Rhamnolipids in lignocellulosic biorefineries: dual roles in waste valorization and process intensification.

The rising climate change concerns over the excessive exploitation of non-renewable sources have necessitated the need for alternative renewable and eco-friendly resources for the production of innovative materials, achieving the targets of bioeconomy. Lignocellulosic biomass (LB) constituted by polymeric sugars and lignin is an abundantly available plant-based renewable material in the form of agro-industrial food waste and crop residues that can be exploited for the production of an array of value-added chemicals and bioproducts. Cellulose is the most abundant natural and biodegradable organic polymer on earth derived from LB, with wide scale applications in the lignocellulosic biorefineries and food industries. The negative effects of food waste from agro-industrial activities could be reduced through the recovery of cellulose from these wastes and converting it into valuable forms. However, the extraction of cellulose from LB is a difficult task owing to the recalcitrant nature of biomass that restricts the easy accessibility of cellulose for value addition. Therefore, a suitable cellulose extraction method through the fractionation of LB is necessary for a better cellulose yield. Furthermore, owing to the enormous potential of nanocellulose (NC), researchers are keenly interested in developing ecologically acceptable cellulose extraction methods. Cellulose nanofibrils and nanocrystals confer excellent mechanical properties, non-toxic characteristics and biodegradability, due to which they possess wide-scale applications in diverse industrial sectors. The current review emphasizes the potential role of cellulose extraction and NC production from agro-food waste. The different pretreatment methods for their extraction from LB are outlined. The applications of nanocellulose in different areas are also discussed. The review also highlights the recent trends, challenges and future directions in the development of cellulose and NC-based commercial products.

Sweet sorghum [Sorghum bicolor (L.) Moench] is considered the most suitable crop for biofuel and grain production in Ethiopia's arid and semi‐arid lowland areas. A study was conducted in the 2017/2018 crop seasons at Melkassa Agricultural Research Center. The study aimed to evaluate sweet sorghum genotypes for grain and ethanol yield potential and to assess their genetic variability. The analysis of variance showed highly significant differences among the 28 genotypes for all traits studied, except for the number of tillers. Genotypes NTJ2, SDSL90167, 104GRD, E36‐1, Ent. #64DTN, IESV92028DL, and S35 were identified as having the highest juice, ethanol, and sugar yields. Additionally, genotypes with high grain yields were also linked to higher juice, sugar, and ethanol production. Both the phenotypic coefficient of variation (PCV) and genotypic coefficient of variation (GCV) were highest for dry stalk yield, sugar, ethanol, and juice yields. The PCV estimates were higher than GCV for all traits, indicating environmental influence. High heritability and genetic advance were observed for dry stalk yield, sugar yield, ethanol yield, and juice yield. Grain yield positively correlated with panicle width, panicle weight, and 1000‐seed weight, while longer days to flowering and maturity negatively impacted grain yield. Additionally, fresh stalk yield, juice yield, sugar yield, and ethanol yield were positively correlated. Sweet sorghum shows great potential for biofuel and grain production in Ethiopia's arid regions, warranting government support for ethanol‐focused projects.

Integrating starchy substrate into cellulosic ethanol production to boost ethanol titers and yields

Influence of impregnation with lactic acid on sugar yields from steam pretreatment of sugarcane bagasse and spruce, for bioethanol production

Sugar beet (Beta vulgaris L. subsp. vulgaris) is deemed to be one of the most promising bioethanol feedstock crops in northern Japan. To establish viable sugar beet‐based bioethanol production systems, energy‐efficient protocols in sugar beet cultivation are being intensively sought. On this basis, the effects of alternative agronomic practices for sugar beet production on total energy inputs (from fuels and agricultural materials during cultivation and transportation) and ethanol yields (estimated from sugar yields) were assessed in terms of (i) direct drilling, (ii) reduced tillage (no moldboard plowing), (iii) no‐fungicide application, (iv) using a high‐yielding beet genotype, (v) delayed harvesting and (vi) root+crown harvesting. Compared with the conventional sugar beet production system used in the Tokachi region of Hokkaido, northern Japan, which makes use of transplants, direct drilling and no‐fungicide application contributed to reduced energy inputs from raising seedlings and fungicides, respectively, but sugar (or ethanol) yields were also reduced by these practices, to a greater equivalent extent than the reductions in energy inputs. Consequently, direct drilling (6.84 MJ L−1) and no‐fungicide application (7.78 MJ L−1) worsened the energy efficiency (total energy inputs to produce 1 L of ethanol), compared with conventional sugar beet production practices (5.82 MJ L−1). Sugar yields under conventional plow‐based tillage and reduced tillage practices were similar, but total energy inputs were reduced as a result of reduced fuel consumption from not plowing. Hence, reduced tillage showed improved energy efficiency (5.36 MJ L−1). The energy efficiency was also improved by using a high‐yielding genotype (5.23 MJ L−1) and root+crown harvesting (5.21 MJ L−1). For these practices, no major changes in total energy inputs were noted, but sugar yields were consistently increased. Neither total energy inputs nor ethanol yields were affected by extending the vegetative growing period by delaying harvesting.

