Acid-catalyzed steam pretreatment of lodgepole pine and subsequent enzymatic hydrolysis and fermentation to ethanol

Utilization of ethanol produced from biomass has the potential to offset the use of gasoline and reduce CO(2) emissions. This could reduce the effects of global warming, one of which is the current outbreak of epidemic proportions of the mountain pine beetle (MPB) in British Columbia (BC), Canada. The result of this is increasing volumes of dead lodgepole pine with increasingly limited commercial uses. Bioconversion of lodgepole pine to ethanol using SO(2)-catalyzed steam explosion was investigated. The optimum pretreatment condition for this feedstock was determined to be 200 degrees C, 5 min, and 4% SO(2) (w/w). Simultaneous saccharification and fermentation (SSF) of this material provided an overall ethanol yield of 77% of the theoretical yield from raw material based on starting glucan, mannan, and galactan, which corresponds to 244 g ethanol/kg raw material within 30 h. Three conditions representing low (L), medium (M), and high (H) severity were also applied to healthy lodgepole pine. Although the M severity conditions of 200 degrees C, 5 min, and 4% SO(2) were sufficiently robust to pretreat healthy wood, the substrate produced from beetle-killed (BK) wood provided consistently higher ethanol yields after SSF than the other substrates tested. BK lodgepole pine appears to be an excellent candidate for efficient and productive bioconversion to ethanol.     

Production of fuels and chemicals from renewable resources using engineered Escherichia coli

Biotechnological production of fuels and chemicals from renewable resources is an appealing way to move from the current petroleum-based economy to a biomass-based green economy. Recently, the feedstocks that can be used for bioconversion or fermentation have been expanded to plant biomass, microbial biomass, and industrial waste. Several microbes have been engineered to produce chemicals from renewable resources, among which Escherichia coli is one of the best studied. Much effort has been made to engineer E. coli to produce fuels and chemicals from different renewable resources. In this paper, we focused on E. coli and systematically reviewed a range of fuels and chemicals that can be produced from renewable resources by engineered E. coli. Moreover, we proposed how can we further improve the efficiency for utilizing renewable resources by engineered E. coli, and how can we engineer E. coli for utilizing alternative renewable feedstocks. e.g. C1 gases and methanol. This review will help the readers better understand the current progress in this field and provide insights for further metabolic engineering efforts in E. coli.     

Simultaneous saccharification and fermentation of Kanlow switchgrass by thermotolerant Kluyveromyces marxianus IMB3: the effect of enzyme loading, temperature and higher solid loadings

Switchgrass (Panicum virgatum) was subjected to hydrothermolysis pretreatment and then used to study the effect of enzyme loading and temperature in a simultaneous saccharification and fermentation (SSF) with the thermotolerant yeast strain Kluyveromyces marxianus IMB3 at 8% solid loading. Various loadings of Accellerase 1500 between 0.1 and 1.1 mL g(-1) glucan were tested in SSF at 45 °C (activity of enzyme was 82.2 FPU mL(-1)). The optimum enzyme loading was 0.7 mL g(-1) glucan based on the six different enzyme loadings tested. SSFs were performed at 37, 41 and 45 °C with an enzyme loading of 0.7 mL g(-1) glucan. The highest ethanol concentration of 22.5 g L(-1) was obtained after 168 h with SSF at 45 °C, which was equivalent to 86% yield. Four different batch and fed-batch strategies were evaluated using a total solid loading of 12% (dry basis). About 32 g L(-1) ethanol was produced with the four strategies, which was equivalent to 82% yield.     

Effects of dissolved oxygen on extracellular enzymes activities and transformation of carbon sources from plant biomass: implications for denitrification in constructed wetlands

Dissolved oxygen (DO) concentrations have often been shown to be important to decomposition rates of plant litter and thus may be a key factor in determining the supply of dissolved organic carbon (DOC) and carbon-dependent denitrification in wetlands. During the 2 months operation, DOC accumulation in anaerobic condition was superior to aerobic condition due to higher activities of hydrolase enzymes and lower hydrolysates converted to gaseous C. Also, much higher denitrification rates were observed in wetland when using anaerobic litter leachate as the carbon source, and the available carbon source (ACS) could be used as a good predictor of denitrification rate in wetland. According to the results of this study, extracellular enzymes activities (EEAs) in wetland would change as a short-term consequence of DO. This may alter balance of litter carbon flux and the characteristics of DOC, which may, in turn, have multiple effects on denitrification in wetlands.     

