Search Results (425)

Cheese whey, a byproduct of the dairy industry, has a high organic load and nutrient availability, associated with parameters such as chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP), representing an environmental problem when improperly disposed, and even considering the traditional biological wastewater treatment (secondary treatment), a polishing step (tertiary treatment) could be required in order to meet legislation parameters of discharge in water bodies. This study evaluated the efficiency of co-cultivation between the microalga Tetradesmus obliquus and the yeast Saccharomyces cerevisiae during the tertiary (advanced) treatment of dairy effluent. The process was operated in batch mode to optimize the COD:N ratio and, subsequently, in semicontinuous mode applying the volumetric replacement rates (VRRs) of 40% and 60%. In the batch stage, the COD:N ratio of 20 stood out as the most balanced in terms of nutritional requirement, achieving removal rates of 85.49% for COD, 96.23% for total Kjeldahl nitrogen (TKN), and 100% for TP. In the semicontinuous system, a VRR of 40% optimized nitrogen (91.67%) and phosphorus (95.93%) recovery while COD was also removed (71.68%). The pH remained stable within the range of 7.0 to 7.5 at the end of the process, indicating self-buffering of the consortium. Biomass production reached 915 mg·L⁻¹ (dry cell weight) in batch operation mode and 720 mg·L⁻¹ in semicontinuous mode (VRR of 40%). The results confirmed that the T. obliquus and S. cerevisiae co-cultivation constitutes a stable and sustainable strategy for nutrient recovery during dairy wastewater treatment, aligning with the principles of circular bioeconomy. Full article

Recently, polyhydroxyalkanoates (PHAs) have gained significant attention as a bioactive material for replacing petrochemical plastics. PHAs can be produced by microorganisms growing on sludge substrates. In this study, fish-processing wastewater was investigated as an alternative substrate for PHA production using Bacillus cereus. Wastewater dilution, carbon-to-nitrogen ratio modification, and the addition of fish oil as a lipidic substrate were examined, and bacterial growth and biopolymer production were optimized. First, wastewater was diluted (25–100%) and examined. The 50% dilution treatment was selected, yielding a CDM of 0.426 g/L and a PHA content of 6.69%. In subsequent steps, the effects of wastewater fermentation and bacterial adaptation prior to the main production processes were investigated. According to the results, the 50% and 100% fermented treatments exhibited higher CDM values (0.970–1.022 g/L) compared to the non-fermented treatments. Cultures inoculated with adapted bacteria showed superior performance (CDM: 1.455 g/L, PHA: 0.499 g/L, PHA content: 34.63%) relative to non-adapted treatments. The effect of the carbon-to-nitrogen (C/N) ratio was also optimized by supplementing two carbon sources: glucose and crude fish oil. The optimal treatment T1 (effluent + 0.6 g/L glucose) had a CDM of 1.32 g/L and a PHA content of 0.215 g/L. Treatment 1, which consisted solely of effluent and fish oil, exhibited higher values (CDM: 1.12 g/L, PHA: 0.65 g/L) and was therefore considered the cost-effective treatment. Subsequently, a scale-up process was conducted in a 4 L bioreactor over 300 h under semi-continuous, long-term cultivation. The optimal harvesting time for the biopolymer was achieved during the fourth cycle (180–240 h). The produced biopolymer was characterized using FTIR, NMR, TGA, DSC, SEM, and XRD analyses, confirming the production of a copolymer, specifically poly(3-hydroxybutyrate-co-3-hydroxyvalerate). This study used wastewater from the fish industry for the production of biodegradable polyhydroxyalkanoates. Full article

In this paper, we establish the large deviation principle for the supremum of partial sums of a sequence of non-independent and non-identically distributed random variables. Let $\{X_n:n\ge 1\}$ be a sequence of random variables with the same negative mean, and denote $S_n={\sum }_{i=1}^n{X}_i$, $S_0=0$, and assume that the limit $\mathsf{\Lambda }\left(\theta \right)={lim}_{n\to \infty }{\displaystyle \frac{1}{n}}{\mathsf{\Lambda }}_n\left(\theta \right)$ of the logarithmic moment generating functions ${\mathsf{\Lambda }}_n\left(\theta \right)=logE\left[e^{\theta S_n}\right]$ exists and is essentially smooth and lower semi-continuous. We prove that the sequence $\left\{{\displaystyle \frac{1}{l}}{sup}_{n\ge 0}{S}_n:l\ge 1\right\}$ satisfies the large deviation principle on $\mathbb{R}$ and provide the exact form of its rate function. As a consequence, we obtain the large deviation principle for the supremum of sums formed by combining independent and identically distributed components with correlated components. As applications, we analyze the first-order autoregressive process and the Poisson–Gaussian mixture case and derive exact expressions for the corresponding rate functions and asymptotic estimates for the decay of tail probabilities. Full article

