Search Results (48)

This paper systematically investigates the failure characteristics and mechanisms of insulating materials in DC voltage dividers under combined high-frequency voltage and high-temperature conditions via simulations and experiments. The results showed that high-frequency harmonics severely degrade the insulation strength of polypropylene/paper/polypropylene (PPLP) at 10 kHz, in which the bulk breakdown strength of PPLP decreases by over 50%. Furthermore, the surface flashover voltage in oil is reduced by 17.7% under high-frequency voltage alone, and by as much as 51% when white flocculent substances are present in the oil. The dielectric properties of PPLP strongly depend on frequency and temperature, which aggravate the heat accumulation of the divider under high-frequency voltage. Furthermore, the multilayer structure of PPLP introduces deeper trap levels due to interfacial states, which reduce the breakdown strength and flashover voltage of PPLP. Electro-thermal coupling induces a rapid temperature rising to 98 °C at 25 kHz caused by dielectric loss, leading to oil turbidity and white precipitation, consistent with finite element simulations. Consequently, a failure mechanism is proposed as follows: prolonged electro-thermal stress causes chain scission in styrene-containing materials, releasing monomers that repolymerize into white polystyrene deposits. Their porous structure and dielectric mismatch distort the interfacial field, trigger partial discharge, and aggravate surface flashover. Full article

Although numerous studies have focused on the potential application of heterotrophic nitrification–aerobic denitrification (HNAD) bacteria in wastewater treatment, research exploring their potential in aquaculture biofloc systems remains limited. In this study, a promising HNAD strain, identified as Stutzerimonas stutzeri MJ20, was isolated from mature biofloc. This strain efficiently utilized low-cost carbon sources (e.g., glucose) and small-molecule carbon sources (e.g., sodium acetate and sodium succinate). Under conditions with glucose as the carbon source, a carbon-to-nitrogen (C/N) ratio of 15, pH 6–9, temperature 25–35 °C, salinity 0–35‰, and shaker speed of 0–150 rpm, it achieved removal rates of 95–100% for NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N at initial concentrations of 100 mg/L each. Even at higher concentrations (up to 200 mg/L NH₄⁺-N and 500 mg/L for both NO₂⁻-N and NO₃⁻-N), removal rates exceeded 99%. Under mixed nitrogen sources, strain MJ20 demonstrated efficient nitrogen removal, preferentially utilizing NH₄⁺-N, with only minimal and transient accumulation of nitrite and nitrate. Genomic analysis revealed that MJ20 carries key denitrification genes, including napA, nirS, norB and nosZ, and possesses complete pathways for nitrate reduction to nitrogen gas and ammonia assimilation, although typical autotrophic nitrification genes were not detected. Combined genomic data and autotrophic culture experiments indicated that, in addition to utilizing various organic carbon sources, the strain also exhibited certain autotrophic growth capabilities. Furthermore, MJ20 showed strong flocculation ability (flocculation rate > 96% within 16 h), sensitivity to multiple common antibiotics, and no toxicity to zebrafish, demonstrating favorable biosafety. In simulated seawater aquaculture wastewater with a C/N ratio of 5, it achieved a total nitrogen removal rate exceeding 94% within 72 h. These results indicate that strain MJ20 possesses comprehensive advantages, including efficient nitrogen removal, broad carbon source adaptability, strong environmental resilience, minimal accumulation of intermediate nitrogen products, excellent flocculation ability, and high biosafety. These traits highlight its potential for application in biofloc systems and in treating aquaculture tail water with a low C/N ratio. This study provides theoretical insights and practical guidance for screening HNAD bacteria suitable for biofloc systems. Full article

