NO20191322A1 - Device for biological treatment of water for Aquaculture facilities - Google Patents

Description

DEVICE FOR BIOLOGICAL TREATMENT OF WATER FOR AQUACULTURE PLANTS

The present invention relates to a biological reactor of the type MBBR (Moving Bed Biofilm Reactor) intended for cleaning processes in aquaculture.

BACKGROUND

In aquaculture facilities, biological treatment of the water in an MBBR is a critical and very important part of a cleaning process. A well-functioning MBBR reactor is important for cleaning the water from fish tanks/tanks etc. that contain inorganic and organic components that you want to reduce/remove. The MBBR reactor is efficient in the turnover of nutrients (organic/inorganic (e.g. NH4, NO2)), but is also important for avoiding diseases in the breeding facility and maintaining a high degree of fish welfare.

The biofilm reactor (MBBR) is thus a critical unit for plants that have RAS (Recirculating Aquacultere Systems) plants and/or plants that purify the water from a flow-through plant (to land/water) to the recipient and/or during transport where biological purification is a part of the cleaning process.

There is a strong need to provide MBBR facilities that are compact in terms of area and volume (reduce construction costs), energy efficient (keep operating costs down), have high operational stability and safety against errors (ensure stability in production), as well as high internal mixing in the reactor with water coming in.

This MBBR reactor will have application possibilities for both flow-through plants on land and/or plants offshore, as well as in RAS (recirculating aquaculture system) plants on land or offshore. This will also be able to be used in cleaning processes for all transport of fish by road, plane, train and/or boat.

The purpose of the present invention is to provide a device for these purposes, which exhibits advantages over known technology.

These and other purposes are achieved by a device as stated in claim 1. Further advantageous and alternative embodiments are stated in the subordinate claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments of the invention will now be described with reference to the attached drawings, where:

Figure 1 shows a longitudinal, cross-sectional side view of an embodiment of the present invention,

Figure 2 shows the end of the tank where the liquid inlet is located,

Figure 3 shows the tank from the top,

Figure 4 shows a perspective view of the tank,

Figure 5 shows a perspective view of the tank from another angle,

Figure 6 shows the same perspective as Figure 5, but with the side wall 9 cut away, Figure 7 shows how the hydraulic flows can move in the tank, and Figure 8 shows a section of the rear end of the tank including air inlets.

DETAILED DESCRIPTION

In aquaculture plants with an associated cleaning process, the treatment plant must be able to process significant amounts of liquid and pollution. It is a challenge to design compact treatment plants that are capable of treating large quantities of liquid, and that do not clog filters and outlets. Treatment plants with biofilters type MBBR (Moving bed biofilm reactor) are often a normal part of the cleaning process in a cleaning system for Aquaculture, either as a unit in a RAS (Recirculating Aquaculture Systems) process or in a flow-through process.

In the biological MBBR biofilter, under conditions with O2 available, ammonium is typically converted to nitrite (NO2) and then to nitrate (NO3). This process is referred to as "nitrification". Turnover of organic material can also take place in this process if there is access to organic material and the right bacterial flora.

The invention is particularly adapted to such a process.

The invention will also be adaptable to a denitrification process, i.e. biological conversion of nitrate (NO3) to N2. Denitrification takes place under O2-poor conditions, i.e. without the addition of air and or O2. Traditionally, mechanical stirring is used during denitrification. However, this reactor has no mechanical moving parts, but ensures internal stirring only with the help of the liquid flow into the biofilter, then without the use of mechanical stirring and/or the addition of a gas. As the reactor mixes the entire volume even without the addition of external gas (air/O2/N2 etc) and/or mechanical stirrers, the biological filter will thus have good conditions for carrying out denitrification under O2-poor conditions. This reactor also uses an external organic carbon source if needed during denitrification.

The reactor's compact design is achieved with an optimization of internal flows. This is done by how the design is arranged, as well as how the inlet/outlet is placed and where air is added. Biofilm support with a very high specific surface area (2000-5000 m^2/m^3) provides the necessary area for the biology to grow in a very compact environment.

Normally, biocarriers with a specific surface area of 500-800 m^2/m^3 are used. A biofilm carrier with a lower specific surface area of 100 to 2000 m^2/m^3 can also be used. However, a lower specific surface area results in a larger reactor volume, which in size will approach conventional available solutions. Air is injected near the bottom of the biofilter tank and an area somewhat higher up in the reactor. Air addition is done at a defined location at the opposite end in relation to the inlet. Air is added via pipes that distribute air to the water masses. The area where air is added helps to provide O2 to the biological processes (ie adding O2 to the water masses) as well as ensuring stirring in the reactor. The addition of air ensures operational stability and an additional safeguard against re-clogging of the strainers as well as increased stirring internally in the biofilter. Stirring is important for hydraulic flow inside the reactor, to prevent re-clogging of sieves and to ensure mass transport of nutrients to the biological processes as well as to ensure an almost completely mixed reactor. According to the invention, the stirring is achieved without moving mechanical stirring means, it is the geometric design of the reactor and the flow pattern that provides the stirring.

