Establishing microalgae biorefinery process for succinic acid production using an immobilized-cell fermentation system

  • 姜 雅筠

Student thesis: Master's Thesis


Succinic acid is one of the intermediates of the tricarboxylic acid (TCA) cycle Succinic acid is potentially used in food pharmaceutics cosmetics surfactants green solvents antiseptics and herbicides also as a precursor of many industrially important chemicals including 1 4-butanediol tetrahydrofuran and so on A new biodegradable polymer poly(butylene succinate) (PBS) with excellent thermal and mechanical properties as well as thermoplastic process ability can be produced by succinic acid and 1 4-butanediol converted from succinic acid Conventional succinic acid production is based on fossil oil refining which involves complicate process and expensive pollutant treatment leading to a high production cost In light of this producing succinic acid from fermentation seems to have the niche due to its merits of low pollution low energy consumption and sustainability Considering the increasing growth in the market for succinic acid it is of great demand to develop more sustainable and cost-effective succinic acid producing process In this study succinic acid was produced by microbial fermentation using polyvinyl alcohol (PVA) immobilized cells of a succinic acid-producing bacterium Actinobacillus succinogenes ATCC55618 To further enhance succinic acid production with immobilized A succinogenes ATCC55618 the PVA particle loading initial glucose concentration and carbon dioxide supply were optimized in batch fermentation The experimental results show that the optimal conditions are: PVA particle loading 15%; pH 7 0; temperature 37oC; carbon dioxide supply 45%/0 02 vvm; glucose concentration 40 g/L This results in a succinic acid concentration productivity and yield of 25 5 g/L 3 23 g/L/h and 0 875 mol/mol respectively Compared with the suspended cells the succinic acid production yield and productivity with PVA-immobilized cell fermentation were significantly improved by 1 35 1 08 1 52 times respectively In addition using 30% w/v PVA particle loading with initial glucose concentration of 40 g/L the batch culture could obtain a maximum productivity of 5 18 g/L/h with a yield and concentration of 0 937 mol/mol and 25 5 g/L respectively In the fed-batch succinic acid fermentation with cyclic glucose concentration feeding the maximum succinic acid concentration was 48 5 g/L and the productivity was 2 63 g/L/h To alleviate product inhibition encountered in fed-batch fermentation the fed-batch process was coupled with ion exchange resin to successfully remove succinic acid from fermentation broth The succinic acid concentration improved by 1 23 fold as it reached 59 5 g/L and the succinic acid yield was improved from 0 583 g/g to 0 699 g/g compared with fed batch fermentation without removal of succinic acid To develop more efficient and cost-effective process for succinic acid production continuous fermentation strategies were examined Continuous production of succinic acid with immobilized cell fermenter was stably operated for a long time (about one month) giving a had maximum productivity of 3 42±0 13 g/L/h with 6 h HRT and glucose utilization of 87 9±2 46% (glucose concentration in the feed was 40 g/L) The microalgae biomass as renewable feedstock was used to overcome the challenge of high production cost The microalgae biomass as renewable feedstock on separate hydrolysis fermentation (SHF) as carbon source and nitrogen source without yeast extract had maximum yield of 0 720 g/g and also reduced 75 8% of its production cost High performance production of succinic acid with immobilized cells using microalgal biomass as renewable feedstock by SHF has the potential to replace glucose for industrial production
Date of Award2016 Aug 30
Original languageEnglish
SupervisorI-Son Ng (Supervisor)

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