Enhanced Product Recovery from Glycerol Fermentation into 3-Carbon Compounds in a Bioelectrochemical System Combined with In Situ Extraction

Optimization of methane production from solid tuna waste: Thermal pretreatment and co-digestion

Fish canning industries generate large amounts of solid waste during their processing operations, creating a significant environmental challenge. Nonetheless, this waste can be efficiently and sustainably treated through anaerobic digestion. In this study, the potential of biogas production from anaerobic digestion of thermally pretreated and co-digested solid tuna waste was investigated. The thermal pretreatment of raw fish viscera resulted in a 50 % increase in methane yield, with a production of 0.27 g COD-CH4/g COD added. However, this pretreatment did not lead to a significant increase in biogas production for cooked tuna viscera. When non-thermally pretreated raw viscera was tested, a large accumulation of volatile fatty acids and long chain fatty acids was observed, with levels reaching 21 and 6 g COD/L, respectively. On the other hand, anaerobic co-digestion of cooked tuna viscera with fat waste significantly enhanced methane production, achieving 0.87 g COD-CH4/g COD added. In contrast, co-digestion of cooked tuna viscera with dairy waste and sewage sludge resulted in notably lower yields of 0.36 and 0.46 g COD-CH4/g COD added, respectively. These results may be related to the C/N ratio, which was found to be within the optimal range for anaerobic digestion only in the tuna and fat waste co-digestion assay.

Current Trends in Biological Valorization of Waste-Derived Biomass: The Critical Role of VFAs to Fuel A Biorefinery

The looming climate and energy crises, exacerbated by increased waste generation, are driving research and development of sustainable resource management systems. Research suggests that organic materials, such as food waste, grass, and manure, have potential for biotransformation into a range of products, including: high-value volatile fatty acids (VFAs); various carboxylic acids; bioenergy; and bioplastics. Valorizing these organic residues would additionally reduce the increasing burden on waste management systems. Here, we review the valorization potential of various sustainably sourced feedstocks, particularly food wastes and agricultural and animal residues. Such feedstocks are often micro-organism-rich and well-suited to mixed culture fermentations. Additionally, we touch on the technologies, mainly biological systems including anaerobic digestion, that are being developed for this purpose. In particular, we provide a synthesis of VFA recovery techniques, which remain a significant technological barrier. Furthermore, we highlight a range of challenges and opportunities which will continue to drive research and discovery within the field. Analysis of the literature reveals growing interest in the development of a circular bioeconomy, built upon a biorefinery framework, which utilizes biogenic VFAs for chemical, material, and energy applications.

Production of plant protection agents in medium containing waste glycerol by Streptomyces hygroscopicus: Bioprocess analysis

The surplus of waste glycerol, by-product of the biodiesel production process, is available at the global market. Some species of the genera Streptomyces have the ability to assimilate glycerol and convert it into valuable metabolic products. In the present study, the ability of Streptomyces hygroscopicus to assimilate waste glycerol and convert it into metabolic compounds with antifungal activity against four phytopathogenic fungi obtained from apple fruit samples expressing rot symptoms, was investigated. Production of antifungal metabolites by S. hygroscopicus was carried out in 3 l stirred tank bioreactor through 7 days. Fermentation was carried out at 27 °C with aeration rate of 1.5 vvm and agitation rate of 100 r.p.m. The aim of this work was to analyse bioprocess parameters and to determine at which stage of bioprocess the production of antifungal metabolites occurs. Activity of the cultivation liquid on two isolates of Alternaria alternata and two isolates of Fusarium avenaceum were determined every 12 h using in vitro well diffusion method. It was found that the maximum production of antifungal metabolites occurred at 108 hour of cultivation. Formed inhibition zones have shown that the produced antifungal metabolites have high efficacy on tested phytopathogenic fungi (inhibition zone diameter higher than 35 mm for all test organisms).

Oral Microbiota Display Profound Differential Metabolic Kinetics and Community Shifts upon Incubation with Sucrose, Trehalose, Kojibiose, and Xylitol