To address early water breakthrough and poor residual-oil mobilization in low-permeability reservoirs, a core–shell nanosphere/surfactant composite system was developed for profile control and enhanced oil recovery. The core–shell nanospheres were prepared by a semi-continuous seed-growth method, and a target particle-size window of 100–200 nm was selected based on pore-throat/particle matching. The representative sample, HK-0417, had an average particle size of about 120 nm and showed good dispersion stability in formation brine at 45 °C. After blending with the surfactant ALT-603, the system achieved an ultralow oil–water interfacial tension on the order of 10⁻³ mN/m and reduced the water contact angle of the oil-aged surface from 125° to 70°, indicating a shift toward near-neutral wettability. Core-flooding tests further showed that, under the same chemical dosage, slug injection (HK-0417 followed by ALT-603) demonstrated better performance than co-injection, with higher incremental oil recovery (15.49% vs. 13.17%) and higher plugging efficiency during subsequent water flooding (81.25% vs. 78.46%). The novelty of this work lies in integrating particle-size-window design, controllable preparation of core–shell nanospheres, and direct comparison of injection strategies within one system. The results provide practical guidance for formulation design and injection-mode selection for enhanced oil recovery in low-permeability reservoirs. Full article

The aim of the article is to introduce a few variants of the generalized quasi-continuity of multifunctions defined on a bitopological space and to study their mutual relationship. The results known for functions are extended to multifunctions, which provide a wider range of relationships, mainly in terms of upper and lower semi-continuities and corresponding continuities with respect to a dual bitopology. The proof procedures are based on a notion of the pseudo-refinement of two topologies and the Baire property in a bitopological space. A characterization of some continuities depending on two topologies by continuities depending only on one topology and the structure of the sets of semi-discontinuity points are given. The equivalence between the upper and lower Baire continuity and upper and lower quasi-continuity (upper and lower continuity with respect to ideal topology) of compact-valued multifunction from a Baire space into a regular one has an important position. The end of this article is dedicated to several interpretations that facilitate and clarify orientation in the achieved results. Full article

Microbial oil production has gained attention as a sustainable and cost-effective alternative to conventional vegetable and fish oils. Among oleaginous microorganisms, Yarrowia lipolytica is notable for its ability to accumulate lipids exceeding 20% of its dry weight. This study aimed to evaluate semi-continuous cultivation as a strategy for sustainable microbial oil production by Y. lipolytica, while also assessing the potential utility of the spent supernatant. Three different feeding frequencies were evaluated. In the 24 h feeding regime, the maximum oil concentration reached 11.22 g/L, decreasing to 8.43 g/L by the 88th hour. In the 6–6–12 h feeding strategy, crude protein content peaked at 43.75% of dry mass at 22 h. Fatty acid profiling revealed consistently low saturated fatty acid (SFA) levels (4.93–10.30%), while unsaturated fatty acids (UFA) dominated (89.69–95.05%). Monounsaturated fatty acids (MUFA) were predominant, reaching up to 81.24%, whereas polyunsaturated fatty acids (PUFA) ranged from 20.78% to 29.98%. Oleic acid was the most abundant fatty acid across all conditions. This composition supports the potential of microbial oil from Y. lipolytica as a sustainable alternative edible lipid ingredient for human food applications, complementing conventional plant-based oils. The favorable unsaturated fatty acid profile indicates its potential suitability for incorporation into food formulations requiring nutritionally desirable lipid sources. As part of the sustainability-oriented approach of the study, the freeze-dried post-culture supernatant was also evaluated for its potential further utilization. With a calorific value of 10.43 kJ/g and significant phosphorus and potassium levels, it shows potential as a biofuel feedstock and as a biofertilizer or biostimulant. Full article

The valorization of agro-industrial byproducts through pyrolysis represents a sustainable route for generating multifunctional raw materials within the framework of a circular bioeconomy. In this study, rice husk (RH) and sugarcane bagasse (SCB) were pyrolyzed in a semi-continuous reactor at 500 °C in order to compare product yields and to characterize resulting gas, aqueous and tar fractions. SCB produced the highest bio-oil yield (44.2 wt%), whereas RH generated the highest char yield (42.9 wt%), consistent with its higher ash and lignin contents. In both cases, tar represented about 12 wt% of the bio-oil. Detailed characterization revealed that the liquid products contained oxygenated compounds of interest, mainly carboxylic acids, ketones, and phenols. Acetic acid was the predominant compound in the aqueous phases, while tars were composed mainly of phenols, ketones, furans, and acids. Particularly, phenols accounted for 52.6% and 37.8% of the total chromatographic area in RH and SCB tars, respectively, whereas ketones represented about 10% in both cases. These results show that pyrolysis of agro-industrial residues not only enables energy recovery but also provides liquid fractions enriched in value-added chemicals. Full article

