SE2151575A1

SE2151575A1 - Water treatment system

Info

Publication number: SE2151575A1
Application number: SE2151575A
Authority: SE
Inventors: David Stenman; Sherjeel Ton
Original assignee: Arctic Sustainability Group Ab
Priority date: 2021-12-21
Filing date: 2021-12-21
Publication date: 2023-06-22
Also published as: WO2023118186A1

Abstract

The present invention relates to a system (10) for treating water to be used in breeding fish, comprising a tank (12), at least one inlet (34) for water to be treated disposed at one end of said tank and at least one outlet (46) for treated water disposed at an opposite end of said tank, wherein a water flow is created in the tank between the inlet and the outlet, a number of water treatment units (36, 38, 40, 42, 50) placed in said tank next to each other in the direction of the water flow.

Description

WATER TREATMENT SYSTEM TECHNICAL AREA The present invention relates to a water treatment system and in particular a system to be used for breeding fish.

BACKGROUND OF INVENTION The focus on breeding fish commercially has increased tremendousiy during the last 20 - 30 years. The majority of the first fish breeding plants were initially designed to be placed in sea water or in lakes and comprised containers immersed in the water and communicating with surrounding water. This provided a natural breeding environment and more or less the only control function of the breeding process was the amount and time interval of fish food to be provided. This has worked well for some types of fish such as salmon. However, the lack of control has also meant that fish have been subjected to diseases and parasites that adversely affect the quality and quantity of the bred fish. Also environmental aspects have been raised because of for instance large amounts of fish food that are not eaten by the fish and fall through the fish containers and collect on the sea or lake bottom. Further, the fish produce waste, and their waste has the potential to build up in the surrounding area, which may deplete the water of oxygen, creating algal blooms and dead zones. The use of pharmaceuticals such as antibiotics to prevent disease may also be a concern regarding the effect of the drugs on the ecosystem surrounding the plants, such as wild fish. ln parallel with the natural water fish farms, fish breeding farms that are placed on land have been developed. These provide the advantage of breeding a larger variety of fish types as well as better control of the breeding environment. One important aspect that has emerged with these land-based fish plants is the recirculation of the water instead of using ground water as incoming water and discarding "used water" in the sewage.

Recirculation of water poses a number of challenges regarding the treatment of used water before re-entering into the fish tanks. Solid matter has to be removed and micro-organisms have to be killed. Further, the water needs to be aerated before fed to the fish tanks. Document CN 110679534 discloses a fish breeding system with a treatment system for circulating water. Water from fish tanks are pumped through cyclone and drum filters for removing solid matter. The water is then collected in a balance tank. From the balance tank, three pipe branches are provided. One branch comprises a protein separator, an ozone unit and a biological filter for treatment of an amount of water before returned to the fish tanks. Another branch comprises a de- aeriation pump followed by a UV unit before returned to the fish tanks. A third branch comprises a pump, a unit for dissolving 02 followed by a UV sterilizer and a temperature control unit. The idea behind dividing the treatment into three branches is to save energy and reduce piping diameter, because it is stated that it might not be necessary to use the second branch when the pH in the fish tank is stable and normal or not to use the third branch if the oxygen levels in the fish tank meet the requirements. However, the solution entails a lot of piping and valves in order to control the ﬂow of water through the branches as well as additional treatment units in the different branches.

BRIEF DESCRIPTION OF INVENTION The aim of the invention is to remedy the drawbacks of the state of the art solution. This aim is obtained by a water treatment system according to the features of the independent patent claim. Preferable embodiments of the invention form the subject of the independent patent claims.

According to a main aspect of the invention it comprises a system for treating water to be used in breeding fish, comprising a tank, at least one inlet for water to be treated disposed at one end of said tank and at least one outlet for treated water disposed at an opposite end of said tank, wherein a water ﬂow is created in the tank between the inlet and the outlet, a number of water treatment units placed in the tank next to each other in the direction of the water flow. With this solution, water is treated in one volume and does not need to be transported between a number of discrete treatment vessels, which otherwise usually entail additional pumping and transporting elements and functions.

