Recent nanoparticle engineering advances in microalgal cultivation and harvesting processes of biodiesel production: a review

Among the various steps entailed in the production of biodiesel from microalgae, the efficiency and cost-reduction of the cultivation and harvesting steps remain key obstacles to its practical commercialization. Recently, in order to overcome the technical bottlenecks and limitations with regard to both steps, nanoparticle engineering based on particles' unique physico-chemical and mechanical properties has been extensively applied as a powerful analytical and practical tool. These applications include the enhancement of cell growth and/or pigments by light back-scattering, the induction of intracellular lipid accumulation by nutritional competition and/or stress environment, the improvement of cell separation efficiency and processing time from culture broth, the multiple reuse of magnetic nanoparticle flocculant, and integrated one-pot harvesting/cell-disruption. This review presents and discusses the recent nanoparticle-engineering-based developments in the implementation of practical microalgal cultivation and harvesting processes.

Isolation and characterization of microalgae for biodiesel production from seawater

As green marine microalgae isolated from local seawater in Tianjin, China, Nannochloropsis gaditana Q6 was tolerant to the variation of salinity with the highest biomass and lipid concentration in natural seawater medium. Although this strain could grow mixotrophically with glycerol, the narrow gap between mixotrophic and autotrophic cultivation suggested that autotrophic cultivation was the optimal trophic type for N. gaditana Q6 growth. In addition, strain Q6 was more sensitive to the variance of NH4HCO3 concentration than NaH2PO4 concentration. Consequently, the lipid production could be maximized by the two-stage cultivation strategy, with an initial high NH4HCO3 concentration for biomass production followed by low NH4HCO3 concentration for lipid accumulation.

Water use and its recycling in microalgae cultivation for biofuel application

Microalgal biofuels are not yet economically viable due to high material and energy costs associated with production process. Microalgae cultivation is a water-intensive process compared to other downstream processes for biodiesel production. Various studies found that the production of 1 L of microalgal biodiesel requires approximately 3000 L of water. Water recycling in microalgae cultivation is desirable not only to reduce the water demand, but it also improves the economic feasibility of algal biofuels as due to nutrients and energy savings. This review highlights recently published studies on microalgae water demand and water recycling in microalgae cultivation. Strategies to reduce water footprint for microalgal cultivation, advantages and disadvantages of water recycling, and approaches to mitigate the negative effects of water reuse within the context of water and energy saving are also discussed.

Combining urban wastewater treatment with biohydrogen production--an integrated microalgae-based approach

The aim of the present work was the simultaneous treatment of urban wastewater using microalgae and the energetic valorization of the obtained biomass. Chlorella vulgaris (Cv), Scenedesmus obliquus (Sc) and a naturally occurring algal Consortium C (ConsC) were grown in an urban wastewater. The nutrient removals were quite high and the treated water fits the legislation (PT Dec-Lei 236/98) in what concerns the parameters analysed (N, P, COD). After nutrient depletion the microalgae remained two more weeks in the photobioreactor (PBR) under nutritional stress conditions, to induce sugar accumulation (22-43%). The stressed biomass was converted into biohydrogen (bioH2), a clean energy carrier, through dark fermentation by a strain of the bacteria Enterobacter aerogenes. The fermentation kinetics were monitored and fitted to a modified Gompertz model. The highest bioH2 production yield was obtained for S. obliquus (56.8 mL H2/gVS) which was very similar when using the same algae grown in synthetic media.

Using recombinant cyanobacterium (Synechococcus elongatus) with increased carbohydrate productivity as feedstock for bioethanol production via separate hydrolysis and fermentation process

In this work, a recombinant cyanobacterium strain with increased photosynthesis rate, cell growth and carbohydrate production efficiency was genetically engineered by co-expressing ictB, ecaA, and acsAB (encoded for bacterial cellulose) in Synechococcus elongatus PCC7942. The resulting cyanobacterial biomass could be effectively hydrolyzed with dilute acid (2% sulfuric acid), achieving a nearly 90% glucose recovery at a biomass concentration of 80 g/L. Bioethanol can be produced from fermenting the acidic hydrolysate of S. elongatus PCC7942 via separate hydrolysis and fermentation (SHF) process at a concentration of 7.2 g/L and with a 91% theoretical yield.

