Volatile fatty acid production from lignocellulosic biomass by lime pretreatment and its applications to industrial biotechnology

Valorisation of industrial hemp (Cannabis sativa L.) residues and cheese whey into volatile fatty acids for single cell protein production

The production of single cell protein (SCP) using lignocellulosic materials stands out as a promising route in the circular bioeconomy transition. However, multiple steps are necessary for lignocellulosics-to-SCP processes, involving chemical pretreatments and specific aerobic cultures. Whereas there are no studies that investigated the SCP production from lignocellulosics by using only biological processes and microbial biomass able to work both anaerobically and aerobically. In this view, the valorisation of industrial hemp (Cannabis sativa L.) biomass residues (HBRs), specifically hurds and a mix of leaves and inflorescences, combined with cheese whey (CW) was investigated through a semi-continuous acidogenic co-fermentation process (co-AF). The aim of this study was to maximise HBRs conversion into VFAs to be further used as carbon-rich substrates for SCP production. Different process conditions were tested by either removing CW or increasing the amount of HBRs in terms of VS (i.e., two and four times) to evaluate the performance of the co-AF process. Increasing HBRs resulted in a proportional increase in VFA production up to 3115 mg HAc L-1, with experimental production nearly 40% higher than theoretical predictions. The synergy between HBRs and CW was demonstrated, proving the latter as essential to improve the biodegradability of the former. The produced VFAs were subsequently tested as substrates for SCP synthesis in batch aerobic tests. A biomass concentration of 2.43 g TSS L-1 was achieved with a C/N ratio of 5.0 and a pH of 9.0 after two days of aerobic fermentation, reaching a protein content of 42% (g protein per g TSS). These results demonstrate the overall feasibility of the VFA-mediated HBR-to-SCP valorisation process.

Enhancing scalability and economic viability of lignocellulose-derived biofuels production through integrated pretreatment and methanogenesis arrest

The pursuit of affordable biofuels necessitates continuous refinement of valorization strategies, focusing on cost-effective feedstocks, accessible bioprocessing, and high-quality products. High energy input required during various stages, including pretreatment, post-pretreatment, and methanogenesis arrest, impeded the economic lignocellulose-derived biofuels production from anaerobic digestion (AD). Addressing this challenge, an upstream process integrating synergistic alkali pretreatment and arrested AD was proposed. Results demonstrated that an optimum reactor pH 10 yielded a volatile fatty acids (VFA) titer of 3.6 gCOD/L, only 23% lower than using methanogenesis inhibitor. The study further explored the interplay between initial pH, cell viability/functionality, and VFA production by assessing cell viability and cell population demographics. This integrated approach demonstrated a VFA yield of 364 gVFA/kgTSsubstrate at a cost of just USD 0.2/kgVFA, encompassing post-pretreatment and methanogenesis arrest, which underscores the viability of combining pretreatment and methanogenesis arrest for cost effective and scalable biofuels production.

Production of polyhydroxyalkanoates as a feasible alternative for an integrated multiproduct lignocellulosic biorefinery

Polyhydroxyalkanoates (PHAs) are considered an alternative to fossil fuel-based plastics. However, in spite of their interesting properties and their multiple applications, PHAs have not taken off as an industrial development. The reason is mainly due to the associated high-production costs, which represent a significant constraint. In recent years, the interest in lignocellulosic biomass (LCB) derived from crop, forestry or municipal waste by-products has been growing, since LCB is plentiful, cheap, renewable and sustainable. On this matter, the valorization of LCB into PHAs represents a promising route within circular economy strategies. However, much effort still needs to be made to improve the bioconversion yields and to enhance PHA production efficiency. So, this review focuses on reviewing the different options for PHA synthesis from LCB, stressing the progress in biomass deconstruction, enzymatic hydrolysis and microbial conversion. In addition, some of the current biological strategies for improving the process of bioconversion are discussed.

Valorisation of industrial hemp (Cannabis sativa L.) biomass residues through acidogenic fermentation and co-fermentation for volatile fatty acids production

In line with the emerging circular bioeconomy paradigm, the present study investigated the valorisation of abundant hemp biomass residues (HBRs) such as hurds (HH) and a mix of leaves and inflorescences (Mix), and other organic wastes (i.e., cheese whey and grape pomace) through the volatile fatty acid (VFA) production in mono- and co-acidogenic fermentation. The highest VFA yields, measured as acetic acid (HAc) per unit of volatile solids (VS), were obtained with the untreated Mix in mono-fermentation (185 ± 57 mg HAc/g VS) and with the combination of Mix and CW in co-fermentation (651 ± 65 mg HAc/g VS), while the highest HAc percentage reached up to 94% of total VFAs. Finally, a preliminary techno-economic evaluation revealed that the mono-fermentation of alkali pretreated HH could lead to the highest revenues among HBRs, reaching up to 710-1810, 618-1577 and 766-3722 €/ha∙year for the production of HAc, single cell protein and polyhydroxybutyrates, respectively.

Review and perspectives of enhanced volatile fatty acids production from acidogenic fermentation of lignocellulosic biomass wastes

Lignocellulosic biomass wastes are abundant resources that are usually valorized for methane-rich biogas via anaerobic digestion. Conversion of lignocellulose into volatile fatty acids (VFA) rather than biogas is attracting attention due to the higher value-added products that come with VFA utilization. This review consolidated the latest studies associated with characteristics of lignocellulosic biomass, the effects of process parameters during acidogenic fermentation, and the intensification strategies to accumulate more VFA. The differences between anaerobic digestion technology and acidogenic fermentation technology were discussed. Performance-enhancing strategies surveyed included (1) alkaline fermentation; (2) co-digestion and high solid-state fermentation; (3) pretreatments; (4) use of high loading rate and short retention time; (5) integration with electrochemical technology, and (6) adoption of membrane bioreactors. The recommended operations include: mesophilic temperature (thermophilic for high loading rate fermentation), C/N ratio (20-40), OLR (< 12 g volatile solids (VS)/(L·d)), and the maximum HRT (8-12 days), alkaline fermentation, membrane technology or electrodialysis recovery. Lastly, perspectives were put into place based on critical analysis on status of acidogenic fermentation of lignocellulosic biomass wastes for VFA production.

