Search Results (2,295)

The biotechnological conversion of CO₂ to biomethane represents an energy-efficient, environmentally friendly, and sustainable approach within the waste-to-energy cycle. This process, in which CO₂ and H₂ are converted to biomethane in anaerobic bioreactors, is referred to as hydrogenotrophic biomethane production. While several studies have investigated hydrogenotrophic biomethane production, there is a lack of research comparing flocculent and granular sludge inoculum in continuously operated systems fed with a gas substrate. Both granular and flocculent sludge possess distinct advantages: granular sludge offers higher density, stronger microbial cohesion, and superior settling performance, whereas flocculent sludge provides faster substrate accessibility and more rapid initial microbial activity. In this study, two UASB (Upflow Anaerobic Sludge Blanket) reactors operated under mesophilic conditions were continuously fed with synthetic off-gas composed of pure H₂ and CO₂ in a 4:1 ratio and were compared in terms of microbial community shifts and their effects on hydrogenotrophic biomethane production. Biomethane production reached 75 ± 2% in the granular sludge reactor, significantly higher than the 64 ± 1.3% obtained with flocculent sludge. Although hydrogen consumption did not differ significantly, the granular sludge reactor exhibited higher CO₂ removal efficiency. Microbial analyses further revealed that granular sludge was more effective in supporting methanogenic archaea under conditions of gas substrate feeding. These findings offer advantageous suggestions for improving biogas production, enhancing waste gas management, and advancing sustainable energy generation. Full article

This study evaluates biogas production through the anaerobic digestion of food waste (FW), cow dung (CD), and green waste (GW), with the primary objective of determining the efficacy of co-digesting these organic wastes commonly generated by households and small farms in Central Queensland, Australia. The investigation focuses on both experimental and technoeconomic aspects to support the development of accessible and sustainable energy solutions. A batch anaerobic digestion process was employed using a 1 L jacketed glass digester, simulating small-scale conditions, while technoeconomic feasibility was projected onto a 500 L digester operated without temperature control, reflecting realistic constraints for decentralized rural or residential systems. Three feedstock mixtures (100% FW, 50:50 FW:CD, and 50:25:25 FW:CD:GW) were tested to determine their impact on biogas yield and methane concentration. Experiments were conducted over 14 days, during which biogas production and methane content were monitored. The results showed that FW alone produced the highest biogas volume, but with a low methane concentration of 25%. Co-digestion with CD and GW enhanced methane quality, achieving a methane yield of 48% while stabilizing the digestion process. A technoeconomic analysis was conducted based on the experimental results to estimate the viability of a 500 L biodigester for small-scale use. The evaluation considered costs, benefits, and financial metrics, including Net Present Value (NPV), Internal Rate of Return (IRR), and Dynamic Payback Period (DPP). The biodigester demonstrated strong economic potential, with an NPV of AUD 2834, an IRR of 13.5%, and a payback period of 3.2 years. This study highlights the significance of optimizing feedstock composition and integrating economic assessments with experimental findings to support the adoption of biogas systems as a sustainable energy solution for small-scale, off-grid, or rural applications. Full article

Background/Objectives: This study aimed to identify the functional adaptations that enable competitive performance in a Paralympic cyclist with optimized bilateral transtibial prostheses compared to a conventional cyclist. Additionally, it describes the development of the prosthesis, designed through a user-centered engineering process incorporating Quality Function Deployment (QFD), Computer-Aided Design (CAD), Finite Element Analysis (FEA), Computational Fluid Dynamics (CFD), and topological optimization, with the final design (Design 1.4) achieving optimal structural integrity, aerodynamic efficiency, and anatomical fit. Methods: Both athletes performed a progressive cycling test with 50-watt increments every three minutes until exhaustion. Cardiorespiratory metrics, lactate thresholds, and joint kinematics were assessed. Results: Although the conventional cyclist demonstrated higher Maximal Oxygen Uptake (VO₂max) and anaerobic threshold, the Paralympic cyclist exceeded 120% of his predicted VO₂max, had a higher Respiratory Exchange Ratio (RER) [1.32 vs. 1.11], and displayed greater joint ranges of motion with lower trunk angular variability. Lactate thresholds were similar between athletes. Conclusions: These findings illustrate, in this specific case, that despite lower aerobic capacity, the Paralympic cyclist achieved comparable performance through efficient biomechanical and physiological adaptations. Integrating advanced prosthetic design with individualized evaluation appears essential to optimizing performance in elite adaptive cycling. Full article