Isolation and screening of heterocystous cyanobacterial strains for biodiesel production by evaluating the fuel properties from fatty acid methyl ester (FAME) profiles

This study reports on the biodiesel quality parameters of eleven heterocystous cyanobacterial strains based on fatty acid methyl esters (FAME) profiles. The biomass productivity of the tested cyanobacterial strains ranged from 9.33 to 20.67 mg L(-1) d(-1) while the lipid productivity varied between 0.65 and 2.358 mg L(-1) d(-1). The highest biomass and lipid productivity was observed for Calothrix sp. MBDU 013 but its lipid content is only 11.221 in terms of percent dry weight, next to the Anabaena sphaerica MBDU 105, whose lipid content is high. To identify the most competent isolate, a multi-criteria decision analyses (MCDA) was performed by including the key chemical and physical parameters of biodiesel calculated from FAME profiles. The isolate A.sphaerica MBDU 105 is the most promising biodiesel feed stock based on decision vector through Preference Ranking Organisation Method for Enrichment Evaluation (PROMETHEE) and Graphical Analysis for Interactive Assistance (GAIA) analysis.

New dual-stage pH control fed-batch cultivation strategy for the improvement of lipids and carotenoids production by the red yeast Rhodosporidium toruloides NCYC 921

The optimal medium pH to produce biomass and fatty acids by the red yeast Rhodosporidium toruloides NCYC 921 is 4.0, and to produce carotenoids is 5.0. Based on this difference, a dual-stage pH control fed-batch cultivation strategy for the enhancement of lipids and carotenoids production by this yeast was studied. The results showed that when the yeast growth phase was conducted at pH 4.0, and the products accumulation phase was conducted at pH 5.0, biomass, total fatty acid and total carotenoid productivities were significantly improved comparing with the yeast fed batch cultivations carried out at fixed medium pH (4 or 5). Under dual-stage pH control conditions, the biomass, carotenoids and lipids productivities attained 2.35 g/Lh, 0.29 g/Lh and 0.40 g/Lh, respectively. It was also observed that the oxygen played a major role in the yeast carotenoid production.

Brettanomyces yeasts--From spoilage organisms to valuable contributors to industrial fermentations

Ever since the introduction of controlled fermentation processes, alcoholic fermentations and Saccharomyces cerevisiae starter cultures proved to be a match made in heaven. The ability of S. cerevisiae to produce and withstand high ethanol concentrations, its pleasant flavour profile and the absence of health-threatening toxin production are only a few of the features that make it the ideal alcoholic fermentation organism. However, in certain conditions or for certain specific fermentation processes, the physiological boundaries of this species limit its applicability. Therefore, there is currently a strong interest in non-Saccharomyces (or non-conventional) yeasts with peculiar features able to replace or accompany S. cerevisiae in specific industrial fermentations. Brettanomyces (teleomorph: Dekkera), with Brettanomyces bruxellensis as the most commonly encountered representative, is such a yeast. Whilst currently mainly considered a spoilage organism responsible for off-flavour production in wine, cider or dairy products, an increasing number of authors report that in some cases, these yeasts can add beneficial (or at least interesting) aromas that increase the flavour complexity of fermented beverages, such as specialty beers. Moreover, its intriguing physiology, with its exceptional stress tolerance and peculiar carbon- and nitrogen metabolism, holds great potential for the production of bioethanol in continuous fermentors. This review summarizes the most notable metabolic features of Brettanomyces, briefly highlights recent insights in its genetic and genomic characteristics and discusses its applications in industrial fermentation processes, such as the production of beer, wine and bioethanol.