Anaerobic fermentation of hybrid Pennisetum mixed with fruit and vegetable wastes to produce volatile fatty acids

The production of volatile fatty acids (VFAs) via anaerobic fermentation is a new technology that provides a high-value utilization of biomass. This work used hybrid Pennisetum (HP) and fruit and vegetable waste (FVW) as raw materials to investigate the influence of different ratios of HP to FVW on the production of VFAs under different methanogenic inhibition conditions. It has been shown that both alkaline and neutral conditions (using methanogenic inhibitors), could generate higher acid yields than acidic conditions. Under initial alkaline conditions, mono-fermentation of HP and FVW could obtain maximum VFA yields of 596 ± 22 mg g-1 VS and 626 ± 7 mg g-1 VS, which were higher than those obtained under neutral conditions. In contrast, there was no remarkable difference in VFA yield between alkaline and neutral conditions when co-fermentation of HP and FVW was carried out. The VFA yields decreased significantly with the process of co-fermentation. The maximum VFA yields were decreased by 33.2% and 21.9% when HP was fermented with 15% and 30% of FVW, respectively. There was a clear difference in the composition of VFAs obtained under different initial conditions. The maximum selectivity was achieved under alkaline conditions, where the acetate content reached more than 85%. This study brings a theoretical basis for optimizing the anaerobic fermentation process of lignocellulose to produce VFAs.

Pretreatment and fermentation of lignocellulosic biomass: reaction mechanisms and process engineering

At a time of rapid depletion of oil resources, global food shortages and solid waste problems, it is imperative to encourage research into the use of appropriate pre-treatment techniques using regenerative raw materials such as lignocellulosic biomass.

Fermentation of wet-exploded corn stover for the production of volatile fatty acids

Volatile fatty acids (VFA) have been used as platform molecules for production of biofuels and bioproducts. In the current study, we examine the VFA production from wet-exploded corn stover through anaerobic fermentation using rumen bacteria. The total VFA yield (acetic acid equivalents) was found to increase from 22.8g/L at 2.5% total solids (TS) to 40.8g/L at 5% TS. It was found that the acetic acid concentration increased from 10g/L to 22g/L at 2.5% and 5% TS, respectively. An increased propionic acid production was seen between day 10 and 20 at 5% TS. Valeric acid (4g/L) was produced at 5% TS and not at 2.5% TS. Composition analysis showed that 50% of the carbohydrates were converted to VFA at 5% TS and 33% at 2.5% TS. Our results show that rumen fermentation of lignocellulosic biomass after wet explosion can produce high concentrations of VFA without addition of external enzymes of importance for the process economics of lignocellulosic biorefineries.

Volatile fatty acids as an added value from biowaste

The aim of the present work was to provide proof of concept of employing a co-culture of K. mobilis and E. coli for producing short and medium chain volatile fatty acids (VFAs) from kitchen biowaste and potato peels. To this aim, experiments were carried out at pilot-scale installation with a bioreactor of 250L. Different feeding strategies were tested under microaerobic conditions, at pH 6.0-6.5 in order to enhance chain elongation. Acetic acid and ethanol were dominating products in the initial stages of the bioprocess, but in a relatively short time of approx. 20-22h from the process start accumulation of propionic acid took place followed by a chain elongation to butyric and valeric acids. The highest final products yield of 325mg/g TS was achieved for the substrate load of 99.1g TS/L (VS of 91.1g/L) and pH 6.5, with the productivity of 448mg/L/h. However, the highest average VFAs chain length (3.77C) was observed in the process run with the loading of 63.2g TS/L and pH 6.0. In this study, we demonstrated that the existing symbiosis of the co-culture of K. mobilis and E. coli favours formation and chain elongation of VFA, induced most likely by the enhanced ethanol formation. Our finding differs from the previous research which focus mostly on anaerobic conditions of VFAs production. The results provide good basis for further optimisation of VFAs production process.

Acidogenic fermentation of Scenedesmus sp.-AMDD: Comparison of volatile fatty acids yields between mesophilic and thermophilic conditions

This study compared the acidogenic fermentation of Scenedesmus sp.-AMDD at laboratory-scale, under mesophilic (35°C) and thermophilic conditions (55°C). Preliminary batch tests were performed to evaluate best conditions for volatile fatty acid (VFA) production from microalgal biomass, with respect to the inoculum, pH and nutrients. The use of bovine manure as inoculum, the operating pH of 4.5 and the addition of a nutrient mix, resulted in a high VFA production of up to 222mgg(-1) total volatile solid (TVS), with a butyrate share of 27%. Both digesters displayed similar hydrolytic activity with 0.38±0.02 and 0.42±0.03 g soluble chemical oxygen demand (COD)g(-1) TVS for the digesters operated at 35 and 55°C, respectively. Mesophilic conditions were more favorable for VFA production, which reached 171±5, compared to 88±12 mg soluble CODg(-1) TVS added under thermophilic conditions (94% more). It was shown that in both digesters, butyrate was the predominant VFA.