Removal of fluoride from water through bacterial-surfactin mediated novel hydroxyapatite nanoparticle and its efficiency assessment: Adsorption isotherm, adsorption kinetic and adsorption Thermodynamics

Green Synthesis of Hydroxyapatite Nanoparticles Using Monoon longifolium Leaf Extract for Removal of Fluoride from Aqueous Solution

Hydroxyapatite (Ca10(PO4)6(OH)2) calcium phosphate is a robust and viable magnetic material for the treatment of polluted air, water, and soil. Because of its unique structure and appealing properties such as high adsorption capabilities, acid-base adaptability, ion-exchange capability, and thermal stability, hydroxyapatite (HAp) has a lot of potential in the field of environmental management. An aqueous extract of Monoon longifolium leaves was used for the preparation of hydroxyapatite nonparticles as the adsorbent for fluoride ion removal from aqueous solution in this work, resulting in bio-based hydroxyapatite nanoparticles. The prepared adsorbent was characterized by using instrumental techniques such as TGA/DTA, XRD, AAS, FT-IR, and UV-Vis spectroscopy as well as SEM. The batch adsorption approach was used to determine the optimum adsorption efficiency of HAp NPs under various experimental conditions. As a result, the best removal efficiency corresponds to 0.75 g HAp NPs, 15 mg/L, and pH 7 at 50 minutes (96%). The equilibrium adsorption data were better fitted into the Freundlich isotherms (R2 = 0.99), and the pseudo-second-order kinetic model was found to be suitable (R2 = 0.99) for the kinetic model. Fluoride ion adsorption on HAp NPs is spontaneous, endothermic, and possible at temperatures over 318 K, according to thermodynamic calculations. The results hint at a conclusion that the synthesized HAp NPs were an efficient adsorbent for the removal of fluoride ions and the overall process can be an economical choice for scaled-up water treatment processes.

Characteristics of Doped TiO2 Nanoparticle Photocatalysts Prepared by the Rotten Egg White

In this study, expired egg white was used as a template, and a sol–gel method was employed to prepare pure-phase TiO₂ nano-powder and mixed-phase powders doped with NaF and NaI. The influences of different calcination temperatures, doping elements, and doping amounts during the preparation process on the photocatalytic performance and activity of the prepared TiO₂ powders were studied. The results of the experiments showed that the F-doped TiO₂ had the highest photocatalytic activity when the doping amount was 1.2%, as examined by EDS, where the sintering temperature was 500 °C. F-doped TiO₂ nanoparticles were also synthesized by the sol–gel method using tetrabutyl titanate and NaF mixed with expired egg white protein as the precursor. The F-TiO₂ photocatalyst was characterized using FE-SEM, HR-TEM, EDS, XPS, and UV-Vis, and the photocatalytic activity was evaluated by photodegradation of methylene blue under visible light. The results showed that doping with F reduced the energy band gap (3.04 eV) of TiO₂, thereby increasing the photocatalytic activity in the visible-light region. The visible-light wavelength range and photocatalytic activity of the catalyst were also affected by the doping amount.

Optimization of fluoride removal by Al doped ZnO nanoparticles using response surface methodology from groundwater

The current novel work presents the optimization of factors affecting defluoridation by Al doped ZnO nanoparticles using response surface methodology (RSM). Al doped ZnO nanoparticles were synthesized by the sol-gel method and validated by FTIR, XRD, TEM/EDS, TGA, BET, and particle size analysis. Moreover, a central composite design (CCD) was developed for the experimental study to know the interaction between Al doped ZnO adsorbent dosage, initial concentration of fluoride, and contact time on fluoride removal efficiency (response) and optimization of the process. Analysis of variance (ANOVA) was achieved to discover the importance of the individual and the effect of variables on the response. The model predicted that the response significantly correlated with the experimental response (R² = 0.97). Among the factors, the effect of adsorbent dose and contact time was considered to have more influence on the response than the concentration. The optimized process parameters by RSM presented the adsorbent dosage: 0.005 g, initial concentration of fluoride: 1.5 g/L, and contact time: 5 min, respectively. Kinetic, isotherm, and thermodynamic studies were also investigated. The co-existing ions were also studied. These results demonstrated that Al doped ZnO could be a promising adsorbent for effective defluoridation for water.