Efficient ethanol production from potato and corn processing industry waste using E. coli engineered to express Vitreoscilla haemoglobin

Engineering of ethanologenic E. coli to express the haemoglobin (VHb) from the bacterium Vitreoscilla has been shown to enhance ethanol production by fermentation of pure sugars, sugars from hydrolysis of lignocellulose, components of whey, and sugars from wastewater produced during potato processing. Here, these studies were extended to see whether the same effect could be seen when a mixture of waste materials from processing of potatoes and corn into potato and corn chips were used as sugar sources. Consistent increases in ethanol production coincident with VHb expression were seen in shake flasks at both low aeration and high aeration conditions. The ethanol increases were due almost entirely to increases in the amount of ethanol produced per unit of cell mass. The VHb strategy for increasing fermentation to ethanol (and perhaps other valuable fermentation products) may be of general use, particularly regarding conversion of otherwise discarded materials into valuable commodities.

Enzymatic production of biodiesel from Nannochloropsis gaditana lipids: Influence of operational variables and polar lipid content

Fatty acid methyl esters (FAMEs, biodiesel) were produced from Nannochloropsis gaditana wet biomass (12% saponifiable lipids, SLs) by extraction of SLs and lipase catalyzed transesterification. Lipids were extracted by ethanol (96%)-hexane, and 31% pure SLs were obtained with 85% yield. When the lipids were degummed, SL purity increased to 95%. Novozym 435 was selected from four lipases tested. Both the lipidic composition and the use of t-butanol instead of hexane increased the reaction velocity and the conversion, since both decreased due to the adsorption of polar lipids on the lipase immobilization support. The best FAME yield (94.7%) was attained at a reaction time of 48h and using 10mL of t-butanol/g SL, 0.225gN435/g SL, 11:1 methanol/SL molar ratio and adding the methanol in three steps. In these conditions the FAME conversion decreased by 9.8% after three reaction cycles catalyzed by the same lipase batch.

Biosynthesis, characterization and enzymatic transesterification of single cell oil of Mucor circinelloides--a sustainable pathway for biofuel production

The filamentous fungus Mucor circinelloides URM 4182 was tested to determine its ability to produce single-cell oil suitable for obtaining biodiesel. Cell growth and lipid accumulation were investigated in a medium containing glucose as the main carbon source. A microwave-assisted ethanol extraction technique (microwave power ⩽200 W, 50-60 °C) was established and applied to lipid extraction from the fungal hyphae to obtain high lipid concentration (44%wt) of the dry biomass, which was considerably higher than the quantity obtained by classical solvent methods. The lipid profile showed a considerable amount of oleic acid (39.3%wt), palmitic acid (22.2%wt) and γ-linoleic acid (10.8%wt). Biodiesel was produced by transesterification of the single-cell oil with ethanol using a immobilized lipase from Candida antarctica (Novozym® 435) as the catalyst. (1)H NMR and HPLC analyses confirmed conversion of 93% of the single-cell oil from M. circinelloides into ethyl esters (FAEE).

Harvesting green algae from eutrophic reservoir by electroflocculation and post-use for biodiesel production

Each year there are more frequent blooms of green algae and cyanobacteria, representing a serious environmental problem of eutrophication. Electroflocculation (EF) was studied to harvest the algae which are present in reservoirs, as well as different factors which may influence on the effectiveness of the process: the voltage applied to the culture medium, run times, electrodes separation and natural sedimentation. Finally, the viability of its use to obtain biodiesel was studied by direct transesterification. The EF process carried out at 10V for 1min, with an electrode separation of 5.5cm and a height of 4cm in culture vessel, obtained a recovery efficiency greater than 95%, and octadecenoic and palmitic acids were obtained as the fatty acid methyl esters (FAMEs). EF is an effective method to harvest green algae during the blooms, obtaining the greatest amount of biomass for subsequent use as a source of biodiesel.

