Search Results (38)

Acid mine drainage (AMD) is an environmental concern that needs to be addressed by some mining industries because of its high concentrations of metals and acidity that destroy affected ecosystems. Its formation typically persists beyond the operating life of a mine site. Its management is even more challenging for sites that are abandoned without rehabilitation. In this study, a legacy copper–gold mine located in Sto. Niño, Tublay, Benguet, Philippines, generating a copper- and manganese-rich AMD (Cu, maximum 17.2 mg/L; Mn, maximum 2.90 mg/L) at pH 4.59 (minimum) was investigated. With its remote location inhabited by the indigenous people local community (IPLC), a novel limestone-based hybrid passive treatment system that combines a limestone leach bed (LLB) and a controlled modular packed bed reactor (CMPB) has been developed from the laboratory and successfully deployed in the field while investigating the effective hydraulic retention time (HRT), particle size, and redox conditions (oxic and anoxic) in removing Cu and Mn and increasing pH. Laboratory-scale and pilot-scale systems using simulated and actual AMD, respectively, revealed that a 15 h HRT and both oxic and anoxic conditions were effective in treating the AMD. Considering these results and unsteady conditions of the stream in the legacy mine, a hybrid multi-stage limestone leach bed and packed bed were deployed having variable particle size (5 mm to 100 mm) and HRT. Regular monitoring of the system showed the effective removal of Cu (88.5%) and Mn (66.83%) as well as the increase of pH (6.26), addressing the threat of AMD in the area. Improvement of the lifespan of the system needs to be addressed, as issues of Cu-armoring were observed, resulting in reduced performance over time. Nonetheless, the study presents a novel technique in implementing passive treatment systems beyond the typical treatment trains reported in the literature. Full article

Brucellosis is caused by Gram-negative coccobacilli of the Brucella genus, with cattle mainly infected with Brucella abortus. The disease burden is a threat to socioeconomic development (agriculture/tourism) as well as to animal health, biodiversity and to human health due to the zoonotic nature of this pathogen. In South Africa (S.A), the prevalence of the disease in cattle and livestock in general is mostly unknown in communal farms. A cross-sectional study with a multistage sampling strategy was applied in communal areas from three district municipalities, i.e., Mopani, Capricorn and Sekhukhune of Limpopo province, South Africa. Sera (n = 1133) were collected and screened for antibodies against the Brucella species using the Rose Bengal Test (RBT) and confirmation of positive reactors with a Complement Fixation Test (CFT). The brucellosis seroprevalence was found to be 0.79% (95% CI: 0.38–1.45) by a CFT. Univariate analysis indicated that only the frequency of birth was significantly associated with CFT positivity (OR = 20; 95% Cl: 1.61–247.99; p = 0.039). The multivariable logistic regression model revealed that the frequency of birth, age, breed, gender, municipality and district were not statistically significant predictors at 0.05 level. However, some variables like cattle aged more than five years, had higher odds of CFT positivity compared to those younger than five years (OR = 5.66; 95% CI: 0.36–87.97), although the association was not statistically significant (p = 0.215). All positive reactors detected originated from the Mopani district municipality. Overall, the findings reveal a much lower seroprevalence of brucellosis in the communal farms of Limpopo province than previously assumed. We are of the opinion that the low seroprevalence is attributed to effective control strategies implemented by the Limpopo provincial veterinary services and hence provide important information to assist the regulatory bodies in the control and eradication of the disease. Full article

