Even before it was discovered as an element in 1809, chlorine was utilized in the textile industry as a bleaching agent. Once its disinfection properties were identified in the 19th century, chlorine was utilized for treatment of water, and in 1881 hypochlorite was shown to be deleterious to bacteria (Wei et al., 1985). Hypochlorite, a liquid, was soon utilized to reduce exposure to chlorine gas but deaths and health problems persisted (Cameron, 1870; Winder, 2001). Globally, chlorine is the most commonly used chemical oxidant for municipal water disinfection (Deborde and Von Gunten, 2008). This is due to its capability to kill microorganisms as well as serve as a taste and odor control (Hoff and Geldreich, 1981; Wolfe et al., 1984). Despite U.S. EPA restrictions of only 4 ppm of chlorine in drinking water, its use as a sanitization method has been shown to be nearly 100% effective against planktonic bacteria when paired with a sand filtration system (United States Environmental Protection Agency, 1992; Dunlop et al., 2002). In municipal wastewater systems chlorine is also utilized as a sanitizer for the disinfection and removal of pathogenic and nonpathogenic bacteria. While this practice has been commonplace in many developed countries, the long-term effects of on the environment of discharging chlorinated waste have not been largely elucidated (NSW Environmental Protection Agency, 2002). It is known that chlorine residues are toxic to aquatic organisms and they tend to persist and bioaccumulate within marine life (NSW Environmental Protection Agency, 2002). Furthermore, all forms of chlorine-based sanitizers are highly corrosive and toxic, and therefore it is encouraged to use the minimum amount of chlorine sanitizer necessary to reduce bacterial loads for each application. One treatment plant in Geneva, New York was able to meet fecal coliform limits, 200 CFU/100 ml, without exceeding 0.25 ppm/L of chlorine in their effluent (NSW Environmental Protection Agency, 2002; Sanders et al., 2013). Other studies have shown 100-fold reductions of enterococci and fecal coliforms in sewage effluents (Tyrrell et al., 1995). The bactericidal effects of chlorine use in municipal water and wastewater are also noted in the food industry.

With the use of chlorine-based products in the food industry not only were pathogenic bacterial levels significantly reduced, but a decrease of microbial slime and spore counts were also observed throughout the processing facilities (Mercer and Somers, 1957; Wei et al., 1985). By neutralizing essential amino acids, and exhibiting other bactericidal mechanisms such as lowering pH, chlorine-based products were considered essential for mid-20th-century food safety (Friberg, 1957; Camper and McFeters, 1979; Foegeding, 1983; Wei et al., 1985). In the fresh produce industry chlorine, ozone, peracetic acid (PAA), and chlorine dioxide (ClO₂) have all been utilized to reduce pathogenic bacteria (Banach et al., 2015). Chlorine dioxide (ClO₂) in particular has been reported to be sevenfold more effective than chlorine or hypochlorite in poultry chiller water (Lillard, 1980; Tsai et al., 1995). It has also been shown to reduce Salmonella incidence in chicken with a concentration as low as 5 ppm, compared to hypochlorite recommended use at 50–100 ppm (Lillard, 1980; Tsai et al., 1995; Casani and Knøchel, 2002). Sodium hypochlorite and other chlorine-based sanitizers function by saponifying fatty acids and glycerol creating byproducts such as chloramines which in turn convert amino acids into forms that antagonize cellular metabolism (Estrela et al., 2002). Acidified sodium chlorite has also been shown to be an effective antimicrobial, but must be in an acidic environment (pH 2.5–3.2), which can be generated by using citric acid (Warf, 2001; Allende et al., 2009).

