the microorganisms and the fibers of the media, increases the surface area, and the media’s pass-through also significantly influences their capture.

This research provides an understanding of the impact of carrier porous structure and spatial shape of media on rapid bacteria attachment, which would benefit the wastewater process in the near future while maintaining the existing infrastructure and even increasing demands on the quality of the wastewater treatment process. The results presented above, as well as the ability to knit different shapes and structures and yarns with different morphologies between them and significantly increase cell capture compared to plastic ones, make them an attractive technology for future wastewater purification applications.

Supplemental Material

sj-docx-1-jef-10.1177_15589250251359271 – Supplemental material for Weft-knitted media development for technical application for wastewater post-treatment: Effect of spatial sample shape and porosity

Supplemental material, sj-docx-1-jef-10.1177_15589250251359271 for Weft-knitted media development for technical application for wastewater post-treatment: Effect of spatial sample shape and porosity by Irena Lenfeldova, Martina Ryvolova and Petra Jiraskova in Journal of Engineered Fibers and Fabrics

Supplemental Material

sj-pdf-2-jef-10.1177_15589250251359271 – Supplemental material for Weft-knitted media development for technical application for wastewater post-treatment: Effect of spatial sample shape and porosity

Supplemental material, sj-pdf-2-jef-10.1177_15589250251359271 for Weft-knitted media development for technical application for wastewater post-treatment: Effect of spatial sample shape and porosity by Irena Lenfeldova, Martina Ryvolova and Petra Jiraskova in Journal of Engineered Fibers and Fabrics

Footnotes

ORCID iDs

Irena Lenfeldova

Martina Ryvolova

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Supplemental material

Supplemental material for this article is available online.

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