The Use of High-Solids Loadings in Biomass Pretreatment – A Review

The use of high‐solids loadings (≥ 15% solids, w/w) in the unit operations of lignocellulose conversion processes potentially offers many advantages over lower‐solids loadings, including increased sugar and ethanol concentrations and decreased production and capital costs. Since the term lignocellulosic materials refers to a wide range of feedstocks (agricultural and forestry residues, distillery by‐products, and dedicated energy crops like grasses), the term “solids loading” here is defined by the amount of dry material that enters the process divided by the total mass of material and water added to the material. The goal of this study is to provide a consolidated review of studies using a high‐solids pretreatment step in the conversion process. Included in this review is a brief discussion of the limitations, such as the lack of available water to promote mass transfer, increased substrate viscosity, and increased concentration of inhibitors produced affecting pretreatment, as well as descriptions and findings of pretreatment studies performed at high solids, the latest reactor designs developed for pretreatment at bench‐ and pilot‐scales to address some of the limitations, and high‐solids pretreatment operations that have been scaled‐up and incorporated into demonstration facilities

Removal of hexavalent chromium of contaminated soil by coupling electrokinetic remediation and permeable reactive biobarriers

PURPOSE: In this study, a novel and ecological alternative have been developed to treat soils contaminated with hexavalent chromium coupling two well-known systems: electrokinetic remediation and permeable reactive biobarriers. The electric field promotes the electromigration of the hexavalent chromium oxyanions towards the anode. The biobarriers were placed before the anode electrode, in order to promote the reduction and retention of the chromium migrating in its direction. Thus, this technology provided a global treatment to soil removal without subsequent treatments of the contaminated effluents. METHODS: The electrokinetic system was coupled with two different permeable reactive biobarriers composed by Arthrobacter viscosus bacteria, supported either in activated carbon or zeolite. An electric field of 10 V was applied and two different treatment times of 9 and 18 days were tested. RESULTS: Removal values of 60% and 79% were obtained when electrokinetic treatment was coupled with zeolite and activated carbon biobarriers, respectively, for a test period of 18 day. The reduction of hexavalent chromium to trivalent chromium was around 45% for both systems. CONCLUSIONS: In this work, two types of biobarriers were efficiently coupled to electrokinetic treatment to decontaminate soil with Cr(VI). Furthermore, the viability of the new coupling technology developed (electrokinetic + biobarriers) to treat low-permeability polluted soils was demonstrated.This work was supported by the Spanish Ministry of Science and Innovation (CTQ2008-03059/PPQ), Xunta de Galicia (08MDS034314PR). The authors are grateful to the Spanish Ministry of Science and Innovation for providing financial support for Marta Pazos under the Ramon y Cajal program and the Fundacao para a Ciencia e Tecnologia, Ministerio da Ciencia e Tecnologia, Portugal through the PhD grant of Bruna Fonseca (SFRH/BD/27780/2006)

Transcriptional Analysis of Shewanella oneidensis MR-1 with an Electrode Compared to Fe(III)Citrate or Oxygen as Terminal Electron Acceptor

Shewanella oneidensis is a target of extensive research in the fields of bioelectrochemical systems and bioremediation because of its versatile metabolic capabilities, especially with regard to respiration with extracellular electron acceptors. The physiological activity of S. oneidensis to respire at electrodes is of great interest, but the growth conditions in thin-layer biofilms make physiological analyses experimentally challenging. Here, we took a global approach to evaluate physiological activity with an electrode as terminal electron acceptor for the generation of electric current. We performed expression analysis with DNA microarrays to compare the overall gene expression with an electrode to that with soluble iron(III) or oxygen as the electron acceptor and applied new hierarchical model-based statistics for the differential expression analysis. We confirmed the differential expression of many genes that have previously been reported to be involved in electrode respiration, such as the entire mtr operon. We also formulate hypotheses on other possible gene involvements in electrode respiration, for example, a role of ScyA in inter-protein electron transfer and a regulatory role of the cbb3-type cytochrome c oxidase under anaerobic conditions. Further, we hypothesize that electrode respiration imposes a significant stress on S. oneidensis, resulting in higher energetic costs for electrode respiration than for soluble iron(III) respiration, which fosters a higher metabolic turnover to cover energy needs. Our hypotheses now require experimental verification, but this expression analysis provides a fundamental platform for further studies into the molecular mechanisms of S. oneidensis electron transfer and the physiologically special situation of growth on a poised-potential surface

Cross-Metathesis approach to a,w-Bifunctional Compounds from Methyl Oleate and cis-2-Butene-1,4-diol