According to one aspect, the treatment units may comprise an ozone generator provided closest to said inlet capable of introducing ozone into the water. ln addition, the treatment units may comprise an oxygenation unit provided after the introduction of ozone in the water flow, capabie of introducing oxygen into the water. Both the produced ozone and the amount of oxygen not transformed to ozone are dissolved in the water, which provides oxygenation/saturation of 02 into the water, as well as furthering the oxidation by increasing the oxidation potential of the water towards unbound organic material. Further, a decomposition takes place of micro-organisms such as viruses, fungi, parasites, which provides a sterilization effect.

The treatment units may further comprise a UV radiation unit provided after the introduction of oxygen in the water flow, capabie of introducing UV radiation in the water. The radiation from the UV unit will break the ozone contained in the water to free radicals that will effectively oxidize all unwanted matter in the water and will ascertain that no ozone will remain in the water to be fed back to the fish tanks. The UV radiation will also cause a sterilization of UV-sensitive micro-organisms.

As a further measure, the treatment units may comprise a foam removal/protein skimming unit in order to remove protein and other organic and inorganic molecules from the water. Moreover, the outlet from the tank may be connected to at least one pump, which is disposed in the tank. The system may further comprise a unit for adding pH controlling chemicals into the tank for adjusting the pH level of the water.

According to a preferable aspect, the system may further comprise a biological sand filter connected to the inlet to the tank for pre-treatment of water before entering the tank.

According a further aspect, an outlet from the biological sand filter is positioned at a higher altitude than the inlet to the tank in order to create a self-ﬂow of water from the biological sand filter to the tank. Thus, a need for pumps is omitted.

Further, the system may comprise a de-gassing unit provided in the water ﬂow between the biological sand filter and the tank for removing in particular C02 from the water that enters the tank. ln this regard, the de-gassing unit may be provided with heating elements for warming the water.

According to yet an aspect, the biological sand filter is provided with an inlet and the system may further comprise a mechanical filter (18) connected to the inlet to the biological sand filter for pre-treatment of water entering the biological sand filter, removing solid matter from the water taken from fish tanks.

These and other aspects of, and advantages with, the present invention will become apparent from the following detailed description of the invention and from the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS ln the following detailed description of the invention, reference will be made to the accompanying drawing, which schematically shows a treatment system according to the invention.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows an example of a water treatment system 10 according to the invention. Water from fish tanks 12 are fed in a piping system 14 to a compartment or tank 16 containing a number of filters 18, for instance drum filters. ln the filters 18, solids from the fish tanks 12 are removed from the water. The filter tank further 16 comprises a number of pumps 20 that pump the water via piping 22 to a biological sand filter 24 in which water from fish tanks enter via an inlet 26. The pumps are chosen to just be able to lift the water from the tank and into the sand filter. The sand filter container 24 is preferably placed on ground level due to the increased cost of placing it in a dug out space in the ground. However, the sand filter 24 may be placed in a shallow recess in the ground. The water in the sand filter will be treated in several ways through a continuous aerobe filtration. An oxidation or nitrification of nitrogen compounds such as amines and nitrite will take place as well as biological fixation of organic material and phosphor. The degradation takes place by minimizing and eliminating forming of geosmin and other smell and tastes substances. This biological stage also affects incoming microbes, viruses, fungi, protozoa from the fish tanks, in this way limiting the spread of such pathogens in the system.

Adjacent the sand filter, a water treatment tank 28, hereafter called reaction pit, is provided. The reaction pit 28 is preferably placed on the ground, but may also be placed in a recess in the ground. However, the placement of the sand filter 24 and the reaction pit 28 should be such that the height of the water surface of the reaction pit 28 is lower than an outlet 30 from the sand filter in order to create a natural ﬂow of water from the sand filter 24 to the reaction pit 28, thereby avoiding the need for a water pump. Regarding the sand filter 24, it is of course possible to place it into the ground and place the tank so that the outlet from the filter tank is above the water level of the sand filter so that there is a natural flow from the filter tank to the sand filter, thus eliminating the pumps between them. The reaction pit 28 is then also placed in the ground or at least at a lower level than the sand filter so that there is a natural ﬂow between the sand filter and the reaction pit. However, as described above, this entails greater costs but would lead to a saving in power for water lift pumps.

