NaOH Research Articles

Cadmium Remediation from Water Using Low-Cost Modified Biochar: An Approach Towards Sustainable Remediation

Biochar is increasingly recognized as an effective adsorbent for the removal of Cadmium (Cd²⁺), a prevalent contaminant in industrial wastewater. This study utilizes rice husk biochar to target aqueous Cd²⁺. The biochar was synthesized through rapid pyrolysis at 450°C. To enhance its Cd²⁺ removal efficiency, the biochar was modified with chitosan, using a treatment with a 2% aqueous acetic acid chitosan solution followed by sodium hydroxide (NaOH) processing. Both the chitosan-modified biochar (CMBC) and the non-modified biochar (NMBC) underwent comprehensive characterization via proximate and ultimate analysis, Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). At pH 5, the Langmuir maximum adsorption capacity of CMBC was 134 mg/g, compared to 48.2 mg/g for NMBC at 318 K. CMBC exhibited a significantly higher Cd²⁺ removal efficiency, attributed to the introduction of amine groups from chitosan modification that enhance Cd²⁺ adsorption. The adsorption mechanisms on CMBC were further explored through FT-IR and SEM comparisons before and after Cd²⁺ uptake. The chitosan modification notably improved the Cd²⁺ adsorption capacity, which was also influenced by pyrolysis temperature; higher temperatures led to reduced biochar yield but increased porosity, surface area, and adsorption capacity. The adsorption process was pH-dependent, with a peak capacity of 161 mg/g observed at pH 5. The Freundlich model effectively described the adsorption equilibrium, suggesting contributions from both chemisorption and physisorption on the heterogeneous biochar surface. In summary, rice husk biochar, especially when modified with chitosan, proves to be a cost-effective, sustainable material for Cd²⁺ removal from aqueous solutions, enhancing water treatment efficiency through improved adsorption capabilities.

Molecular identification of Shiitake (Lentinula edodes), analysis and production of beta-glucan using beech wood sawdust waste

Lentinula edodes has the ability to grow and produce bioactive compounds on industrial by-products. This study aimed to produce B-glucan of cell wall Shiitake on Beechwood Sawdust (BWS) through a two-step procedure, which included fermentation and B-glucan extraction and purification. Shiitake mushrooms are cultivated by solid-state fermentation (SSF) using the Jamas method to increase the purity of B-glucan. The fermented substrate was first separated and then hydrolyzed by sodium hydroxide (NaOH) (10 M, 1 M), followed by acid hydrolysis extraction. The structure and purity of B-glucan were confirmed by FTIR, NMR, and AFM spectroscopy. The fungus used was molecularly identified by the 18 s rRNA method. Shiitake mushroom was produced by SSF using BWS and high purity β-glucan was extracted from the produced polysaccharide in the amount of 67.33 mg/g. FTIR, NMR, and AFM analyses proved the production of beta-glucan, and based on molecular identification, it was determined that the mushroom used was Lentinula edodes. The results obtained show that SSF is a valuable technology for the production of biomass and polysaccharides by utilizing the strain of L. edodes. To the best of our knowledge, the yield reported is the highest by the strain of L. edodes using SSF.

Preparation of solid alkali activator for geopolymer synthesis using vanadium-bearing shale tailing

