Biorefinery Perspective Research Articles

Value-Added Products Derived from Waste Activated Sludge: A Biorefinery Perspective

Substantial research has been carried out on sustainable waste activated sludge (WAS) management in the last decade. In addition to the traditional approach to reduce its production volume, considering WAS as a feedstock to produce bio-products such as amino acids, proteins, short chain fatty acids, enzymes, bio-pesticides, bio-plastics, bio-flocculants and bio-surfactants represents a key component in the transformation of wastewater treatment plants into biorefineries. The quality of these bio-products is a key factor with respect to the feasibility of non-conventional WAS-based production processes. This review provides a critical assessment of the production process routes of a wide range of value-added products from WAS, their current limitations, and recommendations for future research to help promote more sustainable management of this under-utilised and ever-growing waste stream.

Bioenergy production from sweet sorghum stalks via a biorefinery perspective.

Besides free sugars, sweet sorghum stalks contain cellulose and hemicellulose that can be used for biofuel production. The pretreatment of stalks without the extraction of free sugars is more complicated than typical lignocelluloses, because of the degradation of free sugars during most pretreatment processes. In this study, the bioconversion of sweet sorghum stalks into biogas and bioethanol was studied using an improved organosolv pretreatment within a biorefinery framework. The organosolv pretreatment was developed using an aqueous solution of ethanol (EtOH) and isopropanol (IPOH). The process was optimized to obtain a liquor containing free sugars with the least sugar degradations together with a highly degradable solid fraction. The liquor was subjected to anaerobic digestion for biomethane production, while the solid was used for ethanol production via simultaneous saccharification and fermentation (SSF). The most influencing pretreatment parameters, i.e., temperature, time, alcohol to water ratio, EtOH to IPOH ratio, and the presence or absence of sulfuric acid (as a catalyst), were adjusted to achieve the highest yields of bioconversion. The maximum methane and ethanol production yields of 271.2mL CH4/g VS and 87.8% (equal to the gasoline equivalent of 0.170 and 0.241L/kg, respectively) were achieved from the liquor and pretreated solid, respectively; however, they were obtained at different optimum conditions. Considering the biorefinery perspective, the highest gasoline equivalent of 0.249L/kg was efficiently obtained from the whole process after pretreatment at 140°C for 30min using 60:20 EtOH/IPOH ratio in the presence of 1% sulfuric acid. Further analyses, including enzymatic adsorption/desorption, compositional analysis, FTIR, and SEM, were conducted to investigate the effects of this newly developed pretreatment on the substrate.

Food waste as a source of value‐added chemicals and materials: a biorefinery perspective

SummaryAs the availability of fossil‐based resources declines, there is an impending necessity of finding alternative feedstock able to secure the production of fuels and chemicals. Exploitation of biomass as renewable source of chemicals is an attractive possibility, in particular the one derived from food waste (FW). Every year, large amounts of waste are generated within or at the end of the food supply chain at the consumers use stage and hence its valorisation attracts great attention. FW has proven a valuable feedstock for its exploitation to produce a wide array of intermediates and products with promising applications in industry, owing to their similar performance with respect to established products. These include organic acids and furans (generally used as platform chemicals to further products); polymers like bacterial cellulose, polyhydroxyalkanoates or chitin; biosurfactants; biolubricants; or nanoparticles. This overview covers the latest trends in chemical, enzymatic and biotechnological processes reported in literature on the production of these chemicals and materials, with a focus on the use of FW as raw material.

Comparative environmental Life Cycle Assessment of integral revalorization of vine shoots from a biorefinery perspective

The use of vine shoots as feedstock in biorefining activities to obtain bioproducts under efficient and optimized conditions could be crucial to make future high added value compounds and processes more sustainable. In this study, five different potential valorization scenarios from vine shoots differing on diverse extraction and delignification steps were assessed from an environmental perspective using the Life Cycle Assessment methodology to identify the most sustainable biorefining route. The main findings from this study reported that an increment on the number of valorization steps involved higher energy and chemical requirements deriving on worse environmental profiles. Scenarios incorporating fermentation of the glucose liquors or organosolv delignification performed the worst profiles. Autohydrolysis, concentration and freeze drying and enzymatic hydrolysis were the main responsible stages of the environmental burdens. Further research should be focused on optimizing chemicals and electricity requirements to develop greener systems.