Shale gas wastewater from hydraulic fracturing poses significant environmental risks due to its high salinity and complex inorganic composition. This study investigates the behavior of major and trace inorganic constituents across a full-scale treatment train in the Sichuan Basin, China. Despite multi-stage processes including equalization, flocculation, flotation, biological reactors, membrane filtration, and clarification, key inorganic species such as Cl, Na, Br, Sr, Li, and B remained largely persistent in the final effluent with values of 13,760, 8811, 70, 95.9, 26.6, and 60.2 mg/L, respectively. Geochemical tracers including Br/Cl (average: 0.0022 mM/mM), Na/Br (average: 125 mg/mg), and Sr/Ca (average: 0.15 mM/mM) ratios, combined with halide endmember mixing models, revealed that salinity primarily originated from highly evaporated formation brines, with limited evidence for halite dissolution or external contamination. Elevated Sr (average: 89.3 mg/L) and Ca (average: 274 mg/L) levels relative to Mg (average: 32 mg/L) suggest significant water–rock interaction. Environmental risk assessments showed that concentrations of several elements in treated effluent greatly exceeded national and international discharge or reuse standards. These findings underscore the limitations of conventional treatment technologies and highlight the urgent need for advanced processes and regulatory frameworks that address the unique challenges of high-TDS (total dissolved solids) unconventional wastewater. Full article

As a core component of transportation fuels, clean gasoline plays a vital role in environmental protection. Alkylate, with its nearly zero sulfur, aromatic, and olefin contents, coupled with its superior research octane number, serves as an ideal blending component for clean gasoline. This study established a kinetic model for sulfuric-acid-catalyzed isobutane–butene alkylation based on the carbocation reaction mechanism, incorporating 20 lumped components and 37 reaction pathways. Reactor models were developed to reflect the design characteristics of STRATCO and SINOALKY technologies. The model parameters were estimated using industrial operational data via the non-linear least-squares method. The validation results demonstrated excellent agreement with industrial values, showing average relative deviation rates of 1.72% (STRATCO) and 1.73% (SINOALKY) for C₈ product prediction. A prediction analysis revealed that selectivity and alkylate octane number of C₈ exhibit positive correlations with the isobutane-to-olefin ratio, acid-to-hydrocarbon ratio, and space–time relationship. It was also found that the internal circulation in the STRATCO technology enables thorough contact between the acid and hydrocarbon phases, while the multi-stage feeding in the SINOALKY technology maintains a favorable isobutane-to-olefin ratio. Both features are conducive to the alkylation reaction, enhancing the selectivity and octane number of C₈. These trends align with the intrinsic reaction principles of sulfuric-acid-catalyzed alkylation systems, providing theoretical guidance for alkylate production optimization. Full article

Sustainably produced hydrogen has the potential to substitute fossil fuels and significantly reduce CO₂ emissions. Fraunhofer UMSICHT develops a new thermochemical conversion technology to gasify ash-rich biogenic residues and waste materials that are difficult to treat with conventional gasifiers, enabling their conversion into higher-quality energy carriers such as hydrogen and syngas. Ash-rich feedstocks are difficult to convert in conventional gasification methods, as they tend to agglomerate and form slag, leading to blockages in the reactor and process disturbances. In this experimental study, hydrogen-rich syngas is produced from biogenic residual and waste materials (sewage sludge) using the Enhanced Carbon-To-X-Output (EXO) process. The EXO process is a three-stage thermochemical conversion process that consists of a combination of multi-stage gasification and a subsequent reforming step. The influence of temperature in the reforming step on the gas composition and hydrogen yield is systematically investigated. The reformer temperature of the process is gradually increased from 500 °C to 900 °C. The feedstock throughput of the pilot plant is approximately 10 kg/h. The results demonstrate that the temperature of the reforming step has a significant impact on the composition and yield of syngas as well as the hydrogen yield. By increasing the reformer temperature, the syngas yield could be enhanced. The hydrogen yield increased from 15.7 g_H2/kg_Feed to 35.7 g_H2/kg_Feed. The hydrogen content in the syngas significantly increased from 23.6 vol.% to 39 vol.%. The produced syngas can be effectively utilized for sustainable hydrogen production, as a feedstock for subsequent syntheses, or for power and heat generation. Full article

