Abstract: Biomass as a resource is present in large quantities and offers environmental benefits from sequestration of carbon to bioenergy production. Production of renewable and sustainable biofuel (bioethanol) from biomass is gaining overwhelming interest globally. Biofuels are important and beneficial from environmental and economic points of view. The gasohol, ethanol blended gasoline, utilization for the transportation sector significantly reduces greenhouse gas (GHG) emissions as well as consumption of fossil fuels. Bioethanol produced from renewable biomass especially lignocellulosic biomass (LCB) provides opportunities for a sustainable, cleaner, environmentally safe, carbon-neutral fuel, and green alternatives for fossil fuel. Although LCB is present in the massive amounts on planet earth, it is not utilized properly for bioethanol production due to many hurdles in the bioconversion process like pretreatment, high cost of enzymes, mixed sugar conversion, fermentation etc. Great efforts have been devoted in technological improvement in the bioconversion process including biotechnological and metabolic engineering fields. This review focuses on the current status, technological advances, and new interventions in the bioconversion process of LCB into bioethanol with special focus on pre-treatment methods, fermentation approaches, and detoxification processes.

Abstract: Glycerol is a common by-product of industrial biodiesel syntheses. Due to its properties, availability, and versatility, residual glycerol can be used as a raw material in the production of high value-added industrial inputs and outputs. In particular, products like hydrogen, propylene glycol, acrolein, epichlorohydrin, dioxalane and dioxane, glycerol carbonate, n-butanol, citric acid, ethanol, butanol, propionic acid, (mono-, di-, and triacylglycerols), cynamoil esters, glycerol acetate, benzoic acid, and other applications. In this context, the present study presents a critical evaluation of the innovative technologies based on the use of residual glycerol in different industries, including the pharmaceutical, textile, food, cosmetic, and energy sectors. Chemical and biochemical catalysts in the transformation of residual glycerol are explored, along with the factors to be considered regarding the choice of catalyst route used in the conversion process, aiming at improving the production of these industrial products.

Abstract: The seafood industry generates large volumes of wastes. These include processing discards consisting of shell, head, bones, intestine, fin, skin and others, and also low-value under-utilized fish, which are caught as by-catch of commercial fishing operations. In addition, fish processing generates voluminous amounts of wastewater as effluents. The discards, by-catch and effluents are rich in nutrients including proteins, amino acids, polyunsaturated fatty acids (PUFA) rich lipids, carotenoids, and minerals. The seafood wastes lead to losses of nutrients as well as serious environmental hazards. It is important that these wastes are treated by secondary processing to address the problems. Unlike most chemical processes biological treatments are environmental friendly, safe and cost-effective. These are based on bioconversions of components of the seafood waste into valuable ingredients, which are then recovered by green technologies. The bioconversion processes make use of microbial fermentations or direct actions of exogenously added enzymes. Recent developments in algal biotechnology offer novel processes for bioconversion of seafood components into algal biomass, which can be used as feedstock for the recovery of useful ingredients including biofuel. Integration of multiple processes into biorefinery have potentials for eco-friendly and cost-effective valorization of seafood wastes, which in turn can support sustainable seafood production and bioeconomy .

Abstract: Biogas produced in anaerobic digestion contains energetically useable methane (CH4) and unavoidable unwanted carbon dioxide (CO2). To increase the calorific value of this environmental-friendly renewable fuel recovered from wastewater, an upgrading process is necessary to reduce the high concentration of CO2 and increase the associated CH4 content. The pipe-line quality biomethane concentration can be achieved after biologically converting CO2 by either microorganisms or algae. Over the contemporary reviews published on the biogas upgrading, no paper has ever comprehensively covered the emerging biological methods for converting or reducing CO2. Thus, the biotechnologies for CO2 bioconversion such as H2-assisted chemoautotrophic reactor, gas fermentation, microbial electrochemical cells (MEC) and microalgae-based photosynthetic technique are comprehensively reviewed from the aspects of mechanisms, configurations, bottlenecks and efficiencies in this article. The strategies towards improving the performance of each technique regarding CO2 conversion are systematically analysed. The feasibility of each method from economic and environmental perspectives is also outlined. The outlook for biotechnologies with larger scalability and better economic or technical feasibility are then put forward to facilitate their applications for more efficient biogas upgrading.