Environmental sustainability of bioethanol produced from sweet sorghum stem on saline-alkali land

Life cycle assessment was conducted to evaluate the energy efficiency and environmental impacts of a bioethanol production system that uses sweet sorghum stem on saline-alkali land as feedstock. The system comprises a plant cultivation unit, a feedstock transport unit, and a bioethanol conversion unit, with 1000L of bioethanol as a functional unit. The net energy ratio is 3.84, and the net energy gain is 17.21MJ/L. Agrochemical production consumes 76.58% of the life cycle fossil energy. The category with the most significant impact on the environment is eutrophication, followed by acidification, fresh water aquatic ecotoxicity, human toxicity, and global warming. Allocation method, waste recycling approach, and soil salinity significantly influence the results. Using vinasse to produce pellet fuel for steam generation significantly improves energy efficiency and decreases negative environmental impacts. Promoting reasonable management practices to alleviate saline stress and increasing agrochemical utilization efficiency can further improve environmental sustainability.

A constitutive expression system for cellulase secretion in Escherichia coli and its use in bioethanol production

The production of biofuels from lignocellulosic biomass appears to be attractive and viable due to the abundance and availability of this biomass. The hydrolysis of this biomass, however, is challenging because of the complex lignocellulosic structure. The ability to produce hydrolytic cellulase enzymes in a cost-effective manner will certainly accelerate the process of making lignocellulosic ethanol production a commercial reality. These cellulases may need to be produced aerobically to generate large amounts of protein in a short time or anaerobically to produce biofuels from cellulose via consolidated bioprocessing. Therefore, it is important to identify a promoter that can constitutively drive the expression of cellulases under both aerobic and anaerobic conditions without the need for an inducer. Using lacZ as reporter gene, we analyzed the strength of the promoters of four genes, namely lacZ, gapA, ldhA and pflB, and found that the gapA promoter yielded the maximum expression of the β-galactosidase enzyme under both aerobic and anaerobic conditions. We further cloned the genes for two cellulolytic enzymes, β-1,4-endoglucanase and β-1,4-glucosidase, under the control of the gapA promoter, and we expressed these genes in Escherichia coli, which secreted the products into the extracellular medium. An ethanologenic E. colistrain transformed with the secretory β-glucosidase gene construct fermented cellobiose in both defined and complex medium. This recombinant strain also fermented wheat straw hydrolysate containing glucose, xylose and cellobiose into ethanol with an 85% efficiency of biotransformation. An ethanologenic strain that constitutively secretes a cellulolytic enzyme is a promising platform for producing lignocellulosic ethanol.

Organisms for biofuel production: natural bioresources and methodologies for improving their biosynthetic potentials

In order to relieve the pressure of energy supply and environment contamination that humans are facing, there are now intensive worldwide efforts to explore natural bioresources for production of energy storage compounds, such as lipids, alcohols, hydrocarbons, and polysaccharides. Around the world, many plants have been evaluated and developed as feedstock for bioenergy production, among which several crops have successfully achieved industrialization. Microalgae are another group of photosynthetic autotroph of interest due to their superior growth rates, relatively high photosynthetic conversion efficiencies, and vast metabolic capabilities. Heterotrophic microorganisms, such as yeast and bacteria, can utilize carbohydrates from lignocellulosic biomass directly or after pretreatment and enzymatic hydrolysis to produce liquid biofuels such as ethanol and butanol. Although finding a suitable organism for biofuel production is not easy, many naturally occurring organisms with good traits have recently been obtained. This review mainly focuses on the new organism resources discovered in the last 5 years for production of transport fuels (biodiesel, gasoline, jet fuel, and alkanes) and hydrogen, and available methods to improve natural organisms as platforms for the production of biofuels.

