High Alkalinity Research Articles

Waste Bauxite Residue Valorization as Trace Metal Sorbent: Application to Acid Mine Drainage Remediation

With an output of more than two million tons of alumina per year, Venezuela is an important producer. As observed, this mining extraction activity generates a large number of by-products poorly valorized for many reasons (economic, technical, and due to environmental standards and regulations) Venezuela production generates wastes (more than 15 million of m3) called red muds, which are dumped in old lagoons near the Orinoco river or stored. This sludge has a high alkalinity (pH between 10 and 13) and a chemical composition containing some heavy metals (40 ppm Cr, 107 ppm La, 178 ppm Ce) that means it is considered environmentally problematic waste. However, their mineralogical, textural and structural characteristics make them adsorption materials. So, the aim of the study presented here was to investigate the sorption properties of these residues in the case of treatment of water from acid mine drainage. In fact, with an important reactive surface, their capacities to trap by adsorption trace elements such as cadmium, lead or zinc has been studied. Batch sorption tests revealed significant retention of contaminants such as Pb, Zn and As. These retention processes were interpreted using the Langmuir isotherm model. The promising first results indicate that the red mud named Venezuelan bauxite residue (VBR) reveals its great potential as a sorbent of inorganic pollutants. The sorption process is chemically dependent and efficient for certain pH and IS ranges. In addition, the material showed a strong affinity for the adsorption of arsenate (As5+). This was observed during post adsorption chemical speciation experiments, through the very high affinity of this element for the least mobile fractions, including oxyhydroxides mobile fractions, including Fe oxyhydroxides (amorphous). Nevertheless, these mining by-products could be considered as valuable absorbent materials. Despite this promising results, further studies are required to evaluate their potential in different conditions (dynamic tests, pH, IS, inorganic and organic contaminants, concentration and time effect).

Genesis and Tectonic Implications of Early Cretaceous Granites in the Haobugao Area, Southern Great Xing’an Range: Insights from Zircon U–Pb Geochronology, Hf Isotopic Composition, and Petrochemistry

In the Huanggangliang–Ganzhuermiao metallogenic belt in the southern Great Xing’an Range, the Haobugao Pb‒Zn deposit is the most widespread skarn-type polymetallic deposit. The observed mineralization processes in this area are closely associated with both magmatic and tectonic activity. The zircon U‒Pb ages of two granitoid phases are 134.0 ± 0.6 Ma and 133.4 ± 0.9 Ma (Early Cretaceous). High SiO2 content (average mass fractions of 77.98 wt.% and 73.25 wt.%), high alkalinity (average mass fractions of 6.19 wt.% and 8.78 wt.%), and low CaO levels (average mass fractions of 0.16 wt.% and 0.12 wt.%) are characteristic of these rocks. They are also enriched in high-field-strength elements (HFSEs) (Th, U, Ta, Zr, Hf, etc.) and depleted in large ion lithophile elements (LILEs) (Ba, Sr, etc.). Furthermore, the Nb/Ta ratios (7.80~8.82, 10.00~10.83) point to a crustal origin of the magma. The zircon Hf isotopic compositions suggest that the melting of young crust derived from Meso-Neoproterozoic and Neoproterozoic depleted mantle gave rise to the magma in these granite porphyries. These rocks formed in an extensional environment driven by the subduction and retreat of the Paleo-Pacific plate during the Early Cretaceous.

Acidified biochar one-off application for saline-alkali soil improvement: A three-year field trial evaluating the persistence of effects

