Search Results (137)

The global cement industry remains a significant contributor to carbon dioxide (CO₂) emissions, prompting substantial research efforts toward sustainable construction materials. Lithium slag (LS), a by-product of lithium extraction, has attracted attention as a supplementary cementitious material (SCM). This review synthesizes experimental findings on LS replacement levels, fresh-state behavior, mechanical performance (compressive, tensile, and flexural strengths), time-dependent deformation (shrinkage and creep), and durability (sulfate, acid, abrasion, and thermal) of LS-modified concretes. Statistical analysis identifies an optimal LS dosage of 20–30% (average 24%) for maximizing compressive strength and long-term durability, with 40% as a practical upper limit for tensile and flexural performance. Fresh-state tests show that workability losses at high LS content can be mitigated via superplasticizers. Drying shrinkage and creep strains decrease in a dose-dependent manner with up to 30% LS. High-volume (40%) LS blends achieve up to an 18% gain in 180-day compressive strength and >30% reduction in permeability metrics. Under elevated temperatures, 20% LS mixes retain up to 50% more residual strength than controls. In advanced systems—autoclaved aerated concrete (AAC), one-part geopolymers, and recycled aggregate composites—LS further enhances both microstructural densification and durability. In particular, LS emerges as a versatile SCM that optimizes mechanical and durability performance, supports material circularity, and reduces the carbon footprint. Full article

Adequate treatment of the organic fraction of municipal solid waste (OFMSW) in co-digestion with sewage sludge (SS) through dark fermentation (DF) technologies has been widely studied and recognized. However, there is little experience with a high-solids approach, where practical and scalable conditions are established to lay the groundwork for further development of feasible industrial-scale projects. In this study, the biochemical hydrogen potential of OFMSW using a 7 L batch reactor at mesophilic conditions was evaluated. Parameters such as pH, redox potential, temperature, alkalinity, total solids, and substrate/inoculum ratio were adjusted and monitored. Biogas composition was analyzed by gas chromatography. The microbial characterization of SS and post-reaction percolate liquids was determined through metagenomics analyses. Results show a biohydrogen yield of 38.4 NmLH₂/gVS OFMSW, which forms ~60% of the produced biogas. Aeration was proven to be an efficient inoculum pretreatment method, mainly to decrease the levels of methanogenic archaea and metabolic competition, and at the same time maintain the required total solid (TS) contents for high-solids conditions. The microbial community analysis reveals that biohydrogen production was carried out by specific anaerobic and aerobic bacteria, predominantly dominated by the phylum Firmicutes, including the genus Bacillus (44.63% of the total microbial community), Clostridium, Romboutsia, and the phylum Proteobacteria, with the genus Proteus. Full article

Carbon monoxide (CO) is a key reactant in industries like chemicals, pharmaceuticals, and metallurgy, with a projected global market of $8.2 billion by 2032. A novel method of CO production is biowaste composting, but the impact of organic matter content (OMC) on CO yield remains unexplored. Since OMC affects composting costs, optimizing it is crucial for economic feasibility. This study aimed to identify the optimal OMC in bioreactors for CO production during food waste composting. A laboratory process was conducted in bioreactors with forced aeration. Food waste (FW) was mixed with gravelite (G) at ratios of 1:0, 1:1, and 1:2 (FW:G), corresponding to 95%, 40%, and 20% dry OMC. Bioreactors were incubated at 45 °C, 60 °C, and 70 °C with ~5% oxygen. The highest CO levels were at 70 °C for FW:G 1:2, with an average of 655 ppm and a maximum of 2000 ppm. Daily CO emissions were highest at 70 °C, reaching up to 1.25 mg. Therefore, the study demonstrated that even a low organic matter content allows for CO production during composting under thermophilic conditions (~70 °C) with limited oxygen. Industrial modeling estimated daily CO yield from 39.25 to 670.61 g, with a 7-day market value between USD 28.89 and USD 175.86. Further studies are needed for large-scale feasibility. Full article

