Improved high solids loading enzymatic hydrolysis and fermentation of cotton microdust by surfactant addition and optimization of pretreatment

A critical assessment on scalable technologies using high solids loadings in lignocellulose biorefinery: challenges and solutions

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.

Addressing two major limitations in high-solids enzymatic hydrolysis by an ordered polyethylene glycol pre-incubated strategy: Rheological properties and lignin adsorption for enzyme

High-solids enzymatic hydrolysis for biomass has currently received considerable interest. However, the solid effect during the process limits its economic feasibility. This work presented an ordered polyethylene glycol (PEG) pre-incubated strategy for enhancing the auxiliary effect of PEG in a high-solids enzymatic hydrolysis system. The substrate and enzyme were separately pre-incubated with PEG in this strategy. The ordered PEG pre-incubated strategies yielded a maximum glucose concentration of 166.6 g/L from 32 % (w/v) pretreated corncob with an enzymatic yield of 94.1 % by 72 h hydrolysis. Using this method, PEG not only lessened the lignin adsorption to cellulase but also altered particle rheological characteristics in the high-solids enzymatic hydrolysis system as a viscosity modifier. This study offered a new insight into the mechanism behind the PEG synergistic effect and would make it possible to achieve efficient high-solids loading hydrolysis in the commercial manufacture of cellulosic ethanol.

Performance of high solids enzymatic hydrolysis and bioethanol fermentation of food waste under the regulation of saponin

Bioethanol recovery from food waste through high solids enzymatic hydrolysis (HSEH) and high solids bioethanol fermentation (HSBF) alleviate the energy crisis. However, this cause decreased glucose and bioethanol yields due to the high solids content. In this study, saponin was introduced into food waste HSEH and HSBF systems to enhance the product yields. Under the regulation of saponin, the substrate released >90% of the theoretical reducing sugar. The glucose concentration increased by 137.41 g/L after 24 h of HSEH with 2.0% saponin. The bioethanol titer reached 73.2 g/L (1.0%-saponin). Untargeted metabolomics illustrating that saponin had higher antifungal properties at lower concentrations (0.5%-saponin) that caused a decrease in bioethanol yield. The addition of saponin concentrations of 1.0%∼3.0% promoted HSEH, HSBF, and the metabolism of Saccharomyces cerevisiae; thus, 1.0% was suggested for practical use. This study deepened the understanding of saponin in enhancing HSBF and provides theoretical support for further application.

Principal factors affecting the yield of dilute acid pretreatment of lignocellulosic biomass: A critical review

This review provides a critical analysis of the state of the art of dilute acid pretreatment applied to lignocellulosic biomass. Data from 63 publications were extracted and analysed. The majority of the papers used residence times of<30 min, temperature ranges from 100 °C to 200 °C, and acid levels between 0 % and 2 %. Yields are quantified directly after pretreatment (xylose content) or after enzymatic hydrolysis (glucose content). Statistical analyses allowed the time-temperature equivalence to be quantified for three types of biomass: they were formulated by non-linear expressions. In further works, investigating less explored areas, for example moderate temperature levels with longer residence times, is recommended. Pretreatment material (time-temperature kinetics, reactor type) and analytical methods should be standardized and better described. It becomes mandatory to promote the development of an open, findable, accessible, interoperable, and reusable data approach for pretreatments research.

Advances and perspectives on mass transfer and enzymatic hydrolysis in the enzyme-mediated lignocellulosic biorefinery: A review

Enzymatic hydrolysis is a critical process for the cellulase-mediated lignocellulosic biorefinery to produce sugar syrups that can be converted into a whole range of biofuels and biochemicals. Such a process operating at high-solid loadings (i.e., scarcely any free water or roughly ≥ 15% solids, w/w) is considered more economically feasible, as it can generate a high sugar concentration at low operation and capital costs. However, this approach remains restricted and incurs "high-solid effects", ultimately causing the lower hydrolysis yields with increasing solid loadings. The lack of available water leads to a highly viscous system with impaired mixing that exhibits strong transfer resistance and reaction limitation imposed on enzyme action. Evidently, high-solid enzymatic hydrolysis involves multi-scale mass transfer and multi-phase enzyme reaction, and thus requires a synergistic perspective of transfer and biotransformation to assess the interactions among water, biomass components, and cellulase enzymes. Porous particle characteristics of biomass and its interface properties determine the water form and distribution state surrounding the particles, which are summarized in this review aiming to identify the water-driven multi-scale/multi-phase bioprocesses. Further aided by the cognition of rheological behavior of biomass slurry, solute transfer theories, and enzyme kinetics, the coupling effects of flow-transfer-reaction are revealed under high-solid conditions. Based on the above basic features, this review lucidly explains the causes of high-solid hydrolysis hindrances, highlights the mismatched issues between transfer and reaction, and more importantly, presents the advanced strategies for transfer and reaction enhancements from the viewpoint of process optimization, reactor design, as well as enzyme/auxiliary additive customization.

