Biobutanol fermentation with immobilized cells using agricultural wastes and microalgal biomass as feedstock combining VMD in-situ product removal to enhance butanol production

Abstract

This study first investigated the feasibility of using two kinds of pH control methods (i e chemical addition and auto-titration) for bio-butanol production with Clostridium acetobutylicum ATCC 824 Addition of 100 mM acetate buffer could maintain the pH at a constant level and exhibiting an improvement in the butanol concentration from 2 0 g/l to 5 5 g/l Calcium carbonate was also used to maintain the pH of the ABE fermentation When the concentration of calcium carbonate was greater than 8 g/l the pH could effectively be maintained at around 4 8 which is an appropriate pH for ABE fermentation Finally the pH of ABE fermentation was controlled at 4 5 via auto-titration resulting in better butanol production of 11 1 g/l Next the renewable feedstock such as rice straw bagasse starch and microalgae biomass was used for butanol fermentation The results showed that using separated hydrolysis and fermentation (SHF) process the butanol concentration and butanol productivity were 9 1 g/l and 0 79 g/l/h respectively for rice straw and 8 4 g/l and 0 80 g/l/h respectively for bagasse On the other hand microalgal biomass was also used as feedstock for butanol production Because some inhibitors were formed during acidic hydrolysis of microalgal biomass butanol production was conducted directly using non-hydrolyzed microalgae biomass which contained high carbohydrate content (mainly in the form of starch) The results showed that butanol concentration reached 0 34 3 20 and 4 36 g/l with a microalgal biomass concentration of 60 120 and 180 g/l (equivalent to 17 4 34 8 and 52 2 g/l of starch) respectively The butanol yield and productivity found in the continuous mode at the HRT of 24 hr were 0 42±0 03 mol-butanol/mol-glucose and 0 36±0 04 g/l/h respectively In the integrated process of continuous fermentation combined with in-situ butanol removal system by vacuum membrane distillation the butanol yielded and productivity were elevated to 0 48±0 03 mol-butanol/ mol-glucose and 0 51±0 09 g/l/h respectively The feasibility of using PVA-immobilized Clostridium acetobutylicum was also examined for batch fed-batch and continuous butanol production The immobilized cells were operated on the batch mode with different kinds of cells loading and the results showed that the optimum cell loading was 20 63 g-cells/l When using the high cells loading the costly nutrient yeast extract could be completely removed from the medium with similar butanol producing performance on batch mode By integrated with VMD the fed-batch butanol production and yield were 29 g/l and 0 44 mol-butanol/mol-glucose respectively However when continuous butanol fermentation was operated with yeast extract-free medium butanol production cannot maintain steady-state after long-term operation Therefore the optimum yeast extract concentration of 1 25 g/l was used for continuous butanol production and a stable continuous culture was achieved At a HRT of 6 h the butanol concentration and productivity were 8 8±0 8 g/l and 1 47±0 14 g/l/h respectively and the steady-state operation could be maintained for more than 52 days

Date of Award	2014 Aug 9
Original language	English
Supervisor	Jo-Shu Chang (Supervisor)