TECHNICAL FIELD

[0001] The present invention relates to a method and a system for disinfection of conveyor belt in situ. The present invention thus relates to a method and a system for disinfection of conveyor belt enabling disinfection of a conveyor belt during normal production or operation at a production facility, especially food industry. The invention also relates to the use of a microwave generator for disinfecting conveyor belt in situ, and the use of the disinfection system for disinfecting conveyor belt in situ in food processing industry.

BACKGROUND

[0002] Food processing factories, for processing foods such as fish, seafood, meat, poultry, bakery, fruit and vegetables, typically comprise one or more processing lines with different workstations or processing machines. A production line may consist of several conveyor bands for the transport of products through the production line. Microorganisms adhering to surfaces of food processing lines forming biofilms is a generally known problem. Biofilms may increase the risk of growth of pathogenic bacteria and other pathogens (germs) on food processing equipment, and there is a risk that such bacteria and pathogens can contaminate food products. Bacteria such as Listeria, E-coli and salmonella are a major problem globally, and such foodborne diseases lead to sickness, deaths as well as high economic impact. Cleaning and disinfecting food processing equipment normally involves using sanitizing and disinfecting chemicals, possibly combined with hot steam. However, it is an increasing problem that bacteria and pathogens develop resistance to disinfectants. In addition, some biofilms can be difficult to completely remove. Therefore, there is a risk that food processing equipment in food processing lines are inadequately cleaned, hence harmful bacteria and pathogens may remain or develop, e.g. in biofilms, and contaminate the food products being processed.

[0003] A food processing facility may comprise hundreds of meters of conveyor belts. Conveyor belts can be made of multiple modular links made of synthetic resin, such as different types of plastics approved for use in food industry, the modular links are interconnected to one another by connecting pins or other pivoting connections. Conveyor belt may also be made of one continuous belt. Conveyor belts must frequently and routinely be dismantled for cleaning and sanitizing, which is time consuming and laborious, and leads to interruption in the production line. Plastic parts of the conveyor belt may have damages in the surface, or hollow spaces, wherein humidity and food residues may be entrapped creating favorable conditions for growth of biofilms and bacteria. Despite extensive efforts, the traditional cleaning and sanitizing routines for conveyor belts are often insufficient for removing all microorganisms present in the belts, such as bacteria and pathogens.

[0004] There is therefore a desire for a reliable and efficient method for cleaning and disinfecting plastic conveyor belts, especially conveyor belts used in food processing industries prone to harmful pathogens. There is also a desire to substantially reduce the amounts of chemicals production conventionally used for cleaning and sanitizing plastic conveyor belts. [0005] Therefore, the object of the present invention is to provide a disinfection method and a system which at least reduce the disadvantages of conventional cleaning and disinfecting routines of conveyor belts.

SUMMARY OF THE DISCLOSURE

According to a first aspect of the invention, there is provided a method for disinfecting an endless loop conveyor belt in situ, comprising

(i) passing the conveyor belt though a washing zone, wetting the conveyor belt; and

(ii) passing the wetted conveyor belt through a microwave radiation zone, exposing the wetted conveyor belt to microwave radiation.

[0006] According to an embodiment of the method, the washing zone comprises arrangements for rinsing, brushing, jetting, spraying or bathing the conveyor belt with a washing solution.

[0007] According to an embodiment of the method, the method for disinfecting the conveyor belt is performed continuously or periodically.

[0008] According to an embodiment of the method, the method for disinfecting the conveyor belt is performed while operating the conveyor belt in production, such as during processing of food products.

[0009] According to a second aspect of the invention, there is provided a system for disinfecting an endless loop conveyor belt in situ, the endless loop conveyor belt being connected with a conveyor belt drive mechanism configured to run the conveyor belt endless loop, the system comprises

- a washing zone comprising arrangements for rinsing, brushing, jetting, spraying, or bathing the conveyor belt with a washing solution, and

- downstream the washing zone, a microwave radiation zone, comprising a microwave generator, through which the conveyor belt runs.

