Sorption of nitrate onto amine-crosslinked wheat straw: characteristics, column sorption and desorption properties

Competitive adsorption of nitrate, phosphate, and sulfate on amine-modified wheat straw: In-situ infrared spectroscopic and density functional theory study

Amine-modified wheat straw (AMWS) has already been reported as a promising adsorbent for nitrate (NO₃) removal due to its cost-effectiveness and high efficiency. However, the NO₃ removal mechanism has not been well understood, especially in the presence of co-existing ions. Here, the effect of co-existing anions on NO₃ removal by AMWS was investigated and the underlying mechanisms were revealed using a combination of in-situ infrared (IR) spectroscopy and computational modeling. The in-situ IR results indicated that NO₃, sulfate (SO₄), and phosphate (PO₄) are all adsorbed as outer-sphere complexes on AMWS. The two-dimensional-correlation spectroscopy analysis implied the adsorption sequence of SO₄ > PO₄ > NO₃. The adsorption energies obtained from density functional theory calculation range from -0.24 to 0.51 eV (-23.2 to 49.2 kJ/mol), confirming that these anions adsorb on AMWS as outer-sphere complexes. For the first time, this study provides direct spectroscopic evidence of the outer-sphere adsorption of NO₃ on AMWS, as well as identifies the adsorption sequence, confirmed by computational modeling. The competitive mechanism of NO_3, SO₄, and PO₄ revealed in this study is helpful to understand and predict the applications of AMWS.

Nitrate contamination in water resources, human health risks and its remediation through adsorption: a focused review

The level of nitrate in water has been increasing considerably all around the world due to vast application of inorganic nitrogen fertiliser and animal manure. Because of nitrate's high solubility in water, human beings are getting exposed to it mainly through various routes including water, food etc. Various regulations have been set for nitrate (45-50 mgNO₃^-/L) in drinking water to protect health of the infants from the methemoglobinemia, birth defects, thyroid disease, risk of specific cancers, i.e. colorectal, breast and bladder cancer caused due to nitrate poisoning. Different methods like ion exchange, adsorption, biological denitrification etc. have the ability to eliminate the nitrate from the aqueous medium. However, adsorption process got preference over the other approaches because of its simple design and satisfactory results especially with surface modified adsorbents or with mineral-based adsorbents. Different types of adsorbents have been used for this purpose; however, adsorbents derived from the biomass wastes have great adsorption capacities for nitrate such as tea waste-based adsorbents (136.43 mg/g), carbon nanotube (142.86 mg/g), chitosan beads (104 mg/g) and cetyltrimethylammonium bromide modified rice husk (278 mg/g). Therefore, a thorough literature survey has been carried out to formulate this review paper to understand various sources of nitrate pollution, route of exposure to the human beings, ill effects along with discussing the key developments as well as the new advancements reported in procuring low-cost efficient adsorbents for water purification.

Enhanced degradation of phenol by a novel biomaterial through the immobilization of bacteria on cationic straw

As phenol possesses a threat to human health, there is a great demand to search for fast and efficient methods for it to be discharged. In this study, a novel biomaterial was prepared by the immobilization of bacteria on a cationic straw carrier, and the remediation ability of the biomaterial on phenol-containing wastewater was investigated. The free bacteria could degrade 1,000 mg/L phenol within 240 h, while the prepared biomaterial was 192 h, shortening by 48 h that of free bacteria. In addition, the degradation tolerance of biomaterial increased from 1,000 mg/L to 1,200 mg/L than the free bacteria, within 216 h, which shortened by 24 h the degradation time of 1,000 mg/L phenol by free bacteria (240 h). Further, under different pH conditions, the degradation efficiency of phenol by prepared biomaterial was much higher than that of free bacteria. Especially for the lower pH 5, the degradation efficiency of biomaterial was nearly twice that of the free bacteria. This investigation demonstrates that this biomaterial has great potential in the field of remediation of organic pollution.

