WO2017144928A1

WO2017144928A1 - Biofilm carrier

Info

Publication number: WO2017144928A1
Application number: PCT/HU2017/050004
Authority: WO
Inventors: István KENYERES; Ferenc HÁZI
Original assignee: Biopolus Intézet Nonprofit Zrt.
Priority date: 2016-02-26
Filing date: 2017-02-23
Publication date: 2017-08-31
Also published as: CN205500887U; HU4712U

Abstract

This invention relates to a biofilm carrier made of structured yarns (1) comprising filaments (2), where each individual filament (2) constituting the central yarn (1) forms a continuous fiber running over the entire length of the yarn (1) and filaments (2) are fixed to each other by anchor points (3) along the length of the yarn (1), and structured yarns (1) are fixed at fixing points (5) of a mesh structure (6), and each structured yarn (1) forms a loop (4) between two adjacent fixing points (5), the arc length (T) of which is greater than the distance (t) of the two fixing points (5).

Description

Biofilm carrier

The invention relates to a biofilm carrier made of structured yarns comprising filaments, where each individual filament constituting the central yarn forms a continuous fiber running over the entire length of the yarn and filaments are fixed to each other by anchor points along the length of the yarn.

Operations based on micro-biological transformation and microbiologically produced materials are used to a significant and growing extent by modern economy. The operations based on microbiological transformation include, but are not limited to, e.g., biological sewage treatment, anaerobic digestion of organic materials to biogas, several pharmaceutical and food industrial fermentations, and even biological air cleaning. Suffice it to quote a few examples of the biologically producible substances, such as bio-ethanol, bio-polymers (such as e.g., polylactic acid or polyhydroxyalkonates), enzymes, organic acids, antibiotics and numberless other important products.

The microbiological transformations concerned are carried out decisively in liquid- phase and less frequently in gas-phase reactors, so-called bioreactors. Bioreactors provide adequate conditions for the operation of the micro-organisms responsible for the transformation, the necessary nutrients and environmental conditions. Where adequate conditions exist, the performance of the bioreactor is defined basically by the quantity (concentration) and state of the micro-organisms introduced there.

The micro-organisms responsible for biological transformation are present in the bioreactor basically in two forms, free-floating, so-called planktonic, form or attached to a surface, as so-called biofilm phenotype. Under natural conditions and if possible, the microorganisms prefer the biofilm form. Micro-organism colonising on biofilm can attain very high cell concentration and thanks to the complex structure created and the binding materials used for it, they can function substantially more efficiently than their freely floating congeners.

The above realisation has led to the increasing use globally of biofilm-based bioreactors, i.e., so-called biofilm reactors, for the various biological transformations. Industrial-size biofilm reactors have first appeared in biological sewage treatment, but today they are used in a growing number of industrial fermentation technologies. In the biofilm reactors, the micro-organisms colonise and form a biofilm on carriers having an adequate surface for that purpose. Two main groups of biofilm carriers are known, namely the floating carriers (floating in the fluid space of the bioreactor) and carriers of a fixed design. Fixed carriers have moved to the foreground in recent years due to their much more favourable properties than those of the floating carriers (no energy demand for movement, floating, no need for special filtering steps, no mechanical wearing problem due to friction etc.).

One of the most important requirements is that the biofilm carriers must be able to bond the largest possible biomass quantity while making the resulting biofilm permeable for the nutrients in the liquid phase and for the metabolites produced by the micro-organisms. Depending on the design of the carriers, the thickness of the biofilm that is permeable and hence suitable for technological purposes ranges from tenth of millimetres to as many as a few centimetres.

By making biofilm carriers overall objective was so far to use materials having as large specific surface area as possible. This was based on a generally accepted assumption that microorganisms get colonized as a film-like membrane arranged parallelly to the surface (hence the term biofilm comes from). The surface adhered film-like membrane can typically develop from a few tenths of millimeters to several millimeters thick, further thickening is restricted by itself, since vital nutrients required for metabolism of microorganisms can not penetrate a thicker membrane. Therefore, until now, the quantity of biomass that could be arranged in a reactor volume unit in the form of biofilm has been restrained by the specific surface area of the carrier and thickness of biofilm membrane still viable.

