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In this study, the use of eggshells was suggested as an adsorbent for fluoride removal, and their mechanism of fluoride removal was investigated. The eggshells underwent thermal treatment to improve their adsorption capacity; 800 °C was found to be the optimal temperature for treatment. Eggshells thermally treated at 800 °C (ES-800) were mainly composed of Ca (82.4%) and C (15.9%), and the peaks of ES-800 obtained from X-ray diffraction (XRD) corresponded to calcite, portlandite, and lime. Fluorine adsorption by ES-800 reached 70% of the equilibrium adsorption amount within 15 min and gradually increased until 24 h. The maximum adsorption capacity of ES-800 at pH 7 and 25 °C was 258.28 mg/g, which is 18 times larger than that of activated alumina; this is classified as the best available technology by the United States Environmental Protection Agency. Both enthalpy and entropy increased in the process of fluoride adsorption onto ES-800. Fluoride adsorption of ES-800 decreased from 59.16 to 11.85 mg/g with an increase in pH from 3 to 11. Fluoride adsorption decreased in the presence of anions, whose impact follows the order: HPO 4 3− > HCO 3 − >> SO 4 2− > Cl − . XRD, and X-ray photoelectron spectroscopy analysis revealed that fluoride removal was achieved by the formation of calcium fluorite (CaF 2 ). Thus, it can be concluded that eggshells can function as highly efficient adsorbents for fluoride removal, replacing bone char and activated alumina; further, their adsorption capacity can be improved by thermal treatment.

The objectives in this study are to improve the performance of PVDF membrane by incorporating TiO2 and silane at various dosages and optimize fabricating conditions by using response surface methodology (RSM) for membrane distillation (MD) application. The PVDF membrane was synthesized by phase inversion method using various TiO2, silane and polymer concentrations. Membranes were characterized by performing contact angle measurements, SEM and FTIR observations. Ammonia rejection and permeate flux were measured by operating a direct contact distillation module treating ammonium chloride solution. A PVDF membrane created by adding TiO2 modified by silane improved membrane hydrophobicity. However, the effect of silane on membrane hydrophobicity was less pronounced at higher TiO2 concentrations. Highest ammonium rejection was associated with the highest membrane hydrophobicity. RSM analysis showed that fabricating conditions to achieve highest flux (10.10 L/m2·h) and ammonium rejection (100.0%) could be obtained at 31.3% silane, 2.50% TiO2, and 15.48% polymer concentrations. With a PVDF-TiO2 composite membrane for MD application, the effect of TiO2 was dependent upon silane concentration. Increasing silane concentration improved membrane hydrophobicity and ammonium rejection. RSM analysis was found to bea useful way to explore optimum fabricating conditions of membranes for the permeate flux and ammonium rejection in MD.

Cyanide is highly toxic and must be destroyed or removed before discharge into the environment. This study examined the ability of commercial anion-exchange resins to remove residual cyanide complexes from industrial plating wastewater as a complement to conventional treatment. Cyanide removal experiments were conducted with various initial concentrations, reaction times, and temperatures, and the presence of co-existing anions. The maximum cyanide removal capacity ( Q m ) of the Bonlite BAMB140 resin is 31.82 mg/g and effectively removes cyanide from aqueous solution within 30 min. The cyanide removal by the resin is an endothermic process and is affected by the presence of anions in industrial plating wastewater. The relative competitiveness observed in this study was sulfate > nitrate > chloride. A mixture of 0.05 M NaCl and NaOH regenerates resin for continuous reuse for 5 cycles. The Bonlite BAMB140 resin was able to remove residual cyanide complexes from industrial plating wastewater, but the removal capacity of the resin was reduced by more than three times in batch (9.94 mg/g) and column (6349.12 mg/L) systems. Based on the results, the anion-exchange resins are expected to be used as a complementary technique to remove residual cyanide complexes in industrial plating wastewater after conventional treatment.

We assessed the applicability of rice husk (RH) to remove cationic dyes, i.e., methylene blue (MB) and crystal violet (CV), from water. RH thermally treated at 75 °C showed a higher adsorption capacity than that at high temperatures (300–700 °C). For a suitable CV-adsorption model, a pseudo-first-order model for MB adsorption was followed by the kinetics adsorption process; however, a pseudo-second-order model was then suggested. In the qt versus t1/2 plot, the MB line passed through the origin, but that of CV did not. The Langmuir isotherm model was better than the Freundlich model for both dye adsorptions; furthermore, the adsorption capacity for MB and CV was 24.48 mg/g and 25.46 mg/g, respectively. Thermodynamically, the adsorption of both MB and CV onto the RH was found to be spontaneous and endothermic. This adsorption increased insignificantly on increasing the solution pH from 4 to 10. With an increasing dosage of the RH, there was an increase in the removal percentages of MB and CV; however, adsorption capacity per unit mass of the RH was observed to decrease. Therefore, we conclude that utilizing RH as an available and affordable adsorbent is feasible to remove MB and CV from wastewater.