Hydrogen is a clean, non-polluting fuel and a key player in decarbonizing the energy sector. Interest in hydrogen production has grown due to climate change concerns and the need for sustainable alternatives. Despite advancements in waste-to-hydrogen technologies, the efficient conversion of mixed plastic waste via an integrated thermochemical process remains insufficiently explored. This study introduces a novel multi-stage pyrolysis-reforming framework to maximize hydrogen yield from mixed plastic waste, including polyethylene (HDPE), polypropylene (PP), and polystyrene (PS). Hydrogen yield optimization is achieved through the integration of two water–gas shift reactors and a pressure swing adsorption unit, enabling hydrogen production rates of up to 31.85 kmol/h (64.21 kg/h) from 300 kg/h of mixed plastic wastes, consisting of 100 kg/h each of HDPE, PP, and PS. Key process parameters were evaluated, revealing that increasing reforming temperature from 500 °C to 1000 °C boosts hydrogen yield by 83.53%, although gains beyond 700 °C are minimal. Higher reforming pressures reduce hydrogen and carbon monoxide yields, while a steam-to-plastic ratio of two enhances production efficiency. This work highlights a novel, scalable, and thermochemically efficient strategy for valorizing mixed plastic waste into hydrogen, contributing to circular economy goals and sustainable energy transition. Full article

The fuel-cell (FC) power system, utilizing biohydrogen from biomass resources, is a promising alternative to fossil fuels. However, hydrogen sulfide (H₂S) in bio-syngas can severely degrade FC performance and increase environmental impact, necessitating impurity removal. This study investigates a multi-stage desulfurization process using neutralized sediment (NS) and a metal hydride (LaNi₅) as H₂S adsorbents. NS, a mining waste material, can potentially reduce environmental impact when repurposed as an adsorbent, with its performance influenced by pore configuration and Fe content. However, the purified gas does not fully meet FC fuel specifications. To address this, LaNi₅, which selectively absorbs and releases hydrogen, was incorporated to achieve higher purification levels. In our study, H₂S adsorption tests were conducted using two fixed-bed flow reactors heated to 250 °C, where a gas mixture containing 196 ppm of H₂S flowed through the system. The proposed multi-stage system achieved a breakthrough time of 182.5 h with purified gas remaining under 0.1 ppm and an adsorption capacity of 16.4 g/g-sorbent. These results demonstrate the high desulfurization performance achieved using NS and LaNi₅. Full article

The production of hydrogen via dark fermentation generates carbon dioxide, which needs to be separated and re-utilized to minimize the environmental impact. This research investigates the potential of utilizing algae for carbon dioxide sequestration in hydrogen production via dark fermentation. However, algae alone cannot fully use all the carbon dioxide produced, necessitating the implementation of a multistage separation process. This study proposes a purification approach that integrates membrane separation with a photobioreactor in a multistage design layout. Mathematical models were used to simulate the performance efficiency of multistage design layout using MATLAB 2015b (Version 9.3). A detailed parametric analysis and the key parameters influencing the separation efficiency were conducted for each stage. This study explores how reactor geometry, operational dynamics (such as gas transfer rates and light availability), and algae growth impact both CO₂ removal and hydrogen purity. An optimization strategy was used to obtain the set of optimal operating and design parameters. Our results have shown a significant improvement in hydrogen purity, increasing from 55% to 99% using this multistage separation process, while CO₂ removal efficiency rose from 35% to 85% over a week. This study highlights the potential of combining membrane technology with photobioreactors to enhance hydrogen purification, offering a more sustainable and efficient solution for hydrogen production. Full article

The reverse electrodialysis heat engine (REDHE) represents a transformative innovation that converts low-grade thermal energy into salinity gradient energy (SGE). This crucial form of energy powers reverse electrodialysis (RED) reactors, significantly changing wastewater treatment paradigms. This comprehensive review explores the forefront of this emerging field, offering a critical synthesis of key discoveries and theoretical foundations. This review begins with a summary of various oxidation degradation methods, including cathodic and anodic degradation processes, that can be integrated with RED technology. The degradation principles and characteristics of different RED wastewater treatment systems are also discussed. Then, this review examines the impact of several key operational parameters, degradation circulation modes, and multi-stage series systems on wastewater degradation performance and energy conversion efficiency in RED reactors. The analysis highlights the economic feasibility of using SGE derived from low-grade heat to power RED technology for wastewater treatment, offering the dual benefits of waste heat recovery and effective wastewater processing. Full article

Hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP) are prevalent industrial wastewater contaminants that are recalcitrant to natural degradation and prone to migration in aquatic systems, thereby harming biological health and destabilizing ecosystems. Consequently, their removal is imperative. Compared to conventional chemical treatment methods, CW-MFC technology offers broader application potential. Leersia hexandra Swartz can enhance Cr (VI) and 4-CP absorption, thereby improving wastewater purification and electricity generation in CW-MFC systems. In this study, three CW-MFC reactors were designed with L. hexandra Swartz in distinct configurations, namely, stacked, multistage, and modular, to optimize the removal of Cr (VI) and 4-CP. By evaluating wastewater purification, electrochemical performance, and plant growth, the optimal influent hydraulic retention time (HRT) was determined. The results indicated that the modular configuration at an HRT of 5 days achieved superior removal rates and power generation. The modular configuration also supported the best growth of L. hexandra, with optimal photosynthetic parameters, and physiological and biochemical responses. These results underscore the potential of modular CW-MFC technology for effective detoxification of complex wastewater mixtures while concurrently generating electricity. Further research could significantly advance wastewater treatment and sustainable energy production, addressing water pollution, restoring aquatic ecosystems, and mitigating the hazards posed by Cr (VI) and 4-CP to water and human health. Full article

Anaerobic wastewater treatment technology has been intensively and extensively investigated in the industry and scientific research. Inspired by the advantages of multi-stage and multi-phase anaerobic reactor technology (SMPA) in recent years, a three-stage anaerobic reactor (3S-AR) was designed and applied to treat poplar chemical–mechanical pulp wastewater, and various operation parameters, including the volume loading rate (VLR), hydraulic retention time (HRT), ascending velocity, reflux ratio, pH and temperature of the 3S-AR, were optimized to evaluate the reactor’s removal efficiency for poplar wastewater. The properties of anaerobic granular sludge and the composition of wastewater were also characterized to assess microorganism growth and pollutant migration. Results show that the COD removal rate was over 75% with a volume loading rate range of 15–25 gCOD/(L·d) in the 3S-AR; the hydraulic retention time was also found to be an important factor affecting the performance of the 3S-AR reactor. The volume loading rate and degradation efficiency of the 3S-AR reactor are higher than those of the up-flow anaerobic sludge blanket (UASB) reactor. Microorganism separation can be achieved in the 3S-AR, which is conducive to the growth and methanogenesis activity of bacteria, thereby leading to enhanced removal and buffering efficiency. After treatment in the 3S-AR, the main pollutants of poplar wastewater were benzene aromatic acids and long-chain esters, which do no biodegrade easily; in contrast, most of the fatty acid substances with small molecules were completely degraded. Full article

This study reports, for the first time, on the assessment of a multistage sequential system composed of coagulation–flocculation with different electro-Fenton-based configurations, followed by neutralization (N), for the treatment of raw textile wastewater heavily contaminated with acid black 194 dye and other pollutants. Electrochemical peroxidation (ECP-N), electro-Fenton (EF-N) and peroxi-coagulation (PC-N) were tested at laboratory scale and compared in terms of their efficiency for the removal of organic matter and color, current efficiency and energetic parameter, operating cost and environmental sustainability using life cycle analysis conducted in large-scale virtual reactors. The three electro-Fenton-based systems complied with current environmental standards (color removal > 87%, COD < 400 mg/L, among others) requiring different electrolysis times: ECP-N (52 min) < PC-N (120 min) < EF-N (160 min); energy consumptions: ECP-N (2.27 kWh/m³) < PC-N (4.28 kWh/m³) < EF-N (33.2 kWh/m³); operational costs: ECP-N (2.63 USD/m³) < EF-N (6.65 USD/m³) < PC-N (6.98 USD/m³); among others. Electricity (for ECP-N and EF-N) and reagents (for ECP-N and PC-N) were found as main environmental hotspots. ECP-N presented the lowest carbon footprint of 10.3 kg CO₂-Eq/FU (<PC-N (26.3 kg CO₂-Eq/FU) < EF-N (38.0 kg CO₂-Eq/FU), had lower incidence in all the impact categories analyzed (ReCiPe-2016 at midpoint level) and can be considered technically, economically and environmentally sustainable for large-scale applications. Full article

