NL2022454B1 - Water treatment system and method of using the same - Google Patents

Abstract

A water treatment system comprises a reactor (10) having a first zone (11) and having a second zone (12). A water inlet (21) for receiving an intake water flow is provided to said first zone (11) and a water outlet (22) is present for discharging an output water flow from said second zone. Bubble generator means (50) generate, during operation, gas bubbles, particularly micro bubbles, and mix these with the intake water flow. Foam removal means (30) are used for 10 separating and evacuating a foam layer (16) floating at a waterline (15) of said second zone (12). These foam removal means comprise a foam collection device (33) having an entrance (31) beyond a level of said foam layer and having a foam outlet (32). The reactor is provided with water level control means that maintain said waterline (15) within said reactor and said foam layer (16) below a level of said entrance (31) of said foam collection device (30). Said 15 water level control means enable raising said waterline substantially to beyond a level of said entrance of said foam collection device, thereby discharging said foam layer at least substantially from said waterline. Fig. 2

Description

Water treatment system and method of using the same The present invention relates to a system for treatment of water, particularly for process water onboard of a vessel like a boat or a ship, comprising a reactor having a first zone and having a second zone, a water inlet for receiving an intake water flow at said first zone, a water outlet for discharging an output water flow from said second zone, bubble generator means that, during operation, generate and mix gas bubbles, particularly micro bubbles, with said intake water flow, and comprising foam removal means for separating and evacuating, during operation, a foam layer floating at a waterline of said second zone The invention moreover relates to a method of treating waste process water.

The process of salmonid fish growing in net pens ends with the harvest of the fish using purpose-built well boats where the fish are harvested, slaughtered, bled and stored in chilled water until the vessel reaches a processing plant ashore.

The chilled water is kept at 0,5°C by using a water chiller operating in a recirculating circuit.

This ensures that the freshness of the product is kept during its transit to the processing plant.

During the harvest and storage process, the process water for chilling and the salmon storage tanks are contaminated with fish blood and thus, treatment and disinfection are required.

The mixture of process water with the fish blood is known as bloodwater.

This bloodwater will contain blood, micro-organisms which can be pathogens, fish entrails, scales and inorganic solids.

In addition, bloodwater will have i.a certain solids, oils, fats, oil turbidity colour, whose levels may vary in practice.

Overall, the amount of fish blood in the process water will be about 30%-35%, producing a diluted waste stream which will likely contain a relatively high proportion of fine solids, dyes and fluid contaminants, particularly fish oil together with an amount of large solids, like parts of fish carcasses.

Treatment of such slaughterhouse waste water or other processing waste in animal production can be performed with mechanical, biological and physical chemical methods.

The choice of a particular treatment system will be determined inter alia by the strength of the waste stream: high-strength effluents, such as those resulting from terrestrial mammal slaughterhouses, will require a full suite of biological and physical-chemical treatment processes.

-2- Fish slaughterhouse waste streams are, generally, relatively diluted and tend to require specific techniques to treat the different solid fractions that exist in the waste stream, being either settable, suspended, fine or dissolved, aside from biologically inactivating the water. Processing of bloodwater, present in well boats, appears particularly challenging as it will contain a wide variety of different fractions, such as oils, parts of fish carcasses, dyes, small solids and potentially, pathogens. The presence of fish oil and biofilms renders bloodwater less suitable for mechanical filtration, as mechanical filters may suffer from clogging and biofouling growth. Straining with micro-filtration or membrane filtration, for instance, is in itself an efficient method of solids control, but oils and dyes may remain after filtration. Moreover, oils and fats are known to block mechanical filters, including membranes. Chemical treatment using toxic biocides, on the other hand, is undesirable from a safety perspective in an environment for human food processing. A system of the kind described in the opening paragraph uses an alternative filtration mechanism, know as floatation filtering. Such system is based on the use of air bubbles to attract pollutants. Floatation methods may require a larger footprints than other chemical-free filtration methods but have the ability of filtering both solids as well as oils and dyes from a waste stream. The two main floatation techniques are protein skimming (foam fractionation) and dissolved air floatation {DAF), depending on the size of the air bubbles being used.