[0010] According to an embodiment of the system, the conveyor belt comprises an upper production and/or carrying surface run in a forward direction, and a lower, inverted surface run in a return direction, wherein the washing zone and the microwave radiation zone are located by the lower, inverted surface of the conveyor belt.

[0011] According to an embodiment of the system, the conveyor belt comprises an upper production and/or carrying surface run in a forward direction as a carousel, wherein the washing zone and the microwave radiation zone are located at the upper production and/or carrying surface.

[0012] According to an embodiment of the system, the microwave radiation zone comprises a tunnel type microwave generator.

[0013] According to an embodiment of the system, the system is operated continuously or periodically, optionally controlled by a PLC.

[0014] According to a third aspect or the present invention, there is provided a use of a microwave generator for disinfecting a conveyor belt in situ, by exposing the conveyor belt, wetted by water or an aqueous solution, to microwave radiation in a microwave radiation zone, while running the conveyor belt.

[0015] According to a fourth aspect or the present invention, there is provided a use of the system according to the second aspect of the invention, or any of its embodiments, for disinfecting a conveyor belt in situ in food processing industry.

[0016] According to an embodiment, the use of the system according to the second aspect of the invention, or any of its embodiments, for disinfecting a conveyor belt in situ is especially suitable for use in fish processing industry, seafood processing industry, poultry processing industry, meat processing industry, bakery industry, fruit processing industry or vegetable processing industry.

[0017] The expression "during production or operation" should in the present context be understood as running or operating the conveyor belt in its operating position, during production or between production.

[0018] The expression "in situ" should be understood as in its original place, in the present context the conveyor belt is disinfected in its operating position.

[0019] The term "disinfecting" should be understood as removing (destroying, killing) essentially all nucleating vegetative cells and pathogens initially present on and in the plastic device. By "essentially all", it is meant at least 99 %, preferably at least 99.9 % or 99.99 %, of nucleating vegetative cells and pathogens initially present on and in the plastic device.

[0020] The term "vegetative cells" as employed herein denote any bacterium or unicellular alga that is actively growing or forming spores, including but not limiting to Bacillus cereus (gram-positive bacteria), Clostridium perfringens (gram-positive bacteria), C. botulinum (gram-positive bacteria), Listeria monocytogenes (facultative anaerobic bacteria Escherichia coli (gram-negative bacteria), Salmonella spp. (gram-negative bacteria), and Vibrio parahaemolyticus (gram-negative bacteria).

[0021] The term "pathogen" is generally denoting disease-causing microorganisms, such as viruses, bacteria, fungus and parasites.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 illustrates a simplified side view of a conveyor system with two driving rollers, with a washing zone A and a microwave treatment zone B in the inverted return side of the conveyor.

[0023] Figure 2 illustrates a simplified side view of a conveyor system with four driving rollers, with a washing zone A and a microwave treatment zone B in the inverted return side of the conveyor.

[0024] Figure 3 illustrates a simplified top view of a conveyor system of a carousel type, with a washing zone A and a microwave treatment zone B located downstream the washing zone A. DETAILED DESCRIPTION

[0025] According to the first aspect the present invention relates to a method for disinfecting a conveyor belt in situ, that is while the conveyor belt is in its operating position. According to the second aspect, the present invention relates to a system for disinfecting a conveyor belt in situ, that is while the conveyor belt is in its operating position. The present invention will become apparent from the detailed description given below, with reference to the figures. The detailed description and specific examples relate to preferred embodiments of the invention by way of illustration only. Those skilled in the art understand from guidance in the detailed description that changes and modifications may be made within the scope of the invention as defined in the appended claim set. Hence, it is to be understood that the herein disclosed invention is not limited to the particular method and system described since such method and system may vary. It is also to be understood that the terminology used herein is for purpose of describing particular embodiments only, and is not intended to be limiting.

