Current status and perspectives on biobutanol production using lignocellulosic feedstocks

Modified Activated Carbon: A Supporting Material for Improving Clostridium beijerinckii TISTR1461 Immobilized Fermentation

This study aimed to investigate the effect of activated carbon (AC) as an immobilization material in acetone-butanol-ethanol fermentation. The AC surface was modified with different physical (orbital shaking and refluxing) and chemical (nitric acid, sodium hydroxide and, (3-aminopropyl)triethoxysilane (APTES)) treatments to enhance the biobutanol production by Clostridium beijerinckii TISTR1461. The effect of surface modification on AC was evaluated using Fourier-transform infrared spectroscopy, field emission scanning electron microscopy, surface area analyses, and X-ray photoelectron spectroscopy, while the fermented broth was examined by high-performance liquid chromatography. The chemical functionalization significantly modified the physicochemical properties of the different treated ACs and further enhanced the butanol production. The AC treated with APTES under refluxing provided the best fermentation results at 10.93 g/L of butanol, 0.23 g/g of yield, and 0.15 g/L/h of productivity, which were 1.8-, 1.5-, and 3.0-fold higher, respectively, than that in the free-cell fermentation. The obtained dried cell biomass also revealed that the treatment improved the AC surface for cell immobilization. This study demonstrated and emphasized the importance of surface properties to cell immobilization.

Transformation of Agro-Waste into Value-Added Bioproducts and Bioactive Compounds: Micro/Nano Formulations and Application in the Agri-Food-Pharma Sector

The agricultural sector generates a significant amount of waste, the majority of which is not productively used and is becoming a danger to both world health and the environment. Because of the promising relevance of agro-residues in the agri-food-pharma sectors, various bioproducts and novel biologically active molecules are produced through valorization techniques. Valorization of agro-wastes involves physical, chemical, and biological, including green, pretreatment methods. Bioactives and bioproducts development from agro-wastes has been widely researched in recent years. Nanocapsules are now used to increase the efficacy of bioactive molecules in food applications. This review addresses various agri-waste valorization methods, value-added bioproducts, the recovery of bioactive compounds, and their uses. Moreover, it also covers the present status of bioactive micro- and nanoencapsulation strategies and their applications.

Thermophilic microbial deconstruction and conversion of natural and transgenic lignocellulose

The potential to convert renewable plant biomasses into fuels and chemicals by microbial processes presents an attractive, less environmentally intense alternative to conventional routes based on fossil fuels. This would best be done with microbes that natively deconstruct lignocellulose and concomitantly form industrially relevant products, but these two physiological and metabolic features are rarely and simultaneously observed in nature. Genetic modification of both plant feedstocks and microbes can be used to increase lignocellulose deconstruction capability and generate industrially relevant products. Separate efforts on plants and microbes are ongoing, but these studies lack a focus on optimal, complementary combinations of these disparate biological systems to obtain a convergent technology. Improving genetic tools for plants have given rise to the generation of low-lignin lines that are more readily solubilized by microorganisms. Most focus on the microbiological front has involved thermophilic bacteria from the genera Caldicellulosiruptor and Clostridium, given their capacity to degrade lignocellulose and to form bio-products through metabolic engineering strategies enabled by ever-improving molecular genetics tools. Bioengineering plant properties to better fit the deconstruction capabilities of candidate consolidated bioprocessing microorganisms has potential to achieve the efficient lignocellulose deconstruction needed for industrial relevance.

How to outwit nature: Omics insight into butanol tolerance

The energy crisis, depletion of oil reserves, and global climate changes are pressing problems of developed societies. One possibility to counteract that is microbial production of butanol, a promising new fuel and alternative to many petrochemical reagents. However, the high butanol toxicity to all known microbial species is the main obstacle to its industrial implementation. The present state of the art review aims to expound the recent advances in modern omics approaches to resolving this insurmountable to date problem of low butanol tolerance. Genomics, transcriptomics, and proteomics show that butanol tolerance is a complex phenomenon affecting multiple genes and their expression. Efflux pumps, stress and multidrug response, membrane transport, and redox-related genes are indicated as being most important during butanol challenge, in addition to fine-tuning of global regulators of transcription (Spo0A, GntR), which may further improve tolerance. Lipidomics shows that the alterations in membrane composition (saturated lipids and plasmalogen increase) are very much species-specific and butanol-related. Glycomics discloses the pleiotropic effect of CcpA, the role of alternative sugar transport, and the production of exopolysaccharides as alternative routes to overcoming butanol stress. Unfortunately, the strain that simultaneously syntheses and tolerates butanol in concentrations that allow its commercialization has not yet been discovered or produced. Omics insight will allow the purposeful increase of butanol tolerance in natural and engineered producers and the effective heterologous expression of synthetic butanol pathways in strains hereditary butanol-resistant up to 3.2 - 4.9% (w/v). Future breakthrough can be achieved by a detailed study of the membrane proteome, of which 21% are proteins with unknown functions.