Despite the efficacy of chlorine-based products as sanitizers, they are being phased out from many food production systems and are banned in poultry in the European Union since 1997 (Casani and Knøchel, 2002; Johnson, 2015). Several studies have identified chlorine resistance in Gram-positive bacteria and microorganisms in biofilms (Patterson, 1968; Bolton et al., 1988; Ryu and Beuchat, 2005). Biofilms are bacterial communities that live commensally and attach to surfaces and each other (Costerton, 1995). These biofilms increase the resistance of their residential bacterial cells to antibiotics and environmental stressors such as sanitizers (Kumar and Anand, 1998; Frank et al., 2003; Ryu and Beuchat, 2005). Furthermore, while microbial slimes can be removed in the presence of high concentrations of chlorine, it has relatively low activity on microorganisms harbored within the biofilms (Scher et al., 2005; Deborde and Von Gunten, 2008). Salmonella enterica serovar Typhimurium, when subjected to 50 ppm of sodium hypochlorite for 15 min, was completely reduced below the limits of detection (<10 CFU/mL) from an initial concentration of 1^* 10⁸ CFU/mL (Scher et al., 2005). However, when sodium hypochlorite was applied to a pellicle of Salmonella, an air-liquid biofilm, less than a 1 log CFU reduction was observed (Scher et al., 2005). At 250 ppm of sodium hypochlorite, only a 4 log CFU reduction was observed (Scher et al., 2005). This clear increase in resistance encourages higher chlorine use, but this can become dangerous to workers.

The threshold for chlorine gas that should never be exceeded is 1 ppm and is set by the Occupational Safety and Health Administrations (OSHA) Permissible Exposure Limit (PEL) (Occupational Safety and Health Administration, 2017a). If exceeded, chlorine gas can damage the lungs causing difficulty in breathing, coughing, throat irritation, impaired sense of smell, and in extreme cases chronic issues such as bronchitis, emphysema, and permanent pulmonary damage (Winder, 2001). Chlorine can also cause chemical burns and be an irritant in the case of skin or eye contact. An additional concern with chlorine use is that in the presence of high organic matter free chlorine forms trihalomethanes, such as chloroform, which pose a significant danger to plant workers and equipment (Tsai et al., 1992; Fawell, 2000; Casani et al., 2005). The corrosion rate of chlorine depends on a number of factors, mainly chlorine concentration and material (Tuthill et al., 1998; Nielsen et al., 2000). Cast iron, even at low concentrations of chlorine (< 2 mg/L) degrades by 0.1 mm/year, whereas stainless steel (SS) corrosion is insignificant at low concentrations except for localized buildup areas (Tuthill et al., 1998). However, at higher concentrations (5–20 mg/L) many types of SS alloys were not resistant to corrosion, and specific types of SS such as Types 304 and 316 are needed to withstand long exposures to high concentrations of chlorine (Tuthill et al., 1998). This can factor into the cost and be a detriment to poultry processing.

Furthermore, the by-product chloroform is considered carcinogenic, and its inhalation can impair the kidneys and cause liver necrosis (Occupational Safety and Health Administration, 2017a). Poultry processing water, in general, contains a high level of organic material that reacts with chlorine to produce these by-products and this is a concern in the use and reuse of processing water when sanitizing with chlorine or chlorine dioxide (Casani et al., 2005; Northcutt et al., 2008; White, 2010; Meneses et al., 2017). These health concerns have led to regulations limiting reused chiller water to have no more than 5 ppm of free available chlorine, which can be measured with a test kit or amperometric titration system (Tsai et al., 1992; United States Department of Agriculture, 2003b; Northcutt et al., 2008).