This study compares the metabolic properties of kojibiose, trehalose, sucrose, and xylitol upon incubation with representative oral bacteria as monocultures or synthetic communities or with human salivary bacteria in a defined medium. Compared to sucrose and trehalose, kojibiose resisted metabolism during a 48-h incubation with monocultures, except for Actinomyces viscosus Incubations with Lactobacillus-based communities, as well as salivary bacteria, displayed kojibiose metabolism, yet to a lesser extent than sucrose and trehalose. Concurring with our in vitro findings, screening for carbohydrate-active enzymes revealed that only Lactobacillus spp. and A. viscosus possess enzymes from glycohydrolase (GH) families GH65 and GH15, respectively, which are associated with kojibiose metabolism. Donor-dependent differences in salivary microbiome composition were noted, and differences in pH drop during incubation indicated different rates of sugar metabolism. However, functional analysis indicated that lactate, acetate, and formate evenly dominated the metabolic profile for all sugars except for xylitol. 16S rRNA gene sequencing analysis and α-diversity markers revealed that a significant shift of the microbiome community by sugars was more pronounced in sucrose and trehalose than in kojibiose and xylitol. In Streptococcus spp., a taxon linked to cariogenesis dominated in sucrose (mean ± standard deviation, 91.8 ± 6.4%) and trehalose (55.9 ± 38.6%), representing a high diversity loss. In contrast, Streptococcus (5.1 ± 3.7%) was less abundant in kojibiose, which instead was dominated by Veillonella (26.8 ± 19.6%), while for xylitol, Neisseria (29.4 ± 19.1%) was most abundant. Overall, kojibiose and xylitol incubations stimulated cariogenic species less yet closely maintained an abundance of key phyla and genera of the salivary microbiome, suggesting that kojibiose has low cariogenic properties.IMPORTANCE This study provides a detailed scientific insight on the metabolism of a rare disaccharide, kojibiose, whose mass production has recently been made possible. While the resistance of kojibiose was established with monocultures, delayed utilization of kojibiose was observed with communities containing lactobacilli and A. viscosus as well as with complex communities of bacteria from human saliva. Kojibiose is, therefore, less metabolizable than sucrose and trehalose. Moreover, although conventional sugars cause distinct shifts in salivary microbial communities, our study has revealed that kojibiose is able to closely maintain the salivary microbiome composition, suggesting its low cariogenic properties. This study furthermore underscores the importance and relevance of microbial culture and ex vivo mixed cultures to study cariogenicity and substrate utilization; this is in sharp contrast with tests that solely rely on monocultures such as Streptococcus mutans, which clearly fail to capture complex interactions between oral microbiota.

Production of volatile fatty acids through co-digestion of sewage sludge and external organic waste: Effect of substrate proportions and long-term operation

Volatile fatty acids (VFAs) are intermediates of anaerobic digestion with high value and wide range of usage. Co-digestion of sewage sludge and external organic waste (OW) for VFA production can help achieve both resource recovery and ensure sustainable and innovative waste management. In view of this, the effect of substrate proportions on VFA production from co-digestion of primary sewage sludge and OW is studied. Long-term operation in a semi-continuous reactor was performed to assess the resilience of such a system and the VFA-rich effluent was tested for its ability to be used as carbon source for denitrification. Co-digestion was initially carried out in batch reactors with OW proportion of 0%, 25%, 50%, 75%, 100% in terms of COD and scaled up in a semi-continuous reactor operation with 50% OW. In the short-term operation in the batch mode, acetic acid dominated, however, increasing OW fraction resulted in increased valeric and caproic acid production. Moreover, in the long-term semi-continuous operation, caproic acid dominated, accounting for ≈55% of VFAs. The VFA-rich effluent from the semi-continuous reactor achieved the highest denitrification rate as a carbon source when compared with acetic acid and methanol. The results demonstrate that co-fermentation can increase VFA yield and shift products from acetic acid to caproic acid in long-term operation and the VFAs can be used within wastewater treatment plants to close the loop.

A review of recent developments on kinetics parameters for glycerol electrochemical conversion - A by-product of biodiesel

Glycerol is a by-product produced from biodiesel, fatty acid, soap and bioethanol industries. Today, the value of glycerol is decreasing in the global market due to glycerol surplus, which primarily resulted from the speedy expansion of biodiesel producers around the world. Numerous studies have proposed ways of managing and treating glycerol, as well as converting it into value-added compounds. The electrochemical conversion method is preferred for this transformation due to its simplicity and hence, it is discussed in detail. Additionally, the factors that could affect the process mechanisms and products distribution in the electrochemical process, including electrodes materials, pH of electrolyte, applied potential, current density, temperature and additives are also thoroughly explained. Value-added compounds that can be produced from the electrochemical conversion of glycerol include glyceraldehyde, dihydroxyacetone, glycolic acid, glyceric acid, lactic acid, 1,2-propanediol, 1,3-propanediol, tartronic acid and mesoxalic acid. These compounds are found to have broad applications in cosmetics, pharmaceutical, food and polymer industries are also described. This review will be devoted to a comprehensive overview of the current scenario in the glycerol electrochemical conversion, the factors affecting the mechanism pathways, reaction rates, product selectivity and yield. Possible outcomes obtained from the process and their benefits to the industries are discussed. The utilization of solid acid catalysts as additives for future studies is also suggested.

Expanding the product spectrum of value added chemicals in microbial electrosynthesis through integrated process design-A review

Microbial electrosynthesis (MES) is a novel microbial electrochemical technology proposed for chemicals production with the storage of sustainable energy. However, the practical application of MES is currently restricted by the limited low market value of products in one-step conversion process, mostly acetate. A theme that is pervasive throughout this review is the challenges associated with the expanded product spectrum. Several recent research efforts to improve acetate production, using novel reactor configuration, renewable power supply, and various 3-D cathode are summarized. The importance of genetic modification, two-step hybrid process, as well as input substrates other than CO₂ are highlighted in this review as the future research paths for higher value chemicals production. At last, how to integrate MES with existing biochemicals processes is proposed. Definitely, more studies are encouraged to evaluate the overall performances and economic efficiency of these integrated process designs to make MES more competitive.