Technical Aspects of Biofuel Production from Different Sources in Malaysia—A Review

Due to the depletion of fossil fuels, biofuel production from renewable sources has gained interest. Malaysia, as a tropical country with huge resources, has a high potential to produce different types of biofuels from renewable sources. In Malaysia, biofuels can be produced from various sources, such as lignocellulosic biomass, palm oil residues, and municipal wastes. Besides, biofuels are divided into two main categories, called liquid (bioethanol and biodiesel) and gaseous (biohydrogen and biogas). Malaysia agreed to reduce its greenhouse gas (GHG) emissions by 45% by 2030 as they signed the Paris agreement in 2016. Therefore, we reviewed the status and potential of Malaysia as one of the main biofuel producers in the world in recent years. The role of government and existing policies have been discussed to analyze the outlook of the biofuel industries in Malaysia.

Comparison of Biobutanol Production Pathways via Acetone-Butanol-Ethanol Fermentation Using a Sustainability Exergy-Based Metric

The incorporation of sustainability aspects into the design of chemical processes has been increasing since the last century. Hence, there are several proposed methodologies and indicators to assess chemical facilities through process analysis techniques. A comprehensive assessment involving economic, environmental, safety, and exergy parameters of two alternatives for butanol production from Manihot esculenta Crantz (cassava waste) is presented in this study. The modeling of process topologies involved using Aspen Plus software. Topology 1 generated a product flow rate of 316,477 t/y of butanol, while this value was 367,037 t/y for topology 2. Both processes used a feed flow of 3,131,439 t/y of biomass. This study used seven technical indicators to evaluate both alternatives, which include the return of investment, discounted payback period, global warming potential, renewability material index, inherent safety index, exergy efficiency, and exergy of waste ratio. Otherwise, this study implemented an aggregate index to assess overall sustainability performance. The results revealed that topology 2 presented higher economic normalized scores for evaluated indicators, but the most crucial difference between these designs came from the safety and exergetic indexes. Topology 1 and topology 2 obtained weighted scores equaling to 0.48 and 0.53; therefore, this study found that the second alternative gives a more sustainable design for butanol production under evaluated conditions.

Biobutanol production from municipal solid waste: Technical and economic analysis

Novel processes for the production of acetone-butanol-ethanol (ABE) from municipal solid waste (MSW) were developed and simulated using Aspen Plus®. In scenario 1, a conventional distillation system was used, while a gas stripping system was coupled with a fermenter in scenario 2. In scenario 3, pervaporation (PV) and gas stripping systems right after the fermentation reactor were applied. Gas stripping increased the total ABE produced while the addition of the PV module decreased the number of distillation columns from 6 to 2 as well as created 6.4% increments in the amount of butanol in comparison with scenario 1. Economical evaluation resulted in having payout periods of 15.9, 4.4, and 2.9 years for scenarios 1 to 3, respectively. These results show that using MSW as an inexpensive sugar-rich feedstock together with gas stripping PV system is a promising solution to overcome the major obstacles in the way of the ABE production.

Pathway dissection, regulation, engineering and application: lessons learned from biobutanol production by solventogenic clostridia

The global energy crisis and limited supply of petroleum fuels have rekindled the interest in utilizing a sustainable biomass to produce biofuel. Butanol, an advanced biofuel, is a superior renewable resource as it has a high energy content and is less hygroscopic than other candidates. At present, the biobutanol route, employing acetone-butanol-ethanol (ABE) fermentation in Clostridium species, is not economically competitive due to the high cost of feedstocks, low butanol titer, and product inhibition. Based on an analysis of the physiological characteristics of solventogenic clostridia, current advances that enhance ABE fermentation from strain improvement to product separation were systematically reviewed, focusing on: (1) elucidating the metabolic pathway and regulation mechanism of butanol synthesis; (2) enhancing cellular performance and robustness through metabolic engineering, and (3) optimizing the process of ABE fermentation. Finally, perspectives on engineering and exploiting clostridia as cell factories to efficiently produce various chemicals and materials are also discussed.