Thermal–oxidative coking of aviation fuel remains a critical limitation for fuel-cooled aero-engine systems operating under high heat loads. This study systematically investigates the oxidative coking behavior of RP-3 aviation kerosene, focusing on the coupled evolution of deposit morphology, composition, and operating conditions. Experiments were conducted in an electrically heated stainless-steel tube while independently varying dissolved oxygen concentration, fuel temperature, temperature gradient, operating pressure, and heating duration. Deposit layers were characterized by SEM and XPS, and residual fuel chemistry was analyzed using GC/MS. The results show that dissolved oxygen governs both the extent and mechanism of coking in the autoxidation regime (150–450 °C). Normal and elevated oxygen levels promote autoxidation of straight-chain alkanes, generating oxygen-containing intermediates that form flocculent, oxygen-rich deposits, whereas near-deoxygenated conditions suppress autoxidation but sustain sulfur-dominated, needle-like deposits. Temperature primarily controls deposition rate and morphology, with steep temperature gradients inducing localized coke formation, while pressure exerts only a minor indirect influence. Prolonged operation leads to deposit densification and non-linear accumulation behavior. These findings clarify the links between fuel chemistry, thermal conditions, and deposit architecture, providing a basis for morphology-aware coking models in fuel-cooled aero-engine systems. Full article

Industrial wastewater containing heavy metals such as iron (Fe) and copper (Cu) remains a major environmental concern in Malaysia, since industrial effluents significantly contribute to national water pollution loads. Without proper treatment, these contaminants can accumulate in the ecosystem and pose long term risks to human health and aquatic life. This study evaluates the performance, sludge characteristics, and cost implications of alkaline precipitation using sodium hydroxide (NaOH) and calcium oxide (CaO) in the presence and absence of a polymeric flocculant (SW204) for heavy metal removal. Experimental findings reveal that both NaOH and CaO effectively removed heavy metals, where NaOH achieved removal efficiencies of 91.6% for Fe and 93.5% for Cu, while CaO removed 98.9% of Fe and 99.17% of Cu. The addition of polymer improved the treatment efficiency where removal up to 99.73% Fe and 99.80% Cu was achieved with the CaO and polymer system. Settling time improved drastically from 30 min when using NaOH to 2 min when using CaO and the polymer system, indicating the formation of denser and more compact flocs. The specific gravity and sludge weight also increased by approximately 4% with polymer addition, which may influence the disposal costs. Economic analysis revealed that CaO treatment is substantially more cost-effective than NaOH, yielding savings of approximately RM 15.77 per m⁻³ of effluent treated. Therefore, the combination of CaO and polymers provided the best balance of removal efficiency, settling performance, and cost reduction. The findings support the use of CaO-based systems as sustainable, high-efficiency alternatives for industrial wastewater treatment, all of which aligns with UN Sustainable Development Goals 6 (Clean Water and Sanitation) and 12 (Responsible Consumption and Production). Full article

The rapid growth of synthetic textile production has intensified the release of micro- and nanoplastics (MPs/NPs) into aquatic environments, primarily through industrial effluents and domestic laundering. Textile-derived microplastics, especially polyester fibers and polymeric coating fragments, constitute a significant fraction of plastic contamination in wastewater systems. Although wastewater treatment plants (WWTPs) can remove a large proportion of MPs, substantial quantities accumulate in sewage sludge, raising concerns about long-term environmental persistence and secondary release pathways. This review critically examines the sources, classification, and release mechanisms of textile-based micro- and nanoplastics, including fibrous debris and coating-derived fragments. Then it focuses on current identification and removal technologies, such as sedimentation, coagulation/flocculation, electrocoagulation, flotation, membrane filtration, adsorption, and biodegradation, and on the emerging strategy of converting recovered microplastics into value-added porous carbon materials via hydrothermal treatment and pyrolysis. Carbonized microplastics exhibit high surface area and adsorption capacity for dyes, heavy metals, and organic pollutants, offering a circular approach that simultaneously mitigates plastic pollution and enhances wastewater treatment efficiency. By integrating source control, optimized removal technologies, and carbonization-based valorization, this review proposes a dual-benefit framework that transforms textile-derived microplastic waste from an environmental liability into a functional resource for sustainable water purification. Full article

