Air-lift Fermentor

Abstract

Air lift Fermentor (ALF) is used for production of Single-Cell Protein (SCP) from hydrocarbon. In this research, we investigated the performance of ALF using the methanol fermentation system and compared the results with that of CSTR system from the viewpoint of mixing state, since the mixing is done only by seration in ALF. The effect of micro-mixing on cell growth and the parameters which affect the degree of the micro-mixing were also studied. The experiments were carried out in 9- ALF using the Methylomonas, sp. whose miximum specific growth rate and substrate saturation constant was 0.526 hr-1 and 0.085 g/l respectively. When the concentration of sole carbon source, methanol was 0.2\% (V/V), the maximum productivity of SCP in ALF was 0.189 g/l-hr and that of themostat was 0.208 g/l-hr. While the methanol concentration was increased to 1\%, the maximum productivity of chemostat was 0.852 g/l-hr, but that of ALF was 0.465 g/l which was only 55\% of chemostat. To find the reason for low productivity, we carried out the continuous culture in ALF using the oxygen enriched air. The results showed that the main reason was lack of oxygen supply rather than insufficient mixing. But the liquid system was partially segregated, and the micro-mixing effect was observed. To represent the degree of micro-mixing quantitatively, we simulated the cell growth in ALF with aid of a computer, and determined the degree of segregation using the results of computer simulation and experiments. When the methanol concentration was low, the effect of aeration rate was negligible, or degree of segrgation was constant at the 0.05, as long as the oxygen was not limiting. In case of higher methanol concentration, the degree of segregation was increased from 0.2 to 0.34, as the aeration rate was decreased from 3 to 0.5 vvm while dissolved oxygen was kept constant. From these observation, it was concluded that aeration rate and methanol concentration affect the degree of micro-mixing in ALF...