The vanadium-bearing shale tailing (VST) with large reserves pollutes the environment and urgently needs to be utilized as a resource. Due to its main component being silica, VST has great potential as a raw material for geopolymer. Therefore, this study uses VST to prepare the solid alkali activator (SAA) by thermochemical methods. Analysis show that the temperature and NaOH dosage of thermochemical reaction significantly affect the alkaline activation effect of SAA. Temperature affects the silicate content and the amount of NaOH affects the soluble silicate content in SAA. When the reaction temperature is high (such as above 900 ℃) and the amount of sodium hydroxide is low (such as the mass ratio of sodium hydroxide to VST is 0.6), quartz almost transforms into silicates, but the silicates have a stable cyclic chemical structure and are difficult to dissolve during the geopolymerization reaction. When the reaction temperature is low (such as less than 700 ℃) and the amount of sodium hydroxide is high (such as the mass ratio of sodium hydroxide to VST is 0.9), quartz in VST is difficult to fully convert into silicates, there are unreacted quartz and sodium hydroxide in SAA, and SAA has poor alkaline activation performance. The optimal synthesis process conditions for SAA are as follows: synthesis temperature is 900 °C and the mass ratio of sodium hydroxide to VST is 0.95. The main silicate components of SAA are Na2SiO3 and Na15.6Ca3.8Si12O36. During the synthesis of one-part geopolymer (OPG), Na2SiO3 dissolution generates a strong alkaline reaction environment and provides active silicon-oxygen tetrahedron monomers or oligomers, Na15.6Ca3.8Si12O36 is bonded with geopolymer gel structure by stable cyclic silicate structure, which makes OPG have a compact integrated structure. When the mass ratio of SAA to MK is 1:1.3, the 7-day compressive strength of the prepared OPG is about 49 MPa, SAA has the potential as a substitute for commercial sodium silicate to prepare geopolymers.

Influence of vacuum and high-temperature on the evolution of mechanical strength and microstructure of alkali-activated lunar regolith simulant

Alkali-activated lunar regolith (AALR) has become one of the most promising lunar building materials, offering the potential to support the construction of large-scale lunar structures. This paper presents a comprehensive experimental investigation on the fresh properties, physical properties, mechanical performance and microstructural characteristics of alkali-activated lunar regolith simulant (AALRS) considering the effects of lunar environments (high-temperature, vacuum and coupled high-temperature and vacuum), alkaline activators (sodium hydroxide and sodium silicate) and curing age. The results show that AALRS under high-temperature environment exhibits higher strength while the strength development is limited. However, AALRS under vacuum environment exhibits lower strength but the strength increases as the curing time increases. In terms of pore structure, the volume fractions of macro voids for SH-V and SS-V account for up to 50.94 % and 63.64 %, respectively, which are 12.22 % and 7.95 % higher than those of SH-H and SS-H. Regarding the impact of coupled high-temperature and vacuum environment, the compressive strength of SH-HV-7 is reduced by 47.8 % compared to that of SH-H-7, while the compressive strength of SS-HV-7 exhibits a 57.2 % increase over that of SS-H-7. The sodium hydroxide-activated (SH-activated) system and sodium silicate-activated (SS-activated) system demonstrate fundamentally intrinsic differences in terms of reaction products, structure build-up and pore structure. The positive optimization mechanism and reverse degradation effect of vacuum environment on the performance of AALRS paste were revealed. Finally, the evolution of structural characteristics of AALRS paste under different environments was elucidated.

Physical and chemical treatments in obtaining and purifying Kombucha SCOBY Cellulose

SCOBY cellulose (CS) is a biopolymer with exceptional physical properties, serving as a source of fiber, water retention capacity, crystallinity, and purity. Its potential as a byproduct of kombucha production and a source of bacterial cellulose (BC) has been a subject of exploration. This study aims to gather information from experimental studies in the scientific literature on various methods of CS extraction, processing, and purification, and their impact on microscopic, macroscopic structure, and functional characteristics. The purification treatments for CS, as described in the literature, include immersion in deionized, distilled, or sterile water, sodium hydroxide, hydrogen peroxide, and sodium hypochlorite under agitation or static mode at different temperatures (23ºC, 30ºC, 50ºC, 80ºC, 90ºC, 110ºC) and under variable contact times with the substance chosen for treatment (1, 2, 20, 24 hours to 3 days). Alkaline treatments on SCOBY cellulose enhance extensibility, viscoelasticity, absorptivity, tensile strength, heat stability, and remove microorganisms, sugars, and other components of the culture medium adhered to the cellulose. With CS being obtained at a low cost and low complexity in the fermentation process, and the potential for less polluting treatments, it presents a sustainable process and source of CB that can be applied in a variety of industries, particularly in the exciting field of food.