We propose a reformulated notion of Levitin–Polyak (abbreviated as LP) well posedness for fuzzy optimization problems formulated in the fuzzy order-preserving (FOP) setting, where minimizing sequences are governed by a total ordering defined on fuzzy intervals. Under this formulation, we present verifiable sufficient conditions that guarantee LP well-posed behavior. These conditions are derived using ranking mechanisms that maintain interval order relations and ensure solution comparability. One central contribution is an equivalence-based theoretical characterization of LP well posedness obtained through an examination of the topological properties of the approximate solution mapping, particularly its closed-graph structure and upper semicontinuity. In addition, convergence of approximating solution sequences is investigated under the upper Hausdorff metric, leading to stability results for the associated solution sets. The established criteria provide a comprehensive framework for analyzing the convergence performance of algorithms designed for fuzzy optimization environments. Full article

This study evaluated the performance of a pilot unit for the combined removal of microplastics and total suspended solids at the municipal wastewater treatment plant of Mykonos, Greece. The pilot unit was installed downstream of the two-stage conventional activated sludge line and operated in semi-continuous mode to demonstrate its function under real effluent conditions. Across five experimental loops, influent microplastics concentrations ranged from 633 to 5843 microplastics/L, while effluent values were reduced to 96–263 microplastics/L, corresponding to an average removal efficiency of 86 ± 8%. In parallel, total suspended solids decreased by 95 ± 3%, turbidity by 93 ± 7%, and chemical oxygen demand by 70 ± 20%, while pH and conductivity remained stable. Influent water showed pronounced variability in chemical oxygen demand, total suspended solids, and turbidity due to irregular wastewater deliveries, yet the pilot consistently stabilized the effluent quality. A correlation analysis revealed strong associations between turbidity, total suspended solids, and chemical oxygen demand in the influent, while effluent data indicated close links between microplastics removal and particulate reduction. These findings confirm the robustness of the organosilane-based agglomeration process and highlight its potential as an advanced treatment stage to reduce MP emissions, improve effluent stability, and mitigate environmental risks in receiving environments such as the Mediterranean Sea. Full article

Intergranular corrosion (IGC) and exfoliation corrosion (EXCO) limit the durability of 2219 Al–Cu in chloride-rich, cyclic-humidity aerospace environments, and conventional thermal stress relief can worsen grain boundary precipitates and grain boundary non-precipitation zones (PFZs), motivating evaluation of low-temperature resonant vibration stress relief. Using polarization tests and microstructural analysis, we show that RRV lowers corrosion current, strengthens passivation, and reduces IGC and EXCO susceptibility. Alternating tensile–compressive stresses build dislocation networks that convert continuous or semi-continuous grain boundary precipitates into discrete distributions, increasing corrosion path tortuosity and slowing intergranular attack. A more discrete cathodic phase, a narrowed solute-enriched anodic band, and reduced PFZs disrupt corrosion channel continuity, weaken microgalvanic driving forces via a more uniform θ′ distribution, and limit corrosion product wedging, while homogenized precipitates suppress local galvanic coupling in EXCO-like media. Overall, RRV synergistically optimizes dislocation configuration and precipitate redistribution to intrinsically enhance corrosion resistance and offers a practical, low-temperature, scalable route to improve the durability of high-strength aluminum alloy structures in aerospace service. Full article

Efficient inorganic carbon supply is a common limitation in microalgal cultivation, particularly in waste-derived media such as anaerobic digestate. Carbonic anhydrase (CA) accelerates the interconversion of CO₂ and bicarbonate and may therefore enhance carbon utilisation under conditions where inorganic carbon is abundant but not readily available. In this study, crude CA-containing extracts (aCA) were prepared from Scenedesmus-dominated algal biomass, and CA activity was quantified using an esterase assay (EAA). Although EAA activities varied depending on biomass pretreatment (0.15–0.47 U g⁻¹ DW), the physiological response to extract addition was consistent. In batch cultures of Chlorella sorokiniana grown in diluted digestate, aCA supplementation increased the specific growth rate (SGR) by 21–82%. In contrast, stimulation in a mineral medium was minimal, indicating that the benefit of aCA addition is most apparent under reduced inorganic carbon availability. In semi-continuous cultivation, repeated extract addition sustained a higher biomass productivity over time (rather than a specific growth rate). These results demonstrate that crude microalgal extracts containing CA can improve growth performance in digestate-based cultures and may offer a simple, low-cost approach to enhancing inorganic carbon utilisation in waste-integrated algal production systems. Full article

