Disinfection of water process

Disinfection of process water: Alternatives to chlorine in the horticultural industry

Disinfection of water process. Chemical free water disinfection.

Europe is leaning towards banning chlorine use in industrial horticulture. Countries like the UK, Holland and Belgium have already done so. Alternatives are needed.


Growth in demand for packaged fresh-cut fruit and vegetables (“fourth range”) is widespread throughout Europe, and it is a sector which uses significant quantities of drinking water (40 m3 / ton). These industries therefore require new, relatively low-cost, efficient strategies and technologies to reduce and reuse process water. To this end, the need arises for new waste water treatment technologies in the food industry, and new strategies for water re-use in this sector. Chlorine is being banned for this application throughout Europe due to problems arising from carcinogenic byproducts that it generates. Therefore we need to investigate new treatment technologies for this type of process water that eliminate pesticides and preservatives from horticultural products and that control the presence of pathogens responsible for transmission of diseases caused by contaminated food (Escherichia coli O157: H7, Listeria monocytogenes, Salmonella spp.), and also improve the physical and chemical quality of process waters.

Cristina Pablos Carro. URJC Group

Human eating habits have changed a lot in the last two decades. The current pace of life, with little time to prepare balanced meals, has triggered a demand for natural, fresh-cut, healthy and ready-to- consume vegetable products. These are known as minimally processed fresh (MPF), commercially called “fourth (IV) range” [1]. The average annual increase in this type of product in Spain has been 3-5% corresponding to a turnover of 200 million euros [2]. Florette, Verdifresh, or Primaflor are examples of the main companies in Spain that target their products for IV range, while the hotel sector is one of the main sectors that requires IV range products[1].

Thus, the term “IV products” means those fresh-cut fruit and vegetable products which have not undergone any type of heat treatment and only minimal processing (mainly washing, cutting and packaging in a modified atmosphere) and which are more practical to use because they are prepared and ready for consumption or cooking, maintaining their natural and fresh properties. They do not incorporate any type of additive or preservative, and therefore must be kept refrigerated. The useful life of this type of product in microbiological, sensory and nutritional terms varies from 7-10 days. The main processing stages of this type of product are: (i) reception of raw material, (ii) selection of product, (iii) cutting, (iv) washing, and rinsing if a chemical disinfectant is used during washing, (v) centrifuging (drying), and (vi) packaging of the product, always working within a cold temperature range from 3 to 7 ° C [1].

Note the importance of maintaining the microbiological quality of these products since they are made without pasteurization or equivalent to deactivate microorganisms and are also destined for consumption without prior cooking. The cut vegetable products are much more perishable than the intact ones as they are subjected to mechanical stress. This leads to a reduction in useful shelf life as well as biochemical and microbiological alterations that must be controlled to maintain the sensory and nutritional properties of the product. In particular, cutting the product favours the availability of cellular nutrients that can be used by the accompanying microflora for its development during the stage of preserving the product in the package. The loss of water that also occurs as a result of cutting the vegetable equally favours the attack of micro organisms.

In spite of progress being made in the IV range sector to reduce contamination risks, these fruit and vegetable products have been implicated in some public health problems. Psychrotrophic microorganisms in particular are the main reason for concern as they are able to grow at refrigeration temperatures, necessary in the preservation of IV gamma products. The European Food Safety Authority (EFSA) has reported an increase in food borne diseases in relation to this type of product, with the main pathogens being responsible for bacteria such as Shigella, Salmonella, L. monocytogenes and E. coli O157 : H7; And norovirus [3]. Hence the development of new emerging and sustainable technologies to ensure the sensory, nutritional quality and food safety of IV range products.

The quality of water in the processing stage is critical since the use of inferior quality wash water can serve as a vector for propagation of bacterial contamination [4]. Water is used in different stages such as cooling, rehydration, selection and transport, washing and rinsing and surface cleaning. However, the washing and rinsing stage of the process is determinant in guaranteeing the quality, safety and useful life of the product and requires drinking quality water (98/83 / EC) [5]. Its main purpose is to eliminate dirt and the microbial load [6] to reduce microbial growth and to delay enzyme activity.

Requirements imposed by microbiological quality regulations of the final product (RD 3484/2000) [7] are difficult to achieve without adding chemicals to washing systems or using an alternative disinfection technology. Chlorine in the form of sodium hypochlorite (NaOCl) is the most industrially used disinfectant in the washing of IV gamma products at a temperature of 3-7 ° C. The concentration of NaOCl used corresponds to 100-250 ppm. Its most active form as a disinfectant is that of hypochlorous acid (HOCl), but at pH above 5, HOCl dissociates. In such cases, rinsing of the product after washing is needed to remove chlorine residues from the product. Generally, a standard wash with 100-150 ppm of NaClO at pH 6.5 results in a reduction in the concentration of mesophilic, psychotrophic and enterobacterial microorganisms from 1 to 2 log units in the product [8].

However, the use of chlorine as a disinfectant leads to the formation of halogen compounds with carcinogenic potential in the presence of organic matter in water such as trihalomethanes (THM) and haloacetic acids (AHA). In addition, the efficacy of chlorine as a disinfectant in washing is determined by the location of the pathogen in the plant leaf: The internalization of microorganisms in plant tissues, the inaccessibility of chlorine to bacteria in holes or fissures of plant tissue, and the presence of biofilms and waxes in vegetable tissues reduce the efficiency of chlorine disinfection [8]. Nor is there a common regulation in Europe on the use of chlorine in the IV gamma processing industry. Countries such as the Netherlands, Belgium, and the United Kingdom prohibit their use for security reasons. In Europe, its use in organic products is also banned (834/2007 / EC) [9]. In general, the trend in Europe is aimed at eliminating chlorine from the disinfection process [10].

