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

Facile Synthesis of Hydrogel-Based Ion-Exchange Resins for Nitrite/Nitrate Removal and Studies of Adsorption Behavior

This research aimed to create facile, reusable, hydrogel-based anion exchange resins that have been modified with two different amines to test their ability to adsorb nitrate and nitrite in water using batch and continuous systems. In the batch experiment, maximum adsorption capacities of nitrate and nitrite onto poly (ethylene glycol) diacrylate methacryloxyethyltrimethyl ammonium chloride (PEGDA-MTAC) and poly (ethylene glycol) diacrylate 2-aminoethyl methacrylate hydrochloride (PEGDA-AMHC) adsorbents can be obtained as 13.51 and 13.16 mg NO₃⁻-N/g sorbent; and 12.36 and 10.99 mg NO₂⁻-N/g sorbent respectively through the Langmuir isotherm model. After 15 adsorption/desorption cycles, PEGDA-MTAC and PEGDA-AMHC retained nitrate adsorption efficiencies of 94.71% and 83.02% and nitrite adsorption efficiencies of 97.38% and 81.15% respectively. In a column experiment, modified adsorbents demonstrated adsorption efficiencies greater than 45% after being recycled five times. Proposed hydrogel-based adsorbents can be more effective than several types of carbon-based sorbents for nitrate and nitrite removal in water and have benefits such as reduced waste generation, cost-effectiveness, and a facile synthesis method.

Amine-grafted walnut shell for efficient removal of phosphate and nitrate

The presence of emerging pollutants such as PO₄^3- and NO₃^- in water bodies has attracted worldwide concern about their severe effects on water bodies and the health of humankind in general. Therefore, to preserve the health of humankind and environmental safety, it is of the essence that industrial effluents are treated before they are discharged into water bodies. Amine functionalized walnut shells (ACWNS) were synthesized, characterized, and then tested as a novel adsorbent for PO₄^3- and NO₃^- removal. The effects of pH, dosage, initial phosphate concentration, interference ions, and temperature on the removal of phosphate and nitrate were investigated. Notably, the adsorption of PO₄^3- and NO₃^- was exothermic and spontaneous, with a maximum uptake capacity of phosphate and nitrate, at 293 K, 82.2 and 35.7 mg g^-1, respectively. The mechanism by which these ions were adsorbed onto ACWNS could be electrostatic interactions and hydrogen bonding. Pseudo-second-order kinetic model fitted the PO₄^3- and NO₃^- adsorption, while Freundlich and Langmuir models best fitted the PO₄^3- and NO₃^- adsorption, respectively. Furthermore, in the binary system, the uptake capacity of phosphate decreased by 14.4% while nitrate witnessed a reduction in its uptake capacity of 10.4%. ACWNS has a higher attraction towards both ions and this could be attributed to the existence of a variety of active areas on ACWNS that exhibit a degree of specificity for the individual ions. Results obtained from real water sample analysis confirmed ACWNS as highly efficient to be utilized for practical remediation processes.

Energy plants as biofuel source and as accumulators of heavy metals

Fossil fuel depletion and soil and water pollution gave impetus to the development of a novel perspective of sustainable development. In addition to the use of plant biomass for ethanol production, plants can be used to reduce the concentration of heavy metals in soil and water. Due to tolerance to high levels of metals, many plant species, crops, non-crops, medicinal, and pharmaceutical energy plants are well-known metal hyperaccumulators. This paper focuses on studies investigating the potential of Miscanthus sp., Beta vulgaris L., Saccharum sp., Ricinus communis L. Prosopis sp. and Arundo donax L. in heavy metal removal and biofuel production. Phytoremediation employing these plants showed great potential for bioaccumulation of Co, Cr, Cu, Al, Pb, Ni, Fe, Cd, Zn, Hg, Se, etc. This review presents the potential of lignocellulose plants to remove pollutants being a valuable substrate for biofuel production. Also, pretreat-ments, dealing with toxic biomass, and biofuel production are discussed.

