Dramatic increases in the price of crude oil, and consequently, transportation fuels, coupled with increased environmental concerns have resulted in rapid growth in biodiesel production, both in the United States and worldwide. As biodiesel production increases, so does production of the primary coproduct, glycerol. Since the existing glycerol supply and demand market was tight, recent increases in glycerol production from biodiesel refining has created a glut in the glycerol market. As a result, the price of glycerol has fallen significantly and biodiesel refiners are faced with limited options for managing the glycerol by‐product, which in the biodiesel industry, has essentially become a waste stream. This article is a review of promising options for both the catalytic and biological conversion of glycerol into various value‐added products, many of which are bio‐based alternatives to petroleum‐derived chemicals. © 2007 American Institute of Chemical Engineers Environ Prog, 26: 338–348, 2007

The rapidly expanding market for biodiesel is dramatically altering the cost and availability of glycerol, as typical biodiesel production processes generate about 10 wt % glycerol. Biodiesel producers have little financial incentive to purify the crude glycerol, and because it contains methanol, crude glycerol is considered a hazardous waste. Therefore, it is critical that new and innovative processes for managing and utilizing the glycerol co‐product be developed. In the longer term, as supplies continue to increase, glycerol will become a versatile building block chemical for the production of high value compounds within an integrated biorefinery. This research investigated the value‐added conversion of crude glycerol generated during biodiesel production using anaerobic fermentation. Pure cultures of Clostridium pasteurianum have been shown to produce significant amounts of butanol and 1,3‐propanediol when utilizing purified glycerol as the sole substrate. Butanol is of particular interest as a renewable biofuel, as it has a higher heating value, higher octane number, lower vapor pressure, and higher miscibility than ethanol, making butanol preferable to ethanol for blending with petroleum fuels. Preliminary experiments compared growth and product formation of C. pasteurianum (ATCC®6013™) utilizing both purified and biodiesel‐derived crude glycerol as the sole carbon source in batch culture. Cultures utilizing crude glycerol demonstrated significant growth and production of butanol, 1,3‐PDO, and ethanol at concentrations up to 25 g/L crude glycerol. This work is significant in that it is the first report of butanol production from crude glycerol using this organism. The maximum yield of butanol produced from pure glycerol was 0.36 g/g, while the maximum butanol yield produced from crude glycerol was 0.30 g/g. These yields are substantially higher than the 0.15–0.20 g/g butanol yield typically achieved during the fermentation of glucose using C. acetobutylicum. These results indicate that biodiesel‐derived crude glycerol is a promising, low‐cost, renewable feedstock for butanol production. © 2009 American Institute of Chemical Engineers Environ Prog, 2009

During the production of biodiesel, crude glycerol is produced as a byproduct at 10% (w/w). Clostridium pasteurianum has the inherent potential to grow on glycerol and produce 1,3-propanediol and butanol as the major products. Growth and product yields on crude glycerol were reported to be slower and lower, respectively, in comparison to the results obtained from pure glycerol. In this study, we analyzed the effect of each impurity present in the biodiesel-derived crude glycerol on the growth and metabolism of glycerol by C. pasteurianum. The crude glycerol contains methanol, salts (in the form of potassium chloride or sulfate), and fatty acids that were not transesterified. Salt and methanol were found to have no negative effects on the growth and metabolism of the bacteria on glycerol. The fatty acid with a higher degree of unsaturation, linoleic acid, was found to have strong inhibitory effect on the utilization of glycerol by the bacteria. The fatty acid with lower or no degrees of unsaturation such as stearic and oleic acid were found to be less detrimental to substrate utilization. The removal of fatty acids from crude glycerol by acid precipitation resulted in a fermentation behavior that is comparable to the one on pure glycerol. These results show that the fatty acids in the crude glycerol have a negative effect by directly affecting the utilization of glycerol as the carbon source, and hence their removal from crude glycerol is an essential step towards the utilization of crude glycerol.

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Clostridium pasteurianum ATCC 6013 achieves high n-butanol production when glycerol is used as the sole carbon source. In this study, the homeoviscous membrane response of C. pasteurianum ATCC 6013 has been examined through n-butanol challenge experiments. Homeoviscous response is a critical aspect of n-butanol tolerance and has not been examined in detail for C. pasteurianum. Lipid membrane compositions were examined for glycerol fermentations with n-butanol production, and during cell growth in the absence of n-butanol production, using gas chromatography-mass spectrometry (GC-MS) and proton nuclear magnetic resonance ((1)H-NMR). Membrane stabilization due to homeoviscous response was further examined by surface pressure-area (π-A) analysis of membrane extract monolayers. C. pasteurianum was found to exert a homeoviscous response that was comprised of an increase lipid tail length and a decrease in the percentage of unsaturated fatty acids with increasing n-butanol challenge. This led to a more rigid or stable membrane that counteracted n-butanol fluidization. This is the first report on the changes in the membrane lipid composition during n-butanol production by C. pasteurianum ATCC 6013, which is a versatile microorganism that has the potential to be engineered as an industrial n-butanol producer using crude glycerol.

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Liquid-liquid extraction (LLE) of mixtures of butanol, 1,3-propanediol (PDO), and ethanol was performed using soybean-derived biodiesel as the extractant. The composition of the mixtures simulated the product of the anaerobic fermentation of biodiesel-derived crude glycerol, which has recently been reported for the first time by the authors. Using a biodiesel: with an aqueous phase volume ratio of 1:1, butanol recovery ranged from 45 to 51% at initial butanol concentrations of 150 and 225 mM, respectively. Less than 10% of the ethanol was extracted, and essentially no PDO was extracted. The partition coefficient for butanol in biodiesel was determined to be 0.91 ± 0.097. This partition coefficient is less than that of oleyl alcohol, which is considered the standard for LLE. However, butanol is suitable for blending with biodiesel, which would eliminate the need for separating the butanol after extraction. Additionally, biodiesel is much less costly than oleyl alcohol. If biodiesel-derived glycerol is used as the feedstock for butanol production, and biodiesel is used as the extractant to recover butanol from the fermentation broth, production of a biodiesel/butanol fuel blend could be a fully integrated process within a biodiesel facility. This process could ultimately help reduce the cost of butanol separation and ultimately help improve the overall economics of butanol fermentation using renewable feedstocks.

Petroleum products contamination is a world-wide problem that threatens polluting groundwater and surface water systems. However, the problem is not only large-scale in scope when viewed from a case-by-case basis. Many fueling, construction, agricultural, and industrial activities result in the problem of managing smaller quantities of these soils from an ecological safety perspective. Landfilling has been the disposal method of choice in the US; however, this option is becoming economically prohibitive and it does not really offer a true degradation fate for the pollutants. This study focused on the proving of an innovative biocell design that afforded a high level of petroleum degradation within a simple and cost effective design. Additionally, the design offered a remediation solution for sites not easily accessed. Soil contaminated with both diesel fuel and gasoline collected from a former filling station was used in this on-site remediation case study. Rapid biodegradation of the petroleum products were observed at the initiation of the study with rates leveling off as the study progressed with the final total petroleum hydrocarbon concentration being 10 mg/kg at Day 90. Oxygen uptake rates were monitored and found to nicely track both microbial activity and pollutant removal dynamics. The biocell design met all expectations by being effective, yet simple to build and operate.