Chlorine-based sanitizers are also sensitive to temperature, pH, and residence time within the chiller water. As pH increases from pH 7.0 to 8.5 to 9.8 to 10.7, the killing power of chlorine against E. coli decreases, while raising temperature generally increases lethality (Butterfield et al., 1943; Nagel et al., 2013). However, this may result from an increase in temperature of the wash also reducing aerobic microbial populations independent of chlorine presence (Kelly et al., 1981). Due to the organic load within chillers, the bactericidal effects of chlorine sanitizers were found to be extremely low after 5 min of treatment (Tsai et al., 1992; Oyarzabal, 2005). It was determined that for a chiller tank with total dissolved solids of 3,500 ppm over 400 ppm of chlorine would be needed to saturate the demand from organic compounds which react with chlorine and produce by-products that are hazardous and ineffective as bactericidal agents (Tsai et al., 1992). Within this chiller tank, there was no available free chlorine, the agent of sanitation, after 30 min of chlorination with concentrations up to 300 ppm (Tsai et al., 1992). This was determined through a colorimetric assay. As a consequence, to utilize chlorine effectively as a sanitizer under these conditions, especially in the presence of high organic loads, it must be regulated and these physical and chemical characteristics can fluctuate in reuse water systems on a day to day basis (Mead and Thomas, 1973; Northcutt et al., 2008; White, 2010). Due to these issues, poultry processing water, increasingly being treated with peracetic acid as a sanitizer instead of chlorine.

By breaking down into acetic acid, water, and oxygen, PAA has been considered a safer alternative to chlorine and is currently approved for poultry processing water use by the U.S. Food and Drug Administration (FDA) at up to 2,000 ppm (21 CFR 173.370) (FCN No. 1465) (Warburton, 2014; Kim et al., 2017). Studies show PAA is effective against Salmonella and Campylobacter at a concentration of 20 and 200 ppm, respectively, and this is likely achieved through membrane oxidation and acidifying the water (Oyarzabal, 2005; Bauermeister et al., 2008). While the mechanism of disinfection is debated, PAA is believed to function by disrupting enzymatic activity through the binding and reacting with sulfur and double bonds, which denatures proteins (Block, 1991; Lefevre et al., 1992; Liberti et al., 1999; Kitis, 2004). It has also been suggested PAA may disrupt intracellular solute concentrations and impair bacterial cell replication as well as inactivate catalase, which breaks down toxic hydroxyl radicals (Block, 1991; Lubello et al., 2002). Unlike chlorine, PAA is not significantly inhibited by a high organic load, and this has made it a popular alternative in poultry processing (Lillard, 1979; Casani et al., 2005; McKee, 2011). However, in the presence of highly concentrated organic matter the rate of disinfection may be impacted (Gehr and Cochrane, 2002; Gehr et al., 2003). At 200 ppm PAA in chiller water did not influence the sensory characteristics of poultry products including flavor appearance or product acceptability (Bauermeister et al., 2008). Hydrogen peroxide used in combination with peracetic acid has been shown to be beneficial as a synergistic sanitizer improving peracetic acid reductions of Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa (Alasri et al., 1992; McKee, 2011). Hydrogen peroxide (H₂O₂) is an intermediary in the degradation of peracetic acid into acetic acid, but H₂O₂ also has some antimicrobial capacity (Wagner et al., 2002; Bauermeister et al., 2008). However, in the municipal effluent, concentrations of 106 to 285 mg/L of H₂O₂ were required to sufficiently reduce fecal coliforms compared to 0.6–1.6 mg/L of PAA (Wagner et al., 2002). Peracetic acid functions similarly to other peroxides in that it releases active oxygen that oxidizes double bonds, sulfur bonds, and sulfhydryl groups of proteins and enzymes that are located intra- and intercellularly (Block, 1991; Kitis, 2004). The sanitation effect of H₂O₂ can be improved by the addition of PAA as the inactivation of catalase improves the persistence of H₂O₂ (Block, 1991; Kitis, 2004). This effect, along with the equilibrium reached between H₂O₂ and PAA in solution means that these chemicals are often paired to achieve synergistic effects.

The PAA-based sanitizers are used in poultry processing systems reuse water and can also be combined with diatomaceous earth filtration to improve safety (Casani et al., 2005; Lo et al., 2005). However, peracetic acid is corrosive to equipment and can be caustic to exposed skin, eyes and respiratory systems of personnel handling these materials (Casani et al., 2005; Peracetic acid. MSDS No, 2013). Furthermore, the potential for microrganisms to recover from the sanitization treatment and grow may exist due to the decomposition of PAA into acetic acid (Stampi et al., 2001; Kitis, 2004). This rapid decomposition can result in a short shelf life of a few days to weeks if not refrigerated or placed away from light (Deshpande et al., 2013, 2014; Walsh et al., 2018).

