The fuel properties of microalgal biodiesel are predicted using published microalgal fatty acid (FA) compositions and predictive fuel models. Biodiesels produced from the microalgae investigated are predicted to have extremely poor oxidative stabilities and the majority also have poor coldflow properties. The cetane number in most cases is out of specification, but less so than the oxidative stability and cold flow. These findings support the idea that feedstocks rich in monounsaturated fatty acids (MUFAs) are desirable for biodiesel but the composition of the saturated fatty acids (SFAs) is also shown to be of great importance. There is an apparent relationship between algal class and the percentage of FAs represented by MUFA. This potentially allows for the identification of high-MUFA algal classes, or at least provides some basis for researchers to make initial selections of target classes for bioprospecting. Comparisons of FA groups between algal classes also show that the SFAs of Mediophyceae contain significantly higher proportions of C14:0, which is in contrast to the normally abundant C16:0 and the Mediophyceae therefore have better cold-flow characteristics than other classes with similar total SFA contents. Certain particularly promising cases for biodiesel production are presented as species level examples of feedstocks that are close to satisfying the biodiesel standards and to further illustrate the challenges that remain. Variation in FA composition as a response to changes in certain environmental variables forms another important facet to feedstock selection and is briefly considered, with suggestions for further research.
Energy fuels for transportation and electricity generation are mainly derived from finite and declining reserves of fossil hydrocarbons. Fossil hydrocarbons are also used to produce a wide range of organic carbon-based chemical products. The current global dependency on fossil hydrocarbons will not be environmentally or economically sustainable in the long term. Given the future pessimistic prospects regarding the complete dependency on fossil fuels, political and economic incentives to develop carbon neutral and sustainable alternatives to fossil fuels have been increasing throughout the world. For example, interest in biodiesel has undergone a revival in recent times. However, the disposal of crude glycerol contaminated with methanol, salts, and free fatty acids as a by-product of biodiesel production presents an environmental and economic challenge. Although pure glycerol can be utilized in the cosmetics, tobacco, pharmaceutical, and food industries (among others), the industrial purification of crude glycerol is not economically viable. However, crude glycerol could be used as an organic carbon substrate for the production of high-value chemicals such as 1,3-propanediol, organic acids, or polyols. Microorganisms have been employed to produce such high-value chemicals and the objective of this article is to provide an overview of studies on the utilization of crude glycerol by microorganisms for the production of economically valuable products. Glycerol as a by-product of biodiesel production could be used a feedstock for the manufacture of many products that are currently produced by the petroleum-based chemical industry.
The results indicated that the synergistic or additive interactions among the components of the tripartite symbiotic association (Rhizobium-AMF-broad bean) increased plant productivity.
Aims: To test the effects of C : N : P ratio modification of a well‐known nutrient medium formulation, the Endo formulation on biofilm formation by Enterobacter cloacae Ecl and Citrobacter freundii Cf1 in both single‐species and binary species biofilms. Methods and Results: The C : N : P atom : atom ratio of a well‐known nutrient medium formulation, the Endo formulation, that has been applied in fermentative biohydrogen studies, was modified to include two different C concentrations, one containing 17·65 g l−1 and the other 8·84 g l−1 sucrose, each containing four different C : N : P ratios, two at higher C : N : P ratios (334 : 84 : 16·8 and 334 : 84 : 3) and two at lower C : N : P ratios (334 : 28 : 5·6 and 334 : 28 : 1). Attached cells were enumerated after dislodging the biofilms that had formed on granular activated carbon (GAC). The modified medium containing 17·65 g l−1 sucrose and having a C : N : P ratio of 334 : 28 : 5·6 resulted in significantly (P < 0·05) higher counts of attached cells for both single‐species biofilms at 7·73 log10 CFU g−1 GAC and 9·3 log10CFU g−1 GAC for Ent. cloacae Ecl and Cit. freundii Cf1, respectively, and binary species biofilms at 8·2 log10 CFU g−1 GAC and 6·34 log10 CFU g−1 GAC for Ent. cloacae Ecl and Cit. freundii Cf1, respectively. Scanning electron micrographs showed qualitative evidence that the 334 : 28 : 5·6 ratio encouraged more complex and extensive biofilm growth for both single‐species and binary species biofilms. Conclusions: The differences in the attachment numbers between the different ratios were found not to be a result of the individual actions of the bacterial isolates involved but rather because of the effects of the various C : N : P ratios. The 334 : 28 : 5·6 ratio showed significantly (P < 0·05) higher counts of attached cells for both single‐species and binary species biofilms. Significance and Impact of the Study: This study indicates that C : N : P ratios should be a key consideration with regard to maximizing biofilm formation in shake flask and fluidized bed bioreactor studies as well as understanding fundamental factors affecting biofilm growth in natural environments.
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