Biotechnological revalorization of Tequila waste and by-product streams for cleaner production – A review from bio-refinery perspective

In this paper, industrial processing and biotechnological revalorization of Tequila waste and by-product streams have been reviewed. Tequila production process generates different kind of waste and by-products with a huge potential to produce value-added products. Therefore, many research projects, scientific investigations and innovative utilizations of such waste and by-product streams have been the object of recent studies. Moreover, the bio-based transformation from a petrochemical-based economy to a bio-based economy necessitates the novel exploitation of cost-effective natural materials for both future biorefinery development and a range of value-added products of interests. The present review article focuses on an area not comprehensively reviewed previously, the potential of utilizing waste and by-product streams from current Tequila industry activities. The first part of this review focused on various processing aspects and prospects on the fermentative production of Tequila. In the second and third parts, statistical and sustainable aspects and the generation of waste and by-product streams of Tequila industry are critically reviewed, respectively. In the fourth part, various industrial and biotechnological applications of Tequila’s wastes are comprehensively discussed from a bio-refinery perspective. In conclusion, it is evident that biotransformation of waste and by-product streams has great potential and significant prospects for wider industrial and biotechnological applications.

Molecular Identification and Comparative Evaluation of Tropical Marine Microalgae for Biodiesel Production.

Marine microalgae have emerged as important feedstock for liquid biofuel production. The identification of lipid-rich native microalgal species with high growth rate and optimal fatty acid profile and biodiesel properties is the most challenging step in microalgae-based biodiesel production. In this study, attempts have been made to bio-prospect the biodiesel production potential of marine and brackish water microalgal isolates from the west coast of India. A total of 14 microalgal species were isolated, identified using specific molecular markers and based on the lipid content; seven species with total lipid content above 20% of dry cell weight were selected for assessing biodiesel production potential in terms of lipid and biomass productivities, nile red fluorescence, fatty acid profile and biodiesel properties. On comparative analysis, the diatoms were proven to be promising based on the overall desirable properties for biodiesel production. The most potential strain Navicula phyllepta MACC8 with a total lipid content of 26.54 % of dry weight of biomass, the highest growth rate (0.58 day-1) and lipid and biomass productivities of 114 and 431 mgL-1 day-1, respectively, was rich in fatty acids mainly of C16:0, C16:1 and C18:0 in the neutral lipid fraction, the most favoured fatty acids for ideal biodiesel properties. The biodiesel properties met the requirements of fuel quality standards based on empirical estimation. The marine diatoms hold a great promise as feedstock for large-scale biodiesel production along with valuable by-products in a biorefinery perspective, after augmenting lipid and biomass production through biochemical and genetic engineering approaches.

Biorefinery of Safflower Seeds in a Sequential Process for Effective Use of the Substrate for Biofuel Production

Biofuels are a promising alternative to fossil fuels that addresses the associated environmental concerns and satisfies growing global energy demand. In this study, safflower seeds were used to produce multiple biofuels with an integrated biorefinery perspective. The safflower oil was used for biodiesel production while the resultant seed cake was employed in subsequent ethanol production. Pretreatment of the residual solid is necessary in order to improve the ethanol production yield. Contrasting costly chemical pretreatments, the seed cake was instead pretreated using incomplete anaerobic digestion to remove hemicellulose, increase cellulose accessibility for fermentation, and produce methane. The seed cake produced 124.8 ml/g-VS of methane after 20 days of anaerobic digestion. The digestate (biologically pretreated seed cake) produced 92 g ethanol/kg solid, in stark contrast to 42 g ethanol/kg solid from untreated seed cake. This ethanol was later utilized in biodiesel production. The safflower oil produced 85.9% biodiesel via ethanolic transesterification at optimum conditions. From the integrated biorefinery perspective, the seed cake from 1 kg of safflower seeds produced 70 l of methane at NTP and 51.0 g of ethanol—surpassing the 47.6 g of ethanol stoichiometrically necessary to complete transesterification of safflower oil. Thus, this ethanol could be recycled, largely decreasing the need for an external stream of ethanol for biodiesel production. The incomplete anaerobic digestion is an effective and environmentally friendly way to improve the ethanol production from the safflower seed cake with biomethane as an additional valuable byproduct.