The water flows from the sand filter 24 to the reaction pit 28 via a degasser 32. The degasser may be an enclosure or column containing structured or un-structured filling material. The incoming water is sprinkled on the filling material from above while air is introduced at the bottom of the column, such that a continuous gas exchange with air takes place, leading to removal of C02 from the water, removal of geosmin and other volatile compounds that may produce smell and/or taste as well as an increase in the amount of oxygen dissolved in the water. The degasser 32 will further give a cooling effect of the water via evaporation. This may lead to a potential need for warming the water, which may be done by warming the water by incoming air ﬂow or by injection of steam in the air ﬂow. A heat exchanger function of the incoming and outgoing air flows may be included in order to recover energy. lnside the reaction pit 28 a number of water treatment units are provided. Closest to the inlet 34 for incoming water, that may drop from the degasser 32, an ozone injector or diffuser 35 is disposed, connected to an ozone generator 36, capable of injecting ozone in the water, generated by the ozone generator 36. There are numerous well known ozone injectors and generators on the market and will not as such be described in more detail. Next to the ozone injector, an oxygen injector or diffuser 37 is provided in the reaction pit 28, connected to an oxygenation unit 38, capable of injecting oxygen in the water. Also here, these are well known and will not be described in detail. The incoming water that is saturated with oxygen is ozonized. The ozone is formed to a certain extent in an oxygen-rich gas, about 20 - 100% 02.

Both the produced ozone and the amount of oxygen not transformed to ozone are dissolved in the water, which provides an additional oxygenation/saturation of 02 in the water, as well as furthering the oxidation by increasing the oxidation potential of the water towards unbound organic material, which may be measured as BOD (Biochemical Oxygen Demand), COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon). The oxidation may also lead to discoloration of dyes, which may be measured as absorbance or coloration. The oxidation also effects any residues of pharmaceuticals and antibiotics that may be present in the water. The oxidation of particles further provides an increased surface charge, which in turn provides an improved filtration efficiency when passing the filters mentioned above the next time. Moreover, the oxidation provides improved availability for compounds that are difficult to decompose during a subsequent passage through the sand filter as well as further decomposition of odorants and taste substances. Further, a decomposition takes place of micro-organisms such as viruses, fungi, parasites, which provides a sterilization effect. The reaction pit is so constructed as to provide a long enough reaction time for the oxidation processes to efficiently react with both dissolved chemical compounds as well as degrade microorganisms and virus.

Thee system may include flow guiding elements and structures so designed to maximise contacting times between water and gases, as well as to ensure that the residence time of the water is homogenous.

The reaction pit also includes a unit for foam removal and protein skimming 40. Conventionally it comprises a generator of air decomposition bubbles on which protein and other organic and inorganic molecules attach until the bubbles are saturated. The saturated bubbles are then collected in a skimmate waste collector and removed from the reaction pit.

Further along the flow path of water in the reaction pit, a UV radiation unit 42 is provided. The radiation from the UV unit 42 will break the ozone contained in the water to free radicals that will effectively oxidize all unwanted matter in the water and will ascertain that no ozone will remain in the water to be fed back to the fish tanks.

The UV radiation will also cause a sterilization of UV-sensitive micro-organisms.

The reaction pit is made so long in the flow direction that the whole volume of water will undergo treatment for at least four minutes and up to fifteen minutes. The long reaction time provides good use of the ozone, and long response time which in turn provides a good process control for the dosage of ozone such that residual ozone is minimized, reduce periods with low treatment effect and stable trends that a control system can act upon, thus no rapid processes and in all stability of the treatment process. This provides a good mixing and thus homogeneous reaction.

