Search Results (1,252)

This two-part study assesses the impact of biogas inhibition on large-scale waste-to-energy anaerobic digestion (WtE-AD) plants through techno-economic and life cycle assessment approaches. The first part addresses technical and economic aspects. An anaerobic co-digestion system using vegetable waste (FVW) and meat waste (MW) was operated at laboratory scale in a semi-continuous regime with daily feeding to establish a stable process and induce programmed failures causing methanogenic inhibition, achieved by removing MW from the reactor feed and drastically reducing the protein content. Experimental data, combined with bioprocess scale-up models and cost engineering methods, were then used to evaluate the effect of inhibition periods on the profitability of large-scale WtE-AD processes. In the experimental stage, the stable process achieved a yield of 521.5 ± 21 mL CH₄ g⁻¹ volatile solids (VS) and a biogas productivity of 0.965 ± 0.04 L L⁻¹ d⁻¹ (volume of biogas generated per reactor volume per day), with no failure risk detected, as indicated by the volatile fatty acids/total alkalinity ratio (VFA/TA, mg VFA L⁻¹/mg L⁻¹) and the VFA/productivity ratio (mg VFA L⁻¹/L L⁻¹ d⁻¹), both recognized as effective early warning indicators. However, during the inhibition period, productivity decreased by 64.26 ± 11.81% due to VFA accumulation and gradual TA loss. With the progressive reintroduction of the FVW:MW management and the addition of fresh inoculum to the reaction medium, productivity recovered to 96.7 ± 1.70% of its pre-inhibition level. In WtE-AD plants processing 60 t d⁻¹ of waste, inhibition events can reduce net present value (NPV) by up to 40.2% (from 0.98 M USD to 0.55 M USD) if occurring once per year. Increasing plant capacity (200 t d⁻¹), combined with higher revenues from waste management fees (99.5 USD t⁻¹) and favorable electricity markets allowing higher selling prices (up to 0.23 USD kWh⁻¹), can enhance resilience and offset inhibition impacts without significantly compromising profitability. These findings provide policymakers and industry stakeholders with key insights into the economic drivers influencing the competitiveness and sustainability of WtE-AD systems. Full article

Nuclear power continues to be a great promise in the green revolution, as it is a cost-effective, low-emission, and safer alternative to fossil fuels that is capable of continuous operation. A preliminary design evaluation is presented for a submersible nuclear power station capable of operating under its own power during emergencies and routine maintenance. Because it is stationed at sea, it offers a resilient solution to natural disasters such as earthquakes and tsunamis, giving it the capability to disengage and sail to deeper waters in less than a half of an hour. In the present evaluation, the hull dimensions of a very large existing submarine and the turbomachinery layout of a Pebble Bed Modular Reactor cycle were used as baselines. The conceptual design of the submersible nuclear power station includes reactor and turbomachinery integration, preliminary sizing (4 pressure hull design; total length of 57.74 m), and propulsion system analysis, demonstrating the technical viability of the proposed submersible power station. Full article

This study evaluated the effectiveness of individual clean-in-place (CIP) steps in removing biofilms from reverse osmosis (RO) membranes under dynamic flow conditions using the Centers for Disease Control (CDC) biofilm reactor. Biofilms were developed in the laboratory under continuous flow, using mixed-species bacterial isolates obtained from 10-month-old RO membrane biofilms from a commercial facility. Individual CIP chemicals, representative of those used in commercial protocols, were tested against 24 h-old biofilms. Additionally, a complete six-step sequential CIP process was conducted under dynamic conditions, consisting of treatments with alkali, surfactant, acid, enzyme, a secondary surfactant, and sanitizer. All experiments were performed in quadruplicate, and data were subjected to statistical analysis. Among individual treatments, the acid step was the most effective, significantly outperforming the other CIP cleaning steps by reducing bacterial counts from 5.62 to 4.10 log units, a 96.98% reduction. The full six-step CIP protocol reduced counts to 2.24 log units, indicating the persistence of resistant cells. The presence of viable cells post-treatment highlights the limited efficacy of the tested CIP chemicals in fully eradicating mature biofilms. Additionally, skipping any step in the membrane cleaning can significantly compromise the efficiency and performance during production. These findings suggest that biofilms grown in vitro under dynamic conditions using the CDC reactor exhibit a more robust assessment of the CIP treatments in accomplishing the biofilm control. This study highlights the need for optimized, scientifically validated CIP protocols targeting biofilms to improve cleaning efficacy and food safety. Full article