Response Surface Design Models to Predict the Strength of Iron Tailings Stabilized with an Alkali-Activated Cement

Tailing storage facilities are very complex structures whose failure generally leads to catastrophic consequences in terms of casualties, serious environmental impacts on local biodiversity, and disruptions in the mineral supply. For this reason, structures at risk must be reinforced or decommissioned. One possible option is its reinforcement with compacted filtered tailings stabilized with binders. Alkali-activated binders provide a more sustainable solution than ordinary Portland cement but require an optimization of the tailing–binder mixture, which, in some cases, can lead to a substantial experimental effort. Statistical models have been used to reduce the number of those experiments, but a rational design methodology is still lacking. This methodology to define the right mixture for a required strength should consider both the mixture components and in situ conditions. In this paper, response surface methods were used to plan and interpret unconfined compression strength test results on an iron tailing stabilized with alkali-activated binders. It was concluded that the fly ash content was the most important parameter, followed by the liquid content and sodium hydroxide concentration. From the obtained results, several statistical models were defined and compared according to the definition of a strength prediction model based on a mixture index parameter. It was interesting to observe that models with the porosity cement index still provide reasonable adjustment even when different tailings’ water contents are considered.

OPTIMIZATION OF PRODUCTION AND IMPROVEMENT OF CHARACTERISTICS OF WATER-COAL FUEL SUSPENSIONS BASED ON HIGH-ASH COALS

This article explores the possibilities for improving the characteristics of water-coal fuel suspensions (WCFS)based on high-ash coals from Uzbekistan. Investigations indicate that the incorporation of stabilizing and plasticizing additives, such as sodium and calcium hydroxides, can result in notable enhancements in both rheological characteristics and calorific value of WCFS. These results are important for optimizing production and increasing the technological suitability of WCFS based on high-ash coals from Uzbekistan, which allows them to be used as highly effective fuels. This investigation is a significant advancement towards the progress and enhancement of fuel blends and can be valuable for engineers and manufacturers who are engaged in the manufacturing process of WCFS.

MECHANICAL BEHAVIOUR OF ISTLE FIBRE COMPOSITE REINFORCED WITH EPOXY AND E-GLASS AT DIFFERENT FIBRE ORIENTATIONS

This paper was aimed to study the mechanical properties of Istle fibre composites. The process of fabrication was done by hand layup technique at three different fibre orientations i.e., unidirectional, bidirectional and 45 degrees inclined, and also its effect on tensile and flexural property that was studied in the Instron Testing Machine. The fibre volume ratio was kept uniform for the entire specimen as 50:50. The treatment of istle fibre was done with sodium hydroxide to increase the fibre matrix bonding. The effect of E-glass reinforcement has also been studied in both bending tests and flexural tests. The maximum tensile and bending modulus recorded were from unidirectional fibre specimen.

KINETIC AND THERMODYNAMIC ADSORPTION STUDIES ON THE REMOVAL AND TREATMENT OF TEXTILES EFFLUENTS USING ACTIVATED CARBON DERIVED FROM DIOSPYROS MESPILLIFORMIS SEEDS.