[0026] A conveyor belt is the carrying medium of a transport or conveyor system. Conventionally a conveyor system comprises driving mechanisms for running an endless conveyor belt in a loop. A driving mechanism 3 may comprise a sprocket driving assembly, such as two or more conveyor belt driving rollers or wheels connected with driving sprockets, or other means for rotating the driving rollers, driven by a driving motor. The driving rollers 3 are at least positioned at opposite ends of the endless conveyor belt loop, as illustrated in Fig. 1, or possibly two at each end, as illustrated in Fig. 2, the arrows are indicating the travel direction for the conveyor belt. There are several possible arrangements for conveyor system, having different mechanisms for driving the conveyor belt and structures e.g., for supporting the conveyor belt. Fig. 3 illustrates a conveyor belt system of the carousel type, wherein the conveyor belt is an endless loop running in one level (though it should be understood that the conveyor belt might be inclined). The driving means for the carousel type conveyor belt is not shown, however, it is understood that such carousel conveyor belts comprise driving means for running the belt. A conveyor system may be a straight line, or curved, or combination of straight and curved, generally horizontal or sloping. The upper, carrying, surface 1 of the conveyor belt runs in a forward direction, and may include several working stations for handling the products transported on the conveyor belt, such as filleting of fish, or other processing of food products. A conveyor belt may also comprise partitions or other structures for facilitating transport of the products. The conveyor belt system illustrated in Fig. 1 and 2, the lower inverted surface 2 runs in a return direction (may also be denoted "the lower return surface or side") of the conveyor belt. The lower inverted surface 2 runs normally directly underneath the upper surface, separated by a distance. The present invention is suitable disinfecting conveyor belts of both the upper carrying/lower, inverted return type, and the carousel type, as well as other types of conveyor system used in the food industry.

[0027] Conveyor belts can be made of several modular parts or links, which may be interconnected by connecting pins or other pivoting connections, or a continuous belt (not modular). The belts may have closed, or an open or perforated surface, based on type of modular parts being used. Conveyor belts may have different width, thickness, and length. The conveyor belts can be made of different materials, however, in the food industry the belts are often made of synthetic resins, such as food compatible plastic materials. The present method and system is especially suitable for disinfecting conveyor belts made of plastic materials of any type that are conventionally used in food processing industry, with no metals parts, or other materials negatively affected by microwave radiation. [0028] The present method comprises passing (or running, which should be understood as synonymous) the conveyor belt through a washing zone (A) followed by running the conveyor belt through a microwave radiation zone (B). The washing zone A should comprise arrangements for wetting the conveyor belt with a washing solution. Wetting may be carried out by e.g., rinsing, brushing, jetting, spraying, or immersing/bathing the conveyor belt with the washing solution. Preferably, the washing step removes at least partly any adhering product residues and product buildups from the products carried on the conveyor belt. The washing solution may be water, e.g. tap water, or water comprising a food compatible detergent, or water comprising electrolytes, such as one or more dissolved salt, dilute acid, and/or dilute base.

[0029] Examples of salts suitable for a washing solution comprising electrolytes are e.g., one or more of NaCI, KCI, Na ₂ SO ₄ , MgCI ₂ , Na ₂ HPO ₄ , NaH ₂ PO ₄ , K ₂ HPO ₄ , KH ₂ PO ₄ , however not limited to these salts as any food compatible salts may be used. The amount of dissolved salt in the solution is not important, however a concentration up to about 5 % dissolved salt(s), such as from about 0.5 %, or from about 1 % to about 3.5 %, may be suitable. The presence of electrolytes (ions) in the washing water may increase the heating rate when the wetted conveyor belt is radiated with microwaves. Further, as the saline water evaporates during the microwave heating, the salt concentration in the water droplets increases, which may increase the microorganism removal rate.