Abstract: Plant cell wall hydrolysates contain not only sugars but also substantial amounts of acetate, a fermentation inhibitor that hinders bioconversion of lignocellulose. Despite the toxic and non-consumable nature of acetate during glucose metabolism, we demonstrate that acetate can be rapidly co-consumed with xylose by engineered Saccharomyces cerevisiae. The co-consumption leads to a metabolic re-configuration that boosts the synthesis of acetyl-CoA derived bioproducts, including triacetic acid lactone (TAL) and vitamin A, in engineered strains. Notably, by co-feeding xylose and acetate, an enginered strain produces 23.91 g/L TAL with a productivity of 0.29 g/L/h in bioreactor fermentation. This strain also completely converts a hemicellulose hydrolysate of switchgrass into 3.55 g/L TAL. These findings establish a versatile strategy that not only transforms an inhibitor into a valuable substrate but also expands the capacity of acetyl-CoA supply in S. cerevisiae for efficient bioconversion of cellulosic biomass. Cellulosic hydrolysates contain substantial amounts of acetate, which is toxic to fermenting microorganisms. Here, the authors engineer Baker’s yeast to co-consume xylose and acetate for triacetic acid lactone production from a hemicellulose hydrolysate of switchgrass.

Abstract: Industrial lignin such as kraft lignin is an abundant feedstock for renewable chemicals and materials. In this study, a process was developed for depolymerization of kraft lignin followed by an upgrading separation step and further bioconversion of the obtained monoaromatic compounds to muconic acid. First, industrial kraft lignin, Indulin AT, was processed into a guaiacol-rich stream using base-catalyzed depolymerization. This stream was subsequently upgraded using liquid-liquid extraction and evaporation to yield a more concentrated and less inhibitory stream, adapted for bioconversion. Finally, guaiacol was quantitatively converted to muconic acid through bioconversion using an engineered Pseudomonas putida strain containing cytochrome P450 and ferredoxin reductase for guaiacol assimilation and deletion of the native catBC genes for muconic acid production. Isomerization of muconic acid in a fermentation medium depending on pH was also studied. (Less)

Abstract: Bioconversion of medium-chain carboxylic acids (MCCAs) from biowastes through anaerobic mixed-culture fermentation is undergoing a revolution in terms of mitigating the lower fossil fuels requireme...

Abstract: Efficient utilization of all available carbons from lignocellulosic biomass is critical for economic efficiency of a bioconversion process to produce renewable bioproducts. However, the metabolic responses that enable Pseudomonas putida to utilize mixed carbon sources to generate reducing power and polyhydroxyalkanoate (PHA) remain unclear. Previous research has mainly focused on different fermentation strategies, including the sequential feeding of xylose as the growth stage substrate and octanoic acid as the PHA-producing substrate, feeding glycerol as the sole carbon substrate, and co-feeding of lignin and glucose. This study developed a new strategy—co-feeding glycerol and lignin derivatives such as benzoate, vanillin, and vanillic acid in Pseudomonas putida KT2440—for the first time, which simultaneously improved both cell biomass and PHA production. Co-feeding lignin derivatives (i.e. benzoate, vanillin, and vanillic acid) and glycerol to P. putida KT2440 was shown for the first time to simultaneously increase cell dry weight (CDW) by 9.4–16.1% and PHA content by 29.0–63.2%, respectively, compared with feeding glycerol alone. GC–MS results revealed that the addition of lignin derivatives to glycerol decreased the distribution of long-chain monomers (C10 and C12) by 0.4–4.4% and increased the distribution of short-chain monomers (C6 and C8) by 0.8–3.5%. The 1H–13C HMBC, 1H–13C HSQC, and 1H–1H COSY NMR analysis confirmed that the PHA monomers (C6–C14) were produced when glycerol was fed to the bacteria alone or together with lignin derivatives. Moreover, investigation of the glycerol/benzoate/nitrogen ratios showed that benzoate acted as an independent factor in PHA synthesis. Furthermore, 1H, 13C and 31P NMR metabolite analysis and mass spectrometry-based quantitative proteomics measurements suggested that the addition of benzoate stimulated oxidative-stress responses, enhanced glycerol consumption, and altered the intracellular NAD+/NADH and NADPH/NADP+ ratios by up-regulating the proteins involved in energy generation and storage processes, including the Entner–Doudoroff (ED) pathway, the reductive TCA route, trehalose degradation, fatty acid β-oxidation, and PHA biosynthesis. This work demonstrated an effective co-carbon feeding strategy to improve PHA content/yield and convert lignin derivatives into value-added products in P. putida KT2440. Co-feeding lignin break-down products with other carbon sources, such as glycerol, has been demonstrated as an efficient way to utilize biomass to increase PHA production in P. putida KT2440. Moreover, the involvement of aromatic degradation favours further lignin utilization, and the combination of proteomics and metabolomics with NMR sheds light on the metabolic and regulatory mechanisms for cellular redox balance and potential genetic targets for a higher biomass carbon conversion efficiency.