An agricultural waste Diospyros mespiliformis seeds were treated, and activated with 30% of 0.3M sodium hydroxide base, to obtain an activated carbon employed in an adsorption process. It was utilize to treat effluent textile water sample from African Textile Manufacturers Limited in Dala, Kano State, Nigeria. Various techniques, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and proximate analysis were employed to investigate the adsorption process. The adsorbent was able to remove the dark red color to colorless found in textile effluents and shown a higher removal affinity for zinc ( 99.4%) and least affinity for nickel (0.11%), also Chromium (Cr) reduced by 39.4%, Copper (Cu) reduced by 20.9%, Iron (Fe) reduced by 91.9% , Manganese (Mg) reduced by 79.3%, are reduced significantly, the PH change from acidic PH 6.4 to neutral PH 7.1, turbidity decrease from 131 to 14 NTU , electrical conductivity change from 723 to 110 ?s·cm?1 .Diospyros mespiliformis seeds activated carbon was used for removal of congo red and malachite green from an aqueous solution. The effect of adsorbent dose, adsorbate concentration and contact time on the process of adsorption was investigated. The optimum dosage was found to be 0.5g had a percentage removal of 98.1% for congo red and 94.4% for malachite green. 10mg/l and 80minute was found to optimum concentration and optimum time in adsorption of congo red and malachite green. The equilibrium, kinetic and thermodynamic properties of the dyes removal were also investigated. The experimental data were modeled using linear regression method of analysis. The correlation coefficient was used as a criterion for model adequacy and acceptance. The pseudo second-order kinetic model was found to best correlate the experimental data with R2 of 0.9523 for CR and 0.9297 for MG. The experimental data were investigated at three different temperature, 305k, 325k and 335k were found to follow the Langmuir model with R2 of 0.9679, 0.9662 and 0.989 for CR and 0.9529, 0.9662 and 0.994 for MG. also were found to follow Temkinp model with with R2 of 0.9549, 0.9318 and 0.9952for CR and 0.9885, 0.9443 and 0.9209 for MG. The negative free gribbs energy indicated that the adsorption processes were spontaneously feasible. The positive values of +31.66KJ/mol and +92.3KJ/mol on both CR and MG indicate that adsorption process has been found to be endothermic in nature. The removal of congo red was found to be more spontaneous and feasible than the removal of malachite green on the adsorbent. From the study, it was deduced that the Diospyros mespiliformis seeds activated with sodium hydroxide was found to be a good adsorbent for the treatment of textile wastewater containing Congo red and Malachite green.

Development of a Hydrometallurgical Process for the Extraction of Cobalt, Manganese, and Nickel from Acid Mine Drainage Treatment By-Product

Critical minerals (CMs) are pivotal in modern industries, such as telecommunications, defense, medicine, and aerospace, contributing significantly to regional and global economic growth. However, the reliance on external sources for 26 out of 50 identified CMs raises concerns about supply chain vulnerabilities. To address this, the research focused on developing a hydrometallurgical process for extracting cobalt, manganese, and nickel from acid mine drainage (AMD) treatment by-products, emphasizing the need to diversify CM supply chains within the United States (US). A solution composed of an REE solvent extraction raffinate loaded with cobalt, manganese, nickel, and various impurity metals was utilized as a feedstock in this study. The developed hydrometallurgical process involved initial sodium hydroxide precipitation to remove impurities like aluminum and iron from an SX raffinate solution generated during the extraction of rare earth elements (REEs). Precipitation stages were performed in a pH region ranging from 2 to 12 to identify the optimum pH values, achieving a tradeoff between recovery and impurity removal. A subsequent precipitation process at pH 5–10 yielded a product rich in CMs, such as manganese, cobalt, and nickel. Further separation steps involved nitric acid washing, resulting in a Mn product with a purity of 47.9% by weight and a solution with extractable concentrations of cobalt and nickel. Stagewise precipitation with sodium sulfide subsequently produced three solid products: cobalt and nickel product at pH 1–5, manganese product at pH 5–10, and magnesium at pH 10–12. The study also explored other separation approaches, including solvent extraction, to enhance the separation of nickel from cobalt. Overall, the developed hydrometallurgical process generated the following products with varying degrees of purities: cobalt (9.92 wt.%), nickel (14 wt.%), manganese (47.9 wt.%), and magnesium (27.49 wt.%). This research aimed to contribute to the sustainable extraction of CMs from secondary sources, reducing the US’ reliance on imports and promoting a more resilient supply chain for these crucial elements.

