Abstract This study assesses the bioenergy potential of two types of aquatic biomass found in the Republic of Congo: the green macroalgae Ulva lactuca (UL) and Ledermanniella schlechteri (LS).Their combustion behaviour was assessed using elemental and biochemical analysis, TGA, bomb calorimetry and metal analysis. Their anaerobic digestion behaviour was determined using bio chemical methane potential (BMP) tests. The average HHV for LS is 14.1 MJ kg−1 , whereas UL is lower (10.5 MJ kg−1). Both biomasses have high ash contents and would be problematic during thermal conversion due to unfavourable ash behaviour. Biochemical analysis indicated high levels of carbohydrate and protein and low levels of lipids and lignin. Although the lipid profile is desirable for biodiesel production, the levels are too low for feasible extraction. High levels of carbohydrates and protein make both biomasses suitable for anaerobic digestion. BMP tests showed that LS and UL have an average of 262 and 161 mL CH4 gVS−1 , respectively. The biodegradability (BI) of LS and UL had an average value of 76.5% and 43.5%, respectively. The analysis indicated that these aquatic biomasses are unsuitable for thermal conversion and lipid extraction; however, conversion through anaerobic digestion is promising.

Abstract Influences of following anaerobic digestion (AD) parameters like microaeration, pH, and VSS (Volatile Suspended Solid) using sour cabbage as substrate was checked in the publication. Results of fermentation of sour cabbage under the condition of small oxygen addition presented in this research can be classified as dark fermentation (DF—a special case of AD) or hydrogenotrophic anaerobic digestion. The investigations were carried out for two concentrations of 5 g VSS/L and 10 g VSS/L of sour cabbage at pH 6.0. The oxygen flow rates (OFR) for 5 g VSS/L were in the range of 0.53 to 3.3 mL/h for obtaining 2% to 8% of oxygen. At low pH and microaeration, ethylene production was observed at a level below 0.05% in biogas. The highest volume of hydrogen for 5 g VSS/L was obtained for flow rate 0.58 O2 mL/h, giving hydrogen concentration in biogas in the range of 0 to 20%. For VSS 5 g/L and oxygen flow rate 0.58 mL/h; 0.021 L of hydrogen was produced per gram of VSS. At VSS 10 g/L and oxygen flow rate 1.4 mL/h at pH 6.0, 0.03 L of hydrogen was generated per gram. Microaeration from 0.58 mL/h to 0.87 mL/h was propitious for hydrogen production at 5 g VSS/L of sour cabbage and 1.4 mL/h for 10 g VSS/L. Another relevant factor is the volatile suspended solid factor of a substrate. Optimal hydrogen production from sour cabbage was for VSS 89.32%.

Abstract The promoting effect of Pd on a Cu/ZnO/Al2O3 catalyst for the aqueous glycerol hydrogenolysis process to produce 1,2-propanediol was studied. At a lower hydrogen pressure (2.07 MPa), using the Cu/ZnO/Al2O3 catalyst with 2 wt% Pd doped, could significantly improve the glycerol conversion (97.2%) and 1,2-propanediol selectivity (93.3%) compared with the unpromoted catalyst (69.4% and 89.7%, respectively). A power-law kinetic model, which took into account all the elementary reactions including glycerol dehydration and its reverse reaction, acetol hydrogenation, side reactions and ethylene glycol formation, was developed to comprehensively investigate the effect of Pd. Though the rate of glycerol dehydration using the Pd-promoted catalyst was found to be slightly lower, mainly due to the reduced number of acidic sites after adding Pd, the glycerol conversion rate was notably higher compared with using the unpromoted catalyst, mainly attributed to the enhanced activity of acetol hydrogenation by Pd. The rapid hydrogenation of acetol can inhibit the reverse reaction of glycerol dehydration, resulting in a higher glycerol conversion rate, so that glycerol dehydration is considered as the rate-determining step. In contrast, when the unpromoted catalyst was used, the rate of reverse glycerol dehydration was drastically increased due to the elevated acetol concentration, especially at a lower hydrogen pressure, resulting in a slower glycerol conversion rate; thus, acetol hydrogenation became the rate determining step. In addition, Pd can improve the reducibility of the catalyst, allowing the CuO to be reduced in situ during the reaction. Therefore, catalyst deactivation due to any potential oxidation of metallic copper during the reaction can be prevented.

