BIOTECHNOLOGICAL PRODUCTS AND PROCESS ENGINEERING A flow injection analysis system with encapsulated high-density Saccharomyces cerevisiae cells for rapid determination of biochemical oxygen demand Kyo Seong Seo & Kwang Ho Choo & Ho Nam Chang & Joong Kon Park Received: 10 October 2008 / Revised: 23 December 2008 / Accepted: 29 December 2008 / Published online: 20 January 2009 # Springer-Verlag 2009 Abstract The biochemical oxygen demand (BOD) deter- mination was studied using a novel flow injection analysis (FIA) system with encapsulated Saccharomyces cerevisiae cells and an oxygen electrode and was compared with conventional 5-day BOD tests. S. cerevisiae cells were packed in a calcium alginate capsule at a dry cell weight of 250 g/l of capsule core. The level of dissolved oxygen (DO) was reduced due to the enhanced respiratory activity of the microbial cells when the injected nutrient passed through the bioreactor. The decrease in DO (ΔDO) was intensified with the amount of microbial cells packed in the bioreactor. However, the specific ΔDO decreased as the amount of cells loaded in the bioreactor increased. The ΔDO value was dependent on the pH and temperature of the mobile phase and reached its maximum value at 35°C and pH 7–8. Also, ΔDO became larger at longer response times as the flow rate of the mobile phase decreased. The measurement of ΔDO was repeated more than six times consecutively using a 20-ppm standard glucose and glutamic acid solution, which confirmed the reproducibility with a standard deviation of 0.95%. A strong linear correlation between ΔDO and BOD was also observed. The 5-day BOD values of actual water and wastewater samples were in accordance with the BOD values obtained by this FIA method using encapsulated S. cerevisiae cells. Unlike the cell-immobilized bead system, there was no contamination of the bioreactor resulting from any leak of yeast cells from the sensor capsules during BOD measurements. Keywords BOD sensor . FIA . Biochemical oxygen demand . Encapsulation . High cell density . Saccharomyces cerevisiae Introduction The biochemical oxygen demand (BOD) level is used as one of the most important parameters for the estimation of water pollution caused by organic contaminants (Tan and Lim 2005). It is usually determined by measuring the amount of dissolved oxygen (DO) consumed by the inoculated microbial cells for 5 days. Conventional BOD measurements have some problems in that biological oxidation is dependent on the microbial strains, tempera- ture, pH, DO level, and the content of toxicants such as heavy metals. Most of all, the requirement for at least 5 days for BOD measurement is the main drawback (Konig et al. 2000; Liu et al. 2000; Zhang and Claude 2005). The measurement error of BOD is usually more than 10% even for a well-trained expert, and so the BOD measurement often fails to obtain reproducible results. The development of quick BOD measurement methods has been tried since Karube’ s work in 1977 (Karube et al. 1977; Karube and Suzuki 1990; Yang et al. 1997) in order to overcome the disadvantages of the conventional BOD measurement. Previous, quick BOD measurement methods Appl Microbiol Biotechnol (2009) 83:217–223 DOI 10.1007/s00253-008-1852-0 K. S. Seo : J. K. Park (*) Department of Chemical Engineering, Kyungpook National University, Daegu 702-701, Republic of Korea e-mail: parkjk@knu.ac.kr K. H. Choo Department of Environmental Engineering, Kyungpook National University, Daegu 702-701, Republic of Korea H. N. Chang Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Republic of Korea