Developing a highly efficient two-stage continuous butanol fermentation process using immobilized Clostridium acetobutylicum cells

摘要

Previous studies in our laboratory showed that continuous butanol production with immobilized Clostridium acetobutylicum had great butanol productivity but suffered poor glucose utilization efficiency (ca 53%) at a short HRT of 6 h In this study a two-stage fermentation strategy was applied for butanol production to improve glucose utilization efficiency and further increase butanol productivity In this two-stage process the carbon source (totally 60 g/l of glucose) was equally divided into two halves The first half was used in the first stage for the generation of butyric acid via acidogenesis metabolism and the butyric acid was then used as the precursor for butanol production in the next stage where the second half of carbon source (i e 30 g/l glucose) was used for butanol production via solventogenesis pathway Prior to the use of the biologically-produced butyrate a commercially-acquired (synthetic) butyrate was added in batch and continuous modes to investigate the effect of butyric acid on butanol production performance The results indicated that in batch culture the addition of 5 g/l butyric acid with a glucose concentration of 60 g/l resulted in an increase in butanol concentration and yield In continuous culture with 6 h HRT feeding glucose concentration of 60 g/l with the addition of 7 g/l butyric acid the C acetobutylicum culture could achieve the highest butanol concentration productivity and yield of 8 1±0 5 g/l 1 36±0 09 g/l/h and 0 62±0 03 mol butanol/mol glucose respectively When feeding concentration of glucose was decreased from 60 to 30 g/l at an optimal butyric acid supplement of 7 g/l glucose utilization significantly increased from 53% to 100% without obvious changes in butanol production performance Moreover the stable operational period of continuous ABE fermentation with immobilized-cell system was further extended to 88 days without apparent degeneration In addition experimental design tool was applied to optimize the conditions for the continuous culture The optimal conditions determined from experimental design analysis was: glucose concentration 30-33 g/l; butyric acid 5-7 g/l; HRT 6 h Under these optimal conditions the immobilized C acetobutylicum could obtain a butanol productivity and glucose utilization efficiency of 1 2 g/l/h and 95% respectively For the two-stage operation 30 g/l glucose was fermented in the first stage using the same strain under acidogenic conditions producing nearly 8 g/l butyrate in the culture broth The effluent of the first-stage process was used to prepare the culture medium for butanol production in the second stage (solventogenic stage) The butanol fermentation in continuous culture using 30 g/l glucose supplemented with 7 g/l butyrate produced in the first stage showed similar performance to that obtained from using pure butyric acid Therefore the two-stage fermentation strategy could be successfully applied in butanol production to increase the butanol productivity and glucose utilization

獎項日期	2016 8月 25
原文	English
監督員	Jo-Shu Chang (Supervisor)