The anaerobic-multistage anoxic/aerobic (A-MAO) process has shown good potential for advanced nitrogen removal in recent years, but its greenhouse gas emissions still need to be fully explored. The effects of the influent distribution and external carbon source sodium acetate on nutrient removal, greenhouse gas emissions, and the microbial community structure in a continuous plug-flow A-MAO reactor fed with real low C/N ratio domestic sewage were investigated. The results showed that altering the allocation of carbon source resulted in average chemical oxygen demand (COD) and total nitrogen (TN) concentration in effluent reduced to 26.10 ± 4.86 and 6.65 ± 1.73 mg/L, respectively. Both operations reduced the emission rate of greenhouse gas. While the addition of external car-bon sources leaded to lower N₂O emission rates and higher CO₂ and CH₄ emission rates. The addition of sodium acetate facilitated nitrification and denitrification processes, thereby leading to a reduction in N₂O production. Meanwhile, it spurred the growth of methanogenic bacteria and heterotrophic microorganisms, thus boosting the production of CO₂ and CH₄. Influent distribution promoted the increase of Bacteroidota, Chloroflexi and Acidobacteriota of the reactor. The enrichment of typical hydrolytic bacteria and glycogen accumulating organisms (GAOs) increased the utilization efficiency of carbon sources in the system after the addition of sodium acetate. The significant increase of typical denitrifying bacteria (DNBs) Azospira reduced the N₂O emission during heterotrophic denitrification process, which was considered to be an important functional genus for increasing nitrogen loss in this system. The rational utilization of carbon source makes the difference in metabolism function. The study provides a valuable strategy for comprehensively evaluating the pollutant removal and greenhouse gas emission reduction from the A-MAO process. Full article

Methanol is an important raw material widely used in the chemical industry. This article addresses the challenge of fluctuations in green hydrogen as a feed stream for methanol production from renewable feedstock. For a staged reactor design, robust operating conditions are generated through the simultaneous steady-state optimization of 50 process scenarios. The feed can be split and fed separately to the different reactor stages. However, neglected transient effects may render this design infeasible under dynamic conditions concerning carbon conversion and reactor temperature constraints. To overcome this, an additional dynamic optimization is conducted to ensure a feasible operation by an optimized feed-forward control of feed distribution and shell temperatures. In practice, this is possible because the disturbance, i.e., fluctuation, is measurable and predictable in a short time frame. The optimization yields optimal operating conditions, resulting in a reactor that is dynamically feasible for measurable fluctuating inlet conditions. Full article

The hydrodynamic characteristics, mass transfer, and mixing performance of three different reactors, a bubble column reactor (BCR), a single-stage internal-loop airlift reactor (SSALR), and a four-stage internal-loop airlift reactor (FSALR), were investigated systematically through cold model experiments to explore the influence of draft tube configurations on the pilot-scale internal-loop airlift reactor (ILAR). The findings indicated that the BCR yielded a higher gas holdup and mass transfer coefficient due to its longer bubble residence time. Segmenting the draft tube improved the gas holdup in both the riser and downcomer, and the overall gas holdup in the downcomer increased by 9%. Compared with the SSALR, the mass transfer coefficient of the FSALR in the riser and downcomer increased by 10.2% and 9.3% on average, respectively. In addition, a higher liquid circulating velocity was obtained with the ILARs due to a higher gas holdup difference between the riser and the downcomer. Specifically, the liquid circulating velocity of the FSALR was 134.1% higher than that of the BCR and 15.8% higher than that of the SSALR. The mixing time of the ILARs was reduced due to more intense overall circulation. The mixing effect of the FSALR was the best. The mixing time was reduced by 70.2% and 51.3% compared with the BCR and SSALR for U_G ranging from 4.0 cm/s to 9.1 cm/s, respectively. Empirical correlations were proposed for the gas holdup, liquid circulating velocity, mass transfer coefficient, and mixing time on the superficial gas velocity, and agreement with experimental data was satisfactory. Full article