DK202100791A1 - Bioreactor for stationary biofilms of photosynthetically active microorganisms - Google Patents

Abstract

Apparatus for maintaining a stationary biofilm of phototrophic microorganisms alive and a method for air purification and mass production. The live maintenance is carried out for an extended period of time with low maintenance and low energy consumption. The bioreactor contains a flat housing with a transparent front wall and air openings. The biofilm is located on a growth and distribution mat, which lie together against the back wall. A tank supplies the biofilm with medium. The biofilm is not attracted in the housing, but only inserted. Skimming provisions are not necessary. Due to the simple design, the biofilm can be replaced quickly. The water requirement is low. With the process presented here, a larger number of pollutants can be absorbed with low energy and maintenance. Efficient production of organic recyclables is also possible through simple media and air changes and rinsing.

Description

DK 2021 00791 A1 SOL-102 Applicant: Solaga UG Representative: RA Benjamin Herzog Title: Bioreactor for stationary biofilms of photosynthetically active microorganisms.

Description The present invention relates to a bioreactor for maintaining a stationary biofilm of photosynthetically active microorganisms alive and a method for air purification and fabric production.

Interest in photosynthetically active microorganisms (PAMs) is increasing not only in biotechnology.

They are also attracting increasing attention, especially in the energy and food industries.

Photosynthetically active microorganisms include algae in the narrower sense, especially green algae, cyanobacteria, anoxygenic, phototrophic bacteria and certain archaebacteria.

Compared to plant systems, they show much higher growth rates per area and can be grown without soil even on sealed surfaces.

Their metabolism differs from animal and, to some extent, plant systems in such a way that a variety of different metabolic products can be produced by them.

PAM are cultivated in bioreactors.

This is mainly done in liquid reactors.

In these bioreactors, the PAM are circulated mainly by mechanical forces or gassing currents so that all cells are irradiated with light.

In addition, energy- intensive gassing is necessary to ensure that all cells receive the CO2 they need.

In most applications, the PAMs are harvested by separating them from the medium by centrifugation, an energy-intensive process.

The water in the medium is consumed in the process.

In contrast, so-called biofilms of PAM have a number of advantages.

A biofilm is a thin film of slime in which populations of microorganisms are organized.

The majority of all microorganisms in nature occur in such biofilms, which are usually heterogeneous.

The biofilm offers them many advantages.

For example, they can permanently attach themselves to objects, protect themselves from intruders and live in symbiosis with other organisms.

The mucus layer is an exopolysaccharide layer (EPS) mainly consisting of polyuronides, i.e. polysaccharides containing uronic acids such as D-mannuronic acid, D-galacturonic acid or D-glucuronic acid.

The uronic acids are always in pyranose form and give the macromolecules an acidic character, as well as the ability to store water and thus form a gel.

It has been found out in studies that the cells in the biofilm compound also exchange substances among themselves, so that the cells sitting further down, for example, are also supplied with the substances produced by light, oxygen is transported out and CO2 is also transported in and distributed in the form of HCO3-. The EPS protects the PAM from desiccation, large temperature differences, salt stress, strong radiation as well as from predators.

This allows the PAM to survive far better in the wild.

The intention is to make PAM biofilms useful for humans.

In part, their use in water purification is being investigated.

There they are supposed to absorb phosphates and nitrates.

However, these pollutants are also fertilizers for the PAM, so the biofilm would have to grow and be harvested.

However, there are no valid use scenarios for this, especially since a protective skin, once formed, is not extended.

Plant stems or leaves, which are comparable to the organism biofilm, also do not grow in width.

Therefore, only the use of a stationary biofilm can be considered.

Stationary biofilms do not grow.

They have a self-metabolism and an overflow metabolism.

The overflow metabolism, which can lead to the accumulation or secretion of metabolic products, is mainly used when additional energy in the form of light is available.

In the prior art, bioreactors for biofilms are known.

From WO2014172691A4 is a culture system with biofilm adherent surface for, inter alia, algae grown on a circulating element forming multiple accordion pleats supported in a circulating travel path.

The recirculating pleat system has some

DK 2021 00791 A1 disadvantages, including that it consumes a lot of energy. In addition, it does not use a stationary system. Finally, the movement may cause damage to the biofilm.

