Effect of steam explosion on waste copier paper alone and in a mixed lignocellulosic substrate on saccharification and fermentation

Effect of steam explosion on the morphological, textural, and compositional characteristics of betel nut

To reduce the adverse physical effects on the oral mucosa caused by excessive hardness of betel nut fibers, steam explosion was used to soften betel nuts. The effect of three operating parameters (pressure holding time, explosion pressure, and initial moisture content) on the morphology, texture, and chemical composition of the betel nuts was investigated. The fiber hardness and Shore hardness decreased by 56.17%-89.28% and 7.03%-34.29%, respectively, and the transverse tensile strength and fiber tensile strength also decreased by up to 60.72% and 24.62%, respectively. Moreover, the coefficient of static friction and moisture content increased. After steam explosion, the betel nut increased in transverse diameter, became darker and more yellow-red in color, and showed a damaged microstructure. The contents of free phenol and alkaloids decreased after steam explosion treatment, with free phenols and total alkaloids decreasing from 34.32 mg(GAE)/g and 7.84 mg/g to 21.58 mg(GAE)/g and 6.50 mg/g, respectively, after the A-50 s treatment condition. The steam explosion increased the quantity of phenols, alkaloids, and soluble solids released from the betel nut under the same simulated release conditions of the texture analyzer. The research also showed that increased pressure holding time and explosion pressure enhanced the explosion efficiency, while the initial moisture content was reduced the explosion efficiency. Therefore, steam explosion is an effective pretreatment approach to soften betel nut and facilitate healthy development of the betel nut industry.

Bioproduction of Linalool From Paper Mill Waste

A key challenge in chemicals biomanufacturing is the maintenance of stable, highly productive microbial strains to enable cost-effective fermentation at scale. A “cookie-cutter” approach to microbial engineering is often used to optimize host stability and productivity. This can involve identifying potential limitations in strain characteristics followed by attempts to systematically optimize production strains by targeted engineering. Such targeted approaches however do not always lead to the desired traits. Here, we demonstrate both ‘hit and miss’ outcomes of targeted approaches in attempts to generate a stable Escherichia coli strain for the bioproduction of the monoterpenoid linalool, a fragrance molecule of industrial interest. First, we stabilized linalool production strains by eliminating repetitive sequences responsible for excision of pathway components in plasmid constructs that encode the pathway for linalool production. These optimized pathway constructs were then integrated within the genome of E. coli in three parts to eliminate a need for antibiotics to maintain linalool production. Additional strategies were also employed including: reduction in cytotoxicity of linalool by adaptive laboratory evolution and modification or homologous gene replacement of key bottleneck enzymes GPPS/LinS. Our study highlights that a major factor influencing linalool titres in E. coli is the stability of the genetic construct against excision or similar recombination events. Other factors, such as decreasing linalool cytotoxicity and changing pathway genes, did not lead to improvements in the stability or titres obtained. With the objective of reducing fermentation costs at scale, the use of minimal base medium containing paper mill wastewater secondary paper fiber as sole carbon source was also investigated. This involved simultaneous saccharification and fermentation using either supplemental cellulase blends or by co-expressing secretable cellulases in E. coli containing the stabilized linalool production pathway. Combined, this study has demonstrated a stable method for linalool production using an abundant and low-cost feedstock and improved production strains, providing an important proof-of-concept for chemicals production from paper mill waste streams. For scaled production, optimization will be required, using more holistic approaches that involve further rounds of microbial engineering and fermentation process development.

Engineering aspects of hydrothermal pretreatment: From batch to continuous operation, scale-up and pilot reactor under biorefinery concept

Different pretreatments strategies have been developed over the years mainly to enhance enzymatic cellulose degradation. In the new biorefinery era, a more holistic view on pretreatment is required to secure optimal use of the whole biomass. Hydrothermal pretreatment technology is regarded as very promising for lignocellulose biomass fractionation biorefinery and to be implemented at the industrial scale for biorefineries of second generation and circular bioeconomy, since it does not require no chemical inputs other than liquid water or steam and heat. This review focuses on the fundamentals of hydrothermal pretreatment, structure changes of biomass during this pretreatment, multiproduct strategies in terms of biorefinery, reactor technology and engineering aspects from batch to continuous operation. The treatise includes a case study of hydrothermal biomass pretreatment at pilot plant scale and integrated process design.