Synthesis and characterization of etherified cationic starch flocculant derived from Manihot esculenta peel with varying degrees of substitution

Cationic Manihot esculenta (ME) peel starch was synthesized through etherification method using 3-chloro-2-hydroxypropyl trimethylammonium chloride (CHPTAC) as cationizing monomer. The optimization of the main factors influencing the degree of substitution (DS) was conducted using central composite design (CCD) and response surface methodology (RSM). The factors assessed include CHPTAC concentration, catalyst sodium hydroxide (NaOH) concentration, and reaction time. The DS values of the cationic starches were obtained between 0.39 and 0.99. The maximum DS value was up to 0.99 at 0.615 mol/L of CHPTAC, 30 % (w/v) NaOH, and a reaction time of 5 h. The finding based on the optimization using RSM reflected that CHPTAC and NaOH concentrations are the key variables determining the DS value, while reaction time has a negligible impact on the etherification process. Furthermore, the chemical composition, morphology, and structure of the cationic ME peel starch were characterized by scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffractometry (XRD) and nuclear magnetic resonance spectroscopy (1H NMR). It was confirmed that the modifying monomers penetrated the surface layer of the starch granules and attached to the starch backbone.

Comparative Analysis of the Recovery of Cu2+ and Au from Washing Solution of Pyrite Concentrate Slag by Two Processes

A large amount of pyrite concentrate slag washing solution is produced in China every year, and this contains valuable components such as Cu2+ and Au. The traditional treatment method not only pollutes the environment but also wastes metal resources. For the washing solution containing Cu2+ 437 mg/L and Au 0.13 mg/L, two new processes comprehensive recovery schemes were developed and compared in this paper, namely iron powder replacement pore filtration and neutralization precipitation pore filtration. When the iron powder replacement pore filtration process was adopted, Cu2+ and Au were mainly comprehensively recovered in the form of a mixture of sponge copper and particulate gold. The test results showed that the replacement optimal conditions involved a pH of 3.0, iron powder dosage of 6 g/L, and replacement time of 3.0 h. After replacement, the filter cloth with below 1 μm pore size was used for filtration. The recovery rate of Cu2+ in the washing solution was 98.13 and the total recovery rate of Au was 95.83%. Otherwise, when the neutralization precipitation pore filtration process was adopted, Cu2+ and Au were mainly comprehensively recovered in the form of a mixture of copper hydroxide and particulate gold. The test results showed that sodium hydroxide was used as the precipitant and the optimum neutralization pH value was 6.5. After precipitation, the filter cloth with a below 1 μm pore size was used for filtration. The recovery rate of Cu2+ in the washing solution was 97.35% and the total recovery rate of Au was 93.54%. The economic benefit estimation of the two processes showed that the neutralization precipitation pore filtration process had the advantages of low material consumption, low cost and high economic benefit.

Feed additives supplementation: a potential strategy to ameliorate heat stress in sheep

Abstract Given a significant climate-flexible and socio-economic role in developing nations, environmental heat stress imposes a major financial impact on sheep production systems globally endangering their production, reproduction, and growth. In this regard, the adverse effects of heat stress on sheep production systems have to be addressed through adoption of effective heat alleviation measures like animal management, nutritional management and genetic interventions of which the nutritional interventions seems to be the most cost effective way to alleviate heat stress. Nutritional manipulation for heat stress alleviation in sheep involves the use of antioxidant supplements (Vitamin B; Vitamin E and Selenium; Selenium; Zinc sulphate and folic acid; Vitamin C, Vitamin E, Selenium and Zinc; Naringin; Opuntia ficus-indica f. inermis; Açai oil and Brown seaweed like Ascophyllum nodosum and Sargassum latifolium). Further, electrolyte supplements (Dietary Electrolyte Balance (DEB); Sodium bicarbonate and potassium bicarbonate; Sodium hydroxide) have a beneficial effect on thermal responses, respiratory activities, gas exchange parameters, rumen fermentation, blood buffering capacity and acid-base balance. The mineral mixture supplements (Mineral blocks; Mineral mixture and antioxidants; Chromium; Zinc) play a crucial role in increasing the efficiency of antioxidant defence system, immunity-related parameters, production, reproduction, feed digestibility and insulin sensitivity. Probiotic supplements (Lactobacillus acidophilus, Saccharomyces cervisiae, Propionibacterium freudenreichii, Lactobacillus casei, Enterococcus faecium, Lactobacillus lactis, Bacillus subtilis, Propionibacterium freudenreichii, Pediococcus cerevisiae, Megaspha eraelsdenii, Bacillus licheniformis, Aspergillus oryzae, Schizochytrium limacinum, Trichoderma reesei and Saccharomyces cerevisiae) improve lactational performance, dietary energy utilization and productivity. The probiotics (live Saccharomyces cerevisiae) and prebiotics (mannan oligosaccharide plus b-glucans) used in heat stress alleviation improve dietary energy utilisation. Furthermore, the vital role of herbal supplements (Rosemary, Cinnamon, Turmeric, Clove, Naringin, Chestnut tannins, Giloy stem powder, Curcumin, Rocket oil (watercress oil), Flaxseed, Cornus, Oregano, Thyme, Chamomile flowers, Moringa oleifera, Betaine) has been highlighted to promote feed intake, antioxidant status, growth performance, feed utilization, reproductive performance and immune response. Effective adoption of nutritional strategies can thus ensure sustainable sheep production in this changing climate scenario.