In this study, we explored the adsorption potential of biochar derived from palm kernel shell (BC-PKS) as an affordable adsorbent for the removal of crystal violet from wastewater. Kinetics, equilibrium, and thermodynamics studies were carried out to evaluate the adsorption of crystal violet onto BC-PKS. The kinetics adsorption process followed the pseudo-second-order model, indicating that the rate of adsorption is principally controlled by chemisorption. The adsorption equilibrium data were better fitted by the Langmuir isotherm model with a determination coefficient of 0.954 and a maximum adsorption of 24.45 mg/g. Thermodynamics studies found the adsorption of crystal violet by BC-PKS to be endothermic with increasing randomness at the BC-PKS/crystal violet interface. The percentage removal and adsorption capacity increased with the pH of the solution, as the negative charges on the biochar surface at high pH enhance the electrostatic attraction between crystal violet molecules and BC-PKS. Increasing the BC-PKS dosage from 0.1 to 1.0 g increased percent removal and decreased the adsorption capacity of crystal violet onto BC-PKS. Therefore, biochar from agricultural by-products, i.e., palm kernel shell, can be cost-effective adsorbents for the removal of crystal violet from textile wastewater.

This study investigated the applicability of algae (Hizikia fusiformis, Green gracilaria, and Codium fragile) for removing heavy metals (Cd2+, Cu2+, Ni2+, and Pb2+) from aqueous solutions. Among the algae, H. fusiformis was chosen as a bioadsorbent and modified with NaOH and HCl. The results showed that the biosorption capacity of H. fusiformis improved significantly after treatment with NaOH; however, H. fusiformis modified with HCl did not achieve the expected value. The NaOH treatment enhanced the biosorption of metals on the treated H. fusiformis because of the hydrolysis reaction producing carboxylic (–COOH) and hydroxyl groups (–OH). The kinetics for Cd2+, Cu2+, Ni2+, and Pb2+ biosorption well fitted to pseudo-first-order, pseudo-second-order, and Elovich models, with R2 of >0.994. The Freundlich model provided a good fit for the equilibrium biosorption of Cd2+, Cu2+, and Ni2+ by both algae and the Langmuir model for Pb2+. The maximum biosorption of metals was in the order Pb2+ >> Cu2+ ≈ Ni2+ > Cd2+, with qmax of 167.73, 45.09, 44.38, and 42.08 mg/g, respectively. With an increase in the solution pH, metal biosorption was enhanced, and considerable enhancement was observed in the pH range of 2–4. Thus, H. fusiformis is expected to be considered a superior candidate for metal biosorption.

Phosphorus, a limiting element, is essential for living organisms, but the total amount available is decreasing with its increasing use. This problem can be solved by studying the methods of phosphorus recovery from waste. Phosphorus (P 2 O 5 , 13.75%) is abundantly present in cattle manure bottom ash (CMBA), indicating its potential as a source for phosphorus recovery. Herein, phosphorus recovery from CMBA was investigated by acid extraction and precipitation methods. The optimum concentration of sulfuric acid for extraction was 1.4 M, which eluted approximately 90% of the phosphorus contained in CMBA. In the precipitation method, sodium hydroxide and calcium silicate hydrate (CSH, CaSiO 3 ∙nH 2 O) were used to adjust the solution pH to 4 and 8, where more than 99% of the eluted phosphorus was recovered when the pH was adjusted to 8 using CSH alone. The chemical composition and crystal forms of the recovered precipitates were analyzed using X-ray fluorescence and an X-ray powder diffractometer. The results indicated monetite and brushite were the main crystal forms of precipitates at pH 4, and struvite, hydroxyapatite, and tricalcium phosphate were the main crystal forms at pH 8. The availability of phosphorus in the precipitates was also evaluated by quinoline gravimetric analysis using water and 2% citric acid, and the water-soluble precipitate was less than 35%, whereas it ranged from 65 to 97% in 2% citric acid. This study suggests that CMBA can be used as a promising source to recover phosphorus via acid extraction and precipitation processes.