The cross metathesis (CM) of methyl oleate (1) and cis-2-butene-1,2-diol (2) was investigated to access alpha, omega-bifunctional compounds. The optimal CM conditions involve Stewart-Grubbs catalyst at 0 °C, delivering CM product 3 in excellent yield. 3 was converted, in a single step and in >90% yields, to alcohol 7, aldehyde 8, and olefin 10, the useful synthetic intermediates for many specialty chemicals, including PA11 precursor. A tandem CM/isomerization process was also demonstrated for the first time

Production of lipid and carbohydrate from microalgae without compromising biomass productivities: role of Ca and Mg

We report the cultivation of Chlorella sorokiniana str. SLA-04 in media containing trace amounts of Ca and Mg. The differences in productivities of biomass, lipids and carbohydrates were assessed relative to cultures grown in standard media (BG-11) that contain approximately 8 × higher concentration of Ca and 30 × higher concentration of Mg. Culture performance in N-limited standard media was also investigated. In addition to growth and accumulation of storage products (lipid and carbohydrate), we measured the utilization of N, Ca and Mg and monitored changes in cell size and photosynthetic activity. Our results showed that limitation of Ca or Mg did not inhibit cell replication and culture growth. On the contrary, Ca-limited (CaL) limited cultures had ∼30% higher biomass productivity relative to the control with excessive nutrients possibly due to improvement in cell wall flexibility and cell division. We also observed that CaL and Mg-limited (MgL) cultures had nearly 3-fold higher lipid concentration (measured as fatty acid methyl ester) and 50% higher carbohydrate concentration than the nutrient excess control cultures. Simultaneous culture growth and lipid accumulation in CaL and MgL cultures suggest that de novo synthesis was the primary mechanism for lipid accumulation in Ca/Mg-limited media. Overall, our study demonstrates that micronutrient optimization, in addition to optimization of macronutrients, could significantly improve microalgal biorefinery yields

Reactive Extraction of Triglycerides as Fatty Acid Methyl Esters using Lewis Acidic Chloroaluminate Ionic Liquids

This study investigated the <i>in situ</i> production of fatty acid methyl esters (FAMEs) directly from lipid-containing soy flour using a Lewis acidic 1-ethyl-3-methylimidazolium chloroaluminate [EMIM]­Cl·2AlCl₃ (N = 0.67) ionic liquid (IL). The system also contained (i) dichloromethane, added as a cosolvent to reduce IL viscosity and (ii) methanol. The chloroaluminate, methanol, and dichloromethane formed a homogeneous reaction medium that facilitated a relatively rapid rate of FAME formation. IL, methanol, and cosolvent requirements, along with reaction temperature and time needed for high FAME yields, were determined. The highest biomass concentration that could be processed without negatively impacting product yields was also assessed. The results show that FAME yields of >90% can be achieved in 4 h at 110 °C with solids concentrations as high as 20% (w/v). Further, carbohydrates associated with the postreaction residues remained chemically unmodified, which would allow for additional sugar-based coproduct generation. A strategy for recovery of IL is also reported

Cultivation of Microalgae at Extreme Alkaline pH Conditions: A Novel Approach for Biofuel Production

A major challenge to the economic viability of outdoor cultivation of microalgae is the high cost of CO₂ supply, even when microalgae farms are co-located with point sources of CO₂ emissions. In addition, the global capacity for algae biofuel generation is severely restricted when microalgae farm locations are constrained by proximity to CO₂ sources along with the additional limitations of low slope lands and favorable climate. One potential solution to the impediments of CO₂ supply cost and availability is through cultivation of microalgae in highly alkaline pH solutions (pH >10) that are effective at scavenging CO₂ from the atmosphere at high rates. The extremely alkaline pH media would also mitigate culture crashes due to microbial contamination and predators. In this study, we report the indoor and outdoor phototrophic cultivation of a microalgae isolate (<i>Chlorella sorokiniana</i> str. SLA-04) adapted to grow in unusually high-pH environments. The isolate was cultivated in a growth medium at pH >10 without any inputs of concentrated CO₂. Both indoor and outdoor studies showed biomass and lipid productivities that were comparable to those reported for other microalgae cultures cultivated in near-neutral pH media (pH 7–8.5) under similar conditions. SLA-04 cultures also showed high lipid productivity and high glucose-to-lipid conversion efficiency when cultivated mixotrophically in the presence of glucose as an organic carbon source. From the energy content (calorific value) of the lipids produced and glucose consumed, a relatively high amount of lipid calories (0.62) were produced per glucose calorie consumed. In conclusion, our results demonstrate the feasibility of microalgae cultivation in extremely high-pH media (pH >10) as a novel strategy for biofuel production without dependence on concentrated CO₂ inputs