Abstract Olive leaves (OLL) are an agri-food waste that may be regarded as a bioresource rich in bioactive polyphenolic metabolites. In this examination, simultaneous organosolv treatment/extraction of OLL polyphenols at elevated temperatures (>110 ◦C) has been optimized using glycerol, but also two glycerol-based deep eutectic solvents (DES). The assessment of the processes was based on the severity factor and the extraction efficiency factor. In any case, the treatment/extraction with a DES composed of glycerol and citric acid (GL-CA) was found to be the less severe and the most effective in recovering polyphenols from OLL, giving a yield of 69.35 mg gallic acid equivalents per g dry mass. On the other hand, liquid chromatography-mass spectrometry investigation revealed that extraction with either DES used provided extracts with differentiated polyphenolic profile than that obtained when water or 60% (v/v) aqueous ethanol was used as solvents. On the ground of these analysis, evidence emerged regarding hydrolysis of flavone glucosides when the treatment was performed with an alkaline DES composed of glycerol and sodium citrate. The extracts produced also exhibited diversified antioxidant activity, a fact putatively attributed to the different polyphenolic profiles. It was concluded that organosolv treatment/extraction of OLL for polyphenol recovery opens new endeavors in the valorization of this particular waste, but metabolite stability is an issue that merits profounder study.

Abstract Coffee wastes have large amounts of by-products rich in phenolic compounds such as chlorogenic and caffeic acid, with potential applications for developing fine chemicals such as caffeic acid phenethyl ester (CAPE). A screening for microorganisms was undertaken in a coffee plantation environment to isolate native tropical species able to modify secondary metabolites present in this kind of biomass enzymatically. From the screening, 130 fungal strains could grow in lipase inducer media. Fungal strains were identified via ITS-based sequencing. Classification based on BLAST assigned 51 isolates to 12 different genera, including Absidia, Aspergillus, Cunninghamella, Fusarium, Metarhizium, Meyerozyma, Mucor, Neocosmospora, Papiliotrema, Penicillium, Rhizopus, and Trichoderma. DNA sequencing identified 14 putative extracellular lipases. According to the extracellular lipase activity, the most promising strain was identified as Fusarium sp. by DNA barcoding. Extracellular lipases from this strain exhibited maximal hydrolytic activity at a temperature of 45 ◦C, a pH of 7.00, and 200 ppm of NaCl, with an affinity towards substrates having carbon chain lengths of 8 or longer. Under these conditions, lipase instead of esterase activity is the main feature. The Km and Vmax values calculated using p-nitrophenyl palmitate (pNPP) as hydrolysis substrate were 0.003 mM and 299.8 µmol min−1 mg−1 , respectively. Fusarium sp. lipases presented high stability during freeze–thawing, allowing the storage of enzyme solutions at −20 ◦C, but not as a lyophilized powder. According to our kinetic study, these lipases catalyzed CAPE hydrolysis, showing a progressive decrease in the concentration of the CAPE and a correspondent increase in the caffeic acid concentration as a product of this hydrolysis. Being able to carry out this type of reaction under mild conditions shows that Fusarium sp. lipases recognize CAPE as substrate and suggest CAPE synthesis (reverse reaction) and transformation can be engineered, using caffeic acid from coffee biomass, as a potential industrial application for these lipases.

Abstract Microalgae are known to have higher photosynthetic efficiencies when compared to land based plants. The use of microalgae biomass as a protein source is attracting attention due to its interesting protein composition and sustainable character when compared to conventional animal and plant protein-based sources. Nonetheless, the existence of a rigid cell wall is typical for most microalgae species, and this presents a serious obstacle to a higher bioaccessibility of their valuable protein fractions. Depending on the cell wall composition, the gastrointestinal digestion process itself can result in different pathways of protein absorption. It is then important to understand how microalgae cell wall structure can be affected during traditional and industrial production of its biomass once these questions are often overlooked. This review intends to fulfill this gap by addressing the major impacts of innovative sustainable processing of microalgae biomass, giving particular attention to drying operations and cellular disruption methods based on electric field application—such as pulsed electric fields (PEF) and moderate electric fields (MEF). Using microalgae biomass as food supplements at its full potential depends on its protein digestibility patterns, and subsequently their bioaccessibility and bioavailability. The importance of using in vitro gastrointestinal systems to understand the impact of innovative downstream processing of microalgae biomass will be addressed.