Chapter 20 - Valorization of lignocellulosic-based wastes

Technological advancement in the production of biohydrogen from lignocellulosic biomass: A review

Research advances on the consolidated bioprocessing of lignocellulosic biomass

To evaluate sugar recoveries and fermentabilities of eight lignocellulosic raw materials following mild acid pretreatment and enzyme hydrolysis using a recombinant strain of Zymomonas mobilis. Dilute acid pretreatment (2% H(2) SO(4) ) with 10% (w/v) substrate loading was performed at 134°C for 60 min followed by enzyme hydrolysis at 60°C. The results demonstrated that hydrolysis of herbaceous raw materials resulted in higher sugar recoveries (up to 60-75%) than the woody sources (<50%). Fermentation studies with recombinant Z. mobilis ZM4 (pZB5) demonstrated that final ethanol concentrations and yields were also higher for the herbaceous hydrolysates. Significant reduction in growth rates and specific rates of sugar uptake and ethanol production occurred for all hydrolysates, with the greatest reductions evident for woody hydrolysates. Further studies on optimization of enzyme hydrolysis established that higher sugar recoveries were achieved at 50°C compared to 60°C following acid pretreatment. Of the various raw materials evaluated, the highest ethanol yields and productivities were achieved with wheat straw and sugarcane bagasse hydrolysates. Sorghum straw, sugarcane tops and Arundo donax hydrolysates were similar in their characteristics, while fermentation of woody hydrolysates (oil mallee, pine and eucalyptus) resulted in relatively low ethanol concentrations and productivities. The concentrations of a range of inhibitory compounds likely to have influence the fermentation kinetics were determined in the various hydrolysates. The study focuses on lignocellulosic materials available for second generation ethanol fermentations designed to use renewable agricultural/forestry biomass rather than food-based resources. From the results, it is evident that relatively good sugar and ethanol yields can be achieved from some herbaceous raw materials (e.g. sugarcane bagasse and sorghum straw), while much lower yields were obtained from woody biomass.

In this study, wheat straw was pretreated with a microfluidizer to improve its enzymatic hydrolysis and ethanol yields. The pretreatment was performed at various pressures (500, 1000, and 1500 bar) and solid loadings (1, 2, and 3%). The microfluidized biomass was then subjected to hydrolysis and simultaneous saccharification and co-fermentation (SSCF) experiments at different enzyme loadings (5, 10, and 15 FPU/g dry wheat straw) using a mutant yeast. The results indicated that the microfluidization method alters the structure of biomass and leads to a reduction in lignin content. The samples pretreated at 1% solid loading contained the minimum lignin concentration and provided the maximum sugar and ethanol yields. These results signified that the microfluidization method is more effective on biomass at low solid loadings. The process conditions were optimized for higher ethanol and sugar yields using response surface methodology (RSM). The optimum pressure and solid and enzyme loadings were found as 1500 bar, 1%, and 15 FPU/g dry wheat straw, respectively. The yields obtained at this condition were 82%, 94%, and 65% for glucose, xylose, and ethanol, respectively. High sugar yields implied that microfluidization is an effective pretreatment method for cellulosic ethanol production. On the other hand, low ethanol yield may indicate that the microorganism was sensitive to inhibitory compounds present in the fermentation medium.

Relationship to reducing sugar production and scanning electron microscope structure to pretreated hemp hurd biomass (Cannabis sativa)

This issue of Biotechnology Journal is a regular issue edited by Prof. Michael Wink. The issue covers all the major focus areas of the journal, including medical biotechnology, synthetic biology, and novel biotechnological methods.