A Sequential Steam Explosion and Reactive Extrusion Pretreatment for Lignocellulosic Biomass Conversion within a Fermentation-Based Biorefinery Perspective

The present work evaluates a two-step pretreatment process based on steam explosion and extrusion technologies for the optimal fractionation of lignocellulosic biomass. Two-step pretreatment of barley straw resulted in overall glucan, hemicellulose and lignin recovery yields of 84%, 91% and 87%, respectively. Precipitation of the collected lignin-rich liquid fraction yielded a solid residue with high lignin content, offering possibilities for subsequent applications. Moreover, hydrolysability tests showed almost complete saccharification of the pretreated solid residue, which when combined with the low concentration of the generated inhibitory compounds, is representative of a good pretreatment approach. Scheffersomyces stipitis was capable of fermenting all of the glucose and xylose from the non-diluted hemicellulose fraction, resulting in an ethanol concentration of 17.5 g/L with 0.34 g/g yields. Similarly, Saccharomyces cerevisiae produced about 4% (v/v) ethanol concentration with 0.40 g/g yields, during simultaneous saccharification and fermentation (SSF) of the two-step pretreated solid residue at 10% (w/w) consistency. These results increased the overall conversion yields from a one-step steam explosion pretreatment by 1.4-fold, showing the effectiveness of including an extrusion step to enhance overall biomass fractionation and carbohydrates conversion via microbial fermentation processes.

Hydroalcoholic extracts from the bark of Quercus suber L. (Cork): optimization of extraction conditions, chemical composition and antioxidant potential

Cork is the bark of the tree Quercus suber L. which finds use in diverse applications. However, a significant percentage is still rejected and burned for energy production, despite containing valuable molecules for materials processing and with important biological activities. Herein, the optimization of the extraction process to obtain these molecules, using mild solvents and conditions, is described within a biorefinery perspective. The extracts were obtained by direct contact solvent extractions with water, ethanol and its mixtures for different time and temperatures, and evaluated for chemical composition, total phenolic content (TPC) and antioxidant properties [by DPPH radical scavenging, ferric reducing antioxidant power (FRAP), Trolox equivalent antioxidant capacity (TEAC) and oxygen radical absorbance capacity (ORAC) assays]. The results showed that the extraction process is accelerated and higher yields are achieved with the increase in temperature without chemical degradation or compromising the antioxidant capacity. For all solvents, at reflux temperature, more than 90% of the extractable material is obtained within 6 h (80% within 1 h). The highest TPC and antioxidant capacity are observed for the extracts obtained with mixtures of water and ethanol of similar volumes. The antioxidant capacity measured by DPPH, FRAP and TEAC assays was found to be proportional to the extract TPC, while ORAC is favored for higher percentages of ethanol on the extracting solvent. The main constituents of these extracts are the ellagitannins, vescalagin, castalagin and β-O-ethylvescalagin, along with other phenolic acids (mainly ellagic and gallic acids) and various flavonols. The extracts stability was monitored up to 1 year of storage with neither reduction in the antioxidant capacity nor chemical degradation. These results show that extracts with strong antioxidant potential and high content of bioactive molecules can be obtained from the processing of waste streams. Cork is a sustainable forest product and the development of new fields of application contributes toward a zero waste cycle for a complete material biorefinery.