Extremophilic biological process (EBP) pretreatment increases substrate availability in anaerobic digestion, but the effect on downstream microbial community composition in industrial systems is not characterized. Changes in microbial communities were determined at an industrial facility processing dairy manure in a modified split-stream system with three reactor types: (1) EBP tanks at 70–72 °C; (2) mesophilic Continuously Stirred Tank Reactors (CSTRs); (3) mesophilic Induced Bed Reactors (IBRs) receiving combined CSTR and EBP effluent. All reactors had a two-day hydraulic retention time. Samples were collected weekly for 60 days. pH, volatile fatty acid and bicarbonate concentrations, COD, and methane yield were measured to assess tank environmental conditions. Microbial community compositions were obtained via 16S rRNA gene sequencing. EBP pretreatment increased acetate availability but led to a decline in the relative abundance of acetoclastic Methanosarcina species in downstream IBRs. Rather, syntrophic methanogens, e.g., members of Methanobacteriaceae, increased in relative abundance and became central to microbial co-occurrence networks, particularly in association with hydrogen-producing bacteria. Network analysis also demonstrated that these syntrophic relationships were tightly coordinated in pretreated digestate but absent in the untreated CSTRs. By promoting syntrophic methanogenesis while increasing acetate concentrations, EBP pretreatment requires system configurations that enable acetoclast retention to prevent acetate underutilization and maximize methane yields. Full article

A multiphase model of hydrothermal liquefaction (HTL) using the computational fluid dynamics coupling discrete element method (CFD-DEM) is used to simulate biocrude oil production from sludge flocs in a continuous stirred tank reactor (CSTR). Additionally, the influence of the agitator speed and the slurry flow rate on dynamic biocrude oil production is investigated through full transient CFD analysis in a scaled-up CSTR study. The kinetics of the HTL mechanism as a function of temperature, pressure, and residence time distribution were employed in the model through a user-defined function (UDF). The multiphysics simulation of the HTL process in a stirred tank reactor using the Lagrangian–Eulerian (LE) approach, along with a standard k-ε turbulence model, integrated HTL kinetics. The simulation accounts for particle–fluid interactions by coupling CFD-derived hydrodynamic fields with discrete particle motion, enabling prediction of individual particle trajectories based on drag, buoyancy, and interphase momentum exchange. The three-phase flow using a compressible non-ideal gas model and multiphase interaction as design requirements increased process efficiency in high-pressure and high-temperature model conditions. Full article

