Preservation of Industrial Products and Processes
Tony A. Rook
Many waterborne industrial products, and the processes used to manufacture these products, can be susceptible to microbial contamination if adequate microbial control strategies are not employed. These products and processes have become increasingly more susceptible to microbial spoilage mainly due to the increasing use of environmentally favorable raw materials.1,2,3 The development of more sustainable formulations has also seen the replacement of volatile organic compounds with water as raw materials and the incorporation of natural and/or bio-based raw materials.4,5,6 The consequences of microbial spoilage can lead to irreparable damage to industrial products because of changes of viscosity, generation of offensive odors (malodors), gas formation resulting in potential container deformation due to excessive pressure buildup, product changes such as discoloration, or gelling of product and enzyme production resulting in instability of product formulation.7 In addition, the service life of many industrial products may be shortened due to the activities of microbial defacement, such as visible growth of on the surface of materials leading to loss in aesthetic qualities of the product and loss of mechanical integrity due to biodeterioration of the material that may lead to blistering, delamination, or otherwise disfigurement of the products.8 Within industrial products and processes, there are four main focus areas to consider when employing preservation strategies: manufacturing hygiene, wet-state preservation, finished article dry preservation, and functional fluid preservation.
MANUFACTURING HYGIENE OF INDUSTRIAL PROCESSESEffective manufacturing hygiene programs for industrial processes require an understanding of the necessity of microbial control practices to be integral to the process.9,10,11,12 Manufacturing environments for waterborne industrial products are complex engineered built environments that can offer many opportunities for microbial contamination to persist if not otherwise mitigated through a systematic approach to microbial control. A successful industrial manufacturing hygiene program consists of the following major components:
Risk assessment of the manufacturing process, facility, and equipment from a microbial control perspective
Continuous monitoring of the process with microbiological and analytical methods
Management and handling of raw materials to prevent microbial contamination
Effective cleaning and disinfection (or sanitization) of the manufacturing process
Microbiological testing of finished products
Establishment of effective preservation of finished products
Documentation of program, processes, and metrics
Manufacturing Process Equipment Design
The design of the manufacturing process and equipment employed to produce industrial products is an important consideration.13,14,15 The equipment chosen for the manufacture of water-based industrial products such as paints, inks, polymers, paper, leather, textiles, and functional fluids should consider a design that is easy to clean and accessible for routine inspections. The built environment of an industrial product manufacturing facility may consist of raw material storage tanks, pumps, filtration units, production tanks, flexible hoses, transfer manifolds, heat exchangers, transfer piping, pigging systems, and filling lines. Integral to these production processes are water delivery systems for production and/or cleaning of the plant environment.
Raw material holding tanks ideally should be accessible for routine monitoring and scheduled (or unscheduled) cleaning. One important consideration for a good sanitary tank design is a domed interior ceiling that reduces the likelihood of product buildup. The venting of the tanks should be accomplished by incorporating a 180-degree pipe facing downward to discourage the ingress of exterior contamination. Additionally, a filtration unit can be applied to the venting pipe to further reduce the chances of contamination to be introduced.16 Filtration units can either consist of a high efficiency particulate air (HEPA) filter or be designed as a wet air filtration unit, which consists of a small holding vessel containing liquid to entrap airborne particles. If water is used as the liquid for particle entrapment, then it should be treated with a biocide and routinely changed to prevent this filter from becoming the source of contamination.
Production equipment design should be chosen to minimize buildup of product or water within the process. Pumps, pipes, and filter units should allow for easy draining. Whenever possible, the production process lines should be sloped to allow for easy draining.17,18 The pumps and filter units chosen should be designed to minimize any stagnant fluid within the process when not in use. Many production processes incorporate the use of filter bag units. These units should be designed to be bottom exiting to allow for the filter housing to drain completely of fluid between production campaigns.