A floatation filtering system generally is divided over two consecutive zones. In an initial, first zone, intake water and air bubbles are put in contact with each other. A bubble generator mixes said intake water with air bubbles. The process water is then fed to a second zone, referred to as separation zone. In this second zone, the air bubbles are allowed to coagulate with contaminants, which may be enhanced by the addition of flocculent agents and/or coagulants, resulting in a floating foam layer that builds up at the waterline, while cleaned water flows downwards. A foam removal mechanism is used to remove the foam layer from the waterline, for instance by skimming the surface thereby forcing the foam layer to a foam outlet near said surface.

The known design of floatation filtering plants, however, renders this technique less suitable for installation onboard of a vessel that is subject to motion. Vessel motion will disrupt the

-3- symmetry between the water column and floatation reactor, resulting in process water escaping through the foam outlet.

The present invention therefor, inter alia, has for its object to provide a water treatment system based of floatation filtering that, particularly, may also be used onboard of a vessel like a boator a ship.

In order to achieve said object, a water treatment system of the type described in the opening paragraph, according to the invention is characterized in that said foam removal meanscomprise a foam collection device having an entrance beyond a level of said foam layer and having a foam outlet, in that said reactor is provided with water level control means that are configured to maintain said waterline within said reactor and said foam layer below a level of said entrance of said foam collection device, and in that said water level control means enable raising said waterline substantially to beyond a level of said entrance of said foam collectiondevice, thereby discharging said foam layer at least substantially from said waterline.

In this system the waterline and the entrance of the foam collection device are kept in an intentionally spaced relationship during initial operation by maintaining the waterline well below the level of said entrance to allow for a motion of the system without the risk that process water will escape through said foam collection device.

Said waterline, however, may be raised bycontrolling the water level within the reactor once the foam layer needs to be removed.

This will cause said foam layer to reach the entrance of the foam collection device such that it will be drained to the outlet of said foam collection device.

In rough seas, the system can be operated with a low water level, keeping the entrance of thefoam collection device away from the foam/water surface until the vessel has reached calmer waters.

Then, a foam backwash or a continuous foam washing mode of operation may be initiated within the system by increasing its water level.

This change in water level can for instance be accomplished using a motorised valve that restricts the outlet flow without changing the inlet flow.

To that end a particular embodiment of the system according to theinvention is characterized in that said water level control means comprise a pump connected to the water inlet and a shut-off valve at the water outlet of the reactor.

-A- A preferred embodiment of the system according to the invention is characterized in that said first zone surrounds said second zone, and in that said entrance of said foam collection device is located centrally at said second zone.

The contact zone is, hence, placed in an outer rim of the plant and the separation zone in the centre.

This way, even in motion, the plant's contact zone and separation zone will always be hydraulically connected.

The foam collection device is also installed at the centre of the plant.

This will be the place where the water surface effectively pivots.

In other words, the centre of the reactor is where changes in water level elevation will be the smallest.

A dual drain outlet may be provided at the bottom centre of the reactor to ensure both foam and water to exit the plant through the bottom centre, without mixing.

To promote a sufficient settling of the foam layer within the separation zone, a further preferred embodiment of the system according to the invention is characterized in that a screen is provided between said first zone and said second zone, said screen extending from a bottom of said reactor to below said waterline and separating said first zone and said second zone below said waterline from one another.

Said screen between the first zone and the second zone shields the separation zone from any turbulence that may be created in the first zone by the intake of water and the introduction of gas bubbles.

Because the screen ends below the waterline, process water may nevertheless still flow over the screen to reach the separation zone, In view of a homogenous distribution of the intake flow over the first zone, a specific embodiment of the system according to the invention is characterized in that said inlet comprises a perforated duct that extends at least substantially all along said first zone.

This way the intake of process water will be guided substantially all along the first zone.

In a further preferred embodiment the system is thereby characterized in that said bubble generator means are connected upstream of an inlet of said duct.