While some chemical sanitizers are considered corrosive ozone can be utilized as a sanitizer without corrosive damage to equipment (Guzel-Seydim et al., 2004). Ozone (O₃) is generated when oxygen molecules are subjected to high voltage (Horvath et al., 1985). It has been utilized in water disinfection of swimming pools, wastewater treatment plants, and in bottled water production (Rice et al., 1981; Legeron, 1982; Guzel-Seydim et al., 2004). Ozone solubility depends on pH, temperature, ozone bubble size, and water purity, which are difficult to regulate in reuse water systems (Rice et al., 1981). Typically, at 27°C, 270 mL of ozone can be dissolved into a liter of pure water (pH 7.00) (Rice et al., 1981). Water treated with ozone has also been used to chill poultry carcasses with no changes in sensory characteristics (Sheldon and Brown, 1986; Casani et al., 2005). The FDA has affirmed the GRAS status of ozone as a sanitizer but only if the provided applications and concentrations utilized are in agreement with good manufacturing practices (Graham, 1997; Food Drug Administration, 1999; Oyarzabal, 2005).

Ozone has been approved as a sanitizer to reuse poultry chiller water (Kim et al., 1999). Like chlorine, ozone oxidizes critical bacterial membrane proteins, but ozone possesses 1.5 times higher oxidizing effect compared to chlorine (Xu, 1999; Oyarzabal, 2005). This oxidative potential allows for the attack of bacterial membrane glycoproteins and glycolipids, which causes membrane permeability and lysis (Khadre and Yousef, 2001; Guzel-Seydim et al., 2004). Ozone can also decrease pH. For example, after 50 min of ozonation Sheldon and Chang (1987) observed a decreased chiller water pH from 6.9 to 5.6. To generate ozone on a commercial level the corona discharge method is utilized, which splits diametric oxygen into free radicals that, in turn, react with available diametric oxygen to form ozone (Rice et al., 1981). Depending on the system 8–16 kWh is required to generate 1 kg of ozone, and this is achieved by utilizing high and low-tension electrodes separated by a dielectric medium with a narrow discharge gap (Rice et al., 1981). When sufficient kinetic energy exists within the excited electrodes collision occurs through the narrow gap interacting with oxygen to form ozone and produces a 1–3% ozone mixture (Rice et al., 1981). Unlike chlorine, ozone's killing potential is not as drastically impacted by the presence of organic material, and ozone decomposes into nontoxic residues (Restaino et al., 1995; Graham, 1997; Xu, 1999). This effect has been utilized to reduce pathogenic Escherichia coli, Listeria monocytogenes, Pseudomonas spp., Bacillus spp., Salmonella spp., and yeasts (Restaino et al., 1995; Guzel-Seydim et al., 2004; Almeida and Gibson, 2016). By using a recirculating ozone reactor, Restaino et al. (1995) tested the efficacy of 0.188 mg/L of ozone (concentration determined at the outlet) against 10⁶ CFU or spores/mL of several pathogens. The authors reported, at time zero, 5 log reductions of S. Typhimurium and E. coli along with more than a 4 log reduction of Listeria, and 3 log reductions of B. cereus and P. aeruginosa, but only a 1 log reduction in Aspergillus niger (CFU/mL) (Restaino et al., 1995). Using a dipper well ozone sanitation system, a 5 log reduction of E. coli and Listeria innocua was observed at 30 s after exposure to 0.45–0.55 ppm of residual ozone in Almeida and Gibson (2016). In Fabrizio et al. (2002), carcass surfaces were inoculated with Salmonella and allowed to attach, allowing for 3 log CFU/mL of rinsate (Fabrizio et al., 2002). These pathogen-inoculated carcasses were added to an immersion chiller at 4°C with ozone (10 mg/L) (Fabrizio et al., 2002). This led to 0.75 log CFU/mL reduction before storage and a 1 log CFU/mL reduction after storage but required pre-enrichment with tetrathionate to be detectable (Fabrizio et al., 2002). Ozone also reduced aerobic plate counts by 0.5 log CFU/mL which was statistically significant compared to all other treatments tested by Fabrizio et al. (2002). This was compared to 20 ppm of chlorine which was reported to be less effective with no immediate reduction and a 0.25 log CFU/mL reduction of Salmonella before and after storage in at 4°C, respectively (Fabrizio et al., 2002). These low reductions were likely due to the low level of Salmonella inoculation. Comparatively, a 1 h ozone treatment has been shown by Selma et al. (2008) to reduce the microbiota populations of vegetable wash water by 5.9 log CFU/mL.