Biochar derived from food waste was modified with Fe to enhance its adsorption capacity for As(III), which is the most toxic form of As. The synthesis of Fe-impregnated food waste biochar (Fe-FWB) was optimized using response surface methodology (RSM), and the pyrolysis time (1.0, 2.5, and 4.0 h), temperature (300, 450, and 600 °C), and Fe concentration (0.1, 0.3, and 0.5 M) were set as independent variables. The pyrolysis temperature and Fe concentration significantly influenced the As(III) removal, but the effect of pyrolysis time was insignificant. The optimum conditions for the synthesis of Fe-FWB were 1 h and 300 °C with a 0.42-M Fe concentration. Both physical and chemical properties of the optimized Fe-FWB were studied. They were also used for kinetic, equilibrium, thermodynamic, pH, and competing anion studies. Kinetic adsorption experiments demonstrated that the pseudo-second-order model had a superior fit for As(III) adsorption than the pseudo-first-order model. The maximum adsorption capacity derived from the Langmuir model was 119.5 mg/g, which surpassed that of other adsorbents published in the literature. Maximum As(III) adsorption occurred at an elevated pH in the range from 3 to 11 owing to the presence of As(III) as H2AsO3− above a pH of 9.2. A slight reduction in As(III) adsorption was observed in the existence of bicarbonate, hydrogen phosphate, nitrate, and sulfate even at a high concentration of 10 mM. This study demonstrates that aqueous solutions can be treated using Fe-FWB, which is an affordable and readily available resource for As(III) removal.

This study aimed to assess the effectiveness of capping and mixing of calcined dolomite and zeolite for the remediation of sediment contaminated with nitrogen (N) and phosphorus (P). Laboratory incubation experiments were performed to monitor the release of NH 4 -N, NO 3 -N, T-N, PO 4 -P, and T-P from the sediment. pH, electric conductivity (EC), oxidation reduction potential (ORP), and dissolved oxygen (DO) in overlying water for 60 days were evaluated. Dolomite-amended sediment has high pH and EC. Zeolite and dolomite capping effectively interrupted the release of N and P, respectively; capping was found to be more effective than mixing. The mixture of dolomite and zeolite was also effective; however, their efficiencies were influenced by their placement. The remediation efficiencies when the dolomite was placed above the zeolite cap layer (DOL/ZEO_CAP) were 95.9%, 101.6%, and 100.2% for NH 4 -N, PO 4 -P, and total, and the total remediation efficiency of DOL/ZEO_CAP was twice that of the opposite placement (ZEO/DOL_CAP). Low remediation efficiencies for NH 4 -N and T-N were observed in ZEO/DOL_CAP because NH 4 + adsorption on zeolite was hindered by Ca 2+ and Mg 2+ released from the dolomite. The combination of dolomite and zeolite can be used as a capping material for simultaneously interrupting the release of both nitrogen and phosphorus, but their placement should be considered.

This study investigated the potential application of dredged sediments as a medium for cultivating landscape plants, assessing plant performance in contaminated dredged sediment (CDS) and remediated dredged sediment (RDS), using commercial horticultural soil as a control. Three ornamental plant species, Korean lawn grass (KLG), Aster arenarius Nemoto, and English poppy, were grown under distinct soil conditions both with and without the addition of organic and biochar-based amendments. Soil quality indices and responses in plant growth were measured to determine the influence of sediment remediation and amendment application. The findings demonstrated that RDS created a more suitable substrate for plant development compared to CDS, with KLG exhibiting the most pronounced growth improvement, especially when supplemented with wood-derived biochar and soil conditioner (SC). Incorporating SC into CDS markedly improved KLG biomass, with dry weight increases of 7.4 % and 136.9 % at 2 % and 5 % SC, respectively. Significant correlations (p < 0.05) were observed between soil and leaf Ni concentrations. Additionally, the study analyzed how soil properties impacted heavy metal(loid) accumulation in KLG, showing that soil pH, electrical conductivity, and cation exchange capacity exerted significant effects on Pb and Zn levels in plant tissues. Overall, these results indicate that adequately remediated and amended RDS has the potential to be utilized as a sustainable medium for landscape plant production and may play a role in environmental restoration initiatives. [Display omitted] •Remediated dredged sediment (RDS) was assessed as a sustainable growth medium for plants.•Korean lawn grass (KLG) showed optimal growth in RDS, especially with 5 % biochar (WB).•Soil pH, EC, and CEC influenced KLG uptake of metals like Cd and Zn.•RDS with SC and WB amendments supports sustainable landscaping/remediation efforts.