Alkali-Activated Binders as Sustainable Alternatives to Portland Cement and Their Resistance to Saline Water.

Alkali-activated binders have emerged as promising alternatives to Ordinary Portland Cement (OPC) due to their sustainability features and potential advantages. This study evaluates the durability properties of heat-cured fly ash (FA) and ground granulated blast-furnace slag (GGBFS) geopolymer mortars activated with sodium hydroxide, which were subjected to wet-dry cycling in saline environments. Three series of FA, a FA/GGBFS blend, and GGBFS mortars previously optimized on a compressive strength basis were investigated and compared against two control OPC mixes. Performance indicators such as the water absorption, porosity, flexural strength, and compressive strength were analyzed. The results demonstrate that geopolymer mortars have significantly reduced water absorption and porosity with increasing wet-dry cycles. The compressive strength of the FA/GGBFS mortars also increased from 66.5 MPa (untreated) to 87.9 MPa over 45 cycles. The flexural strength remained stable or improved slightly across all geopolymer mortars. The control OPC specimens experienced significant deterioration, with compressive strength in CEM I 42.5R dropping from 51.8 to 17.1 MPa. These findings highlight the superior durability of geopolymer mortars under harsh saline conditions, demonstrating their potential as a resilient alternative for coastal and marine structures.

“Treating Waste with Waste”: Utilizing Phosphogypsum to Synthesize Porous Calcium Silicate Hydrate for Recovering of Fe2+ from Pickling Wastewater

Phosphogypsum is a by-product of the wet-process phosphoric acid production, and it is rich in Ca and S. Long-term storage of Phosphogypsum can cause serious pollution to the environment; therefore, promoting the sustainable utilization of Phosphogypsum is crucial. This study proposes the use of Phosphogypsum and silicic acid in a sodium hydroxide solution for the hydrothermal synthesis of porous calcium silicate hydrate adsorbent, which is used for adsorbing Fe2+ from simulated hydrochloric acid pickling wastewater. Under the optimal synthesis conditions (37.5 g/L of NaOH, calcium/silicon ratio of 1.0, liquid/solid ratio of 15:1 mL/g, 110 °C, and 4 h), the conversion rate of SO42− in Phosphogypsum is 87.41%. Porous calcium silicate hydrate exhibits excellent OH− release capability in Fe2+-containing pickling wastewater. The adsorption process for Fe2+; is mainly chemical adsorption, involving ion exchange between Ca2+ and Fe2+, as well as complexation reactions of O-Si-O group, -OH group, and Si-O group with Fe2+. This technology aims to provide a solution for the sustainable utilization of Phosphogypsum and the recovery of Fe2+ from pickling wastewater, which has significant practical importance.