This study explores the visible-light-driven photolysis of Ferrioxalate complexes for the degradation of Toluidine Blue (TB), a persistent phenothiazine dye, using a 1 L recirculating batch-loop photoreactor. The reactor system incorporated two tubular photochemical units (35 cm × 3 cm each) in series: the first equipped with an immersed blue fluorescent lamp (12 W, 30 cm-tube), and the second with dual external blue LED lamps (18 W total, 30 cm) encasing a double-walled glass cell. Continuous flow between the units was maintained via a peristaltic pump. Experimental investigations were used to evaluate the effects of key parameters such as Fe(III) and oxalate concentrations, initial TB load, pH, light source, flow rate, ligand type, dissolved gas type, external H₂O₂ addition, and the presence of various inorganic ions. The results demonstrate efficient dye degradation, with ~75% TB removal within 1 h under combined fluorescent and LED irradiation, where each reactor contributing comparably. The optimal performance was achieved at pH 4, with a 10 oxalate-to-Fe(III) molar ratio (1 mM:0.1 mM) and a flow rate of 25 mL s⁻¹. Among various ligands tested (oxalate, acetate, citrate, EDTA), oxalate proved to be the most effective. The presence and type of anions significantly influenced degradation efficiency due to their potential scavenging effects. Although the process achieved high dye removal, TOC analysis indicated only moderate mineralization, suggesting the accumulation of non-colored intermediates. External H₂O₂ addition moderately improved TOC removal, likely due to enhanced hydroxyl radical generation via the Fenton mechanism. These findings highlight the promise of Ferrioxalate-based photochemical systems under visible light for dye removal, while also emphasizing the need for further research into by-product identification, mineralization enhancement, and toxicity reduction to ensure safe effluent discharge. Full article

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

Polymer fouling in batch and tubular reactors creates safety hazards from heat buildup and blockages. The continuous Corning Advanced-Flow™ Reactor (AFR) offers enhanced mass and heat transfer, improving safety and efficiency. This study evaluated three reactor systems—a monolithic AFR, an AFR with an external pipe, and a conventional tubular reactor—for the mini-emulsion polymerization of styrene and subsequent styrene–acrylic acid copolymerization. The AFR operability under varying monomer concentrations was assessed and investigated, with the residence time’s effects on conversion. For styrene polymerization at 20–35 wt% monomer, the highest conversions achieved were 88.0% in the AFR, 85.8% in the tubular reactor, and 98.9% in the AFR with pipe. Uniform particles were obtained at ≤30 wt%, whereas at 35 wt%, the monolithic AFR experienced clogging and loss of particle uniformity. Similarly, in styrene–acrylic acid copolymerization (15–17.5 wt% monomer), the maximum conversions reached 80.1% in the AFR and 95.4% in the AFR with pipe, while the monolithic AFR again experienced blockage at 17.5 wt%. In conclusion, integrating an external pipe with the AFR, coupled with higher flow rates, significantly improved initiator diffusion, enhanced monomer conversion, and mitigated blockage. This approach enabled the efficient, continuous production of nanoscale, uniformly sized polystyrene and styrene–acrylic acid copolymers even at high monomer concentrations. 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

This paper presents an original approach through Transfer-Matrix Method applied for the calculus of the continuous circular plate embedded at the exterior circumference, charged with asymmetrical uniform load on the entire upper surface of the plate. Continuous circular plates are elements often found in practice, in the machine building, aeronautics, chemical industries (the bottoms of chemical reactors), and in petrochemical, mechanical, robotic, medical, military, nuclear, and aerospace industries. The calculus of continuous circular plates is a special problem both from the point of view of the theory of elasticity and from the point of view of the mathematical approach. The results obtained with Transfer-Matrix Method were compared and validated with those obtained from classical analytical calculation, the Theory of Elasticity. Transfer-Matrix Method is an elegant method and relatively easy to program. In future research, we want to validate our results with those given by the Finite Elements Method and those measured experimentally. 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

In this study, high-yield biopolymer/ceramic hollow fibers were fabricated via a facile, modified polyol process in a spinneret setup, enabling the controlled adsorption of Cu²⁺ ions. Post sintering transformed these into catalytic copper-decorated carbon/ceramic (alumina) composite hollow fibers, with alginate serving as both a metal ion binder and a copper nanoparticle stabilizer. The resulting hollow fibers featured porous walls with a high surface area and were densely decorated with copper nanoparticles. Their structural and morphological characteristics were analyzed, and their NO reduction performance was assessed in a continuous flow configuration, where the gas stream passed through both the shell and lumen sides of a fiber bundle in a tangential flow mode. This study also examined the stability, longevity and regeneration potential of the catalytic fibers, including the mechanisms of deactivation and reactivation. Carbon content was found to be decisive for catalytic performance. High-carbon fibers exhibited a light-off temperature of 250 °C, maintained about 90% N₂ selectivity and sustained a consistently high NO reduction efficiency for over 300 h, even without reducing gases like CO. In contrast, low-carbon fibers displayed a higher light-off temperature of 350 °C and a reduced catalytic efficiency. The results indicate that carbon enhances both activity and selectivity, counterbalancing deactivation effects. Owing to their scalability, durability and effectiveness, these catalytic fibers and their corresponding bundle-type reactor configuration represent a promising technology for advanced NO abatement. Full article

