Effect of operating conditions of thermochemical liquefaction on biocrude production from Spirulina platensis.

This study investigated the optimum thermochemical liquefaction (TCL) operating conditions for producing biocrude from Spirulina platensis. TCL experiments were performed at various temperatures (200-380°C), holding times (0-120 min), and solids concentrations (10-50%). TCL conversion at 350°C, 60 min holding time and 20% solids concentration produced the highest biocrude yield of 39.9% representing 98.3% carbon conversion efficiency. Light fraction biocrude (B(1)) appeared at 300°C or higher temperatures and represented 50-63% of the total biocrude. Biocrude obtained at 350-380°C had similar fuel properties to that of petroleum crude with energy density of 34.7-39.9 MJ kg(-1) compared to 42.9 MJ kg(-1) for petroleum crude. Biocrude from conversion at 300°C or above had 71-77% elemental carbon, and 0.6-11.6% elemental oxygen and viscosities in the range 40-68 cP. GC/MS of biocrude reported higher hydrocarbons (C(16)-C(17)), phenolics, carboxylic acids, esters, aldehydes, amines, and amides.

Effect of redox potential on stationary-phase xylitol fermentations using Candida tropicalis.

Redox potential was used to develop a stationary-phase fermentation of Candida tropicalis that resulted in non-growth conditions with a limited decline in cell viability, a xylitol yield of 0.87 g g(-1) (95% of the theoretical value), and a high maximum specific production rate (0.67 g g(-1) h(-1)). A redox potential of -100 mV was found to be optimum for xylitol production over the range 0-150 mV [correction]. A shift from ethanol to xylitol production occurred when the redox potential was reduced from 50 mV to 100 mV as cumulative ethanol (Y(ethanol)) decreased from 0.34 g g(-1) to 0.025 g g(-1) and Y(xylitol) increased from 0.15 g g(-1) to 0.87 g g(-1) (alpha=0.05). Reducing the redox potential to 150 mV did not improve the fermentation. Instead, the xylitol yield and productivity decreased to 0.63 g g(-1) and 0.58 g g(-1) h(-1) respectively and cell viability declined. The viable, stationary-phase fermentation could be used to develop a continuous fermentation process, significantly increasing volumetric productivity and reducing downstream separation costs, potentially by the use of a membrane cell-recycle reactor.

Oxygen starvation induces cell death in Candida shehatae fermentations of D-xylose, but not D-glucose.

Candida shehatae cells, cultivated on D-glucose and D-xylose, were subjected to a shift from fully aerobic to anaerobic fermentative conditions. After anaerobic conditions were imposed, growth was limited to approximately one doubling or less as C. shehatae rapidly entered a stationary phase of growth. Following the shift to anoxia, cell viability rapidly declined and the total cell volume declined in the D-xylose fermentations. Moreover, the cell volume distribution shifted to smaller volumes. Cell viability, measured by plate counts, declined nine times faster for D-xylose fermentations than for D-glucose fermentations. Anaerobic growth did not occur on either D-glucose or D-xylose. Selected vitamins and amino acids did not stimulate anaerobic growth in C. shehatae, but did enhance anaerobic growth on D-glucose in S. cerevisiae. The decline in cell viability and lack of anaerobic growth by C. shehatae were attributed to oxygen deficiency and not to ethanol inhibition. The results shed light on why C. shehatae anaerobic fermentations are not currently practical and suggest that research directed towards a biochemical understanding of why C. shehatae can not grow anaerobically will yield significant improvements in ethanol fermentations from D-xylose.

Microbial Production of Poly-beta-Hydroxybutyric Acid from d-Xylose and Lactose by Pseudomonas cepacia.

Poly-beta-hydroxybutyric acid (PHB) was produced from xylose and lactose by using Pseudomonas cepacia. Approximately 50% PHB (grams of PHB total/grams of biomass total) was produced. With a laser-based fluorescent probe, beta-galactosidase activity was shown to be induced in P. cepacia cells grown on lactose but not in those grown on glucose or xylose. P. cepacia has the potential to produce biodegradable thermoplastics from hemicellulosic hydrolysates and cheese whey.

Viability of Candida shehatae in D-xylose fermentations with added ethanol.

Ethanol was added at concentrations of 25 and 50 g/L to active cultures of Canida shehatae under oxygen-limited (fermentative) conditions. Added ethanol completely inhibited growth and fermentation of D-xylose by C. shehatae. Cultures with added ethanol rapidly declined in cell viability as measured by plate counts and methylene blue staining. The rate of decline in cell viability was dependent on the amount of added ethanol. Over the course of the fermentation, cell viability, as measured by plate counts, was significantly lower in all experiments (with or without ethanol addition) compared with the viability measurements by methylene blue staining. Thus, data from the plate counts provided a more sensitive measure of the toxic effects of added ethanol and long-term anaerobiosis on C. shehatae growth/fermentation. Mean cell volume and total cell volume declined in fermentations with added ethanol.