Regulation of Osteogenic and Angiogenic Markers in Alkali Treated Titanium for Hard Tissue Engineering Applications.

Titanium (Ti) and Ti alloys are of great interest in bone and dental tissue engineering applications due to their biocompatibility, corrosion resistance, and close mechanical properties to natural bone. However, the formation of fibrous tissue prevents osteointegration and results in implant loosening. Thus, physical and chemical methods are used to improve the surface properties of Ti. This study aimed to understand the role of alkali treatment conditions, including alkali medium concentration, temperature, rotation speed, and post-heat treatment. Our results showed that alkali treatment using 5 and 10 molar sodium hydroxide solution allows the formation of web-like microstructure. However, a higher concentration of 15 molar resulted in cracks along the surface. Interaction between the human fetal osteoblast cells (hfOBs) and Ti samples showed that heat treatment is necessary for increased cellular proliferation, which was not significantly different at later time points compared to the polished Ti. Alkali heat treatment did not induce inflammatory reactions at later time points. It showed an increase in vascular endothelial growth factor, osteoprotegerin/nuclear factor kappa-В ligand ratio, and osteocalcin expression, which is evidence for accelerated osteoblast cell maturation and bone remodeling in surface-modified samples. Together, these data show that alkali treatment using 5 or 10 molar of NaOH followed by heat treatment may have therapeutic effect and assist with bone tissue integration with Ti implant.

Research on the Cell Wall Breaking and Subcritical Extraction of Astaxanthin from Phaffia rhodozyma.

This study focused on developing an effective cell wall-breaking method for Phaffia rhodozyma, followed by utilizing subcritical fluid extraction to isolate, extract, and concentrate astaxanthin from the complex fermentation products of P. rhodozyma. A comprehensive comparison of seven distinct methods for disrupting cell walls, including dimethyl sulfoxide treatment, lactic acid treatment, sodium hydroxide treatment, β-glucanase enzymatic digestion, β-mannanase enzymatic digestion, and a combined enzymatic treatment involving both β-mannanase and β-glucanase was conducted. The results identified the lactic acid method as the most effective in disrupting the cell walls of P. rhodozyma. The software, Design Expert, was used in the process of extracting astaxanthin from cell lysates using a subcritical extraction method. Through fitting analysis and response surface optimization analysis by Design Expert, the optimal extraction conditions were determined as follows: an extraction temperature of 41 °C, extraction frequency of two times, and extraction time of 46 min. These parameters facilitated the efficient extraction, concentration, and enrichment of astaxanthin from P. rhodozyma, resulting in an astaxanthin concentration of 540.00 mg/L. This result can establish the foundation for its high-value applications.

Strength, durability, and toxicity characteristics of water treatment sludge based geopolymers for subgrade application

This study examined the strength, durability and toxicity characteristics of geopolymer made from water treatment sludge (WTS) using fly ash (FA) and ground granulated blast furnace slag (GGBS) as binding materials for the subgrade application. The mechanical properties of WTS-FA-GGBS geopolymers were assessed considering various parameters such as binder proportions, curing period, curing condition, Sodium silicate (SS) to Sodium hydroxide (SH) ratio (i.e. SS/SH), and Sodium hydroxide (NaOH) concentration. The results showed that increasing binder proportions, NaOH concentration, and curing period positively impacted the strength of the WTS-FA-GGBS geopolymer. The unconfined compressive strength (UCS) of the geopolymer samples with an SS/SH ratio of 2.5 showed higher compressive strength than those at an SS/SH ratio of 1. WTS-FA-GGBS geopolymers cured at 100°C showed increased UCS values after 1 to 3 days, but strength decreased after 7 days due to a faster geopolymerisation reaction, resulting in excessive moisture loss and microcracks in the geopolymerized samples. The study also found that all the geopolymer samples met the minimum strength criteria for cement-stabilized mix with a maximum mass loss of 8.17 % are well within the specified limits (<14 %) as per IRC:37–2018. The California Bearing Ratio (CBR) values of WTS-FA-GGBS geopolymers, which range from 41.11 % to 260.32 %, surpass the minimum criteria for cement stabilized subgrade or subbase material, as specified by IRC: SP:89–2010. Additionally, the changes during geopolymerization were confirmed by FESEM, EDS, and XRD analysis. The toxicity characteristic leaching procedure (TCLP) test results showed that the amounts of heavy metals in the geopolymer leachate were within the USEPA-mandated limits.