Salinization is a global soil degradation issue threatening agricultural productivity and environmental sustainability. Native biochar is a promising soil amendment, but its high alkalinity limits its use in saline-alkali lands. Acidified biochar, with a lower pH, is theoretically more suitable. This study aims to evaluate the persistence of effects of acidified biochar one-off application on soil particle size distribution, physicochemical properties, water retention, temperature regulation, and evaporation conditions of saline-alkali soil, thereby verifying its feasibility and exploring the optimal application range. We conducted a three-year cotton field experiment using palm fruit branch biochar as the raw material, acidified with ferrous sulfate, which involved four biochar applications (0, 10, 20, and 30 t ha−1) and four irrigation quotas (60 %, 80 %, 100 % and 120 % ETc). The results indicated that the initial acidified biochar application slightly increased surface soil (0–20 cm) pH by 0.1 %–3.9 %, this negative effect was nearly eliminated by the third year. Biochar application significantly altered surface soil particle size distribution, increasing sand content by 1.6 %–8.4 %, and persistently improved soil hydraulic properties, with water holding capacity still showing a 6.5 %–16.7 % increase in the third year. Biochar enhanced soil thermal insulation and suppressed soil evaporation, but these benefits gradually diminished with increasing cultivation years. Acidified biochar effectiveness was closely linked to irrigation quota. Significant differences in soil water and heat indicators were observed between the 20 and 30 t ha⁻¹ biochar treatments only under low irrigation quotas. Under sufficient irrigation (100 % and 120 % ETc), the optimal biochar application range was 15–20 t ha⁻¹, while under low irrigation (60 % and 80 % ETc), the optimal range was 20–25 t ha⁻¹. This study demonstrated that acidified biochar one-off application has significant multi-year benefits in improving soil structure and hydrothermal properties, providing a scientific basis for the improvement and sustainable utilization of saline-alkali soil.

Unveiling the Ecological and Pharmacological Perspectives of Lithophytic Life Form

Environmental extremes such as high temperature, cold, alkalinity, drought, and rocky substrate modulate plant growth and promulgate adaptive characteristics in plants. The same plants can be found inhabited in different life forms, namely epiphytic, lithophytic, terrestrial, halophytic, and psammophytic, based upon adaptive characteristics essential for their survival. Microorganisms residing on the surface or within rocks make a unique habitat referred to as “lithobiontic habitat,” which further facilitates weathering phenomena and accumulates water and nutrients from the ecosystem to form a lithobiontic ecological niche. Lithobionts are divided into two groups, namely epiliths and endoliths, based on their presence on rock surfaces. Lithophytes, the rock-inhabiting plants, thriving under extreme stress conditions adapted successfully and their extraordinarily challenging atmosphere encouraged them to make new forms of life. Many biotic and abiotic factors are responsible for dwelling in such environments. Lithophytes interact with their surroundings to obtain vital elements necessary for their metabolism and, because of natural selection, their morphology and physiology help them with better adaptation. Another factor that facilitates such adaptation in lithophytes is the association of a fungus with lithophytic roots to ensure nutrient supply for their survival and facilitate growth in extreme conditions. Arbuscular mycorrhizal (AM) root fungal associations commonly found among plants under stressed conditions help hosts adapt and promote plant life. In lithophytes, AM association aids in nutrient uptake from soil and facilitates plant survival under harsh conditions. The present review provides a comprehensive account of lithophytic life forms and covers different aspects of rock-dwelling plants concerning their historical background, classification, habitat, distribution in various families, root adaptive mechanisms, and phytopharmacological status. This review focused on plant species that can be considered among the most common representatives of lithophytes. This manuscript furnishes insights into different perspectives on the ecological and biological properties of the most common lithophytic species adapted to extreme rocky structures and explains their wide array of applications for pharmacological use.

Iron-loaded activated carbon cloth as CDI electrode material for selective recovery of phosphate.

This study investigated the efficacy of oxidised iron-loaded activated carbon cloth (Fe-ACC) for selective recovery of phosphorous. The capacitive deionisation (CDI) technology was employed, for rapid removal of phosphate, with the aim of reducing the reliance on high alkalinity environment for the regeneration of Fe-ACC electrode. Multiple experimental parameters, including applied potential, pH, and co-existing ions, were studied. Additionally, the CDI system was tested on a real water matrix (Lake Ormstrup, Denmark) to elucidate the electrodes' performance on selective recovery of phosphate. About 69 ± 10% of the adsorbed phosphate were released at pH 12 via pure chemical desorption, which was ~ 50% higher than that at pH 9. The CDI system successfully demonstrated the selective removal of phosphate from the lake water. It reduced the concentration of phosphate from 1.69 to 0.49mg/L with a 71% removal efficiency, while the removal percentages of other anions, namely chloride, sulphate, bromide, nitrite, nitrate, and fluoride, were 10%, 7%, 1%, 1.5%, 4%, and 7%, respectively.