This will ensure that also the introduction of gas bubbles will be distributed substantially homogeneously over the first zone.

To avoid clogging of the entrance of the foam collection device and to promote a swift discharge of the foam layer, a further preferred embodiment of the system according to the invention is characterized in that spray nozzle means are provided at said entrance of said foam collection device that, during operation, direct a water spray to said entrance.

-5- In order to ensure an adequate inactivation of possible pathogens with the process water, specifically infectious salmon anaemia virus (ISA virus} aeromonas salmonicida, subsp.salmonicida, a further specific embodiment of the system according to the invention is characterized in that said reactor is provided with dosing means for holding and dosing a disinfectant and/or oxidant agent to said water, particularly for dosing an agent from a group of peracetic acid, ozone gas and hydrogen peroxide. Preferably one of these food grade disinfectants are used in case the water treatment system is part of a food processing environment.

A further specific embodiment of the system according to the invention is characterized in that said water outlet is connected to a disinfectant station comprising at least one of a source of ozone and a source of ultra violet radiation. This disinfectant station may be applied alternatively or additionally, as an option, to the introduction of a disinfectant agent already in the reactor. Action of this system may be prompted based on the output of sensor means that monitor a biological activity within the output water of the reactor. Both UV radiation and ozone are non-toxic in the end to human to ensure food safety.

In a further preferred embodiment the system according to the invention is characterized in that a pre-filter is connected upstream of the inlet to the reactor, particularly a drum filter or a bead filter. This pre-filter may be relatively coarse as its main purpose is to separate the larger solid fraction from the process water, like for instance remainders of fish carcasses.

In a method of treating process water, according to the invention, said process water is fed to the water treatment system according to one or more embodiments of the invention as described hereinbefore, wherein cleaned water is collected at the water outlet of said water treatment system, and wherein said collected water is re-circulated to said process plant.

In a preferred embodiment the method according to the invention is thereby characterized in that a oxidant is added form a group containing peracetic acid, ozone gas and hydrogen peroxide, particularly a stabilized hydrogen peroxide solution. The addition of such oxidative agent may be prompted based on the output of sensors that monitor any microbial activity or redox potential within the reactor and/or at the output of the reactor. The use of a the listed oxidants is allowed to inactivate microbial activity in a food processing environment from a

-6- perspective of food safety and happens to be specifically effective against infectious salmon anaemia virus (ISA virus) aeromonas salmonicida, subsp.salmonicida, that may contaminate bloodwater from a fish industry plant.

To further enhance the flocculation of foam layer to create a floating foam layer and to promote the coagulation of substantially all contaminations within the process water, a further embodiment of the method according to the invention is characterized in that a flocculent and/or coagulant agent is introduced in the reactor in order to enhance flocculation of contaminants contained therein.

The invention will be described below in greater detail with reference to a few particular exemplifying embodiments and an accompanying drawing. In the drawing: figures 1A-C show schematically the basic operation of a water treatment system according to the invention; figure 2 provides a perspective view of a first example of a water treatment system according to the invention; figure 3 gives a schematic presentation of a practical setup of a water treatment system according to the invention; Figure 4-6 show respectively a perspective view, cross section and top view of a second embodiment of a water treatment system in accordance with the invention, having a rectangular footprint; and Figure 7-9 show respectively a perspective view, cross section and top view of a second embodiment of a water treatment system in accordance with the invention. having a round footprint.

It should be noticed that the drawings are drafted purely schematically and not to a same scale. In particular, certain dimensions may have been exaggerated to a lesser or greater extent for sake of clarity and understanding. Corresponding parts have been identified with same reference numerals throughout the drawing.

The basic operation of a water treatment system according to the invention is depicted schematically in figures 1A-1C. The system comprises a reactor 10 having a first zone 11 and a second zone 12. These zones will also be referred to as contact zone 11 and separation zone 12 respectively. Both zones are divided by a screen 13 that extends from a bottom 14 of the

-7- reactor to below a water line 15. The reactor may have a polygonal, e.g rectangular, square or octagonal, or circular footprint, the separation zone 12 being entirely surrounded by the contact zone 11.