Ethanol and xylitol are valuable bioproducts synthesized by non-conventional yeasts from lignocellulosic sugars. However, their biosynthesis requires distinct cultivation conditions. This study evaluated the production of ethanol and xylitol by Clavispora lusitaniae using saccharified sugarcane bagasse (SSCB) under three aeration conditions: microaerobic (C1), anaerobic (C2), and a combination of anaerobic followed by a microaerobic phase (C3). Ethanol production was maximum under anaerobic conditions (C2), followed by combined anaerobic–microaerobic conditions (C3). Meanwhile, xylitol production was most efficient under microaerobic conditions (C1). Notably, anaerobic conditions were ineffective for xylitol production. Enzyme activities of xylose reductase (XR) and xylitol dehydrogenase (XDH), key enzymes in xylose metabolism, were highest under microaerobic conditions with activities of 2.88 U/mg and 1.72 U/mg, respectively, after 48 h of culture. Gene expression analysis of XYL1 and XYL2 correlated with the corresponding enzyme activities (XR) and (XDH) with increased levels of 32.38 and 7.88 fold, respectively, compared to the control in C1. These findings suggest that C. lusitaniae co-produces ethanol efficiently under anaerobic conditions, while xylitol biosynthesis is optimized under microaerobic conditions when using xylose-rich saccharified lignocellulosic substrates. Full article

This study demonstrated the effectiveness of using autoclaved aerated concrete AAC waste as a low-cost filtering material for removing hydrogen sulfide (H₂S) from gas streams. A long-term experiment (89 days) was conducted in a packed bed reactor to purify synthetic biogas composed of N₂, CO₂, H₂S, and O₂. Optimal H₂S removal efficiencies, reaching up to 100%, were achieved under highly acidic conditions (pH ≈ 1–3) and low oxygen concentrations (<1%). In the presence of oxygen, calcium oxides in the AAC waste react with H₂S to form gypsum (CaSO₄ 2H₂O). The simultaneous removal of both oxygen and H₂S by AAC waste, following an approximate 2:1 molar ratio, may be particularly beneficial for biogas streams containing unwanted traces of oxygen. The transformation and lifespan of AAC waste were monitored through sulfur accumulation in the material and pressure drop measurements, which indicated structural changes in the AAC waste. At the end of its lifespan, the AAC waste exhibited an H₂S removal capacity of 185 g_H2S kg_AAC⁻¹. This innovative and sustainable process not only provides a cost-effective and environmentally sound solution for the simultaneous removal of H₂S and O₂ from biogas, but also promotes waste valorization and aligns with circular economy principles. Full article

Towards the bioremediation of toxic compounds from aquatic environments using living microalgae, Chlorella vulgaris has emerged as a promising candidate for the removal of heavy metals. The present study advances the scale-up of the microalga’s culture and investigates its efficiency in multi-metal removal (Cu, Cd, Ni, Pb, and Zn at 1 ppm each). Two aeration conditions were investigated: standard/conventional aeration (SA), and an innovative, custom-built micro-bubble aeration (MBA), which optimizes CO₂ residence time to enhance photosynthesis. Conducted in a pilot-scale 30 L photobioreactor (PBR) over a cultivation period of 7 days, control and multi-metal treated cultures were monitored for pH, cell population growth, and pigment content. Heavy metal removal efficiency was evaluated by means of atomic absorption spectroscopy (AAS) on Days 3 and 7 of cultivation. The comparative results reveal that MBA significantly enhances both the population and the photosynthetic pigment content of the cultures. Furthermore, the heavy metal removal efficiency under MBA reached up to 95% even by Day 3 of cultivation, remarkably higher than the 67% of the SA treated culture. These findings not only demonstrate Chlorella vulgaris’s effectiveness in multi-metal treated systems but also highlight the potential of advanced aeration systems to enhance bioremediation efficiency in larger-scale aquatic environments. Full article