Release characteristics of inorganic nitrogen in different water layers and its impact on overlying water from Liaohe River, China

Migration and release of sediment pollutants has become one of the important causes of water pollution, but the contribution of different forms of nitrogen in different water layers to the water quality of the overlying water is unclear. In this study, the main stream of Liaohe River with heavy nitrogen pollution was taken as an example. The static simulation method and related analysis techniques were used to explore the release characteristics of different forms of inorganic nitrogen and its effect on TN and Chla in overlying water from the different water layers. The results showed that the release rates of TN, NH₄⁺-N and NO₃^--N from upstream, midstream and downstream sections were different, but the release characteristics of them in different water layers were the same basically. Generally, the inorganic nitrogen in the pore water of the sediment was released to the water body rapidly in the early 0-8 days. The contribution rate of NH₄⁺-N and NO₃^--N to the change of TN_o was 76.85% for the upstream section, and the contribution rate of NO₃^--N to the change of TN_o was 65.02% for the midstream section. NH₄⁺-N and NO₃^--N in the different water layers from downstream did not showed a significant correlation with TN of overlying water. NO₃^--N in sediments was the main contributor of TN and Chla changes in the overlying water and its content can reflect the nitrogen pollution trend of the water body to a certain extent. When the water retention time was 4-16 days, the TLI in the water body was relatively high. After effective control of exogenous pollution, the release of endogenous nutrients in Liaohe River should be paid more attention.

Highly efficient and antibacterial ion exchanger based on graphene oxide for removal of chromate and nitrate from water: synthesis, characterization and application

A novel recyclable antibacterial anion exchanger based on graphene oxide (GO) and quaternary ammonium chloride (TMSQA) as a crosslinker/ion exchanger was prepared and used for the removal of chromate and nitrate from water.

Fabrication of a Novel Bifunctional Nanocomposite with Improved Selectivity for Simultaneous Nitrate and Phosphate Removal from Water

Phosphorus and nitrogen compounds are both the main sources of eutrophication and coexist in some municipal effluents or eutrophic waters; elimination of phosphorus and nitrogen from wastewater is becoming an imperative but also a hard task. Herein, an innovative bifunctional nanocomposite HFO@TPR was developed for synchronous nitrate/phosphate elimination from water. A macroporous polystyrene microspheres modified with triethylamine functional groups was synthesized as the host of HFO@TPR for selective nitrate removal, and Fe(III) hydroxide (HFO) nanoparticles were implanted inside as the active species for specific phosphate removal. Compared to other commercial adsorbents, HFO@TPR exhibited outstanding selectivity and preference toward nitrates and phosphates, and the coexisting anions exert an insignificant effect on adsorption performance. Such exceptional bifuntionality of HFO@TPR was achieved through two pathways, that is, nitrate was preferentially adsorbed by the fixed triethylamine groups through the electrostatic attraction, and phosphate was preferentially captured by the encapsulated HFO nanoparticles through the inner-sphere complexation. The exhausted HFO@TPR could be effectively regenerated by using a NaOH-NaCl mixed reagent for cyclic use with a relative constant efficiency. In addition, column adsorption experiments demonstrated that HFO@TPR could eliminate nitrate from 18 to <10 mg N/L with the treatment capacity of ∼600 bed volume (BV), and meanwhile remove phosphate from 2.5 to <0.2 mg P/L with the treatment capacity of ∼750 BV. We believe what we found in this study could advance the method on how to develop bifunctional adsorbents for synchronous removal of coexisting contaminants from water.

Bio-attenuation of arsenic and iron coupled with nitrate remediation in multi-oxyanionic system: Batch and column studies

Co-occurrence of arsenic and iron along with nitrate in groundwater makes the trio an onerous combination both in terms of potability and treatment. To meet drinking water guidelines, batch and column laboratory trials were conducted on simulated and bore-well water for attenuation of arsenic (1000 μg/L), iron (5 mg/L) and nitrate (150 mg/L). Increment in sulphate showed a direct individual impact on iron removal, meeting WHO guidelines. The bio-kinetic parameters were in the range of: μ_max = 0.079-0.551/d, K_s = 116.18-645.19 mg/L, K_d = 0.0009-0.0077/d and Y = 0.034-0.094 mg MLVSS/mg COD. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) confirmed orpiment precipitation and/or co-precipitation with mackinawite are the key mechanisms for arsenic and iron attenuation. Column experiments were conducted by charging simulated groundwater containing arsenic (500 μg/L), nitrate (50 mg/L), sulphate (25 mg/L) and iron (3 mg/L) in an acetate (105 mg/L as COD) fed flow-through bioreactor at constant empty bed contact time of 60 min. Profile sampling illustrated segregation of different terminal electron accepting zones following thermodynamic yield for sequential removal of different oxyanions. This study showed the importance of considering microbially mediated terminal electron-accepting processes (TEAP) for multi-oxyanion removal in engineered systems.