Bioaccumulation of Fluoride in Plants and Its Microbially Assisted Remediation: A Review of Biological Processes and Technological Performance

Fluoride is widely found in soil–water systems due to anthropogenic and geogenic activities that affect millions worldwide. Fluoride ingestion results in chronic and acute toxicity, including skeletal and dental fluorosis, neurological damage, and bone softening in humans. Therefore, this review paper summarizes biological processes for fluoride remediation, i.e., bioaccumulation in plants and microbially assisted systems. Bioremediation approaches for fluoride removal have recently gained prominence in removing fluoride ions. Plants are vulnerable to fluoride accumulation in soil, and their growth and development can be negatively affected, even with low fluoride content in the soil. The microbial bioremediation processes involve bioaccumulation, biotransformation, and biosorption. Bacterial, fungal, and algal biomass are ecologically efficient bioremediators. Most bioremediation techniques are laboratory-scale based on contaminated solutions; however, treatment of fluoride-contaminated wastewater at an industrial scale is yet to be investigated. Therefore, this review recommends the practical applicability and sustainability of microbial bioremediation of fluoride in different environments.

Evaluation of bentonite clay in modified and unmodified forms to remove fluoride from water

The feasibility of fluoride adsorption from aqueous solutions using naturally available bentonite clay in both modified and unmodified forms is investigated in this report. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy analysis was applied to describe the structure and nature of modified and unmodified bentonite clay. The physicochemical characteristics of the adsorbent were also investigated for moisture content, pH, apparent density, specific surface area, cation exchange capacity and its point-of-zero charge. SEM images reveal particles are dispersed homogeneously and are irregular in shape. XRD and EDX analyses reveal that the bentonite is composed of seven materials: calcite, silica, alumina, hematite, bornite and green cinnabar, and chloride which are considered as impurities. Raw bentonite clays have shown very low fluoride removal efficiency (47.19%). Modification of the clay surface with HCl and aluminum oxide, on the other hand, increased fluoride removal efficiency to 79.77% and 94.38%, respectively. At 5 mg/L initial fluoride concentration, 10 cm bed depth packed dose of adsorbent, and 180 min breakthrough time, a 2.88 mg/g of fluoride removal capacity was observed. As a result, aluminum oxide modified bentonite clay was chosen for further investigation and the results are not presented here.

Impact of C/N ratio on the fate of simultaneous Ca2+ precipitation, F- removal, and denitrification in quartz sand biofilm reactor

The coexistence of F^-, Ca²⁺, nitrates, and other pollutants in water body has aroused widespread concern. In this research, a novel quartz sand biofilm reactor was established, aiming to study the key factors of different carbon to nitrogen (C/N) ratios (5:1, 4:1, and 3:1), initial Ca²⁺ concentration (180 mg L^-1, 144 mg L^-1, and 108 mg L^-1), and hydraulic retention time (HRT) (4 h, 6 h, and 8 h) on simultaneous Ca²⁺ precipitation, F^- removal, and denitrification. Results showed that the removal efficiencies of Ca²⁺, F^-, and nitrate were 55.04%, 82.64%, and 97.69% under the low C/N ratio of 3:1, initial Ca²⁺ concentration of 180 mg L^-1, and HRT of 8 h. 3-D Excitation-Emission Fluorescence Spectroscopy (3-D EEM) demonstrates that extracellular polymeric substances (EPS) was generated during the growth metabolism. Scanning Electron Microscopy (SEM) and X-ray diffractometer images showed that Ca²⁺, F^- removed in the form of CaCO₃, Ca₅(PO₄)₃F and CaF₂ under Acinetobacter sp. H12 induction. Moreover, high-throughput sequencing results display that the biomineralized bacteria Acinetobacter sp. H12 exerted great influence in the bioreactor. This research will underpin the practical use of multiple pollutants such as F^- and Ca²⁺ wastewater under the different C/N ratios.