This review systematically examines the critical mechanisms and process optimization strategies of algal–bacterial granular sludge (ABGS) technology in wastewater treatment. The key findings highlight the following: (1) enhanced pollutant removal—ABGS achieves >90% COD removal, >80% total nitrogen elimination via nitrification–denitrification coupling, and 70–95% phosphorus uptake through polyphosphate-accumulating organisms (PAOs), with simultaneous adsorption of heavy metals (e.g., Cu²⁺, Pb²⁺) via EPS binding; (2) energy-saving advantages—microalgal oxygen production reduces aeration energy consumption by 30–50% compared to conventional activated sludge, while the granular stability maintains >85% biomass retention under hydraulic shocks; (3) AI-driven optimization—machine learning models enable real-time prediction of nutrient removal efficiency (±5% error) by correlating microbial composition (e.g., Nitrosomonas abundance) with operational parameters (DO: 2–4 mg/L, pH: 7.5–8.5). This review further identifies EPS-mediated microbial co-aggregation and Chlorella–Pseudomonas cross-feeding as pivotal for system resilience. These advances position ABGS as a sustainable solution for low-carbon wastewater treatment, although challenges persist in scaling photobioreactors and maintaining symbiosis under fluctuating industrial loads. Full article

This study examined the carbon footprints of freshwater fish farming and Euryale ferox seed (gorgon fruit) production, comparing integrated ecological mode and traditional farming practices based on ISO 14067 and PAS 2050 standards. The ecological mode achieved a 24% lower carbon footprint per unit product than traditional practices, driven by reduced material and energy use. Key emission sources included aeration electricity, feed, and wastewater treatment for fish farming, fertilizers, insecticides, and drainage energy for E. ferox planting. The integrated model combining high-density fish ponds and E. ferox pond reduced the overall carbon footprint (Micropterus salmoides: 4.342 kg CO₂-eq/kg; E. ferox seed: 0.208 kg CO₂-eq/kg) compared to traditional practices (Micropterus salmoides: 5.672 kg CO₂-eq/kg; E. ferox seed: 0.297 kg CO₂-eq/kg). It also lowered production costs, increased profits, and mitigated GHG emissions by using E. ferox and lotus ponds as treatment facilities and reducing fertilizer use. The ecological model showed lower unit costs and higher profits (Micropterus salmoides: 4.01 RMB/kg vs. 2.46 RMB/kg; E. ferox seed: 2.53 RMB/kg vs. 1.93 RMB/kg) than those of the traditional mode. This study underscores the potential of ecologically integrated modes to mitigate water pollution and carbon emissions in agriculture, offering a sustainable solution to meet the rising demand for aquatic products. Full article

Constructed wetlands (CWs) attempt to simulate the physicochemical and biological processes that occur within a natural wetland and have been employed in recent decades for wastewater treatment. This work aims to review the use of CWs for domestic wastewater treatment in undeveloped or developing areas, including the amount of literature produced, the type of constructed wetland, the vegetation, the substrate, and the social benefits that have been achieved, through a qualitative methodology where different articles are collected from the Scopus and Web of Science databases after a strict revision by means of the PRISMA method (Preferred Reporting Items of Systematic Reviews and Meta-Analyses) and CASP (Critical Appraisal Skills Program). A total of 49 articles were selected, and co-occurrence and density maps were obtained; following this, three main themes and the five keywords with the highest correlation were identified. The literature analyzed in this work exposes different types of CWs where not only the hybrid, vertical, and horizontal flow systems stand out, but also the floating and aerated wetlands, which present high removal efficiencies. Additionally, new substrate materials, such as olote, palm shells, and coconut peat, and the ornamental plants usually used, such as Phragmites australis and Thypha latifolia, are discussed; however, new studies with vegetation that has been little studied but has a high potential to be implemented in areas with silvicultural characteristics stand out: Duranta repens, Pennisetum pedicellatum, and Pistia stratiotes. In conclusion, there is an advancement in the research of these systems, new configurations, substrates, and vegetation to treat domestic wastewater; in addition, these studies present an opportunity to continue studying the installation of CWs at the household level; however, compared to the other areas of application mentioned above, its implementation requires a greater challenge, since it requires a compact design and easy handling. Full article