Heterotrophic nitrification and aerobic denitrification (HN–AD) is an emerging biological process capable of achieving efficient nitrogen removal in a single reactor. This study investigates the HN–AD performance of a sequencing batch reactor (SBR) operated with a simple anaerobic–aerobic cycle for treating high C/N wastewater. Over a 220-day operation, the system achieved average removal efficiencies of 98.6% for COD, 93.3% for NH₄⁺-N, and 87.1% for total nitrogen. Effluent concentrations of NO₂⁻-N and NO₃⁻-N remained negligible at the end of each aerobic phase. Concentration profiles of NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N throughout the operation cycles confirmed the occurrence of simultaneous nitrification and aerobic denitrification. The consistently high COD removal and robust nitrogen reduction highlight the stability of the HN–AD microbial consortia enriched from activated sludge. Phosphorus removal (average removal efficiency 66.3%) may be enhanced by increasing the activity of phosphate-accumulating organisms (PAOs) through process optimization. This study demonstrated effective HN–AD using activated sludge in SBRs. Future work will focus on evaluating the system with real wastewater and continuous-flow setups to further refine operational parameters for sustained HN–AD performance. Full article

Given the increasing volume of selectively collected bio-waste and the requirement to increase waste treatment system energy efficiency, dry anaerobic digestion (DAD) represents a more sustainable choice for the treatment of municipal organic fraction instead of conventional technologies. The current paper provides an overview of the existing knowledge on DAD of green waste or kitchen waste collected selectively. Key substrates characteristics (chemical composition, methane potential), novel reactor design and process conditions relevant to effective digestion at elevated dry matter content are considered. Of special interest is the process intensification techniques, impact of contamination and co-fermentation opportunity with other biodegradable wastes. This article also discusses energy and economic performance of DAD plants and puts their environmental burden in perspective versus other bio-waste treatment processes. The current legislation and DAD’s role in the circular economy are also considered. Selectively collected biowaste has significant energy potential and dry anaerobic digestion is an effective technology, especially in areas with limited water availability, offering both waste volume reduction and minimized energy losses. The aim of this work is to introduce the potential of this technology as a sustainable option within the context of renewable energy and modern waste management. Full article

With increasing wastewater treatment demands and decarbonization goals, synergistic reduction in pollutants and green house gas (GHG) emissions is crucial. High process emissions like N₂O pose significant challenges, yet optimized carbon reduction strategies for conventional plants are lacking. This study developed three mathematical models to quantify the impact of dissolved oxygen (DO), influent salinity, and C/N ratio on direct emissions (CH₄, N₂O) and indirect emissions. Response Surface Methodology (RSM) optimized these factors to minimize GHG emissions under three accounting scenarios: (1) plants with CH₄ reuse systems: salinity = 0.5 g L⁻¹, DO = 3.67 mg L⁻¹, C/N = 12.75; (2) plants focusing solely on direct emissions: salinity = 0.5 g L⁻¹, DO = 3.35 mg L⁻¹, C/N = 3; and (3) plants assessing total emissions: salinity = 0.5 g L⁻¹, DO = 2.5 mg L⁻¹, C/N = 7.18. Key findings indicated that increasing salinity exacerbated greenhouse gas emissions. Elevated DO levels in the aerobic stage reduced N₂O emissions but increased indirect emissions in the A²/O process. Higher C/N ratios promoted anaerobic CH₄ production, but sufficient carbon reduced N₂O by enabling complete heterotrophic denitrification. A 60−day continuous GHG emissions monitoring campaign was conducted at a WWTP to validate the actual emission reductions achievable under the identified optimal control conditions. An analysis and comparison of operational and economic costs were also performed. The findings provide practical insights into sustainable GHG emission management and offer potential solutions to advance the synergistic reduction in GHG emissions and pollutants. Full article