Regardless of these bacterial reductions, there are several drawbacks to utilizing ozone as a sanitizer such as human health concerns, instability, and degradation (Hoof, 1982; Kim et al., 1999; Fabrizio et al., 2002; Casani et al., 2005). Ozone primarily affects the respiratory tract in humans and generates headaches, dizziness, and a burning sensation in the eyes and throat (Hoof, 1982; Guzel-Seydim et al., 2004). When exposed to chronic toxicity, memory can be affected, and an increased prevalence of bronchitis and muscular excitability can be observed (Hoof, 1982). Due to these effects, OSHA guidelines state that levels are not to exceed 0.1 ppm of air for 8 h of light work and no more than 0.05 ppm for heavy work, where the definitions of light and heavy workloads are defined by Occupational Safety and Health Administration (2017a,b). Additionally, while from a health perspective rapid degradation of ozone is beneficial, utilizing the product as a sanitizer can be difficult when considering its short half-life of 2–165 min (Wynn et al., 1973; Wickramanayake, 1984; Khadre et al., 2001). The degradation rate of aqueous ozone is dependent on alkalinity, mechanical stirring, water impurities, and temperature (Hill and Rice, 1982; Khadre et al., 2001). For instance, while ozone's half-life at 20°C is 20–30 min a shorter half-life of 2–4 min was observed at pH 7.0 and 25°C while stirring occurred (Wynn et al., 1973; Wickramanayake, 1984). At pH 9.0, no ozone was detected by Kim (1998) while lower pH levels appeared to be more favorable to ozone stability.

Independent of these factors, this degradation forces on-site generation of ozone, which may be a potential practical obstacle for some poultry processing operations (Pryor and Rice, 1999; Fabrizio et al., 2002. Furthermore, while organic loads found in chiller tanks have been shown not to impact ozone initial killing potential, 20 ppm of bovine serum albumin, a protein concentrate, significantly impacts the stability of ozone which reduces its killing potential over time (Horvath et al., 1985; Restaino et al., 1995). As a consequence of these negative effects, ozone has been investigated more as a synergistic sanitizer rather than a standalone application (Khadre et al., 2001). Since ozone disrupts membrane permeability, combining it with chlorine allows for deleterious effects on parasites such as Cryptosporidium parvum (Gyurek et al., 1996; Khadre et al., 2001). This occurs by denaturation of membrane proteins due to the oxidation potential of ozone, which eventually leads to leakage and cell death (Zhang et al., 2011). Ozone has been utilized along with filtration in poultry chiller water and reduced microbial counts by 99% and have been shown by Unal et al. (2001) to inactivate E. coli and L. monocytogenes when utilized with a pulse electrified field (Sheldon and Brown, 1986).

The potential for ozone as an independent sanitizer or synergistic sanitizer is promising. However, while significant log reductions of pathogens in poultry chiller water have been indicated, there are concerns with worker safety and the need for an on-site generation due to ozone's short half-life. As such, alternative sanitizers still need to be investigated to achieve further food safety improvements.