At the end of the reaction pit as seen in the flow direction, pumps 44 are provided with outlets 46 that are connected to piping 48 for feeding the water to the tanks 12. ln addition, a unit for adding pH controlling chemicals 50 is connected to the reaction pit.

The whole system and the units are controlled by a suitable controller. To the controller, a number of sensors are connected for providing input and feedback of the status of the treated water in the reaction pit. Also samples may be taken and analysed for obtaining information regarding residual micro-organisms, bacteria and parasites.

The system described uses very few pumps compared to conventional systems. ln this regard, it might be possible to reduce the number of pumps further. For instance, the pump or pumps 20 used for lifting water from the tank 16 with the mechanical filters 18 may be omitted if the tank is placed such that the inlet 26 of the piping 22 to the sand filter 24 is placed higher than the water surface of the sand filter 24, whereby a natural flow of water from the tank 16 to the sand filter 24 is created. This may be obtained without the need for placing the sand filter 24 in the ground if the system is placed in a building with several stories. The fish tanks 12 and the tank or tanks 16 with the mechanical filters 18 may then be placed on a story or level above where the sand filter 24 and the reaction pit 28 are placed. This is shown schematically in Fig. 1 where 60 denotes an upper floor ofa building and 62 denotes a lower or ground floor of the building, or even a basement. A pipe 64 providing a natural flow of water from the tank 18 to the sand filter 24 may then be provided. The only pumping capacity needed is then to transport the treated water from the reaction pit 28 up to the upper story or level and to the fish tanks 12. This creates a substantial energy saving because the water to be treated from the fish tanks is transported only by gravity to the different treatment components of the system. An additional benefit is that the pump flows does not require ﬂow baiancing or regulation, thus lowering the requirements on process automation. lt is to be understood that the embodiment described above and shown in the drawing is to be regarded as a non-limiting example of the invention and that it may be modified in many ways within the scope of the patent claims.

Claims

1.Claims

2.System (10) for treating water to be used in breeding fish, comprising a tank (12), at least one inlet (34) for water to be treated disposed at one end of said tank and at least one outlet (46) for treated water disposed at an opposite end of said tank, wherein a water ﬂow is created in the tank between the inlet and the outlet, a number of water treatment units (36, 38, 40, 42, 50) placed in said tank next to each other in the direction of the water flow.

3.System according to claim 1, wherein said treatment units comprise an ozone generator (36) provided closest to said inlet.

4.System according to claim 2, wherein said treatment units comprise an oxygenation unit (38) provided after said ozone generator in the water flow. _ System according to claim 3, wherein said treatment units comprise a UV radiation unit (42) provided after said oxygenation unit in the water flow.

5.System according to any of the claims 2 - 4, wherein said treatment units comprise a foam removal/protein skimming unit (40).

6.System according to any of the preceding claims, wherein said at least one outlet is connected to at least one pump (44), which is disposed in said tank.

7.System according to any of the preceding claims, further comprising a unit for adding pH controlling chemicals (50).

8.System according to any of the preceding claims, further comprising a biological sand filter (24) connected to said at least one inlet (34) for pre- treatment of water before entering the tank (28).

9.System according to claim, 8, wherein an outlet from said biological sand filter (24) is positioned at a higher altitude than the inlet (34) to the tank (28) in order to create a self-ﬂow of water from the biological sand filter to the tank.

10.System according to any of the claims 8 or 9, further comprising a de-gassing unit (32) provided in the water flow between the biological sand filter and the tank.

11.System according to claim 10, wherein said de-gassing unit is provided with heating elements for warming the water.

12.System according to any of the claims 8 - 11, wherein said biological sand filter is provided with an inlet (26), further comprising a mechanical filter (18) connected to said inlet to said biological sand filter for pre-treatment of water entering said biological sand filter.

13.System according to claim 12, arranged and set up such that a natural self- flow is created from the tank containing mechanical filters to the at least one pump in said tank.

14.System according to claim 13, wherein fish tanks and the tank containing mechanical filters are placed on an upper level of a building while the sand filter and the reaction pit are placed on a lower level.