In rural Ghana, limited access to affordable, clean cooking fuels drives the need for decentralised waste-to-energy solutions. Anaerobic co-digestion (AcoD) offers a viable route for transforming organic residues into renewable energy, with the added benefit of improved process stability resulting from substrate synergy. This study aims to evaluate the technical feasibility and stabilisation challenges of AcoD, using locally available fruit waste and beet molasses at a secondary school in Bedabour (Ghana). Biological methane potential (BMP) assays of different co-digestion mixtures were conducted at two inoculum-to-substrate (I/S) ratios (2 and 4), identifying the highest yield (441.54 ± 45.98 NmL CH₄/g VS) for a mixture of 75% fruit waste and 25% molasses at an I/S ratio of 4. Later, this mixture was tested in a 6 L semi-continuous AcoD reactor. Due to the high biodegradability of the substrates, volatile fatty acid (VFA) accumulation led to acidification and process instability. Three low-cost mitigation strategies were evaluated: (i) carbonate addition using eggshell-derived sources, (ii) biochar supplementation to enhance buffering capacity, and (iii) the integration of a bioelectrochemical system (BES) into the AcoD recirculation loop. The BES was intended to support VFA removal and enhance methane recovery. Although they temporarily improved the biogas production, none of the strategies ensured long-term pH stability of the AcoD process. The results underscore the synergistic potential of AcoD to enhance methane yields but also reveal critical stability limitations under high-organic-loading conditions in low-buffering rural contexts. Future implementation studies should integrate substrates with higher alkalinity or adjusted organic loading rates to ensure sustained performance. These findings provide field-adapted insights for scaling-up AcoD as a viable renewable energy solution in resource-constrained settings. Full article

Industrial processes like farming, food processing, petroleum refinery, and leather manufacturing produce a lot of high-salinity wastewater. This wastewater presents serious environmental risks, such as soil degradation, eutrophication, and water salinization, if it is released without adequate treatment. The sources and features of high-salinity wastewater are outlined in this review, along with the main methods for removing organic pollutants, such as physicochemical, biological, and combined treatment approaches. Membrane separation, coagulation–flocculation, and advanced oxidation processes are the primary physicochemical techniques. Anaerobic and aerobic technologies are the two categories into which biological treatments fall. Physicochemical–biological combinations and the fusion of several physicochemical techniques are examples of integrated technologies. In order to achieve sustainable and effective treatment and resource recovery of high-salinity wastewater, this review compares the effectiveness and drawbacks of each method and recommends that future research concentrate on the development of salt-tolerant catalysts, anti-fouling membrane materials, halophilic microbial consortia, and optimized hybrid treatment systems. Full article

The biochemical conversion of biomass waste and organic slurries into clean methane is a valuable strategy for both reducing environmental pollution and advancing alternative energy sources to support energy security. Anaerobic digestion (AD), a mature renewable technology operated in high-performance bioreactors, continues to attract attention for improvements in energy efficiency, profitability, and long-term sustainability at scale. Recent efforts focus on optimizing biochemical reactions throughout all phases of the anaerobic process while mitigating the production of inhibitory compounds that reduce biodegradation efficiency and, consequently, economic viability. A relatively underexplored but promising strategy involves supplementing fermentation substrates with nanoscale additives to boost biomethane yield. Laboratory-scale studies suggest that nanoparticles (NPs) can enhance process stability, improve biogas yield and quality, and positively influence the value of by-products. This paper presents a comprehensive overview of recent advancements in the application of nanoparticles in catalyzing anaerobic digestion, considering both biochemical and economic perspectives. It evaluates the influence of NPs on bioconversion efficiency at various stages of the process, explores specific metabolic pathways, and addresses challenges associated with recalcitrant biomass. Additionally, currently employed and emerging pre-treatment methods are briefly discussed, highlighting how they affect digestibility and methane production. The study also assesses the potential of various nanocatalysts to enhance anaerobic biodegradation and identifies research gaps that limit the transition from laboratory research to industrial-scale applications. Further investigation is necessary to ensure consistent performance and economic feasibility before widespread adoption can be achieved. Full article

