Nikolay Stepanov

Production of biofuels from pretreated microalgae biomass by anaerobic fermentation with immobilized Clostridium acetobutylicum cells.

The purpose of this work was to study the possible use of pretreated biomass of various microalgae and cyanobacteria as substrates for acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum cells immobilized into poly(vinyl alcohol) cryogel. To this end, the biochemical composition of photosynthetic microorganisms cultivated under various conditions was studied. The most efficient technique for pretreating microalgal biomass for its subsequent conversion into biofuels appeared to be thermal decomposition at 108 °C. For the first time the maximum productivity of the ABE fermentation in terms of hydrogen (8.5 mmol/L medium/day) was obtained using pretreated biomass of Nannochloropsis sp. Maximum yields of butanol and ethanol were observed with Arthrospira platensis biomass used as the substrate. Immobilized Clostridium cells were demonstrated to be suitable for multiple reuses (for a minimum of five cycles) in ABE fermentation for producing biofuels from pretreated microalgal biomass.

Immobilised cells of Pachysolen tannophilus yeast for ethanol production from crude glycerol

Screening among naturally occurring yeast strains of Pachysolen spp. that are capable of producing ethanol from glycerol under aerobic conditions identified the most active culture, P. tannophilus Y -475. Conversion of glycerol by this producer immobilised in poly(vinyl alcohol) cryogel resulted in a 90% yield of ethanol relative to the theoretical limit. The maximum rate of alcohol accumulation was 0.64±0.01gL-1h-1 at a 25gL-1 concentration of glycerol in the culture medium. We demonstrated the efficacy of reusing immobilised cells (for a minimum of 16 working cycles for batch mode of crude glycerol conversion to ethanol) and the possibility of long-term (for a minimum of 140h) use of the cells in continuous mode with a maximum process productivity of 0.63±0.02gL-1h-1, while the medium dilution rate in the reactor was 0.062±0.001h-1. Reduction of metabolic activity did not exceed 5-7% relative to baseline. Immobilised cells were demonstrated to withstand long-term storage in frozen form for at least 2 years while retaining high metabolic activity.

Complex effect of lignocellulosic biomass pretreatment with 1-butyl-3-methylimidazolium chloride ionic liquid on various aspects of ethanol and fumaric acid production by immobilized cells within SSF

The pretreatment of softwood and hardwood samples (spruce and hornbeam wood) with 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) was undertaken for further simultaneous enzymatic saccharification of renewable non-food lignocellulosic biomass and microbial fermentation of obtained sugars to ethanol and fumaric acid. A multienzyme cocktail based on cellulases and yeast or fungus cells producing ethanol and fumaric acid were the main objects of [Bmim]Cl influence studies. A complex effect of lignocellulosic biomass pretreatment with [Bmim]Cl on various aspects of the process (both action of cellulases and microbial conversion of hydrolysates to target products) was revealed. Positive effects of the pretreatment with [Bmim]Cl included decreasing the lignin content in the biomass, and increasing the effectiveness of enzymatic hydrolysis and microbial transformation of pretreated biomass. Immobilized cells of both yeasts and fungi possessed improved productive characteristics in the biotransformation of biomass pretreated with [Bmim]Cl to ethanol and fumaric acid.

Biocatalytic production of extracellular exopolysaccharide dextran synthesized by cells of Leuconostoc mesenteroides

Results are presented from studies and a comparative analysis of the production of the commercially important product dextran from sucrose using fed-batch cultivated cells of the Leuconostoc mesenteroides subsp. dextranicum B-5481 bacterium either immobilized in a polyvinyl alcohol (PVA) cryogel or in the form of a suspension. It is shown that under identical process conditions, the concentration of dextran is 1.2 times higher when using immobilized cells instead of free cells. The high productivity of dextran formation (4.2 g/(L h)) under the conditions of fed-batch cultivation of the immobilized cells and the ability of these cells to function without losing their metabolic activity for at least five operating cycles are demonstrated. The productivity of the developed biocatalyst is 5 times higher than that of Weissella confusa cells immobilized in a calcium alginate gel and 34 times higher than that of Leuconostoc mesenteroides KIBGE HA1 cells immobilized in a polyacrylamide gel. The molecular weight of the dextran samples produced by the immobilized L. mesenteroides B-5481 cells is half that of the polymer produced by the free cells, expanding the range of possible applications of the polysaccharide with no additional hydrolysis.

Production of various organic acids from different renewable sources by immobilized cells in the regimes of separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SFF)

The study was aimed at production of different organic acids (OA) (lactic, fumaric, or succinic) by various microbial cells (filamentous fungi Rhizopus oryzae (F-814, F-1127) and bacteria Actinobacillus succinogenes B-10111) immobilized into poly(vinyl alcohol) (PVA) cryogel from diverse renewable raw materials (wheat and rice straw, aspen and pine sawdust, Jerusalem artichoke stems and tubers, biomass of macro- and microalgae) under batch conditions. The process productivity, bulk output and OA concentrations were higher in case of using immobilized cells than in case of free cells under identical conditions. A higher OA productivity was reached via simultaneous enzymatic saccharification and microbial fermentation (SSF) of same raw materials as compared to their separate enzymatic hydrolysis and fermentation of accumulated reducing sugars (SHF). Maximal concentrations of all OAs studied were obtained for bioconversion of Jerusalem artichoke tubers. The immobilized cells were used in long-term conversion of various renewable materials to OAs in SSF.