Search Results (146)

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

Food waste (FW) sourced from treatment facilities is predominantly in solid form, with low water content and high variations in organic content. High organic content in FW is ideal in anaerobic digestion for bioenergy applications, but proper monitoring during start-up operations should be employed to avoid imbalance in the acidogenic/methanogenic population due to volatile fatty acid (VFA) accumulation in the system. The seed inoculum (5 L) in each horizontal anaerobic reactor (HAR) was fed with food waste without effluent flow (filling-up phase) until it reached the final working volume of 10 L (continuous phase). The pH, alkalinity, chemical oxygen demand (COD), VFA, biogas production, methane concentration, and microbial community dynamics were set as stability indicators during reactor operation. The results revealed that introducing fluctuations in FW concentrations does not negatively affect the biogas production (1.7 ± 0.2 L/L_R/d) and methane concentration (59.0 ± 2.5%). Acclimatization of the methanogenic and bacterial population was also observed. This study aimed to evaluate the influence of fluctuating FW concentrations on the process performance of horizontal anaerobic reactors, focusing on process stability, microbial dynamics, and biogas output during filling-up and continuous phases. Full article

Sugarcane vinasse, a byproduct of ethanol production, presents environmental challenges due to its high organic content and occasional contamination with antibiotics, such as monensin. This study successfully evaluated thermophilic two-phase anaerobic digestion for simultaneous monensin degradation and biogas production. The system, consisting of an acidogenic anaerobic structured-bed bioreactor (ASTBR) operating at with a hydraulic retention time (HRT) of 7.5 h followed by a methanogenic reactor at HRT = 24 h, with two options of the methanogenic phase, an upflow anaerobic sludge blanket (UASB), and an ASTBR, operated continuously for 254 days with incremental monensin concentrations (0–2000 ng·mL⁻¹). The acidogenic reactor consistently removed over 70% of monensin across all phases, demonstrating its effectiveness as a pretreatment step. At realistic residual concentrations (20–100 ng·mL⁻¹), monensin not only failed to inhibit biogas production but enhanced methane yield by up to 100% through selective pressure on the microbial community. This study demonstrated that anaerobic digestion can effectively degrade monensin while increasing the value of vinasse, providing a scalable solution for mitigating antibiotic contamination and enhancing bioenergy recovery in the sugarcane–ethanol industry. 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

Background: Salivary pH plays a critical role in oral health by influencing enamel demineralization, buffering capacity, and the ecology of oral microbiota. Essential oils such as Origanum vulgare (oregano) possess well-documented antimicrobial properties that may reduce acidogenic bacterial activity. However, the effects of edible delivery systems like jellies on salivary pH modulation and their potential interactions with hormonal states remain poorly understood. Methods: This study evaluated the in vitro antimicrobial activity of an oregano-oil-based jelly formulation against standard bacterial (Staphylococcus aureus, Streptococcus pyogenes, and Escherichia coli) and fungal (Candida albicans) strains using the Kirby–Bauer disc diffusion method. Additionally, a human trial (n = 91) measured salivary pH before and after administration of the oregano-oil jelly. Participants were characterized by age, smoking status, menopausal status, and presence of menstruation. Multiple linear regression was used to identify predictors of final salivary pH. Results: The oregano-oil jelly demonstrated strong in vitro antimicrobial activity, with inhibition zones up to 8 mm for E. coli and C. albicans. In vivo, mean unstimulated salivary pH increased from 6.94 to 7.07 overall, indicating a mild alkalinizing effect. However, menstruating participants showed a significant decrease in final pH (from 7.03 to 6.78). Multiple regression identified menstruation as a significant negative predictor (β = −0.377, p < 0.001) and initial pH as a positive predictor (β = +0.275, p = 0.002). Menopausal status was not a significant predictor, likely due to the small sample size. Conclusions: Oregano-oil jellies may represent a promising natural approach to support oral health by increasing salivary pH and providing strong antimicrobial activity. However, physiological states such as menstruation can significantly modulate this response, underscoring the importance of personalized or phase-aware oral care strategies. Further studies with larger, diverse cohorts and controlled hormonal assessments are needed to validate these findings and optimize product formulations. Full article

Penicillium expansum is an acidogenic fungal species that belongs to the phylum Ascomycota. During the infection and colonization of host fruits, P. expansum can efficiently express glucose oxidase (GOX) and oxidize β-D-glucose to generate gluconic acid (GLA). In this study, the bioinformatics analysis method was employed to predict and analyze the function of the GOX protein. In addition, a comprehensive assessment was conducted on the P. expansum GOX coding gene GOX2, and the expression response rules of GOX2 under different external stress environments were explored. The results show that GOX is an unstable hydrophilic protein. It is either an integrated membrane protein (such as a receptor or channel) that is directly anchored to the membrane through a transmembrane structure or a non-classical secreted protein that is secreted extracellularly. RNA-seq data analysis shows that the GOX2 gene is regulated by multiple environmental factors, including pH, temperature, carbon base, and chemical fungicides. The expression level of GOX2 reaches its maximum value under alkaline conditions (pH 8–10) and at approximately 10 °C. Using starch as the carbon source and adding sodium propionate or potassium sorbate has the effect of inhibiting the expression of the GOX2 gene. The analysis of the function of the GOX protein and the characteristics of the GOX2 gene in P. expansum provides new insights into the glucose oxidase-encoding gene GOX2. The research results provide significant value for the subsequent development of new disease resistance strategies by targeting the GOX2 gene and reducing post-harvest disease losses in fruits. 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