Grasslands are crucial for sequestering carbon underground, but disturbances like ploughing can lead to significant soil organic carbon (SOC) loss as CO₂, a potent greenhouse gas. Thus, managed grasslands should be maintained to minimize GHG emissions. A field study was carried out to investigate how varying sward diversity influences soil respiration following the ploughing of temporary grassland. This study investigated the extent of CO₂ emissions from different species mixtures immediately after ploughing, as well as C losses when straw was added to plots, over a 142-day period. The species mixture treatments consisted of a binary mixture (BM), a tertiary mixture (TM), and a complex mixture (CM), which were compared to two bare plot treatments, one of which was also ploughed. The highest CO₂ flux occurred immediately after ploughing and was observed in the BM treatment (1.99 kg CO₂-C ha⁻¹ min⁻¹). Accumulated CO₂ emissions ranged from 0.4 to 14.8 t CO₂ ha⁻¹. The ploughing effect on CO₂ emissions was evident for bare soils, as ploughing increased soil aeration, which enhanced microbial activity and accelerated the decomposition rate of soil organic matter. However, different mixtures did not affect the C turnover rate. Adding straw to treatments resulted in 43% higher CO₂ emissions compared to bare plots. The BM treatment likely induced a higher priming effect, suggesting that the incorporated straw, under different sward residues, influenced CO₂ emissions more than the mechanical disturbance caused by ploughing. Findings suggest that using complex species mixtures can be recommended as a strategy to reduce CO₂ emissions from incorporated biomass and minimize the priming effect of native soil carbon. Full article

Chlorella sp. was cultivated in a closed system using PET bottles (5 L) and with the continuous injection of air and commercial gas (98% CO₂) and in simulated conditions (15% CO₂, 73% N₂, and 12% O₂). The culture medium was prepared using well water and mining wastewater, the cultivation period occurred in a 10-day cycle, and the cell growth curves were evaluated through cell counting using a Neubauer chamber. The cultivation was carried out under the following conditions: temperature at 22 °C to 25 °C; aeration rate with commercial and simulated CO₂ gas at 0.01 vvm; and synthetic air containing 0.042% CO₂. The dry biomass productivity was 0.81 g·L⁻¹·day⁻¹ and the maximum CO₂ fixation rate was 0.90 g·L⁻¹·day⁻¹ when the microalgae were cultivated with a continuous flow of simulated waste gas and a culture medium composed of wastewater. The percentages of macromolecules obtained in the biomass cultivated in wastewater reached 20.95%, 26.48%, and 9.3% for lipids, proteins, and carbohydrates, respectively. Full article

Microalgae are small, single-celled, or simple multicellular organisms that contain Chlorophyll a, allowing them to efficiently convert CO₂ and water into organic matter through photosynthesis. They are valuable in producing a range of products such as biofuels, food, pharmaceuticals, and cosmetics, making them economically and environmentally significant. Currently, CO₂ is delivered to microalgae cultivation systems mainly through aeration with CO₂-enriched gases. However, this method demonstrates limited CO₂ absorption efficiency (13–20%), which reduces carbon utilization effectiveness and significantly increases carbon-source expenditure. To overcome these challenges, innovative CO₂ supplementation technologies have been introduced, raising CO₂ utilization rates to over 50%, accelerating microalgae growth, and reducing cultivation costs. This review first categorizes CO₂ supplementation technologies used in photobioreactor systems, focusing on different mechanisms for enhancing CO₂ mass transfer. It then evaluates the effectiveness of these technologies and explores their potential for scaling up. Among these strategies, membrane-based CO₂ delivery systems and the incorporation of CO₂ absorption enhancers have shown the highest efficiency in boosting CO₂ mass transfer and microalgae productivity. Future efforts should focus on integrating these methods into large-scale photobioreactor systems to optimize cost-effective, sustainable production. Full article