Investigation on the mechanical and microstructure properties of masonry cement-red mud-carbide slag-based paste

The high alkalinity and complex phase composition of red mud pose significant challenges for its direct utilization. The construction industry is widely regarded as the most viable option for large-scale consumption of red mud to mitigate its continuous accumulation globally. Activation treatment is a crucial prerequisite for preparing cementitious materials from red mud, but traditional methods either require high-temperature calcination of red mud or the use of substantial amounts of strong alkaline substances as alkaline activators, thereby increasing costs and hindering the large-scale application of red mud. This paper presents an alternative method where 4% carbide slag is used as an activator to prepare cement-red mud-carbide slag-based composite pastes, substituting 10%-90% of masonry cement with red mud. As the red mud content increases, the compressive and flexural strengths of the hydrated pastes significantly decrease; the compressive strength of the material with 10% red mud is 13.4 times that of the material with 90% red mud. The addition of 4% carbide slag enhances the compressive and flexural strengths of the red mud-based cementitious material, with increases of 1.67%, 17.9%, and 34.6% in compressive strength at 3d, 7d, and 28d, respectively, and increases of 2.38%, 6.67%, and 7.36% in flexural strength. This indicates that carbide slag is beneficial for activating the reactivity of red mud. There is an incremental relationship between the flexural and compressive strengths of the cementitious material, and a fitting formula can be used to quantify the relationship between red mud content and these strengths. Microstructural analysis confirms that the addition of carbide slag significantly optimizes the pore structure, promoting the formation of Ca(OH)2 and C-S-H gel, which leads to improved mechanical properties of the red mud-containing composites. This study provides a feasible solution for the large-scale application of red mud in the cement industry.

Study on the physiological responses and tolerance mechanisms to subchronic carbonate alkalinity exposure in the gills of Paramisgurnus dabryanus

Given the reduction of freshwater resources, saline-alkaline aquaculture has emerged as an effective approach to expand the fishery's accessible space. High carbonate alkalinity (CA) is a major stressor for aquatic organisms in saline-alkaline environments. Paramisgurnus dabryanus is a potential species for culture in saline-alkaline water, making it an ideal model for investigating the physiological responses and tolerance mechanisms to CA exposure in freshwater fishes. In the current study, P. dabryanus were exposed to 15 and 30mmol/L NaHCO3, combining blood biochemical, gill histological, transcriptomic, and metabolomic methods for conjoint analysis of response mechanisms. After 28-d exposure, the gill ventilation frequency of P. dabryanus decreased significantly, gill lamellae twisted and atrophied, and gill filament epithelial cells proliferated, potentially limiting gas exchange, whereas the accessory air-breathing frequency increased significantly, possibly for greater oxygen uptake. Serum osmolality and blood pH remained relatively steady, while serum ammonia levels rose significantly. A total of 3718 differentially expressed genes (DEGs) and 205 differential metabolites (DMs) were identified between the control group and 30mmol/L NaHCO3 group, involved in ion transport (Na+/K+-ATPase, V-type ATPase, carbonic anhydrase, and ABC transporters), ammonia transport (Rh glycoproteins and Aquaporins), amino acid metabolism, carbohydrate metabolism, and fatty acid metabolism. Furthermore, DEGs were significantly associated with cell-cell/ extracellular matrix interaction and protein synthesis. An integrated multi-omics analysis revealed the activation of carbon metabolism and TCA cycle. These results indicate that in response to CA exposure, P. dabryanus may facilitate carrier-mediated ion and ammonia transport to maintain the internal osmotic equilibrium and lessen the deleterious effects of blocked ammonia excretion. Meanwhile, amino acid metabolism and protein synthesis are disturbed, P. dabryanus can modulate carbohydrate catabolism to maintain energy homeostasis. The above findings provide novel insights into saline-alkaline adaptation in freshwater fishes, paving the way for future research and development of saline-alkaline-tolerant Cobitidae strains.

