Search Results (82)

Volatile fatty acids (VFAs) are essential precursors in chemical synthesis for various chemicals, polymers, pharmaceuticals, and fragrance compounds. Acidogenic anaerobic digestion (or arrested methanogenesis) is a promising method to stabilize organic wastes and convert them to value-added products such as VFAs. However, the VFAs’ accumulation could in turn suppress the fermentation process through product inhibition and limit the titer of VFA in the digestate. Therefore, in situ separation and recovery of VFAs from the fermentate is crucial to constructing an effective continuous VFA-producing system. Recent research has been dedicated to addressing these issues and advancing the utilization of biobased VFAs, particularly through process-intensified strategies employing novel green solvents such as natural deep eutectic solvents. Furthermore, in situ conversion of VFAs into esters is another potential strategy for VFA removal. However, VFA esterification in an aqueous medium is challenging due to the abundant water driving the reaction toward hydrolysis. Recent advances in free or immobilized enzyme catalysis in solvents have demonstrated improved ester yield by providing a hydrophobic space for the esterification reaction in aqueous solution. In this review, we present an overview of critical aspects on the state-of-the-art of green solvent-based process intensification strategies, including feedstock selection and pretreatment, operating condition optimization, advances in membrane- and solvent-based recovery methods, and biocatalytic in situ esterification. Lastly, we provide perspectives toward cost-effective, continuous, high-solid, environmental-benign, and industrial-relevant VFA production applications. Full article

Acidogenic fermentation of organic wastes represents a strategic platform for the co-production of H₂, CO₂, and volatile fatty acids (VFAs), which are potential key intermediates for cost-effective polyhydroxyalkanoate (PHAs) biosynthesis. This typically relies on carbon sources that are too expensive and hinder the commercialization of PHAs. This study provides metagenomic insights into the microbial dynamics underpinning the acidogenic conversion of waste melon under increasing organic loading rates (OLRs). Metabarcoding revealed that Megasphaera dominated the community, with its abundance rising markedly from 5 to 20 gCOD/L, accompanied by relevant contributions from Solobacterium, Prevotella, and Clostridium. These taxa were associated with the formation of acetic, propionic, and butyric acids and with enhanced hydrogenogenesis. Higher OLRs, up to 20 gCOD/L, promoted hydrogen-producing species while suppressing lactic acid bacteria, thereby improving H₂ and VFAs yields up to 26.7% v/v and 13 gCOD/L, respectively. By linking microbial shifts to metabolic outputs, this work advances the understanding of acidogenic pathways essential for integrating dark fermentation-derived H₂, CO₂, and VFAs into sustainable PHAs production systems. Full article

Anaerobic digestion is a key technology for chicken manure valorization, but ammonia accumulation often causes system instability. In this study, a 100-day continuous stirred tank reactor (CSTR) experiment was conducted under mesophilic conditions to investigate the mechanisms of ammonia inhibition in chicken manure at total solids (TS) contents of 8% (T1), 12% (T2), and 16% (T3). Compared to T1, the peak TAN concentrations in T2 and T3 were 64.28% and 73.82% higher. After 100 days, pH in T2 and T3 dropped by 5.19% and 7.65% relative to T1. Volatile fatty acid (VFA) accumulation increased by 4.6- and 6.5-fold, while the TS-based methane yield decreased by 52.94% and 73.11%, respectively. Metagenomic analysis revealed the mechanisms of ammonia inhibition: high-ammonia conditions not only directly suppressed the gene abundance of methanogenic pathways but also systematically reduced the abundance of hydrolytic bacteria and acidogenic fermentative bacteria, leading to a disruption in the supply chain of methanogenic precursors, while ammonia-tolerant microbiota became competitively enriched. This study elucidates the multi-level mechanism of ammonia inhibition in high-TS chicken manure digestion at the functional gene level, providing a theoretical basis for the precise regulation of ammonia stress and improvement of system stability. Full article