Rapid growth of water conservancy/hydropower projects has spurred rising demand for sand-gravel aggregates. Under strict water use and zero-waste policies, treating wet-process aggregate washing wastewater is challenging. Flocculants—key chemicals in this process—directly influence treatment efficiency and operational costs via their type, dosage, and efficacy. Further development of the intelligent control system for flocculant dosing can reduce flocculant consumption by 50% to 67%. However, existing studies have an insufficient understanding of the identification of emerging contaminants in aggregate washing wastewater and the migration of flocculants in multi-medium environments, as well as a lack of research on the synergistic effects of multiple flocculants. Another key core challenge lies in the accurate identification of the impact of flocculant residues on concrete performance, along with the problems of high cost and poor adaptability of intelligent systems. Future research directions will focus on precise flocculation, residue control and resource utilization to drive the development of efficient and environmentally friendly treatment technologies. Full article

The final stage of the drinking water treatment process yields two distinct outputs: treated water and the resulting sludge. This sludge is composed of raw water impurities, coagulation and flocculation agents, and various other additives. In any volume of processed drinking water, the continuous production of sludge is not negligible, leading to a significant environmental impact. This is particularly concerning when aluminium-based agents are used, as these compounds are strongly implicated in potential detrimental health risks. This situation is significantly worsened when raw water temperature approaches zero, as the treatment process efficiency is greatly diminished. Drinking water treatment at low temperatures faces a culmination of adverse effects, including a lower rate of hydrolysis and a reduced floc size, both of which negatively impact sedimentation. An effective strategy for suppressing the high dosing of chemicals is the suitable choice of ratio between acidity and the basicity of the treated water. Simply maintaining the pH value that was optimised for higher temperatures is detrimental, leading to, among other issues, increased sludge accumulation. Therefore, attention should instead be concentrated on the pOH value. A simple algebraic relation is proposed for converting the optimised pH value for higher temperatures to an optimum value for more moderate or low-temperature conditions. The application of this method results in a reduction in the amount of chemical agents required and consequently a reduction in the volume of sludge produced. Full article

Lactic acid is an important biobased chemical widely used in the production of biodegradable plastics, food, and pharmaceuticals. However, the application of flocculant Saccharomyces cerevisiae remains limited in addressing stresses such as high-glucose and inhibitor-rich conditions derived from biomass, particularly in D-lactic acid (D-LA) production. This study investigates two genetically engineered S. cerevisiae F118 strains, ΔCYB2::LpDLDH and ΔPDC1::LpDLDH, for D-LA production under high-glucose and inhibitor-stress conditions that mimic lignocellulosic hydrolysates in shake-flask fermentation. At 150 g/L glucose, ΔCYB2::LpDLDH produced 41 ± 0.73 g/L D-LA, whereas ΔPDC1::LpDLDH yielded 80 ± 1.78 g/L, corresponding to 27% and 53% of the theoretical yield, respectively. Calcium carbonate (CaCO₃) supplementation enhanced glucose consumption and strengthened flocculation in ΔPDC1::LpDLDH. The addition of 5% inhibitory chemical compounds (ICCs) consisting of furfural, HMF, and weak acids redirected carbon flux in ΔCYB2::LpDLDH toward D-LA formation and reduced ethanol byproduct accumulation. Transcriptomic analysis revealed the upregulation of stress-response genes (HOG1, TPS1) and cell-wall remodeling genes (CRH1, SCW10) in response to high-glucose stress. The strongly flocculent F118ΔCYB2::LpDLDH strain exhibited greater tolerance to weak acids and furfural than the weakly flocculent F118ΔPDC1::LpDLDH strain. Metabolomic profiling indicated that under inhibitor stress, carbon flux was diverted from the TCA cycle toward lactate synthesis to maintain redox balance. These findings highlight the multifaceted benefits of flocculation in enhancing strain robustness and D-LA productivity under harsh fermentation environments, providing insights for developing resilient yeast platforms for lignocellulosic bioprocessing. Full article