A bioreactor for PAM biofilms is also known from WO2014085869A1. According to this, fluid- permeable layers form a first surface on which photosynthetic microorganisms can be cultured to form a biofilm. A second surface is in fluid communication with a fluid source. The fluid-permeable layer is rotated. This consumes additional energy. Last but not least, the system is designed for ineffective biofilm growth. In the round system, the application and maintenance of the biofilm are much more difficult.

US10072239B1 discloses a system for growing at least one photosynthetic microorganism and converting CO2 to O2 with reduced water consumption. The system includes a liquid transport capillary channel, a photosynthetic mixed culture biofilm, and a liquid transport substrate positioned between and adjacent to the capillary channel and the biofilm, wherein the liquid transport rate is adjustable by adjusting the local humidity. This system is modeled on the supply principle that trees use to supply water to their leaves. The only difference is that the salts produced there are consumed by the leaves. In the system proposed here, it is not apparent how the salts left over from evaporation are used and how long the system will run as a result or, for example, how much function will be lost. The liquid tank is always placed at the bottom, so it has energetic disadvantages, because against gravity the water is transported. The whole system is highly dependent on the available humidity. If this is excessive, it does not work. The system is also designed for growth and not stationary existence of biofilms.

Various biofilm reactors have been developed in the non-patent literature. Naumann et al. have published a system in which microalgae are immobilized by self-adhesion to vertically oriented bilayer modules. The bilayer modules consist of glass fiber nonwoven fabric, through which the culture medium is transported by gravity, and printer paper, which supports the algae on both surfaces of the modules. The growing microalgae are used for aquaculture feeding. A stationary biofilm is not cultivated. Furthermore, a reserve tank is not available. The multi-module design is complex and prone to contamination.

Podola et al. and Liu et al. propose a system in which an algal biofilm grows on a microporous membrane. Behind it is a culture medium. Several modules are supplied by a pump. In so-called biofilm PBR (porous substrate bioreactors), biofilms grow on a liquid-distributing structure provided as an attachment for an internal supply channel on a suspended module. An immediately adjacent liquid tank is not present. Also, multiple modules are present with orientation on both sides. The sole purpose of the device is to grow biofilms, i.e., to produce biomass, with the attendant problems of harvesting and regrowth of an inherently self-contained system.

The present invention is intended to provide a bioreactor for maintaining a stationary biofilm of photosynthetically active microorganisms alive for an extended period of time with low maintenance and low energy operation.

The problem is solved by a bioreactor for a stationary biofilm of photosynthetically active microorganisms consisting of a cuboidal, flat, elongated housing, wherein one wall of the elongated- width side, the front wall, is at least partly made of transparent material and air openings are present in the side walls. The biofilm is grown on porous material, the growth mat. A layer of liquid easily spreading material, the spreading mat, is underneath. The mats with the biofilm rest against or are attached to the inside of the back wall. A tank with medium for supplying the biofilm is present on the outside of the back wall or as a protrusion of the housing, the tank being in communication with the interior of the housing via openings and having an opening for refilling.

DK 2021 00791 A1 An advantage of the present solution is that a stationary biofilm can be maintained with low maintenance and energy.

The rearing can be done at a different location.

The biofilms are simply inserted into the housing.

Since a stationary biofilm is used, no skimming provisions are necessary.

Using this method and setup, biofilms have already been successfully kept alive for 2 years in the laboratory without any loss of CO2 uptake or other changes.

Once formed, the protective skin in the form of the EPS is comparable to a cuticle.

Another advantage is the construction and robustness.

Due to the simple construction, the biofilm can be replaced quickly and in a less time-consuming manner if necessary.

Moreover, no complex sterilization has to be performed.

Due to this simple manageability, the application is also possible outside the laboratory: at home, in the office or even as a stand-alone system outdoors.

Another advantage is that little maintenance is required.

The water requirement is low, as the biofilm no longer grows.

On average, with a biofilm area of 30 x 40 cm and average humidity, a 100 ml tank only needs to be refilled once or twice a month.

The PAMs only consume as much as they actually need.

Due to the optimal distribution of the liquid in the growth mat and the distribution mat, low-energy operation is possible.

Any metabolic end products or daughter cells can accumulate in the housing.