Functionalized Fe3O4@silica core-shell nanoparticles as microalgae harvester and catalyst for biodiesel production

Core-shell Fe3O4@silica magnetic nanoparticles functionalized with a strong base, triazabicyclodecene (TBD), were successfully synthesized for harvesting microalgae and for one-pot microalgae-to-fatty acid methyl ester (FAME, or so-called biodiesel) conversion. Three types of algae oil sources (i.e., dried algae, algae oil, and algae concentrate) were used and the reaction conditions were optimized to achieve the maximum biodiesel yield. The results obtained in this study show that our TBD-functionalized Fe3O4@silica nanoparticles could effectively convert algae oil to biodiesel with a maximum yield of 97.1 %. Additionally, TBD-Fe3O4@silica nanoparticles act as an efficient algae harvester because of their adsorption and magnetic properties. The method presented in this study demonstrates the wide scope for the use of covalently functionalized core-shell nanoparticles for the production of liquid transportation fuels from algal biomass.

Effect of food wastewater on biomass production by a green microalga Scenedesmus obliquus for bioenergy generation

Effect of food wastewater (FW) on the biomass, lipid and carbohydrate production by a green microalga Scenedesmus obliquus cultivated in Bold's Basal Medium (BBM) was investigated. Different dilution ratios (0.5-10%) of BBM either with FW or salt solution (NaCl) or sea water (SW) were evaluated. S. obliquus showed the highest growth (0.41 g L(-1)), lipid productivity (13.3 mg L(-1) day L(-1)), carbohydrate productivity (14.7 mg L(-1) day L(-1)) and nutrient removal (38.9 mg TN L(-1) and 12.1 mg TP L(-1)) with 1% FW after 6 days of cultivation. The FW promoted algal autoflocculation due to formation of inorganic precipitates at an alkali pH. Fatty acid methyl ester analysis revealed that the palmitic and oleic acid contents were increased up to 8% with FW. Application of FW improved the growth, lipid/carbohydrate productivity and biomass recovery efficiency of S. obliquus, which can be exploited for cost effective production of microalgae biomass.

Variations of organic matters and microbial community in thermophilic anaerobic digestion of waste activated sludge with the addition of ferric salts

Ferric salts will influence the thermophilic anaerobic digestion of waste activated sludge (WAS). FeCl3 was found to contribute to the anaerobic digestion process with a cumulative biogas production of 357 mL/gVS, 79.6% higher than that in the control group, and Fe2(SO4)3 had no distinct impact, while Fe(NO3)3 inhibited the methanogenesis process. A favorable balance between the release of organic matters from WAS and consumption rate was established after dosing FeCl3 from the perspective of variations of soluble COD, volatile fatty acids (VFAs) and the dissolved organic matters (DOM) assessed by EEM fluorescence spectroscopy and fluorescence regional integration (FRI) technique. Conversely, the system with Fe(NO3)3 achieved an unsuitable substrates environment. Pyrosequencing revealed that the anaerobic digestion system with FeCl3 enriched Coprothermobacter for proteins fermentation and Methanosarcina for methanogenesis with the values of 18.7% and 63.2%, respectively, while that with the supplementation of Fe(NO3)3 obtained the lowest relative abundance.

Development and validation of a screening procedure of microalgae for biodiesel production: application to the genus of marine microalgae Nannochloropsis

Nannochloropsis has emerged as a promising alga for biodiesel production. However, the genus consists of 6 species and hundreds of strains making strain selection a challenge. Furthermore, oil productivity is instrumental to economic viability of any algal strain for industrial production, which is dependent on growth rate and oil content. In most cases, these two parameters have been studied independently. Thus, the goal of this study is to provide a combined method for evaluating strain performance in specially designed photobioreactors together with an in-depth lipidomic analyses. The nine strains of Nannochloropsis tested showed considerable variations in productivity and lipidomics highlighting the importance of strain selection. Finally, Nannochloropsis gaditana CCMP527 and Nannochloropsis salina CCMP537 emerged as the two most promising strains, with an oil content of 37 and 27 dry wt% after 11-day nitrogen starvation, respectively, resulting in TAG productivity of 13×10(-3) and 18×10(-3) kg m(-3) d(-1), respectively.

