Application of 222 nm KrCl excilamp and 280 nm UVC LED for water disinfection

Abstract

In the food industry, cross-contamination, which can occur through post-harvest, process, and storage, is an important part of the food safety (Chen et al. 2001). Especially cross-contamination caused by contaminated water is more important when processing raw foods, such as fresh products and seafoods. Seafood-borne illnesses, which are a major public health problem, have been continuously reported and have increased in recent decades worldwide (Elbashir et al. 2018). Among the hazards of seafood, researchers have not only focused on norovirus, Vibrio parahaemolyticus, V. cholera, and V. vulnificus (Bonnin-Jusserand et al. 2019, Hassard et al. 2017) but have also acknowledged the risk of Salmonella and Listeria spp. contamination in seafood (Feldhusen 2000). (Amagliani et al. 2012) indicated that Salmonella has caused seafood-related outbreaks worldwide. The outbreaks are attributed to the survival ability of Salmonella under frozen, dried and high-salt conditions. (Feldhusen 2000) indicated that 4.40% of 2453 and 14.84% of 1321 investigated samples were positive for Listeria monocytogenes, a psychrotrophic pathogen that can grow at refrigerator temperature (4 °C). Therefore, it is crucial to inactivate Salmonella and Listeria spp. In seafood contaminated naturally from polluted water or cross-contaminated during the processing stage. These outbreaks show that the safety of water used for processing and washing is critical. It is obvious that disinfection is one of the most critical processing steps in fresh-cut vegetable production, affecting the quality, safety, and shelf-life of the end product (Gil et al. 2009). As mentioned above, water serves as a source of cross-contamination as re-using processing water may result in the build-up of microbial loads. Therefore, it is important to maintain the safety of wash water. Water disinfection with chlorine is a usual method in industrial, which is inexpensive and convenient to introduce it. However, there is a trend in avoiding chlorine from disinfection process because of the concern about its efficiency and more about the environmental and health risk associated with the formation of carcinogenic halogenated disinfection by products (Ölmez and Kretzschmar 2009). For these reasons, alternative methods for disinfecting water have been proposed and the most promising one is UVC irradiation. Among the ultraviolet (UV) ranges, the UV-C (200-280 nm) wavelength having the most effective bactericidal ability is widely used as antibacterial agent in water and air treatments using Hg germicidal lamps (254 nm) (Chang et al. 1985). Mercury-based UV lamps have been widely used. However, under the Minamata Convention, which came into force in August 2017 in South Korea, the manufacturing and export of germicidal lamps using mercury for industrial use will be phased out from 2020. The Minamata Convention on Mercury is dedicated to the life-cycle management of mercury in order to reduce the risks to human health and the environment (Selin 2014). Therefore, many researchers have interest in alternative light sources, such as the excimer lamp and light emitting diode (LED). The wavelengths of the excilamp vary depending on the type of rare gas and halogen used inside of the lamp. A typical example is the krypton chlorine (KrCl) excilamp that emits 222 nm UV-C light, and studies on pathogen inactivation with the KrCl excilamp have been reported recently. (Ha et al. 2017) identified that the bactericidal effect of the KrCl excilamp was more significant than the conventional mercury lamp. Pathogen inactivation mechanism by KrCl excilamp was investigated by (Kang et al. 2018), who identified that KrCl excilamp damage not only DNA but also cell membrane. The applicability of UVC LED to inactivate bacteria, yeast, and viruses was also investigated recently(Beck et al. 2017, Kim and Kang 2018, Kim et al. 2017a, b). However, many of these studies were conducted using one UV-C source, and comparative studies between the 222 nm KrCl excilamp and 280 nm UVC LED are limited. One of major applications of UV-C irradiation application is water disinfection. The inactivation trend by UV-C irradiation in water usually follows first-order kinetics, from which the inactivation rate constant (k) is calculated. The inactivation rate constant (k) not only can be used to compare the susceptibility of a pathogen to UV-C irradiation (Kim and Kang 2018) but can also be used to analyze the effect of intrinsic or extrinsic factors on the inactivation of foodborne pathogens. There are many factors affecting the inactivation of pathogens by UV-C irradiation, but turbidity is one of the most important intrinsic factors affecting the inactivation efficacy in water. When we applied alternative UV-C irradiation, such as the KrCl excilamp and UVC LED, simultaneously with the spindle system, which is used for pathogen detachment and inactivation, the turbidity of water can be varied depending on the seafood samples. For example, oysters can make water significantly turbid, while flatfish make water less turbid. Therefore, we investigate the influence factor by irradiating UVC with spindle to the seafood samples and the effect of turbidity on the inactivation of pathogens by combination treatment of the spindle system with the 222 nm KrCl excilamp or 280 nm UVC LED. Mathematical analysis was used to compare the pathogen inactivation efficacy of the KrCl excilamp and UVC LED. In addition compared the bactericidal efficacy of the KrCl excilamp and UVC LED in scale-up situation.

222nm KrCl 엑실램프 및 280 nm 자외선 발광 다이오드의 물살균에 대한 적용을 위한 연구를 진행하였다. Salmonella Typhimurium 과 Listeria monocytogenes는 다양한 탁도를 갖는 물 샘플과 접종된 해산물에 스핀들이 처리되는 물샘플에서 KrCl 엑실램프와 자외선 발광 다이오드 처리에 의해 저감화 되었다. 해산물 적용하는 실험의 샘플은 굴과 광어를 이용했는데, 굴의 경우 스핀들 처리 시에 물의 탁도가 증가하는 현상이 발생하였다. 이때 자외선 발광 다이오드 조사시 예상되는 바와 같이 굴 보다 광어 처리수에서 저감화 효과가 좋았지만, KrCl 엑실램프에서는 반대의 경향성이 나타났다. 이러한 결과는 샘플의 종류와 병원성균과 같이 탁도 이외의 요소 역시 고려해야 한다는 점을 시사한다. 탁도를 가진 물에 자외선을 처리하는 실험에서, 생존곡선을 로그 선형 모델을 사용하여 분석하여 유도된 불활성화 속도 상수 (k)를 구하였으며, Exponential one phase decay model을 통해서 불활성화 속도 상수와 탁도 간의 예측모델을 얻을 수 있었다. 이러한 예측 모델은 실제 실험을 진행하지 않은 탁도에서 얻은 실험 결과를 이용하여 검증되었다. KrCl 엑실램프 및 자외선 발광 다이오드 처리에 의한 물살균 효과는 탁도가 증가함에 따라 감소하였으며, 개발된 예측 모델은 처리하는 장치, 자외선 조사량, 샘플 탁도에 따라 두 병원균의 저감화 수준을 잘 예측하였다. 스케일 업 상황에서 KrCl 엑실램프 및 자외선 발광 다이오드의 저감화 효과를 비교한 실험 결과를 Weibull 모델을 통해 분석하였으며 계산을 통해서 D5d 값을 얻었다. 처리되는 물의 부피가 100배 증가할 때, 두 병원균 모두에서 D5d 값이 대략 KrCl 엑실램프에서는 5배, 자외선 발광 다이오드에서는 대략 3배 증가하였다. 따라서 스케일 업 환경에서 KrCl 엑실램프보다 자외선 발광 다이오드를 통한 물살균이 더욱 효과적이었다.