Effect of pH and buffer on butyric acid production and microbial community characteristics in bioconversion of rice straw with undefined mixed culture

Critical impact of pressure regulation on carbon dioxide biosynthesis

Carbon dioxide (CO2) biosynthesis is a promising alternative to traditional chemical synthesis. However, its application in engineering is hampered by poor gas mass transfer rates. Pressurization is an effective method to enhance mass transfer and increase synthesis yield, although the underlying mechanisms remain unclear. This review examines the effects of high pressure on CO2 biosynthesis, elucidating the mechanisms behind yield enhancement from three perspectives: microbial physiological traits, gas mass transfer and synthetic pathways. The critical role of pressurization in improving microbial activity and gas transfer efficiency is emphasized, with particular attention to maintaining pressure within microbial tolerance limits to maximize yield without compromising cell structure integrity.

Efficient butyrate production from rice straw in an optimized cathodic electro-fermentation process

Butyrate production from renewable biomass shows great potential against climate change and over-consumption of fossil fuels. Herein, key operational parameters of a cathodic electro-fermentation (CEF) process were optimized for efficient butyrate production from rice straw by mixed culture. The cathode potential, controlled pH and initial substrate dosage were optimized at -1.0 V (vs Ag/AgCl), 7.0 and 30 g/L, respectively. Under the optimal conditions, 12.50 g/L butyrate with yield of 0.51 g/g-rice straw were obtained in batch-operated CEF system. In fed-batch mode, butyrate production significantly increased to 19.66 g/L with the yield of 0.33 g/g-rice straw, but 45.99% butyrate selectivity still needs to be improved in future. Enriched butyrate producing bacteria (Clostridium cluster XIVa and IV) with proportion of 58.75% on the 21st day of the fed-batch fermentation, contributed to the high-level butyrate production. The study provides a promising approach for efficient butyrate production from lignocellulosic biomass.

Butyric acid: fermentation production using organic waste as low-cost feedstocks

Butyric acid is an important chemical which has many applications in the chemical, food, and pharmaceutical industries. Butyraldehyde, which is derived from propylene, is now converted into butyrate by petrochemical processes known as oxo synthesis. Because of its poor productivity and low butyrate concentration in the fermentation broth, biotechnological production of butyric acid is not economically viable. Typically, a sizable amount of the overall production expenses goes toward the cost of the fermentation substrate. If the fermentation process can use minimal biomass as the feedstock, a cost-competitive production of butyric acid from the fermentation technique would be generated with a strong market prospect. Organic wastes are recommended as a source of butyric acid fermentation feedstock because they are inexpensive, can be generated in huge numbers, and are biodegradable. With a focus on the low-cost feedstock, the many uses of butyric acid are discussed, with its present production status. As a result, this paper explores several butyric acid fermentation-related problems and offers ideas for potential solutions.

Microbial communities for valorizing biomass using the carboxylate platform to produce volatile fatty acids: A review

The carboxylate platform employs a diverse microbial consortium of anaerobes in which the methanogens are inhibited. Nearly all biomass components are digested to a mixture of C1-C8 monocarboxylic acids and their corresponding salts. The methane-arrested anaerobic digestion proceeds readily without needing to sterilize biomass or equipment. It accepts a wide range of feedstocks (e.g., agricultural residues, municipal solid waste, sewage sludge, animal manure, food waste, algae, and energy crops), and produces high product yields. This review highlights several important aspects of the platform, including its thermodynamic underpinnings, influences of inoculum source and operating conditions on product formation, and downstream chemical processes that convert the carboxylates to hydrocarbon fuels and oxygenated chemicals. This review further establishes the carboxylate platform as a viable and economical route to industrial biomass utilization.

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.

Modified anaerobic digestion model No.1 (ADM1) for modeling anaerobic digestion process at different ammonium concentrations

Anaerobic digestion (AD) is an established method for sustainable energy production. Anaerobic digestion model No.1 (ADM1) was used to simulate methane production (MP) and volatile fatty acid (VFA) concentrations at different ammonium concentrations. In accordance with the incomplete description of several biochemical reactions and the omission of several reaction processes, ADM1 was modified with the consideration of acetic acid inhibition and valeric acid existence. ADM1_ac (ADM1 added acetic acid inhibition) could obtain better simulation accuracy of MP (goodness-of-fit value = 0.945), and VFA concentrations (goodness-of-fit values > 0.39) were all higher than ADM1_original, but cannot explain the valeric acid production. ADM1_va (ADM1 added valeric acid existence) could achieve better simulation of valeric acid (achieving a breakthrough of zero), nevertheless the accuracy of propionic and butyric acids was poorer than ADM1_ac with differences between experimental and simulation values were 5%-10% lower. With both factors coordinated, MP and VFA concentrations could be simulated accurately by ADM1_ac_va (ADM1 added acetic acid inhibition and valeric acid existence), with the highest goodness-of-fit values (>0.85). The results of a verification experiment with ADM1_ac_va simulation further indicated that acetic acid inhibition and valeric acid as new component were both important in ADM1. PRACTITIONER POINTS: ADM1_ac could simulate MP and acetate, propionate and butyrate concentrations better. ADM1_va could explain the valerate production during AD of glucose. ADM1_ac_va could simulate AD process quite accurately, with the highest goodness-of-fit values (>0.85). Acetate inhibition and valerate existence were both important and should be considered in ADM1.