The contact zone 11 is provided with an inlet 21 for the intake of process water. The system moreover comprises bubble generation means, not shown in the figure, to generate and mix air micro bubbles with the intake water flow. Preferably the bubble generator means are located upstream of the inlet 21, such that a water/bubble mixture will enter the contact zone 11. The reactor is filled to beyond a level of the screens 13 such that said process water wil! also fill the separation zone 12, as shown in figure 1A. Said separation zone 12 is provided with a drain 22 at the bottom 14 that allows cleaned water to be discharged. The air bubbles will coagulate with any contaminations that may reside in said process water to create flogs that eventually form a foam layer 16 floating at the surface 15, while cleaned water is flowing down to the drain 22. The reactor 10 further comprises a foam collection device 30 having a entrance 31 centrally within the separation zone and well above the waterline 15 with the foam layer 16. The foam collection device has a foam outlet 32 outside the reactor 10 where foam that was evacuated from the surface may be collected and discharged. The reactor may be closed by a lid 17, preferably one having an inspection door.

As illustrated in figure 1B, due to the elevated and central position of the foam inlet 31, the system may cope with a relatively severe movement of the waterline 15 are may be experienced onboard of sea going vessels, like boats and ships. The waterline 15 may pivot within the reactor 10 due to waves that are encountered by the vessel, as shown in figure 1B, but as long as the foam inlet 31 remains above the waterline 15 this will have hardly any impact on the performance of the system. In rough seas, the system can be operated with a low water level, figure 1B, keeping the entrance 31 of the foam collection device 30 away from the foam/water surface until the vessel has reached calmer waters. Then, a foam backwash or a continuous foam washing mode of operation may be initiated within the system by increasing its water level as shown in figure 1C. This change in water level can for instance be accomplished using a motorised valve that restricts the flow from the outlet 22 without changing the intake at the inlet 21.

-8- At the higher water level the foam layer 16 will be raised to beyond the entrance 31 of the foam collection device and foam starts to enter the foam collection device 30 to be guided to the foam outlet 32. A spray nozzle 33 that is directed to the foam inlet 31 may be operated to create a water spray that promotes the flow of foam down the foam collection device 30 and avoids clogging of the entrance 31. At the same time cleaned water may be collected at the drain 22 to be re-circulated to a process plant. A perspective view of an embodiment of such a reactor is shown in figure 2. The reactor 10 has a square or rectangular footprint and is preferably made out of stainless steel or food grade plastic. Basically the reactor 10 is a large tank of several metres in all directions, e.g. 2x2x2 metre, with a central section that forms the separation zone 12 and a surrounding rim where the contact zone 11 is located. Both parts of the reactor are separated by a screen 15 of stainless steel. The reactor allows for radial flow, so water can always flow in and out of the reactor despite external {e.g. vessel} motion. The contact zone 11 is placed in an outer rim of the reactor and the separation zone 12 in the centre. This way, even in motion, the reactor's contact zone 11 and separation zone 12 will always be connected hydraulically. The reactor is further fitted with a foam collection device 30 that has an entrance 31 within a foam cup 35 that is installed at the centre of the reactor. This will be the place where the water surface effectively pivots. In other words, the centre of the reactor is where changes in water level elevation will be the smallest. A dual drain outlet 32 at the bottom centre of a false bottom 19 of the reactor ensures both foam and water exit the reactor through the bottom centre, without mixing. The reactor is further fitted with an auxiliary draining port 25. At a top of the reactor a spray nozzle 33 is connected to a water duct to allow spraying of fresh water onto and into the foam cup 35. the reactor is closed by a lid 17 having an inspection door 18 that may be opened for visual inspection of the reactor content. External of the reactor is mechanical filter 40 that is mounted to an inlet 21 of the contact zone. In this case this mechanical filter consists of a drum filter with an inlet 41 and an outlet 42.