Without stress conditions, the release of the latter was very rarely observed.

The PAMs also secrete substances that prevent the growth of undesirable organisms such as fungi and the like.

Due to the structure of the bioreactor and its ease of handling, a permanent and sustainable coexistence of microorganisms with a high utilization potential with humans is now possible.

The housing has a flat design, i.e. there is a large front wall and a large rear wall.

The width of the side walls, ceiling wall and floor wall is small compared to these surface extents.

Air openings are located in the latter walls.

The flat design allows passive air flow through the enclosure (chimney effect). Due to the light irradiation, the PAMs produce warm air which rises to the top.

Cold air flows in.

This process also produces humidity, which can be released to the outside.

Especially in low- energy houses, dry, synthetic air produced by large energy-wasting filter systems is a major problem.

In addition, these houses are usually not allowed to ventilate through to avoid too much energy loss.

The elongated design is of great importance for ergonomic and space-saving application also outside the laboratory for user-friendliness.

Last but not least, an elongated vessel can accommodate the largest possible biofilm.

Little shading also occurs.

Light is admitted through transparent material on the front side.

This consists of glass or polymethyl methacrylate (acrylic glass, Plexiglas). The medium differs depending on the PAM used.

It does not contain any fertilizers, especially nitrates and phosphates.

The salt content is low, so there is a sufficient concentration gradient of the dissolved substances to the air to be cleaned.

It diffuses through the distribution mat and thus feeds the entire biofilm.

In particular, the liquid runs downward over time due to gravity.

The distribution mat is an absorbent mat, absorbent mat or absorbent fleece.

The main property is to absorb and evenly distribute liquid from a point source of liquid.

It is advantageous if the mat has a fibrous structure due to the presence of microfibers.

Materials are found in diapers and mats for handling incontinence.

The mat can be made of e.g. cellulose, polypropylene, copolymer fibers, bico fibers.

It is attached to the wax-up mat.

The mat can be e.g. a nonwoven, i.e. a structure of fibers of limited length, continuous fibers (filaments) or cut yarns of any kind and any origin, which have been joined together to form a nonwoven (a fiber layer, a fiber pile) and connected to each other in a way without interlacing or intertwining of yarns, as it happens in weaving, knitting, lace production, braiding and production of tufted products.

These can be, among others, films, papers or fiber- reinforced plastics.

DK 2021 00791 A1 A biofilm is grown on the waxing mat.

To create the biofilm, the PAMs are previously grown in liquid culture and applied to the grow-up mat so that they can grow into it and form the exopolysaccharide layer.

Both homogeneous and heterogeneous biofilms with different PAM or even other species can be used.

Among the PAM, algae and cyanobacteria such as Axodine, Bacillariophyceae, Bryopsidophyceae, Chlorophyceae, Cyanophyceae, Dinophyceae, Eustigmatophyceae, Labyrinthulea, Mesostigmatophyceae are suitable, Pelagophyceae, Phaeophyceae, Phaeothamniophyccac, Pleurastrophyceae, Prasinophyceaer phidophyceae, Synurophyceae, Trebouxiophyceae, Ulvophyceae, Xanthophyceae, Gloeothecae, Plectonemae, Anabaena sp. and Nostoc sp.

In particular, cyanobacteria are able to function effectively in low light conditions, such as those found in shaded rooms, due to additional photopigments.

The PAM absorb light and convert some of it into heat.

This causes the air in the housing to rise and be forced out through the air openings.

New air flows in (chimney effect). A thin liquid film is present on the biofilm, at the interface of which gas can be exchanged with the air in a similar way to the lungs or the stomata of plants.

Short diffusion paths allow rapid exchange with the cells.

The medium with few components also flows past the air in countercurrent flow (countercurrent principle). Whether the tank is on the back or as a protrusion of the housing depends on which design is easier to implement.

This is particularly crucial when using 3D printing processes or higher volumes.

In a preferred embodiment, air openings are present in the smallest walls, i.e. in the bottom wall and the ceiling wall.

They are thus opposite each other along a vertical axis.

This arrangement makes optimum use of the chimney effect and the counterflow principle.

The shape of the air openings does not matter.

The size should be chosen according to desired air exchange rates.

The larger they are, the more air can flow through.

This also depends on the environment, especially its humidity.