Acidogenic fermentation is a promising biotechnology for converting organic wastes into carboxylic acid (CA), which has significant commercial value and diverse applications in the food, chemical, pharmaceutical, and cosmetic industries. However, major challenges such as limited substrate hydrolysis and lower CA production hinder further development of this biotechnology towards full-scale implementation. This review provides a comprehensive overview of the current status of acidogenic fermentation, focusing on substrate composition, inoculum, and reactor design, along with potential strategies to overcome reactor-specific limitations and enhance CA production. It was found that the substrate composition, particularly its carbohydrate, protein, and lipid contents, strongly influences both CA production and yield. Specifically, carbohydrate-rich substrates yield higher CA production compared to protein- and lipid-rich substrates. These substrates have been investigated in different reactor configurations for CA production. Among them, the leachate bed reactor and anaerobic membrane bioreactor have demonstrated superior performance, achieving higher CA production with acetic and butyric acids as the dominant CA composition. These reactors are generally operated using three types of inocula: aerobic and anaerobic inoculum, enriched inoculum, and rumen microorganisms. Interestingly, rumen microorganisms are effective in degrading complex substrates, whereas enriched inoculum accelerates hydrolysis and acidogenesis processes within a shorter fermentation time. The findings presented herein will provide valuable information for addressing the challenges associated with acidogenic fermentation and lay the foundation for future research aimed at upscaling this biotechnology to a commercial scale. Full article

The urgent need for effective food waste management, coupled with the scarcity of carbon sources for sewage treatment, highlights the potential of producing carbon sources from food waste as a mutually beneficial solution. This study investigated the production of carbon sources through anaerobic fermentation using the liquid phase of food waste three-phase separation. Compared with previous studies using raw food waste or mixed substrates, the liquid phase derived from three-phase separation is richer in soluble organic matter and has been pre-heated (80 °C), which facilitates subsequent fermentation and offers easier integration into existing food waste treatment plants. A series of lab-scale batch fermentation experiments were carried out at different temperatures, including ambient, mesophilic, and thermophilic conditions, as well as varying initial pH levels (uncontrolled, neutral, and alkaline). The experimental results indicated that optimal production parameters involve a 4-day mesophilic fermentation at 35 °C with an initial alkaline pH, which increased the total VFAs yield by 252.5% to 40.26 g/L and raised the acetic acid fraction to 45.5% of total VFAs. Under these conditions, there was an observed increase in the relative abundance of acidogenic bacteria and a decrease in that of methanogen archaea. Furthermore, the denitrification performance of the produced carbon source was evaluated in short-term tests, and near-complete nitrate removal was achieved within approximately 2 h. These findings suggest the fermented liquid phase of food waste is a promising partial substitute for conventional external carbon sources. Full article

Capsicum residue generated from industrial capsaicin extraction is rich in nutrients and represents a significant fraction of solid waste in the food processing industry. Despite its potential value, limited efforts have been devoted to its resource recovery, leading to considerable resource loss and environmental burdens. This study systematically evaluates the applicability of existing food waste recycling technologies for capsicum residue and assesses its valorization potential through comprehensive characterization. The results indicate that capsicum residue holds promise as a feedstock for pectin extraction and as a component in animal feed. Regarding anaerobic fermentation for acid production, the maximum volatile fatty acids (VFAs) yield and VFAs/SCOD ratio reached 462.09 mg·L⁻¹ and 3.16%, respectively, suggesting moderate potential for acidogenic conversion but limited suitability for methanogenesis. Fluorescence spectroscopy of dissolved organic matter revealed that microbial humic-like substances (C1) were the dominant fluorophore, accounting for 42.64% of the total fluorescence, followed by terrestrial humic-like (C2, 19.28%), fulvic-like (C3, 19.12%), and tryptophan-like (C4, 18.95%) components. The favorable C/N ratio of amino acids and humic substances supports the feasibility of composting. Additionally, trace levels of residual capsaicin may confer antibacterial benefits and enhance soil fertility, further supporting the potential of capsicum residue as a value-added resource. Full article

