1 2012 International Conference on Environmental Quality Concern, Control and Conservation (EQC 2012) Application of chlorine dioxide for disinfection of student cafeteria Ching-Shan Hsu * , Da-Ji Huang and Hsin-Yi Wang Department of Environmental Resource Management, Chia-Nan University of Pharmacy and Science, Tainan, Taiwan * e-mail: hsuhsu@chna.edu.tw Abstract In Taiwan, the immediate food and drink requirements of students and faculty members are satisfied by student cafeteria. The air quality within these student cafeteria should comply with the guidelines laid down by the Taiwan Environmental Protection Agency (EPA). Accordingly, this study performed an experimental investigation into the efficiency of various chlorine dioxide applications in disinfecting a local student cafeteria (SC). The air quality before and after disinfection was evaluated in terms of the bioaerosol levels of bacteria and fungi. The average background levels of bacteria and fungi before disinfection were found to be 972.5 ± 623.6 CFU/m 3 and 1534.1 ± 631.8 CFU/m 3 , respectively. Chlorine dioxide was applied using two different methods, namely a single, one-off application, and twice applications within a single day. Among the two disinfection methods, the twice application method was found to yield a higher disinfection efficiency. Thus, using a ClO 2 disinfectant to maintain the air quality is of great importance to reduce infectious diseases in the student cafeteria. The average bacterial and fungus restraining rate for the sampling points are 64.05 % and 33.8 %, respectively. Therefore, the results suggest that the air quality guidelines prescribed by the Taiwan EPA for SCs and other healthcare facilities can best be achieved by applying chlorine dioxide at regular (twice/daily) intervals. Keywords: student cafeteria, chlorine dioxide, bioaerosols 1. Introduction The term “bioaerosols” refers to microorganisms, particles, gases, vapors or fragments of biological origin (either alive or released from a living organism) which exist in the air [1]. Bioaerosols may be suspended in the air, attached to indoor surfaces, or present in the dust accumulated within a building or any of its internal parts or operating systems (e.g. the inside walls, air-conditioning units, ducts, etc.). Given favorable conditions, bioaerosols are able to grow and propagate on a wide variety of building materials and indoor surfaces, leading to significant indoor air pollution [2]. Research has shown that prolonged exposure to bioaerosols in indoor environments may lead to infectious disease, sick building syndrome (SBS) or organic dust toxic syndrome [3]. Furthermore, elevated levels of particulate air pollution are associated with decreased lung function, increased respiratory symptoms such as coughing, shortness of breath, wheezing and asthma attacks, as well as chronic obstructive pulmonary disease, cardiovascular disease and lung cancer [4]. As a result, exposure to bioaerosols in the workplace has been a subject of growing concern in recent years [5]. In non-industrial indoor environments, the principal source of airborne bacteria is the presence of humans and related activities such as talking, sneezing, coughing, walking, washing and toilet flushing [6]. Thus, while indoor environments are supposed to be protective, they can in fact become contaminated with particles which present different and sometimes more serious risks than those in outdoor environments if their concentration levels exceed recommended safety limits. According to the National Institute of Occupational Safety and Health (NIOSH) in America and the American Conference of Governmental Industrial Health (ACGIH), the total number of bioaerosol particles in indoor environments should not exceed 1000 CFUs/m 3 , while the total culturable count for bacteria should be no higher than 500 CFUs/m 3 [7]. In Taiwan, the indoor air quality should conform to the guidelines prescribed by the Environmental Protection Agency (EPA) [8]. For schools, educational facilities, playgrounds, hospitals, clinics, and healthcare facilities for older citizens and the disabled, the indoor bacteria concentration should be no higher than 500 CFU/m 3 , while that of fungi should not exceed 1000 CFU/m 3 [9]. However, Taiwan lies in a subtropical zone, and is usually warm and humid throughout the entire year. As a result, the local climate is highly conductive to the growth of bioaerosols [10]. According to the results of one long-term monitoring study, the concentration of biological contamination in Taiwan is much higher than the value of 1000 CFU/m 3 recommended by the WHO [11]. Thus, to satisfy the EPA guidelines for the air quality in indoor environments, effective disinfection treatments are required. In Taiwan, the immediate food and drink requirements of students and faculty members are satisfied by student cafeterias. Student cafeterias (SCs) are characterized by a high level of human activity and are conducive to the generation and propagation of a large number of bioaerosols by their very nature. As a result, stringent disinfection protocols are required to ensure the