In rooms, especially radiators and radiators, where warm air flows upwards, there are mainly vertical currents, which are exploited by this design.

In a further preferred embodiment, a filter or a grid, which has a minimum mesh size of 0.2 mm, is integrated or connected in the air openings.

A filter in particular a grid in the openings with minimum mesh size of 0.2 mm made of stainless materials such as stainless steel or plastic effectively prevents insects from entering, but still allows air and dust to pass through.

In a further preferred embodiment, the air openings are extended inwardly, particularly as channels, or there is a web on the inside of the bottom wall, so that in both cases a catch basin is formed.

Tubes or channels adapted to the hole format in each case can be used as channels.

The bar is located between the pane and the back wall and connects to the air openings.

This keeps the catch basin larger.

The bar can be an extension of an opening in the form of a wide gap.

The catch basin obtained by the additional fixtures or protrusions serves as a leakage protection if the liquid passes too quickly from the tank.

Without a catch basin, the fluid could drip out through the air openings.

The channels or the bar are made of e.g. plastic and preferably transparent so that more of the biofilm is visible to the outside.

The length of the extension or web should preferably be chosen so that there is no shadowing of the biofilm or no visibility from the outside, if a frame is used.

In a further preferred embodiment, the catch basin is filled with water absorbent material.

Leakage is thus even better prevented during rotation.

Water-absorbent material is, for example, water storage granules.

This can be a cross-linked copolymer based on potassium salts.

It absorbs up to 300 times its own volume of water.

However, sponges or the like are also possible.

In a further preferred embodiment, a narrow cavity with, in particular, water-absorbent material is provided on the rear wall with an opening to the catch basin.

A small opening for the discharge of otherwise accumulating air may be provided.

This embodiment provides an additional catch basin in which even more medium can be absorbed by the biofilm for temporary storage.

The water

DK 2021 00791 A1 absorbent material may be designed as before. Mats may also continue beyond the biofilm into the cavity. They also have absorption capacity. The cavity allows for lower air opening channels or web, which contributes to a better design. Also, the space below the tank, when placed higher up, is unused. An evenly shaped surface is created as a result. Most importantly, the housing can then be mounted straight for attachment to the wall. Since it is preferably located below the tank, optimum use of space is ensured. The housing does not become too deep as a result.

In a further preferred embodiment, tapes, in particular cords of water-transporting material, connect the tank to the interior of the housing via the openings, which in this embodiment are the same size as the tapes, and rest there against the distribution mat. In particular, they dip into the medium in the tank from above, or there is a membrane in the openings that allows the medium to pass through only in the event of suction, which is in communication with the distribution mat.

The cords or filaments may be made of wool, plastic or the like, wound like wicks or braided. The fibers represent fine channels. Water transport in these is caused by capillary forces (wicking effect) and evaporation at the other end. However, driving force can also be caused by hydrostatic pressure if the opening is attached to the lower side of the tank. However, since this can cause too much flow after filling, it is preferable for the cords to only dip into the medium and for water transport to occur only when evaporation is so high that capillary forces or evaporative suction outweigh gravity. Alternatively, a membrane preferably a hydrophobic one that allows little medium to pass through can be used. If evaporation is high, then the resulting evaporative suction can overcome the hydrophobic membrane back pressure.

In a further preferred embodiment, the tank is flattened and a level window is provided on the side facing away from the housing. Due to the flattening, the bioreactor takes up little space when attached to the wall into the room. This has advantages in terms of installation and design. The level window allows the level to be read at any time, so the user knows when to add new medium through the opening of the tank. Complete transparency of the tank would result in PAM possibly growing there as well, which is undesirable.