The pretreatment and the enzymatic saccharification are the key steps in the extraction of fermentable sugars for further valorization of lignocellulosic biomass (LCB) to biofuels and value-added products via biochemical and/or chemical conversion routes. Due to low density and high-water absorption capacity of LCB, the large volume of water is required for its processing. Integration of pretreatment, saccharification, and co-fermentation has succeeded and well-reported in the literature. However, there are only few reports on extraction of fermentable sugars from LCB with high biomass loading (>10% Total solids-TS) feasible to industrial reality. Furthermore, the development of enzymatic cocktails can overcome technology hurdles with high biomass loading. Hence, a better understanding of constraints involved in the development of technology with high biomass loading can result in an economical and efficient yield of fermentable sugars for the production of biofuels and bio-chemicals with viable titer, rate, and yield (TRY) at industrial scale. The present review aims to provide a critical assessment on the production of fermentable sugars from lignocelluloses with high solid biomass loading. The impact of inhibitors produced during both pretreatment and saccharification has been elucidated. Moreover, the limitations imposed by high solid loading on efficient mass transfer during saccharification process have been elaborated.

Thermophilic bacteria have gained increased attention as candidates for bioethanol production from lignocellulosic biomass. This study investigated ethanol production by Thermoanaerobacter strain J1 from hydrolysates made from lignocellulosic biomass in batch cultures. The effect of increased initial glucose concentration and the partial pressure of hydrogen on end product formation were examined. The strain showed a broad substrate spectrum, and high ethanol yields were observed on glucose (1.70 mol/mol) and xylose (1.25 mol/mol). Ethanol yields were, however, dramatically lowered by adding thiosulfate or by cocultivating strain J1 with a hydrogenotrophic methanogen with acetate becoming the major end product. Ethanol production from 4.5 g/L of lignocellulosic biomass hydrolysates (grass, hemp stem, wheat straw, newspaper, and cellulose) pretreated with acid or alkali and the enzymes Celluclast and Novozymes 188 was investigated. The highest ethanol yields were obtained on cellulose (7.5 mM·g−1) but the lowest on straw (0.8 mM·g−1). Chemical pretreatment increased ethanol yields substantially from lignocellulosic biomass but not from cellulose. The largest increase was on straw hydrolysates where ethanol production increased from 0.8 mM·g−1 to 3.3 mM·g−1 using alkali-pretreated biomass. The highest ethanol yields on lignocellulosic hydrolysates were observed with hemp hydrolysates pretreated with acid, 4.2 mM·g−1.

Production of biofuel such as ethanol from lignocellulosic biomass is a beneficial way to meet sustainability, energy security, and environmental goals. Lignocellulosic biomass such as source-separated organic (SSO) waste is particularly attractive since it is widely available, often at a negative cost, reduce the land depletion from using food-based biomass for ethanol production and reduce the amount of generated waste. Therefore, in order to meet the future fuel demands and cope with increasing volume of municipal waste this study was a first attempt to use SSO as a feedstock for ethanol production. The main objectives of the study were: a) to compare standard and modified celluloseorganic- solvent-based lignocellulosic fractionation (COSLIF) pretreatment of SSO waste for ethanol production in terms of enzyme savings, sugar formation and ethanol yields; b) to produce ethanol from SSO by using modified COSLIF pretreatment and fermentation with two different recombinant strains: Z. mobilis 8b and S. cerevisiae DA2416; and c) to develop experimental kinetic model capable of predicting behavior of batch SSCF on SSO waste with different SSO substrate concentrations using Berkeley Madonna program. Based on the obtained results, it was found that SSO is an excellent feedstock material for ethanol conversion. The efficiency of modified COSLIF pretreatment was improved by 20% compared to standard method using ethanol washing of pretreated SSO samples during the experimental procedures instead of acetone. On average, glucose yield from SSO samples pretreated by modified COSLIF was about 90% compared to 10% for untreated samples. S. cerevisiae DA2416 outperformed Z. mobilis 8b on ethanol yields during the fermentation process, with 0.50 g ethanol/g potential sugar fed on SSO in less than 5 days, with a 96% cellulose conversion, totalling in 150 g/L ethanol produced. A kinetic model with newly integrated values of experimentally defined SSO feedstock constants was proven to predict the ethanol yield accurately with substrate concentration ranges of 20 g/L - 50 g/L. Model prediction at higher substrate concentration (e.g. 100 g/L) deviated from the experimental values, suggesting that ethanol inhibition is a major factor in bioethanol conversion.