Unveiling the depression role of quercetin in selective flotation separation of chalcopyrite from pyrite at low alkalinity

In flotation, the separation and concentration of copper-iron sulfide ores are usually carried out at high alkalinity to depress pyrite, and plenty of lime could block the flotation pipeline and affect the recovery of precious metals during practical operation. Herein, the current research hotspot to achieve the separation of copper-iron sulfide ores under low alkalinity. This paper presented an eco-friendly reagent, quercetin, for the flotation separation of chalcopyrite and pyrite, and investigated the effect on the flotation performance of the two minerals. The interaction mechanism of quercetin with mineral was demonstrated using zeta potential measurements, atomic force microscopy (AFM), surface adsorption measurements, Fourier-transform infrared spectroscopy (FT-IR), and X-ray Photoelectron Spectroscopy (XPS). The flotation results showed that the depressive effect of quercetin on pyrite was more pronounced in comparison to its impact on chalcopyrite at pH 8.0, and the chalcopyrite recovery reached 90 %, whereas that of pyrite was under 10 %. The surface analysis revealed quercetin chemisorption on the mineral surface through interaction with metal sites. In the presence of quercetin, the quercetin significantly diminished the ability of pyrite to adsorb xanthan but had minor effects on the adsorption of chalcopyrite.

Enhancing methane production from distillers’ grains by cattle manure in solid-state anaerobic digestion: Focusing on biodegradability, acidification and indigenous microorganisms

Distillers’ grains has high potential in methane production but the process is affected by the acidification in anaerobic digestion. To enhance the methane production in solid-state anaerobic digestion, distillers’ grains was co-digested with cattle manure in different proportions in this study. Compared to distillers’ grains, cattle manure performed lower biodegradability but higher alkalinity and nutrients, hence relieved acidification and drove microbial succession for methane enhancement in the co-digestion with distillers’ grains. The highest increase in total methane yield (10.67 %) was observed in the co-digestion of distillers’ grains and cattle manure at the proportion of 70:30 (T3). This was the synergistic action of reduced acidification, relatively high biodegradability of feedstocks, and balanced composition of hydrolytic bacteria, syntrophic bacteria and acetoclastic methanogens. Further analysis revealed the positive effects of indigenous microorganisms derived from distillers’ grains and cattle manure in methane enhancement. The enrichment of Sedimentibacter, Desulfitibacter, Tepidanaerobacter from distiller's grains, and Eubacterium, Methanoculleus, Methanobacterium, Methanobrevibacter mainly from cattle manure synergistically promoted organics conversion and methane production in T3. This study further affirmed the potential use of distillers’ grains in solid-state anaerobic digestion and provided a favorable strategy for its better methane production.

Python-Based Water Quality Evaluation of Tranza and Albarika Wells

Introduction: The increase in waterborne diseases in certain remote areas of Benin led the study to conduct surveys on the different waters used by these inhabitants. Aims: This study is conducted to assess the probable risks related to the physicochemical and bacteriological quality of well water consumed by the population of the Tranza and Albarika neighborhoods. Place and Duration of Study: Water samples were collected from 20 wells (open and closed in Albarika and Tranza districts) in the Parakou commune and analyzed at the LaKReCA laboratory between April and July 2024. Methodology: A two-stage methodology was used to approach this study. Thus, a survey was conducted with the aim of determining the actual fraction of the population using well water as drinking water. The physicochemical and bacteriological parameters were determined according to standard normalization in order to assess water quality using Python software for the statistical study. Results: The results show that 26.66% of the inhabitants of the Tranza and Albarika districts are subscribers to SONEB against 20.01% who use well water as drinking water. In addition, the waters are colored (16.16±5.86 Pt/Co), cloudy (69±3.22 NTU), loaded (678.58±6.07 µS/cm), rich in magnesium (132.42±7.87mg/L), calcium (52.73±1.68mg/L), chlorine (88.23±1.96mg/L) and have high alkalinity contents (194.49±16.57mg/L). They are hard (185.09±5.09 mg/L) and can cause waterborne diseases depending on their total coliform (23 CFU) and E. coli (5 CFU) contents. The correlation between the parameters shows that a magnesium content equal to 67 mg/L leads to a high value of total coliform and calcium in well water. Conclusion: Ultimately, the origin of the pollution can be attributed to sanitation, household waste, the transfer of pollutants from surface layers, the conditions of drawing water and the structure of the wells. In the long term, the use of well water could constitute a significant health risk for the majority of the inhabitants of Tranza and Albarika in the city of Parakou.