Biochar supplementation has gained a lot of interest in recent years as a strategy to improve anaerobic digestion. As a result, research on the field has expanded in diverse directions, yet a clear pathway is not being followed, which can lead to unexpected or contradictory results. This review analyzed the most recent literature (2020–2024) on this topic and identified three major research trends: (i) investigating the mechanisms behind biochar enhancement of anaerobic digestion (analysis of microbial communities, interspecies electron transfer, metabolic pathways, enzymatic activity, gene expression, extracellular polymeric substances, quorum sensing, and antibiotic resistance genes); (ii) maximizing biochar applications in anaerobic digestion through the use of novel tools (biochar engineering, modeling and optimization, and integration of anaerobic digestion and other technologies); (iii) advancing towards the large-scale implementation of biochar addition to anaerobic digestion (continuous operation, biochar effects on digestate, techno-economic analysis, and life cycle assessment). By investigating these topics, key knowledge gaps and challenges to be addressed in future research were defined and discussed. This review aims to provide a clear and insightful picture of the current state and future prospects of scientific research in this field, which may be of great relevance given the current rise in this technology. Full article

This study adopts a biochemical approach to sequester CO₂ while producing biomass rich in protein and lipids, using an adapted strain of Chlorella vulgaris (ALE-Cv), which had previously evolved to tolerate a gas mixture containing 10% CO₂ and 90% air. The research studied the operating parameters of the batch photobioreactor for ALE-Cv to evaluate the effects of inoculum size, photoperiod, light intensity, pH of culture, and CO₂ supply rate on biomass productivity and CO₂ bio-fixation rate. The optimal conditions were identified as 16:8 h light–dark cycles, 5000 lux, pH 7, 20 mL of 10 g/L inoculum, and 0.6 VVM; the system achieved a maximum total biomass production of 7.03 ± 0.21 g/L with a specific growth rate of 0.712 day⁻¹, corresponding to a CO₂ bio-fixation of 13.4 ± 0.45 g/L in batch cultivation. While the pre-adapted strain of Chlorella vulgaris under the same operating conditions, except for the gas supply, which was air, achieved a maximum total biomass production of 0.52 ± 0.008 g/L, and the total CO₂ bio-fixation was 1.036 ± 0.021 g/L during 7-day cultivation. A novel semi-continuous harvesting process, with and without nutrient addition, was also investigated to maximise biomass yield and enable water recycling for culture media. The maximum biomass production in semi-continuous harvesting process with and without nutrition added was 5.29 ± 0.09 and 9.91 ± 0.11 g/L, while the total corresponding CO₂ bio-fixation was 9.70 ± 0.13 and 18.16 ± 0.11 g/L, respectively, during 15-day cultivation. The findings provide critical insights into enhancing CO₂ bio-fixation through adaptive evolution of ALE-Cv and offer optimal operational parameters for future large-scale microalgae cultivation. This research also links microalgae-based CO₂ sequestration to green technologies and the bioeconomy, highlighting its potential contribution to climate change mitigation while supporting environmental sustainability, food security, and ecosystem resilience. Full article

This study evaluated low-cost food waste anaerobic digestion (FWAD) designed for African urban informal settlements, where electricity and process control are limited. Eight small-scale reactors were operated under varying mixing, pH control, and temperature conditions to assess the feasibility of stable operation with minimal input. Results showed no significant difference in methane yield between continuously mixed and minimally mixed (48-hourly) systems, nor between reactors with continuous pH dosing and those adjusted every 48 h (ANOVA p > 0.05 for all comparisons). The highest mean methane yield, 0.267 L CH₄ g VS⁻¹, was achieved by the minimally mixed reactor with 48-hourly pH control at 30 °C, while the controlled reactor at 37 °C produced a comparable 0.247 L CH₄ g VS⁻¹. Total methane production was similar at both temperatures, although gas generation was faster during the first 24 h at 37 °C. Compared to gas recovery achieved by extended batch operation following semi-continuous feeding, 58–73% of total methane was produced within the 48-h cycle, suggesting conversion could increase by 30–40% with extended liquid retention. Microbial analyses showed compositional differences but consistent performance, indicating functional redundancy within the microbial consortia. These results confirm the capacity of FWAD for stable, efficient biogas production without continuous energy input. Full article