As the environmental burden of traditional plastics continues to grow, bioplastics (BPs) have emerged as a promising alternative due to their renewable origins and potential for biodegradability. However, the most popular anaerobic systems (ASs)—anaerobic digestion (AD), acidogenic fermentation (AF), and enzyme hydrolysis (EH)—for BPs degradation still face many challenges, e.g., low degradation efficiency, process instability, etc. As a sustainable clean energy technology, bioelectrochemical systems (BESs) have demonstrated strong potential in the treatment of complex organic waste when integrated with ASs. Nevertheless, research on the synergistic degradation of BPs using BES-ASs remains relatively limited. This review systematically summarizes commonly used anaerobic degradation methods for BPs, along with their advantages and limitations, and highlights the BES-AS as an innovative strategy to enhance BPs degradation efficiency. BESs can accelerate the decomposition of complex polymer structures through the activity of electroactive microorganisms, while also offering benefits such as energy recovery and real-time process monitoring. When coupled with anaerobic digestion, the BES-AS demonstrates significant synergistic effects, improving degradation efficiency and promoting the production of high-value-added products such as volatile fatty acids (VFAs) and biogas, thereby showing great application potential. This review outlines current research progress, identifies key knowledge gaps in mechanism elucidation, system design, source recovery, etc., and proposes future research directions. These include system optimization, microbial community engineering, development of advanced electrode materials, and omics-based mechanistic studies. Advancing multidisciplinary integration is expected to accelerate the practical application of BES-ASs in BP waste management and contribute to achieving the goals of sustainability, efficiency, and circular utilization. Full article

Polyhydroxyalkanoate (PHA) bioplastics are produced from wastewater as a carbon recovery strategy. However, the tuneable characteristics of PHAs and wastewater biorefinery potential have not been comprehensively reviewed. The aim of this study is to review the main challenges and strategies for carbon recovery from wastewater feedstocks via PHA production, assessing potential target biopolymer applications. Diverse PHA-accumulating prokaryotes metabolize organic pollutants present in wastewater through different metabolic pathways, determining the biopolymer characteristics. The synthesis of PHAs using mixed microbial cultures with wastewater feedstocks derived from municipal, agro-industrial, food processing, lignocellulosic biomass processing and biofuel production activities are described. Acidogenic fermentation of wastewater feedstocks and mixed microbial culture enrichment are key steps in order to enhance PHA productivity and determine biopolymer properties towards customized bioplastics for specific applications. Biorefinery of PHA copolymers and extracellular polysaccharides (EPSs), including alginate-like polysaccharides, are alternatives to enhance the value-chain of carbon recovery from wastewater. PHAs and EPSs exhibit a wide repertoire of applications with distinct safety control requirements; hence, coupling biopolymer production demonstrations with target applications is crucial to move towards full-scale applications. This study discusses the relationship between the metabolic basis of PHA synthesis and composition, wastewater type, and target applications, describing the potential to maximize carbon resource valorisation. Full article

This study examines the impact of hydrothermal pretreatment operation time (10, 20, and 30 min) on the following four lignocellulosic feedstocks with different lignin content: sugar beet pulp (SBP), brewers spent grain (BSG), orange peel (OP), and rice husk (RH). The objective of pretreatment is twofold, as follows: (1) to enhance the organic matter solubilization and the release of value-added bioproducts, such as total reducing sugars (TRS), total proteins (PR), and volatile fatty acids (VFAs); and (2) to improve VFA and hydrogen production during a subsequent stage of acidogenic anaerobic digestion (Dark Fermentation, DF). In this context, OP reported the highest overall yields across all pretreatment durations. Specifically, at 30 min, it achieved a maximum solubilization of 57.3 gO₂/L in terms of soluble chemical oxygen demand (sCOD), 19.1 gTRS/L and 20.6 gPR/L. Regarding VFA and hydrogen production via dark fermentation, the best results were obtained with SBP pretreated for 20 and 30 min, yielding 15.1 g H-Ac/L and 97.5 mL H₂ (n.c.)/g (d.m.), respectively. BSG displayed an intermediate performance, whereas RH consistently showed the lowest yields across all evaluated parameters, primarily due to its high lignin content. These findings highlight the pivotal role of pretreatment duration in the valorization of lignocellulosic biomasses, primarily aimed at the recovery of high-value-added biochemicals and biofuels, such as hydrogen, thereby supporting the development of integrated biorefinery systems. Full article