In a further preferred embodiment, an irrigation unit, in particular in the form of a drip tube or hose with openings transversely less than 2 cm above the upper edge of the biofilm or below the distribution mat in the upper area, and a pump are present, whereby medium is pumped through the irrigation unit by means of the pump from the catch basin. In this embodiment, the medium reaches the biofilm through an irrigation unit operated by a pump. The irrigation unit may be designed as a drip unit, which is placed horizontally above the biofilm or the distribution mat or the growing mat, which is not necessarily overgrown at this location. Thus, the mats should protrude into the housing or be offset to the rear so that they can be drip-fed from above. On the other hand, spraying of the biofilm is also conceivable. However, this requires a higher pump pressure. It is also conceivable that an irrigation unit is present below the mats. The diameter of the openings is 0.2 to a few millimeters (equivalent to the diameter of a cannula). It is necessary to prevent algae from growing into these openings. Therefore, they should not be illuminated. On the other hand, there should be a possibility for cleaning. For example, a short-term, rotational pressure increase should be considered, by which the openings are pressed free again without damaging the biofilm. The tubes or hoses should have a diameter of a few millimeters to centimeters and be made of plastic, for example. A flow from both sides is preferred, since the medium meets in the middle and thus the pressure is greater to flow through the small openings. Due to gravity, the medium runs down the mats and irrigates the biofilm.

In a further preferred embodiment, a collection edge is provided below the irrigation unit with a gap of less than 1 mm to the biofilm on the grow mat. The collecting edge, made of e.g. plastic, enables a

DK 2021 00791 A1 better distribution or collection of the individual droplets. It thus prevents, above all, the formation of webs on the biofilm, which would mean uneven supply. In addition, the collection edge allows shading of the irrigation unit and thus undesirable growth of PAM in the irrigation unit.

In a further preferred embodiment, the transparent material of the front wall is in the form of a glass or polymethyl methacrylate sheet and a groove is provided in each of the side walls and the bottom wall into which the sheet is inserted. The top wall is removable and serves as the top closure. To open the housing, the top wall must be removed and the pane pulled out upwards. This allows easy opening. To prevent medium from flowing out of the catch basin when the housing is tilted if there is no web, the disc must be sealed at the bottom. This can be achieved, for example, by a foam rubber on which the disc rests and which is located on the sides. It is also conceivable that the mats are clamped in place by the ceiling wall, so that no clamping rail or similar device visible in the upper area is necessary. The groove can be realized, among other things, by attaching a U-profile to the side walls and the bottom wall.

In further preferred embodiments, the side walls and the bottom wall have a groove for insertion of the back wall with biofilm and mats thereon or a layer separate from the back wall with biofilm and mats thereon. These embodiments allow for easy replacement of the biofilm when replacement is necessary. Especially the exchange of the biofilm has to be done under as sterile conditions as possible. Careless movement can further lead to a tear. For the user without these skills, it is easier to change only the solid base of the biofilm. Thus, these embodiments increase ease of use. Also in these embodiments, a detachable blanket wall is a suitable closure. However, a slot in the ceiling wall through which the layer with biofilm is pushed is also conceivable.

In further preferred embodiments, the front side and the rear side have curves in whole or in part. In particular, the housing is cylindrical in shape. For functionality, it is important here that the front and back sides have the same shape. The rectangular shape is based on the distribution of the medium by gravity. However, since capillary forces can also distribute medium sideways in the distribution mat, another shape is also possible. A polygon, a twisted quadrilateral or, for example, a rhombus are also possible, in addition to round shapes such as circles, ovals or the like.

In further preferred embodiments, the mats are fixed by pins, Velcro, a clamping rail, chords and/or on a grid. For vertical use, a fixation is necessary. The attachment should be as little visible as possible and at the same time robust. Needles with a small head are particularly suitable for this purpose. They should be made of stainless material (steel, treated iron, plastic), preferably transparent or dark green in color. When using Velcro, it is possible to detach them easily. The pores of the mats, especially the wax-up mat, allow a good grip. If necessary, a distribution mat can be dispensed with if the Velcro does not adhere there. The use of transparent tendons also has advantages. These can be used for fixation on a grid. Likewise, the biofilm with the mats can be fixed on a grid without chords. The grid can be fixed to the back wall.

In further preferred embodiments, a frame is provided in front of the front wall or the front wall has a non-transparent surface and the frame or non-transparent surface is equipped with or forms a photovoltaic system. This allows the surface to be used to provide self-sufficient operation. Power cables are also no longer necessary. Just as solar-powered calculators can be operated with little light, direct operation of a consumer or charging of a battery is conceivable.