Waste paper: An underutilized but promising source for nanocellulose mining

Nanocellulose has achieved an inimitable place and value in nano-materials research sector. Promising and exclusive physical, chemical and biological properties of nanocellulose make it an attractive and ideal material for various high end-user applications. Conventionally, the base material for nanocellulose i.e. cellulose is being extracted from various lignocellulosic raw materials (like wood, agro-industrial-residues, etc.) using pulping followed by bleaching sequences. As an alternate to lignocellulosic raw materials, waste paper also showed potential as a competent raw material due to its abundant availability and high cellulosic content (60-70%) with comparatively less hemicelluloses (10-20%) and lignin (5-10%) without any harsh treatments. The production yields of nanocellulose were reported to vary from 1.5% to 64% depending upon the waste papers and treatments given. The diameters of these nanocelluloses were reported in the range of 2-100 nm and crystallinity range around 54-95%. Thermal degradation of waste paper nanocellulose was varied from 187 °C to 371 °C. Although these properties are comparable with the nanocellulose obtained from lignocellulosic raw materials, yet waste paper is an underutilized source for nanocellulose preparation due to its ordinary fate of recycling, dumping and incineration. In the sight of necessity and possibility of waste paper utilization, this article reviews the outcomes of research carried out for preparation of nanocellulose using waste paper as a source of cellulose. There is a need of sincere investigation to convert this valuable waste to wealth i.e. waste papers to nanocellulose, which will be helpful in solid waste management to protect environment in economical way.

Process simulation and economic assessment of hydrothermal pretreatment and enzymatic hydrolysis of multi-feedstock lignocellulose - Separate vs combined processing

Biorefinery based on multi-feedstock lignocellulose can be viable where a sustainable supply of a single substrate is limited, for example in arid regions. Processing of mixed feedstocks has been studied in lab scale, however, its economics are less studied. In this study, an economic comparison was made between separate and combined (mixed) processing approaches for multi-feedstock lignocellulose for the production of monomeric sugars. This modular approach of focusing on sugar platform makes the results applicable for many applications using the sugars as feedstock. Feedstock considered in this study were the green and woody lignocellulose residues: Bermuda grass, Jasmine hedges, and date palm fronds. Results showed that, at an identical total feed rate, combined processing was more advantageous as compared to separate processing. A further sensitivity analysis on mixed combined processing showed that the cellulase enzyme price and feed price are the two major factors affecting the production cost.

Bioethanol production from spent mushroom compost derived from chaff of millet and sorghum

BACKGROUND

In Uganda, the chaff remaining from threshed panicles of millet and sorghum is a low value, lignocellulose-rich agricultural by-product. Currently, it is used as a substrate for the cultivation of edible Oyster mushrooms (Pleurotus ostreatus). The aim of this study was to assess the potential to exploit the residual post-harvest compost for saccharification and fermentation to produce ethanol.

RESULTS

Sorghum and millet chaff-derived spent oyster mushroom composts minus large mycelium particles were assessed at small-scale and low substrate concentrations (5% w/v) for optimal severity hydrothermal pre-treatment, enzyme loading and fermentation with robust yeasts to produce ethanol. These conditions were then used as a basis for larger scale assessments with high substrate concentrations (30% w/v). Millet-based compost had a low cellulose content and, at a high substrate concentration, did not liquefy effectively. The ethanol yield was 63.9 g/kg dry matter (DM) of original material with a low concentration (19.6 g/L). Compost derived from sorghum chaff had a higher cellulose content and could be liquefied at high substrate concentration (30% w/v). This enabled selected furfural-resistant yeasts to produce ethanol at up to 186.9 g/kg DM of original material and a concentration of 45.8 g/L.