Temperature-dependent transformation of biogas-producing microbial communities points to the increased importance of hydrogenotrophic methanogenesis under thermophilic operation

Stability of biogas production is highly dependent on the microbial community composition of the bioreactors. This composition is basically determined by the nature of biomass substrate and the physical-chemical parameters of the anaerobic digestion. Operational temperature is a major factor in the determination of the anaerobic degradation process. Next-generation sequencing (NGS)-based metagenomic approach was used to monitor the organization and operation of the microbial community throughout an experiment where mesophilic reactors (37°C) were gradually switched to thermophilic (55°C) operation. Temperature adaptation resulted in a clearly thermophilic community having a generally decreased complexity compared to the mesophilic system. A temporary destabilization of the system was observed, indicating a lag phase in the community development in response to temperature stress. Increased role of hydrogenotrophic methanogens under thermophilic conditions was shown, as well as considerably elevated levels of Fe-hydrogenases and hydrogen producer bacteria were observed in the thermophilic system.

Rapid bio-methanation of syngas in a reverse membrane bioreactor: membrane encased microorganisms

The performance of a novel reverse membrane bioreactor (RMBR) with encased microorganisms for syngas bio-methanation as well as a co-digestion process of syngas and organic substances was examined. The sachets were placed in the reactors and examined in repeated batch mode. Different temperatures and short retention time were studied. The digesting sludge encased in the PVDF membranes was able to convert syngas into methane at a retention time of 1 day and displayed a similar performance as the free cells in batch fermentation. The co-digestion of syngas and organic substances by the RMBR (the encased cells) showed a good performance without any observed negative effects. At thermophilic conditions, there was a higher conversion of pure syngas and co-digestion using the encased cells compared to at mesophilic conditions.

Ultraviolet and 5'fluorodeoxyuridine induced random mutagenesis in Chlorella vulgaris and its impact on fatty acid profile: a new insight on lipid-metabolizing genes and structural characterization of related proteins

The present study was aimed at randomly mutating the microalga, Chlorella vulgaris, in order to alter its cellular behaviour towards increased lipid production for efficient biodiesel production from algal biomass. Individual mutants from ultraviolet light (UV-1 (30 s exposure), UV-2 (60 s exposure) and UV-3 (90 s exposure)) and 5'fluorodeoxyuridine (5'FDU-1 (0.25 mM) and 5'FDU-2 (0.50 mM)) exposed cells were identified to explore an alternative method for lipid enhancement. A marginally significant decrease in biomass in the UV mutants; marked increase in the lipid content in UV-2 and 5'FDU-1 mutants; significant increase in saturated fatty acids level, especially in UV-2 mutant; insignificant increase in lipid production when these mutants were subjected to an additional stress of nitrogen starvation and predominantly enhanced level of unsaturated fatty acids in all the strains except UV-2 were noted. Chloroplast ultrastructural alterations and defective biosynthesis of chloroplast specific lipid constituents were observed in the mutants. Modelling of three-dimensional structures of acetyl coA carboxylase (ACCase), omega-6, plastid delta-12 and microsomal delta-12 fatty acid desaturases for the first time and ligand-interaction studies greatly substantiated our findings. A replacement of leucine by a serine residue in the acetyl coA carboxylase gene of UV-2 mutant suggests the reason behind lipid enhancement in UV-2 mutant. Higher activity of ACCase in UV-2 and 5'FDU-1 strongly proves the functional consequences of gene mutation to lipid production. In conclusion, algal mutants exhibited significant impact on biodiesel production through structural alterations in the lipid-metabolizing genes, thereby enhancing lipid production and saturated fatty acid levels.