Harmful algal blooms (HABs) caused by the dinoflagellate Karenia brevis present serious ecological and public health concerns due to the production of brevetoxins (BTX). Clay flocculation and sedimentation of cells, particularly with polyaluminum chloride (PAC)-modified clays, is a promising HAB mitigation approach. This study evaluated the efficacy of Modified Clay-II (MCII), a PAC-modified kaolinite clay, in reducing K. brevis cell abundance in mesocosm experiments and examined the bioavailability of BTX potentially released from settled floc back into the water column and sediment over the first 72 h after treatment. Additionally, we quantified trace metals in benthic clams (Mercenaria mercenaria) exposed to the floc post-treatment to assess metal accumulation and potential toxicological effects from MCII application. MCII treatment (0.2 g/L) resulted in a 91% reduction in K. brevis cell density and a 50% decrease in waterborne brevetoxins after 5 h. Brevetoxins accumulated in sediment post-flocculation, with BTX-B5 emerging as the dominant congener. Clams exposed to MCII-treated floc showed comparable tissue BTX levels to controls and significantly elevated aluminum concentrations, though without mortality. The aluminum accumulations in this study do not raise concerns for the health of the clams or the humans who eat them, given other dietary exposures. These findings support the potential of MCII for HAB mitigation while underscoring the need for further evaluation of exposure risks to all benthic species. Full article

Microplastic pollution represents a significant environmental challenge, as microplastics accumulate in effluents and soils, causing serious risks to ecosystems and human health. Efficient removal of these contaminants is essential to mitigate their potential adverse effects. This review summarizes and critically analyses current methods for the removal of microplastics from effluents and soils, focusing on their effectiveness, advantages, and limitations. Conventional techniques—including filtration, flotation, chemical coagulation, flocculation, and adsorption—are discussed in the context of wastewater treatment and soil remediation. Emerging approaches, such as flocculation processes with special focus on the application of bio-based flocculants, are also highlighted as promising solutions. Key challenges in microplastic removal, including the diversity of microplastic types, their small size, and the complexity of environmental matrices, are addressed. This work intends to contribute to the urgent need for further research to develop more efficient and sustainable strategies for microplastic removal from environmental systems. Full article

In the process of oilfield development, the surfactant–polymer (SP) composite system has shown significant effects in enhancing oil recovery (EOR) due to its excellent interfacial activity and viscoelastic properties. However, with the continuous increase in the volume of composite flooding injection, a decline in injection–production capacity (I/P capacity) has been observed. Through the observation of frozen core slices, it was found that during the secondary composite flooding (SCF) process, a large amount of residual oil in the form of intergranular adsorption remained in the core pores. This phenomenon suggests that the displacement efficiency of the composite flooding may be affected. Research has shown that polymers undergo flocculation reactions with clay minerals (such as kaolinite, Kln) in the reservoir, leading to the formation of high-viscosity mixtures of migrating particles and crude oil (CO). These high-viscosity mixtures accumulate in local pores, making it difficult to further displace them, which causes oil trapping and negatively affects the overall displacement efficiency of secondary composite flooding (SCF). To explore this mechanism, this study used a microscopic visualization displacement model (MVDM) and microscopy techniques to observe the migration of particles during secondary composite flooding. By using kaolinite water suspension (Kln-WS) to simulate migrating particles in the reservoir, the displacement effects of the composite flooding system on the kaolinite water suspension, crude oil, and their mixtures were observed. Experimental results showed that the polymer, acting as a flocculant, promoted the flocculation of kaolinite during the displacement process, thereby increasing the viscosity of crude oil and affecting the displacement efficiency of secondary composite flooding. Full article

Poly-γ-glutamic acid (γ-PGA) is a natural polymer whose molecular weight and viscosity are critical for its application in various fields. However, research on super-high-molecular-weight or -viscosity γ-PGA is limited. In this study, the pgdS gene in Bacillus licheniformis WX-02 was knocked out using homologous recombination, and the batch fermentation performances of the recombinant strain WX-ΔpgdS were compared to those of WX-02. Nitrate accumulation was observed in the early fermentation stages of WX-ΔpgdS, and gene transcription analysis and cell morphology observations revealed that nitrite accumulation was caused by oxygen limitation due to cell aggregation. When the aeration and agitation rates were increased to 2.5 vvm and 600 r/min, respectively, and citrate was used as a precursor, nitrite accumulation was alleviated in WX-ΔpgdS fermentation broth, while γ-PGA yield and broth viscosity reached 17.3 g/L and 4988 mPa·s. Scanning electron microscopy (SEM) showed that the γ-PGA produced by WX-ΔpgdS exhibited a three-dimensional porous network structure. At a γ-PGA concentration of 5 mg/L, the fermentation broth of WX-ΔpgdS achieved a flocculation efficiency of 95.7% after 30 min of microalgae settling. These findings demonstrate that pgdS knockout results in super-high-viscosity γ-PGA, positioning it as an eco-friendly and cost-effective biocoagulant for microalgae harvesting. Full article

