Chain elongation is a process that produces medium chain fatty acids such as caproic acid, which is one of the promising products of the carboxylate platform. This study analyzed the impact of bioaugmentation of heat-treated anaerobic digester sludge with Clostridium kluyveri (AS + Ck) on caproic acid production from a mixed substrate (lactose, lactate, acetate, and ethanol). It was compared with processes initiated with non-augmented heat-treated anaerobic digester sludge (AS) and mono-culture of C. kluyveri (Ck). Moreover, stability of the chain elongation process was evaluated by performing repeated batch experiments. All bacterial cultures demonstrated efficient caproate production in the first batch cycle. After 18 days, caproate concentration reached 9.06 ± 0.43, 7.86 ± 0.38, and 7.67 ± 0.37 g/L for AS, Ck, and AS + Ck cultures, respectively. In the second cycle, AS microbiome was enriched toward caproate production and showed the highest caproate concentration of 11.44 ± 0.47 g/L. On the other hand, bioaugmented culture showed the lowest caproate production in the second cycle (4.10 ± 0.30 g/L). Microbiome analysis in both AS and AS + Ck culture samples indicated strong enrichment toward the anaerobic order of Clostridia. Strains belonging to genera Sporanaerobacter, Paraclostridium, Haloimpatiens, Clostridium, and Bacillus were dominating in the bioreactors.

Enrichment Versus Bioaugmentation-Microbiological Production of Caproate from Mixed Carbon Sources by Mixed Bacterial Culture and Clostridium kluyveri.

Biological production of medium-chain carboxylates through chain elongation: An overview

There is a general interest in finding new ways of valorizing fruit and vegetable processing by-products. With this aim, applications of industrial fermentation to improve nutritional value, or to produce biologically active compounds, have been developed. In this sense, the fermentation of a wide variety of by-products including rice, barley, soya, citrus, and milling by-products has been reported. This minireview gives an overview of recent fermentation-based valorization strategies developed in the last 2 years. To aid the designing of new bioprocesses of industrial interest, this minireview also provides a detailed comparison of the fermentation conditions needed to produce specific bioactive compounds through a simple artificial neural network model. Different applications reported have been focused on increasing the nutritional value of vegetable by-products, while several lactic acid bacteria and Penicillium species have been used to produce high purity lactic acid. Bacteria and fungi like Bacillus subtilis, Rhizopus oligosporus, or Fusarium flocciferum may be used to efficiently produce protein extracts with high biological value and a wide variety of functional carbohydrates and glycosidases have been produced employing Aspergillus, Yarrowia, and Trichoderma species. Fermentative patterns summarized may guide the production of functional ingredients for novel food formulation and the development of low-cost bioprocesses leading to a transition toward a bioeconomy model.

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Valorization of Vegetable Food Waste and By-Products Through Fermentation Processes

To enhance hydrogen production efficiency and energy recovery, a sequential dark fermentation and microbial electrochemical cell (MEC) process was evaluated for hydrogen production from food waste. The hydrogen production, electrochemical performance and microbial community dynamics were investigated during startup of the MEC that was inoculated with different sludges. Results suggest that biogas production rates and hydrogen proportions were 0.83 ​L/L d and 92.58%, respectively, using anaerobic digested sludge, which is higher than that of the anaerobic granular sludge (0.55 ​L/L d and 86.21%). The microbial community were predominated by bacterial genus Acetobacterium, Geobacter, Desulfovibrio, and archaeal genus Methanobrevibacter in electrode biofilms and the community structure was relatively stable both in anode and cathode. The sequential system obtained a 53.8% energy recovery rate and enhanced soluble chemical oxygen demand (sCOD) removal rate of 44.3%. This research demonstrated an important approach to utilize dark fermentation effluent to maximize the conversion of fermentation byproducts into hydrogen.

Enhancement of hydrogen production and energy recovery through electro-fermentation from the dark fermentation effluent of food waste

Opportunities and challenges in microbial medium chain fatty acids production from waste biomass.

Performance and microbial characterization of two-stage caproate fermentation from fruit and vegetable waste via anaerobic microbial consortia.

The bioproduction of caproate from organic waste by anaerobic mixed culture is a very attractive technology for upgrading low-grade biomass to a high-value resource. However, the caproate production process is markedly restricted by the feedback inhibition of caproate. In this study, four types of anion-exchange resin were investigated for their enhancing capability in caproate fermentation of anaerobic mixed culture. The strong base anion-exchange resin D201 showed the highest adsorption capacity (62 mg/g), selectivity (7.50), and desorption efficiency (88.2%) for caproate among the test resins. Subsequently, the optimal desorption temperature and NaOH concentration of eluent for D201 were determined. The adsorption and desorption efficiency of D201 remained stable during eight rounds of the adsorption–desorption cycle, indicating a satisfactory reusability of D201. Finally, performances of caproate fermentation with and without resin adsorption for carboxylate were evaluated. The results demonstrated that the final concentration of caproate was improved from 12.43 ± 0.29 g/L (without adsorption) to 17.30 ± 0.13 g/L (with adsorption) and the maximum caproate production rate was improved from 0.60 ± 0.01 g/L/d to 2.03 ± 0.02 g/L/d. In the group with adsorption, the cumulative caproate production was increased to 29.10 ± 0.33 g/L broth, which was 134% higher than that of the control group. Therefore, this study provides effective approaches to enhance caproate production.

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Enhanced Anaerobic Mixed Culture Fermentation with Anion-Exchange Resin for Caproate Production

The invention discloses a method for preparing caproic acid through two-phase process anaerobic fermentation, and belongs to the technical field of waste resource treatment techniques and environment-friendly purification treatment. The method utilizes fruit and vegetable waste as an acidogenic-phase substrate, and the fruit and vegetable waste serving as the acidogenic-phase substrate builds a stable acidogenic fermentation system at the temperature of 35 DEG C and with the pH value being 6.0; the acidogenic-phase fermented liquid serves as a substrate, the caproic acid yield can reach 12.85g.L under the conditions that the temperature is 30 DEG C, the pH value is 6.8-7.0, the alcohol acid ratio is 4 to 1, that is, the ethyl alcohol additive amount is 17.22g.L , and thus efficientgeneration of caproic acid is achieved.

Method for preparing caproic acid through two-phase process anaerobic fermentation

The invention discloses a method for recycling and treating hexanoic acid in anaerobic fermentation effluents and belongs to the technical field of waste recycling and environment protection purification treatment. According to the method, a strong basicity ionic exchange resin D201 is applied to the anaerobic fermentation process, hexanoic acid is extracted in the carbon chain extension process,toxicity of molecular state hexanoic acid can be inhibited, positive reactions can be promoted, and hexanoic acid synthesis can be intensified. In the reaction process, the yield of the hexanoic acidcan be up to 17.31g*L-1, the production rate of the hexanoic acid can be 1.89g*L-1d-1, and the accumulation yield of the hexanoic acid is 27.47g*L-1.

Chunmei Liu

Papers

Performance and microbial characterization of two-stage caproate fermentation from fruit and vegetable waste via anaerobic microbial consortia.

Enhanced Anaerobic Mixed Culture Fermentation with Anion-Exchange Resin for Caproate Production

Method for preparing caproic acid through two-phase process anaerobic fermentation

Method for recycling and treating hexanoic acid in anaerobic fermentation effluent