Wastewater treatment plants (WWTPs) are critical infrastructure that lessen the environmental impacts of human activity by stabilizing wastewaters laden with organics, chemicals, and nutrients. WWTPs face an increasing global population, greater wastewater volumes, stricter environmental regulations, and additional societal pressures to implement more sustainable and energy-efficient waste management strategies. WWTPs are energy-intensive facilities that generate significant GHG emissions and involve high operational costs. Therefore, improving the process efficiency can lead to widespread environmental and economic benefits. One promising approach is to integrate anaerobic digestion (AD) with hydrothermal carbonization (HTC) to enhance sludge treatment, optimize energy recovery, create valuable bio-based materials, and minimize sludge disposal. This study employs an LCA to evaluate the environmental impact of coupling HTC with AD compared to conventional AD treatment. HTC degrades wastewater sludge in an aqueous medium, producing carbon-dense hydrochar while reducing sludge volumes. HTC also generates an aqueous byproduct containing >30% of the original carbon as simple organics. In this system model, the aqueous byproduct is returned to AD to generate additional biogas, which then provides heat and power for the WWTP and HTC process. The results indicate that the integrated AD + HTC system significantly reduces environmental emissions and sludge volumes, increases net energy recovery, and improves wastewater sludge valorization compared to conventional AD. This research highlights the potential of AD + HTC as a key circular bioeconomy strategy, offering an innovative and efficient solution for advancing the sustainability of WWTPs. Full article

Butyric acid is one of the main volatile fatty acids (VFAs) in Maotai-flavor liquor wastewater (MFLW), and its degradation process exhibits a positive Gibbs free energy, making it prone to accumulation during high-load anaerobic digestion (AD), which can lead to system instability or even failure. In this study, hydrochar (HTC) was prepared from rice husk obtained from distiller’s grains, and butyrate-degrading microbiomes were selectively enriched under acidic conditions with butyric acid as the sole carbon source. Through co-incubation, the butyrate-degrading microbiomes were successfully pre-coupled with HTC, forming a “hydrochar–microbe” composite, which was then applied to the AD of MFLW. The experimental results demonstrated that this composite enhanced system performance. The hydrochar–butyrate pre-coupling group (HBA-C) showed a 15.48% increase in methane yield compared to the control group (CK), with a soluble chemical oxygen demand (sCOD) removal rate of 75.02%, effectively mitigating VFA accumulation. Microbial community analysis indicated higher bacterial and archaeal diversity indices in the HBA-C group. qPCR results showed that the bacterial and archaeal copy numbers in the HBA-C group were 22.06-times and 13.80-times higher than those in the CK group, respectively. Moreover, the relative abundance of the genes for the key enzymes methylmalonyl-CoA carboxyltransferase (EC: 2.1.3.1) and succinate dehydrogenase (EC: 1.3.5.1) was significantly increased, indicating that the “hydrochar–microbe” coupling enhanced carbon flow distribution efficiency and energy metabolism by optimizing metabolic pathways. This study provides an innovative strategy for MFLW treatment and offers practical value for anaerobic digestion optimization and high-strength wastewater management. Full article

Producing Class A biosolids is a beneficial way to reuse wastewater treatment solids, but most conventional processes are energy-intensive and expensive. There is growing interest in the use of low-cost, low-tech (LCLT) Class A biosolids treatment processes, especially at small water resource recovery facilities (WRRFs). This study used a holistic sustainability assessment to examine the environmental, economic, and social sustainability of conventional and LCLT processes at small WRRFs. The technologies studied were Direct Heat Drying, Composting, Lagoon Storage, Air Drying, and Temperature-Phased Anaerobic Digestion (TPAD). Environmental impacts were determined by conducting life-cycle assessments for all technologies, which is described in detail in prior published work. Economic impacts were quantified with a life-cycle cost assessment approach over a 25-year time horizon. Potential social impacts of each process were assessed by investigating case studies and surveys of social response to biosolids and estimating a relative impact score in a number of categories reported to be important to stakeholders in this technical domain. Impacts were normalized and compared to assess the best processes under a range of weighting scenarios. TPAD and Air Drying were the most sustainable processes when all domains were weighted equally. TPAD was projected to have low environmental and social impacts, which made up for its relatively high lifetime cost. Air Drying was the least expensive process in our analysis and had a modest environmental footprint, but there is potential for higher social impacts if the process is not sited and maintained properly. Because different communities are likely to prioritize or weight environmental, economic, and social impacts differently, a three-component mixing diagram was used to illustrate that Air Drying (economic), TPAD (environmental), or Direct Heat Drying (social) could become the preferred biosolids treatment process depending on which of the three sustainability domains was prioritized in the analysis. Full article