Alkaline hydrogen peroxide pretreatment combined with bio-additives to boost high-solids enzymatic hydrolysis of sugarcane bagasse for succinic acid processing

Alkaline hydrogen peroxide (AHP) pretreatment of sugarcane bagasse (SCB) at mild conditions was optimized with response surface methodology (RSM), then enzymatic hydrolysis was performed at high-solids substrate loading (30 %, w/v), followed by fed-batch fermentation to convert the fermentable sugars into succinic acid (SA). Results showed the AHP pretreatment conditions of H₂O₂ concentration 5.5 % (v/v), solid-to-liquid ratio 0.08, pretreatment temperature 65 °C and time 5 h could achieve the highest sugar yield (74.3 %); both additives and fed-batch strategy were favored to boost enzymatic hydrolysis, the concentration and yield of total sugars reached to 195 g/L and 70 % with cellulase dosage of only 6 FPU/g dry biomass (DM); all glucose and xylose could be utilized after fed-batch fermentation, and the obtained concentration and yield of SA reached 41.4 g/L and 63.8 %. In summary, a SA conversion rate high to 0.29 g/g SCB raw material could be achieved via the developed process.

Medical Waste Treatment Technologies for Energy, Fuels, and Materials Production: A Review

The importance of medical waste management has grown during the COVID-19 pandemic because of the increase in medical waste quantity and the significant dangers of these highly infected wastes for human health and the environment. This innovative review focuses on the possibility of materials, gas/liquid/solid fuels, thermal energy, and electric power production from medical waste fractions. Appropriate and promising treatment/disposal technologies, such as (i) acid hydrolysis, (ii) acid/enzymatic hydrolysis, (iii) anaerobic digestion, (vi) autoclaving, (v) enzymatic oxidation, (vi) hydrothermal carbonization/treatment, (vii) incineration/steam heat recovery system, (viii) pyrolysis/Rankine cycle, (ix) rotary kiln treatment, (x) microwave/steam sterilization, (xi) plasma gasification/melting, (xii) sulfonation, (xiii) batch reactor thermal cracking, and (xiv) torrefaction, were investigated. The medical waste generation data were collected according to numerous researchers from various countries, and divided into gross medical waste and hazardous medical waste. Moreover, the medical wastes were separated into categories and types according to the international literature and the medical waste fractions’ percentages were estimated. The capability of the examined medical waste treatment technologies to produce energy, fuels, and materials, and eliminate the medical waste management problem, was very promising with regard to the near future.

Hot Compressed Water Pretreatment and Surfactant Effect on Enzymatic Hydrolysis Using Agave Bagasse

Agave bagasse is a residual biomass in the production of the alcoholic beverage tequila, and therefore, it is a promising raw material in the development of biorefineries using hot compressed water pretreatment (hydrothermal processing). Surfactants application has been frequently reported as an alternative to enhance monomeric sugars production efficiency and as a possibility to reduce the enzyme loading required. Nevertheless, the surfactant’s action mechanisms in the enzymatic hydrolysis is still not elucidated. In this work, hot compressed water pretreatment was applied on agave bagasse for biomass fractionation at 194 °C in isothermal regime for 30 min, and the effect of non-ionic surfactants (Tween 20, Tween 80, Span 80, and Polyethylene glycol (PEG 400)) was studied as a potential enhancer of enzymatic saccharification of hydrothermally pretreated solids of agave bagasse (AGB). It was found that non-ionic surfactants show an improvement in the conversion yield of cellulose to glucose (100%) and production of glucose (79.76 g/L) at 15 FPU/g glucan, the highest enhancement obtained being 7% regarding the control (no surfactant addition), using PEG 400 as an additive. The use of surfactants allows improving the production of fermentable sugars for the development of second-generation biorefineries.