Bioassay-guided fractionation, GC–MS identification and in vitro evaluation of antioxidant and antimicrobial activities of bioactive compounds from Eucalyptus globulus stump wood methanolic extract

The biomass of Eucalyptus globulus, and particularly the stump wood, has received increased attention in recent years, including in a biorefinery perspective. A previous work evaluated the crude methanolic extract of E. globulus stump wood regarding its potential antioxidant and antimicrobial properties. That work concluded that E. globulus stump wood could be considered as a source of bioactive polyphenols. In the present study, the crude methanolic extract of E. globulus stump wood was thus fractionated in order to isolate the components responsible for such biological properties. This extract was subjected to bioassay-guided fractionation and the antioxidant and antimicrobial properties of the fractions were then evaluated. The antioxidant activity was assessed by the DPPH scavenging assay and the antimicrobial properties were studied by bioautography and resazurin microtiter methods. The fractions presented considerable capacity to scavenge the DPPH free radicals and to inhibit the growth of bacterial and yeast strains. The results obtained for the fractions were even better than the ones obtained with the crude extract. The GC–MS analysis revealed that the major compounds present in the extract were gallic acid, ellagic acid, citramalic acid and citric acid.

Effect of aluminium sulphate-catalysed hydrolysis process on furfural yield and cellulose degradation of Cannabis sativa L. shives

Commercially, furfural is produced from pentosan-rich biomass using mineral acids as homogeneous catalysts. This study investigated a novel hydrolysis method that allows to obtain furfural from hemp shives with high yield and also to preserve the cellulose in the remaining biomass for other bioconversion processes. To date, hemp shives have not been investigated for furfural production. Cannabis sativa L. (“Bialobrzeskie” variety) shives were used as a feedstock due to the high content of pentosan (17.6% of oven-dried biomass). It means that the theoretically possible amount of furfural was 12.8% of oven-dried hemp shives. The effect of temperature (140–180 °C), the amount of catalyst (3–7% of oven-dried biomass) and the treatment time (10–90 min) on the furfural formation were studied. Whereas, the effect of the same temperature and the amount of catalyst on the changes of lignocellulose were studied after 90 min treatment time. Al2(SO4)3*18H2O was used as a catalyst for the conversion of C5-sugars to furfural. To show the catalytic properties of Al2(SO4)3*18H2O, autocatalysis was performed as a reference process using the same parameters. The highest yield of furfural, 73.7% of the theoretical yield, was obtained at 180 °C, 5% Al2(SO4)3*18H2O of oven-dried mass and 90 min. From the biorefinery perspective, the optimal hydrolysis parameters were 160 °C, 5% Al2(SO4)3*18H2O of oven-dried mass and 90 min. With these parameters, the yield of furfural was 62.7% of the theoretical yield, 99.2% of hemicelluloses were removed and 95.8% of cellulose was preserved and slightly depolymerized.

Forest residues as renewable resources for bio-based polymeric materials and bioenergy: chemical composition, structure and thermal properties

The potential of three different logging residues (woody chips, branches and pine needles) as renewable resources to produce environmentally friendly polymeric materials and/or biofuel has been critically evaluated in terms of their structure, chemical composition and thermal properties. Woody chips constitute the most attractive forest residue to be processed into polymeric materials in terms of their highest cellulose content, crystallinity and thermal stability. In contrast, pine needles and branches offer higher heating values and optimum product distribution for solid fuel applications due to their higher lignin content. In general, forest residual biomass has great potential for conversion into new added value products, such as composites or solid biofuel, thus constituting a sustainable waste management procedure from a biorefinery perspective. The correlation between the chemical and structural properties with the thermal/pyrolytic behavior of residual biomass offers valuable insights to assess their sustainable exploitation.