During the engineering design of a new manufacturing facility or during the review of an existing facility, the ability to effectively clean the process should be considered.19 Consideration should be given to minimize the overall complexity of the process to aide in the ability to clean, disinfect, and fully drain the production process in place. Table 38.1 provides a summary of best practices for facility design of industrial manufacturing processes.20
TABLE 38.1 Important considerations for facility design of industrial manufacturing processes | ||||||||||||||||||||||||||
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Continuous Monitoring of Production Process and Products
A central component to an effective microbial control program is the implementation of a continuous monitoring program of the manufacturing environment and the products manufactured by the process. A continuous monitoring program should consist of evaluation of the microbial condition of process equipment and manufacturing environment, raw materials, and finished products.21 Within the manufacturing process, locations that may provide an early indication of the microbial condition of the process should be selected to be evaluated in a routine basis for the presence of microbial contamination.22,23,24,25 These locations may be considered critical control points because determining the microbial conditions of these locations can provide an estimated understanding of the overall control of microbial contamination within the entire production process. Critical control points should be selected throughout the process and be relatively easy to access to ensure continuous monitoring of the process will take place. Some common locations within industrial product manufacturing systems include bulk tank lids and side walls, flexible transfer hoses, pump inlet/outlet, filtration unit housings, intermediate and process tank sidewalls, fill bowls, and fill heads (Figure 38.1). In addition to directly sampling process equipment, the routine sampling of representative raw materials should determine the microbial status of these materials.26 Special attention should be focused on waterborne raw materials that are transported and stored within bulk storage tanks as well as raw materials known to potentially contain high numbers of microorganisms, such as specific dry raw materials.
 FIGURE 38.1 General layout of an industrial manufacturing facility for paint production, showing examples of critical control points. HSD, high speed dispersion; SCU, self cleaning filter; TiO2, titanium dioxide. |
 FIGURE 38.2 An example of a common microbiological sampling/transport swab and a test dip slide. For a color version of this art, please consult the eBook. |
Assessment of microbial contamination within critical control points are commonly carried out through surface sampling using a sterile transport swab26 (Figure 38.2). Ideally, the swab should contain a media, such as Aimes Gel, to minimize microbial cell death during transport. If the system is known to contain residual equipment disinfectants during the sampling process, the transport media should also contain a component known to neutralize commonly used agents. The swabs are transported to a laboratory to be evaluated by streaking onto a solid microbiological media known to support the growth of microorganisms commonly known to cause spoilage
within the process or products. Alternatively, facilities may choose to employ the use of dip slides.27 These sampling devices consist of a plastic paddle attached to the inside of a screw top (see Figure 38.2). Typically, the paddles contain a bacterial growth media on one side and a fungal growth media on the other side. The manufacturing operator should be trained to open the twist-off lid without touching the inside of neither the container nor the media and dip the paddle into a raw material, process fluid or finished product. The paddle is then placed back into the sterile container and typically incubated at room temperature. After a specified incubation time, microbial growth can be more easily detected using chromogenic media to induce a color change upon growth. Processes for measuring the presence of microbial contamination consist of traditional microbiological growth media and/or several rapid microbiological methods.28,29
within the process or products. Alternatively, facilities may choose to employ the use of dip slides.27 These sampling devices consist of a plastic paddle attached to the inside of a screw top (see Figure 38.2). Typically, the paddles contain a bacterial growth media on one side and a fungal growth media on the other side. The manufacturing operator should be trained to open the twist-off lid without touching the inside of neither the container nor the media and dip the paddle into a raw material, process fluid or finished product. The paddle is then placed back into the sterile container and typically incubated at room temperature. After a specified incubation time, microbial growth can be more easily detected using chromogenic media to induce a color change upon growth. Processes for measuring the presence of microbial contamination consist of traditional microbiological growth media and/or several rapid microbiological methods.28,29
PROCESS WATER CONTROLSProcess water within industrial manufacturing processes of waterborne products can be a primary source of bacterial contamination within the process, within the raw material storage, and ultimately within the final products manufactured. Therefore, the manufacturing facilities should ensure measures have been taken to periodically monitor process water for bacterial contamination, consider adding treatments to reduce the incoming microbiological load of the water, and employ sanitary designs of the engineered water systems to increase the likelihood for effective disinfection of these systems.30,31,32
It is critical for any waterborne industrial process to implement a program to sample and monitor the bacterial contamination of the incoming process water. Employment of aseptic sampling techniques for collection of the water is critical to ensure that the data generated is truly representative of current condition of the process water.33 Sample points within the process should be selected where water samples can be taken that are truly representative of the process water. Some locations to be considered are water lines at point of entry into the manufacturing facility; water lines at the receiving area for raw materials being stored in bulk storage tanks; water lines entering the process, such as an in-process mixing tanks; and water lines at the filling lines. Consideration should be given to how the water is being used within the process and emphasis on water directly impacting the manufacturing for process or being used in the manufacturing of the final products. For instance, special attention should be focused on water that is being directly added to any process tank as a product raw material. Any water being used to clean or rinse the process equipment should also ensure low microbiological content because this water may ultimately be the source of bacterial biofilms within the process that ultimately may lead to quality issues within the final product.34
Engineering of a process water system should consider sanitary design both within the material of construction and the overall functioning of the water systems. If possible, water systems should be designed to be compatible with disinfection treatments that may be employed to control the microbiological load within the incoming water. Areas within the water process with little to no flow should be avoided. If these areas are unavoidable due to the design and function of the process, consideration should be taken to consider adding a flowing circulation within the process. An additional area of consideration within an engineered process water system are any flexible hoses that are attached to the water process lines for process equipment rinsing and our addition to production batches. It has been well documented that flexible hoses can be a location for microbiological contamination.9,15,20,21,33 Consideration should be given to implement a program for removal of the flexible hoses for routine disinfection followed by hanging of the hoses for draining and drying between uses. Allowing the hoses to remain attached to the process and filled with water can create a stagnant zone that increases the opportunity for microbial growth to occur.