Characterization, fractionation and untapped potential of phosphate-amended sewage sludge biochar in soil-plant systems

Sewage sludge, a byproduct of wastewater treatment, poses serious environmental and health risks due to its content of organic contaminants, heavy metals, and pathogenic microorganisms. With the growing global production of municipal wastewater, finding effective methods for managing and disposing of sewage sludge has become increasingly urgent. Traditional methods such as land disposal, dumping, and incineration have limitations and environmental drawbacks. However, recent advancements have shown promise in the valorization of sewage sludge, particularly through pyrolysis, which converts it into biochar for use in soil amendment and pollutant mitigation. This study aims to characterize and fractionate phosphate-amended sewage sludge biochar produced at 300 °C, 400 °C, and 500 °C, and to evaluate its potential use in soil-plant systems. It examines nutrient bioavailability in soil after the addition of this biochar and its effects on plant growth. The pyrolysis process resulted in biochar with high alkalinity (7.2–11.1), ash content ranging from 56.9% to 87.3%, and significant phosphorus retention, with phosphorus concentrations increasing with pyrolysis temperature (5.35%–9.38%). Phosphorus fractionation showed a shift toward more stable fractions particularly at 500 °C. Soil incubation experiments indicated increased phosphorus availability with HCl-extractable P showing a high extraction efficiency of up to 94.95%. In plant growth experiments, the amended biochar significantly enhanced growth, with corn showing an increase of up to 28.8% and wheat showing an increase of up to 86% compared to the control in the first four weeks after emergence. These findings indicate that phosphate-amended sewage sludge biochar enhances nutrient availability and supports plant growth, providing a sustainable solution for sewage sludge management, contributing to soil improvement and carbon sequestration, thereby addressing global environmental challenges.

Using plasma-activated water for decontamination of Salmonella spp. on common building surfaces in poultry houses

Plasma-activated water (PAW) has been shown to have antimicrobial properties, making it a promising tool for surface decontamination. This study evaluated the ability of PAW generated from high voltage atmospheric cold plasma to remove Salmonella from common surfaces (stainless steel (SS), polyvinyl chloride (PVC), concrete, and wood) found in poultry houses. PAW was generated by exposing distilled water to atmospheric cold plasma in 80% humid air at 90 kV and 60 Hz for 30 min. The resulting PAW contained 1120 ppm of nitrate and 1370 ppm of hydrogen peroxide, with a pH of 1.83. PAW was then applied to coupons of SS, PVC, wood, and concrete surfaces inoculated with 7–8 log10 CFU of cocktail of Salmonella spp. (S. Typhimurium, S. Newport, S. Montevideo, and S. Enteritidis). PAW effectively reduced Salmonella levels on SS and PVC surfaces to below the detection limit within 30 s. On wood surfaces, a longer treatment time of 7.5 min was required to achieve a maximum reduction of 2.63 log10 CFU, likely due to the porosity of the wood limiting PAW contact with the bacteria. On concrete surfaces, the reduction in Salmonella levels was only 0.98 log10 CFU. This was likely due to the greater surface roughness and high alkalinity, which neutralized the PAW species.