This study investigates the microstructural evolution and its effect on the fatigue performance of a novel nickel-based powder superalloy FGH4113A (WZ-A3) after long-term aging at 760 °C and 815 °C. The results show that long-term aging both at 760 °C and 815 °C has no significant effect on the grain size and morphology of the alloy. After aging at 760 °C for up to 2020 h, the size of the γ′ phase remains unchanged, and its morphology transitions from nearly square to nearly spherical. During long-term aging at 815 °C for 440 h, γ′ phase coarsening and spheroidizing occur simultaneously. With prolonged aging time, the size and spheroidization degree of the γ′ phase further increase. During long-term aging up to 440 h at 760 °C, the dispersed granular MC and M₆C carbides dissolve and re-precipitate. By 2020 h of aging, flocculent carbides precipitate and non-continuous M₆C and M₂₃C₆ accumulate at grain boundaries. After long-term aging at 815 °C for 440 h, flocculent carbides begin to precipitate within the grains. By 2020 h of aging, a large amount of flocculent carbides precipitate with significant coarsening and enrichment of the grain boundary carbides. Due to the insignificant coarsening of the γ′ phase as well as the enrichment and precipitation of the grain boundary carbides, the fatigue performance of the alloy decreases slightly after long-term aging. Full article

Water recycling in mining is essential to decrease water usage, which results in the accumulation of high concentrations of inorganic and organic substances in the process water. Consequently, adverse impacts on the flotation process of copper sulfides may arise. High-molecular-weight polymers based on anionic polyacrylamides (PAMs) are used as tailing flocculants in mineral processing plants. The recirculation of water recovered from the tailing thickeners to the flotation process introduces residual PAMs, which can impact the flotation of important copper sulfides like chalcopyrite, bornite, and enargite. This issue has been rarely studied. In this work, results on the effect of an anionic polyacrylamide (PAM) of medium–low anionicity on the flotation of chalcopyrite, enargite, and bornite are reported and analyzed. The results show that PAM molecules depress the flotation of chalcopyrite, enargite, and bornite under a wide range of pH values. The experimental data indicate that the depressing effect of PAMs on copper sulfides increases with pH. The zeta potential results reveal that this parameter becomes less negative with the addition of PAMs, indicating interactions between PAM molecules and the surfaces of the copper sulfides. PAM adsorption on copper sulfides increases with pH, which correlates with the flotation and zeta potential data. It is proposed that the interactions between PAM molecules and copper sulfides are explained by the presence of surface iron and copper hydroxides that create chemically active adsorption sites. Full article

Currently, the alteration of external factors during crude oil extraction easily disrupts the thermodynamic equilibrium of asphaltene, resulting in the continuous flocculation and deposition of asphaltene molecules in crude oil. This accumulation within the pores of reservoir rocks obstructs the pore throat, hindering the efficient extraction of oil and gas, and consequently, affecting the recovery of oil and gas resources. Therefore, it is crucial to investigate the principles of asphaltene deposition inhibition and the synthesis of asphaltene inhibitors. In recent years, the development of nanotechnology has garnered significant attention due to its unique surface and volume effects. Nanoparticles possess a large specific surface area, high adsorption capacity, and excellent suspension and catalytic abilities, exhibiting unparalleled advantages compared with traditional organic asphaltene inhibitors, such as sodium dodecyl benzene sulfonate and salicylic acid. At present, there are three primary types of nanoparticle inhibitors: metal oxide nanoparticles, organic nanoparticles, and inorganic nonmetal nanoparticles. This paper reviews the recent advancements and application challenges of nanoparticle asphaltene deposition inhibition technology based on the mechanism of asphaltene deposition and nano-inhibitors. The aim was to provide insights for ongoing research in this field and to identify potential future research directions. Full article