Some key factors should be considered when selecting a microbicidal treatment for any water system within an industrial manufacturing process. A critical and often overlooked criteria for determining a treatment process for process water lines is the type of microorganisms that are known to be present within the incoming water itself or known to be resident within the water process equipment of the system. This information can provide critical information regarding the potential presence of aggressive biofilm formers that may require rigorous water treatment for full control.35,36 This information will also allow the measurement of effectiveness to control these specific microorganisms during the validation of the water treatment system. Another important factor to consider when selecting a disinfection process is the nonmicrobiological (or chemical) quality of incoming water including the residual levels of disinfectant from municipal treatment (if applicable), water hardness, pH, and turbidity of the water. These factors may influence the choice and efficacy of the water treatment process selected.
Treatments of process water can be divided into two major categories: chemical or physical treatments. The chemical treatments of process water can further be divided into two major categories: oxidizing or nonoxidizing chemistries. Physical treatment programs may consist of applying heat to intermediate water storage tanks, where periodic heat treatment of temperature at 180°F (82°C) or higher can be applied through a recirculation loop. Alternatively, water may be treated using physical filtration to remove both gross contamination as well as microbiological contamination with the incoming water. The most commonly used filtration methods include reverse osmosis, membrane filtration, and ultraviolet (UV) filtration.
Reverse osmosis filtration systems should include scheduled maintenance to periodically disinfect the filters. Membrane filter systems should be maintained and evaluated to ensure the membranes remain integral and undamaged during the use life. Filter membranes with larger pores sizes of 5 to 10 µm are commonly installed to remove gross contamination to be filtered out upstream of the terminal (eg, 0.45 µm) filters membranes intended to remove microbial contamination. This design protects and extends the effective life of the downstream filters. The UV disinfection can be applied to treat industrial process water (see chapter 9); however, there are several factors that should be considered for successful implementation. The factors that impact the effectiveness of a UV disinfection system are water turbidity, light intensity, and resident time within the treatment unit. These factors should be measured over the life of the system to ensure the system is effective for microbicidal activity. Additional consideration should be given to the placement of the UV system within the manufacturing process. Installing a single UV filtration unit at a single point where the process water first enters the production plant may not always be the best choice, especially when installing systems within existing manufacturing process with a known history of microbial contamination of process water. In this instance, the UV system may help knock down any incoming microbiological load but will not do anything for the microorganisms that are already resident within the water distribution systems of the plant. Another consideration is to install UV treatment units at the point of water addition to the process, for example, directly prior to point of addition at the processing tanks. This may become cost restrictive for larger manufacturing processes but may be a good choice for smaller processes.