The Use of Waste Materials Red Mud and Fly Ash as Road Embankment Fill

This study provides a comprehensive evaluation of red mud as a sustainable material for road base construction, particularly in combination with bottom ash. Red mud, a by-product of the Bayer process used in alumina extraction, is known for its high alkalinity and heavy metal content. For this reason, this waste material causes environmental challenges. Red mud sourced from the Eti Aluminum Factory in Seydişehir, Konya (Turkey), was stabilized with bottom ash. Then, these waste materials were tested through a number of experiments, such as in relation to their Atterberg limits, compaction characteristics, unconfined compressive strength (UCS), California bearing ratio (CBR), and microstructure through a scanning electron microscopy (SEM) analysis. The results highlight that the UCS of stabilized red mud samples significantly improved with the addition of bottom ash and longer curing periods. Specifically, the UCS values increased from 0.5 MPa to 2.5 MPa after 28 days of curing. Moreover, RM specimens stabilized with 25% bottom ash achieved a CBR value of 146.64% after 28 days, far exceeding Turkey’s road fill material requirement, which mandates a minimum unsoaked CBR value of 15%. These findings indicate that red mud stabilized with bottom ash not only meets but exceeds the structural requirements for road base materials. This approach provides a sustainable solution for the environmental management of red mud while contributing to infrastructure development. Through the recycling of these industrial by-products, this study presents a viable method to reduce waste and support economic and environmental sustainability in road construction projects.

Assessing suitability of surface water from Oued El Gourzi for irrigation east of Alger

The study was conducted to determine the suitability of surface water from Oued El Gourzi for irrigation in the Fesdis area, Algeria, during irrigation season of July 2022. The suitability was assessed by analysing eight water samples collected from various sites along the Oued. A range of physicochemical parameters were examined, including EC, pH, Mg2+, Na+, Ca2+, K+, HCO3– and Cl–, alongside other indices such as sodium absorption ratio (SAR), soluble sodium percentage (SSP), residual sodium carbonate (RSC), permeability index (PI) and magnesium adsorption ratio (MAR) using standard procedures. The Richards classification shows that these waters are characterised by high salinity and low alkalinity hazard (C3–S1). According to the Wilcox classification, the majority of these waters are of doubtful quality, with only 25% exhibiting good quality for irrigation. Based on the RSC and MAR, all water samples are deemed safe and suitable for irrigation. However, PI values suggest that all sampling sites are of marginal quality for irrigation (class II). In terms of sodium and chloride concentration, all water samples were deemed unsuitable for irrigation. Based on these results, the waters pose risks for irrigation, particularly due to salinity, necessitating the implementation of special management practices and the selection of salt-tolerant crops.

Insights into potential of banana leaf powder as a mud soil stabilizer

This study proposes a novel method for managing surplus soil in urban construction projects by investigating the use of banana leaf powder (BLP) as an eco-friendly and efficient mud-soil stabilizer. This study is pioneering in its focus on the use of an agricultural waste product, BLP, as an alternative to conventional methods that frequently rely on cement or lime, which pose environmental concerns owing to their high alkalinity and carbon emissions. BLP, derived from dried and pulverized banana leaves, traditionally used in various industries, was evaluated for its suitability as a stabilizer against orange peel biopolymer (OBP) and fly ash (FA). The findings of this study are groundbreaking. BLP's water absorption capacity, Wab, although lower than that of OBP, was significantly higher than that of FA, demonstrating its potential as a mud soil stabilizer. BLP increased the compaction and strength of the treated clay, whereas OBP made it more challenging to compact the clay owing to gelatinization. The ease of compaction with BLP is attributed to the absorption of free water into the pores of the particles. These results suggest that differences in the stabilizer's water absorption mechanism affect the effectiveness of the post-treatment compaction process on the treated soil. An analysis of the impact of water absorption capacity on the cone index, qc, revealed a material-independent relationship between the parameter β (=Wab × A, where A denotes stabilizer addition content) and qc for BLP and FA. This is because, in contrast to OBP, BLP and FA did not gelatinize the free water that was not absorbed by the stabilizer and remained in the same form within the treated clay. This indicates that understanding the water absorption capacity and mechanism of organic- or inorganic-based stabilizers is important for predicting the strength of treated soil. The same relationship between β and qc holds true for the hybrid-treated clay using both BLP and FA, with β considered to be the sum of β for both BLP and FA. Furthermore, this study innovatively addresses the concern of BLP decay in treated soil by creating a hybrid stabilizer with FA and conducting experiments to accelerate BLP decay using fungal mycelia. These experiments revealed that the hybrid-treated clay exhibited a more gradual decrease in carbon content and stabilized pH levels, implying that FA could inhibit decay by fungal mycelia, improving the BLP-treated soil's long-term durability. These findings suggest that agricultural wastes with high organic content can be effectively used for soil stabilization and ground improvement in civil engineering construction and maintenance projects by combining inorganic materials and taking advantage of their properties, such as high water absorbency. This can address the issues (such as high alkalinity and high carbon dioxide emissions) associated with cement- and lime-based stabilizers, which were previously widely used.