Adsorption of Nitrate by a Novel Polyacrylic Anion Exchange Resin from Water with Dissolved Organic Matters: Batch and Column Study

A novel anion exchange resin AEE-3 was synthesized by N-alkylation of a weakly basic polyacrylic anion exchanger D311 with 1-bromopropane to effectively remove nitrate (NO3−-N) from aqueous solution. The related finding revealed that its adsorption isotherm obeyed the Langmuir model well, and the second-order model was more validated for the NO3−-N adsorption kinetics study. Compared to commercially-available polystyrene-based nitrate specialty resin Purolite A 520E (A520E), AEE-3 resin has a higher adsorbed amount and better regeneration performance toward NO3−-N in the existence of dissolved organic matter (DOM) using static and dynamic methods. Notably, a real secondary treated wastewater (STWW) obtained from a local municipal wastewater treatment plant was also assessed for NO3−-N removal in fixed-bed columns. Observations from this study indicated that AEE-3 could effectively remove NO3−-N from contaminated surface water.

Adsorption of phosphate from aqueous solution by vegetable biochar/layered double oxides: Fast removal and mechanistic studies

Two biochars, from Chinese cabbage (Cc, Brassica rapa pekinensis) and rape (Ra, Brassia campestris L.), were used to prepare biochar/Mg-Al layered double oxides (LDOs) as adsorbents for phosphate removal from aqueous solution. The biochar/LDOs were horizontally alternated lamellar particles and had abundant groups of oxides and biochars. The phosphate removal percentage remained above 92% at a pH range of 2-10, and above 95% during the first 5 min for 50 mg/L phosphate by 0.05 g biochar/LDOs. The adsorption kinetics and isotherms data were well fitted by the pseudo-second-order kinetic equation, as well as by the Freundlich and Langmuir models. Based on FTIR, XPS, and zeta potential analysis, the interaction mechanisms were defined as "memory effect", electrostatic attraction, surface complexation, and anion exchange. The results indicate that vegetable biochar/LDOs can be considered a novel and efficient sorbent for phosphate removal from water or wastewater.

Ion selectivity in capacitive deionization with functionalized electrode: Theory and experimental validation

Capacitive deionization (CDI) is a promising technique for salt removal and may have potential for highly selective removal of ion species. In this work, we take advantage of functional groups usually used with ionic exchange resins and apply these to CDI. To this end, we functionalize activated carbon with a quaternary amines surfactant and use this surface to selectively and passively (no applied field) trap nitrate ions. We then set the cell voltage to a constant value to regenerate these electrodes, resulting in an inverted capacitive deionization (i-CDI) operation. Unlike resins, we avoid use of concentrated chemicals for regeneration. We measure the selectivity of nitrate versus chloride ions as a function of regeneration voltage and initial chloride concentration. We experimentally demonstrate up to about 6.5-fold (observable) selectivity in a cycle with a regeneration voltage of 0.4 V. We also demonstrate a novel multi-pass, air-flush i-CDI operation to selectively enrich nitrate with high water recovery. We further present a dynamic, multi-species electrosorption and equilibrium solution-to-surface chemical reaction model and validate the model with detailed measurements. Our i-CDI system exhibits higher nitrate selectivity at lower voltages; making it possible to reduce NaNO3 concentrations from ∼170 ppm to below the limit of maximum allowed values for nitrate in drinking water of about 50 ppm NaNO3.

Selenate tolerance and selenium hyperaccumulation in the monocot giant reed (Arundo donax), a biomass crop plant with phytoremediation potential

The response of giant reed (Arundo donax L.) to selenium (Se), added as selenate, was studied. The development, stress response, uptake, translocation, and accumulation of Se were documented in three giant reed ecotypes STM (Hungary), BL (USA), and ESP (Spain), representing different climatic zones. Plantlets regenerated from sterile tissue cultures were grown under greenhouse conditions in sand supplemented with 0, 2.5, 5, and 10 mg Se kg^-1 added as sodium selenate. Total Se content was measured in different plant parts using hydride generation atomic fluorescence spectroscopy. All plants developed normally in the 0-5.0 mg Se kg^-1 concentration range regardless of ecotype, but no growth occurred at 10.0 mg Se kg^-1. There were no signs of chlorosis or necrosis, and the photosynthetic machinery was not affected as evidenced by no marked differences in the structure of thylakoid membranes. There was no change in the maximum quantum yield of photosystem II (F_v/F_m ratio) in the three ecotypes under Se stress, except for a significant negative effect in the ESP ecotype in the 5.0 mg Se kg^-1 treatment. Glutathione peroxidase (GPx) activity increased as the Se concentration increased in the growth medium. GPx activity was higher in the shoot system than the root system in all Se treatments. All ecotypes showed great capacity of take up, translocate and accumulate selenium in their stem and leaf. Relative Se accumulation is best described as leaf ˃˃ stem ˃ root. The ESP ecotype accumulated 1783 μg g^-1 in leaf, followed by BL with 1769 μg g^-1, and STM with 1606 μg g^-1 in the 5.0 mg Se kg^-1 treatment. All ecotypes showed high values of translocation and bioaccumulation factors, particularly the ESP ecotype (10.1 and 689, respectively, at the highest tolerated Se supplementation level). Based on these findings, Arundo donax has been identified as the first monocot hyperaccumulator of selenium, because Se concentration in the leaves of all three ecotypes, and also in the stem of the ESP ecotype, is higher than 0.1% (dry weight basis) under the conditions tested. Tolerance up to 5.0 mg Se kg^-1 and the Se hyperaccumulation capacity make giant reed a promising tool for Se phytoremediation.