[0030] Suitable diluted acid may be chosen from e.g., hydrochloric acid (HCI) and phosphoric acid (HaPC ), which are food compatible, however not limited to said acids as any food compatible acid can be used. Food compatible diluted bases are such as NaOH and KOH, however not limited to said bases as any food compatible bases can be used. Both bases and acids may kill microorganisms by itself. It is however desired to reduce the usage of chemicals, as well as to provide a safe work environment, therefore the aqueous acid or aqueous base solution should be diluted, such as from about 0.1 % to about 2 %, such as between 0.2 to 1.5 %, or about 0.2 to about 0.5 %. Comparable to a solution comprising dissolved salts, as water evaporates during the microwave heating, the acid or base concentration in the water droplets increases, which may increase the microorganism removal rate.

[0031] The washing solution may comprise a detergent, which may also comprise a foaming agent (bubble forming substance). The detergent may be any detergent approved for use in the food industry. The amount of the detergent may be according to recommended amounts indicated by the producer. Advantageously the amount of detergent is in the lower recommended range, as some detergent may remain on the plastic surface after disinfection treatment. Presence of a bubble forming agent in the washing solution may give positive effects in connection with the treatment in the microwave radiation zone, since bubbles are produced during the microwave treatment as the water starts boiling. The bubbles expand the volume of washing solution present on the conveyor belt moving the heat over larger areas. If required, any residues of detergent, salt, acid or base on the conveyor belt may be rinsed off after the microwave radiation zone.

[0032] Clearly, the washing solution for washing the conveyor belt does not contain any strong sanitizing and/or disinfecting chemicals that require additional precautions for handling, storing or use beyond normal protective equipment for industrial washing procedures, such as gloves and eye protection. Furthermore, the present washing solution does not contain harmful substances which may put the workers and/or the environment at risk. The present method and system therefore represent a sustainable and "green" technology. [0033] In an embodiment involving a conveyor system as illustrated in Fig. 1 and 2; a conveyor system having an upper carrying surface, and a lower, inverted return, the washing zone A may be located underneath the conveyor belt, by the lower, inverted return side 2. Some conveyor belts may be flexible, thus the return side need not be located directly underneath the upper, carrying surface 1. The washing zone A may include more than one washing step, such as a first washing step which may include using a washing solution comprising a detergent, and a second washing step including rinsing of the conveyor belt using water or water comprising one or more electrolytes, such as dissolved salts, dilute acid, or dilute base, as discussed above. Preferably, the washing zone comprises washing means, including immersing bath, nozzle(s) for spraying or jetting, shower(s) for rinsing, rolling and/or spinning brush(es), or any other suitable means for wetting and washing the conveyor belt in the washing zone.

[0034] In an embodiment as illustrated in Fig. 3, a carousel type conveyor belt, the washing zone A is arranged at a suitable location by the conveyor belt. In a carousel type conveyor belt runs in one level, hence it does not have any inverted return side. However, similar as the embodiment relating to Fig. 1 and 2, the washing zone A may include more than one washing step, such as a first washing step which may include using a washing solution comprising a detergent, and a second washing step including rinsing of the conveyor belt using water or water comprising one or more electrolytes, such as dissolved salts, dilute acid, or dilute base, as discussed above. Preferably, the washing zone comprises washing means, including immersing bath, nozzle(s) for spraying or jetting, shower(s) for rinsing, rolling and/or spinning brush(es), or any other suitable means for wetting and washing the conveyor belt in the washing zone.