A second problem presented by these types of industries is the need to minimize water consumption and rate of waste water discharge. In these processes a continuous intake of drinking water (5-10 l / kg product) is necessary to maintain the quality of wash water and to prevent the accumulation of microorganisms in the water, as well as the transfer of microorganisms from the wash water to the next batch of the product. The accumulation of color, organic matter, pesticides and microorganisms makes it unfeasible to reuse water without prior treatment. Also note the importance of reducing the presence of pesticides in vegetable wash water. European legislation establishes the maximum permissible levels of pesticides in water: 0,1 μg / L per pesticide individually and 0,5 μg / L as a sum of components (98/83 / EC 1998) [5]. Although the legislation establishes maximum levels of pesticides in the final product corresponding to 0.01 mg / kg (396/2005 / EC) [11]. When present in the product at trace levels they may, by transfer through wash water, contaminate the next batch of the product.

Pre-tested and authorized chlorine alternative disinfectants (Generally Regarded as Safe, GRAS) are being studied. Currently, disinfectants that can replace NaClO are peroxyacetic acid, acidified sodium clorite, sodium dodecyl benzene sulfonate, chlorine dioxide and lactic acid among others [8,12-14]. Note the recent commercial application in the horticultural industry itself of washing with ozonated water (O3) and washing with ozone (O3) and electro-oxidation (EO) [15, 16]. Ozone scrubbing is also being applied along with UV-C radiation to induce the synthesis of compounds beneficial to health in the product, such as resveratrol in grapes [12], as well as to inactivate enzymes related to the processes of maturation and senescence of the product.

Under this framework, the coordinated project “Development and Evaluation of Novel Photochemical and Biological Processes for Treatment and Reuse of Water in Food Industries” (WATER4FOOD, CTQ2014-54563) is being developed. This research project is funded by the Ministry of Economy and Competitiveness. Its objectives include: (i) increasing the safety of plant products in IV range and (ii) offering alternative ways to reduce water consumption and, consequently the energy cost of the process. The participating research groups are the Rey Juan Carlos University, CIEMAT-PSA, and the University of Córdoba. In this project disinfection treatments of wash water are being developed with the objective of reusing water in the industrial plant itself or even for irrigation. The main technologies to be developed are based on Advanced Oxidation Processes (PAO’s) such as photocatalysis with TiO2 (UV-A / TiO2); Photocatalysis with TiO 2 / microfiltration (UV-A / TiO 2 / MC); UV-C / microfiltration light (UV-C / MC); Ozone / hydrogen peroxide (O3 / H2O2); H2O2 / sunlight; and photo-fenton solar). These technologies also allow the oxidation of pesticides.


[1] Newsletter “Infoagro”, “Fourth range. An alternative of the future “. Http:// Date of last access: 20/02/2017.

[2] Afhorla, Spanish Association of Fruits and Vegetables Washed Lists for use (IV Range). Http:// Date of last access: 12/15/2016

[3] Callejón, R. M., Rodríguez-Naranjo, M. Isabel, Úbeda, C., Hornedo-Ortega, R., Garcia-Parrilla, M. C., Troncoso, A. M. (2015). Reported foodborne outbreaks due to fresh produce in the United States and European Union: trends and causes. Foodborne Pathogens and Disease, 12 (1), 32-38.

[4] Gil, M. I., Selma, M. V., López-Gálvez, F., Allende, A. (2009). Review: Fresh-cut product sanitation and wash water disinfection: Problems and solutions. International Journal of Food Microbiology, 134, 37-45.

[5] European Directive 98/83 / EC, 1998 on the quality of water intended for human consumption.

[6] Artés, F. (2000). Processed fresh vegetables. In: Application of cold to food. Publisher: M. Lamúa. A. Madrid Editions. Cap.5. 127-141.

[7] Royal Decree 3484/2000 of 29 December 2000 laying down hygiene rules for the preparation, distribution and trade of prepared foods

[8] Sapers, G.M. (2001). Efficacy of washing and sanitizing methods for disinfection of fresh fruit vegetable products. Food Technology and Biotechnology, 39 (4), 305-311.

[9] European Directive 834/2007 / EC, 2007 on the production and labeling of organic products.

[10] Ölmez, H., & Kretzschmar, U. (2009). Review: Potential alternative disinfection methods for organic fresh-cut industry for minimizing water consumption and environmental impact. LWT – Food Science and Technology, 42, 686-693.

[11] European Directive 396/2005 / EC, 2005 on maximum residue limits of pesticides in food and feed of plant and animal origin.

[12] Gil, M. I., Allende, A., Beltrán, D., Selma, D. (2005). New Trends in Processing and Conservation of IV Range Vegetable Foods. CTC Feeding, 26, 146-151. Http:// Date of last access: 21/02/2017.

[13] Artés, F., Gómez, P.A., Aguayo, E., Escalona, ​​V. H., Artés-Hernández, F. (2009). Sustainable sanitation techniques for keeping quality and safety of fresh-cut plant commodities. Postharvest Biology and Technology, 51, 287-296.

[14] Aguayo, E., Escalona, ​​V. H., Artés-Hernández, F., Artés, F. (2007). Emerging and sustainable techniques for the disinfection of minimally processed fruits and vegetables. Phytoma, 189, 138-142.

[15] Newsletter “Water Blog”, February 2017. “APRIA and SITRA participate in a water treatment research project for the horticultural industry.” Http:// -in-a-project-of-research-of-treatment-of-water-for-industry-hortofruticola / Date of last access: 02/20/2017.

[16] El Periódico Mediterráneo, January 2017. “Ozoncas revolutionizes the purification of waters and organic in horticultural plants.” Http:// -hortofruticolas_1045915.html Date of last access: 02/20/2017.