The advantages of chlorine, peracetic acid, and ozone, are clear as they can greatly reduce microbial loads and do not alter product quality if used in low-dose quantities resulting in their widespread use in poultry processing (Wei et al., 1985; Gehr et al., 2003; Northcutt and Jones, 2004; Casani et al., 2005). However, these sanitizers can be corrosive, dangerous to workers, difficult to transfer in large quantities, and ineffective against biofilms in low doses. Sodium bisulfate may be an alternative solution as it is a dry acid which is soluble in water and is generally regarded as safe (GRAS, 21 CFR 582.1095) (United Stated Department of Agriculture., 2015; Jones-Hamilton., 2018). Recently, SBS has been listed as a safer choice as an antimicrobial and processing aid by the Environmental Protection Agency (United States Environmental Protection Agency, 2018). Sodium bisulfate can be transported as a granular solid. It dissociates into nontoxic sodium, hydrogen, and sulfate ions and has a pKa of 1.99 (Sun et al., 2008). It also possesses the ability to lower the pH of water without producing off flavors in finished products (Sun et al., 2008). Based on the U.S. National Fire Protection Agency (NFPA) code 704, sodium bisulfate is a class 2 health hazard where intense or continued exposure could cause injury, compared to PAA and hypochlorite, which are class 3 health hazards that could cause serious temporary or moderate residual injury on brief exposure (Sodium bisulfate. MSDS No., 2013; United Stated Department of Agriculture., 2015). Approved as a food ingredient and general purpose animal feed additive, SBS has wide range of applications including use in beverages, soups, dressings, ready-to-eat meals, vegetables, fruits, pet food, poultry feed, and in drinking water (Sun et al., 2008; Calvo et al., 2010; Kassem et al., 2012; Kim et al., 2018). Sodium bisulfate is especially attractive to alternative processing facilities as it is considered “natural” according to the FDA and the International Association of Natural Product Producers (IANPP) (Kim et al., 2018).

Sodium bisulfate has several potential properties that would make it an ideal alternative sanitizer, and while limited, there is information regarding its use as a sanitizer in the food industry. Campylobacter levels were reduced by 2 to 3 log over a 6 week period when 1.13 or 1.81 kg SBS was applied to 4.6 m² poultry litter (Line, 2002). In SBS was effective in reused poultry processing water by reducing 1.5e8 CFU/100 mL of Salmonella to below the limit of detection, which was not accomplished by 200 ppm PAA. Dittoe et al. (2018) also demonstrated a 2 log reduction of Salmonella on poultry carcass rinses. To reduce S. Typhimurium on chicken carcasses 10% SBS solution was sprayed reducing concentrations by 2.4 logs (Yabin et al., 1997). Total aerobic microbial populations were decreased by 1.61 logs, and Salmonella counts were reduced by 2 logs when 5% SBS was utilized in the inside-outside bird washer (Yang et al., 1998). However, at this concentration slight discoloration was observed on the chicken carcass (Yang et al., 1998). The antimicrobial efficacy of SBS has also been tested on apples. When washed with a 1% solution of SBS and 60 ppm PAA reduced Listeria innocua by 5 logs after seven days storage compared to 150 ppm of chlorine which had only a 3.5 log reduction (Kim et al., 2018). When the treatment was increased to a 3% SBS solution with 60 ppm PAA, the 5 log reduction was also observed at day 14 (Kim et al., 2018). This bactericidal activity on apples corroborates findings in Fan et al. (2009) which demonstrated reduced total aerobic plate counts by SBS on apple slices. Further investigations into SBS efficacy as sanitizers must be performed, but due to its ability to be transported as a solid, and its relative safe use, there is noted interest on its use in poultry processing reuse water (Micciche et al., 2018).

CK is employed by the company Jones-Hamilton. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.