The energy efficiency of water treatment plants (WTPs) plays a key role in the sustainable management of water resources. In the face of increasing water demand, climate change, and increasingly stringent environmental regulations, optimising the energy consumption of treatment processes is becoming a priority for water system operators and decision-makers alike. Water treatment plants, depending on the type of water source served (groundwater, infiltration, surface water), vary considerably in terms of their technological design, which directly affects their energy efficiency and operating costs. According to the International Water Association, the water sector accounts for approximately 4% of global electricity consumption, a significant proportion of which is consumed by water treatment and distribution processes. Electricity is used in many process steps, such as water pumping, aeration, filtration, disinfection, and filter flushing. The energy consumption of a System for Upgrading Water (SUW) depends not only on the quality of taken raw water, but also on the size of the station, used technologies, and operation organisation. This study shows that implementing high-efficiency pumping systems and AI-based optimisation can reduce energy consumption in WTPs by 20–30%. The introduction of membrane filtration in surface water plants has demonstrated a reduction in energy use by up to 50%, while the use of biogas from sludge treatment has cut external energy demand by 15–25%. The results emphasise the potential to reduce CO₂ emissions by 10–20% compared to conventional treatment methods. However, achieving significant reductions in energy consumption in SUW requires a comprehensive understanding of the diversity of water facilities, technological processes, and specific energy requirements. Full article

Understanding the scaling behavior of geothermal water is essential for optimizing geothermal plant performance and ensuring sustainable energy use. However, research on the effects of common ionic components in geothermal environments on scaling is still insufficient, and there is a lack of in-depth exploration of the quantitative control of ion concentrations. This study selected common ionic components based on the ionic composition of geothermal water samples and simulated a realistic geothermal environment by setting concentration gradients. Static aeration immersion experiments, combined with XRD and SEM analysis, were conducted to systematically investigate the effects of various ionic components on scaling behavior. The results indicate that CaCO₃ is the primary scaling substance in the simulated geothermal water. Ca²⁺, HCO₃⁻, and SiO₃²⁻ significantly influence scaling. Specifically, the scaling amount increases with higher Ca²⁺ concentration. HCO₃⁻ exhibits a nonlinear trend, with scaling initially increasing and then decreasing once its concentration exceeds approximately 1000 mg/L. This inhibition is likely due to HCO₃⁻’s pH-buffering effect, restricting its conversion to CO₃²⁻ and limiting CaCO₃ precipitation. SiO₃²⁻ significantly inhibits scaling, reducing the scaling amount by about 88.91% when its concentration increases from 0 to 200 mg/L. The effect of Mg²⁺ is relatively minor, with a 13.21% reduction in scaling as its concentration increases from 0 to 50 mg/L. However, Mg²⁺ notably alters the crystal phase of CaCO₃, promoting aragonite formation. Without Mg²⁺, CaCO₃ predominantly forms as calcite. These findings emphasize the crucial role of ionic components and their concentration gradients in scaling, providing theoretical support for effective scaling prevention and control strategies. Full article

Effective vessel design is crucial for the viability and practicality of microalgae cultivation, aiming for high biomass production. This study tested two different 5-litre vessel designs for cultivating Chlorella vulgaris, aiming to produce a high biomass and evaluate lipid production. The study varied pH medium (6.5–10.5), light intensity (200–1000 lux), and CO₂ concentrations (5–15%) to assess each reactor’s performance. The aerated vessel (tubular shape) produced 21.05% lipid concentration, while the fabricated vessel (oval shape) produced 20.14% at optimum conditions. The aerated vessel performed best at pH 10.5, 5% CO₂, and 1000 lux light intensity, whereas the fabricated vessel’s optimum conditions were pH 10.5, 15% CO₂, and a white LED system. The highest biomass was 0.432 g/L in aerated tubular vessels and 0.281 g/L in fabricated oval-shaped vessels. Both systems performed well and are suitable for further study with other microalgae types. Full article