Non-alkaline solubilization of arabinoxylans from destarched wheat bran using hydrothermal microwave processing and comparison with the hydrolysis by an endoxylanase

Destarched wheat bran (DWB) contained 47.7% hemicellulose, with an arabinose/xylose ratio (A/X) equal to 0.54. When hydrolyzed by an endoxylanase, around 25% of the DWB was solubilized within 4h mostly as monomer-free arabinoxylans (AX) and predominantly arabinoxylo-oligosaccharides (AXOS), with A/X of 0.22. After 20h, the solid residue still contained more than 35% non-cellulosic saccharides. Then, microwave heating in pressure vessels was used to extract the AX from DWB under acid to neutral pH according to a Box–Behnken experimental design. The effects of temperature, time and pH were assessed on: (1) matter solubilization, (2) its content in total and free monosaccharides, (3) HMF and 2-furaldehyde, (4) A/X of the released polymers, (5) AX remaining in the residues. Those responses were also plotted against the combined severity factors (CSF). Such processes led to fast and efficient solubilizations of the hemicellulose into AX/AXOS/monosaccharides with variable yields and proportions. Three independent runs were conducted with the parameters optimizing the total saccharides of the solubilized matter in order to verify the model. Both processes can lead to tailored AX/AXOS mixtures with various A/X, according to the intended application. The microwave-screened parameters may be upscaled in a hydrothermal reactor in a multi-product biorefinery perspective.

ChemInform Abstract: Hydrothermal Liquefaction for Algal Biorefinery: A Critical Review

AbstractReview: 166 refs.

Environmental implications of crude glycerin used in special products for the metalworking industry and in biodegradable mulching films

Crude glycerin from biodiesel supply chain can replace synthetic glycerol or other chemicals in industrial applications. To improve sustainability according to the biorefinery perspective, a purification phase will be carried out only if it is really necessary to reach standards for industrial processes or final products. In metal working, the use of crude glycerin-based hydraulic fluids, replacing mineral oil-based and glycol-based ones, has fulfilled industrial requirements and made it possible to increase (i) worker safety because of its non-flammability; (ii) biodegradability and (iii) time-life of the product due to anti-wear properties; in addition, post-use waste management will be simplified, due to the possibility to declassify fluids as special waste. In biodegradable mulching films, the replacement of synthetic glycerol was successful because it made it possible both to maintain the same compounding conditions and to obtain the same yields and film biodegradation in an agronomic trial on muskmelon. The benefits compared with conventional polyethylene films are the same as conventional readily biodegradable films. The key parameters in the analytical composition of glycerin concerning specific industrial applications are discussed; the environmental benefits in metal working fluid formulation and in mulching film compounding are then assessed.

Laminaria digitata as a potential carbon source for succinic acid and bioenergy production in a biorefinery perspective

A novel biorefinery concept utilizing macroalgae Laminaria digitata to produce succinic acid, and direct the process residues for feed and energy production, is investigated in the present study. Enzymatic hydrolysis was performed at high solid loading (25%wv−1) resulting in solubilization of the carbohydrates to soluble sugars, which accumulated in the liquid hydrolysate. The overall sugar recovery in the macroalgae hydrolysate was 78.23%. Actinobacillus succinogenes 130Z was able to ferment macroalgae hydrolysate to succinic acid with a yield of 86.49% (gg−1 of total sugars) and an overall productivity of 0.50gL−1h−1. Removal of carbohydrates from the macroalgal biomass through enzymatic hydrolysis resulted in up-concentration of protein and lipid fractions in the post-hydrolysis solid residue (PHSR). Energy recovery of PHSR and fermentation broth through anaerobic digestion corresponded to 298 and 285NmLCH4g−1 VSadded, respectively. PHSR could potentially be used for: dietary food additive, fish feed, bioenergy production and added value products. This study opens possibility to conceive different biorefinery scenarios in which the efficient use of the macroalgal biomass fractions can provide numerous added-value bio-based products and energy.