This study evaluated the efficacy of acclimated cow manure as a seed microbiome to enhance food waste hydrolysis. Anaerobic hydrolysis was performed on simulated food waste in a hydrolytic–acidogenic leach bed reactor (LBR) operated in batch mode under mesophilic conditions (35 °C) for 16 days. The acclimation process involved three sequential runs: Run-1 utilized 20% (w/w) cow manure as seed, Run-2 employed the digestate from Run-1 (day 5), and Run-3 used the digestate from Run-1 (day 10). Run-3 achieved 70.4% removal of volatile solids (VSs), surpassing Run-1 (47.1%) and Run-2 (57.1%). Compared with the first run, the production of chemical oxygen demand (COD) and total soluble products (TSPs) increased by 48.7% and 75.9%, respectively, in Run-3. The hydrolysis rate of proteins was 48.4% in Run-1, while an increase of 16.9% was achieved in Run-3 with the acclimatized consortium. A molecular analysis of the microbial community existing in the reactors of Run-2 and Run-3 indicated that the improvement in process performance was closely related to the selection and enrichment of specific hydrolytic–acidogenic bacteria in the reactor. A functional analysis showed that the gene copy numbers for pyruvate synthesis and fatty acid synthesis and metabolism pathways were higher in all bacterial species in Run-3 compared to in those of the other two runs, indicating improved capacity through acclimation in Run-3. The experimental results demonstrate that the hydrolysis of food waste can be enhanced through the acclimation of seed microbes from cow manure. 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

Oak infusions enriched with agavins may offer nutraceutical benefits in the development of iced teas. This study evaluated infusions of Quercus sideroxyla and Quercus eduardii leaves formulated with different concentrations of agavins (0, 2, 6, and 10%), analyzing their physicochemical and sensory properties, chemical stability, and antioxidant capacity. The incorporation of agavins resulted in substantial modifications to physicochemical parameters, including pH, titratable acidity, and soluble solids, thereby enhancing product stability and consistency. Notable distinctions were observed between the two species with respect to their acidogenic response and soluble solid concentration. Interactions between agavins and phenolic compounds, as discerned by UPLC-PDA-ESI-MS/MS and FT-IR, exerted a significant influence on bioactivity of the phenolic constituents, thereby affecting the nutraceutical potential of the infusions. These interactions, facilitated by hydrogen bonds, led to reduction in phenolic acids, such as quinic acid (↓ 43%), and alteration in antioxidant capacity at high concentrations of agavins. The findings underscore the significance of meticulously designing balanced formulations that optimize chemical stability, functionality, and sensory acceptance, thereby ensuring the quality of the final product. Full article

Ionic rare earth ore (IREO) has a high abundance of medium and heavy rare earth elements (REEs), making it a vital strategic resource for China. In this work, two typical microorganisms, Aspergillus niger and Acidithiobacillus ferrooxidans, were used to study the interaction mechanism during the bioleaching of IREO under acidic conditions. The results revealed some differences in the interaction and leaching effects of A. niger and A. ferrooxidans on ionic rare earth minerals. A. niger mainly forms rare earth complexes with rare earth ions in IREO by secreting metabolites such as organic acids, thereby promoting the release of REEs, and it has a strong adsorption capacity for Yb. A. ferrooxidans promotes the release of REEs from rare earth minerals, primarily through iron–sulfur oxidation. The differential expression of metabolic genes (e.g., gpmL, FabF, FASN) associated with major metabolite secretion indicates their correlation with the leaching process. The above results reveal the role of the typical acid-producing microorganisms A. niger and A. ferrooxidans and their metabolites in the leaching of IREO, which is valuable for understanding the interaction mechanisms between microorganisms and IREO under acidic conditions. Full article

Peracetic acid (PAA) oxidation, which is a kind of chemical method for sludge pretreatment, has been verified to be valid for promoting sludge anaerobic digestion performance. However, the methane production is still limited at certain levels by this method, because excess PAA has negative effects on methanogens. This work selected a freezing method combined with PAA to form a composite sludge pretreatment technology for synergistically improving the biomethane production. According to the experimental data, the methane yield was largely enhanced from 166.4 ± 5.6 mL/g volatile suspended solids (VSS) in the control to 261.5 ± 7.3 mL/g VSS by the combined freezing (−10 °C) and PAA (0.08 g/g TSS) pretreatment, with a 57.2% increase rate. Kinetic analysis showed that the methane production potential, methane production rate, and hydrolysis rate were promoted, respectively, from 159.4 mL/g VSS, 17.18 mL/g VSS/d, and 0.104 d⁻¹ to 254.9 mL/g VSS, 25.69 mL/g VSS/d, and 0.125 d⁻¹ by the freezing + PAA pretreatment. Mechanism analysis revealed that the freezing + PAA pretreatment destroyed both extracellular polymeric substances (EPS) and microbial cells in the sludge, resulting in the increase in hydrolysis efficiency. Gene analysis showed that the hydrolytic microbes (Hyphomicrobium and norank_f_Caldilineaceae), acidogens (e.g., Petrimonas, Tissierella, and Mycobacerium) and methanogens (Methanosaeta, Methanosarcina, and Methanobacterium) were all enriched by the freezing + PAA pretreatment, with the total abundances calculated to be 10.65% and 22.07% in the control and pretreated reactors, respectively. Considering both technical and economic factors, the freezing + PAA method is feasible for sludge pretreatment. Full article