La-Ca-quaternary amine-modified straw adsorbent for simultaneous removal of nitrate and phosphate from nutrient-polluted water

Insight into the wheat residues-derived adsorbents for the remediation of organic and inorganic aquatic contaminants: A review

Wheat is a major grain crop of the world that provides a stable food for human consumption. Large amounts of by-products/waste materials are produced after the harvesting and processing of wheat crop. Such materials can cause an environmental issue if not disposed of properly. Several studies have shown that wheat residues can be efficient precursors for adsorbents because of their availability, renewability, lignocellulosic composition, and surface active groups enriched structure. In the literature, there are few review articles that address wheat residues-based adsorbents. However, these reviews were specific in terms of adsorbate or adsorbent and did not provide detailed information about the modification, properties, and regeneration of these adsorbents. This article extensively reviews the utilization of wheat biomass/waste including straw, bran, husk, and stalk as precursors for raw or untreated, chemically treated, carbonaceous, and composite adsorbents against various environmental pollutants. The influences of inlet pollutant amount, adsorbent dose, pH, temperature, and time on the performance of adsorbents against pollutants were considered. The maximum uptakes, equilibrium time, and adsorption nature were identified from isotherms, kinetic, and thermodynamic studies. The highest adsorbed amounts of most tested contaminants were 448.20, 322.58, and 578.13 mg/g for lead, chromium, and copper, 1374.6 and 1449.4 mg/g for methylene blue and malachite green, and 854.75, 179.21, and 107.77 mg/g for tetracycline, phosphate, and nitrate, respectively. For the studied adsorbate/adsorbent systems the adsorption mechanism and regeneration were also discussed. Significant results and future directions are finally presented.

Green synthesis of CaxLa1-xMnO3 with modulation of mesoporous and vacancies for efficient low concentration phosphate adsorption

Phosphate concentrations in eutrophic surface waters are usually low, and efficient removal of low concentration phosphate remains a challenge. In this study, Ca-doped LaMnO3 synthesized at doping ratios, designated as CaxLa1-xMnO3 (x = 0, 0.2, 0.4, 0.7), were compared. It was found that, the adsorption capacity of Ca0.4La0.6MnO3 material reached 63.01 mg/g at pH = 5, increased by 63.6% over the undoped LaMnO3 perovskite. For long-term adsorption, Ca0.4La0.6MnO3 could constantly adsorb phosphate to avoid phosphate accumulation (<0.05 mg/L). This proves that Ca0.4La0.6MnO3 has the ability to control dynamic water eutrophication. Characterization and density functional theory results confirmed that CaxLa1-xMnO3 can increase the content of mesopores and oxygen vacancies, providing additional active sites. This reduces the adsorption energy of the La site, promotes electron transfer, and increases its affinity. It provides a new method for removing low-concentration phosphates.

Simultaneous removal of phosphate and tetracycline using LaFeO3 functionalised magnetic biochar by obtained ultrasound-assisted sol-gel pyrolysis: Mechanisms and characterisation

Excessive phosphate and tetracycline (TC) contaminants pose a serious risk to human health and the ecological environment. As such exploring the simultaneous adsorption of phosphate and TC is garnering increasing attention. In this study, an efficient lanthanum ferrate magnetic biochar (FLBC) was synthesised from crab shells using an ultrasound-assisted sol-gel method to study its performance and mechanisms for phosphate and TC adsorption in aqueous solutions in mono/bis systems. According to the Langmuir model, the developed exhibited a maximum adsorption capacity of 65.62 mg/g for phosphate and 234.1 mg/g for TC (pH:7.0 ± 0.1, and 25 °C). Further, it exhibited high resistance to interference and pH suitability. In practical swine wastewater applications, whereby the concentrations of phosphate and TC are 37 and 19.97 mg/L, respectively, the proposed material demonstrated excellent performance. In addition, electrostatic adsorption, chemical precipitation and ligand exchange were noted to be the main mechanisms for phosphate adsorption by FLBC, whereas hydrogen bonding and π-π interaction were the main adsorption mechanisms for TC adsorption. Therefore, this study successfully prepared a novel and efficient adsorbent for phosphate and TC.