Nitrate removal from aqueous solutions by magnetic cationic hydrogel: Effect of electrostatic adsorption and mechanism

Excessive nitrate (NO₃^-) is among the most problematic surface water and groundwater pollutants. In this study, a type of magnetic cationic hydrogel (MCH) is employed for NO₃^- adsorption and well characterized herein. Its adsorption capacity is considerably pH-dependent and achieves the optimal adsorption (maximum NO₃^--adsorption capacity is 95.88 ± 1.24 mg/g) when the pH level is 5.2-8.8. The fitting result using the homogeneous surface diffusion model indicates that the surface/film diffusion controls the adsorption rate, and NO₃^- approaches the center of MCH particles within 30 min. The diffusion coefficient (D_s) and external mass transfer coefficient (k_F) in the liquid phase are 1.15 × 10^-6 cm²/min and 4.5 × 10^-6 cm/min, respectively. The MCH is employed to treat surface water that contains 10 mg/L of NO₃^-, and it is found that the optimal magnetic separation time is 1.6 min. The high-efficiency mass transfer and magnetic separation of MCH during the adsorption-regeneration process favors its application in surface water treatment. Furthermore, the study of the mechanism involved reveals that both -N⁺(CH₃)₃ groups and NO₃^- are convoluted in adsorption via electrostatic interactions. It is further found that ion exchange between NO₃^- and chlorine occurs.

Valorization of biomass into amine- functionalized bio graphene for efficient ciprofloxacin adsorption in water-modeling and optimization study

A green synthesis approach was conducted to prepare amine-functionalized bio-graphene (AFBG) as an efficient and low cost adsorbent that can be obtained from agricultural wastes. In this study, bio-graphene was successfully used to remove Ciprofloxacin (CIP) from synthetic solutions. The efficacy of adsorbent as a function of operating variables (i.e. pH, time, AFBG dose and CIP concentration) was described by a polynomial model. A optimal99.3% experimental removal was achieved by adjusting the mixing time, AFBG dose, pH and CIP concentration to 58.16, 0.99, 7.47, and 52.9, respectively. Kinetic model revealed that CIP diffusion into the internal layers of AFBG controls the rate of the process. Furthermore, the sorption process was in monolayer with a maximum monolayer capacity of 172.6 mg/g. Adsorption also found to be favored under higher CIP concentrations. The thermodynamic parameters (ΔG°<0, ΔH°>0, and ΔS°>0) demonstrated that the process is endothermic and spontaneous in nature. The regeneration study showed that the AFBG could simply regenerated without significant lost in adsorption capacity.

Chitosan Modified Zeolite Molecular Sieve Particles as a Filter for Ammonium Nitrogen Removal from Water

Drinking water containing a high amount of ammonium-nitrogen (NH₄⁺-N) is not effectively removed by conventional treatment processes and can cause eutrophication. In this research, a composite adsorbent based on chitosan crosslink with zeolite molecular sieve (CTS-ZMS) was prepared for NH₄⁺-N removal through dynamic adsorption filter experiments. Effect of bed depth (30, 50 and 70 cm), flow rate (32, 49 and 65 mL/min), initial pH value (4.5, 6.5 and 8.5) and influent NH₄⁺-N concentration (3, 5 and 7 mg/L) was examined by using a filter column packed with CTS-ZMS particles. The Thomas model was applied to study the breakthrough curves and adsorption capacity. The optimal process parameters of the aforementioned factors were obtained at bed depth of 70 cm, flow rate of 32 mL/min, pH of 6.5 and initial NH₄⁺-N concentration of 7 mg/L. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier Transform Infrared Spectroscopy (FTIR) were investigated to analyze the structure and morphology of the CTS-ZMS adsorbents before and after 3 months running. The EDS and FTIR results showed Na⁺ and the active functional groups of -OH, -NH₂ and -COO⁻ on CTS-ZMS adsorbent particles reacted with ammonium nitrogen. The results of this study supported the use of CTS-ZMS to improve drinking water filtration processes by increasing ammonium nitrogen reductions.