Synthesis of MgAl-LDH from three alkali sources for boosting flame retardancy of EP with APP

Epoxy resin (EP) is used in construction materials due to its low curing shrinkage, excellent chemical stability, and mechanical properties. However, its flammability limits applications in the field of construction. Co-precipitation method with sodium hydroxide as the alkali source and hydrothermal method with urea as the alkali source are the common ways to prepare MgAl-LDH. In this study, MgAl-LDH1 (abbreviated as LDH1) was prepared by using NaOH as the alkali source at 65 ℃ for 12 h, MgAl-LDH2 (abbreviated as LDH2) by using urea as the alkali source at 120 ℃ for 12 h, and MgAl-LDH3 (abbreviated as LDH3) was prepared by using triethanolamine as the alkali source at 100 ℃ for 2 h. Then, LDH1, LDH2, LDH3 were compounded with ammonium polyphosphate (APP) to synergistically enhance the flame retardant properties of EP (Composite material abbreviated as LDH1-APP-EP, LDH2-APP-EP, LDH3-APP-EP). The results showed that the best flame retardant effect was achieved after compounding APP (5 wt%) with LDH3 (5 wt%) prepared with triethanolamine as the alkali source. Compared with Pure-EP, the peak exothermic rate and peak smoke production rate of LDH3-APP-EP prepared with triethanolamine as the alkali source decreased by 74.54 % and 67.44 %, respectively. Compared with LDH prepared with NaOH and urea as the alkali source, LDH prepared with triethanolamine as the alkali source has a larger layer spacing and a higher weight loss percentage which releases more gases, moisture, and carbon layers formed by triethanolamine during the combustion process to reduce the heat release from the fire. It’s evident that LDH3-APP-EP prepared with triethanolamine as the alkali source has higher residual carbon densities and the lowest residual carbon values based on SEM and Raman test results. This result proves that the LDH3 with triethanolamine as the alkali source has a good effect on EP flame retardation in this paper which provided a new way to design new efficient flame retardants.

Revolutionizing Waste Management: Solidification of Landfill Leachates Using Alkali-Activated Slag

AbstractLandfill leachate is a highly hazardous effluent characterized by a high concentration of recalcitrant pollutants, presenting a significant environmental challenge. This study investigated the solidification of landfill leachate contaminants using sodium hydroxide-activated Granulated Blast Furnace Slag (GBFS). The stability of the resulting geopolymer was evaluated through unconfined compressive strength and leaching tests. Optimal curing conditions were identified as 7 days at a sodium hydroxide concentration of 12 M, achieving an unconfined compressive strength of 45.738 MPa at a liquid-to-solid ratio of 15%. A linear relationship was observed between the liquid-to-solid ratio and flow workability, with maximum flow workability evidenced by an average diameter of 242 mm at a liquid-to-solid ratio of 0.25. However, a minimum liquid-to-solid ratio of 0.15 was necessary to obtain a workable mortar. The produced geopolymers were characterized using X-ray Fluorescence (XRF) for mineralogical analysis, Scanning Electron Microscopy (SEM) for morphological examination, and the Toxicity Characteristic Leaching Procedure (TCLP) for leaching tests. The findings demonstrated the successful solidification of landfill leachate using GBFS geopolymer. The leachability tests revealed that the geopolymer did not release metals in concentrations exceeding the allowable limits set by the United States Environmental Protection Agency (USEPA), indicating effective encapsulation of the pollutants within the geopolymer matrix. Furthermore, the resultant geopolymer brick is eco-sustainable and can be classified as a green construction material.