Influence of starch on microalgal biomass recovery, settleability and biogas production

In the context of wastewater treatment with microalgae cultures, coagulation–flocculation followed by sedimentation is one of the suitable options for microalgae harvesting. This process is enabled by the addition of chemicals (e.g. iron). However, in a biorefinery perspective, it is important to avoid possible contamination of downstream products caused by chemicals addition. The aim of this study was to evaluate the effect of potato starch as flocculant for microalgal biomass coagulation–flocculation and sedimentation. The optimal flocculant dose (25mg/L) was determined with jar tests. Such a concentration led to more than 95% biomass recovery (turbidity<9NTU). The settleability of flocs was studied using an elutriation apparatus measuring the settling velocities distribution. This test underlined the positive effect of starch on the biomass settling velocity, increasing to >70% the percentage of particles with settling velocities >6.5m/h. Finally, biochemical methane potential tests showed that starch biodegradation increased the biogas production from harvested biomass.

Hydrothermal liquefaction for algal biorefinery: A critical review

Abstract Hydrothermal liquefaction (HTL) has recently received increasing attention due to its advantages in rapid reaction, using wet feedstocks with no lipid-content restriction. These characteristics make HTL especially suitable for conversion of algae into biocrude oil. This paper aims to provide a state-of-the-art review of HTL technologies from a perspective of algal biorefinery. In this review, we first summarize the updated researches and technologies of algae HTL. Specially, an “ Environmental-Enhancing Energy ” (E2E) paradigm based on algal biorefinery has been proposed and discussed. Second, the principles and crucial factors for algae HTL are discussed with focus on (1) algae species and characteristics including lipids, proteins and carbohydrates; (2) the operational parameters including total solids, holding temperature, retention time and catalysts; and (3) the critical principles of HTL reaction and the role of deoxygenation and denitrogenation. In addition, potential applications of HTL are discussed. Prospective and challenges of HTL for algal biorefinery are finally addressed including feedstock preparation, scale-up of algae HTL, and process integration.

Isolation and characterization of cellulose nanocrystals from spruce bark in a biorefinery perspective

The present study reports for the first time the isolation of cellulose fibers and cellulose nanocrystals (CNCs) from the bark of Norway spruce. The upgrading of bark cellulose to value-added products, such as CNCs, is part of the “bark biorefinery” concept. The removal of non-cellulosic constituents was monitored throughout the isolation process by detailed chemical composition analyses. The morphological investigation of the CNCs was performed using AFM and showed the presence of nanocrystals with an average length of 175.3nm and a diameter of 2.8nm, giving an aspect ratio of around 63. X-ray diffraction (XRD) analyses showed that the crystallinity index increased with successive treatments to reach a final value greater than 80% for CNCs. The thermal degradation of the isolated bark CNCs started at 190°C. Spruce bark appeared to be a new promising industrial source of cellulose fibers and CNCs.

Biomass feedstock contracts: Role of land quality and yield variability in near term feasibility

In the absence of an infrastructure for the harvest, storage and purchase of cellulosic biomass, contracting is an important mechanism through which biorefineries can ensure adequate feedstock supply. We develop an optimization model to assess the economic potential of dedicated energy crops when profit-maximizing farmers allocate croplands of varying quality toward biomass in response to multi-year contracts. We evaluate the economic competitiveness of perennial grasses with traditional commodity crops, in a case study of switchgrass production in Tennessee. Assuming short-term contracts, we consider the importance of payment structure, land quality, energy crop yield and projected commodity crop returns on a farmer's decision to accept a contract for biomass production. We find that a wholesale contract, in which the farmer is guaranteed a price per unit biomass, is most effective on the highest quality of land, while a contract in which the farmer is guaranteed a price per acre is most effective on lower quality land. From the biorefinery perspective, a wholesale contract is most effective for short-term contracts while an acreage contract is most effective for long-term contracts. Breakeven pricing will only secure feedstock from farmers who produce commodity crops with unfavorable price outlooks on lower quality land; therefore, the contract price must include a premium in order to compete for space in the crop mix. The yield profile of energy crops has a significant effect on the terms at which short-term contracts will be accepted and land allocated toward feedstock production. The extent to which energy crop yields observed in field trials can be maintained at commercial scale also has a substantial effect on the scale at which farmers would be willing to participate in energy crop production.