A cellulolytic fungal biofilm enhances the consolidated bioconversion of cellulose to short chain fatty acids by the rumen microbiome

The ability of the multispecies biofilm membrane reactors (MBM reactors) to provide distinguished niches for aerobic and anaerobic microbes at the same time was used for the investigation of the consolidated bioprocessing of cellulose to short chain fatty acids (SCFAs). A consortium based consolidated bioprocess (CBP) was designed. The rumen microbiome was used as the converting microbial consortium, co-cultivated with selected individual aerobic fungi which formed a biofilm on the tubular membrane flushed with oxygen. The beneficial effect of the fungal biofilm on the process yields and productivities was attributed to the enhanced cellulolytic activities compared with those achieved by the rumen microbiome alone. At 30 °C, the MBM system with Trichoderma reesei biofilm reached a concentration 39% higher (7.3 g/L SCFAs), than the rumen microbiome alone (5.1 g/L) using 15 g/L crystalline cellulose as the substrate. Fermentation temperature was crucial especially for the composition of the short chain fatty acids produced. The temperature increase resulted in shorter fatty acids produced. While a mixture of acetic, propionic, butyric, and caproic acids was produced at 30 °C with Trichoderma reesei biofilm, butyric and caproic acids were not detected during the fermentations at 37.5 °C carried out with Coprinopsis cinerea as the biofilm forming fungus. Apart from the presence of the fungal biofilm, no parameter studied had a significant impact on the total yield of organic acids produced, which reached 0.47 g of total SCFAs per g of cellulose (at 30 °C and at pH 6, with rumen inoculum to total volume ratio equal to 0.372).

Recent advances and strategies in process and strain engineering for the production of butyric acid by microbial fermentation

Butyric acid is an important platform chemical, which is widely used in the fields of food, pharmaceutical, energy, etc. Microbial fermentation as an alternative approach for butyric acid production is attracting great attention as it is an environmentally friendly bioprocessing. However, traditional fermentative butyric acid production is still not economically competitive compared to chemical synthesis route, due to the low titer, low productivity, and high production cost. Therefore, reduction of butyric acid production cost by utilization of alternative inexpensive feedstock, and improvement of butyric acid production and productivity has become an important target. Recently, several advanced strategies have been developed for enhanced butyric acid production, including bioprocess techniques and metabolic engineering methods. This review provides an overview of advances and strategies in process and strain engineering for butyric acid production by microbial fermentation. Additionally, future perspectives on improvement of butyric acid production are also proposed.

Butyric acid production from lignocellulosic biomass hydrolysates by engineered Clostridium tyrobutyricum overexpressing Class I heat shock protein GroESL

Lignocellulosic biomass is the most abundant and renewable substrate for biological fermentation, but the inhibitors present in the lignocellulosic hydrolysates could severely inhibit the cell growth and productivity of industrial strains. This study confirmed that overexpressing of native groESL in Clostridium tyrobutyricum could significantly improve its tolerance to lignocellulosic hydrolysate-derived inhibitors, especially for phenolic compounds. Consequently, ATCC 25755/groESL showed a better performance in butyric acid fermentation with hydrolysates of corn cob, corn straw, rice straw, wheat straw, soybean hull and soybean straw, respectively. When corn straw and rice straw hydrolysates, which showed strong toxicity to C. tyrobutyricum, were used as the substrates, 29.6 g/L and 30.1 g/L butyric acid were obtained in batch fermentation, increased by 26.5% and 19.4% as compared with the wild-type strain, respectively. And more importantly, the butyric acid productivity reached 0.31 g/L·h (vs. 0.20-0.21 g/L·h for the wild-type strain) due to the shortened lag phase.

Preeminent productivity of 1,3-propanediol by Clostridium butyricum JKT37 and the role of using calcium carbonate as pH neutraliser in glycerol fermentation

Calcium carbonate was evaluated as a replacement for the base during the fermentation of glycerol by a highly productive strain of 1,3-propanediol (PDO), viz., Clostridium butyricum JKT37. Due to its high specific growth rate (µ_max=0.53h^-1), 40g/L of glycerol was completely converted into 19.6g/L of PDO in merely 7h of batch fermentation, leaving only acetate and butyrate as the by-products. The accumulation of these volatile fatty acids was circumvented with the addition of calcium carbonate as the pH neutraliser before the fermentation was inoculated. An optimal amount of 15g/L of calcium carbonate was statistically determined from screening with various glycerol concentrations (20-120g/L). By substituting potassium hydroxide with calcium carbonate as the pH neutraliser for fermentation in a bioreactor, a similar yield (Y_PDO/glycerol=0.6mol/mol) with a constant pH was achieved at the end of the fermentation.

Consolidated Bioprocessing for Butyric Acid Production from Rice Straw with Undefined Mixed Culture

Lignocellulosic biomass is a renewable source with great potential for biofuels and bioproducts. However, the cost of cellulolytic enzymes limits the utilization of the low-cost bioresource. This study aimed to develop a consolidated bioprocessing without the need of supplementary cellulase for butyric acid production from lignocellulosic biomass. A stirred-tank reactor with a working volume of 21 L was constructed and operated in batch and semi-continuous fermentation modes with a cellulolytic butyrate-producing microbial community. The semi-continuous fermentation with intermittent discharging of the culture broth and replenishment with fresh medium achieved the highest butyric acid productivity of 2.69 g/(L· d). In semi-continuous operation mode, the butyric acid and total carboxylic acid concentrations of 16.2 and 28.9 g/L, respectively, were achieved. Over the 21-day fermentation period, their cumulative yields reached 1189 and 2048 g, respectively, corresponding to 41 and 74% of the maximum theoretical yields based on the amount of NaOH pretreated rice straw fed in. This study demonstrated that an undefined mixed culture-based consolidated bioprocessing for butyric acid production can completely eliminate the cost of supplementary cellulolytic enzymes.