Adsorption performance of packed bed column for nitrate removal using PAN-oxime-nano Fe2O3
© Jahangiri-rad et al.; licensee BioMed Central Ltd. 2014
Received: 18 January 2014
Accepted: 28 May 2014
Published: 4 June 2014
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A continuous fixed bed study was carried out by using PAN-oxime-nano Fe2O3 as a sorbent for the removal of nitrate from aqueous solution. The effect of factors, such as flow rate (2, 5 and 7 mL/min) and bed depth (5, 10 and 15 cm) were studied. Data confirmed that the breakthrough curves were dependent on flow rate and bed depth. The adsoption capacities observed in diffent conditions of flow rates (2,5 and 7 mL/min) were 11.65, 24.38 and 25.89, respectively. Thomas model was applied to experimental data to predict the breakthrough curves using linear regression and to determine the characteristic parameters of the packed bed column. Bed depth/service time analysis (BDST) model was used to investigate the effect of bed depth on breakthrough curves. The results showed that Thomas model was suitable for the normal description of breakthrough curve at the experimental condition. The data were in good agreement with BDST model with R2 > 0.98. Statistical analyses were performed on fluoride removal obtained from different flow rates using SPSS16 software by applying Kruskal- Wallis test. These findings suggested that PAN-oxime-nano Fe2O3 in the column structure presents a great potential in removal of nitrate from aqueous solutions.
KeywordsPAN-oxime-nano Fe2O3 Niatrate Sorption Packed bed column Breakthrough curve
The principal sources of nitrogen are from nitrogeneous compounds produced by plant and animals or the mining of sodium nitrate for use in fertilizers, and the atmosphere. The most oxidized form of nitrogen is nitrate[1, 2]. World wide, the average intake of nitrate is about 75 to 100 mg/d, of which approximately 80 to 90 percent comes from vegetables. people on a vegetarian diet may consume as much as 250 mg/d of nitrate. Accordingly, drinking water accounts for only 5 to 10 percent of nitrates consumed. However, if the nitrate levels in the water are five times the MCL (10 mg/L), water may supply a person about half the daily diet requirements3. Nitrate is of primary concern for infants younger than 6 months of age. Infants are very susceptible to methemoglobinemia, a condition known as “blue baby syndrome.” High nitrate levels that are reduced in the stomach and/or the saliva of an infant to nitrite cause blue baby syndrome. Nitrite in the blood combines with hemoglobin to form methemoglobin, which reduces the capability of the blood to transport oxygen throughout the body. This results in the skin of a baby turning blue and can be fatal. The present MCL in the United States is 10 mg/L as nitrate and Canada has established a maximum acceptable concentration (MAC) of 10 mg NO3 (N/L). Due to the fact that nitrate is a stable, highly soluble ion, it is difficult to remove by conventional processes. Present technologies for nitrate removal from water supplies include chemical and biological denitrification, reverse osmosis, electrodialysis, ion exchange and adsoprtion. The process of adsorption of the material through of a fluid mixture flowing in to a packed column has gained great interest in recent years. There is a need to carry out the column studies to assess the required contact time for the adsorbate to achieve equilibrium as the results obtained from the batch studies for the contaminants adsorption studies may not be directly applied for field application in the treatment of polluted water. In the present study, PAN-oxime-nano Fe2O3 were used for nitrate removal. Continuous adsorption experiments were conducted to understand and quantify the effect of influencing parameters such as, initial floe rates and bed heights on breakthrough curve. BDST model, which offers a simple approach and rapid prediction of adsorber performance, is applied for modelling adsorption of nitrate in PAN-oxime-nano Fe2O3 column.
Material and methods
Preparation and characterization of PAN-oxime-nano Fe2O3
Hydroxilamine hydrochloride (16 g), sodium carbonate (12 g), and 0.4 g of PAN powder were added to a 250 mL bottle to which 100 mL of deionized water was added and shaken. The reaction was carried out at 70°C for 120 min. After reaction, the resultant was filtered and let to dry. Fe2O3 was coated on PAN functionalized by adding 0.2 g of selected Fe2O3 and 100 mL deionized water in a sealed bottle. The solution was shaken at 70°C for 120 min. The resultant was filtered and dried in a vacuum oven at 60°C. PAN functionalized-Fe2O3 was used as an adsorbent. The characteristics of PAN-oxime-nano Fe2O3 was studied by XRD, FTIR and SEM in our earlier study.
Where qe is the nitrate adsorbed (mg/g), C0 is the influent nitrate concentration (mg/L) Ce is effluent nitrate concentration (mg/L), Ve is the volume of solution required to reach the exhaustion point (L) and m is the mass of adsorbent (g).
Modeling of column operation
Full-scale column operation was designed according to the data collected in laboratory level. Many mathematical models have been used for the evaluation of efficiency and applicability of the column models for full scale operations. To design a column sorption process it was necessary to predict the breakthrough curve or concentration time profile and sorption capacity of the sorbent for the selected sorbate. Many models have been developed to predict the sorption breakthrough behaviour with high degree of accuracy. In this study the Thomas model was used to evaluate the behaviour of the selected adsorbent-adsorbate system.
Results and discussion
Adsorption capacity of the column
Descriptive statistical analysis of various flow rates on fluoride removal at time of 9 h
Results of Kruskal Wallis test statistics
Effect of flow rate
Effect of bed height
The Thomas and BDST model parametres for adsorption of nitrate on PAN-oxime-nano Fe 2 O 3
Thomas model parameters
Flow rate (mL/min)
BDST model parameters
K a (L/mg h)
A good removal of nitrate was observed by fixed-bed by PAN-oxime-nano Fe2O. The adsorption studied showed that at longer bed depth better removal of nitrate would be achieved. The calculated adsorption capacity (N0) and the rate constant (Ka) were 1433 Mg/L and 0.0112 L/mg h, respectively. Thomas and BDST models were successfully used for predicting breakthrough curves for nitrate removal using different flow rates and depth. The application of the BDST model at 10% of breakthrough point gave satisfactory results with an R2 = 0.999.
The authors would like to thank the staff of medical sciences research center, Islamic Azad University, Tehran, Iran for their collaboration in this research.
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