Optimal pathways for upgrading China's wastewater treatment plants for achieving water quality standards at least economic and environmental cost

Wastewater treatment plants (WWTPs) in China must be upgraded to meet new discharge standards, but this incurs both economic and environmental costs and benefits. To select the optimal upgrade pathway, we developed ten upgrade paths based on two common decision-making scenarios for WWTP upgrade in developing countries. Using model simulation, life-cycle assessment, life-cycle cost, and multiple-attribute decision-making, we incorporated the full costs and benefits associated with the construction and operation into the decision-making process. We used a weighting scheme of attributes for the three regions and ranked the upgrade paths using the technique for order preference by similarity to an ideal solution (TOPSIS). The results showed that constructed wetlands and sand filtration were advantageous in terms of lower economic costs and environmental impacts, while the denitrification filter pathways required less land. Optimal pathways differed by region, highlighting the importance of a detailed and integrated assessment of the costs and benefits of WWTP upgrade options over the full life cycle. Our findings can inform decision-making on upgrading China's WWTPs to meet stringent discharge standards and protect inland water and coastal environments.

KOH-modified bamboo charcoal loaded with α-FeOOH for efficient adsorption of copper and fluoride ions from aqueous solution

In this work, bamboo charcoal (BC) is prepared by pyrolysis of bamboo. Then, KOH modification and surface deposition of Goethite (α-FeOOH) are performed to obtain a new KOH-modified BC loaded with α-FeOOH (FKBC) adsorbent for copper (Cu2+) and fluoride (F-) ion adsorption from aqueous solution. Surface morphology and physiochemical properties of the prepared adsorbent are characterized by scanning electron microscopy-energy dispersive spectrometer, X-ray diffraction, and N2 adsorption-desorption. The effect of pH, contact time, adsorbent dosage, and initial concentration on Cu2+ and F- adsorption is also investigated. In addition, adsorption kinetics and isotherms are fitted to pseudo-second-order kinetics and Langmuir model, respectively. Thermodynamic parameters suggest that the adsorption process is spontaneous and endothermic. The adsorption mechanism is further characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The Cu2+ absorption mainly occurs through ion exchange, coordination reactions, and surface precipitation, while the F- adsorption mainly occurs via ion exchange and hydrogen bonding. The selective adsorption experiments reveal that FKBC has good selectivity for Cu2+ and F-. The adsorption-desorption experimental results indicate that FKBC can be reused for Cu2+ and F- adsorption after regeneration. Results indicate that FKBC can be a promising adsorbent for Cu2+ and F- removal from aqueous solutions.

Optimization of Removal of Phosphate from Water by Adsorption Using Biopolymer Chitosan Beads

The need for clean water is the most basic human right. Water scarcity will be one important environmental problem of all countries in the future. Phosphate is a harmful matter for public health and the environment. In this study, the removal of phosphate from water by chitosan, which is an environmentally friendly material, was investigated. Chitosan adsorbent spheres were prepared for phosphate separation from water by adsorption, which is a feasible method. The effects of phosphate concentration, adsorbent dosage, and operation time on the removal were investigated. The removal increased with acid concentration and adsorbent amount. The maximum adsorption capacity of chitosan beads is 87.26 mg/g. Adsorption behavior of the chitosan beads were examined by Langmuir and Freundlich isotherms and pseudo-first and second-order kinetic models. The adsorption process was optimized by the response surface method (RSM). Trial version of Design Expert® 12.0 was used in the study. It has been understood as a result of the RSM statistical analysis that higher phosphate removal values would be obtained by increasing the amount of adsorbent. ANOVA analysis showed that adsorbent dosage had the biggest effect on removal of phosphate using chitosan beads prepared for adsorption.