Evaluation of Integrated Anaerobic/Aerobic Conditions for Treating Dye-Rich Synthetic and Real Textile Wastewater Using a Soda Lake Derived Alkaliphilic Microbial Consortia

Textile industry wastewater (WW) has intense color, high chemical oxygen demand (COD), pH, and salinity, making it challenging for conventional treatment. Soda lakes, with high alkalinity and salinity, host diverse microbes capable of textile dye degradation. This study evaluated anaerobic/aerobic reactors using alkaliphilic microbial consortia from Lake Chitu, an Ethiopian soda lake, for treating synthetic and real textile WW. The experimental setup consisted of a first-stage anaerobic reactor followed by a second-stage aerobic reactor, operating continuously with a predetermined flow rate and hydraulic residence time. After evaluating synthetic WW, real textile WW was collected in two batches (rounds I and II). The treatment setup removed 99% of the dye color for synthetic WW, 98% for round I, and 96% for round II. COD removal was 87% for synthetic WW, 86% for round I, and 93.37% for round II. TKN removal reached 90% for synthetic WW, 91% for round I, and 96% for round II at a steady state. Residual COD and TKN values met the final effluent discharge standards. GC–MS and IR analyses revealed that dyes were broken down into intermediate organic compounds under anaerobic conditions and further degraded into smaller molecules under aerobic conditions. This integrated reactor approach effectively removes dyes and enhances COD and TKN removal. The study’s novelty lies in evaluating both synthetic and real textile WW using integrated reactors under alkaline conditions in a continuous process, inoculating alkaliphilic consortia, without pre-enrichment or external nutrient addition to real WW. The study provides insights into the effectiveness of alkaliphilic microbial consortia derived from soda lakes for treating textile WW using integrated reactor conditions. Reactor microbiome characterization is needed to further explore microbial diversity and community structure.

Passivation and depassivation of reinforcement steel in alkali-activated materials—A review

This paper reviews the formation and breakdown of passive film on the surface of reinforcement steel in alkali-activated materials (AAMs) considering the characteristics of reaction product and pore solution chemistry. The literature review shows that the pore solution of AAMs has higher concentrations of OH−, Na+, silica and aluminium compared to Portland cement (PC). This relatively high alkalinity contributes to the generation of a passive film, which has positive effects on the corrosion resistance of reinforcement steel embedded in AAMs. The silica-aluminium zeolite layer present on the surface of passive film adsorbs chloride ions and effectively inhibits chloride-induced depassivation. Generally, lower ratios of [Cl−]/[SO42−] and [Cl−]/[S2O32−] potentially inhibit the depassivation of reinforcement steel. The high pH value and the elevated concentrations of HS− of AAMs contribute to the increase of critical chloride content (Ccrit). However, the higher content of reduced sulfide mainly dissolved from slag results in the consumption of dissolved oxygen, which is necessary for the formation of passive film. Generally, the presence of reduced sulfide forms Fe-S complexes on the surface of reinforcement steel in AAMs. Even so, higher corrosion resistance for AAMs is mostly expected with longer depassivation time due to finer microstructure and lower chloride penetration rates compared to PC-based materials. The decrease in pH value in the pore solution of the AAMs is the main factor affecting carbonation-induced depassivation of reinforcement steel, while high concentrations of bicarbonate and carbonate ions inhibit depassivation.

