Biotreatment of Ammonia from Air by an Immobilized Arthrobacter oxydans CH8 Biofilter Ying-Chien Chung, † Chihpin Huang,* ,†,‡ and Ching-Ping Tseng § Institute of Environmental Engineering and Institute of Biological Science and Technology, National Chiao Tung University, Hsinchu, Taiwan 30039, ROC A heterotrophic Arthrobacter oxydans CH8 that was capable of removing NH 3 from NH 3 containing gas was isolated from livestock farming wastewater. The A. oxydans CH8 was immobilized with calcium alginate packed into filter column. Metered NH 3 - containing gas was partially humidified and passed through the glass column. Extensive tests including the removal characteristics, the removal efficiencies, and the metabolic products of NH 3 by A. oxydans CH8 were conducted. Additionally, the operation criteria for the biofilter was also established. NH 3 removal capacities were elevated by the immobilized-cell (biological conversion) method and the BDST (bed depth service time) method (physical adsorption), respectively. The optimum tem- perature for removing NH 3 was 30 °C, while the nitrification ability remained 80% at 40 °C. The high efficiency (>97%) in the removal of NH 3 was attained at 36 L/h with pH control and was not decreased because of high NH 3 inlet concentration. In addition, the high maximum removal rate (1.22 g of N/day‚(kg of bead)) enhanced the use of the biofilter in industrial-scale NH 3 (g) pollution control. The ability to remove NH 3 at high inlet concentration and temperature suggested that the immobilized A. oxydans CH8 biofilter has potential in processing NH 3 gas. Introduction Ammonia (NH 3 ) is a colorless air pollutant with a strong and repellent odor. The ammonia emissions range from 10 to 60 ppm in livestock farming in Taiwan (Chung et al., 1996a). A considerable amount of NH 3 is also released by industrial processes, such as petrochemical refining, metal manufacturing, food preparation, paper and pulp manufacturing, and textile industries (Ryer- Power, 1991). Control of NH 3 emissions is essential to mitigate the environmental impact (Prosser, 1989) and to protect public health (Ryer-Power, 1991). The physical and chemical processes that have been used to remove NH 3 from waste gas and wastewater include activated carbon adsorption, wet-scrubber, incineration, and air stripping (Durme et al., 1992; Barth et al., 1984; Man- nebeck, 1986). But, the corresponding costs for such technologies and their disposals are economically incom- petitive, and secondary-pollutant issues may arise. Re- cently, the focus has been shifted to investigation of the microbial alternatives to conventional methods (Bohn, 1992). Biofiltration has been proven to be an effective and inexpensive method, especially when applied to dilute, easily biodegradable waste gases under appropri- ate sets of conditions (Leson and Winer, 1991). However, the biofilter may cause environmental risks because bioaerosols (fungi and bacteria) can be released from the biofilter into the ambient air (Hartikainen et al., 1996). Recently, these disadvantages have been overcome by using an immobilized-cell method. The immobilized-cell technology has been applied for wastewater treatment because of its many advantages, such as prevention of cell losses, high microbe contents, high tolerance to environmental impact, and high stabil- ity during the operation period (Ginkel et al., 1983; Asano et al., 1992). However, little information is available for NH 3 (g) removal from air gas by immobilized-cell technol- ogy. In addition to selection of appropriate packing materi- als, it is also important to use an effective species for optimizing ammonia treatment. Autotrophic bacteria, such as ammonia oxidizers, have been characterized phylogentically Teske et al. (1994). The most extensively studied and applied ammonia oxidizer is Nitrosomonas europaea (Hunik et al., 1992). Autotrophic nitrifiers have a high nitrification rate, but it would lose superiority in the nitrification processes under certain conditions, such as low oxygen concentration, high NH 3 concentration, and high temperature (Prosser, 1989). Conversely, the het- erotrophic nitrifiers, such as Alcaligenes, Pseudomonas, Bacillus, and Arthrobacter species, are superior competi- tors, especially under acid environments (Kuenen and Robertson, 1988). Although the data indicate that the nitrification rate of the heterotrophs is 10 3 -10 4 times smaller than that of the autotrophs, the biomass con- centrations of heterotrophic nitrifiers are 10 4 -10 5 times greater than those of autotrophs which can compensate for the removal capacity (Prosser, 1989). Growth of autotrophic ammonia oxidizers is considered inefficient in comparison to that of heterotrophs due to the small energy gain obtained from the oxidation of ammonia. Hence, the use of heterotrophic ammonia oxidizers for NH 3 containing waste gas was evaluated. Cells immobilized in calcium alginate beads for H 2 S- (g) removal has been regarded as a potential method because of their high removal efficiency, removal capacity (Chung et al., 1996b; Huang et al., 1996), and the economic consideration. In this study, we developed an innovative NH 3 gas treatment method by an immobilized Arthrobacter oxydans CH8 biofilter and also conducted a quantitative investigation into the principles and operation of a biofilter system for NH 3 removal. * To whom correspondence should be addressed. † Institute of Environmental Engineering. ‡ E-mail: cphuang@green.ev.nctu.edu.tw. § Institute of Biological Science and Technology. 794 Biotechnol. Prog. 1997, 13, 794-798 S8756-7938(97)00065-9 CCC: $14.00 © 1997 American Chemical Society and American Institute of Chemical Engineers