Process optimization of anammox-driven hydroxyapatite crystallization for simultaneous nitrogen removal and phosphorus recovery

Based on the requirements for advanced treatment and resource recovery of nitrogen and phosphorus pollutants in wastewater, the coupled anammox and hydroxyapatite crystallization (anammox-HAP) process was studied with an aim of achieving high efficiency and low energy consumption during simultaneous nitrogen and phosphorus removal. In the long-term experiments and batch tests, the effects of substrate conditions (nitrogen and phosphorus load, calcium concentration, etc.) on the nitrogen removal and phosphorus recovery efficiencies were investigated. The granular structure and crystal properties were analyzed together with microscopic characterization methods, and the formation mechanism of coupled anammox-HAP granules was verified. Based on these experiments, a theoretical model and technical method for realizing the coupled process were established, and a reference for practical engineering application was provided.

Uptake of As(V) from Groundwater Using Fe-Mn Oxides Modified Kaolin Clay: Physicochemical Characterization and Adsorption Data Modeling

The present study evaluated the effectiveness of Fe-Mn modified kaolin clay in the uptake of As(V) from the solution. The elemental composition was characterized using X-ray fluorescence (XRF), while the surface morphology was characterized using Scanning Electron Microscopy (SEM). The surface area, pore diameter, and pore volume were determined using Brunauer, Emmett, and Teller (BET) and Barrett-Joyner-Halenda (BJH) techniques. The efficiency of the Arsenic removal of the adsorbent was evaluated using batch experiments. The results showed that the percentage of As(V) removal is optimum at acidic pH and decreased as the solution pH becomes more alkaline. The adsorption kinetics data fitted better to pseudo-second-order compared to the pseudo-first-order of reaction kinetics. The adsorption isotherm data fitted to the Langmuir isotherm model showing a maximum adsorption capacity of 2.44 mg/g, adsorbate concentration range of 1–30 mg/L, and adsorbent dosage of 0.4 g/100 mL. The value of ∆G° of the thermodynamic parameter was found to be negative, while ∆H° and ∆S° were found to be positive. For the regeneration-reuse study, the percentage of removal was found to be >85% after the sixth cycle of reuse. The results obtained from this study showed that Fe-Mn modified kaolin (FMK) is suitable for use in the uptake of As(V) from groundwater.

Application of hydroxyapatite and its modified forms as adsorbents for water defluoridation: an insight into process synthesis

Fluorosis is a major scourge in many countries caused by prolonged consumption of drinking water with high fluoride content found in groundwater resources. Hydroxyapatite (Hap) and its composite forms are excellent biomaterials that recently gained attention as efficient adsorbents, owing to its physical and chemical nature as it can substitute both cationic and anionic complexes present in an aqueous solution in its atomic arrangement. Its biological nature, biocompatibility and biodegradability along with its chemical characteristics such as crystallinity, stability, ion adsorption capability and highly specific catalytic activity make it suitable for a variety of applications especially in water treatment for fluoride removal. This review describes various techniques for synthesis of a wide variety of biogenic, synthetic, composite and modified forms of Hap for application in water defluoridation. Hap derived from natural sources or synthesized using conventional methods, hydrothermal, sol-gel or advanced sonication-cum-precipitation technique varied in terms of its crystallinity, structure, size, etc., which affect the fluoride removal capacity. The advantage and disadvantages of various synthesis methods, process parameters and product characteristics have been compiled, which may help to identify a suitable synthesis method for a desired Hap product for potential application and future perspectives in water treatment.