In further preferred embodiments, air composition sensors and other sensors are provided in or on the housing. Air composition sensors may determine, for example, humidity or levels of COx, NOx, SOx, ozone, volatile chemicals, or ammonia. Another sensor may be, for example, an environmental sensor such as a temperature sensor or a pH sensor. Among other things, the control can be before and after: At the inlet and outlet separately or connected via a common air tube. Power for the

DK 2021 00791 A1 sensors can come from an external source, an integrated mini PV system and/or battery. It can be used for the sensors and, if necessary, control the space on the back side below the tank, among others. Measurements are taken at specific times to save power. In the meantime, the sensors are in sleep mode. This can be controlled by a controller.

In a further preferred embodiment, data transmission is provided, in particular a radio link for sending data from the sensors to a receiver. This allows the user to see at any time how the air in the room is composed or other environmental conditions. The data can be sent to a server, a cloud or to an app, etc. It is also possible to directly control or communicate with, for example, ventilation equipment or sun shading devices. Power for the system can come from an external source, an integrated mini PV system and/or battery.

In a further preferred embodiment, the enclosure is actively ventilated via the air openings. In particular, a fan is provided in the air openings for this purpose. Due to the active ventilation, a higher air throughput is possible. Small fans or even ventilators can be used for this purpose, among other things. They can be inside or outside the case. Power can come from an external power source or from a mini PV system and/or battery.

In a further preferred embodiment, air is introduced into the tank to gasify the medium. This can effectively dissolve substances from the air passed through the medium, which in turn releases them to the biofilm.

In a further preferred embodiment, a frame or a non-transparent section of the front wall is provided from which lamps, not visible from the outside, illuminate the interior of the housing and thus the biofilm. This not only serves to supply the biofilm with light energy and heat, but also highlights the biofilm more visually. LEDs or similar can be used as lamps. The use of black light to take advantage of the bioluminescence of the PAM, which absorb light in the invisible range but re-emit it in the visible range, is also possible. The power may come from an external power source or from a mini PV system and/or battery.

In a further preferred embodiment, lamps are provided in whole or in part below the biofilm or mats for backside illumination. This not only allows light energy and heat to be supplied to the PAM, it also allows for visual highlighting. In particular, the projection of certain shapes such as logos etc. is possible. Economical LEDs can be used as the light source. The power can come from an external power source or from a mini PV system and/or battery. With full illumination, it is possible to use the bioreactor as a wipeable board with dark color of the pens. With only partial illumination or even no illumination, white pens are to be used.

In further preferred embodiments, the bioreactor is mounted in the ceiling or floor area of a room, with the front wall reinforced in the floor area. If the bioreactor is mounted in the ceiling area, the biofilm is supplied, for example, via a hydrophobic membrane that allows only a small amount of medium to pass through and over which the medium is located. It must be ensured that, as far as possible, no medium drips onto the pane. A pump can be used to deliver medium to the ceiling via a pipe, with automatic supply being preferred when the level is low. Alternatively, the use of rainwater collected on the roof is also conceivable. If the tank is installed in the floor area, the medium diffuses e.g. from below through the mats to the biofilm or it is moistened from above by a spraying method or similar. The tank is refilled through an opening or connection pointing upwards. A stable disc with reinforcements, if necessary, should be used. The advantage of these embodiments is the use of areas that are otherwise not used or used only sparingly. In particular, a bioreactor illuminated from the back or front can be used as a lamp.

DK 2021 00791 A1 In the prior art, few processes are known that are used for air purification by PAM.

In JPH11226351A, actively polluted air is fed to algae.

The algae, which grow in a medium, are subsequently harvested in an energy-intensive manner for use as food.

In EP3368650A1, a method and apparatus is provided for removing air pollutants from air.

A microfluidic chip is used that includes a fluid flow path in fluid communication with a surface comprising a phototrophic organism.

Air is brought into contact with this surface and the air pollutant is removed.

This solution is also a liquid system, the use of which may be compromised by biofilm formation or require algae removal.

The currently existing, mechanical solutions are focused on single pollutants and consume energy.

The task of the presented invention is to find a solution for an efficient and especially low- maintenance air purification.

With the method presented here, a larger number of pollutants can be absorbed with low energy and low maintenance.

The task is solved by claim 21. According to the method herein, in the previously described bioreactor, polluted air flows into the housing through the air openings and pollutants are taken up by the stationary phototrophic biofilm, which is supplied with medium from a tank via openings or an irrigation unit.

