Conversion of Food Waste into 2,3-Butanediol via Thermophilic Fermentation: Effects of Carbohydrate Content and Nutrient Supplementation

Fermentation of food waste into 2,3-butanediol (2,3-BDO), a high-value chemical, is environmentally sustainable and an inexpensive method to recycle waste. Compared to traditional mesophilic fermentation, thermophilic fermentation can inhibit the growth of contaminant bacteria, thereby improving the success of food waste fermentation. However, the effects of sugar and nutrient concentrations in thermophilic food waste fermentations are currently unclear. Here, we investigated the effects of sugar and nutrients (yeast extract (YE) and peptone) concentrations on 2,3-BDO production from fermenting glucose and food waste media using the newly isolated thermophilic Bacillus licheniformis YNP5-TSU. When glucose media was used, fermentation was greatly affected by sugar and nutrient concentrations: excessive glucose (>70 g/L) slowed down the fermentation and low nutrients (2 g/L YE and 1 g/L peptone) caused fermentation failure. However, when food waste media were used with low nutrient addition, the bacteria consumed all 57.8 g/L sugars within 24 h and produced 24.2 g/L 2,3-BDO, equivalent to a fermentation yield of 0.42 g/g. An increase in initial sugar content (72.9 g/L) led to a higher 2,3-BDO titer of 36.7 g/L with a nearly theoretical yield of 0.47 g/g. These findings may provide fundamental knowledge for designing cost-effective food waste fermentation to produce 2,3-BDO.

Bioethanol production of second generation from corn cob

Bioethanol production from lignocellulosic materials has several environmental and economic advantages. In this work, corn cob was used to produce ethanol by fermentation. The cob was grounded, hydrolyzed chemically, and then enzymatically. Later, hydrolysates were used as a carbon source to formulate culture media that were inoculated with Saccharomyces cerevisiae; hollocellulose content was quantified by the ASTM D-1104 method; cellulose content by the TAPPTI 212 method; lignin content by the NREL / TP-510-42618 method; and ethanol was quantified by HPLC. In fermentation, bioethanol yields of up to 3.5 g / L were found, equivalent to YP/S value of 0.46, representing approximately 90% of the theoretical yield.

Enhanced Energy Recovery from Food Waste by Co-Production of Bioethanol and Biomethane Process

The primary objective of this research is to study ways to increase the potential of energy production from food waste by co-production of bioethanol and biomethane. In the first step, the food waste was hydrolysed with an enzyme at different concentrations. By increasing the concentration of enzyme, the amount of reducing sugar produced increased, reaching a maximum amount of 0.49 g/g food waste. After 120 h of fermentation with Saccharomyces cerevisiae, nearly all reducing sugars in the hydrolysate were converted to ethanol, yielding 0.43–0.50 g ethanol/g reducing sugar, or 84.3–99.6% of theoretical yield. The solid residue from fermentation was subsequently subjected to anaerobic digestion, allowing the production of biomethane, which reached a maximum yield of 264.53 ± 2.3 mL/g VS. This results in a gross energy output of 9.57 GJ, which is considered a nearly 58% increase in total energy obtained, compared to ethanol production alone. This study shows that food waste is a raw material with high energy production potential that could be further developed into a promising energy source. Not only does this benefit energy production, but it also lowers the cost of food waste disposal, reduces greenhouse gas emissions, and is a sustainable energy production approach.

Developing an Ethanol Utilization Pathway based NADH Regeneration System in Escherichia coli

Interests remain in searching for cofactor regeneration system with higher efficiency at lower substrate cost. Glucose dehydrogenase (GDH) system has been dominant in NADH regeneration, but it only has a theoretical yield of one NADH per glucose molecule. This work sought to explore the utility of a two-step ethanol utilization pathway (EUP) in pathway-based NADH regeneration. The pathway runs from ethanol to acetaldehyde and to acetyl-CoA with each step generating one NADH, that together results in a higher theoretical yield of two NADH per ethanol molecule. In this project, anaerobic biotransformation of ketone (acetophenone or butanone) to alcohol by cpsADH from Candida parapsilosis was used as readout for evaluating relative efficacy and operating modes for EUP cofactor regeneration in Escherichia coli BL21 (DE3). Experiment tests validated that EUP was more efficient than GDH in NADH regeneration. Further, growing cell delivered higher biotransformation efficiency compared to resting cell due to the driving force generated by cell growth. Finally, preculture or cultivation in M9 + 10 g/L ethanol medium delivered higher biotransformation efficiency compared to LB medium. Overall, EUP could help regenerate NADH in support of a biocatalytic reaction, and is more efficient in cofactor regeneration than GDH.

Mutations in adaptively evolved Escherichia coli LGE2 facilitated the cost-effective upgrading of undetoxified bio-oil to bioethanol fuel

Levoglucosan is a promising sugar present in the lignocellulose pyrolysis bio-oil, which is a renewable and environment-friendly source for various value-added productions. Although many microbial catalysts have been engineered to produce biofuels and chemicals from levoglucosan, the demerits that these biocatalysts can only utilize pure levoglucosan while inhibited by the inhibitors co-existing with levoglucosan in the bio-oil have greatly limited the industrial-scale application of these biocatalysts in lignocellulose biorefinery. In this study, the previously engineered Escherichia coli LGE2 was evolved for enhanced inhibitor tolerance using long-term adaptive evolution under the stress of multiple inhibitors and finally, a stable mutant E. coli-H was obtained after ~ 374 generations’ evolution. In the bio-oil media with an extremely acidic pH of 3.1, E. coli-H with high inhibitor tolerance exhibited remarkable levoglucosan consumption and ethanol production abilities comparable to the control, while the growth of the non-evolved strain was completely blocked even when the pH was adjusted to 7.0. Finally, 8.4 g/L ethanol was achieved by E. coli-H in the undetoxified bio-oil media with ~ 2.0% (w/v) levoglucosan, reaching 82% of the theoretical yield. Whole-genome re-sequencing to monitor the acquisition of mutations identified 4 new mutations within the globally regulatory genes rssB, yqhA, and basR, and the − 10 box of the putative promoter of yqhD-dgkA operon. Especially, yqhA was the first time to be revealed as a gene responsible for inhibitor tolerance. The mutations were all responsible for improved fitness, while basR mutation greatly contributed to the fitness improvement of E. coli-H. This study, for the first time, generated an inhibitor-tolerant levoglucosan-utilizing strain that could produce cost-effective bioethanol from the toxic bio-oil without detoxification process, and provided important experimental evidence and valuable genetic/proteinic information for the development of other robust microbial platforms involved in lignocellulose biorefining processes.