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.

Quaternized pine sawdust in the treatment of mining wastewater

Mining wastewater was treated using quaternized pine sawdust (QPSD) anion exchanger. The wastewater contained heavy metals (e.g. Sb, As, Co, Cr, Ni, V, U), NO3(-), among others, and a high concentration of SO4(2-). A series of column cycles imitating a real treatment process was conducted (three sorption/desorption cycles, a maintenance cycle with HCl and two sorption/desorption cycles). The effects of contact time and temperature (5°C and 23°C) were studied to assess the applicability of QPSD in the treatment of cold mining effluents. At 5°C, 85% of nickel was removed but the sorption was slower than at 23°C (initial Ni concentration was about 39 µg/l). Nickel was also removed in column efficiently (85-100% reduction). Treatment with HCl during the maintenance cycles did not hinder nickel sorption. Nickel was desorbed with both NaCl and HCl. Contrary to expectations, nitrate was not sorbed. QPSD showed selectivity towards nickel. However, uptake of uranium and cobalt was detected in column. Neutron activation analysis was used to detect metals sorbed onto the QPSD, and uptake of several metals was confirmed.

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.

Arundo donax L.: a non-food crop for bioenergy and bio-compound production

Arundo donax L., common name giant cane or giant reed, is a plant that grows spontaneously in different kinds of environments and that it is widespread in temperate and hot areas all over the world. Plant adaptability to different kinds of environment, soils and growing conditions, in combination with the high biomass production and the low input required for its cultivation, give to A. donax many advantages when compared to other energy crops. A. donax can be used in the production of biofuels/bioenergy not only by biological fermentation, i.e. biogas and bio-ethanol, but also, by direct biomass combustion. Both its industrial uses and the extraction of chemical compounds are largely proved, so that A. donax can be proposed as the feedstock to develop a bio-refinery. Nowadays, the use of this non-food plant in both biofuel/bioenergy and bio-based compound production is just beginning, with great possibilities for expanding its cultivation in the future. To this end, this review highlights the potential of using A. donax for energy and bio-compound production, by collecting and critically discussing the data available on these first applications for the crop.

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.

Synthesis and surfactant modification of clinoptilolite and montmorillonite for the removal of nitrate and preparation of slow release nitrogen fertilizer

This article introduces the synthesis of clinoptilolite and montmorillonite, and their surfactant modification by using solutions of hexadecyltrimethylammonium bromide (CH(3)(CH(2))(15)N(Br)(CH(3))(3), HDTMAB) and dioctadecyldimethylammonium bromide ((CH(3)(CH(2))(17))(2)N(Br)(CH(3))(2), DODMAB). The feasibility of using surfactant modified silicates (SMSs) as a potential adsorbent for nitrate and for slow release of nutrient has been investigated. Adsorption isotherms of NO(3)(-) on SMSs have been measured at aqueous concentration of 160-280 mg L(-1). The SMSs show much higher adsorption capacity than the unmodified materials as determined by Langmuir adsorption isotherm. The surfactant modification and increased surfactant loading concentration enhance the nitrate anion retaining capacity of silicates (montmorillonite (16.05 mg g(-1))<clinoptilolite (30.58 mg g(-1))<DODMAB loaded clinoptilolite (75.19 mg g(-1))<DODMAB loaded montmorillonite (76.92 mg g(-1))<HDTMAB loaded montmorillonite (80.65 mg g(-1))<HDTMAB loaded clinoptilolite (125.00 mg g(-1))). The adsorption data fitted well with the Langmuir and Freundlich isotherms. The slow nutrient release studies have been performed by thin layers-funnel analytical test and soil column percolating system. The obtained results indicate that SMSs are very good adsorbent for NO(3)(-) and a slow release of nitrogen is achievable as it releases NO(3)(-) still after 15-20 days of leaching study.