The now more purified air leaves the enclosure again through the air openings.

Uptake is aided by the moist, large surface area on the biofilm, which provides short diffusion paths.

PAM do not take up their nutrients from the soil and therefore rely on the uptake of nutrients from the air.

These are used intracellularly for maintenance metabolism.

The inventors have already shown that not only CO2 is taken up, but also NO2 in the form of nitrate, which forms in the medium and is needed by the PAM for photosystem regeneration.

In the prior art, few processes are known in which algae are used to produce valuable materials by means of PAM.

In US20100297714A1, phagotrophic algae are used for this purpose.

In the process, microorganisms are produced that are eaten by the phagotrophic algae, which are harvested again.

However, these various steps are very costly.

A comparatively laborious harvesting is also provided in US8084038B2. The task of the presented invention is furthermore a solution for an efficient production of organic recyclables by means of PAM.

For a bio-based economy, feedstocks are sought that can be effectively extracted from atmospheric carbon and allow a shift away from petroleum products.

The problem is solved by claim 22. In the disclosed process, the biofilm produces organic recyclables that are separated and collected by rinsing from it.

The media can be easily changed in the bioreactor.

It is known that different substances are secreted under different media or air conditions (Akihiro Kato et al.). PAM have substances in their metabolism that only they can produce.

They secrete small molecules such as fatty acids, polysaccharides, small peptides and amino acids, and exotoxins into their environment.

Extracellular secretions from Chlorella algae, for example, diffuse through the cell walls and enter the culture medium (Pratt et al.). Algal exudate (chlorellin) had inhibitory effects on bacteria and algae.

Fatty acids are also secreted by Chlorella (Dellagreca et al.). The secretion of a number of amino acids is synchronized with the light cycle of algal photosynthesis (Chang et al.). Bell and Mitchel observed that bacteria of the genus Spirillum were attracted to algal exudates from the diatom algal Skeletonema (Bell et al.). Toxic algal secretions including domoic acid or brevetoxins occur during harmful algal blooms and threaten other wildlife species (Hallegraeff et al.). On the other hand, these are complicated valuable substances that cannot be produced by chemical synthesis.

It has been suggested that algae and bacteria release mucilages to protect against ultraviolet radiation (Amsler et al.). In diatoms, the extracellular mucilages contain a complex mixture of proteoglycans and sulfated polysaccharides (McConville et al.).

PAM secretions can also be used for biofuel production. This is the case in WO2016207338A1, where secreted organics such as glycolic acid are used for biogas production. The secretions may originate from air pollutant uptake and abundance metabolism produced by high irradiation.

Other advantages of the present invention can be seen in the detailed description and drawings. Description of the drawings: Fig. 1 is a perspective view of a bioreactor from the front with front wall.

Fig. 2 is a perspective view of a bioreactor from the front with front wall and biofilm in place.

Fig. 3 is a perspective view of a bioreactor from the back without a front wall with a visible tank on the back wall.

Fig. 4 is an ion chromatographic diagram showing nitrite converted from nitrogen dioxide after 4 minutes retention time (measured by conductivity in pS).

Fig. 5 is an ion chromatographic diagram with reduced content of nitrite converted from nitrogen dioxide after 4 minutes retention time (measured by conductivity in pS).

In the following, reference is made to Figs. 1 - 3. Accordingly, the selected embodiment comprises: A bioreactor consisting of a cuboidal, flat, elongated housing (1), wherein a flat wall (front wall (2)) is bonded to the side walls (4) as a polymethyl methacrylate disk. The housing (1) has air openings in the smallest walls (bottom wall (12) and top wall (13)), visible in Fig. 1.

Fig. 2 shows: A static, phototrophic biofilm (5) of filamentous blue-green algae has grown on non- woven fabric (grow-on mat (6)). This layer lies on a distribution mat (8) as an absorbent fleece. The mats are clamped into the clamping rail (17) at the upper end and rest against the back wall (7).

Fig. 3 shows: A flat tank (9) is glued to the outside of the rear wall (7), which is in communication with the interior of the housing (1) via openings (10) and has an opening for refilling (11) and a filling level window (18). In the openings there are cords (16) in the form of wool threads, which are connected to each other on the inside of the housing (1), where they rest against the distribution mat (8) and transport medium present in the tank to the mats and the biofilm (5) due to an evaporation suction. The fill level can be read through the fill level window (18). As soon as the medium is used up, medium can be refilled as required through the opening for refilling (11). The medium contains the minerals and trace elements necessary for the blue-green algae.

