Browsing by Subject "Co-culture"

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    Bio-fuel production by using integrated anaerobic fermentation.
    (2012-01) Xu, Lei
    Saccharification is one of the most critical steps in producing lignocellulose-based bio-ethanol through consolidated bioprocessing (CBP). However, extreme pH and high ethanol concentrations are commonly considered potential inhibitors for the application of Clostridium sp. in CBP. The fermentation of several saccharides derived from lignocellulosics was investigated with a co-culture consisting of Clostridium themocellum and Clostridium thermolacticum with or without immobilization. Alkali environments proved to be more favorable for ethanol production. Fermentation inhibition was observed at high ethanol concentrations (>8g/L) and extreme pH (>10). However, low levels of initial ethanol addition resulted in an unexpected stimulatory impact on the final ethanol productions for all cultures under selected conditions. The co-culture was able to actively ferment glucose, xylose, cellulose and micro-crystallized cellulose (MCC). The ethanol yield observed in the co-culture was higher (up to two-fold) than in mono-cultures, especially in MCC fermentation. The highest ethanol yield (as a percentage of the theoretical maximum) observed were 75% (w/w) for MCC and 90% (w/w) for xylose. Immobilization technique using sodium alginate is efficient in improve the ethanol production during co-culture fermentation, although the immobilization is not able to change the ethanol sensitivity of this co-culture. The ethanol yield through the use of immobilized technique increased to 97% of the theoretical efficiency for glucose. For cellobiose and MCC under optimized condition, the ethanol yields were approaching 85% of the theoretical efficiency. In order to examine the feasibility of this immobilization co-culture on lignocellulosic biomass conversion, untreated and pretreated aspen fermentations were performed. The immobilization co-culture shows clear benefit in bio-ethanol production in CBP process. With a 3h, 9% NaOH pretreatment, the aspen powder fermentation yield approached 78% of the maximum theoretical efficiency, which is almost twice the yield of the untreated aspen fermentation. Keywords: Consolidated bioprocessing, Clostridium sp., Fermentation, Co-culture, Lignocellulosic ethanol, Immobilization, Alginate gel.
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    Microalgae harvesting via co-culture with filamentous fungus
    (2013-07) Gultom, Sarman Oktovianus
    Microalgae harvesting is a labor- and energy-intensive process. For instance, classical harvesting technologies such as chemical addition and mechanical separation are economically prohibiting for biofuel production. Newer approaches to harvest microalgae have been developed in order to decrease costs. Among these new methods, fungal co-pelletization seems to be a promising technology. By co-culturing filamentous fungi with microalgae, it is possible to form pellets, which can easily be separated. In this study, different parameters for the cultivation of filamentous fungus (Aspergillus niger) and microalgae (Chlorella vulgaris) to efficiently form cell pellets were evaluated under heterotrophic and phototrophic conditions, including organic carbon source (glucose, glycerol and sodium acetate) concentration, pH, initial concentration of fungal spores, initial concentration of microalgal cells, concentration of ionic strength (Calcium and Magnesium) and concentration of salinity (NaCl). In addition, zeta-potential measurements were carried out in order to get a better understanding of the mechanism of attraction. It was found that 2 g/L of glucose, a fungus to microalgae ratio of 1:300, and uncontrolled pH (around 7) are the best culturing conditions for co-pelletization. Under these conditions, it was possible to achieve a high harvesting performance (>90%). In addition, it was observed that most pellets formed in the co-culture were spherical with an average diameter of 3.5 mm and in concentrations of about 5 pellets per mL of culture media. Under phototrophic conditions, co-pelletization required the addition of glucose as organic carbon source to sustain the growth of fungi and to allow the harvesting of microalgae. Zeta-potential measurements indicated that (i) both microalgae and fungi have low zeta-potential values regardless of the pH on the bulk (i.e. <-10 mV) (ii) fungi can have a positive electric charge at low pH (ie. pH=3). These values suggest that it might be possible that the degree of repulsion and dispersion between these organisms is low which facilitates the attraction between them.