[0035] Downstream the washing zone A the wetted conveyor belt runs through a microwave generator in a microwave radiation zone B. In the embodiment as illustrated in Fig. 1 and 2, the microwave radiation zone B in located downstream the washing zone A by the lower, inverted return side, preferably immediately downstream the washing zone A. In the embodiment illustrated in Fig. 3, the microwave radiation zone B is located downstream the washing zone A, preferably immediately downstream the washing zone A. The microwave radiation zone B is located sufficiently near the washing zone A, such that the conveyor belt is still wet after the washing step. Exposing the wet conveyor belt to microwave radiation leads to rapid heating of the water present on the conveyor belt to a temperature effecting killing and removal of essentially all bacteria and pathogens present on the conveyor belt. As microwaves penetrate through plastic material, without significantly heating the plastic material itself, water or liquid containing areas and cavities within the conveyor belt will also be rapidly heated, removing essentially all bacteria and pathogens that are not easily washed away, including in biofilms. By essentially all, it should be understood that at least 99 % of the bacteria and pathogens initially present are killed, preferably 99.9 % and even 99.99 % removal of bacteria and pathogens. (It should be understood that the term "removal" in this context is denoting the destroying or killing of bacteria and any other pathogens initially present on the conveyor belt.) Any ions (electrolytes) in the washing solution may increase the heating rate significantly, therefore even small droplets will be heated fast enough to kill the bacteria and pathogens before the droplets evaporate. In addition, the number of bacteria being killed increases due to increasing osmolarity of the solution as the water is evaporating. Since microwaves especially heat water and humid environment, the energy supplied is converted to heat in locations where most of the microorganisms are present, providing efficient and reliable removal of any potentially harmful microorganisms. The washing solution may also comprise a foaming agent which may aid the disinfection process by bubble formation during the microwave treatment, by moving the heated electrolyte solution to colder areas, and thereby increasing the areas being treated. Heating is, of course, not limited to the water or washing solution applied to the belt as part of the process. Since plastic materials are somewhat pliable, may be subject to cuts or damages, and conveyor belts may include parts that may overlap in varying degrees when they move relative to each other, cavities may open and close in a manner that allows moisture containing microorganisms to enter but is hard to reach with washing solutions and mechanical means such as brushes and jetting. However, such moisture will also be heated by the microwave radiation and kill microorganisms in such cavities.

[0036] The microwave radiation zone may comprise a tunnel type microwave generator through which the conveyor belt is running. Hence, the microwave radiation zone may be defined by the walls, bottom and top of a tunnel type microwave generator. Microwave generators may comprise a number of magnetrons, generating the microwaves, and each magnetron may have an effect of e.g. 0.5 to 5 kW, such as 1 to 4 kW. The frequency of a suitable microwave generator for the present invention should be within the normal range of industrial microwave systems for heating. The microwave radiation zone should cover the whole breadth (i.e. width transversely to the longitudinal, running direction) of the conveyor belt. The microwave radiation zone should cover a length of the conveyor belt's travelling direction allowing sufficient treatment time in the microwave generation zone for heating the conveyor belt to a temperature effecting killing of microorganisms present. A sufficient length of the microwave treatment zone B may depend on the conveyor belt speed; higher speeds might need a longer microwave treatment zone, while slower speeds might need shorter microwave treatment zone. A sufficient length of the microwave treatment zone B may alternatively depend on the microwave power; higher speeds might require a higher microwave power in the microwave treatment zone, while slower speeds might require lower microwave power in the microwave treatment zone to achieve sufficient heating of the water on the conveyor belt. By adjusting the microwave power in relation to the conveyor belt speed the method and system is flexible and can be adapted for different kinds of operations of the conveyor system. The effect of the present method is measurable, it is possible measure the removal or killing rate obtained by the treatment and adjust by e.g., increasing or decreasing the microwave radiation effect in the microwave radiation zone B if necessary.