Moreover, among the biofilm carriers of fixed design the previously experienced rigid structures have been replaced by flexible structures and in particular - due to their favourable surface and cost characteristics - the fibrous and filamentary, essentially textile-based, carriers are the most widespread. One of the most preferred designs of biofilm carriers made of woven synthetic textiles is disclosed in patent specification HU 227 984, whereas examples of looped synthetic textile carriers are disclosed in patent documents US 5,771,716 and US 7,862,890. It can be said that, of the flexible, textile-based biofilm carriers, the looped arrangements have proved to be more favourable due to the fact that the loops provide some kind of protection to the micro-organisms adhering to the surface of the textile yarns against the shear effect of the liquid flow, and thus a bigger volume of biomass can adhere to the surface. However, even though the textile-based and in particular looped textile biofilm carriers constitute the most favourable binding surface for the micro-organisms in the biofilm reactors today, the currently well-known and widespread solutions have serious drawbacks.

The main drawback of the known solutions is that, due to their design, the specific textile material quantity used for bonding a unit of biomass (1 kg of dry matter) is rather significant (around 0.2 to 0.5 kg).

The quantity and adequate operation of the biofilm developing on the surface of the carrier is limited, moreover, by the speed and depth of entry of the nutrients required for the metabolism of the micro-organisms in the biofilm and the way the resulting metabolites can be released from it. These imply limits for the volumetric efficiency and utilisation of the bioreactors.

Therefore, it would be advantageous to develop a biofilm with loose, filamentous structure growing perpendicularly to the surface of the biofilm carrier, into which the nutrients can penetrate deeply and metabolites can leave the deeper layers as well. Such a biofilm structure can develop to several centimeters thickness compared to conventional tenth of a millimeter magnitude and liquids would flow in its loose and filamentous structure freely.

The aim of the present invention is to create a biofilm carrier in which a biofilm having a loose and filamentous structure develops perpendicularly to the surface of the biofilm carrier. Thus, the amount of biofilm adhered to the biofilm carrier can reach many times the amount of biomass created on carriers of traditional design, so the speed of biological transformations in unit reactor volume significantly increases. The material properties and heat transfer ability of so-formed biofilm are more favorable than that of traditional biofilms, so as the specific energy demand of oxygen transfer, mixing and temperature control can be significantly improved.

The aim above can be achieved by a biofilm carrier according to the present invention made of structured yarns comprising filaments, where each individual filament constituting the central yarn forms a continuous fiber running over the entire length of the yarn and filaments are fixed to each other by anchor points along the length of the yarn, and structured yarns are fixed at fixing points of a mesh structure, and each structured yarn forms a loop between two adjacent fixing points, the length of which is greater than the distance of the two fixing points.

Each fixing point coincides with a nodal point of the mesh structure and an anchor point of the yarn. Anchor points of at least two yarns are fixed on a fixing point.

The arc length of the loop is between 5 mm and 50 mm.

The yarn is attached to the mesh structure at fixing point by means of gluing, mechanical attachment or heat welding.

The distance between adjacent fixing points is 10-70 mm.

The invention will be disclosed further in details by referring to attached drawings. In the drawings

Figure 1. shows structured yarn forming the base element of the biofilm carrier according to the model,

Figures 2a,2b,2c. show an arrangement of yarns of a biofilm carrier according to the present invention on a mesh structure in front elevational view (2a) and side view (2b, 2c), and

Figures 3a,3b. show a thin biofilm layer formed on a conventional biofilm carrier (3a), and a loose and thick biofilm layer formed on a carrier according to the present invention (3b).

Figure 1 show a structured yarn 1 forming the base element of the biofilm carrier according to the present invention. Yarn 1 advantageously made of polypropylene, polyethylene or polyamide comprises preferably 50 to 300 pieces of continuous filaments 2, each sized 10 to 100 microns in diameter, running over the whole length of the yarn 1, and fixed to each other by gluing, knotting or heat - thermal welding, heat sealing -at nodes 3 arranged equal length T preferably 5-50 mm therebetween.