Alternatively a bead filter may be used. This mechanical pre-treatment step is used to remove larger solid fractions from the waste water that is led to the reactor. Downstream of the filter 40 and upstream of the inlet 21 to the contact zone 11 is a bubble generator 50 that generates micro air bubbles and introduces these in the intake water flow before reaching the inlet of theq- contact zone 11. The inlet 21 of the contact zone opens into an inlet manifold 24. This manifold comprises a perforated pipe of for instance stainless steel and extends substantially all along the contact zone to distribute the water/bubble mixture substantially homogeneously over said contact zone 11.

The treatment system according to the invention is particularly suitable for use onboard of purpose-built well boats that are used for harvesting fish, particularly Atlantic salmon growing in net pens. Using these boats, the fish are harvested, slaughtered, bled and stored in chilled water until the vessel reaches a processing plant ashore. Figure 3 gives a diagram of a possible setup of such a processing plant onboard of a ship. In this figure straight lines denote ducts and pipes (e.g. of PE or stainless steel) to connect parts of the plant, whereas dashed lines denote electrical control lines between sensors and actors. The entire assembly is monitored and controlled by a central processing unit. Further the following reference number have the following meaning: 10 : dissolved air floatation (DAF) reactor 21 ; waste water inlet 22 : cleaned water outlet 32 : foam exhaust 40 : rotary drum filter 44 : back-wash pump 50 micro bubble generator and pump 60 : fish holding tank 61 : RSW circuit 62 : centrifugal circulation pump 70 : blood and waste water tank 80 disinfectant container 81 : peristaltic dosing pump 82 : peristaltic dosing pump The disinfectant container holds a quantity of a food grade oxidant that may be added to the reactor in order to suppress pathogens. In this example a stabilized hydrogen peroxide solution is used as disinfectant agent, commercially available under the trademark Oxyl-Pro®, Hydrogen peroxide reacts quickly with organic matter, degrading in the process. Aeration also increases the degradation rate. Single-point dosing of hydrogen peroxide (in this case, dosed at the

-10- reactor) Will result in a gradual decrease of hydrogen peroxide concentration across the fish holding tanks and the water refrigeration system. Therefore, monitoring the degradation of hydrogen peroxide through the different compartments and pipes of the plant will provide an indication of which concentrations are to be kept at the reactor. The main control parameter will be RedOx (Reduction-oxidation reaction) potential, which is used as an indication of the concentration of hydrogen peroxide. Redox and hydrogen peroxide strips can be used during trials to find a correlation between hydrogen peroxide concentration and redox values across the system.

Oxidants such as hydrogen peroxide, peracetic acid and ozone are effective to inactivate particularly infectious salmon anaemia virus (ISA virus) aeromonas salmonicida, subsp.salmonicida, that may contaminate bloodwater from a fish industry plant. The system further comprises a variety of valves, pumps and sensors to monitor and control the waste water flow. As such water quality parameters to control in the system include: 15 . Dissolved oxygen/Nitrogen/TGP: this is used to know the amount of gas bubbles that are being injected in the system . Turbidity: to know the solids removal capacity of the plant in combination with an disinfectant/oxidant . Redox potential (ORP) for oxidation control. This is the main parameter controlling disinfectant/oxidant dosing.

. Acidity {pH): to monitor that the oxidation reaction is taking place.

. Temperature to adjust gas injection ° Bacterial counts (optional): an additional device working in a similar way to turbidity control: the more organic matter in the water there is, the more bacteria will be present in the process water.

Equipment control includes: ° Speed control in all water pumps: to avoid any overflows or malfunctions. . Saturator flow and bubble size: to adjust for flows and changes in temperature 30 . Water level: critical in a tank subject to motion. Controls normal operation of the plant and backwash cycles, . Automatic backwash of drum filter and foam collection device ° Automated disinfectant/oxidant dosing

-11- Alarms may include: . High Redox . Water levels . Pump / saturator malfunctioning

The reactor may have a rectangular foot print as shown in figures 4-6. In this case the internal corners are chamfered by baffles 27. Putting baffles on these corners of the separation zone 12 of the tank will help reduce solids accumulation in the corners and improve hydraulics.