[0037] Since different installations of embodiments of the invention may vary with respect to many of the parameters mentioned above, and since these parameters to a large extent depend on each other, it is impossible to provide specific values that will apply in all cases. The extent to which microorganisms are killed depend on, and increases with, treatment temperature and treatment time. An important parameter is the D-value, which is defined as the conditions required to reduce the number of viable cells (living microorganisms) with a factor of ten. Consequently, there is a tradeoff between temperature and time such that for a given temperature, the D-value is the time required to kill 90 % of the relevant microorganisms. Another parameter is the z-value, which is defined as the temperature increase required to reduce the D-value with a factor of ten. Both the D-value and the z- value are species and strain specific, and dependent on the medium that surrounds the microorganisms, but for vegetative bacteria and fungi the D-value at 65 ^g C (D65) is usually 0.5-2 minutes and in wet heat situations the z-value is often 4-6 ⁹ C. Thus, if D65 = 0.5-2 minutes, then D77 will be 0.03-1.2 seconds showing the strong effect on the killing rate of a temperature increase once above a critical minimum heat treatment temperature. [0038] Thus, a treatment time of 5-10 seconds at 80 ^g C should reduce the number of viable, vegetative microorganisms by at least a factor of 1 million. Bacterial endospores are much more heat resistant than vegetative cells and will only be killed to a very limited degree at temperatures below 90-100 ⁹ C. However, in most of the intended uses of the present invention the number of bacterial endospores will be limited, and they will be much less important as a hygienic and pathogenic challenge than viable, vegetative microorganisms. Important problematic bacteria such as Listeria monocytogenes, Escherichia coli and Salmonella spp. do not form endospores.

[0039] In view of the above, a designer looking to configure a system according to the invention should determine a required combination of time and temperature required given the species and strains of microorganisms that can be expected to be present, and the solution used for washing and wetting the conveyor belt. Having done this the designer should determine the required power and number of magnetrons required to obtain this temperature and the combination of length of the tunnel, speed of the belt and physical distribution and configuration of the magnetrons and waveguides required to maintain this temperature for the required period of time. Since the belt is continuously moving, homogeneity of the microwave field may be less important, but it may be necessary to ensure that the required temperature is obtained across the entire breadth of the belt. The determination of these parameters may partly be done by calculations, but it may also be necessary to install temperature sensors and adjust parameters during configuration and also enable adjustments while the system is in use. For most installations an initial estimate could be that 99-99.9 % death rate may be achieved in 2-4 seconds at 80 C and in 20-40 seconds at 75 C. At 70 C the time may have to be increased to 200-400 seconds, which may be too long for practical and efficient installations (i.e., the belt would have to move too slow, or the tunnel would have to be too long if disinfection is taking place continuously during production and not only intermittently).

[0040] The disinfection system may be operated continuously such that the conveyor belt is continuously heat treated and disinfected during production operation of the conveyor belt. Alternatively, the disinfection system may be operated periodically, such as at certain time intervals or at predetermined periods, either during production operation, or outside production operation, or both. The operation of the system for cleaning and disinfecting conveyor belts may be automatically controlled by a PLC.

[0041] The present disinfection system is particularly suitable for disinfecting conveyor belts in fish industry, especially processing of fish in the family Salmonidae, which is commonly referred to as salmon. The bacteria Listeria monocytogenes has been a serious challenge in the salmon processing industry for many years. The present disinfection method and disinfection system present a reliable and effective way to mitigate the problem of Listeria monocytogenes bacteria, as well as other potentially pathogen microorganisms. The same applies to poultry industry, which is also facing great challenges with potentially pathogen microorganisms. It should also be noted that the present method and system is suitable for use in any food industry which involves the use of conveyor belt, in addition to the mentioned fish and poultry industries, such as meat industry, seafood industry, fruit and vegetable industry, bakery industry etc.

[0042] The present method and system for cleaning and disinfecting conveyor belts enables effective and reliable disinfection of conveyor belts in situ, hence it is possible to disinfect the conveyor belt during production. Thus, the method and system lead to less interruption in production as there will be less need of demounting conveyor belts for cleaning and disinfection. The disinfection system including washing zone and microwave radiation zone, is easy to install and can be adapted for different types of conveyor systems. Heating by microwave radiation is generally an energy effective way of heating water or moist material comprising water, allowing relatively low operation cost of the system while achieving the desired results. The disinfection method and disinfection system also allow a high degree of automation, in a safe and effective operational process.