Reverse osmosis filtration systems should include scheduled maintenance to periodically disinfect the filters. Membrane filter systems should be maintained and evaluated to ensure the membranes remain integral and undamaged during the use life. Filter membranes with larger pores sizes of 5 to 10 µm are commonly installed to remove gross contamination to be filtered out upstream of the terminal (eg, 0.45 µm) filters membranes intended to remove microbial contamination. This design protects and extends the effective life of the downstream filters. The UV disinfection can be applied to treat industrial process water (see chapter 9); however, there are several factors that should be considered for successful implementation. The factors that impact the effectiveness of a UV disinfection system are water turbidity, light intensity, and resident time within the treatment unit. These factors should be measured over the life of the system to ensure the system is effective for microbicidal activity. Additional consideration should be given to the placement of the UV system within the manufacturing process. Installing a single UV filtration unit at a single point where the process water first enters the production plant may not always be the best choice, especially when installing systems within existing manufacturing process with a known history of microbial contamination of process water. In this instance, the UV system may help knock down any incoming microbiological load but will not do anything for the microorganisms that are already resident within the water distribution systems of the plant. Another consideration is to install UV treatment units at the point of water addition to the process, for example, directly prior to point of addition at the processing tanks. This may become cost restrictive for larger manufacturing processes but may be a good choice for smaller processes.
Process water can be treated with oxidizing microbicides such as halogenated chemicals (including chlorine or bromine) or nonhalogenated oxidizing chemicals such as ozone (see chapters 15, 17, 18, and 33). Addition of chlorinated disinfectants to process water creates a mixture of hypochlorous acid and hypochlorite ions with the disinfecting properties being contributed by the hypochlorous acid (see chapter 15). Because stability of hypochlorous acid is pH dependent, chlorinated microbicides such as sodium hypochlorite are most effective when the process water pH is between 6.0 and 7.5 and will quickly lose any meaningful efficacy at pH levels above 8.0. Any residual organic matter present within the process water will react with chlorinated biocide treatments; therefore, higher chlorine concentrations will be required within process that contain higher organic content.
Chlorine dioxide (ClO2) can effectively be used as a chemical water treatment at much lower concentrations than other chlorinated microbicides (see chapter 27). Systems commonly used within industrial processes generate on-site ClO2 gas, which can be directly added to a process water stream. This can be accomplished by either mixing a strong chlorine solution with sodium chlorite or by mixing hydrochloric acid with a mixture of hypochlorite and sodium chlorite solutions. Safety precautions should be considered during installation because ClO2 gas can be explosive. The benefits of ClO2 treatment is that the active ingredient remains more effective at higher pH ranges than traditional chlorinated biocide choices and is not as highly reactive to residual organic content within process water.
Process water can also be treated with brominated microbicides and are becoming more popular within processes with higher pH because active ingredient of hypobromous acid maintains its biocidal properties across a broader pH range than chlorinated treatments (see chapter 15). Typically, a mixture of hypobromous acid and hydrochloric acid with sodium chloride are prepared through the hydrolysis of either an activated bromide salt or bromine chloride.37 An additional advantage of using brominated treatment process is that any bromamines generated during the treatment are generally considered to be more environmentally favorable than the chloramines generated during chlorinated treatments.
Ozone is a strong oxidizing agent that can effectively be employed to control incoming microbial contamination of industrial process water (see chapter 33). Systems using ozone as the active biocidal ingredient to treat process water require commitment to install capital equipment to generate ozone on-site. Important factors to consider when implementing an ozone treatment process are pH, temperature, and organic content within the process water because each of these factors impacts on stability of the ozone within the treatment system. One main benefit of using an ozonation system is lower potential of corrosivity than traditional chlorinated treatment systems.
PRESERVATION OF RAW MATERIALSIt is critical to ensure raw materials being received, stored, and used to manufacture waterborne industrial products, such as paints, coatings, and inks, are controlled for unacceptable levels of microbial content that may lead to spoilage events within the process and within the final products. A program should be established to sample and evaluate incoming raw materials as well as raw materials maintained under bulk storage conditions on a continuous frequency to ensure the materials are within good microbiological quality. Raw materials used to manufacture industrial products are not required to be sterile; however, effective wet-state preservation strategies often provide effective control of microorganisms that may lead to product spoilage.7,38,39 The current industry guidance suggests the upper limit for a microbial content specification should be no more than 1000 colony-forming units (CFUs)/mL within aqueous solutions and suspensions, and no more than 1000 CFUs/g for anhydrous raw materials.40
The manufacturing process design can contribute to contamination of waterborne raw materials that are stored in bulk vessels. The production process lines used to off-load bulk raw materials from tanker wagons or railcars should not contain any dead-legs where stagnant raw material may remain as a source of contamination within the delivery lines. The flexible hoses used for off-loading of raw materials are commonly a source of microbial contamination (as discussed earlier), which can contribute to contamination of an entire bulk tank. Systems should be considered that allow for the flexible hoses to be cleaned and disinfected on a regulatory basis and are stored in a manner to facilitate draining and drying of the hoses between uses. The bulk storage tanks themselves can contribute to contamination of the raw material being stored within the tanks. A critical area of a bulk tank that should be monitored is the interior ceiling. The condensation cycle within the tank may deposit raw material and degrade any preservative within the material leading to a potential source of contamination, which may be deposited back into the raw material within the tank upon subsequent condensation cycling.41 Because the majority of preservatives used within industrial products today do not have a high enough vapor pressure to provide any significant protection of the headspace of a bulk raw material tank, this portion of the process has become an area where alternate strategies are required to provide microbial control. Other important areas to consider within the headspace of the bulk tank where raw material build up can occur is on the side walls of a bulk tank and the shaft of the mixing blades within the tanks. A program should be considered to periodically empty the bulk tanks of the raw material content, physically remove any buildup within the tank through a combination of physical and/or chemical cleaning methods, and then disinfection of the interior surfaces of the bulk tank.