CONCLUSIONS

Spent mushroom compost derived from sorghum chaff has the potential to be an industrially useful substrate for producing second-generation bioethanol. This might be improved further through fractionation and exploitation of hemicellulosic moieties, and possibly the exploitation of the mycelium-containing final residue for animal feed. However, spent compost derived from millet does not provide a suitably high concentration of ethanol to make it industrially attractive. Further research on the difficulty in quantitatively saccharifying cellulose from composted millet chaff and other similar substrates such as rice husk is required.

Hydrothermal pretreatment and enzymatic hydrolysis of mixed green and woody lignocellulosics from arid regions

Utilization of multi-specie feedstocks is imperative for application of lignocellulosic biorefineries in arid regions. Different lignocellulosic residues vary in composition and anatomical features. Pretreatment and enzymatic hydrolysis are two processes at the front end of any lignocellulosics biorefinery applying biochemical pathway, and have to efficiently deal with the variance in the feedstock composition and properties. However, there is limited knowledge about effect of mixing different lignocellulosics on pretreatment and enzymatic hydrolysis yields. In this study effect of mixing on the yields from hydrothermal pretreatment and enzymatic hydrolysis was analyzed by mixing three different lignocellulosic residues - Bermuda grass, Jasmine hedges, and date palm fronds. Results showed that the individual and the mixed lignocellulosics gave same yields when treated under similar conditions of hydrothermal pretreatment and enzymatic hydrolysis. It indicates that this mixture can be a suitable feedstock for lignocellulosic biorefinery.

Improve the Anaerobic Biodegradability by Copretreatment of Thermal Alkali and Steam Explosion of Lignocellulosic Waste

Effective alteration of the recalcitrance properties like crystallization of cellulose, lignin shield, and interlinking of lignocellulosic biomass is an ideal way to utilize the full-scale potential for biofuel production. This study exhibited three different pretreatment effects to enhance the digestibility of corn stover (CS) for methane production. In this context, steam explosion (SE) and thermal potassium hydroxide (KOH-60°C) treated CS produced the maximal methane yield of 217.5 and 243.1 mL/gvs, which were 40.0% and 56.4% more than untreated CS (155.4 mL/gvs), respectively. Copretreatment of thermal potassium hydroxide and steam explosion (CPTPS) treated CS was highly significant among all treatments and improved 88.46% (292.9 mL/gvs) methane yield compared with untreated CS. Besides, CPTPS also achieved the highest biodegradability up to 68.90%. Three kinetic models very well simulated dynamics of methane production yield. Moreover, scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction (XRD) analyses declared the most effective changes in physicochemical properties after CPTPS pretreatment. Thus, CPTPS might be a promising approach to deconstructing the recalcitrance of lignocellulosic structure to improve the biodegradability for AD.

Simultaneous saccharification and fermentation of steam exploded duckweed: Improvement of the ethanol yield by increasing yeast titre

This study investigated the conversion of Lemna minor biomass to bioethanol. The biomass was pre-treated by steam explosion (SE, 210°C, 10 min) and then subjected to simultaneous saccharification and fermentation (SSF) using Cellic® CTec 2 (20 U or 0.87 FPU g(-1) substrate) cellulase plus β-glucosidase (2 U g(-1) substrate) and a yeast inoculum of 10% (v/v or 8.0×10(7) cells mL(-1)). At a substrate concentration of 1% (w/v) an ethanol yield of 80% (w/w, theoretical) was achieved. However at a substrate concentration of 20% (w/v), the ethanol yield was lowered to 18.8% (w/w, theoretical). Yields were considerably improved by increasing the yeast titre in the inoculum or preconditioning the yeast on steam exploded liquor. These approaches enhanced the ethanol yield up to 70% (w/w, theoretical) at a substrate concentration of 20% (w/v) by metabolising fermentation inhibitors.