The present invention can be described as an ultra-compact MBBR purification step for use in RAS aquaculture facilities and/or flow-through facilities. This ultra-compact MBBR reactor converts/purifies water with a high content of nitrogen compounds as well as dissolved/solid particulate components from fish in RAS facilities, breeding tanks and/or open/closed cages, flow-through facilities and/or all transport of live fish.

The reactor is typically 1/3 in size compared to conventional MBBR reactors for aquaculture facilities. The reactor has a very short hydraulic residence time of around 1.5-5 minutes as it uses a biofilm carrier with specific areas in the range of 2000-5000m^2/m^3. This provides a very compact design with the necessary bifilm areas without this being at the expense of the biofilm's prerequisites for turnover of organic / inorganic components. Compared to traditional MBBR solutions, the energy input in the form of added air is reduced by 60-70%.

In the following, a non-limiting example is given:

With a liquid circulation in the RAS of 200 m^3/min, this gives an MBBR volume requirement of only 500 m^3. In such a compact volume, the area required for necessary biofilm growth will be in the region of 650,000 m^2. Without enough biofilm area available, the necessary biological turnover of organic/inorganic compounds (NH4, NO2, NH3) is not achieved.

The consequence of this is high NH4/NH3 and NO2 values in the facility, i.e. a water quality that degrades quality and increases the loss of fish due to death and disease. The reactor can be operated with one or more types of biofilm carrier or combine several types of biofilm carrier. In this example, "biofilm carrier type A" with a specific surface of 2000-5000 m^2/m^3 is combined with a "biofilm carrier type B" in the range of 300-1000 m^2/m^3. For example, 70-90% of "biofilm carrier type A" can be used in combination with "Biofilm carrier type B". A combination thus gives different properties to the reactor. Degree of filling is max. up to 60% depending on organic/inorganic load. Due to the internal design, scar of inlet and outlet as well as combination of biofilm carrier, the present MBBR has no need/very limited need for air addition for mechanical stirring, it is mainly only necessary for biological turnover. In traditional MBBR processes, up to 80% of all air is used for mechanical stirring, while the remaining 20% goes to the biological reactions. The air requirement in this reactor is typically reduced by 60% -70% compared to traditional MBBR processes. Due to the design and placement, internal liquid flows are thus achieved which further ensure that biofilm carrier type A and/or B (or combinations of further types of biofilm carrier) do not stick to strainers, clog the outlets in the reactor and have high internal self-cleaning. Clogging of the MBBR reactor is a very big problem in traditional MBBR reactors. This is solved in this invention. The reactor is theoretically not possible to seal. The reason, as mentioned, is that an increased amount of fluid enters increases internal fluid flows, which in turn increases the internal self-cleansing, i.e. a self-reinforcing effect. In this reactor, the air additions help to provide increased operational reliability, and help to strengthen the already internal liquid circulation. Without liquid into the reactor, air alone will set up the same internal liquid flows inside the reactor. The reactor has virtually no dead zones, even when the plant is in operation. Dead zones, i.e. areas with poor stirring, which provide stagnant water and a basis for sedimentation, H2S formation etc. are therefore not likely to be a problem in this reactor.

Due to liquid flows at the top of the reactor, two flows that meet inside the top area at the inlet have a crucial property to ensure that biofilm carriers that may float on the liquid surface will be drawn back down into the reactor. This is a particular problem in a start-up phase. This invention has solved this problem. In traditional solutions, you have to use mechanical stirring and or pumps where biofilm carriers floating on top are exposed to water supply via pumps.

The design together with the placement of inlet/outlet scars is critical in order to achieve and to reinforce the internal fluid flows in the reactor, which in turn provides enough internal self-cleaning to prevent the biofilm carrier (Type A, B possibly a combination of these or a combination of several types) onto the outlet strainers and clogs the reactor.

Figure 1 shows an arrangement at a biofilm reactor for purifying water in aquaculture, comprising a tank 1 for a liquid with a given geometric design, an inlet 2 for liquid to the tank, an outlet 3 for liquid from the tank, and an air inlet 4 arranged in the tank.

The tank has a bottom 5, two opposite end walls 6, 7 and two opposite side walls 8, 9 with a length, a width and a depth. The inlet 2 for liquid preferably extends along the bottom 5 and preferably mainly along the entire width of one of the end walls 6. It is understood that the inlet can be designed in different ways. It can be designed as one or more slots as shown in the figures, or have other designs, e.g. a number of pipe inlets. Preferably, the inlet should be designed so that it provides an appropriate and even flow of liquid in the tank. A number of air inlets 4, at least one, are arranged along the bottom and essentially the entire width of the second of the end walls 7.

The outlet 3 for liquid is tubular and arranged between the side walls 8, 9 of the tank.

The figures show two outlets 3. The outlets include outlet scars, i.e. a combination of perforated and sealed pipes is marked with hatching in figures 1 and 3.

The outlet scars are placed on the outlet pipes in such a way that it is appropriate in relation to the eddy currents you want to achieve, for example the one shown in figure 7.