Air flows in from the outside through the openings (10) in the bottom wall (12) and moves over the biofilm (5). The biofilm heats the air, which thus flows upwards. The medium with few salts runs in countercurrent. Air pollutants are absorbed. Clean air leaves the air openings (3) in the ceiling wall (13).

The following non-patent literature was cited: Akihiro et al: Removal of the product from the culture medium strongly enhances free fatty acid production by genetically engineered Synechococcus elongatus, Biotechnology for Biofuels 10, p.

141.

Amsler et al: Algal Chemical Ecology, 2008, Springer Berlin/Heidelberg, p. 273.

Bell et al: Chemotactic and growth responses of marine bacteria to algal extracellular products, 1972 Biol. Bull, pp. 265-77.

Chang et al: Excretion of glycolate, mesotartrate and isocitrate lactone by synchronized cultures of Ankistrodesmus braunii, 1970 Plant Physiol. 46, pp. 377-385.

Dellagreca et al: Fatty Acids Released by Chlorella vulgaris and Their Role in Interference with Pseudokirchneriella subcapitata: Experiments and Modelling, 2010 Journal of Chemical Ecology 36(3), pp. 339-49.

Hallegraeff et al: A review of harmful algal blooms and their apparent global increase, 1993 Phycologia 32, pp. 79-99.

Pratt et al: Some properties of the growth inhibitor formed by Chlorella vulgaris, 1942 Amer. J. Bot. 29, S. 142-148.

McConville et al: Subcellular location and composition of the wall and secreted extracellular sulphated polysaccharides/proteoglycans of the diatom Stauroneis amphioxys, 1999 Bacic A. Protoplasma 206, p. 188.

Claims (10)

Claims

1. Bioreactor consisting of a cuboidal, flat, elongated housing (1), wherein one wall of the elongated-width side (front wall (2)) consists at least in part of transparent material and air openings (3) are present in the side walls (4), characterised in that a stationary, phototrophic biofilm (5), which has grown on porous material (growth mat (6)), in particular non-woven fabric, on a layer of liquid easily distributing material, a distribution mat (8), which rests against the inside of the rear wall (7) or is fastened there, and a tank (9) with medium for supplying the biofilm (5) are present on the outside of the rear wall (7) or as a protrusion of the housing (1), the tank (9) being in communication with the interior of the housing (1) via openings (10), in which bands (16) of water-transporting material connect the medium of the tank (9) to the interior of the housing (1), rest there against the distribution mat (8) and the tank (9) has an opening for refilling (11).

2. Bioreactor according to claim 1, characterised in that air openings (3) are present in the ceiling wall (13).

3. bioreactor according to one of the preceding claims, characterised in that a filter or a grid, which has a minimum mesh size of 0.2 mm, is integrated or connected into the air openings (3).

4. Bioreactor according to one of the preceding claims, characterised in that the tank (9) is flattened and a filling level window is present in the tank (9).

5. bioreactor according to one of the preceding claims, characterized in that the front wall (2) is designed as a glass or polymethyl methacrylate pane, a groove is provided in each of the side walls (4) and the bottom wall (12), into which the pane is inserted from above, the top wall (13) is removable and serves as an upper closure.

6. bioreactor according to one of the preceding claims, characterized in that the side walls (4) and the bottom wall (12) have a groove for the insertion of the back wall (7) with biofilm (5) and mats thereon or a plane separate from the back wall (7) with biofilm (5) and mats thereon.

7. bioreactor according to any one of the preceding claims, characterized in that the mats are fixed by a clamping rail (17).

8. bioreactor according to any one of the preceding claims, characterized in that air composition sensors and other sensors are present in or on the housing (1) together with a control unit.

9. Bioreactor according to claim 15, characterised in that a data transmission, in particular a radio link, is present for transmitting data from the sensors to a receiver.

10. Bioreactor according to one of the preceding claims, characterised in that the housing (1) is actively ventilated via the air openings (3), in particular a fan is present in the air openings (3).