Comparative analysis on adsorption properties and mechanisms of nitrate and phosphate by modified corn stalks

We compare and analyze the different properties and mechanisms of MCS on nitrate and phosphate.

Enhanced removal of nitrate from water using amine-grafted agricultural wastes

Adsorption using low-cost adsorbents is a favourable water treatment method for the removal of water contaminants. In this study the enhanced removal of nitrate, a contaminant at elevated concentration affecting human health and causing eutrophication of water, was tested using chemically modified agricultural wastes as adsorbents. Batch and fixed-bed adsorption studies were performed on corn cob and coconut copra that were surface modified by amine-grafting to increase the surface positive charges. The Langmuir nitrate adsorption capacities (mgN/g) were 49.9 and 59.0 for the amine-grafted (AG) corn cob and coconut copra, respectively at pH6.5 and ionic strength 1×10(-3)M NaCl. These values are higher than those of many commercially available anion exchange resins. Fixed-bed (15-cm height) adsorption capacities (mgN/g) calculated from the breakthrough curves were 15.3 and 18.6 for AG corn cob and AG coconut copra, respectively, for an influent nitrate concentration 20mg N/L at a flow velocity 5m/h. Nitrate adsorption decreased in the presence of sulphate, phosphate and chloride, with sulphate being the most competitive anion. The Thomas model fitted well to the fixed-bed adsorption data from four repeated adsorption/desorption cycles. Plug-flow model fitted well to the data from only the first cycle.

Removal of nitrate by modified pine sawdust: effects of temperature and co-existing anions

The effect of temperature, sulphate and phosphate, and the initial nitrate concentration on nitrate removal was studied with synthetic solutions. Chemically modified pine sawdust (Pinus sylvestris) anion exchange resin (MPSD) was used in the sorption studies. The resin was synthesized by reacting pine sawdust with epichlorohydrin, ethylenediamine and triethylamine in the presence of N,N-dimethylformamide. Nitrate removal was successful at 5-70 °C. Higher temperatures caused nitrate removal to decrease moderately, but sorption capacities of 22.2-32.8 mg/g for NO3-N were achieved. The removal of nitrate in the presence of sulphate or phosphate was studied at concentrations of 30 mg N/l, 10-500 mg S/l and 1-50 mg P/l. A significant decrease in nitrate reduction was observed at sulphate and phosphate concentrations of 100 mg S/l and 50 mg P/l, respectively. The effect of initial nitrate concentration was studied in column. Nitrate sorption was clearly dependent on the initial concentration. Desorption of nitrate in column was completed using about 80 bed volumes of 0.1 M NaCl solution. The sorption data were fitted to the Langmuir, Freundlich and Redlich-Peterson adsorption models. The Redlich-Peterson and Langmuir models gave the best fit, which suggests monolayer sorption. Thermodynamic studies revealed that the sorption of nitrate was spontaneous and exothermic in nature. The results imply that modified pine sawdust could be a feasible alternative in the treatment of real industrial wastewaters.

Enhanced removal of nitrate from water using surface modification of adsorbents--a review

Elevated concentration of nitrate results in eutrophication of natural water bodies affecting the aquatic environment and reduces the quality of drinking water. This in turn causes harm to people's health, especially that of infants and livestock. Adsorbents with the high capacity to selectively adsorb nitrate are required to effectively remove nitrate from water. Surface modifications of adsorbents have been reported to enhance their adsorption of nitrate. The major techniques of surface modification are: protonation, impregnation of metals and metal oxides, grafting of amine groups, organic compounds including surfactant coating of aluminosilicate minerals, and heat treatment. This paper reviews current information on these techniques, compares the enhanced nitrate adsorption capacities achieved by the modifications, and the mechanisms of adsorption, and presents advantages and drawbacks of the techniques. Most studies on this subject have been conducted in batch experiments. These studies need to include continuous mode column trials which have more relevance to real operating systems and pilot-plant trials. Reusability of adsorbents is important for economic reasons and practical treatment applications. However, only limited information is available on the regeneration of surface modified adsorbents.

