Performance evaluation and microbial community analysis of the biofilter for removing grease and volatile organic compounds in the kitchen exhaust fume
Graphical abstract
Introduction
Kitchen exhaust fume, industrial pollution and vehicle exhaust emission are regarded as the “three killers” of urban air (Zhang et al., 2020). Due to the popularization of commercial kitchens in China, the complaints about kitchen exhaust fume have accounted for an increasing proportion of the overall environmental complaints (Li et al., 2017, Li et al., 2018, Zhang et al., 2020). Commercial kitchens in China have their own cooking characteristics, such as long cooking time, serried kitchenware, large amount of oil and various cooking seasoning (Song et al., 2018). The emission method of kitchen exhaust fume is usually low-altitude ventilation, which makes the fume difficult to diffuse. Moreover, urban “heat island effect” makes the exhaust fumes stay in the atmosphere for a long time, seriously affecting the ecological environment and human health (Tan et al., 2010).
The main components of kitchen exhaust fume are oil droplets with different diameters and various volatile organic compounds (VOCs). Edible oil is decomposed into oil droplets with a diameter of more than 10−3 cm at 100 ~ 270 °C and 10−7 ~ 10−3 cm above 270 °C, respectively (Kalua et al., 2007). Some organic substances in ingredient have oxidation reaction, cracking reaction and hydrolysis reaction with oil at high temperature, producing a variety of complex organic compounds such as aldehydes, ketones, alkanes and polycyclic aromatic hydrocarbons (Gutierrez et al., 2008). At the same time, fuels such as coal and liquefied gas release SOx, COx, NOx and other pollutants during the combustion process. Specially, various aldehydes have different degrees of pungent odor and toxicity, which is the main reason of complaints about kitchen exhaust fume. Owing to the unique cooking recipes in Chinese commercial kitchens, the exhaust fumes contain a variety of toxic and harmful substances, such as benzothiazole, phenanthrene and polycyclic aromatic hydrocarbons (PAH) , which are strong carcinogens (Ravindra et al., 2008). After entering the human body, these harmful substances will cause strong stimulation to the respiratory system and reduce the body's immunity, resulting in respiratory diseases such as rhinitis, pharyngitis, bronchitis, and asthma. A number of accumulations in the body may even cause chronic poisoning, genetic mutations, and gene damage. Therefore, how to deal with kitchen exhaust fume has become a hotspot in the control of urban air pollution (Mudie & Vahdati, 2017).
Treatments of kitchen exhaust fume have been rapidly developed due to the increasing concerns of the public on the wide variety of pollution and poor environmental sanitation caused by kitchen exhaust fume. Cheng and Hsieh (2010) integrated the chemical scrubber with sodium hypochlorite and surfactants to remove non-methane hydrocarbons in cooking oil fume, and 85% of removal efficiency was obtained. Li et al. (2018) used nano-sized TiO2 photocatalytic reaction combined with ozone oxidation technique to remove volatile organic compounds in cooking fume. Compared with the chemical absorption and the photocatalytic reaction, the biological method has been paid attention to the removal of kitchen waste due to low operating costs and no secondary pollution. Mudie et al. (2017) utilized the biological activity of Bacillus subtilis and associated enzymes to reduce the fat, oil and grease in commercial kitchen ductwork. The results indicated that the deposition thickness of fat, oil and grease decreased by 47% within 7 weeks. Biofilter, a new type of biotechnology, has been widely used to remove volatile organic pollutants, such as aldehydes, benzenes, and polycyclic aromatic hydrocarbons (Hajizadeh et al., 2018, Jamshidi et al., 2018). When the kitchen exhaust fume was absorbed in the packing media, microorganisms then consume these substrates in the liquid phase as carbon sources (Yang et al., 2018a). However, as far as we know, there is still a lack of research on the removal of kitchen exhaust fume through biological filters. Filler is the key component of the biofilter to remove kitchen exhaust fume, playing an important role in substance transfer and providing an environment for microorganisms to grow (Yan et al., 2020b). Corncob is an easily available and cheap agricultural by-product. The activated carbon derived from corncob has a large specific surface area and strong adsorption property, thus it can be used as filler for biofilters to remove grease and total volatile organic compounds (TVOCs) in kitchen exhaust fume (Kumar et al., 2019). Therefore, it is essential to optimize the operation conditions of the biofilter and analyze the microbial community structure of corncob-based activated carbon as filler (Yang et al., 2018a).
The main objective of this study was to evaluate the performance of a biofilter packed with corncob-based activated carbon under various inlet loading rates of grease and TVOCs. Based on the analysis of the removal efficiency, pH, elimination capacity, and filler moisture content in the 45-day experiment period, the performance of the biofilter was further evaluated to obtain a new idea for degradation of kitchen exhaust fume. Additionally, special attention was paid to investigate the variation of the microbial community, providing guidance for practical applications (Han et al., 2016).
Section snippets
Experimental setup
The schematic diagram of the experimental setup used in this study is illustrated in Fig. 1. The exhaust fume to be purified was derived from a commercial kitchen in the High-Tech Development Zone in Zhengzhou City. The biofilter was made from fiberglass with a thickness of 5 mm, a length of 1.5 m, a width of 1.5 m, and a height of 1.5 m. The filler packed in the biofilter is corncob-based activated carbon (produced by the activation of corncob at 850 °C; equivalent diameter 6 ± 1 cm) with a
Performance of the biofilter for grease and TVOCs removal
The time-dependent removal efficiencies of the grease (a) and TVOCs (b) with change of pH (c) are presented in Fig. 2. In the start-up phase, the removal efficiency of grease dropped rapidly from 92% to 46% on the 3th day as the inlet loading rate increased from 56.9 to 87.5 g/(m3·h), and then showed a continuous growth trend to 92% until the 10th day. Unlike grease, the RE of TVOCs has increased steadily from 47% to 90%. This phenomenon may be due to that the fillers, activated carbon,
Conclusion
The biofilter packed with the corncob-based activated carbon could start up quickly with high RE, and it can tolerate the change of transient shock loadings. During the 45-day experimental period, the ECmax of the biofilter for grease and TVOCs were 112 and 235 g/(m3·h), respectively. In addition, the pH and moisture content of the filler had a certain effect on the removal efficiency. Compared with the suspension, the microbial community structure of the filler was more concentrated, mainly
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was funded by the National Natural Science Foundation of China (No.U1304216), the Science and Technology Plan of He’nan Province, China (No. 122102310366), and the University Key Research Project of He’nan Province, China (No. 19A610002 and 19A150010).
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