Development and physiological characterization of cellobiose-consuming Yarrowia lipolytica

Yarrowia lipolytica is a promising production host for a wide range of molecules, but limited sugar consumption abilities prevent utilization of an abundant source of renewable feedstocks. In this study we created a Y. lipolytica strain capable of utilizing cellobiose as a sole carbon source by using endogenous promoters to express the cellodextrin transporter cdt-1 and intracellular β-glucosidase gh1-1 from Neurospora crassa. The engineered strain was also capable of simultaneous co-consumption of glucose and cellobiose. Although cellobiose was consumed slower than glucose when engineered strains were cultured with excess nitrogen, culturing with limited nitrogen led to cellobiose consumption rates comparable to those of glucose. Under limited nitrogen conditions, the engineered strain produced citric acid as a major product and we observed greater citric acid yields from cellobiose (0.37 g/g) than glucose (0.28 g/g). Culturing with a sole carbon source of either glucose or cellobiose induced additional differences on cell physiology and metabolism and a link is suggested to evasion of glucose-sensing mechanisms through intracellular creation and consumption of glucose. We ultimately applied this cellobiose-utilization system to produce citric acid from bioconversion of crystalline cellulose through simultaneous saccharification and fermentation (SSF).

Ultrasound pretreatment for enhanced biogas production from olive mill wastewater

This study investigates applicability of low frequency ultrasound technology to olive mill wastewaters (OMWs) as a pretreatment step prior to anaerobic batch reactors to improve biogas production and methane yield. OMWs originating from three phase processes are characterized with high organic content and complex nature. The treatment of the wastewater is problematic and alternative treatment options should be investigated. In the first part of the study, OMW samples were subjected to ultrasound at a frequency of 20kHz with applied powers varying between 50 and 100W under temperature controlled conditions for different time periods in order to determine the most effective sonication conditions. The level of organic matter solubilization at ultrasound experiments was assessed by calculating the ratio of soluble chemical oxygen demand/total chemical oxygen demand (SCOD/TCOD). The results revealed that the optimum ultrasonic condition for diluted OMW is 20kHz, 0.4W/mL for 10min. The application of ultrasound to OMW increased SCOD/TCOD ratio from 0.59 to 0.79. Statistical analysis (Friedman's tests) show that ultrasound was significantly effective on diluted OMW (p<0.05) in terms of SCOD parameter, but not for raw OMW (p>0.05). For raw OMW, this increase has been found to be limited due to high concentration of suspended solids (SS). In the second part of the study, biogas and methane production rates of anaerobic batch reactor fed with the ultrasound pretreated OMW samples were compared with the results of control reactor fed with untreated OMW in order to determine the effect of sonication. A nonparametric statistical procedure, Mann-Whitney U test, was used to compare biogas and methane production from anaerobic batch reactors for control and ultrasound pretreated samples. Results showed that application of low frequency ultrasound to OMW significantly improved both biogas and methane production in anaerobic batch reactor fed with the wastewater (p<0.05). Anaerobic batch reactor fed with ultrasound pretreated diluted OMW produced approximately 20% more biogas and methane compared with the untreated one (control reactor). The overall results indicated that low frequency ultrasound pretreatment increased soluble COD in OMW and subsequently biogas production.

A biorefining process: Sequential, combinational lignocellulose pretreatment procedure for improving biobutanol production from sugarcane bagasse

Here, for the first time, we designed a sequential, combinatorial lignocellulose pretreatment procedure (SCLPP) for microbial biofuel fermentation to reduce generation of microbial growth inhibitors and furthermore increase sugar yields. We tested this pretreatment process using sugarcane bagasse as substrate and assessed the effectiveness by analysis of biobutanol production through microbial clostridium beijerinckii NCIMB 8052 conversion. Our results showed that there were no inhibitory effects when using the hydrolysates as fermentation substrate. Under the SSF scheme, we observed the highest concentrations of butanol (6.4g/L) and total ABE (11.9g/L), resulting in a higher ABE productivity, compared with the SHF method. These findings suggest that the SCLPP is a feasible method for improving ABE production, lowering microbial inhibitor generation, and ensuring success in the subsequent fermentation process. Therefore, our work demonstrated developing a tractable integrated process that facilitates to increase biofuel production from agricultural residues rich in lignocellulose is feasible.