Iron, an essential element for virtually all known organisms, serves not only as a micronutrient but also as an energy source for bacteria. Iron-oxidizing microorganisms mediate Fe(II) oxidation under diverse redox conditions, yielding amorphous iron (hydr)oxides or crystalline iron minerals. This globally significant biogeochemical process drives modern iron cycling across terrestrial and aquatic ecosystems. The resulting biomineralization not only produces secondary minerals but also effectively immobilizes heavy metals, offering a sustainable strategy for environmental remediation. This review systematically examines (1) the biogeochemical mechanisms and mineralogical signatures of Fe(II) oxidation by four distinct iron oxidizers: acidophilic aerobes (e.g., Acidithiobacillus), neutrophilic microaerophiles (e.g., Gallionella), nitrate-reducing anaerobes (e.g., Acidovorax), and anoxygenic phototrophs (e.g., Rhodobacter); (2) research advances in heavy metal immobilization by biogenic iron minerals: adsorption, coprecipitation, and structural incorporation; and (3) the impact of pH, temperature, organic matter, and coexisting ions on Fe(II) oxidation efficiency and iron mineral formation by iron-oxidizing bacteria. By characterizing iron-oxidizing bacterial species and their functional processes under varying pH and redox conditions, this study provides critical insights into microbial behaviors driving the evolution of acid mine drainage (AMD). Full article

This study investigated the feasibility of using both the solid and the liquid fractions of waste from the anaerobic digestion process—the digestate—as a possible liquid growth medium for fungal production of chitosan. An enriched liquid phase (ELP), combining both fractions, and derived from mild acid hydrolysis treatment at 120 °C with 6% H₂SO₄ (w/v) for 70 min, was screened for its ability to support biomass and chitosan production by 17 fungal strains. The best results were obtained with Absidia blakesleeana NRRL 2696 and Rhizopus oryzae NRRL 1510 cultures, which yielded chitosan volumetric productions of 444 and 324 mg L⁻¹, respectively. The chitosan preparations of the former and the latter strain, characterized by infrared spectroscopy, elemental analysis, viscosimetry and thermogravimetric analysis, showed deacetylation degrees of 79% and 84.2%, respectively, and average viscosimetric molecular weights of around 20 and 5.4 kDa, respectively. Moreover, both fungal chitosan samples exerted significant antibacterial activity towards Gram-negative (i.e., Pseudomonas syringae and Escherichia coli) and Gram-positive (i.e., Bacillus subtilis) species. Full article

Lately, anaerobic digestion has become a promising method for producing bioenergy from organic waste and is considered a model of the circular economy. At the same time, the concept of circular economy has gained particular attention in environmental policy agendas supporting the transition towards climate neutrality and the promotion of clean energy sources. Although the main objective of anaerobic digestion is to produce biogas, a significant part of the used substrate is converted into digestate, a by-product. Digestate is composed of organic and inorganic matter, which are considered dangerous contaminants for the environment if not properly treated, but also potential renewable resources if properly recovered. Digestate has enormous potential as an organic fertilizer, soil improver and landfill cover soil, but its disposal and use present significant challenges. The main aim of this review paper is to present the current routes for solid and liquid anaerobic digestate valorization according to circular economy principles and to highlight the relation between anaerobic digestion processes and circular economy models. It further focuses on the aspects regarding anaerobic digestate processing technologies, standards and regulations for digestate use and environmental benefits of its use as soil fertilizer. Full article