The inlet 21 is provided with a back-wash bypass 29 as shown in the drawing.

Alternatively the reactor may have a round footprint as shown along the embodiment of figures 7-9. Although the system according to the invention has been elucidated in further detail along a limited number of examples only, it will be appreciated that the invention is by no means limited to those examples.

On the contrary many different embodiments and variations are possible to a skilled person without departed from the true scope and spirit of the present invention.

As such a secondary oxidant/disinfectant contactor may be added to add any extra oxidant/disinfectant downstream of the reactor and/or to feed an extra dose of oxidant/disinfectant to the chilling water circuit.

A UV irradiation treatment step may be inserted downstream of the reactor to enhance the oxidation process and to provide the plant with a water disinfection method which is food approved.

A food-grade flocculent tank may be added, including dosing means, to add a flocculation agent for enhanced flock/foam formation.

Claims (1)

-12- Conclusions: A water treatment system, in particular for process water on board a vessel such as a boat or a ship, comprising a reactor having a first zone and having a second zone, a water inlet for receiving an inlet water flow at the first zone, a water inlet. outlet for discharging an outgoing water flow from said second zone, bubble-forming means which, during operation, generate and mix gas bubbles, in particular micro-bubbles, with said inlet water flow and comprising foam discharge means for separating and evacuating, during operation, a foam layer floating on a water line of the second zone, characterized in that the foam discharge means comprises a foam collecting device with an entrance beyond a level of the foam layer and with a foam outlet, the reactor being provided with water level control means which are arranged to keep within the reactor the said waterline and foam layer below a level of said entrance of geno and that said water level control means enables said water line to substantially increase beyond a level of said entrance of said foam collector and thereby remove said foam layer at least at least substantially from said water line. to feed. A water treatment system according to claim 1, characterized in that the first zone surrounds the second zone and that the entrance of the foam collecting device is centrally located in the second zone. Water treatment system according to claim 1 or 2, characterized in that a screen is arranged between the first zone and the second zone, extending from a bottom of the reactor to below the waterline and the first zone and the second zone below the waterline. 4. Water treatment system according to any one or more of the preceding claims, characterized in that the inlet comprises a perforated channel extending at least substantially along the entire first zone. -13- Water treatment system according to claim 4, characterized in that the bubble-forming means are connected upstream of an inlet of the conduit. Water treatment system according to one or more of the preceding claims, characterized in that spray nozzle means are provided at the entrance of the foam collecting device which, during operation, direct a water mist at the entrance. A water treatment system according to any one or more of the preceding claims, characterized in that the reactor is provided with dosing means for holding and dosing a disinfectant and / or an oxidizing agent! in water, in particular for dosing an oxidant from a group of peracetic acid, ozone gas and hydrogen peroxide. Water treatment system according to one or more of the preceding claims, characterized in that the water outlet is connected to a disinfection station comprising at least one of a source of ozone and a source of ultraviolet radiation. Water treatment system according to one or more of the preceding claims, characterized in that a pre-filter is connected upstream from the inlet to the reactor, in particular a drum filter or a grain filter. Water treatment system according to one or more of the preceding claims, characterized in that the water level control means comprise a pump connected to the water inlet and a shut-off valve at the water outlet of the reactor. Water treatment system according to one or more of the preceding claims, characterized in that the reactor has a rectangular footprint with corners that are chamfered inside, in particular by baffles. A method for treating process water, wherein the process water from a process installation is supplied to the water treatment system according to one or more of the preceding claims, wherein cleaned water is collected at the water outlet of the water treatment system, and wherein the collected water is recycled to the water treatment system. said process plant. 14. A method according to claim 12, wherein a disinfectant is added from a group comprising peracetic acid, ozone gas and hydrogen peroxide, in particular a stabilized hydrogen peroxide solution. A method according to claim 12 or 13, wherein a flocculant and / or coagulant is introduced into the reactor to promote flocculation of contaminants contained therein.