Volatile fatty acids derived from waste organics provide an economical carbon source for microbial lipids/biodiesel production

Abstract

Volatile fatty acids (VFAs) derived from organic waste, were used as a low cost carbon source for high bioreactor productivity and titer. A multi-stage continuous high cell density culture (MSC-HCDC) process was employed for economic assessment of microbial lipids for biodiesel production. In a simulation study we used a lipid yield of 0.3 g/g-VFAs, cell mass yield of 0.5 g/g-glucose or wood hydrolyzates, and employed process variables including lipid contents from 10-90% of cell mass, bioreactor productivity of 0.5-48 g/L/h, and plant capacity of 20 000-1 000 000 metric ton (MT)/year. A production cost of USD 1.048/kg-lipid was predicted with raw material costs of USD 0.2/kg for wood hydrolyzates and USD 0.15/kg for VFAs; 9 g/L/h bioreactor productivity; 100,000 MT/year production capacity; and 75% lipids content. The variables having the highest impact on microbial lipid production costs were the cost of VFAs and lipid yield, followed by lipid content, fermenter cost, and lipid productivity. The cost of raw materials accounted for 66.25% of total operating costs. This study shows that biodiesel from microbial lipids has the potential to become competitive with diesels from other sources. Keywords: Economic assessment · Low cost biomass · Microbial lipids · MSC-HCDC · VFAsCorrespondence: Prof. Ho Nam Chang, Laboratory of Biochemical Engineering, Department of Chemical and Biomolecular Engineering, KAIST, Yuseong-gu, Daejeon 305-701, Korea E-mail: hnchang@kaist.edu Current address: Qiang Fei, National Bioenergy Center, National Renewable Energy Laboratory, Golden, Colorado, U.S.A.Abbreviations: AOC, annual operating costs; B, bleed ratio; C X , concentration of cell; C L , concentration of lipid; DFC, direct fixed capital costs; MSC-HCDC, multistage continuous high cell density culture; MT, metric ton, 1000 kg; PHB, poly-β-hydroxybutyric acid; RT, residence time; TBV, total bioreactor volume; VFAs, volatile fatty acids; WH, wood hydrolyzates Biotechnol. J. 2014Biotechnol. J. , 9, 1536Biotechnol. J. -1546 Biotechnology JournalVolatile fatty acids (VFAs), which can be produced from food waste, sludge, and a variety of biodegradable organic wastes under anaerobic conditions, are the basis for a VFAs platform [3,4]. VFAs are a potential economical alternative carbon source for lipid accumulation by oleaginous microorganisms [5]. Although many batch or fed-batch cultures have been carried out for lipid production [6][7][8], bioreactor productivity was not high enough for viable commercial production. Multi-stage continuous high cell density culture (MSC-HCDC) is considered to be a fermentation technology that can lead to high productivity and titer for both extracellular and intracellular products [9,10]. High cell density culture fermentation gives a very high productivity because of its high cell density achieved by membrane cell recycling, or a moderate cell density attained by using a packed-bed combined with gravity settling [11][12][13][14].Fei et al. [15,16] achieved a lipid content of 55% (w/w) using VFAs...

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