Anaerobic acidogenic fermentation presents a promising approach for sustainable carbon emission mitigation in livestock waste management, addressing critical environmental challenges in agriculture. This study systematically investigated the synergistic effects of composting-assisted pretreatment coupled with micro-aeration and methanogenesis suppression to enhance volatile fatty acid (VFA) production from swine manure supplemented with wheat straw, valorizing agricultural waste while reducing greenhouse gas emissions. The experimental protocol involved sequential optimization of pretreatment conditions (12 h composting followed by 10 min thermal pretreatment at 85 °C), operational parameters (300 mL micro-aeration and 30 mmol/L 2-bromoethanesulfonate (BES) supplementation), and their synergistic integration. The combined strategy achieved peak VFA production (5895.92 mg/L, p < 0.05), with butyric acid constituting the dominant fraction (2004.42 mg/L, p < 0.05). Enzymatic analysis demonstrated significantly higher activities of key hydrolytic enzymes (protease, α-glucosidase) and acidogenic enzymes (butyrate kinase, acetate kinase) in the synergistic treatment group compared to individual BES-supplemented or micro-aeration-only groups (p < 0.05). This integrated approach provides a technically feasible and environmentally sustainable pathway for circular resource recovery, contributing to low-carbon agriculture and waste-to-value conversion. Full article

The sustainable production of bioplastics is increasingly important for reducing reliance on fossil fuels and addressing environmental challenges. The acidogenic fermentation of waste streams offers a promising pathway for generating key bioplastic precursors, such as volatile fatty acids, which can be used to produce polymers like polyhydroxyalkanoates. This review explores the potential of various waste streams, including agricultural residues, industrial by-products, and food waste, as substrates for acidogenic fermentation, aligning with circular economy principles by reducing waste and environmental impact. A key feature of this review is its focus on targeted acidogenic fermentation, which optimizes process conditions to maximize the production of specific acids based on waste characteristics. The analysis emphasizes how the chemical composition and biodegradability of waste streams influence the selection of microbial consortia and metabolic pathways, determining the yield and composition of the products generated. The review also highlights the adaptability of acidogenic fermentation to heterogeneous and variable waste streams, underlining its potential as a scalable and sustainable solution for bioplastic precursor production. By tailoring process parameters such as pH and hydraulic retention time to the specific characteristics of the substrate, targeted acidogenic fermentation can effectively transform waste into high-value intermediates. Finally, challenges related to the scalability and economic feasibility of these processes are discussed, along with opportunities for integrating acidogenic fermentation with complementary waste valorization technologies to advance the bio-based economy. The findings underscore the critical role of waste streams in enabling the sustainable and efficient generation of bioplastic precursors, contributing to a circular economy framework. Full article

This study aims to investigate the effect of different applied voltages on the biomethanation performance and microbial community characteristics of corn stover (CS) in a microbial electrolysis cell (MEC)-assisted anaerobic digestion (AD) system (MEC-AD). The results showed that the MEC-AD system operating at 0.8 V achieved the highest methane yield of 192.40 mL CH₄/g VS (volatile solids), an increase of 14.98% compared to the conventional AD. The system obtained methane yields of 187.74 to 191.18 mL CH₄/g VS at lower voltages (0.4 V and 0.6 V), and 156.11–182.75 mL CH₄/g VS at higher voltages (1.0 V and 1.2 V), respectively, suggesting that lower or higher voltages would have adversely impacted the methane yield. Correspondingly, the MEC-AD system operating at 0.4–0.8 V achieved over 71.47% conversion rates of total solids (TS), VS, and cellulose. The microbial community analysis revealed that 0.8 V optimally enriched fermentative acidogenic bacteria (FABs, 24.55%) and electroactive bacteria (13.50%), enhancing both hydrolysis acidification efficiency and direct interspecies electron transfer (DIET). Both Methanosarcina and Methanoculleus demonstrated significant positive correlations with FABs, SOBs, and electroactive bacteria. This study reveals that 0.8 V represents the optimal operating voltage for biomethane production in MEC-AD systems, providing critical insights for agricultural waste valorization. Full article