Enhanced glyoxylate shunt for efficient production of C4 derivatives using fatty acids feedstocks

Biosynthesis of TCA cycle-derived C4 chemicals through glyoxylate shunt is an attractive metabolic route because it can be drived by TCA-glyoxylate cycle force under aerobic conditions. However, yield of this route is low with at least 1/3 carbon loss from glucose. FAs could sufficiently provide acetyl-CoA by β-oxidation without carbon loss and directly enter the TCA-glyoxylate cycle, which is acknowledged as a promising alternative feedstock. Here β-alanine was selected as the target TCA cycle-derived chemical, of which the theoretical yield is 1.391 g/g FAs, much higher than that of glucose(0.49 g/g). By adopting multi-metabolic engineering strategies and relieving the active oxygen damage caused by FAs utilization, β-alanine production reached 78.05 g/L with a yield of 1.2 g/g, about 86% of theoretical yield. Our study establish a promising bioproduction route of β-alanine from waste FAs (such as gutter oil, palm fatty acid distillate etc.), and more importantly, provide an efficient platform for TCA cycle-derived C4 chemicals biosynthesis.

Anaerobic Codigestion of Slaughter Residues with Agricultural Waste of Amaranth Quinoa and Wheat

The objective of this research is to experimentally evaluate the anaerobic co-digestion of slaughterhouse residues in the city of Guaranda with straw residues from agriculture, such as: amaranth, quinoa and wheat. The study was carried out on a laboratory scale using 311 ml biodigesters under mesophilic conditions of 37 °C. Anaerobic co-digestion resulted in methane yields of 407 ml CH4/g VS, with a methane content in the biogas of 77% for the mixture of slaughterhouse waste and quinoa (RM-QU (25:75)). The increase in inoculum in the mixtures composed of slaughterhouse residues and quinoa increased the biodegradability between 17 and 22%. However, in the mixtures of slaughterhouse waste and amaranth (RM-AM (0:100)), a further increase in inoculum decreased biodegradability by 5%. To predict and simulate methane production, 5 kinetic models were used: modified Gompertz, logistic equation, transfer, cone and Richards. The cone model was the one that best adjusted the experimental values ​​with those predicted with an R2 of 0.982 to 0.999 and RMSE of 0.61 to 6.92 ml CH4/g VS. The calculation of the theoretical yield was carried out by stoichiometry and elemental analysis of the samples. Theoretical yields ranged between 480-564 ml CH4/g VS for all mixtures of RM with agricultural residues.

Evaluation of Cassava (Manihot esculenta Crantz) Productivity in Relation to Termite Attacks in Rural Area in Tivaouane (Senegal)

In Senegal, the cassava harvest, produced mainly in the department of Tivaouane (Thies), is 7.5 t/ha on average for a potential of 40 t/ha. The main variety produced in Tivaouane is Soya. The objective of this study is to evaluate the productivity of the soya variety farmed in Tivaouane in relation to termite damage. Specifically, it is intended to i) evaluate losses caused by termites and missing plants ii) evaluate the average number of tubers per plant, the average weight of a tuber and iii) calculate the yield of cassava production of the Soya variety farmed in Tivaouane. The methodology is based on sampling in order to evaluate parameters such as losses due to termites and missing plants, evaluation of the number of tubers per plant, the average weight of a tuber and the productivity of this variety of cassava. The average loss due to termite attack on dead feet is 1.2 t/ha and the loss due to missing feet is estimated at 3.4 t/ha. The average number of tubers per stand is 2.8 with an average weight of 1.1 kg per tuber. The theoretical yield obtained is 11 t/ha. The low average number of tubers is related to the variety, the quality of the soil and the crop conditions. However, the productivity of this variety of cassava cropped in Tivaouane is still low considering the potential of Senegal in terms of annual cassava production. An improvement in crop conditions, such as the way cuttings are planted, would be an advantage in increasing the productivity of the Soya variety.

Biodiesel from fish waste oil: synthesis via supercritical methanol and thermodynamic optimization

This study evaluates the potential of local fish waste oil as a feedstock for biodiesel via supercritical methanol transesterification (SCMT). Hexane was used as a cosolvent and the transesterification reaction was carried out in a continuous reactor under supercritical conditions. The response surface methodology (RSM) method was applied to analyse the effect of four independent variables, including the weight ratio of methanol to fish-waste oil (W), the reaction temperature (T), the pressure (P) and the feed flow rate (F), on the yield of the biodiesel production in supercritical methanol. According to the calculated optimal operating condition for the RSM, the values of W (22.3 weight ratio of methanol to fish waste oil), T (270°C), P (112.7 bar) and F (2.0 mL min–1) were achieved. Under the optimum conditions, the highest yield was estimated to be 94.6% (g/g). The obtained yield was found to be close to the theoretical yield (95.2%). This value suggests that the proposed strategy has a promising potential in the production of biodiesel fuel.