The device according to the present invention is arranged so that a vortex flow is formed in the tank which runs in from the inlet 2, runs along the bottom 5, upwards along the end wall 7 which is opposite the inlet, back along the basin surface, down along the inlet end wall 6, and then into a new or several new rounds until the vortex flow ends in the outlet 3, where the outlet 3 is arranged just outside the central eye of the vortex flow. Again with reference to figure 7, the said "central eye of the eddy flow" of the eddy flow will be between the parts of the outlets (round circles) which are marked with the reference numbers 3. In this central eye the flow will be mostly calm. It is a point that the outlet's 3 openings are located directly outside this eye, where the flow rate is high, which helps to prevent deposits on the outlet.

The device according to the invention is designed so that the liquid's residence time (hydraulic residence time) in the tank will be able to operate in a theoretical interval from approximately 30 seconds and up to 15 minutes. A hydraulic residence time in the tank ensures contact between liquid and biofilm carrier. The residence time, liquid velocity and liquid movement are parameters that ensure that all liquid undergoes the desired biological turnover, good agitation and that deposits do not form in the tank that block the outlets or require an unwanted cleaning stop. According to another preferred embodiment (practical expectation), the liquid residence time in the tank should lie within the interval 1.5 to 5 minutes. The pressure drop in such a configuration is expected to be in the range of 5-10 cm liquid column depending on the liquid load. The reactor according to the present invention in and of itself has no known theoretical lower limit for how low a hydraulic residence time can be (a low hydraulic residence time means a high amount of liquid entering the reactor), but at one point or another a practical limit is approached, as high liquid flows results in significantly increased energy use, large pressure drop across the reactor, wear and tear on biofilm carriers, possibly other wear/breakage of equipment/collapse of strainers, etc., which give unwanted costs for operation. One can also imagine that the residence time will be so short that the biological processes you want to promote do not get good enough conditions to develop enough biofilm area and/or thickness. High mechanical stress can also cause wear and tear on the biofilm carriers, which over time is not desirable for several reasons, for example also microplastics. The points above help to determine where the boundaries of the system go.

In order to optimize the hydraulic flow and "shape" the vortex flow/effect in the tank, a deflector or guide plate/baffle 10, 11 can be arranged in at least one of the corners between end wall 6, 7 and bottom 5, designed to deflect the water flow in desired direction.

A deflector 10 can also advantageously be arranged directly above the inlet 2, this because this is an area where dead zones or other inappropriate, local eddy currents can occur.

Figure 8 shows a possible design of air inlet 4. The addition of air can modify and/or remedy the biological transformation in the tank, i.e. make the transformation more or less aerobic, depending on the amount of added air, as well as act as gas lift of the liquid column, so that the liquid circulation are stimulated/influenced. If a more anaerobic conversion is desired, it is understood that less or no air is added. It is also understood that the design shown in figure 8 is only an example. The air can also be supplied by means of one or more air injection nozzles, a single pipe or the like. Gas other than air or O2 can also be added, e.g. an inert gas or possibly some form of liquid. The addition of such other fluids can have two functions, either supporting internal fluid flows and/or adding a carbon source (possibly other additives).

To adapt the capacity of a facility, either the dimensions of the tanks can be changed, or the number of tanks can be added or subtracted.

An aspect of the invention that distinguishes it from previously known solutions is that a "standing" vortex flow is created.

Claims (6)

PATENT CLAIMS 1. Device at biofilm reactor for purifying water in aquaculture, comprising; a tank (1) for a liquid with a given geometric design, an inlet (2) for liquid to the tank, an outlet (3) for liquid from the tank, an air inlet (4) arranged in the tank, characterized in that the tank has a bottom (5), two opposite end walls (6, 7) and two opposite side walls (8, 9) with a length, a width and a depth, where the inlet (2) for liquid extends along the bottom (5) and essentially the entire width of one of the end walls (6), where air inlets (4) are arranged along the bottom and essentially the entire width of the second of the end walls (7), where the outlet (3) for liquid is tubular and arranged between the side walls (8, 9) of the tank, where the device is arranged so that a vortex flow is formed in the tank which runs in from the inlet (2), along the bottom (5), upwards along the end wall (7) which is opposite the inlet, back along the bag surface of the tank, downwards along the inlet end wall (6) ), and then a new or several new rounds until the eddy flow ends in the outlet (3), where the outlet (3) is arranged just outside the central eye of the eddy flow. 2. Device according to claim 1, where in at least one of the corners between the end wall (6, 7) and the bottom (5) a deflector (10, 11) arranged to deflect the water flow is arranged. 3. Device according to claim 2, where the deflector (10) is arranged directly above the inlet (2). 4. Device according to claim 1, where two tubular outlets (3) for liquid from the tank are arranged between the side walls (8, 9), where both outlets are arranged just outside the central eye of the vortex flow. 5. Device according to claim 1, where the residence time for the liquid in the tank is from at least 30 seconds and up to 15 minutes. 6. Device according to claim 5, where the residence time for the liquid in the tank is within the interval 1.5 minutes to 5 minutes.