To investigate the effects of intermittent pH regulation on volatile fatty acid (VFA) production during kitchen waste fermentation and its impact on nitrogen removal efficiency in the anaerobic/anoxic/oxic (A²O) process, five experimental groups were set up (pH = 3, 5, 7, 9, and control). The study examined the promotion of soluble chemical oxygen demand (SCOD) and VFA release under different pH conditions and their contribution to total nitrogen (TN) release. Additionally, methanol was used as a control carbon source to explore the enhancement of denitrification efficiency when kitchen waste fermentation broth was used as a carbon source in the A²O process. The results indicated that neutral and alkaline conditions could enhance the release of SCOD and the conversion of VFAs, with a more pronounced effect under alkaline conditions. The maximum concentrations of SCOD and VFAs reached 36,412 and 5947 mg/L, respectively. Furthermore, TN release was most significant under alkaline conditions, being 2.39 times that of the control group. When kitchen waste fermentation broth was used as a carbon source, Proteobacteria and Bacteroidota were significantly enriched. Additionally, the relative abundance of key functional genes (napA, norB, and nosZ) involved in nitrogen cycling and key enzymes ([EC: 1.7.1.15], [EC: 1.7.2.1], and [EC: 1.7.2.5]) were enhanced, which strengthened the denitrification performance. Full article

The production of volatile fatty acids (VFAs) through the acidogenic fermentation of wastewater has garnered significant attention in recent years. This study examines the kinetics of VFA production in batch reactors using cassava wastewater as a substrate under previously identified conditions (initial pH of 5.7, S/M ratio of 4 gCOD/gVS, and temperature of 34 ± 1 °C). Additionally, this study identifies the best-fit models for estimating kinetic parameters related to the consumption of soluble organic matter and VFA production. VFA production yields ranged from 0.15 to 0.44 gCOD_VFA/gCOD over the 12-day fermentation period, with the highest yield observed on day 9. The acids produced consisted of 29.7% acetic acid, 43.3% propionic acid, and 27.0% butyric acid. The modified Gompertz and first-order with residual models effectively described the consumption of soluble organic matter, while the first-order and BPK models accurately represented the VFA production. These models showed the highest R² values and the lowest RMSE and AIC values. Cassava wastewater is a low-cost substrate with potential for VFA recovery. Its kinetic modeling provides valuable insights for the design, control, and scale-up of acidogenic reactors. Full article

The production of volatile fatty acids (VFAs) through the acidogenic fermentation of wastewater is an emerging technology that requires further research to optimize operational variables for specific substrates. Cassava wastewater, which is a byproduct of the cassava sour starch extraction process, has been minimally studied regarding its potential for VFA production through acidogenic fermentation. Batch reactors were used to evaluate the effects of the substrate-to-microorganism (S/M) ratio and temperature on VFA production from cassava wastewater. The results showed no statistically significant differences between the evaluated S/M ratios. The maximum total VFA concentration observed was 2214.64 mg of acetic acid (HAc)/L (0.32 gCOD_VFA/gCOD), which was achieved at a S/M ratio of 4 gCOD/gVS. This concentration was predominantly composed of acetic acid (42.7%), followed by butyric acid (30.1%) and propionic acid (24.6%), with a minor quantity of isovaleric acid (2.6%). The statistical analysis for the temperature variable showed significant differences between the evaluated conditions. The maximum concentration of total VFAs was 2650.19 mgHAc/L (0.45 gCOD_VFA/gCOD) at 34 ± 1 °C, with acetic (40.9%), butyric (29.8%), and propionic (29.3%) acids as primary metabolites. Cassava wastewater shows promise as a potential substrate for VFA production, warranting evaluation in continuous reactors. Full article