It is critical to ensure aqueous-based raw materials include an effective preservative, which can control the growth of microorganisms known to cause spoilage issues within the raw material or the subsequent finished product.41,42 Any contamination of raw materials above specified levels can increase the likelihood of quality defects, such as off-odor, discoloration, or viscosity drift within the raw material, and may lead to issues within the performance of the finished product.43 It is important to consider the handling of raw materials that are susceptible to microbial contamination throughout the supply chain. Many raw materials such as polymer or latex dispersions, emulsions, and pigment slurries may have increased susceptibility due to the extent of handling and time frame within storage prior to being used in the manufacture of a finished product.7,41,44,45,46 Raw materials are often manufactured and placed in bulk storage at the raw material manufacturing site until being transferred to a transport vessel. This storage period may significantly vary depending on the current market for the specific raw material. During transfer to a transport vessel, such as a tote, tank wagon, or railcar, the raw material is pumped through a filling line process being exposed to potential microbial insults within the equipment. The transport vessels may then be transferred to a depot or delivered directly to the manufacturer of finished products. Raw materials that are placed within a depot may further be exposed to environmental pressures such as elevated temperatures, which may reduce the level of preservation within the material. Once the materials are received at the finished product manufacturing sites, the materials are off-loaded by pumping out of the transport vessels through flexible hoses, delivery lines, and/or filtration equipment before being placed into bulk storage. During the off-loading process and storage within bulk containers, the raw materials are once again exposed to potential microbial insults from microorganisms that may persist within the product equipment. Exposure to such microorganisms within a dedicated production process can be especially challenging because they have become accustomed to growth on the very same ingredients that are being delivered and may have acquired an increased level of tolerance to the preservatives within the formulations.
The continuous monitoring of the bulk raw materials for microbial contamination will allow for a plan to quickly remediate high levels through the addition of a biocidal process to reduce the contamination population within the material. One of the most commonly employed biocides for remediation of contaminated waterborne raw materials of industrial products is 2,2-dibromo-3-nitrilopropionamide (DBNPA) due to its very fast-acting activity (Figure 38.3). The DBNPA can break down into inactive decomposition components through either interaction with nucleophilic substances, UV radiation via light, or through a pH-dependent hydrolysis mechanism (Figure 38.4).47 The hydrolyzed degradation of DBNPA proceeds through decarboxylation to dibromoacetonitrile, whereas the nucleophilic and UV degradation pathway proceeds through debromination to cyanoacetamide. The microbicidal rate of DBNPA is very rapid within materials such as latex or paints; however, the impact of the alkaline pH ranges and/or high processes high temperatures should be considered because these factors can significantly impact the degradation rate of DBNPA (Figure 38.5).47 Other rapid-acting biocides for consideration include peracetic acid, hydrogen peroxide, glutaraldehyde, and sodium hypochlorite. It is important to consider compatibility of any biocide
with the raw material matrix that is being treated. Finally, during the remediation of a contaminated raw material, it is important to consider the addition of a long-term preservative appropriate for the raw material to ensure a regrowth of the contamination does not occur within the bulk material (Table 38.2).
with the raw material matrix that is being treated. Finally, during the remediation of a contaminated raw material, it is important to consider the addition of a long-term preservative appropriate for the raw material to ensure a regrowth of the contamination does not occur within the bulk material (Table 38.2).
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