Physiological and molecular responses of juvenile silver crucian carp (Carassius gibelio) to long-term high alkaline stress: Growth performance, histopathology, and transcriptomic analysis

Salty-alkaline waters are widely distributed globally, and how to effectively develop saline-alkaline water to improve the utilization rate of water resources has become a global challenge. This study examined the survival performance of juvenile silver crucian carp (Carassius gibelio) under alkaline gradient acclimation conditions and explored the regulatory mechanisms for their adaptation to high alkalinity. Compared to directly immersing in high concentrations, alkaline gradient acclimation significantly improved the survival rate of juvenile silver crucian carp. Long-term high alkaline stress caused significant reduction in the growth performance of juvenile silver crucian carp. After alkaline stress, the enzyme activities of Na+-K+-ATP (NKA) and Ca2+-Mg2+-ATP (CMA) in the gills were significantly decreased. Meanwhile, histopathology of the gills showed structural changes, indicating that the physiological functions of juvenile silver crucian carp were impaired under alkaline conditions. Transcriptomic analysis found that the expression of genes related to metabolism and immune response pathways in the gill and kidney underwent significant changes. Genes related to carbohydrate metabolism were upregulated while those related to protein metabolism were downregulated, indicating that alkaline stress caused the organism to utilize carbohydrates rather than proteins as much as possible to meet enhanced metabolism. The HIF pathway that maintains the body's survival was significantly up-regulated, at the expense of high energy consumption. Dysregulation of genes related to the formation of neutrophil extracellular traps (NETosis) pathway indicated that the immune function of the fish was suppressed. Overall, this study revealed the physiological and molecular responses of juvenile silver crucian carp to alkaline stress, deepening our understanding of their adaptation strategies and the potential impact of alkaline environments on aquatic life.

Kinetic research of red mud waste oxidative pyrolysis and comparison under different atmospheres

Red mud, as a solid waste with high alkalinity, had a detrimental impact on the environment and required urgent attention. Currently, the mass processing and consumption of red mud were typically conducted under thermal conditions, so it was essential to gain a comprehensive understanding of the oxidative pyrolysis process. The thermogravimetric experiments were conducted at multiple heating rates in air and exhibited three obvious stages. The activation energy and reaction mechanism of three oxidative pyrolysis stages were explored using model-free and model-fitting methods, revealing the activation energies of 162.2, 265.8, 214.1 kJ/mol and the most suitable reaction mechanisms of g(α)=[-ln(1-α)]³, g(α)=1-(1-α)1/⁴, g(α)=[-ln(1-α)]1/2 for each stage, respectively. Furthermore, the estimated kinetic parameters and reaction mechanisms were applied to extra heating rate to verify the accuracy. More important, the effect of air on the pyrolysis process of red mud was examined by comparing the results with those obtained from pure nitrogen pyrolysis. The obtained oxidative pyrolysis characteristics of red mud could provide valuable insights of its co-pyrolysis or combustion for resources recycling.

Recycling steel slag as aggregate in developing an ultra-thin friction course with high comprehensive road performance

The demand for skid-resistant and wear-resistant alternative aggregates in the preparation of ultra-thin friction course (UTFC) asphalt mixtures is a key direction for achieving high durability and low-carbon development in pavement maintenance. As a typical industrial waste, steel slag with high alkalinity and strong adhesion can facilitate the mechanical property of asphalt mixtures. However, few researches focused on the impact of steel slag on the comprehensive road performance of UTFC mixtures. Hence, the issue merits systematic exploration. In this study, the chemical components, microstructure and morphological characteristics of three steel slags (GXSS, HBSS and IMSS) obtained from different sources were surveyed. Then the stone matrix asphalt (SMA)-5 and open-grade friction courses (OGFC)-5 mixtures with different steel slags were fabricated. And their comprehensive road performances were quantitatively explored via the improved radar chart. The results indicate that steel slag with approximately 40 % Ca content, about 20 % Fe content, irregular shapes and tiny pores endows its wear resistance and strong adhesion. IMSS demonstrates the largest average angularity and form 2D values of 3850 and 7.28, respectively, representing its significant crowding function and interlocking structure. Incorporating steel slag remarkably reinforces the rutting resistance, skid resistance and anti-interlayer shear performance of UTFC. While the effect of water stability and crack resistance of UTFC depend on the category of steel slag. All three steel slags manifest the improvement function on the comprehensive assessment indexes (CAI) of OGFC-UTFC. IMSS-OGFC reveals the optimal comprehensive road performance, achieving the highest CAI of 0.9909. It is inferred that steel slag is more suitable for OGFC-UTFC than SMA-UTFC due to its relatively high CAI and consistent performance regardless of the steel slag type.