A necessary condition of forming a sufficient biofilm layer is that structured yarn 1 be fixed as seen in Figure 2a-c on a mesh structure 6 in the reactor for receiving biofilm carriers, the arrangement of yarns 1 of the biofilm carrier on the mesh structure 6 is shown in front elevation (Fig. 2a) and side elevation (2b, 2c), that is each yarn 1 forms a loose loop 4 between fixing points 5 arranged advantageously by 1-7 cm distance t from each other and including an angle with the plane of the mesh structure 6 (Figs. 2b, 2c), but this loop 4 is not stressed anyway. In view of practical use - e.g. for applications of cleaning waste water, where blocking is a huge problem - it is especially preferable if fixing points 5 can move in all directions of the space in relation to each other.

It is clearly seen in Fig 2a that fixing points 5 of structured yarns 1 are formed preferably on a mesh structure 6. In the embodiment shown each fixing point 1 coincides with a nodal point of the mesh structure 6. As shown in the plane of the mesh structure 6 in Fig. 2b yarns 1 forming loops 4 stand in relief out of the plane of mesh structure 6. In an embodiment shown in Fig 2c bulging loops 4 of yarns 1 are arranged on both sides of the plane of mesh structure 6, since two or more yarns 1, 1b are fixed to each fixing points 5.

In Fig 3a a thin biofilm 7a layer formed on solutions according to the state of the art is shown, and a loose and relatively thick biofilm 7 layer formed on biofilm carrier according to the present model can be seen in Fig. 3b, wherein yarns 1 are situated in a sufficiently big distance, advantageously by 1-10 cm apart in the space, thus a large amount of loose and fibrous biofilm 7 can be formed as compared to prior art solutions. While in the conventional textile based biofilm 7a carriers yarns 1 are intended to be placed as closer as possible to each other in order to increase the surface area, an adequate distance between properly fixed structured yarns 1 is held in order to maintain efficiency for the carrier according to the model, on the contrary. Material and surface property of mesh structure 6 for fixing yarns 1 are such that an adhesion of biofilm 7 is minimal.

Main advantage of a biofilm carrier according to the present invention in comparison with prior art solutions is that the thickness of biofilm adhered to the biofilm carrier can reach many times of some tenth millimeter thickness of biomass created on carriers of traditional design, so liquids flow freely in its loose and fibrous structure. Thus the amount of biofilm 7 adhered to the carrier outruns many times of a biofilm 7a volume adhered to conventional carriers, thus the speed of biological transformations per unit reactor volume can be significantly increased. The material properties and heat transfer ability of so-formed biofilm 7 are more favorable than that of traditional biofilms 7a, so as the specific energy demand of oxygen transfer, mixing and temperature control can be significantly improved.

Claims

1. A biofilm carrier made of structured yarns (1) comprising filaments (2), where each individual filament (2) constituting the central yarn (1) forms a continuous fiber running over the entire length of the yarn (1) and filaments (2) are fixed to each other by anchor points (3) along the length of the yarn (1), characterized in that structured yarns (1) are fixed at fixing points (5) of a mesh structure (6), and each structured yarn (1) forms a loop (4) between two adjacent fixing points (5), the arc length (T) of which is greater than the distance (t) of the two fixing points (5).

2. Biofilm carrier according to claim 1, characterized in that each fixing point (5) coincides with a nodal point of the mesh structure (6) and an anchor point (3) of the yarn (1).

3. Biofilm carrier according to claim 2, characterized in that anchor points (3) of at least two yarns (1) are fixed on a fixing point (5).

4. Biofilm carrier according to any one of claims 1-3, characterized in that the arc length (T) of the loop (4) is between 5 mm and 50 mm.

5. Biofilm carrier according to any one of claims 1-4, characterized in that the yarn (1) is attached to the mesh structure (6) at fixing point (5) by means of gluing, mechanical attachment or heat welding.

6. Biofilm carrier according to any claims 1-5, characterized in that the distance (t) between adjacent fixing points (5) is 10-70 mm.