Conversion for Avicel and AFEX pretreated corn stover by Clostridium thermocellum and simultaneous saccharification and fermentation: insights into microbial conversion of pretreated cellulosic biomass

In this study, efforts were taken to compare solubilization of Avicel and AFEX pretreated corn stover (AFEX CS) by SSF and Clostridium thermocellum fermentation, with an aim to gain insights into microbial conversion of pretreated cellulosic biomass. Solubilization rates for AFEX CS are comparable for the two systems while solubilization of Avicel is much faster by C. thermocellum. Initial catalyst loading impacts final cellulose conversion for SSF but not for C. thermocellum. Hydrolysis of the two substrates using cell-free C. thermocellum fermentation broth revealed much smaller difference in cellulose conversion than the difference observed for growing cultures. Tests on hemicellulose removal and particle size reduction for AFEX CS indicated that substrate accessibility is very important for enhanced solubilization by C. thermocellum.     

Phytoremediation of selenium using subsurface-flow constructed wetland

The potential of two plant species, Phragmites australis (common reed) and Typha latifolia (cattail), in the phytoremediation process of selenium (Se) was studied in subsurface-flow constructed wetland (SSF). Se was supplemented continuously at a concentration of 100 microg Se L(-1) in the inlet of the cultivation beds of the SSF. Water samples collected from the outlet of the Phragmites bed after 1, 3, 6, 9, and 12 wk of treatments showed that Se content was under detectable limits. Water samples collected from the Typha bed at the same five periods showed that Se concentrations in the outlet were 55, 47, 65, 76, and 25 microg/L, respectively. The results of bioaccumulation in the biomass of both species after 12 wk of treatment indicated that Typha plants accumulated Se mainly in fine roots. Phragmites accumulated Se mainly in leaves and rhizomes, and moderate levels were found in stems and fine organic materials. The results indicate that common reed is a very good species for Se phytoextraction and phytostabilization (immobilization) and that cattail is only a phytostabilization species. The use of common reed and cattail for Se phytoremediation in a SSF system and in constructed wetland models are discussed.     

Ethanol production from maize silage as lignocellulosic biomass in anaerobically digested and wet-oxidized manure

In this communication, pretreatment of the anaerobically digested (AD) manure and the application of the pretreated AD manure as liquid medium for the simultaneous saccharification and fermentation (SSF) were described. Furthermore, fermentation of pretreated maize silage and wheat straw was investigated using 2 l bioreactors. Wet oxidation performed for 20 min at 121 °C was found as the most suitable pretreatment conditions for AD manure. High ammonia concentration and significant amount of macro- and micro-nutrients in the AD manure had a positive influence on the ethanol fermentation. No extra nitrogen source was needed in the fermentation broth. It was shown that the AD manure could successfully substitute process water in SSF of pretreated lignocellulosic fibres. Theoretical ethanol yields of 82% were achieved, giving 30.8 kg ethanol per 100 kg dry mass of maize silage.     

An Improved CARV Process for Bioethanol Production from a Mixture of Sugar Beet Mash and Potato Mash

A mixed mash of sugar beet roots and potato tubers with a sugar concentration of 23.7% w/v was used as a feedstock for bioethanol production. Enzymatic digestion successfully reduced the viscosity of the mixture, enabling subsequent heat pretreatment for liquefaction/sterilization. An energy-consuming thick juice preparation from sugar beet for concentration and sterilization was omitted in this new process.     

Optimization of fermentation conditions for the production of ethanol from sago starch using response surface methodology

The quantitative effects of temperature, pH and time of fermentation were investigated on simultaneous saccharification and fermentation (SSF) of ethanol from sago starch with glucoamylase (AMG) and Zymomonas mobilis ZM4 using a Box–Wilson central composite design protocol. The SSF process was studied using free enzyme and free cells and it was found that with sago starch, maximum ethanol concentration of 70.68 g/l was obtained using a starch concentration of 140 g/l, which represents an ethanol yield of 97.08%. The optimum conditions for the above yield were found to be a temperature of 36.74 °C, pH of 5.02 and time of fermentation of 17 h. Thus by using the central composite design, it is possible to determine the accurate values of the fermentation parameters where maximum production of ethanol occurs.