As the demand for effective wastewater treatment continues to rise, the application of three-dimensional (3D) electrochemical particle electrodes for the removal of organic compounds from industrial wastewater has emerged as a promising solution. This approach offers significant advantages, including high treatment efficiency, operational flexibility, high current efficiency, low energy consumption, and the ability to degrade non-biodegradable organic pollutants, ultimately mineralizing them. This review provides a comprehensive and systematic exploration of the research and development of particle electrodes for use in 3D electrochemical reactors in wastewater treatment. The pivotal role of particle electrodes in removing organic contaminants from wastewater was highlighted, with most materials used as particle electrodes characterized by a specific surface area and well-defined porous structure, both of which were thoroughly discussed. Through the synergistic mechanism of adsorption, the particle electrode aids in the breakdown of organic contaminants, demonstrating the 3D particle electrode’s effectiveness in facilitating multiple oxidation mechanisms for organic wastewater treatment. Furthermore, this review categorized various particle electrode types used in 3D electrochemical wastewater treatment based on their primary components or carriers and the presence or absence of catalysts. Finally, the current status and prospects for the development and enhancement of 3D electrode particles were presented. This review offers valuable insights into the application of the 3D electrode process for environmental water treatment. Full article

The one-step method in reactor physics has become one of the important research directions in recent two decades. Based on the open-source OpenMOC code, the following work was carried out. Firstly, the global–local resonance method with multi-group and continuous neutron libraries was researched and established. Next, based on the 2D and 3D MOC solver, the 2D/1D and the MOC/DD transport methods were realized in OpenMOC. Finally, verification of the transport and resonance methods was conducted using the C5G7 macro benchmark and the VERA micro benchmark. The numerical results demonstrated that the average eigenvalue deviation was 44 pcm and average maximum pin power distribution deviation was 0.37% in the VERA-2 benchmark, which showed the good accuracy of the resonance method. As for the transport method, the 3DMOC method exhibited better accuracy in strong anisotropic cases, but the computational time was 38 times that of the 2D/1D method. Full article

This study presents a four-year evaluation (2020–2024) of an integrated climate mitigation project on a pig farm in Ávila, Spain, at an elevation of over 1100 m above sea level with continental climate conditions. The project aimed to reduce greenhouse gas emissions (GHG) and nitrogen pollution by implementing solid–liquid filtration followed by biological treatment in a 625 m³ Sequencing Batch Reactor (SBR) operating under a nitrification–denitrification (N-DN) regime. The SBR carried out four daily cycles, alternating aerobic and anoxic phases, with 5 and 8 m³ inlets. Aeration intensity and redox potential were continuously monitored to optimize bacterial activity. Analytical parameters (pH, electrical conductivity, solids content, nitrogen, phosphorus, and potassium) were measured using ISO methods and tracked frequently. Annual emission reductions were 75% for N₂O, up to 97% for NH₃, and 80% for N₂. In the summer months, we observed higher efficiency reduction for N₂, NH₃, and NO₂. Additionally, there was a 75% average reduction for COD and up to 92% for total GHG emissions. This real-world case study highlights the effectiveness of SBR-based N-DN systems for nutrient removal and emission reduction in high-altitude, climate-sensitive regions, contributing to EU nitrate directive compliance and circular economy practices. Full article