Effect of dissolved organic matter on nitrate-nitrogen removal by anion exchange resin and kinetics studies

The effects of dissolved organic matter (DOM) on the removal of nitrate-nitrogen from the model contaminated water have been investigated utilizing the strong base anion exchange resins. With the increase of gallic acid concentration from 0 to 400 mg/L, the adsorption amount of nitrate-nitrogen on the commercial resins, including D201, Purolite A 300 (A300) and Purolite A 520E (A520E), would significantly decrease. However, the presence of tannin acid has little impact on nitrate-nitrogen adsorption on them.Compared to D201 and A300 resins, A520E resin exhibited more preferable adsorption ability toward nitrate-nitrogen in the presence of competing organic molecules, such as gallic acid and tannin acid at greater levels in aqueous solution. Attractively, the equilibrium data showed that the adsorption isotherm of nitrate-nitrogen on A520E resin was in good agreement with Langmuir and Freundlich equations. The rate parameters for the intra particle diffusion have been estimated for the different initial concentrations. In batch adsorption processes, nitrate-nitrogen diffuse in porous adsorbent and rate process usually depends on t1/2 rather than the contact time. The pseudo first- and the second-order kinetic models fit better for nitrate-nitrogen adsorption onto A520E resin. The observations reported herein illustrated that A520E resin will be an excellent adsorbent for enhanced removal of nitrate-nitrogen from contaminated groundwater.

Nitrate removal from aqueous solution by Arundo donax L. reed based anion exchange resin

Arundo donax L. reed based anion exchange resin (ALR-AE resin) was prepared by the amination reaction for the adsorption of nitrate from aqueous solution. The physicochemical properties of the ALR-AE resin as well as its adsorption properties for nitrate were measured. Results indicated that large amounts of amine groups have been grafted onto the structure of the resin. The FTIR and Raman spectra validated the ion exchange mechanism for nitrate adsorption by ALR-AE resin. The adsorption data showed an exothermic nature for the adsorption of nitrate by ALR-AE resin, and the equilibrium time for the adsorption process was about 10 min. The maximum adsorption capacity (Q(max)) for nitrate was 44.61 mg/g. The saturated adsorption capacity of ALR-AE resin in column was about 38.9 mg/g, which accounted for about 87.2% of the resin's Q(max). The preferential adsorption capacity of the ALR-AE resin followed the order as: SO(4)(2-)>NO(3)(-) ≈ PO(4)(3-)>NO(2)(-). In addition, the utilization of the resin in actual water samples indicated that the ALR-AE resin could be used for the treatment of many ionic polluted wastewaters.

Formaldehyde removal by potted plant-soil systems

Formaldehyde is a major indoor air pollutant. Formaldehyde removal from indoor air conduces to decrease the health risk for urban inhabitants. In this study, a dynamic chamber technique was employed to investigate formaldehyde removal by potted spider plant (Chlorphytum comosum), aloe (Aloe vera) and golden pothos (Epipremnum aureum) with potted soils. The results showed that the potted plant-soil systems could remove formaldehyde from air in a long time. The spider plant-soil system had the highest formaldehyde removal capacity compared with others. Higher metabolisms in plants and microorganisms in daytime may give a reasonable explanation for higher formaldehyde removal capacities for plant-soil systems in daytime. The order of formaldehyde removal capacity for the three plant species agreed well with the sequence of formaldehyde dehydrogenase activities from plant leaves. Formaldehyde removal by plant may be diffusion-limited rather than reaction-limited since the detached formaldehyde dehydrogenase activities from the leaves of the three plant species were higher than in vivo metabolic capacities. Formaldehyde in air can be largely absorbed and metabolized by the microorganisms in the potted soils indicating that further elevating formaldehyde removal capacity for plant-soil system will be realized by increasing exposed surface of potted soil.